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السبت، 11 فبراير 2012

The future of anti-diabetics in T2DM therapy

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Unmet needs in T2DM therapy
As we have seen in Chapter 1, T2DM is a huge, global problem. Many
treatments are available to tackle this chronic and potentially serious
condition, but the fact is that, in many patients, long-term glycaemic
control and adherence to therapies is far from optimal; limited by a
lack of sustained efficacy, safety and tolerability issues and product
label restrictions. These problems are compounded in those patients
with comorbidities that interfere with diabetes therapy, such as renal
impairment.
Beyond HbA1c in assessing treatment efficacy
Assessing the degree to which glycaemic control is achieved hinges on
a number of parameters. If these targets are not met then glycaemia is
considered to be uncontrolled. These targets are as follows:
zzHbA1c: <7.0%1
zzFPG: 3.9 – 7.2 mmol/L (70 – 130 mg/dl)2
zz2-hour postprandial blood glucose: <7.8 mmol/L (<140 mg/dl)3, 4 up to <10
mmol/L (<180 mg/dl)5
As these targets indicate whether glycaemia is controlled or not, they
relate directly to the efficacy of any given therapy in lowering blood
glucose levels in patients with T2DM. For this reason, the level of efficacy
of any treatment will remain an important decision factor in choosing
the most appropriate agent.
HbA1c, as a proxy for efficacy, is the current gold standard in monitoring
treatment and informing management decisions in people with diabetes.
6 However, using this measure in isolation is not without its limitations.6
HbA1c reflects the mean blood glucose level during the preceding six
to eight weeks, but this is true only for the population as a whole, not
the individual patient.6 For assessing the efficacy of a given treatment
in the future we should take a more holistic approach. It is known that
about 33% of people diagnosed as having T2DM based on postprandial
(PPG) hyperglycaemia have normal fasting plasma glucose (FPG).7 It
has been shown that the deleterious effects of dysglycaemia – daily
excursions in FPG and PPG – develop before diabetes is diagnosed.8
The degree to which FPG and PPG influence overall glycaemia is relatively
complex, but we know that PPG contributes ~70% to the total
glycaemic load in patients who are fairly well controlled (HbA1c <7.3%).
In patients who are very poorly controlled (HbA1c >10.2) it is FPG that
contributes around 70% to the total glycaemic load (Figure 1).7, 9 Furthermore,
there is a Iinear relationship between the risk of CV death and the
2-hour oral glucose tolerance test (OGTT).7 These data suggest that all
the parameters for assessing glycaemia (HbA1c, FPG, and PPG) should
be considered in the management of T2DM.7 In assessing the efficacy of
a T2DM therapy we should take into account not only its ability to lower
HbA1c, but also its ability to normalise the blood glucose excursions that
can occur during the day i.e. the spikes in FPG and PPG.10, 11
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Beyond glycaemic measures in assessing treatment efficacy
In addition to glycaemic parameters for assessing the efficacy of T2DM
treatment, it is becoming increasingly clear that other parameters beyond
glycaemic control are important. T2DM is a complex condition
that is often part of a much broader metabolic syndrome that manifests
itself with obesity, hypertension and dyslipidaemia. Also, the side
effects associated with some treatments can have a negative impact
on the patient’s quality of life.12

In terms of dyslipidaemia it is known that pioglitazone is associated with
improvements in triglycerides, HDL cholesterol, LDL particle concentration,
and LDL particle size, whereas rosiglitazone is not.13 Rosiglitazone
has since been associated with a number of adverse effects, but this
example illustrates the point that the variation in efficacy of the various
T2DM treatments, even those in the same therapeutic class, extends
beyond simple glucose lowering.
Obesity can complicate the management of diabetes by increasing
insulin resistance and blood glucose concentrations as well as negatively
impacting lipidaemia,14 but it is well known that some T2DM treatments,
such as SUs, Glinides, and TZDs are associated with significant
increases in weight.15 Impact on body weight and in turn lipidaemia
will be increasingly recognised as an important measure of efficacy for
new and emerging T2DM treatments. Some new therapies have demonstrated
favourable characteristics with regard to body weight. For
example, the DPP-4 inhibitors are weight neutral and the GLP-1 mimetics/
analogues can reduce body weight significantly.16-20
Treatment adherence and the needs of the patient
Intimately related to the clinical parameters of efficacy discussed
above is the perennial problem of treatment adherence. The full benefits
of a T2DM treatment are only gained if the patient takes the medications
as prescribed. It has been generally acknowledged for years
that non-adherence rates for chronic illness regimens and for lifestyle
changes are ~ 50%.21 As a group, patients with diabetes find it difficult
to adhere to their treatment regimens.22
Complex regimens
One treatment-related factor that is known to influence adherence is
regimen complexity. It is well known that people with diabetes have
to take several medications every day for their T2DM and concurrent
conditions.23 Given the fact that patients often have to take different
medications, with different dosage frequencies, at different times of
the day, it is hardly surprising that many of them are unable to follow
treatment regimens closely.23 Simplifying treatment regimens using
single pill formulations that can be taken at any time of the day can
potentially help patients to adhere to their medication and consequently
improve the clinical efficacy of T2DM treatments.21
Tolerability is another treatment-related issue that can seriously impact
treatment adherence. T2DM treatment options offer a trade off between
efficacy and tolerability due to product label restrictions and
adverse effects, e.g. weight gain, hypoglycemia, injections, heart failure
and GI problems.24, 25 Common side effects of current treatments
(metformin, SUs, glinides, TZDs, insulin, α-glucosidase inhibitors and GLP-1
mimetics/analogues) are headache, nausea, GI disorders, weight gain
and hypoglycaemia. These side effects are sometimes accompanied
by subsequent, more severe complications, e.g. hypoglycaemia may
influence cardiovascular events and dementia.26, 27 In view of these tolerability
issues, the guidelines make specific recommendations regarding
each class of T2DM treatment (Figure 2).
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“Failure-based” treatment strategies
Several large, randomised trials have demonstrated that intensive
treatment can improve outcomes in people with T2DM. For example,
post-trial monitoring data from the UKPDS shows that patients who received
intensive treatment during the study continue to have a significantly
decreased risk of any diabetes-related endpoint over the long
term; an effect that is known as “a legacy of improved outcomes” because
early intensive treatment leaves a legacy of clinical benefits.29, 30
Controlling glycaemia more aggressively, instead of simply waiting for
treatment failure aims to avoid the phenomenon known as ”metabolic
memory”. This concept, which refers to diabetic vascular stresses persisting
after glucose normalisation, has been supported by laboratory
and clinical data.31, 32
The progressive nature of T2DM requires regular monitoring and adjustment
of treatment, but all too often management strategies for this
condition are ‘failure based’, in that there is a tendency to persist with
monotherapy until blood glucose levels are no longer controlled.23
There appears to be inertia in primary care impeding the adoption of
an aggressive, treat-to-target approach (i.e. early enforced normalization
of blood glucose levels) even though the benefits of intensive
management in the short- and long-term have been demonstrated by
some long-term studies.
An early switch to antidiabetic combination treatment that addresses
the dual endocrine defects of insulin resistance and β-cell dysfunction,
would deliver a markedly greater reduction in HbA1c for those patients
who are struggling to meet their glycaemic targets.33
Predictability of treatment response and the need for
individualised treatment
Currently, T2DM management is very much a ‘one treatment fits all’
affair.34 People with T2DM are generally treated in the same way regardless
of underlying differences that may affect their therapeutic response.
34 There is a huge variation in response, which makes it almost
impossible to predict the treatment effect in any given patient.34 Differences
in genotype interact with external environmental factors to produce
an in-vivo milieu that varies from person to person thus impacting
the effects of a medication.34
Analyses have shown that in the USA only 56% of patients diagnosed
and treated for diabetes reach their glycaemic targets, whereas in
Germany the figure is 48% (glycaemic target for both the USA and
Germany is <7% HbA1c).35, 36 This failure in treatment leaves a substantial
population exposed to prolonged periods of damaging hyperglycaemia.
34 There is now a consensus that further insight into the differences
between people with T2DM, both physiologic and genetic, should not
only help elucidate the pathogenesis of this disease, but lead to individualised
treatments for patients that will improve glycaemic control,
maximise individual benefit, minimise risk, reduce diabetes complications,
and ultimately provide reductions in global health cost.34 The recent
consensus published in the Journal of Clinical Endocrinology and
Metabolism (Smith et al., 2010) makes a series of recommendations for
increasing understanding of the heterogeneity of T2DM and achieving
the goal of individualising therapy and improving treatment response
(Table 1).34
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Cardiovascular safety
Completed studies
Numerous observational studies have shown a clear relationship between
hyperglycaemia and cardiovascular (CV) disease. Because of
the known increase in the risk of CV disease in T2DM and the emphasis
on CV safety in the development of T2DM medications by regulatory
authorities there is considerable interest in the degree to which T2DM
treatments influence CV health.37 However, very little is known about
the CV effects of newer T2DM treatments.
Several large, long-term studies have investigated the CV safety of T2DM
treatments, i.e. UKPDS, ACCORD, ADVANCE and VADT, all of which
failed to show that intensive glucose control significantly reduces CV
events.33, 38-40 Indeed, ACCORD was terminated early due to higher
(non-significant) mortality in the intensive treatment group, which has
led to the conclusion in some quarters that intensive glucose control
not only has no effect on the risk of CV events, but can even be harmful
in patients at high CV risk.38 It is possible to argue that in the UKPDS
metformin was associated with an improvement in CV mortality (this is
supported by recent meta-analyses – see the end of this chapter).41 This
follow-up study of the tight glucose intervention in the UKPDS showed
that intensive glucose control was associated with a significant reduction
in the risk for myocardial infarction, diabetes-related deaths and
all-cause mortality.41 This suggests that early, strict glucose control generates
a legacy that is eventually translated into CV protection. Currently,
this is nothing more than a hypothesis that requires testing.41
The PROACTIVE study showed that pioglitazone can reduce the risk
of secondary macrovascular events in a high-risk patient population
with T2DM and established macrovascular disease; however, the study
failed on the primary composite endpoint and only demonstrated CV
benefit on a secondary endpoint.42-45
The RECORD trial demonstrated that while the addition of rosiglitazone
to glucose-lowering therapy did not increase the risk of overall mortality
and morbidity, it did increase the risk of heart failure.46 In the STOPNIDDM
trial, acarbose was associated with a CV benefit, however, this
was a trial in IGT, not T2DM, and the number of observed CV events was
very low.47 Whether early insulin treatment results in a beneficial effect
on the CV system remains an open question,47 but one that the ORIGIN
trial will attempt to answer, the first results of which are expected in
2012. The Steno-2 study demonstrated CV risk improvement, but this is
a small study and the multi-factorial interventions make it impossible to
attribute the observed effect to a single compound.48
Definitive proof for CV protection afforded by T2DM treatment is scant
to say the least, so much so that the spectre of increased CV risk due to
T2DM treatment looms large in the minds of many experts.
The results from these trials may relate to the particular drugs used rather
than difference between intensive and conventional management.
There have been many high profile cases concerning the use of some
compounds and an associated increase in CV events with the most
infamous being rosiglitazone and to a lesser extent the first generation
SU, tolbutamide.49, 50 Naturally, these fears have placed the TZDs, as a
class, under great scrutiny, but the fact remains that large trials and
meta-analyses (i.e. PROactive, Nissen and Wolski’s meta-analyses and
RECORD) do not provide definitive answers with regard to the CV safety
of these compounds.42, 46, 50, 51
Prompted by these concerns, the FDA conducted a systematic review
of epidemiologic studies of CV risk in patients treated with rosiglitazone
or pioglitazone,52 the results of which are consistent with results of the
same organisation’s meta-analyses of randomised clinical trials with
these two TZDs.53 The salient point from these analyses is that it is highly
likely that rosiglitazone therapy is associated with increased risk of adverse
CV outcomes.53
Ongoing studies
There are a number of ongoing trials investigating the CV outcomes
associated with T2DM treatment. The driving force behind the relatively
recent initiation of these large trials, often involving more than 10,000
patients, is the fact the regulatory bodies now require CV safety on all
new and emerging T2DM treatments. These CV outcome trials are summarised
in Table 2.
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Should the results of the above trials be overwhelmingly positive, they
will prove that T2DM treatments can provide benefits beyond simply
lowering blood glucose levels. The data will provide an insight into the
cardiovascular safety and potential cardiovascular protection of the
compounds being investigated. The results of these trials in conjunction
with an increased knowledge of disease genetics and drug mode of
actions could stimulate a reappraisal of T2DM management.
Emerging therapeutic classes
DPP-4 inhibitors
DPP-4 inhibitors are oral anti-diabetics. They do not require an uptitration
period, are weight neutral and are associated with significant
improvements in glucose control in patients with T2DM by preventing the
inactivation of the incretin hormone GLP-1, which stimulates glucosedependent
insulin secretion and suppresses glucagon secretion.16
DPP-4 inhibitors are efficacious over a broad range of HbA1c levels.
They have shown to be effective as both monotherapy and as add-on
therapy to metformin, SUs, TZDs and insulin in subjects who lack adequate
glycaemic control.16 In addition to their demonstrated efficacy
as mono- and add-on therapy they are also generally safe and have a
placebo-like tolerability profile.16
Long-term safety data for DPP-4 inhibitors is still lacking, although they
are now included in the most recent US and European guidelines2, 62
There are concerns regarding the ubiquitous tissue expression (liver,
lung, lymphocytes, etc) of the DPP enzymes, their role in tumour suppression
and their interaction with other hormones besides GLP-1.63-67 To
date there is nothing in the safety record of DPP-4 inhibitors to suggest
these concerns have any clinical grounding Also, due to the way that
sitagliptin, vildagliptin and saxagliptin are cleared from the body, their
use is not recommended in patients with moderate to severe renal insufficiency
and because they have not been studied in severe hepatic
insufficiency their use is also not recommended in the these patients
(vildagliptin should not be used in any type of hepatic impairment).68-70
Linagliptin on the other hand can be used without dose adjustment in
all stages of renal impairment. Table 3 presents a ‘SWOT’ analysis of the
DPP-4 inhibitors.
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GLP-1 mimetics and analogues
Exenatide and liraglutide are injected drugs that also act on the incretin
system. Instead of impeding the degradation of native GLP-1
like DPP-4 inhibitors, exenatide mimics GLP-1, whereas as liraglutide is
an analogue of this incretin. Both of these agents offer considerable
reductions in blood glucose levels and body weight (see Chapter 4).
In addition, exenatide has been shown to have favourable effects on
lipidaemia.71 The drawbacks of GLP-1 mimetics/analogues include
their need to be injected, gastrointestinal side effects and a potential
link with acute pancreatitis. Table 4 presents a ‘SWOT’ analysis of these
agents.

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SGLT-2 inhibitors
In the kidneys, two transporter proteins, sodium-glucose co-transporter-
1 (SGLT-1) and SGLT-2 are crucial in regulating the reuptake of sodium
and glucose back into ultra-filtrated blood.72 Inhibiting SGLT-2 has
been identified as a way of reducing glucose re-uptake and therefore
reducing blood glucose levels. 72
No compounds in this class are currently available on the market. Dapagliflozin
has filed for approval, while canagliflozin/empagliflozin are in
Phase 3 development. Initial SGLT-2 inhibitor data shows there are no
excessive losses of fluid, sodium, or potassium; very low risk of hypoglycaemia;
significant reductions in HbA1c (~0.7%) modest weight loss
(1 to 4 kg) and a lowering of systolic blood pressure (1 to 4 mmHg).72-
75 Potential drawbacks of SGLT-2 inhibition include a slight increase
in urine volume and a tendency to increase urinary tract infections
and genital mycosis. The latter drawback is thought to be due to the
increased levels of glucose in the urine, which supports the growth of
yeasts, etc.72 Table 5 presents a ‘SWOT’ analysis of the SGLT-2 inhibitors.


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11β-HSD1 inhibitors
This enzyme is responsible for the regeneration of cortisol from its inert
form, cortisone (Figure 3). Inhibitors of 11β-HSD1 have reached Phase
IIb clinical trials for the treatment of T2DM. These compounds act by
decreasing the cortisol generated in liver and adipose tissue, thereby
reducing tissue-specific gluconeogenesis and fatty acid metabolism.76
11β-HSD1 inhibitors are predicted to be at least weight neutral, if not
leading to some weight loss. In addition, they should improve glycaemia
without inducing hypoglycaemia.76 The concern of physiologists is
that if you artificially reduce the level of circulating cortisol by means of
the 11β-HSD1 pathway, you run the risk of adrenal gland compensation
and activation of the hypothalamic-pituitary-adrenal (HPA) axis,
resulting in the production of more cortisol.76 In this scenario, the
adrenal glands might also simultaneously produce excess adrenal
androgens, which, at high concentrations are associated with numerous
negative effects.
To date, these fears have not been borne out in animal studies where
the complete deletion of the 11β-HSD1 gene in mice had, overall, inconclusively
minimal effects on adrenal action.76 Harno and White
(2010) conclude that 11β-HSD1 inhibition represent a compelling treatment
strategy for T2DM.76 Table 6 presents a ‘SWOT’ analysis of the
11β-HSD1 inhibitors.
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Glucagon antagonism
Glucagon plays a central role in glucose homeostasis, namely by increasing
hepatic glucose production and raising blood glucose levels.
Blunting the effects of has long been considered a means of reducing
hyperglycaemia in T2DM. There are two ways in which to limit the
activity of glucagon. Firstly, immuno-neutralisers effectively reduce the
amount of glucagon in the body, but the development of such compounds
for use in humans has not progressed because of limitations imposed
by the delivery methods necessary to achieve significant levels
of exposure for the peptide agents.77
Secondly, and more promisingly, are small molecules that inhibit the
glucagon receptor. Several examples of these are in early Phase 2 clinical
development. They act by preventing glucagon binding to its receptor
and triggering the increased production of glucose.78 Blocking
the action of glucagon is predicted to be an effective means of controlling
hepatic glucose production, thereby lowering fasting and postprandial
hyperglycaemia in T2DM.77 Table 7 presents a ‘SWOT’ analysis
of glucagon receptor antagonists.
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Interleukin-1β receptor antagonists
Interleukin-1β is a proinflammatory cytokine that inhibits the function
and promotes the apoptosis of pancreatic β-cells.79 β-cells producing
this cytokine have been observed in pancreatic sections obtained from
patients with T2DM. Depending on culture conditions, high glucose levels
have been shown to increase β-cell production and the release of
interleukin-1β, followed by functional impairment and apoptosis.79 Using
an antagonist to prevent interleukin-1β from binding to its receptor
protects human β-cells from glucose-induced functional impairment
and apoptosis.80 This therapeutic approach has the potential to block
the pathogenic progression of T2DM.
Anakinra, a recombinant human interleukin-1–receptor antagonist, is
currently in Phase 2 development. A recent study has demonstrated
that HbA1c levels in T2DM patients treated with this compound for 13
weeks were 0.46% lower than in those treated with placebo.79 In addition,
anakinra was associated with improved β-cell secretory function
and reduced markers of systemic inflammation.79 In terms of safety, no
cases of symptomatic hypoglycaemia or serious, drug related adverse
events were observed during this study.79 Table 8 presents a ‘SWOT’
analysis of interleukin-1β receptor antagonists.
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Beyond glycaemic control
In this chapter we have already discussed the trials that have investigated
the degree to which T2DM treatments influence CV risk. Fifty
percent of people diabetes die from CV disease, primarily heart disease
and stroke,81 so there’s intense interest in defining the degree to
which specific drugs and combinations of drugs influence CV risk.
Since the 1990s, the options for OAD treatment have increased markedly.
The expanded selection has created a need for comparative
data on the risks and benefits of anti-diabetic drugs, particularly in light
of the greater cost of newer agents.82 A meta-analysis of forty clinical
trials shows that metformin is associated with a 26% reduction in the
relative risk of CV mortality compared with SUs, TZDs, glinides and placebo.
82 A meta-analysis is only as good as the studies it includes and
the authors of this particular analysis conclude: “larger, long-term studies
taken to hard endpoints and better reporting of CV events in shortterm
studies will be required to draw firm conclusions about major clinical
benefits and risks related to OADs.”82
It is increasingly evident that controlling weight, hypertension and dyslipidaemia
is tantamount to reducing CVD outcomes in patients with
T2DM.83 Some emerging T2DM treatments, such as the SGLT-2 inhibitors,
have been shown to reduce blood pressure and body weight (1–4 kg).73
As monotherapy or add-on to metformin over periods of 12–24 weeks,
dapagliflozin at a dose of 10 mg/day reduced systolic blood pressure
(3–5 mmHg) and diastolic blood pressure (~2 mmHg) with no apparent
change in heart rate.74, 84, 85 These results are promising, but it remains to
be seen if these agents can sustain this level of blood pressure reduction
in the long term. Sustained improvements in glycaemia and one of
the most important CV risk factors would represent a significant breakthrough
in the management of T2DM. Furthermore, SGLT-2 inhibitors
could offer a clinically meaningful treatment opportunity even in T1DM.86
Certain T2DM therapies have also demonstrated their ability in improving
dyslipidaemia. A meta-analysis shows that metformin significantly
reduces total and low-density lipoprotein (LDL) cholesterol, although
these reductions are rather small.87 In a study in T2DM patients, pioglitazone
improves levels of triglycerides, HDL cholesterol, LDL particle concentration,
and LDL particle size.13 In 3-year open-label extension studies
the incretin therapy exenatide was associated with a 12% decrease
in triglycerides, a 6% decrease in LDL and 24% increase in HDL.71 It has
been postulated that the weight loss/weight neutrality of incretin therapies
contributes to lipid improvements.83 In a four week study the DPP-4
inhibitor vildagliptin was shown to improve postprandial plasma triglyceride
levels.88 Large, long term studies are the only definitive way of
elucidating the influence that T2DM treatments have on CV risk factors.
Intimately linked to T2DM and CV disease is obesity and this is another
area where certain agents may offer significant benefits. It is well known
that some compounds, such as SUs, non-SU secretagogues, insulin and
TZDs are associated with significant increases in weight.15 However, the
incretin therapies, with their novel mode of action, and several of the
emerging therapies are weight neutral or associated with significant
weight loss (reviewed in Chapter 4), which has implications for lipidaemia
and patient quality of life.
In addition to potential CV protection afforded by some drugs there
is also intriguing evidence that certain T2DM treatments may even reduce
the risk of developing cancer. A cohort study has demonstrated
that metformin use reduces the risk of developing cancer by 37%, even
after taking into account various factors such as age, blood sugar control,
smoking and weight.89 The authors of this study conclude “a randomised
trial is needed to assess whether metformin is protective in a
population at high risk for cancer.”89 Treatments such as metformin reduce
insulin resistance and it has been suggested that insulin resistance
is associated with an increased risk of cancer.90 Correspondingly, it has
been found that SUs are associated with a higher risk of cancer-related
mortality than metformin.91
We are still largely in the dark with respect to the full range of effects
associated with the use of T2DM treatments. The ongoing CV outcome
studies outlined earlier in this chapter will go some way to defining the
degree to which several of these treatments influence CV risk, but this
may represent the tip of the physiological iceberg. The widely used
medications used in the treatment of T2DM may have effects way beyond
lowering glycaemia and improving the various risk factors of CV
disease.
Unmet needs and emerging risks/benefits shaping future
trends in the use of T2DM treatments
There are certainly a number of important unmet needs in T2DM, but
how will these shape the management of this condition? How will T2DM
be managed in the next ten or even the next twenty years? Naturally,
this is speculation, but we base it on the information we have reviewed
above and in the previous chapters. We can be fairly certain that metformin
will remain the gold standard antidiabetic treatment simply because
of the long experience with the drug, its high level of efficacy,
good tolerability profile, overall cost-effectiveness and possible benefits
beyond simple glycaemic control (cardiovascular protection and
reduced risk of cancer). In contrast we will very likely see a progressive
move away from SUs, TZDs and glinides due to potential safety and
tolerability issues.
Future trends in the use of incretin therapies such as the DPP-4 inhibitors
and the GLP-1 mimetics/analogues are more difficult to speculate
on. Both are effective in improving glycaemia, but many questions still
linger over this therapeutic approach. In part, these questions have
been addressed by emerging DPP-4 inhibitors that possess high potency,
high selectivity and non-renal elimination. The GLP-1 mimetics and
analogues may become increasingly important because of their very
high level of glycaemic efficacy and associated weight loss, although
the need for subcutaneous injections will always be a significant barrier
to their widespread use.
With metformin as the gold standard the importance of combination
therapy will also continue to rise as those people poorly controlled on
metformin monotherapy are treated with combination regimens containing
familiar OADs and those with novel modes of action that are still
in development.92 The earlier use of combination therapy in T2DM will
probably also increase over time.92 Furthermore, we can expect that
treatment decisions in T2DM will increasingly hinge on a number of factors,
rather than just the glycaemic lowering ability and tolerability profile
of a drug.93, 94 Factors such as comorbidities (e.g. renal impairment),
compliance and adherence, CV protection and cost-effectiveness will
all be important in the more holistic management of T2DM.93, 94
A further likely trend is the increasing influence of patient organisations
and other groups in driving the issue of patient-centric treatment,
which has always been something of a neglected area in the management
of chronic conditions. To improve the way in which individuals
with T2DM are treated we may see a progressive move to tailored
therapy that builds on advances in the understanding of the genetics
of this disease as well as the various products of the drug development
pipeline.
It is well established that obesity, reduced physical activity, and aging
increase susceptibility to T2DM; however, many people exposed to
these risk factors do not develop the disease.95 Recent genome studies
have identified a number of genetic variants that explain some of the
inter-individual variation in diabetes susceptibility.95 In addition to the
genetic markers of T2DM there is also a growing body of evidence suggesting
a role for epigenetic factors (heritable changes in gene function
that occur without a change in the nucleotide sequence) in the
complex interplay between genes and the environment (Figure 4).95
Environmental factors of considerable note include persistent organic
pollutants (POPs), the presence of which have been shown to be related
to the prevalence of diabetes (dose response relationship).96, 97
It has also been suggested that as people become more overweight,
the retention and toxicity of POPs related to the risk of diabetes may
increase.96, 97
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Understanding the underlying genetic and epigenetic defects in blood
sugar homeostasis and how these interact with environmental factors
(e.g. persistent organic pollutants) will help direct T2DM management,
perhaps drawing on new therapies with novel modes of action that
target specific defect(s).34, 95
Drug development is promising to deliver a range of therapies that
will directly address a number of the unmet needs currently facing the
management of T2DM. Compounds such as the SGLT-2 inhibitors promise
to deliver significant improvements in blood glucose levels as well

as reducing body weight, blood pressure and major CV risk factors.
Other agents in clinical development offer a variety of novel modes of
action, some which even target the pathogenesis of T2DM. The arrival
of new drugs onto the market is widely anticipated. However, the enthusiasm
for using new therapies needs to be tempered with data that
validates the safe and effective use of these agents in T2DM.
Chapter 5 Summary
zzGlycaemic control should take into account FPG and PPG as well as HbA1c.
zzThe effect of treatment on body weight, hypertension, lipidaemia and other
CV risk factors is also very important.
zzTreatment adherence may be improved by better tolerability and reduced
pill burden.
zzThe importance of co-morbidities (e.g. renal impairment) are often
neglected in treatment decisions.
zzT2DM treatment requires regular adjustment and a deliberate treat-to-target
strategy.
zzIntensive management increases the cost of treatment, but can reduce the
cost of complications considerably as well as increasing the time free of
complications.
zzDebate continues regarding the effect of intensive versus conventional
glucose control on the risk of CV events, although a number of large studies
will shed more light on this subject.
zzEmerging treatments will be useful in addressing the unmet needs in T2DM
management:
◦◦ Incretin therapies have been shown to have positive effects on lipidaemia.
◦◦ The SGLT-2 inhibitors can reduce weight and blood pressure –
important CV risk factors.
◦◦ Incretin therapies are weight neutral or are associated with significant
weight loss.
◦◦ Metformin appears to reduce the risk of cancer, while drugs that elicit an
increase in circulating insulin levels (SUs, insulin) may have the opposite
effect.
zzMetformin will most likely remain the gold standard in T2DM management.
zzNew treatments, such as those targeting the incretin system may become
increasingly important, especially in combination therapy.
zzAdvances in our understanding of the disease, its treatment and the needs
of the patient will drive the individualisation of T2DM therapy.
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Diabetes Care 2007;30(6):1596-8.

DPP-4 inhibitors in general and linagliptin in particular as a new treatment option in T2DM

" "
The incretin effect
DPP-4 inhibition as a means of controlling blood sugar levels has attracted
considerable attention in recent decades. In order to understand
how DPP-4 inhibitors work, it is pertinent to briefly review the incretin
hormones and the physiological phenomenon known as the incretin
effect.
Insulin and glucagon play a central role in blood sugar homeostasis;
they are influenced by a group of gastrointestinal hormones – the incretins.
More than a century ago it was suggested that a hormone produced
by the gastrointestinal tract stimulated secretory activity in the
pancreas.1 Building on these ideas it was later discovered that eating
promotes a much greater degree of insulin secretion compared with
simply infusing glucose into the circulation, thus bypassing the gut.1 This
phenomenon was termed the incretin (the crude intestinal extract being
named secretin, with excretin stimulating the exocrine portion of
the pancreas, and incretin acting on the endocrine pancreas) effect
and it has since become clear that it involves several hormones (incretin
hormones) of which the most important are glucagon-like peptide-1
(GLP-1) and gastric inhibitory peptide (glucose-dependent insulinotropic
peptide or GIP).1
Both GLP-1 and GIP are similar to glucagon in terms of their amino
acid sequence. The former is secreted primarily by L-cells, which occur
most abundantly in the ileum, colon and rectum, but also, to a
lesser degree, in the upper gastrointestinal (GI) tract while the latter is
secreted by K-cells in the duodenum/upper jejunum. The incretin hormones,
GLP-1 and GIP, are released throughout the day, with levels increasing
several-fold in response to a meal (Figure 1).2 They act on the
pancreas augmenting glucose-induced insulin secretion. GLP-1 also
suppresses glucagon secretion (GIP tends to stimulate glucagon secretion).
3 When blood glucose concentrations are normal or elevated,
GLP-1 and GIP stimulate insulin production and release from pancreatic
b-cells thereby enhancing glucose uptake by insulin-dependent
tissues, effects that are complemented by the ability of GLP-1 to lower
glucagon secretion from the pancreatic a-cells (Figure 1).2 Decreased
glucagon levels, along with higher insulin levels, lead to reduced gluconeogenesis
in the liver, thus lowering blood glucose levels in the fasting
and fed states (Figure 1).2
Dr Thomas Hach
TA Metabolism
Boehringer Ingelheim Pharma GmbH & Co. KG
Ingelheim, Germany
Professor Michael Nauck
Diabeteszentrum Bad Lauterberg
Bad Lauterberg im Harz, Germany
http://img259.imageshack.us/img259/2221/72511648.jpg
Incretin hormones stimulate insulin release from pancreatic β-cells in a
glucose-dependent manner (i.e. the insulin release happens only when
glucose concentrations are normal or elevated, as typically observed
in response to glucose ingestion); therefore the glucose-lowering effect
they elicit does not result in hypoglycaemia. There is even evidence to
suggest that GLP-1 may stimulate increases in β-cell mass and function;
attributes we’ll consider later in this chapter.4 5
The incretin effect and T2DM
Several abnormalities have been observed in the entero-insular axis in
T2DM patients.6 These defects include:
zzReduced GLP-1 response to food (Figure 2).7 8 This has not been uniformly
confirmed, the majority of studies showing unchanged GLP-1 secretion
comparing T2DM patients and healthy control subjects (Figure 3).9
zzA somewhat decreased potency of GLP-1 in stimulating the release of insulin
(Figure 3).10 However, exogenous GLP can still lower glucose concentrations
into the normal range in patients with T2DM.
zzAn almost complete loss of insulin secretion in response to even high doses
of GIP.11 12
zzSuppression of glucagon secretion is impaired during oral glucose tolerance
tests (OGTTs) as opposed to isoglycaemic intravenous glucose infusion.13
This is also true in healthy subjects,14 so it is not an abnormality in T2DM.
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The DPP-4 enzyme
Discovered in 1967, the DPP-4 enzyme has attracted a great deal of
interest because of its role in a number of important cellular processes,
not least of all its function in blood sugar homeostasis. This enzyme occurs
as a membrane bound form abundant in several body tissues (e.g.
kidney, heart and liver) and a free form that circulates in the blood
stream. It is classed as a glycoprotein and a serine exopeptidase that
cleaves peptides with proline and alanine in the pen-ultimate N-terminal
position in a diverse range of substrates, including regulatory peptides
(e.g. GLP-1 and GIP), chemokines, neuropeptides, and vasoactive
peptides.15 Especially intact GLP-1 (sequence [7-36 amide] or [7-37]) is
avidly attacked and degraded (products [9-36 amide] or [9-37]). Even
during a continuous intravenous infusion, only 15 % of GLP-1 remains in
its intact, biologically active state.16 DPP-4 thus limits and terminates the
biological activity of GLP-1 (and, to a lesser degree, GIP).
DPP-4 inhibitors
Background and mode of action
The DPP-4 enzyme is very important in the incretin system as it rapidly
inactivates the incretin hormones, GLP-1 and GIP, thereby regulating
their effects (Figure 4).2 Following the discovery that GLP-1 and GIP
are degraded various inhibitors of the DPP-4 enzyme were identified.
These findings paved the way for a novel means of reducing blood
glucose levels via modulation of the incretin effect; namely prolonging
the effect of native GLP-1, the biological activity of which is limited by
a half-life of less than 2 minutes.17 Inhibition of DPP-4 has been shown
to increase endogenous GLP-1 levels by 2-to-3 fold, thereby improving
insulin secretion, suppressing glucagon, and lowering blood sugar.
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Administration
Crucially, in terms of patient convenience, DPP-4 inhibitors are orally
active. Furthermore, sitagliptin, saxagliptin, linagliptin and alogliptin
only have to be taken once a day, while vildagliptin is taken twice
a day. With many oral antidiabetic drugs (OADs), a dose-finding period
is required at the initiation of therapy, in which the most appropriate
dose for a particular patient is determined. With DPP-4 inhibitors,
a dose-finding period is unnecessary due to the way in which they act,
the speed with which they act and the fact that gastrointestinal disturbances,
such as nausea and vomiting are not common problems.
These characteristics of DPP-4 inhibitors make them suitable for use in
combination regimens.18-21
Efficacy
HbA1c lowering
Currently, there are four DPP-4 inhibitors on the market: sitagliptin, vildagliptin,
saxagliptin and linagliptin, while the arrival of alogliptin onto the
market is imminent. All of these agents have a unique mechanism of
action compared with the other OADs, namely their ability to potentiate
the activity of GLP-1 and enhance insulin secretion in a glucosedependent
manner.22 Numerous randomised controlled clinical trials have
demonstrated that DPP-4 inhibitors can reduce HbA1c, fasting plasma
glucose (FPG) and postprandial glucose (PPG) versus placebo. Tables
1–4 present some of the key information from the sitagliptin, vildagliptin,
saxagliptin and alogliptin clinical trials. The efficacy of linagliptin is discussed
in some detail later in this chapter.
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Cardiovascular protection
Long-term safety data for DPP-4 inhibitors are not yet available. However,
there is evidence to suggest these agents may confer some degree
of cardiovascular protection.63 64 Further data to support or refute
this hypothesis is currently being collected in large, prospective studies.63
A number of meta-analyses have recently been published that investigate,
in detail, the cardiovascular safety of OADs. Sitagliptin was not
associated with an increased risk of major adverse cardiovascular
events.65 Likewise, vildagliptin was not associated with an increased risk
of adjudicated cardiovascular and cerebrovascular events, even in
a patient population that included subjects at increased risk of these
events.66
Preservation of β-cell function
There is growing evidence that progressive β-cell dysfunction is crucial
for the development and progression of T2DM,67 68 the exact nature of
which is still not fully understood, although several β-cell “aggressors”
have been identified (Figure 5).69 In patients with T2DM it has been observed
there is a reduced islet number and/or diminished b-cell mass
in the pancreas due to increased apoptosis and inadequate regeneration.
70 β-cells are known to have a very low antioxidant capacity,
which has the potential to render them vulnerable to oxidative stress
by reactive oxygen and nitrogen species.71 This process is believed to
be central in the impairment of b-cell function during the development
of T2DM. 71
Although T2DM is associated with a progressive decline in b-cell function,
it has been shown that certain pharmacological treatments, such
as DPP-4 inhibitors, metformin and TZDs can ameliorate b-cell function.
72-74 In-vivo studies, usually performed in young rodents, have demonstrated
that DPP-4 inhibitors exhibit favourable actions on islet and
b-cell mass, morphology, and survival.74 75 Since similar beneficial effects
were not observed with sulphonylurea treatment, it is believed that the
effects on insulin-secreting cells in these in-vivo studies are mediated
through specific actions of the drug(s) directly on b-cells rather than by
an improvement of the metabolic milieu.76
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Safety and tolerability
Besides their demonstrated efficacy in lowering blood glucose levels,
DPP-4 inhibitors have proven to be safe and well tolerated, with an
overall incidence of adverse events similar to placebo.19-21 The incidence
of specific adverse events is not increased with DPP-4 inhibitor
treatment compared with placebo, and the dropout rates from studies
due to adverse events are low.77
In some studies, upper respiratory tract infection, nasopharyngitis and
headache have been reported in patients treated with DPP-4 inhibitors;
a truly enhanced frequency has not been established.77 Even though
DPP-4 inhibitors appear to be generally well tolerated, the collective experience
with these drugs in the clinical setting has been relatively short;
therefore, long-term surveillance is critical for the detection of potential
adverse events that may occur rarely or following long-term use.77
In addition to its role in blood sugar homeostasis, the DPP-4 enzyme may
play a role in the immune system (CD26, a marker of activated T-lymphocytes,
is identical to DPP-4) and perhaps also in tumour biology.78 79
Extensive animal toxicology studies with high doses and long duration,
however, do not provide evidence to support the theory that DPP-4
inhibitors have the potential to cause or promote tumours. A recent
analysis of the FDA adverse events reporting database has been much
debated, with the preliminary conclusion that the findings of an elevated
risk for acute pancreatitis and pancreatic carcinoma found in
the case of sitagliptin80 contradict findings from other analyses, are in
part biologically implausible, and most likely are the result of reporting
bias. However, a final judgement cannot be made based on findings
currently available, and results from larger and longer duration clinical
trials and other methods of surveillance need to be waited for to allow
firmer conclusions.
Hypoglycaemia
An important consideration in the tolerability of OAD therapy is hypoglycaemia;
however, compared to some of the OADs on the market,
DPP-4 inhibitors are associated with a low incidence of hypoglycaemia
thanks to their novel mode of action.18 DPP-4 inhibitors avoid the risk of
hypoglycaemia in two ways:
zzGLP-1, the levels of which are increased by DPP-4 inhibition, suppresses
glucagon release only at euglycaemia, but not at hypoglycaemic plasma
glucose concentrations.81
zzDPP-4 inhibitors may, in addition, enhance α-cell responsiveness to the
suppressive effects of hyperglycaemia and the stimulatory effects of hypoglycaemia,
as shown for vildagliptin.82
Even though DPP-4 inhibitor treatment by itself is associated with a minimal
risk of hypoglycaemia, caution is required when they are added to
agents, which themselves can cause hypoglycaemia, such as SUs or insulin.
Recently updated prescribing information in the US recommends
that when sitagliptin is used with insulinotropic agents, a lower dose of
the latter may be required to reduce the risk of hypoglycaemia.83 If at
all possible, this combination should be avoided.
Weight gain
Weight gain is another important concern in OAD therapy as some
compounds, such as SUs, non-SU secretagogues and TZDs are associated
with significant increases in weight.84 Clinical studies have demonstrated
that DPP-4 inhibitors are body-weight neutral.77
Other safety issues
Angioedema has been reported in patients receiving vildagliptin and
concomitant ACE inhibitors. Also, there have been incidences of skin
lesions with vildagliptin, including blistering and ulceration, in nonclinical
toxicology studies.85 Vildagliptin has not been approved in the U.S.
due to a lack of studies in patients with renal impairment. In addition, in
those markets where vildagliptin is approved, liver function monitoring
is recommended with vildagliptin at three-month intervals during the
first year and periodically thereafter.21 With saxagliptin, a dose-related
mean decrease in absolute lymphocyte count was observed during
clinical development, but the clinical relevance of this is unknown.86
Post-marketing reports of serious hypersensitivity reactions in patients
treated with sitagliptin have been reported. These reactions include
anaphylaxis, angioedema, and exfoliative skin conditions including
Stevens-Johnson syndrome.20 Pending approval and the appropriate
dose reduction, sitagliptin and saxagliptin may be used in patients with
renal impairment. Alogliptin has been withdrawn from the FDA approval
process due to insufficient cardiovascular safety data, but it has
been approved in Japan.
Elimination and implications for renal impairment
The DPP-4 inhibitors, sitagliptin, vildagliptin, saxagliptin and alogliptin
are primarily excreted via the kidneys. This route of elimination has
obvious implications for the use of these agents in patients with renal
impairment. Consequently, the prescribing information for sitagliptin,
vildagliptin and saxagliptin in the EU recommend these agents should
not be used in patients with moderate or severe renal impairment.19-21
The equivalent information in the US recommends these agents can be
used in patients with moderate and severe renal impairment with the
appropriate dose adjustment.83

Guidelines
DPP-4 inhibitors have become an important part of the T2DM treatment
strategy, to the extent where a number of the relevant guidelines make
specific recommendations concerning the use of these compounds in
people with this condition (Table 5).
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Other incretin therapies
DPP-4 inhibitors are not the only incretin therapies available for the
management of T2DM. Exenatide and liraglutide are two other drugs
that act on the incretin system. Instead of impeding the degradation
of native GLP-1, exenatide mimics GLP-1, whereas as liraglutide is an
analogue of this incretin (both stimulate GLP-1 receptors and, thus, are
GLP-1 receptor agonists). In this section we will compare and contrast
these agents with the DPP-4 inhibitors.
Exenatide is a peptide hormone and a synthetic version of exendin-4, a
hormone found in the saliva of the venomous lizard, the Gila monster.
This hormone is composed of 39 amino acids, of which >50% are the
same as those found in human GLP-1.92 The actions this drug has on the
body in terms of glucose homeostasis are very similar to GLP-1. However,
unlike endogenous or human recombinant GLP-1, it is more resistant
to being broken down by the DPP-4 enzyme because of its different
molecular structure, thereby extending its duration of action in vivo.92
Liraglutide is a human GLP-1 analogue produced by recombinant DNA
technology in a species of yeast (Saccharomyces cerevisiae). The
linked amino acids that form the backbone of liraglutide are genetically
engineered so that it bears a small fatty-acid chain, an addition
to the hormone that renders it more resistant to degradation by the
DPP-4 enzyme. This modification extends the half-life of liraglutide in the
body.93
Differentiating DPP-4 inhibitors from GLP-1 mimetics and
analogues
Administration
Being peptides, both exenatide and liraglutide would be digested in the
GI tract if they were swallowed as an oral formulation; therefore, they
must be administered via subcutaneous injection into the abdomen,
upper thigh or arm. Exenatide must be injected twice a day, whereas
liraglutide only needs to be injected once a day.94 95 Oral administration
of a drug is more convenient for the patient than an injection and this
route of administration may be a barrier to using exenatide and liraglutide
in patients with such preferences.
Efficacy
Both DPP-4 inhibitors and GLP-1 mimetics/analogues differ in their efficacy
and adverse event profiles. In clinical trials exenatide treatment
was shown to be safe and efficacious. This GLP-1 mimic significantly
reduced HbA1C by -0.4% to -0.86% and body weight by 1.6kg to 2.8kg depending
on the dose and the study.96-98 A study has shown that liraglutide
is superior to sitagliptin in terms of HbA1c reduction (-1.5% vs. -0.9%).99 In a
head-to-head study, liraglutide also out-performed exenatide; reducing
HbA1c by -1.12% compared with -0.79% for exenatide.100
With increasing interaction of GLP-1 or GLP-1 receptor agonists with
GLP-1 receptors, as obtained with both GLP-1 analogues (high, pharmacological
concentrations) and DPP-4 inhibitors (near-physiological
concentrations, approximately 2-3 fold above placebo levels), there
are significant effects on the pancreatic islets and the respective glucose
homeostasis. Higher concentrations (which may not be reached
with DPP-4 inhibitor therapy due to their mechanism of action) are
needed to slow down gastric emptying and to reduce appetite – characteristics
of exenatide and liraglutide. Significant weight loss is one of
the major advantages of GLP-1 mimetic/analogue therapy.
Safety and tolerability
In terms of safety tolerability, exenatide and liraglutide appear to be
generally well tolerated, although they are associated with gastrointestinal
adverse events, such as nausea, diarrhoea and vomiting.101 Both,
exenatide and liraglutide have been shown to be associated with improved
cardiovascular disease risk factors.102 103 Exenatide should not
be used in patients with severe renal impairment or end-stage renal disease
and should be used with caution in patients with renal transplantation.
94 Liraglutide should be used with caution in renal impairment due
to limited experience in this patient population.95 Acute pancreatitis is
a potential concern for all incretin-based therapies. There have been
reports of acute pancreatitis in people treated with exenatide. Albeit
rare, these prompted the regulatory bodies to release safety warnings
regarding the use of this drug.94 It seems that acute pancreatitis is not
limited to the GLP-1 mimetics. As of January 2010 88 cases of acute
pancreatitis in patients taking sitagliptin had been reported to the FDA,
prompting a revision of the package insert for this drug as well.104 The
recent analysis of the FDA adverse events reporting database concludes
that careful long-term monitoring of patients treated with GLP-1 mimetics
or DPP-4 inhibitors is required.80
Linagliptin – key characteristics
Linagliptin is a forthcoming addition to the DPP-4 inhibitor class. This section
looks at the key attributes of this drug, especially those that differentiate
it from the other DPP-4 inhibitors.
Pharmacology and pharmacokinetics
The affinity of linagliptin for the DPP-4 enzyme is high, which results in a
slow dissociation of this compound from its substrate. Compared with
vildagliptin, linagliptin has a 10-fold slower dissociation/off-rate.105 The
very low dissociation of linagliptin complements the potency of this
drug, which is the highest in its class.105 Linagliptin has the highest selectivity
for DPP-4 relative to DPP-8 and DPP-9 of all the DPP-4 inhibitors.106-110
Linagliptin is 10,000 times more selective for DPP-4 than it is for either
DPP-8 or DPP-9. This has potential implications for the tolerability and
long-term safety of linagliptin, since the specific functions of DPP-8 and
DPP-9 have not yet been elucidated. A high selectivity for DPP-4 reduces
the likelihood of possible adverse effects related to the inadvertent
inhibition of DPP-8 and DPP-9.111
Early clinical studies involving healthy volunteers demonstrated that
linagliptin is rapidly absorbed following oral administration of a 5 mg
dose. Peak plasma concentrations were reached after 1.5 hours. As a
consequence of the tight binding of linagliptin to its substrate it has a
long terminal half-life of more than 100 hours, but this does not contribute
to the accumulation of the drug. The effective half-life for accumulation
of linagliptin is approximately 12 hours. After once-daily dosing,
steady-state plasma concentrations of 5 mg linagliptin are reached by
the third dose.112 The co-administration of a high-fat meal with linagliptin
had no clinically relevant effects on pharmacokinetics; therefore
it may be administered with or without food.
Perhaps the most salient of linagliptin’s pharmacokinetic characteristics
is its primarily non-renal route of excretion. Renal excretion accounts for
only 5% of the dose. One main metabolite was detected during the
course of preclinical studies, but this was found to be pharmacologically
inactive. With its primarily non-renal route of elimination linagliptin
can be used in patients with any degree of renal or liver impairment or
cardiac insufficiency. No warnings/precautions, dose adjustments and
additional monitoring of renal or liver function are required in patients
treated with linagliptin.
Efficacy
Linagliptin was tested in a large clinical trial program involving >6,500
patients in more than 40 countries. These randomised, controlled studies
have shown that linagliptin reduces HbA1c in all stages of T2DM and in
combination with all currently used treatment regimens. In addition, improvements
in FPG, PPG and β-cell function have been demonstrated.
Key information from these studies is summarised in Table 6. As monotherapy,
linagliptin has been shown to provide a significant and clini
cally meaningful treatment option for T2DM patients including those
whose treatment options are limited due to renal impairment.
As monotherapy and in combination with metformin and metformin
and a SU, linagliptin was proven to be most efficacious in patients with
higher baseline HbA1c values. In addition to significantly lowering HbA1c
(Table 6), linagliptin as monotherapy also had favourable effects on
FPG and 2h PPG. At 24 weeks these glycaemic parameters were reduced
by -23 mg/dL (-1.3 mmol/L) and -58 mg/dL (-3.2 mmol/L), respectively
versus placebo.113
As an add-on to metformin, linagliptin therapy significantly reduced
HbA1c at 24 weeks (Table 6), and also yielded significant, placebocorrected
reductions in mean FPG (-23 mg/dL, or -1.3 mmol/L) and 2h
PPG (- 67 mg/dl).114 Likewise, triple therapy (metformin + SU + linagliptin)
significantly reduced HbA1c (Table 6). The placebo-adjusted reduction
in FPG with this triple therapy regimen was -13 mg/dL at 24 weeks.115
In initial combination therapy with a pioglitazone, linagliptin therapy
significantly reduced HbA1c (Table 6).116
cally meaningful treatment option for T2DM patients including those
whose treatment options are limited due to renal impairment.
As monotherapy and in combination with metformin and metformin
and a SU, linagliptin was proven to be most efficacious in patients with
higher baseline HbA1c values. In addition to significantly lowering HbA1c
(Table 6), linagliptin as monotherapy also had favourable effects on
FPG and 2h PPG. At 24 weeks these glycaemic parameters were reduced
by -23 mg/dL (-1.3 mmol/L) and -58 mg/dL (-3.2 mmol/L), respectively
versus placebo.113
As an add-on to metformin, linagliptin therapy significantly reduced
HbA1c at 24 weeks (Table 6), and also yielded significant, placebocorrected
reductions in mean FPG (-23 mg/dL, or -1.3 mmol/L) and 2h
PPG (- 67 mg/dl).114 Likewise, triple therapy (metformin + SU + linagliptin)
significantly reduced HbA1c (Table 6). The placebo-adjusted reduction
in FPG with this triple therapy regimen was -13 mg/dL at 24 weeks.115
In initial combination therapy with a pioglitazone, linagliptin therapy
significantly reduced HbA1c (Table 6).116
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Safety and tolerability
The linagliptin studies conducted to date have demonstrated weight
neutrality in mono- and combination therapies. Additionally, there was
no increased risk of hypoglycaemia attributed to linagliptin use in monotherapy
or combination therapy with metformin or pioglitazone. Like
the other DPP-4 inhibitors, the overall incidence rate of adverse events
reported for linagliptin was similar to placebo (55.0% versus 53.8%). Discontinuation
of therapy due to adverse events was higher in patients
who received placebo as compared to linagliptin 5 mg (3.6 % versus
2.3 %). The most frequently reported adverse event in the linagliptin
clinical trial programme was hypoglycaemia because of those cases
observed in the triple combination study (metformin + sulphonylurea +
linagliptin). The incidence of hypoglycaemia in this study was 22.9% in
the treatment arm compared with 14.8% in the placebo arm. None of
these cases of hypoglycaemia was classified as severe.
What do these attributes mean for patients with T2DM?
It is anticipated that the primarily non-renal route of elimination of linagliptin
will allow this compound to be used in people with renal insufficiency
without dose adjustments. This has potentially important implications
for T2DM management in light of the fact that at least a third of
people with diabetes have some degree of renal impairment and that
many current T2DM treatments are contraindicated in patients with
renal impairment.84 122
The high potency of linagliptin means that a low dose of linagliptin can
be administered to T2DM patients in small tablets; features that are crucial
to the good tolerability of a drug and the willingness of people with
T2DM to take their medication as prescribed. Additionally, these attributes
lend linagliptin to inclusion in fixed-dose combinations. The high
selectivity of linagliptin for the DPP-4 enzyme rather than DPP-8 or DPP-9
is reassuring, in that no untoward off-target interactions are expected,
helping to confer a placebo-like tolerability profile. As linagliptin binds
tightly to the DPP-4 enzyme, a single dose taken at any time of the day
is sufficient to provide a full 24 hours of glycaemic control.
Chapter 4 Summary
zzEating promotes a much greater degree of insulin secretion compared with
intravenous injection of glucose. This is the incretin effect, a physiological
phenomenon mediated by the incretin hormones, notably glucagon-like
peptide-1 (GLP-1) and gastric inhibitory peptide (GIP).
zzIncretin hormones elicit an increase in glucose-dependent insulin secretion
and suppress glucagon secretion as well as increasing sensitivity to insulin
and glucose uptake in the peripheral tissues, independent of insulin secretion.
zzGLP-1 may stimulate increases in β-cell mass and function (animal and cell
line studies).
zzIn people with T2DM there are several defects in the incretin effect:
◦◦ Decreased potency of GLP-1 in stimulating the production and release
of insulin.
◦◦ An almost complete loss of late-phase insulin secretion in response to GIP.
◦◦ Suppression of glucagon secretion is impaired during oral glucose tolerance
tests (OGTTs) as opposed to isoglycaemic intravenous glucose infusion.
zzDPP-4 inhibitors can enhance and prolong the effects of endogenous GLP-1
by inhibiting the enzyme that rapidly degrades this incretin hormone.
zzThese DPP-4 inhibitors are orally active, do not require a dose-finding period
and two of the three types currently available only have to be taken
once a day.
zzDPP-4 inhibitors can significantly reduce HBA1c, FPG and PPG. There is also
some evidence to suggest they may preserve β-cell function and provide
some degree of cardiovascular protection. However, studies proving a
lasting improvement in the course of diabetes progression still have to be
initiated.
zzGenerally, DPP-4 inhibitors have proven to be safe and well tolerated, with
an overall incidence of adverse events similar to placebo.
◦◦ DPP-4 inhibitor treatment is associated with a low incidence of hypoglycaemia
due to their glucose-dependent mode of action (as derived from
studies with GLP-1).
◦◦ DPP-4 inhibitors are body-weight neutral.
◦◦ Specific issues with vildagliptin may be angioedema, skin lesions and elevation
in liver enzymes (with uncertain impact on the spectrum of adverse
events observed with clinical use). Saxagliptin has been associated
with a minor decrease in absolute mean lymphocyte count, again with
uncertain clinical significance.
◦◦ All the currently available DPP-4 inhibitors (sitagliptin, saxagliptin, vildagliptin
and alogliptin) are primarily excreted via the kidneys with implications for
their use in people with renal impairment (dose reduction or avoidance of
use in that particular population).
◦◦ The suspicion has been raised based on analyses from an adverse events
reporting database located at the FDA that pancreatitis and pancreatic
carcinoma may be observed more often with sitagliptin treatment, but
this evidence is considered non-convincing due to the nature of this database
and the high likelihood for reporting bias.
zzSeveral guidelines make specific recommendations concerning the use of
DPP-4 inhibitors.
zzExenatide and liraglutide are injected incretin therapies.
◦◦ They are effective in reducing HbA1c as well as body weight.
◦◦ They are generally well tolerated and the most common adverse events
are gastrointestinal disturbances.
◦◦ Exenatide should not be used in patients with severe renal impairment or
end-stage renal disease and liraglutide should only be used with caution
in renal impairment.
◦◦ Acute pancreatitis is a potential concern for all incretin-based therapies,
including DPP-4 inhibitors and GLP-1 mimetics/analogues.
zzLinagliptin is a relatively new addition to the DPP-4 inhibitor market. It has the
following characteristics:
◦◦ A very high affinity for its substrate and a high level of potency compared
with the other compounds in its class.
◦◦ 10,000 times more selective for DPP-4 than it is for either DPP-8 or DPP-9.
◦◦ Rapidly absorbed and has a long terminal half-life of more than 100 hours.
◦◦ Administered as a single 5 mg tablet at any time of the day with or without
food.
◦◦ Primarily excreted non-renally; therefore it can be used without dose adjustments
or warnings in patients with renal impairment.
◦◦ In clinical trials, linagliptin alone or in combinations with other OADs has
demonstrated its ability to improve HbA1c, FPG, PPG and β-cell function.
◦◦ Linagliptin is weight neutral and has proved to be well tolerated.

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