Oral Antidiabetic Agents - Luzimar Teixeira
Oral Antidiabetic Agents - Luzimar Teixeira
Oral Antidiabetic Agents - Luzimar Teixeira
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<strong>Oral</strong> <strong>Antidiabetic</strong> <strong>Agents</strong> 403<br />
sustained. [48] The explanation may have been, at<br />
least in part, a spuriously low mortality rate in the<br />
comparator sulphonylurea monotherapy group. [47,49]<br />
The small number of events in this substudy adds to<br />
the uncertainty.<br />
Sulphonylurea plus metformin is a commonly<br />
used combination and it would be reassuring to have<br />
definitive safety data. Since each class as monotherapy<br />
appears safe from the cardiovascular perspec-<br />
tive, alternative explanations have been postulated<br />
to explain similar findings seen in observational<br />
studies. [49] One plausible confounder might be great-<br />
er cardiovascular risk attributable to more severe<br />
metabolic derangements in patients treated with the<br />
combination. Results from US trials and various<br />
large databases of follow-up with sulphonylurea<br />
plus metformin combination therapy have been re-<br />
assuring. [21,49,50] Additional well designed compara-<br />
tive studies of appropriate statistical power would be<br />
required to quantify the risk to benefit equation for<br />
combination treatment with sulphonylurea plus met-<br />
formin. However, recent results from the 5-year<br />
follow-up of UKPDS – with no further attempt to<br />
continue in randomised groups – show that the adverse<br />
impact of sulphonylurea plus metformin com-<br />
bination seen initially is no longer evident. [48] At this<br />
point, the aforementioned benefits observed on mor-<br />
tality and cardiovascular disease in overweight patients<br />
initially randomised to metformin monother-<br />
apy, while diminished, remained significant.<br />
Consistent with the action of metformin on insulin<br />
sensitivity, addition of metformin to patients<br />
receiving insulin therapy may necessitate a reduction<br />
of insulin dosage. Some patients also show an<br />
improvement in glycaemic control, although this is<br />
not always impressive. Metformin reduces the<br />
weight gain associated with insulin therapy and, by<br />
decreasing the insulin dosage, there may be a decrease<br />
in hypoglycaemic episodes. The regimen has<br />
usually involved once-daily bedtime long-acting<br />
(lente) insulin or twice-daily insulin suspension isophane<br />
with metformin at mealtimes. In the US Diabetes<br />
Prevention Program, metformin reduced the<br />
incidence of new cases of diabetes in overweight<br />
and obese patients with impaired glucose tolerance<br />
by 33% overall. This compares with an intensive<br />
regimen of diet and exercise, which reduced the risk<br />
by 58%. [51] Younger, more obese individuals show-<br />
ed the most response to the preventive effects of<br />
metformin.<br />
3.1.5 Adverse Effects<br />
Abdominal discomfort and other gastrointestinal<br />
adverse effects, including diarrhoea, are encountered<br />
fairly commonly during the introduction of<br />
metformin. Symptoms may remit if the dose is re-<br />
duced and re-titrated slowly, but about 10% of patients<br />
cannot tolerate the drug at any dose. The most<br />
serious feared adverse event associated with metfor-<br />
min is lactic acidosis; the occurrence is rare (about<br />
0.03 cases per 1000 patient-years), but the mortality<br />
rate is high. [14,38] Since the background incidence of<br />
lactic acidosis amongst type 2 diabetic patients has<br />
not been established, it is possible that a proportion<br />
of cases that have been attributed to the drug were<br />
caused by other factors; this remains an area of<br />
controversy. Most cases of lactic acidosis in patients<br />
receiving metformin are due to inappropriate pre-<br />
scription of the drug. [23,40,46,52] The leading contraindication<br />
is renal insufficiency. [52] Metformin increases<br />
glycolysis to lactate, particularly in the<br />
splanchnic bed. The situation will be aggravated by<br />
any hypoxic condition or impaired liver function. [53]<br />
Hyperlactataemia occurs in cardiogenic shock and<br />
other illnesses that decrease tissue perfusion, and<br />
metformin is often only an incidental factor in these<br />
cases. [54] In the absence of reliable data to the con-<br />
trary, metformin treatment should be stopped im-<br />
mediately in all cases of suspected or proven lactic<br />
acidosis, regardless of cause. Lactic acidosis is typi-<br />
cally characterised by a raised blood lactate concen-<br />
tration (e.g. >5 mmol/L), decreased arterial pH and/<br />
or bicarbonate concentration with an increased ani-<br />
on gap ([Na + ] – [Cl – + HCO3 – ] >15 mmol/L).<br />
Presenting symptoms are often nonspecific, but fre-<br />
quently include hyperventilation, malaise and abdominal<br />
discomfort. Treatment should be commenced<br />
immediately without waiting to determine whether<br />
metformin is a cause; bicarbonate remains the ther-<br />
apy of choice but evidence of its efficacy is scanty.<br />
The value of haemodialysis in removing accumulat-<br />
© 2005 Adis Data Information BV. All rights reserved. Drugs 2005; 65 (3)