Oral Hypoglycaemic Drugs: Clinical Pharmacology and Therapeutic Use

Summary

There are two main groups of oral hypoglycaemic compounds — the sulphonylureas and the biguanides. The sulphonylureas act by stimulating release of insulin in the intact pancreas. Animal studies show that the β-cells of the islets may be stimulated to divide. Long-term hypoglycaemic effects cannot be explained solely by the extra release of insulin.

Suitable diabetics for sulphonylurea treatment are typically those of maturity onset type and showing no ketonuria. Since weight gain is stimulated, obese subjects are not ideal candidates for sulphonylurea therapy. The ‘second generation’ sulphonylureas are more active weight-for-weight than their predecessors but not necessarily therapeutically superior. Factors such as potency, pharmacokinetic properties, cross reactivity as allergens and cost influence selection for individual patients. Primary or secondary failure of the hypoglycaemic effect of sulphonylureas may often be overcome by adding a biguanide, with its different mode of action. Side-effects of sulphonylureas include rashes, dyspepsia, flushing after alcohol and occasional jaundice or depression of the bone marrow. A few commonly used drugs, notably phenyl- and oxyphenbutazone, may increase the hypoglycaemic activity of the sulphonylureas, while others such as the thiazides and steroids may decrease it. Hypoglycaemia may also be simply an overdose effect.

The biguanide compounds do not produce hypoglycaemia in their own right and do not increase insulin output. Rather, peripheral uptake of glucose is increased and, in large doses, intestinal absorption is decreased. Suitable recipients are maturity onset, non-ketotic diabetics of above average weight who have not responded adequately to diet alone. Primary and secondary failures can be treated by adding a sulphonylurea. Of the two commonly used compounds, phenformin carries a slight but significant risk of inducing dangerous lactic acidosis. More common side-effects of both metformin and phenformin are anorexia, nausea, vomiting and diarrhoea with malaise. Slow increase in dosage can largely avoid these side-effects. Long-term large dose treatment may produce malabsorption of various dietary elements, such as vitamin B₁₂ and folate.

The University Group Diabetes Program (UGDP) study on early diabetics brought to light possible serious cardiovascular toxicity of both tolbutamide and phenformin, but other studies have tended to indicate possible benefit to cardiovascular morbidity. The fact that the diet-treated group fared better than the tablet-treated group has however, stressed the importance of diet as the main treatment of early diabetes.