Glucose tolerance during antihypertensive therapy in patients with diabetes mellitus.

Many antihypertensive drugs have adverse effects on glycemic control when they are used in diabetic patients. This was noted for thiazide diuretics in 1960, and the mechanism of the effects remains uncertain. Indirect evidence suggests that changes in the serum potassium are at least contributory, although the principal mechanism of thiazide-induced hyperglycemia is probably a reduction in the insulin response to glucose. Beta blockers also adversely affect blood sugar control but only by a small margin. The main cause for concern with beta blockers, however, is their effect during hypoglycemia in which nonselective agents delay blood sugar recovery. In diabetic patients, the institution of antihypertensive therapy should be followed by a reassessment to note any changes in sugar, potassium, and lipids, or side effects.