Effects of drugs on glucose tolerance in non-insulin-dependent diabetics (Part I).

Non-insulin-dependent diabetes mellitus (NIDDM) is being increasingly diagnosed as its importance as a risk factor for the development of cardiovascular disease continues to be recognised. Good metabolic control remains a major goal of drug therapy as it decreases the severity and incidence of diabetic complications. Many drugs have been known to interfere with glucose control, either in a beneficial or, more commonly, in a deleterious fashion. Unfortunately in many instances drug-induced effects have not been looked at specifically in NIDDM. Thiazide diuretics have been shown to cause a deterioration in glucose control not only in the general population but especially in patients who have impaired glucose tolerance. While the effect appears less with potassium supplementation and the lower dosage employed nowadays, thiazide diuretics are best avoided in diabetic patients. Loop diuretics have been reported to reduce glucose control to a lesser extent than thiazides. Although indapamide would appear not to interfere with blood sugar control in NIDDM, higher doses that cause potassium loss may cause a deterioration. beta-Adrenoceptor antagonists have been reported to cause a rise in blood sugar and glycosylated haemoglobin in NIDDM. The effect may be more marked in patients on oral hypoglycaemic agents as opposed to diet alone and in those on concomitant thiazide diuretics. The greatest effect was seen with propranolol, and the least with cardioselective and the less lipophilic beta-blockers. It is of interest that alpha-blockade with prazosin seems to antagonise beta-adrenoceptor blocker-induced deterioration in glucose control. The calcium antagonists have differing effects which may be structure related. In some, but not all, studies use of the dihydropyridines such as nifedipine has been associated with a deterioration in glucose control in NIDDM. Long term studies are needed to assess definitively their effect on glucose control. Verapamil, on the other hand, has in 1 small study been found to have a beneficial effect on glucose control in NIDDM. Centrally acting alpha-agonists such as the antihypertensive drug clonidine have not been shown to result in a deterioration in glucose control when used in NIDDM, although there are isolated case reports. Long term therapy with the more specific agonist guanfacine was reported in 1 uncontrolled study to have a beneficial effect on glucose tolerance in NIDDM. Uncontrolled studies suggest that phenothiazines may aggravate diabetic control. The significance of a number of recent observations is not fully clear.(ABSTRACT TRUNCATED AT 400 WORDS)