Choosing Antihypertensive Therapy for a Diabetic Cardioselectlve ~·blockers and potassium-sparing diuretics appear suitable

The control of BP in diabetic patients is important because of the possible increased risks 01 coronary heart disease, exudative retinopathy and nephropathy. However, the requirement for therapy must be weighed against the fisk of drug-induced metabolic effects. Non-drug therapy such as salt restriction and weight reduction should be considered initially.

,8-Blockers are frequently used in hypertension but delay recovery 'rom hypoglycaemia. Non-cardioselective tJ-blockers delay blood glucose recovery, probably by impairing .B2-mediated glycogenolysis. In addition, the subsequent rise in catecholamines during hypogtycaemia causes on increase in a-receptor stimulation and an increase in BP. Some studies have also shown ,B-blockade to mask the patient's awareness of hypoglycaemia. Non-cardioselective drugs also affect glycaemic control by blockade of ,B-2"receptors which leads to a decreased release of insulin. ,B-Blockers may also have adverse effects on lipid metabolism and cause cold extremities (an important consideration as diabetics are prone to vascular disease).

Diabetes mellitus may be worsened in a dose-related manner by thiazide diuretics. However, the resultant hyperglycaemia may be related 10 Ihe coexistent hypokalaemia. Potassium-sparing diuretics possibly have less hyperglycaemic effect than other diuretics but more of an effect than cardioselective ,B-blockers. Thiazide diuretics also have adverse effects on serum lipids and cause some impotence_ Nifedipine, diltiazem and verapamil inhibit insulin release from perfused islets in vitro. but they have little or no effect in vivo.

The effects of hydralazine have not been properly evaluated. Prazosin has been shown by some studies to improve glucose tolerance, however angiotensin converting enzyme inhibitors cause increased blood glucose in some studies and further trials are required. Methyldopa and clonidine both cause a slight worsening of glucose tolerance, and in addition methyldopa causes a significant increase in triglycerides and some postural hypotension.

Cardioselective ,B-blockers are an acceptable first line treatment in diabetics. If this therapy fails a potassium-sparing diuretic is suitable for insulin dependent patients or prazosin can be used for non-insulin dependent patients. Struthers. A.D.: Postgradu"a Medical Journal 51: 563·569 (Ju/I985)

4 INPHARMAa 14 StJp 1985 OI55-2703/85/0gr4-0004/0S01.00/0 ~ ADIS Press