Aggravation by propranolol of hyperglycaemic effect of hydrochlorothiazide in type II diabetics without alteration of insulin secretion.

14 hypertensive men with type II diabetes sequentially received, in random order, hydrochlorothiazide 50 mg twice a day, propranolol 80 mg twice a day, and both drugs in combination. The 3-week treatment periods were separated by a 1-week washout period. Hydrochlorothiazide significantly increased fasting glucose by 31% (p less than 0.05) and glycosylated haemoglobin (HbA1c) by 6.0% (p less than 0.10). A similar treatment period of propranolol 80 mg twice a day caused no significant increases. However, when both drugs were taken in combination, fasting glucose rose by 56% and HbA1c by 14.7% (p less than 0.01). The hyperglycaemic effect of hydrochlorothiazide and its potentiation by propranolol were independent of serum potassium and of endogenous insulin secretion as measured by urine C-peptide excretion. The combination of hydrochlorothiazide and propranolol thus seems to cause serious disturbances in glycaemic control in type II diabetics by mechanisms independent of insulin secretion.