Antihypertensive drugs and glucose metabolism: comparison between a diuretic, a beta-blocker and felodipine, a new calcium antagonist in subjects with arterial hypertension and diabetes. Felodipine, a new antihypertensive calcium antagonist, was compared with metoprolol, a beta-blocker, and hydrochlorothiazide, a diuretic, with respect to glucose tolerance in a randomized double-blind cross-over study consisting of 11 patients, of age range 50-70 years, who had developed diabetes during antihypertensive treatment. Each treatment period lasted for 10 weeks. The blood pressure was similar irrespective of treatment. Serum glucose levels during the oral glucose tolerance test were significantly lower when the patients were treated with felodipine than when they were taking hydrochlorothiazide. Serum insulin levels appeared to decrease at an earlier stage of the test when the patients were treated with felodipine, the calcium antagonist, than with the other two antihypertensive substances, which suggests that glucose tolerance is impaired to a lesser extent during treatment with the calcium antagonist. Glucose tolerance was never completely normalized with any of the drugs tested. 