Serum potassium and uric acid changes during treatment with timolol alone and in combination with a diuretic.

Timolol, 10 to 40 mg daily, given to 103 patients with uncomplicated arterial hypertension induced significant increments of serum potassium at all dose levels (p less than 0.05). The magnitude of the increments was dependent on daily timolol dosage. When hydrochlorothiazide and amiloride were added, serum potassium decreased (p less than 0.001), but a major determinant of the magnitude of the decrease was the dosage change of the timolol. Serum uric acid was influenced in a paradoxical way during timolol monotherapy; there was a rise in all 3 dosage groups (p less than 0.02) but the lowest group showed the largest increase and vice versa. On addition of hydrochlorothiazide and amiloride, there was a further increase in serum uric acid, the magnitude of which depended on the concomitant reduction in the dose of timolol, with reductions in dose causing a larger rise in serum uric acid and increments, a smaller rise. The increments of serum uric acid were greater in females than in males during both treatment periods. The results indicate that beta blockers induce dose-dependent rises in serum potassium and may counteract undesirable effects of diuretics on serum potassium. Beta blockers seem to have a paradoxical effect on serum uric acid and may aggravate the hyperuricemia induced by diuretics.