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

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Abstract
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 < 0.05). The magnitude of the increments was dependent on daily timolol dosage. When hydrochlorothiazide and amiloride were added, serum potassium decreased (p < 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 < 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.