Piretanide, a potassium stable diuretic, in the treatment of essential hypertension: a double-blind comparison of two formulations.

In a randomized double-blind parallel group study the effects of two formulations of piretanide (standard tablet and slow-release capsule) were compared in patients with mild to moderate essential hypertension. Forty patients entered the study and thirty-seven completed it. Both formulations of piretanide produced a significant reduction in erect and supine blood pressure which was evident at 2 weeks and was maintained and further enhanced over the ensuing trial period. A mean maximal fall in supine diastolic pressure of 22% was observed in the piretanide tablet group, and of 20% in the slow-release piretanide group. Blood pressure fell more quickly at the beginning of treatment with the tablet preparation, such that there was a significant difference between the groups up to the fourth week. After this point the blood pressure lowering effect was very similar in both groups and there was a progressive reduction in supine blood pressures over the 12-week active-treatment period. Slow-release piretanide produced a smoother effect than the tablet formulation. There were no significant changes in serum potassium and serum magnesium in either treatment group. Minor changes were seen in some other biochemical and haematological variables but these were of no clinical significance. Three patients were withdrawn from the study because of side-effects: one because of an excessive antihypertensive response to the tablet formulation; and two because of allergic reactions to the slow-release preparation. Side-effects were otherwise mild and infrequent.