Acute and long-term renal and metabolic effects of piretanide in congestive cardiac failure.

1. The renal and metabolic effects of the sulphamoylbenzoic acid diuretic, piretanide, have been studied, under controlled dietary conditions, in 39 patients with congestive cardiac failure. 2. In acute studies, peak saluresis occurred within 4 h of oral piretanide administration; saluresis was complete within 6 h, after which a significant antidiuretic effect was observed. Addition of triamterene, 50 mg, blunted the 0-6 h kaliuretic effect of piretanide. Over 24 h, piretanide, alone, caused insignificant urinary losses of potassium when compared with control. 3. In comparative studies, the piretanide dose-response curve was found to be parallel to that of frusemide over the dose range studied. The 0-6 h saluretic responses of piretanide, 6, 12 and 18 mg, were found to be equivalent to frusemide, 40, 80 and 120 mg respectively. The collective mean ratios of all the saluretic responses to each dose of piretanide with the corresponding dose of frusemide was observed to be 0.99 +/- 0.12, over 0-6 h period, and 0.86 +/- 0.09 over the 24 h period. The relative potency of piretanide, when compared with frusemide was found to be 6.18 (95% confidence limits 4.87-8.33), over the 0-6 h period, and 4.73 (95% confidence limits 3.65-6.14), over 24 h period. 4. In 15 patients in severe cardiac failure, urinary recovery of piretanide, over first 6 h, at the start of treatment was 21.2 +/- 2.1% while efficiency of the diuretic (mmol Na/mg drug) was 47.3 +/- 4.1. Long-term piretanide therapy was continued in the same group for up to and in some cases over 3 years. No other diuretics or potassium supplements were given. Piretanide dosage ranged from 6 to 24 mg day-1 according to clinical need. Plasma potassium fell significantly at 12 and 24 months, though remaining within the normal range. At these same times, significant elevations in both plasma urate and total fasting cholesterol were observed. Two patients developed overt gout on high dose piretanide therapy (24 mg day-1). Piretanide was well tolerated, and effective in the management of congestive cardiac failure without any other recognized metabolic or electrolyte changes.