Constant K+/Na+ excretion ratio during peak diuresis after piretanide but insignificant K+ loss during 24 hours.

The effect of piretanide on Na+ and K+ excretion and on renal haemodynamics has been studied in 14 subjects with a GFR (Inulin clearance) ranging from 140 to 2 ml.min-1. After a two day fluid and salt balance control period, oral piretanide 6 mg induced a natriuresis and kaliuresis, which was proportional to the GFR of the patients. The ratio of drug-induced K+ to Na+ excretion was always 0.13, independent of individual GFR. This was only true for the duration of the action of piretanide, tau, which was 6 h in subjects with normal GFR and 5 h in patients with impaired kidney function. Surprisingly, after tau, i.e. for 24 h after drug administration, less potassium was lost than in the pretreatment period. Neither the GFR nor the renal blood flow (PAH clearance) of the patients were affected by piretanide. In conclusion, piretanide given once a day was an effective natriuretic agent, even in end-stage renal disease, and it produced relatively little K(+)-loss when given once daily.