Pharmacokinetics of furosemide urinary elimination by nephrotic children.

Single doses of 2 mg/kg of furosemide (F) were given postprandially as tablets to 17 steroid-responsive nephrotic syndrome (NS) patients, 2.5-15 years old, and seven control children requiring F therapy. One-half, 1, and 2 h after administration, F absorption rate, calculated from the drug urinary excretion data, was significantly more rapid in the NS patients compared to that in the controls. Bioavailability of F in the nephrotic children averaged 58.8% indicating that the gastrointestinal absorption of the drug was unaffected by the disease and by the age of the patients. The first pass effect of F was 24% of the administered dose. The elimination half-life of F, calculated from the drug urinary excretion data in the NS patients was 2.06 +/- 0.96 h (mean +/- SD), whereas in the control children, it was 2.14 +/- 0.69 h. There seems to be no relationship between F elimination half-life and the serum albumin concentration in the NS patients. Also, no correlation was found between the amount of F (mg) excreted in urine during 2 or 6 h after administration (the time of complete absorption of F from the gastrointestinal tract, and the time of the drug diuretic effect, respectively) and the serum albumin concentration in the NS patients. Moreover, no significant difference in the cumulative F urinary excretion was found between both groups of children. The data indicate that factors in addition to serum albumin concentration play a role in the elimination kinetics of F in nephrotic children.