Bumetanide and furosemide.

We assessed the response to and handling of furosemide and bumetanide in 30 experiments with the former and 46 with the latter in normal subjects. Oral doses of furosemide (20, 40, and 80 mg) were used, and subjects received oral doses of 0.5, 1, and 2 mg bumetanide and intravenous doses of 0.5 and 1 mg bumetanide. both drugs were quickly absorbed and peak urinary amounts were reached at 75 min (median). Approximately 30% of an oral dose of each drug was excreted unchanged in the urine with no evidence of dose-dependent elimination. After intravenous injection, 36% of the bumetanide was excreted unchanged. Consequently, bumetanide has an estimated bioavailability of 80% (approximately 40% for furosemide). The relationship between the logarithm of the urinary bumetanide excretion rate and the logarithm of the sodium excretion rate was described by a sigmoid-shaped dose-response curve, with a dose inducing half-maximal response of 1 +/- 0.04 micrograms/min; it was 69.8 micrograms/min for furosemide. Overall, the distinguishing features between the two drugs are the 200% greater bioavailability and the much greater potency of bumetanide.