Multiple peaks and low bioavailability of furosemide correlate with the volume of fluid ingested

Two different single dose cross-over bioavailability studies were performed comparing a new oral furosemide preparation (test preparation = preparation A) with a marketed standard with a marketed standard preparation (reference preparation = preparation B). Test and reference preparation contained 40 mg of furosemide each. Into both studies, 18 healthy male volunteers were included; 4 volunteers participated in both studies. In study 1, the volunteers ingested the tested preparations together with 300 ml of an electrolyte solution in order to substitute volume and electrolyte deficits. Additional 200 ml were given 30 min post dose, 500 ml during the next 30 min and 1000 ml during the second hour after drug intake. In study 2, the tested preparations were ingested together with 200 ml of water without any additional volume substitution. The plasma concentration curves of study 1 showed a double peaking with a first maximum of furosemide levels at 1 h and a second peak at 3 h and 4 h, respectively, on average. The concentration-time curves of study 2 showed a single peak 1 h p.a. in the mean for both preparations. The relative bioavailability of preparation A was about 67% in study 1 compared to study 2. Preparation B showed a relative bioavailability of 59% in study 1 compared to study 2.