Comparative bioavailability of furosemide from solution and 40 mg tablets with different dissolution characteristics following oral administration in normal men

Furosemide tablets, with markedly different dissolution characteristics, and solution were orally administered to 21 healthy adult males to determine the effect of in vitro dissolution rate on in vivo bioavailability profiles. Furosemide 40 mg was given as Tablet A (fast dissolution characteristics), Tablet B (slow dissolution characteristics), and an aqueous solution. Both batches of tablets had identical formulae and were produced by a common process. The dissolution rate of the slower Tablet B was probably retarded by extension of the wet granulation time. Blood was collected for 12 h postdose and urine for 24 h. Peak plasma furosemide concentrations after the solution were significantly greater than after the tablets; there was no significant difference between the tablets. The time to peak occurred significantly earlier with the solution, with no significant difference between the tablets. Relative bioavailabilities of Tablet A and B were 89 per cent and 101 per cent, respectively, as determined by AUC, and 79 per cent and 84 per cent, respectively, as determined by urine recovery. These differences are not statistically significant. These results indicate that dissolution rate profiles of furosemide tablets may not be predictive of in vivo bioavailability.