Ciprofloxacin biliary disposition in cholecystectomised patients with special references to HPLC and bioassay data

The biliary disposition of ciprofloxacin was studied in 12 recently cholecystectomised patients during 24 hours following a single oral administration of 500 mg of the drug. Ciprofloxacin was measured in serum, urine, bile and faeces by both high performance liquid chromatography (HPLC) and bioassay. The results were found to be comparable for the concentrations in serum (mean Cmax = 0.97 +/- 0.17 microgram/ml by HPLC and 1.08 +/- 0.19 microgram/ml by bioassay) and in urine (0.6 h: 267 +/- 74 micrograms/ml and 241 +/- 58 micrograms/ml respectively). Higher concentrations were found in bile when measured by bioassay compared with HPLC (peak concentration = 10.3 +/- 3.4 micrograms/ml and 7.5 +/- 2.8 micrograms/ml respectively; p less than 0.02). The total biliary elimination was also significantly higher according to bioassay data (2167 +/- 288 micrograms/ml versus 1587 +/- 222 micrograms/ml; p less than 0.01). This suggests a first pass effect and hepatic biotransformation of ciprofloxacin to one or more active metabolite (s).