Rectal bioavailability of bacampicillin hydrochloride in man as determined by reversed-phase liquid chromatography

The relative bioavailability of bacampicillin hydrochloride, a pro-drug of ampicillin, was compared after rectal and oral administration. Bacampicillin was administered rectally as a microenema . The oral formulation was an aqueous microcapsule suspension. They were given as single doses of 400 mg to 12 healthy volunteers after overnight fasting using a randomized cross-over design. Ampicillin and bacampicillin were determined in plasma and blood, respectively, using HPLC. Bacampicillin was rapidly absorbed from the rectum but to a much smaller degree compared to the oral dose. The median t-max was 0.5 and 0.75 h after the rectal and oral doses, respectively. The mean (SD) Cp-max was 1.2 (0.33) mg/l after rectal and 4.8 (0.98) mg/l after oral administration, respectively. Blood concentrations of bacampicillin were extremely low or undetectable with no indication of differences between the two modes of administration. The 95% confidence limits for the relative bioavailability of the microenema were 22.4-39.2 and 22.5-40.4% based on area under the plasma concentration time curve and urinary recovery, respectively. The rectal dose was followed by distress, diarrhea or pain, in 7 subjects. There were no adverse reactions after the oral dose. Bacampicillin was unaffected by beta-lactamases produced by intestinal bacteria.