Pharmacokinetics of ampicillin in serum and in dermal suction blisters after oral administration of bacampicillin.

After oral administration of 0.8 g of bacampicillin, the median concentration of ampicillin in serum peaked at 1-2 hr and reached 8.4 and 12.3 micrograms/ml in two groups of 13 and four healthy volunteers, respectively. In the fluid of dermal blisters produced by suction, the peak values were 2.6 and 2.7 micrograms/ml, respectively. After oral administration of 1.6 g of bacampicillin to four healthy individuals, the median peak concentrations were 15.5 micrograms/ml in serum and 3.8 micrograms/ml in blister fluid. The rate of penetration of ampicillin into the blister fluid was lower than the rate of gastrointestinal absorption of bacampicillin, and the elimination of ampicillin from the blister fluid was slower than from serum; the half-life in blister fluid was approximately twice that in serum. Concentrations of ampicillin in the blister fluid exceeded those in serum at greater than or equal to 3 hr. Concentrations of less than 0.7 micrograms/ml were observed in blister fluid 11 hr after administration of the dose. The bioavailability of ampicillin was relatively greater after a 1.6-g dose of bacampicillin than after a 0.8-g dose. Inflammation in the blister fluid that was induced by endotoxin, which provoked a strong cellular response but cased no increase in the concentration of protein in the fluid, did not significantly influence the pharmacokinetics of ampicillin. The results suggest that the pharmacokinetics of antimicrobial agents in serum and in extravascular foci may be relevant to the setting of breakpoints between sensitivity and resistance of pathogens of antimicrobial agents.