Bioavailability of ampicillin and amoxicillin in fasted and nonfasted subjects.

The influence of various test meals and fluid volume on the relative bioavailability of ampicillin and amoxicillin was studied in healthy human subjects. Serum amoxicillin levels were somewhat, but not always, significantly higher than those of ampicillin from equivalent oral doses. Food ingested immediately before dosing reduced serum levels and urinary excretion of both antibiotics to a similar extent. Reduction of dosed water volume caused a marked decrease in serum amoxicillin levels in fasted subjects.