Pharmacokinetics of Erythromycin on Repetitive Dosing

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Abstract
Serum erythromycin concentration data from several repetitive dosing studies were analyzed with newly developed computer methods for fitting multiple-dose data and generating nonlinear least-squares estimates of pharmacokinetic parameters. This analysis indicates that pharmacokinetics of erythromycin can be described by a one-compartment linear model with the following characteristics: a lag time between time of drug administration and onset of absorption, apparent zero-order rather than first-order absorption, dose-to-dose variability in rate and extent of absorption, and day-to-day variability in kinetics of elimination. Bioavailability of the 3rd dose of erythromycin on a given day is considerably lower than that of the 2nd dose or of the 4th and last dose of the day. The average apparent half-life of erythromycin was 1.8 h on day 1 and 2.6 h on day 3 of the repetitive dosing regimen.