The objective of our study was to characterize the pharmacokinetics of azithromycin after the oral administration of multiple doses in suspension to children with acute otitis media. Thirteen children (ranging in age from 7.5 months to 5 years) received a single oral dose of 10 mg of azithromycin per kg of body weight on day 1 followed by single daily doses of 5 mg/kg on days 2 to 5. Each child fasted overnight before receiving the final dose on day 5. Multiple blood samples were collected after the last dose. Concentrations of azithromycin in serum were measured by a specific high-performance liquid chromatography-mass spectrometry method. The means and standard deviations for the maximum concentration of azithromycin in serum, the time to maximum concentration of azithromycin in serum, the area under the concentration-time curve (from 0 to 24 h), and the elimination half-life were 224 +/- 120 ng/ml, 1.8 +/- 0.4 h, 1,841 +/- 651 ng.h/ml, and 31.6 +/- 6.6 h, respectively. Concentrations in serum (means +/- standard deviations) at 0 h (predose) and at 24, 48, and 72 h after the final dose were 51 +/- 26, 47 +/- 21, 27 +/- 17, and 17 +/- 13 ng/ml, respectively. Thus, the once-daily administration of azithromycin resulted in sustained systemic exposure to the drug. The drug dosage regimen used in this study should lead to tissue drug concentrations exceeding the MICs for common pathogens.