[Clinical pharmacokinetics of azithromycin].

The bioavailability of azithromycin is approximately 37%. Concomitant administration of oral azithromycin with food significantly decreases by 50% drug bioavailability. Following a single oral 500 mg dose, peak plasma concentrations of about 0.35-0.45 mg/l are attained within approximately 2 hours. With a 500 mg oral dose on day 1, followed by 250 mg daily on days 2 to 5, peak and through plasma concentrations on day 5 are around 0.25 and 0.05 mg/l respectively. These low plasma concentrations are the consequence of extensive and rapid distribution from plasma to tissues. Plasma protein binding is low, less than 50% at plasma concentrations obtained with the usual dosage regimen. Apparent volume of distribution is very large, 25 to 35 l/kg. Azithromycin is mainly eliminated unchanged in the faeces via biliary excretion and transintestinal secretion. Urinary excretion is a minor elimination route: about 6% and an oral dose and 12% of an intravenous dose are recovered unchanged in urine. The mean terminal elimination half-life of azithromycin is 2 to 4 days. The pharmacokinetics of azithromycin is not significantly altered in elderly subjects and in patients with mild to moderate renal or hepatic insufficiency.