Pharmacokinetics of roxithromycin (RU 965).

This report contains the findings of five studies performed to evaluate the pharmacokinetics of roxithromycin (RU 965), a new macrolide antibiotic. Roxithromycin was given as 150- and 300-mg film-coated tablets. The drug is rapidly absorbed after oral administration. Peak plasma levels following 150- and 300-mg doses occur within two hours. Steady state is reached within four days with doses of 150 mg twice a day or 300 mg once daily. The plasma half-life is approximately 12 hours. About 10% of the dose is excreted in urine. Although dose dependency was observed for the various pharmacokinetic parameters, dose proportionality could be demonstrated only in terms of the percentage of the dose excreted in urine. The rate of absorption is not affected by age. The rate of elimination and renal clearance are decreased in healthy elderly subjects, however, these differences should not be clinically meaningful. The bioavailability of the drug is not affected to a clinically meaningful extent when it is given with milk. Less than 0.05% of the administered dose is excreted in the breast milk of lactating women. Roxithromycin was safe and well tolerated with no clinically meaningful changes in any of the safety variables in any of the five studies reported.