Zithromax - Warnings & Precautions

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Coadministration of a single oral dose of 1200 mg azithromycin (2 x 600 mg ZITHROMAX tablets) with steady-state nelfinavir (750 mg tid) to healthy adult subjects produced a decrease of approximately 15% in mean AUC0-8 of nelfinavir and its M8 metabolite. Mean Cmax of nelfinavir and its M8 metabolite were not significantly affected. No dosage adjustment of nelfinavir is required when nelfinavir is coadministered with azithromycin.

Coadministration of nelfinavir (750 mg tid) at steady state with a single oral dose of 1200 mg azithromycin increased the mean AUC0- of azithromycin by approximately a factor of 2-times (range of up to 4 times) of that when azithromycin was given alone. The mean Cmax of azithromycin was also increased by approximately a factor of 2-times (range of up to 5 times) of that when azithromycin was given alone. Dose adjustment of azithromycin is not recommended. However, when administered in conjunction with nelfinavir, close monitoring for known side effects of azithromycin, such as liver enzyme abnormalities and hearing impairment, is warranted. (See ADVERSE REACTIONS.)

Following administration of trimethoprim/ sulfamethoxazole DS (160 mg/ 800 mg) for 7 days to healthy adult subjects, coadministration of 1200 mg azithromycin (2 x 600 mg ZITHROMAX tablets) on the 7 th day had no significant effects on peak concentrations (Cmax), total exposure (AUC), and the urinary excretion of either trimethoprim or sulfamethoxazole.

Coadministration of trimethoprim/ sulfamethoxazole DS for 7 days had no significant effect on the peak concentration (Cmax) and total exposure (AUC) of azithromycin following administration of the single 1200 mg tablet dose to healthy adult subjects. Administration of a 600 mg single oral dose of azithromycin had no effect on the pharmacokinetics of efavirenz given at 400 mg doses for 7 days to healthy adult subjects.

Efavirenz, when administered at a dose of 400 mg for seven days produced a 22% increase in the Cmax of azithromycin administered as a 600 mg single oral dose, while the AUC of azithromycin was not affected. Azithromycin (500 mg Day 1, 250 mg Days 2-5) did not affect the plasma levels or pharmacokinetics of theophylline administered as a single intravenous dose.