Zithromax

[Azithromycin]

Dose adjustments are not indicated when azithromycin and zidovudine are coadministered. When zidovudine (100 mg q3h x5) was coadministered with daily azithromycin (600 mg, n= 5 or 1200 mg, n= 7), mean Cmax, AUC and Clr increased by 26% (CV 54%), 10% (CV 26%) and 38% (CV 114%), respectively. The mean AUC of phosphorylated zidovudine increased by 75% (CV 95%), while zidovudine glucuronide Cmax and AUC increased by less than 10%. In another study, addition of 1 gram azithromycin per week to a regimen of 10 mg/ kg daily zidovudine resulted in 25% (CV 70%) and 13% (CV 37%) increases in zidovudine Cmax and AUC, respectively. Zidovudine glucuronide mean Cmax and AUC increased by 16% (CV 61%) and 8.0% (CV 32%), respectively. Doses of 1200 mg/ day azithromycin for 14 days in 6 subjects increased Cmax of concurrently administered didanosine (200 mg q. 12h) by 44% (54% CV) and AUC by 14% (23% CV). However, none of these changes were significantly different from those produced in a parallel placebo control group of subjects.

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Preliminary data suggest that coadministration of azithromycin and rifabutin did not markedly affect the mean serum concentrations of either drug. Administration of 250 mg azithromycin daily for 10 days (500 mg on the first day) produced mean concentrations of azithromycin 1 day after the last dose of 53 ng/ mL when coadministered with 300 mg daily rifabutin and 49 mg/ mL when coadministered with placebo. Mean concentrations 5 days after the last dose were 23 ng/ mL and 21 ng/ mL in the two groups of subjects. Administration of 300 mg rifabutin for 10 days produced mean concentrations of rifabutin one half day after the last dose of 60 mg/ ml when coadministered with daily 250 mg azithromycin and 71 ng/ mL when coadministered with placebo. Mean concentrations 5 days after the last dose were 8.1 ng/ mL and 9.2 ng/ mL in the two groups of subjects.

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