ZITHROMAX for injection contains the active ingredient azithromycin, an azalide, a subclass of macrolide antibacterial drug, for intravenous injection. Azithromycin has the chemical name (2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13- [(2,6-dideoxy-3-C-methyl-3-O -methyl-α-L-ribo-hexopyranosyl)oxy]-2-ethyl-3,4,10-trihydroxy-3,5,6,8,10,12,14-hepta-methyl- 11- [[3,4,6-trideoxy-3-(dimethylamino)-β-D-xylo-hexopyranosyl]oxy]-1-oxa- 6-azacyclopentadecan-15-one. Azithromycin is derived from erythromycin; however, it differs chemically from erythromycin in that a methyl-substituted nitrogen atom is incorporated into the lactone ring. Its molecular formula is C38H72N2O12, and its molecular weight is 749. Azithromycin has the following structural formula:
Azithromycin, as the dihydrate, is a white crystalline powder with a molecular formula of C38H72N2O12∙ 2H2O and a molecular weight of 785.
ZITHROMAX for injection consists of azithromycin dihydrate and the following inactive ingredients: anhydrous citric acid and sodium hydroxide. Sodium hydroxide is added to adjust the pH. ZITHROMAX for injection is supplied as white to off-white lyophilized powder in a single-dose vial for intravenous administration. Each vial contains azithromycin dihydrate equivalent to 500 mg of azithromycin, 384.6 mg anhydrous citric acid, and sodium hydroxide. Reconstitution, according to label directions, results in approximately 5 mL of ZITHROMAX for intravenous injection with each mL containing azithromycin dihydrate equivalent to 100 mg of azithromycin, 76.9 mg anhydrous citric acid, and sodium hydroxide.