Azithromycin for Injection, USP contains the active ingredient azithromycin, an azalide, a subclass of macrolide antibiotics, 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 monohydrate, is a white crystalline powder with a molecular formula of C38H72N2O12 ∙ H2O and a molecular weight of 767.
Azithromycin for Injection, USP consists of azithromycin monohydrate and the following inactive ingredients: anhydrous citric acid and sodium hydroxide. Sodium hydroxide is added to adjust the pH. Azithromycin for Injection, USP is supplied as white to off-white lyophilized powder in a single-dose vial for intravenous administration. Each vial contains azithromycin monohydrate equivalent to 500 mg azithromycin, 413.6 mg anhydrous citric acid and sodium hydroxide for pH adjustment. Reconstitution, according to label directions, results in approximately 5 mL of azithromycin for intravenous injection with each mL containing azithromycin monohydrate equivalent to 100 mg of azithromycin, 76.9 mg of anhydrous citric acid and sodium hydroxide.