Zithromax: Dosages and Ingredients Full Prescribing Information
Azithromycin is the first of a subclass of macrolide antibiotics, known as azalides, and is chemically different from erythromycin. Chemically it is derived by insertion of a nitrogen atom into the lactone ring of erythromycin A. 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. Its molecular formula is C 38H 72N 2O 12, and its molecular weight is 749.00.
Presentation and Dosage Forms
The following table summarizes the available dosage forms and their respective strengths:
| Dosage Form | Strength | Identification Details |
|---|---|---|
| Film-coated Tablet | 250 mg | Capsular shaped, engraved with "Pfizer" and "ZTM 250" |
| Film-coated Tablet | 500 mg | Capsular shaped, engraved with "Pfizer" and "ZTM 500" |
| Powder for Oral Suspension | 200 mg per 5 mL | White to off-white dry powder; orange to brown when reconstituted |
| Powder for Intravenous (IV) Solution | 500 mg per vial | Lyophilized form under a vacuum in a 10 mL vial |
Film-coated Tablets
Each tablet contains azithromycin dihydrate equivalent to 250 mg or 500 mg azithromycin. Film-coated Tablet 250 mg: Azithromycin film-coated tablets are capsular shaped and contain azithromycin dihydrate equivalent to 250 mg of azithromycin and engraved with "Pfizer" on one side and "ZTM 250" on the other side. Film-coated Tablet 500 mg: Azithromycin film-coated tablets are capsular shaped and contain azithromycin dihydrate equivalent to 500 mg of azithromycin and engraved with "Pfizer" on one side and "ZTM 500" on the other side.
Powder for Oral Suspension
Azithromycin powder for oral suspension is presented as a white to off-white dry powder which yields, on reconstitution with water, off-white to orange to brown suspension containing the equivalent of 200 mg azithromycin per 5 mL. When reconstituted as directed, each teaspoonful (5 mL) contains azithromycin dihydrate equivalent to 200 mg of azithromycin.
Powder for Intravenous (IV) Solution
Azithromycin is supplied in lyophilized form under a vacuum in a 10 mL vial equivalent to 500 mg azithromycin for intravenous administration. Upon reconstitution, azithromycin powder yields a solution containing the equivalent of 100 mg azithromycin per 1 mL. Each vial contains azithromycin dihydrate, equivalent to 500 mg of azithromycin, providing 100 mg/mL solution following recommended reconstitution.
Excipients and Inactive Ingredients
- Film-coated Tablets: The tablets contain pregelatinized starch, calcium phosphate dibasic anhydrous, croscarmellose sodium, magnesium stearate and sodium lauryl sulfate. The film coating contains hydroxypropyl methylcellulose, triacetin and titanium dioxide (E171).
- Powder for Oral Suspension: The powder for oral suspension contains sucrose (1.94 g per 100 mg dose), sodium phosphate tribasic anhydrous, hydroxypropyl cellulose, xanthan gum, artificial cherry, creme de vanilla and banana flavors.
- Powder for Intravenous Solution: The IV formulation contains citric acid (anhydrous) 384.6 mg, and sodium hydroxide 198.3 mg.
Pharmacology and Mode of Action
Pharmacotherapeutic group: Macrolides. ATC code: J01FA. Azithromycin binds to the 23S rRNA of the 50S ribosomal subunit. It blocks protein synthesis by inhibiting the transpeptidation/translocation step of protein synthesis and by inhibiting the assembly of the 50S ribosomal subunit.
Cardiac Electrophysiology
QTc interval prolongation was studied in a randomized, placebo-controlled parallel trial in 116 healthy subjects who received either chloroquine (1000 mg) alone or in combination with azithromycin (500 mg, 1000 mg, and 1500 mg once daily). Co-administration of azithromycin increased the QTc interval in a dose- and concentration-dependent manner. In comparison to chloroquine alone, the maximum mean (95% upper confidence bound) increases in QTcF were 5 (10) ms, 7 (12) ms and 9 (14) ms with the co-administration of 500 mg, 1000 mg and 1500 mg azithromycin, respectively.