Zithromax Full Prescribing Information: Description, Dosages, and Ingredients
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. The pharmacotherapeutic group is Macrolides with the ATC code J01FA.
Chemical Description and Action
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. It is also known as 9-deoxy-9a-aza-9a-methyl-9a-homoerythromycin A. Its molecular formula is C 38H 72N 2O 12, and its molecular weight is 749.00. In its dihydrate form, it is a white crystalline powder with a molecular formula of C 38H 72N 2O 12·2H 2O and a molecular weight of 785.0.
Mode of action: 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.
Dosage Forms and Presentations
The following table summarizes the available dosage forms for Zithromax:
| Formulation | Strength/Concentration |
|---|---|
| Film-coated Tablet | 250 mg |
| Film-coated Tablet | 500 mg |
| Powder for Oral Suspension | 200 mg per 5 mL |
| Powder for Intravenous (IV) Solution | 500 mg per vial (100 mg/mL upon reconstitution) |
Film-coated Tablets
Azithromycin film-coated tablets are capsular shaped. Each 250 mg tablet is engraved with "Pfizer" on one side and "ZTM 250" on the other side. Each 500 mg tablet is engraved with "Pfizer" on one side and "ZTM 500" on the other side. These tablets contain azithromycin dihydrate equivalent to the specified amount of azithromycin.
Powder for Oral Suspension
Azithromycin powder for oral suspension is presented as a white to off-white dry powder. When reconstituted as directed, each teaspoonful (5 mL) contains azithromycin dihydrate equivalent to 200 mg of azithromycin. It yields an off-white to orange to brown suspension.
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.
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: This form 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.
Cardiac Electrophysiology
QTc interval prolongation was studied in a randomized, placebo-controlled parallel trial in 116 healthy subjects. In comparison to chloroquine alone, the maximum mean 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. Co-administration of azithromycin increased the QTc interval in a dose- and concentration-dependent manner.