What Medication is in a Z-Pack?
A Z-Pack contains azithromycin, a macrolide antibiotic that is structurally related to erythromycin but modified with a methyl-substituted nitrogen atom incorporated into the lactone ring. 1
Active Ingredient and Chemical Structure
- Azithromycin is an azalide antimicrobial agent, which is a subclass of macrolide antibiotics 1
- The chemical formula is C38H72N2O12, with a molecular weight of 749 1
- Azithromycin is supplied as the dihydrate form (C38H72N2O12•2H2O) with a molecular weight of 785 1
- It appears as a white crystalline powder and is acid-stable, allowing for oral administration 1, 2
Tablet Formulations
- Z-Pack tablets contain azithromycin dihydrate equivalent to either 250 mg or 500 mg of azithromycin 1
- The tablets are film-coated, white, oval-shaped, and biconvex 1
- Inactive ingredients include dibasic calcium phosphate dihydrate, hydroxypropyl cellulose, croscarmellose sodium, magnesium stearate, and Opadry II white coating 1
Mechanism of Action
- Azithromycin works by interfering with bacterial protein synthesis through binding to the 50S component of the 70S ribosomal subunit, similar to erythromycin 3
- This mechanism prevents bacterial growth by blocking protein production necessary for bacterial survival 3
Spectrum of Activity
- Azithromycin demonstrates activity against major respiratory pathogens including Streptococcus pneumoniae, Haemophilus influenzae (including ampicillin-resistant strains), and Moraxella catarrhalis 4, 5
- It is active against atypical pathogens such as Chlamydia pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila 5, 2
- Azithromycin is superior to erythromycin against gram-negative bacilli while being slightly less potent against gram-positive organisms, though this difference is not clinically significant 3, 2
Common Pitfalls
- Do not confuse azithromycin with erythromycin—while structurally related, azithromycin has distinct pharmacokinetic properties including a much longer half-life (up to 5 days) that allows for once-daily dosing 3
- Azithromycin should not be taken simultaneously with aluminum- or magnesium-containing antacids, as they reduce absorption by up to 50% 1, 3