Zithromax (Azithromycin) 250 mg & 500 mg Tablets (Z-Pak): Prescription Macrolide Antibiotic for Pneumonia, Chlamydia, Sinusitis, Whooping Cough & Bronchitis

Information last reviewed: May 2026 — for educational purposes only.

Azithromycin, sold as Zithromax and widely known by the informal term Z-Pak or Z-Pack, is a second-generation macrolide antibiotic with a broad spectrum of activity including gram-positive bacteria, atypical pathogens, and select gram-negative organisms. It requires a prescription. Due to its exceptionally long tissue half-life (>60 hours), it achieves sustained antibacterial concentrations in infected tissues for up to 10 days after the final dose — enabling short 3- to 5-day treatment courses. It is one of the most prescribed antibiotics worldwide.

What Is Azithromycin (Zithromax) Used For?

Azithromycin has a wide range of FDA-approved and guideline-supported uses:

• Community-acquired pneumonia (CAP) — mild-to-moderate, especially atypical pathogens (Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella)
• Acute bacterial sinusitis and acute exacerbations of chronic bronchitis
• Uncomplicated chlamydia (urogenital) — single 1 g oral dose is the standard treatment
• Pertussis (whooping cough) — reduces transmission and duration of illness
• Streptococcal pharyngitis in penicillin-allergic patients
• Uncomplicated skin and soft-tissue infections
• MAC prophylaxis — azithromycin 1200 mg once weekly in HIV-positive patients with CD4 count <50

Is Azithromycin Available Over the Counter?

No. Azithromycin is a prescription-only antibiotic in the US, UK, EU, Canada, and Australia. It is not available without a prescription. While some countries historically allowed OTC access, inappropriate use has contributed to increasing macrolide resistance — particularly in Streptococcus pneumoniae and Mycoplasma pneumoniae — making prescriber oversight important. Some telehealth platforms can provide azithromycin prescriptions after an online consultation for appropriate indications such as chlamydia.

Tablet Strengths and Dosing Regimens

• 250 mg tablets — the Z-Pak (original Zithromax 6-Tablet Pack): 500 mg on Day 1, then 250 mg once daily on Days 2–5 (total 5 days)
• 500 mg tablets — used for community-acquired pneumonia (500 mg once daily for 3 days) and as the loading dose in various regimens
• Single 1 g oral dose (four 250 mg tablets taken at once) — standard treatment for uncomplicated urogenital chlamydia (Chlamydia trachomatis)
• Oral suspension 200 mg/5 ml — for pediatric use; 10 mg/kg once daily on Day 1, then 5 mg/kg once daily on Days 2–5

QT Prolongation Warning

Azithromycin can prolong the QT interval on an ECG, increasing the risk of a rare but potentially fatal arrhythmia called torsades de pointes. The FDA issued a drug safety communication in 2013 noting this risk. Patients with known QT prolongation, hypokalaemia, hypomagnesaemia, or those taking other QT-prolonging drugs (antipsychotics, certain antiarrhythmics, some antifungals) should use azithromycin with caution and prescriber oversight. For most healthy outpatients, this risk is very low.

Price of Generic Azithromycin

Generic azithromycin is one of the most affordable prescription antibiotics available. A standard Z-Pak (6 tablets of 250 mg) typically costs $10–$20 with a GoodRx or similar discount card in the US. The single 1 g dose for chlamydia is usually under $10. NHS prescriptions are issued at the standard charge in the UK.

Frequently Asked Questions

Does azithromycin treat gonorrhoea?

Azithromycin is no longer recommended as part of the standard treatment for gonorrhoea (Neisseria gonorrhoeae) due to high and rising rates of resistance. Current guidelines recommend ceftriaxone (an injectable cephalosporin) as the preferred treatment for gonorrhoea. Azithromycin may be used concurrently if co-infection with chlamydia is confirmed or suspected.

How long does azithromycin stay in your system?

Azithromycin has an exceptionally long tissue half-life of approximately 68 hours and continues to act in tissues for several days after the last dose. After a 5-day Z-Pak course, therapeutic concentrations in respiratory or urogenital tissue may persist for 7–10 days. This is why short courses of azithromycin are clinically effective despite the brief dosing schedule.

Can I drink alcohol while taking azithromycin?

There is no direct dangerous interaction between alcohol and azithromycin. However, alcohol can worsen GI side effects (nausea, stomach upset) that azithromycin itself can cause, so moderate use is advisable during a course of treatment. Alcohol does not significantly reduce the effectiveness of azithromycin.

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