Azithromycin is a macrolide antibiotic, and the “Z-Pack” is its best-known form: six 250 mg tablets taken as 500 mg on day one, then 250 mg once a day for four more days. Azithromycin treats certain bacterial infections of the lungs, throat, sinuses, skin and genital tract, though some of those use a different schedule than the Z-Pack. It does nothing for colds, flu or most coughs, because those are viral. That last point is the most common misunderstanding about the drug.
The Z-Pack earned its reputation by being short, simple and easy on the stomach compared with older antibiotics. That convenience also made it one of the most overprescribed antibiotics in the US. Here’s what it actually treats, how the five-day schedule works, and the safety questions a prescriber checks first.
Why five days is enough
Azithromycin moves out of the bloodstream and into tissue, where it lingers. Its half-life is about 68 hours, so the drug is still present for several days after the last tablet. That’s why the schedule looks short next to a 10-day amoxicillin course, and why you shouldn’t add extra days on your own if you still feel tired on day five.
What azithromycin treats
- Community-acquired pneumonia (mild cases): one of the approved uses, though providers now weigh local resistance before choosing it
- Strep throat in people allergic to penicillin: penicillin or amoxicillin stays first-line for everyone else
- Flare-ups of chronic bronchitis (COPD): when a bacterial cause is likely
- Acute bacterial sinusitis: usually as 500 mg once daily for 3 days rather than a Z-Pack, and only when a bacterial cause is likely
- Uncomplicated skin infections
- Chlamydia and some other sexually transmitted infections: as a single 1 g dose, not a Z-Pack. CDC now lists doxycycline as preferred, with azithromycin as the alternative, except in pregnancy, where azithromycin is the recommended choice
- Traveler’s diarrhea (off-label): not an FDA-labeled use, but CDC travel guidance supports it, especially for South and Southeast Asia, where resistance to ciprofloxacin is widespread (see our traveler’s diarrhea guide)
What it won’t help: the common cold, flu, most sore throats, and most cases of acute bronchitis. Those are viral. For flu, the antiviral that matters is oseltamivir, and timing is everything.
The Z-Pack schedule
| Day | Dose | Tablets (250 mg) |
|---|---|---|
| Day 1 | 500 mg | 2 tablets at once |
| Days 2 to 5 | 250 mg once daily | 1 tablet each day |
| Total | 1.5 g | 6 tablets |
Tablets can be taken with or without food. If your stomach is sensitive, food helps. Don’t take it at the same time as antacids containing aluminum or magnesium. Other infections use different schedules, such as a single 1 g dose or three days of 500 mg, so follow the label your prescriber gives you.
Most people start feeling better within two to three days. If you’re getting worse after three days, or not improving by the end of the course, contact a provider.
Side effects and the QT caveat
The most common side effects are stomach-related: diarrhea, nausea and belly pain. They are usually mild.
The safety question prescribers take seriously is heart rhythm. In 2013 the FDA warned that azithromycin can prolong the QT interval and, rarely, trigger a dangerous arrhythmia. Risk is highest in older adults and in people with a known QT problem, a slow heart rate, heart failure, or low potassium or magnesium. It’s also higher with other QT-prolonging drugs, including antiarrhythmics like amiodarone and sotalol, some antidepressants and antipsychotics, and anti-nausea medications like ondansetron. That’s a big reason a provider reviews your health history and medication list before prescribing.
Don’t take azithromycin if you’re allergic to it or to other macrolide antibiotics like erythromycin, or if azithromycin has caused jaundice or liver problems for you before. If you take warfarin, your provider may want to check your blood clotting more often.
Less common but important:
- Severe or watery diarrhea, even weeks after finishing, can signal C. difficile infection and needs a call to your provider
- Liver problems are rare; yellowing skin or eyes or dark urine needs prompt care
- It can worsen myasthenia gravis
- Stop and get emergency help for hives, facial swelling or trouble breathing
Azithromycin vs. other antibiotics
Azithromycin is not a universal backup. Amoxicillin-clavulanate covers more sinus and ear infections. Doxycycline is preferred for chlamydia and is a common choice for pneumonia and malaria prevention. Cephalexin is usually first for skin infections. The right antibiotic depends on the infection, your allergies and local resistance, which is the whole case for a prescriber choosing it.
Getting it prescribed
Azithromycin requires a prescription. Through OZIO, you complete an online health assessment, a licensed physician reviews it, and if an antibiotic is appropriate, azithromycin 250 mg ships from a licensed US pharmacy. Many travelers keep a course in a travel medical kit for exactly the traveler’s diarrhea scenario above.
FAQ
What does a Z-Pack treat? The 5-day Z-Pack is used for infections like mild pneumonia, strep throat in penicillin-allergic patients, COPD flare-ups and some skin infections. Other infections, such as chlamydia or sinusitis, use different azithromycin schedules. It does not treat viral infections like colds or flu.
How fast does azithromycin work? Most people feel better within two to three days.
Why is a Z-Pack only five days? Azithromycin stays in the body’s tissues for a long time, with a half-life of about 68 hours, so a short course is enough for the infections it’s prescribed for.
Can I drink alcohol on azithromycin? Alcohol doesn’t block azithromycin, but it can worsen stomach side effects and slow recovery. Ask your provider.
Is azithromycin safe if I have a heart condition? It depends. Azithromycin can affect heart rhythm, so people with QT problems or on certain medications need a provider to weigh the risk first.
This article is for informational purposes only and is not medical advice. Azithromycin requires evaluation by a licensed healthcare provider. Seek emergency care for chest pain, fainting, a fast or irregular heartbeat, or signs of a severe allergic reaction.
