Azithromycin: What it treats and how to use it safely

Azithromycin is a common antibiotic you might hear called Z‑Pak. It treats several bacterial infections quickly and often with a short course, which is why doctors prescribe it a lot. But antibiotics aren’t harmless—so knowing when and how to use azithromycin matters.

What azithromycin treats

This drug is used for respiratory infections (like bronchitis and some pneumonias), sinusitis, ear infections, certain skin infections, and sexually transmitted infections such as chlamydia. Doctors also use it for some atypical bacteria that don’t respond to penicillin. It won’t help viral infections like colds or most sore throats—so don’t expect it to work for every cough.

Because azithromycin can knock out susceptible bacteria fast, many courses are short—helpful if you want fewer days of pills. Still, your provider should confirm the need before you start.

How to take azithromycin

One common regimen is the Z‑Pak: 500 mg on day 1, then 250 mg once daily on days 2–5. For chlamydia, a single 1 g dose is often used. Kids get weight-based doses—your pediatrician will tell you the right amount. Take it exactly as prescribed and finish the full course even if you feel better.

Azithromycin can be taken with or without food. If you use antacids that contain aluminum or magnesium, space them at least 2 hours apart—these antacids can reduce azithromycin’s absorption.

Don’t share antibiotics or use leftover pills. Using azithromycin when it’s not needed helps bacteria become resistant and makes future infections harder to treat.

Quick tip: if you’re on blood thinners like warfarin, tell your doctor—antibiotics can sometimes change how these drugs act and may require extra monitoring.

Azithromycin has fewer CYP3A4 interactions than some macrolides, but be cautious with other medicines that affect heart rhythm.

Side effects and warnings

Most people tolerate azithromycin well. Common side effects are nausea, diarrhea, stomach pain, and headache. If you get severe diarrhea, bloody stools, or prolonged belly pain, contact your provider—this could signal C. difficile infection.

Serious but rare problems include allergic reactions, liver inflammation, and heart rhythm changes (QT prolongation). If you feel dizzy, faint, have fast or irregular heartbeat, or notice yellowing of skin or eyes, stop the drug and seek medical help.

If you’ve had jaundice or liver problems after a macrolide before, tell your doctor—azithromycin may not be right for you. Pregnant or breastfeeding? Talk to your provider; many clinicians use azithromycin when needed, but they’ll weigh risks and benefits.

Bottom line: azithromycin is a useful, often short-course antibiotic. Use it when a doctor prescribes it, follow dosing advice, watch for side effects, and avoid using it for viral illnesses to keep it effective when you really need it.