Azithromycin

Key facts

• Azithromycin (Zithromax) is a macrolide antibiotic that stops bacteria producing the proteins they need to grow.
• It's often given as a short course, three to five days, because it stays active in body tissues long after the last dose.
• It can prolong the heart's QT interval and raise the risk of a dangerous irregular heartbeat, especially with existing heart rhythm problems or low potassium or magnesium.
• Seek urgent care for fainting, a pounding or irregular heartbeat, or signs of a severe allergic reaction.

What Azithromycin treats

Azithromycin treats respiratory infections such as bronchitis, pneumonia and sinusitis, ear infections, certain skin infections, and sexually transmitted infections including chlamydia. It doesn't treat colds, flu or other viral illnesses; using it for these only encourages resistant bacteria.

How Azithromycin works

Azithromycin attaches to the ribosome, the machinery bacteria use to build proteins, and blocks it. Without new proteins, susceptible bacteria can't grow or multiply, which lets your immune system clear the remaining infection.

Before you take it

• Tell your prescriber if you have a heart rhythm disorder, a slow heartbeat, or a family history of QT prolongation, or if you take other medicines that affect heart rhythm, such as certain antiarrhythmics, antipsychotics or antimalarials.
• Avoid azithromycin if you've had liver problems or jaundice with a previous course, or a known allergy to macrolide antibiotics.
• Tell your prescriber if you have myasthenia gravis; azithromycin can worsen muscle weakness.
• Antacids containing aluminium or magnesium can reduce absorption if taken at the same time; space doses two hours apart.

Side effects

Nausea, diarrhoea, abdominal pain and a temporary metallic taste are common.

Stop and seek urgent medical care for any of these:

• Fainting, or a pounding, fluttering or irregular heartbeat.
• Yellowing of the skin or eyes, dark urine, or severe abdominal pain.
• Hives, facial or throat swelling, or difficulty breathing.
• Severe or bloody diarrhoea, which can signal a C. difficile infection.

Safety essentials

• Because azithromycin can prolong the QT interval and trigger a dangerous heart rhythm, tell your prescriber about any heart condition or QT-prolonging medicine before you start it.
• Finish the full course exactly as prescribed, even once you feel better, to clear the infection and limit antibiotic resistance.
• Don't take azithromycin left over from a previous illness or prescribed for someone else; the dose and duration are matched to the specific infection being treated.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.