What Is Azithromycin? Uses, Dosage & How It Works

This is the general azithromycin drug guide. For chlamydia specifically, see the section below or the chlamydia treatment service.

What Is Azithromycin and How Does It Work?

Azithromycin is a macrolide antibiotic — a class that kills or inhibits bacteria by binding to the bacterial ribosome and blocking protein synthesis. Unlike some antibiotics that stay mostly in the bloodstream, azithromycin concentrates inside cells and tissues and has an unusually long half-life. That's why short courses — or, for some infections, a single dose — can clear the infection, and why it's effective against intracellular bacteria like Chlamydia trachomatis.

What Does Azithromycin Treat?

Azithromycin treats a range of bacterial infections (it does nothing for viruses such as colds, flu or most sore throats):

• Chest infections — some cases of pneumonia and bronchitis, and infective exacerbations of COPD;
• Throat and sinus infections — as an alternative in penicillin-allergic people (see below);
• Skin and soft-tissue infections in some cases;
• Sexually transmitted infections — chlamydia (as an alternative to doxycycline) and as part of some other STI regimens.

Azithromycin for Sore Throat / Tonsillitis

Most sore throats and tonsillitis are viral and settle without antibiotics. Where a bacterial (streptococcal) throat infection is confirmed or strongly suspected and an antibiotic is needed, the first-line choice is phenoxymethylpenicillin (penicillin V). Azithromycin (or clarithromycin) is reserved for people who are allergic to penicillin. So while azithromycin can be used for bacterial tonsillitis, it isn't the default — a clinician assesses whether an antibiotic is needed at all and which one is appropriate.

Dosage & Common Courses

The dose depends entirely on the infection being treated. Common regimens include:

Take it as prescribed and finish the whole course, even if you feel better. Doses and durations differ between infections — follow the exact course your prescriber gives you rather than a generic figure.

Azithromycin for Chlamydia

Chlamydia is the most commonly diagnosed STI in the UK and often causes no symptoms, so it can go unnoticed — yet untreated it can cause pelvic inflammatory disease, infertility and ectopic pregnancy in women, and epididymo-orchitis in men. Treatment matters.

After chlamydia treatment

• No sex for 7 days after you and any partners have completed treatment (including oral sex).
• Tell recent partners (usually the last 6 months) so they can test and treat.
• Retest at 3 months — reinfection is common (BASHH).
• Test of cure if you were pregnant, had rectal/pharyngeal infection, or symptoms persist 3–4 weeks after treatment.

Side Effects & Safety

Azithromycin is generally well tolerated. The most common side effects are mild nausea, tummy discomfort and diarrhoea, which usually settle. It can occasionally cause dizziness — if so, don't drive or operate machinery until it passes. Rarely, macrolides can affect heart rhythm (QT prolongation), so tell your prescriber about heart conditions or other medicines you take. Seek urgent help for signs of a severe allergic reaction (rash, swelling, difficulty breathing).

Finishing the Course & Antibiotic Resistance

Completing the full prescribed course — even once you feel better — is essential. Stopping early can let surviving bacteria develop resistance, causing treatment failure and contributing to wider public-health resistance. Only take azithromycin when a clinician has confirmed it's appropriate.