Macrolide

Azithromycin

An azalide macrolide with a long tissue half-life, used for pneumonia, throat infections, chlamydia, typhoid and trachoma.

Drug card

Class: Macrolide
How it works: Binding the 50S ribosomal subunit so the growing protein chain cannot move on
Used for: Community-acquired pneumonia
Chlamydia, urethritis and cervicitis
Typhoid (enteric fever)
Strep throat when first-line drugs cannot be used
Known for: QT prolongation and torsades de pointes
Its name: -mycin means an antibiotic from Streptomyces bacteria

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Mechanism of action

How does azithromycin work?

Azithromycin is an azalide, a macrolide derived from erythromycin. It binds the 23S rRNA of the 50S subunit, blocking translocation and the assembly of new 50S subunits. It stays in tissues for a long time, which allows short courses.

Like other macrolides: Macrolides are large lactone-ring antibiotics that bind the 23S rRNA of the bacterial 50S ribosomal subunit and block translocation, so the growing peptide chain cannot move on and protein synthesis stalls. They are mainly bacteriostatic. Bacteria resist by methylating the 23S rRNA, which also defeats lincosamides, or by pumping the drug out.

Uses

What is azithromycin used for?

Community-acquired pneumonia
Chlamydia, urethritis and cervicitis
Typhoid (enteric fever)
Strep throat when first-line drugs cannot be used
Middle ear infections in children
Trachoma (eye infection)

Side effects

Side effects of azithromycin

QT prolongation and torsades de pointesKnown forSerious
Diarrhea
Nausea
Abdominal pain
Vomiting
Ventricular arrhythmias and cardiovascular deathSerious
Hepatitis and cholestatic jaundiceSerious
Hearing loss and tinnitusSerious
Changes in taste and smell
Pyloric stenosis in newbornsSerious
Worsening of myasthenia gravisSerious
Allergic reactions that can return after stoppingSerious

Known for marks what an exam expects you to know it for.

Watch for

Cautions and what sets it apart

QT risk: avoid with known QT prolongation, torsades, low potassium or magnesium, or other QT-prolonging drugs.
Past azithromycin-related cholestatic jaundice is a contraindication; stop it if hepatitis develops.
Warfarin: its effect can increase, so the prothrombin time is monitored.
Newborns: pyloric stenosis has followed its use, so vomiting or irritability with feeds needs review.

Good to know: WHO lists it as a first-choice Watch antibiotic for typhoid, cholera, chlamydia, trachoma and yaws. CDC no longer recommends it alone for gonorrhea because of resistance.

Remember it

A way to remember it

MACRO

M: Myasthenia gravis can worsen
A: Arrhythmia from QT prolongation (torsades de pointes)
C: Cholestatic jaundice
R: Reversible hearing loss
O: Other drugs' levels rise: clarithromycin and erythromycin inhibit CYP3A4

Think MACRO for the macrolide warnings. Stomach upset (nausea, vomiting, diarrhea) is the commonest complaint of all.

Written for biofideX

Its name

-mycin means antibiotic from Streptomyces bacteria
Spans classes: macrolides (azithromycin), lincosamides (clindamycin), glycopeptides (vancomycin), aminoglycosides (streptomycin) and anticancer bleomycin. Gentamicin is spelled -micin.
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Its class

Macrolides

Other macrolides with a card:

Easily mixed up with lincosamides, tetracyclines and fluoroquinolones.

All about macrolides

Sources

Checked against

Written for biofideX in plain words, after checking these references:

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.

Practice it

Antibiotics: protein synthesis

Azithromycin is one of 10 drugs practiced together here: their classes, how they work, what they treat and what they're known for.

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