Macrolide

Clarithromycin

A macrolide for chest, throat, sinus and skin infections, part of triple therapy to clear H. pylori, and used for Mycobacterium avium complex.

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
H. pylori eradication, with amoxicillin and a PPI
Strep throat when first-line drugs cannot be used
Sinusitis
Known for: QT prolongation and torsades de pointes
Its name: -mycin means an antibiotic from Streptomyces bacteria

Study it as a flashcard, and it comes back before you forget it.

Mechanism of action

How does clarithromycin work?

Clarithromycin is a semisynthetic 14-membered macrolide that binds the 50S ribosomal subunit and halts protein synthesis; beta-lactamases do not affect it. It also inhibits CYP3A and P-glycoprotein, which drives its many drug interactions.

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 clarithromycin used for?

Community-acquired pneumonia
H. pylori eradication, with amoxicillin and a PPI
Strep throat when first-line drugs cannot be used
Sinusitis
Skin infections, such as cellulitis
Middle ear infections in children

Side effects

Side effects of clarithromycin

QT prolongation and torsades de pointesKnown forSerious
Altered taste (dysgeusia)
Nausea and vomiting
Diarrhea
Abdominal pain
Headache
Hepatitis, with or without jaundiceSerious
HallucinationsSerious
Hearing loss, mostly reversibleSerious
Worsening of myasthenia gravisSerious
Low blood glucose with diabetes medicinesSerious
Acute pancreatitisSerious

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

Watch for

Cautions and what sets it apart

CYP3A4 inhibitor: never with simvastatin, lovastatin, ergotamine or pimozide, or with colchicine in kidney or liver impairment.
QT risk: avoid with long QT, low potassium or magnesium, bradycardia, or class IA or III antiarrhythmics.
Pregnancy: not recommended unless no other treatment suits, because of animal findings.
Coronary artery disease: deaths rose a year or more after treatment, so the benefit is weighed against this risk.

Good to know: Its CYP3A and P-glycoprotein inhibition raises levels of drugs such as digoxin, calcium channel blockers and some statins, and the INR can rise with warfarin.

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

Clarithromycin 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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