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.

• AzithromycinWHO 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.
• ClarithromycinIts 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.
• ErythromycinAzithromycin is derived from it. In young infants, treated for whooping cough or chlamydia, the risk of pyloric stenosis is weighed against the danger of the infection.

• Community-acquired pneumonia, including atypical
• Strep throat when penicillin cannot be used
• Chlamydia and other sexually transmitted infections
• H. pylori eradication (clarithromycin)
• Skin and soft tissue infections
• Middle ear infections (otitis media)

• Nausea and vomitingKnown for
• QT prolongation and torsades de pointesKnown forSerious
• Diarrhea
• Cholestatic jaundiceSerious
• Hepatitis and, rarely, liver failureSerious
• Taste disturbance
• Hearing loss and tinnitus, usually reversibleSerious
• Worsening of myasthenia gravisSerious
• C. difficile colitisSerious
• Severe skin reactions (SJS, TEN, DRESS)Serious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• QT risk: avoid with long QT, low potassium or magnesium, slow heart rate, or other QT-prolonging drugs such as amiodarone.
• Clarithromycin and erythromycin inhibit CYP3A4: avoid simvastatin and lovastatin, and take care with colchicine, warfarin and many others.
• Past macrolide-related cholestatic jaundice is a contraindication; stop the drug if hepatitis develops.
• Myasthenia gravis: macrolides can worsen muscle weakness.

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

• Macrolide Antibiotic (NCI Thesaurus)
• Azithromycin tablets: label (DailyMed)
• Clarithromycin tablets: label (DailyMed)
• Erythromycin ethylsuccinate: label (DailyMed)
• Side effects of clarithromycin (NHS)
• WHO Model List of Essential Medicines, 24th list (2025) (WHO)

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.