Azithromycin

Macrolides

ATC code: J01FA10 (Azithromycin)

Mechanism of action

Binds the 50S ribosomal subunit and inhibits bacterial protein synthesis. Bacteriostatic at standard concentrations, bactericidal at high levels. Broad spectrum: gram-positive cocci, select gram-negatives, and atypical pathogens – Mycoplasma pneumoniae, Chlamydia trachomatis, Legionella pneumophila. Accumulates intracellularly, providing a prolonged effect after a short course.

Indications

Chlamydial infection

First line

First-line for uncomplicated chlamydial infection. A single 1 g oral dose achieves eradication in over 95 % of patients. The alternative is doxycycline 100 mg twice daily for 7 days, which may have a slight edge per recent meta-analyses.

Community-acquired pneumonia

First line

First-line when atypical etiology is suspected in community-acquired pneumonia – Mycoplasma, Chlamydophila, Legionella. Also used in penicillin-allergic patients. Per IDSA/ATS 2019, azithromycin is given as outpatient monotherapy in patients without comorbidities or combined with a beta-lactam.

Acute bacterial rhinosinusitis

Second line

Second-line for acute bacterial sinusitis. First-line is amoxicillin or amoxicillin-clavulanate. Macrolides are given in penicillin allergy, but growing pneumococcal macrolide resistance limits their use.

Streptococcal pharyngitis

Second line

Second-line for streptococcal pharyngitis, indicated only when the patient has a penicillin allergy. A 5-day course is standard. Penicillin V or amoxicillin remain first-choice per IDSA 2012.

Practical notes

Timing and administration

Take 1 hour before or 2 hours after meals – food reduces capsule absorption. Film-coated tablets (Zithromax) may be taken with food. Standard respiratory course: 500 mg on day 1, then 250 mg on days 2 through 5. For chlamydia – single 1 g dose.

Special situations

Azithromycin prolongs the QT interval. Avoid combining with other QT-prolonging drugs – class IA and III antiarrhythmics, fluoroquinolones, certain antipsychotics. ECG monitoring in patients with risk factors. Contraindicated in severe hepatic impairment.

Safety

Contraindications

Hypersensitivity to macrolides
Severe hepatic impairment

Serious adverse effects

QT prolongation and ventricular arrhythmias (including torsades de pointes)
Hepatotoxicity (cholestatic jaundice, hepatitis)
Clostridioides difficile-associated diarrhea
Anaphylaxis (rare)

Common adverse effects

Diarrhea
Nausea
Abdominal pain
Flatulence

Uncommon adverse effects

Headache
Dizziness
Taste disturbance
Rash

PregnancyFDA B

FDA category B. Observational data have not shown an increased risk of congenital anomalies. Used when the benefit outweighs potential risk.