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# Azithromycin
## Overview
Azithromycin is an azalide antibiotic (a subclass of macrolides) that inhibits protein synthesis by binding to the 50S ribosomal subunit. It is characterized by a long half-life, allowing for short-course therapy and tissue accumulation.
## Primary Indications
* Community-acquired pneumonia
* Acute bacterial exacerbations of COPD
* Pharyngitis/tonsillitis (due to *S. pyogenes* in penicillin-allergic patients)
* Skin and skin structure infections
* Sexually transmitted infections (chlamydial urethritis/cervicitis)
* *Mycobacterium avium* complex (MAC) prophylaxis and treatment
## Adult Dosing
* **Respiratory/Skin Infections:** 500 mg on Day 1, followed by 250 mg once daily on Days 2–5.
* **STIs (Chlamydia trachomatis):** 1 gram orally as a single dose.
* **COPD Exacerbations:** 500 mg once daily for 3 days.
## Pediatric Dosing
* **Acute Otitis Media:** 30 mg/kg as a single dose OR 10 mg/kg once daily for 3 days (max 500 mg/day).
* **Community-Acquired Pneumonia:** 10 mg/kg on Day 1, followed by 5 mg/kg once daily on Days 2–5 (max 500 mg on Day 1, 250 mg on Days 2–5).
* **Pharyngitis/Tonsillitis:** 12 mg/kg once daily for 5 days (max 500 mg/day).
## Dose Adjustments
* **Renal Impairment:** No dosage adjustment is typically required in mild to moderate impairment (CrCl >10 mL/min). Use with caution in severe impairment.
* **Hepatic Impairment:** Azithromycin is primarily eliminated by the liver; monitor closely in patients with significant hepatic dysfunction.
## Contraindications
* Known hypersensitivity to azithromycin, erythromycin, or any macrolide antibiotic.
* History of cholestatic jaundice or hepatic dysfunction associated with previous use of azithromycin.
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain.
* **Serious:** QT interval prolongation (risk of Torsades de Pointes), hepatotoxicity, Clostridioides difficile-associated diarrhea (CDAD), hypersensitivity reactions (Stevens-Johnson syndrome).
## Key Drug Interactions
* **QT Prolonging Agents:** Increased risk of cardiac arrhythmias.
* **Warfarin:** May potentiate anticoagulant effects; monitor INR.
* **Digoxin:** May increase digoxin serum concentrations.
* **Antacids:** Aluminum or magnesium-containing antacids may reduce the rate of absorption; separate administration by 2 hours.
## Monitoring
* Monitor for signs of anaphylaxis or severe hypersensitivity during initiation.
* Monitor ECG in patients with known risk factors for QT prolongation (e.g., electrolyte imbalances, bradycardia).
* Monitor liver function tests if symptoms of hepatotoxicity (e.g., jaundice, dark urine) develop.
## Clinical Pearls
* **Tissue Half-life:** Due to tissue penetration, clinical effect may persist for several days after the last dose.
* **Administration:** May be taken with or without food. However, taking with food may reduce potential gastrointestinal distress.
* **Resistance:** Increasing rates of macrolide-resistant *Streptococcus pneumoniae* limit use as monotherapy in some regions; align with local antibiograms.
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**EDUCATIONAL DISCLAIMER:** This information is for educational purposes only. Always verify drug doses, contraindications, and potential interactions against current institutional protocols, official package inserts, and evidence-based clinical databases (e.g., UpToDate, Lexicomp) before prescribing or administering medication.
