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# Azithromycin
## Overview
Azithromycin is an azalide antibiotic (subclass of macrolides) that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. It is characterized by a long tissue half-life and high intracellular concentration.
## Primary Indications
Common indications include community-acquired pneumonia, pharyngitis/tonsillitis (due to *Streptococcus pyogenes* in penicillin-allergic patients), skin and soft tissue infections, acute bacterial exacerbations of chronic bronchitis, and sexually transmitted infections (specifically *Chlamydia trachomatis*).
## Adult Dosing
* **Respiratory tract/skin infections:** 500 mg orally on Day 1, followed by 250 mg once daily on Days 2–5 (Total 1.5 g).
* **Chlamydia trachomatis (urethritis/cervicitis):** 1 g orally as a single one-time dose.
* **Community-acquired pneumonia (alternative regimens):** 500 mg IV/PO daily for 2–5 days depending on severity and local susceptibility patterns.
## Pediatric Dosing
* **General infections:** 10 mg/kg (max 500 mg) on Day 1, followed by 5 mg/kg/day (max 250 mg) on Days 2–5.
* **Acute otitis media:** 30 mg/kg as a single dose OR 10 mg/kg once daily for 3 days.
* **Group A Strep Pharyngitis:** 12 mg/kg/day once daily for 5 days (max 500 mg/day).
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment recommended for mild-to-moderate impairment (CrCl >10 mL/min). Use with caution in severe renal impairment.
* **Hepatic Impairment:** Metabolized by the liver; use with caution in patients with hepatic dysfunction. Contraindicated in patients with a history of cholestatic jaundice/hepatic dysfunction associated with prior azithromycin use.
## Contraindications
Hypersensitivity to azithromycin, erythromycin, or any macrolide/ketolide antibiotic. History of cholestatic jaundice or hepatic impairment during prior use.
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain.
* **Severe/Serious:** QT interval prolongation (risk of Torsades de Pointes), hepatotoxicity, *Clostridioides difficile*-associated diarrhea (CDAD), and hypersensitivity reactions (e.g., Stevens-Johnson syndrome).
## Key Drug Interactions
* **QT Prolonging Agents:** Additive risk of arrhythmias (e.g., amiodarone, ondansetron, fluoroquinolones).
* **Warfarin:** May potentiate the anticoagulant effect; monitor INR.
* **Digoxin:** May increase digoxin levels; monitor toxicity.
* **Statins:** Potential for increased risk of myopathy/rhabdomyolysis (limited documentation, but prudent to monitor).
## Monitoring
* Monitor for signs of anaphylaxis or severe skin reactions.
* In patients with risk factors for cardiovascular disease, monitor ECG for QTc prolongation.
* Assess for persistent watery diarrhea (signs of *C. difficile*).
## Clinical Pearls
* Azithromycin is not the first-line choice for invasive pneumococcal disease due to increasing resistance.
* Oral suspension should be taken at least 1 hour before or 2 hours after a meal; however, food does not significantly affect bioavailability.
* Dosing varies significantly based on local institutional guidelines and antibiograms. Always consult hospital-specific protocols for empiric therapy.
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**Disclaimer:** This information is for educational purposes only. Clinical practice guidelines and local resistance patterns change frequently. Verify all dosages, contraindications, and drug interactions against institutional policies and current prescribing information (e.g., DailyMed or clinical decision support tools) before administration.
