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# Azithromycin
## Overview
Azithromycin is a second-generation macrolide (azalide) antibiotic. It works by binding to the 50S ribosomal subunit, inhibiting bacterial protein synthesis. It possesses a long half-life (~68 hours), allowing for once-daily dosing and short therapy courses.
## Primary Indications
Commonly used for community-acquired pneumonia (CAP), pharyngitis/tonsillitis (due to *S. pyogenes* in penicillin-allergic patients), skin and skin structure infections, acute bacterial exacerbations of COPD, and sexually transmitted infections (specifically *Chlamydia trachomatis* and *Neisseria gonorrhoeae* co-infection).
## Adult Dosing
* **Most Infections (e.g., CAP, skin/soft tissue):** 500 mg on day 1 followed by 250 mg once daily on days 2–5 (Total 1.5g).
* **Chlamydia trachomatis (urethritis/cervicitis):** 1 g orally as a single dose.
* **Gonococcal urethritis/cervicitis (if susceptible):** 2 g orally as a single dose.
## Pediatric Dosing
* **Safety/Efficacy:** Not established for children <6 months.
* **General Bacterial Infections (Otitis media, CAP):** 10 mg/kg once daily on day 1 (max 500 mg), followed by 5 mg/kg once daily on days 2–5 (max 250 mg/day).
* **Alternative (Otitis media):** 30 mg/kg as a single dose or 10 mg/kg once daily for 3 days.
## Dose Adjustments
* **Renal Impairment:** No Dosage adjustment required for mild to moderate impairment. Use caution in severe renal impairment (CrCl <10 mL/min).
* **Hepatic Impairment:** Use caution; azithromycin is primarily eliminated via the liver. Avoid in patients with significant hepatic dysfunction.
## Contraindications
* Known hypersensitivity to azithromycin, erythromycin, or any macrolide/ketolide antibiotic.
* History of cholestatic jaundice or hepatic dysfunction associated with prior azithromycin use.
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain.
* **Serious:** QT interval prolongation (risk of Torsades de Pointes), hepatotoxicity, *Clostridioides difficile*-associated diarrhea, and hypersensitivity reactions (e.g., Stevens-Johnson syndrome).
## Key Drug Interactions
* **QT Prolonging Agents:** Increased risk of cardiac arrhythmias when combined with drugs like amiodarone, ondansetron, or fluoroquinolones.
* **Warfarin:** May potentiate the anticoagulant effect; monitor INR closely.
* **Digoxin:** May increase digoxin levels; monitor for toxicity.
* **Antacids:** Aluminum or magnesium-containing antacids may reduce the rate of absorption; separate doses by at least 2 hours.
## Monitoring
* **Cardiac:** Baseline ECG if the patient has known risk factors for QT prolongation or severe electrolyte disturbances.
* **Hepatic:** Monitor for signs of hepatotoxicity (dark urine, jaundice, abdominal pain) if therapy is extended.
* **GI:** Monitor for signs of *C. difficile* infection (persistent, watery or bloody diarrhea).
## Clinical Pearls
* Azithromycin has historically been used for its anti-inflammatory properties in chronic airway diseases; ensure indication is appropriate to minimize antibiotic resistance.
* The 3-day or 5-day treatment pack is highly convenient, potentially improving patient adherence.
* Always verify regional antibiotic resistance patterns, as *S. pneumoniae* resistance to macrolides is high in many areas.
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**Educational Disclaimer:** This information is for educational purposes only. Always consult current institutional guidelines, local antibiograms, and official package inserts (e.g., DailyMed) to verify up-to-date dosing, safety information, and prescribing recommendations before administering any medication.
