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# Azithromycin
## Overview
Azithromycin is an azalide antibiotic (subclass of macrolides) that inhibits protein synthesis by binding to the 50S ribosomal subunit. It is bacteriostatic, has a long tissue half-life, and provides excellent intracellular concentration.
## Primary Indications
* Community-acquired pneumonia (CAP)
* Acute bacterial exacerbations of COPD
* Acute bacterial sinusitis
* Pharyngitis/Tonsillitis (group A streptococcal)
* Skin and skin structure infections
* Chlamydia trachomatis urethritis/cervicitis
* Mycobacterium avium-intracellulare (MAC) prophylaxis/treatment
## Adult Dosing
* **Most Infections:** 500 mg orally on Day 1, followed by 250 mg once daily on Days 2–5 (Total 1.5g).
* **Chlamydia trachomatis:** 1 g orally as a single dose.
* **CAP/COPD Exacerbation:** Some protocols allow for 500 mg daily for 3 days.
* **MAC Prophylaxis:** 1,200 mg orally once weekly.
## Pediatric Dosing
* **General Infections (bacterial):** 10 mg/kg (max 500 mg) on Day 1, followed by 5 mg/kg (max 250 mg) daily on Days 2–5.
* **Pharyngitis/Tonsillitis:** 12 mg/kg per day orally for 5 days.
* **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 is required for mild-to-moderate renal impairment (CrCl >10 mL/min). Use caution in severe impairment; limited data available.
* **Hepatic Impairment:** Use with caution as it is primarily excreted via the liver. Avoid in patients with severe hepatic disease.
## 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, abdominal pain, vomiting.
* **Serious:** QT interval prolongation (torsades de pointes), cardiovascular death (in high-risk cardiac patients), hepatotoxicity, C. difficile-associated diarrhea, and hypersensitivity reactions (SJS/TEN).
* **Pediatric:** Pyloric stenosis (possible association in neonates).
## Key Drug Interactions
* **Warfarin:** May increase INR and bleeding risk—monitor PT/INR.
* **QT-Prolonging Agents:** Avoid concurrent use with drugs like amiodarone, sotalol, or fluoroquinolones due to additive QT prolongation.
* **Digoxin:** May increase serum concentrations of digoxin.
* **Statins:** Potential for increased risk of myopathy/rhabdomyolysis.
## Monitoring
* Monitor for signs of superinfection/C. difficile (watery, persistent diarrhea).
* In patients with high cardiovascular risk, monitor ECG for QTc prolongation.
* LFTs if prolonged therapy is required or if symptoms of hepatitis develop.
## Clinical Pearls
* Azithromycin is not the first-line treatment for syphilis or gonorrhea due to emerging resistance.
* For optimal absorption of capsules, avoid administration with food (tablets/suspensions may be taken with or without food).
* The "Z-Pak" dosing (5-day course) is highly convenient, improving patient compliance compared to traditional long-course antibiotics.
* *Note: Always consult local institutional antibiograms, as macrolide resistance in S. pneumoniae varies by geographic region.*
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**Educational Disclaimer:** This information is for educational purposes only. Clinical guidelines and prescribing protocols change frequently. Always verify current dosage, contraindications, and drug interaction data through primary resources such as the FDA-approved package insert, UpToDate, or Lexicomp before prescribing or administering medication.
