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# Azithromycin
## Overview
Azithromycin is a macrolide antibiotic that inhibits protein synthesis by binding to the 50S ribosomal subunit. It is characterized by a long half-life, allowing for short treatment courses and excellent tissue penetration.
## Primary Indications
* Community-acquired pneumonia (CAP)
* Pharyngitis/Tonsillitis (group A streptococcal alternative)
* Acute bacterial exacerbations of chronic bronchitis
* Uncomplicated skin and skin structure infections
* Sexually transmitted infections (e.g., *Chlamydia trachomatis*)
* MAC prophylaxis/treatment (HIV/AIDS)
## Adult Dosing
* **Respiratory/Skin infections:** 500 mg orally on Day 1, followed by 250 mg once daily on Days 2–5.
* **Chlamydia:** 1 gram orally as a single dose.
* **MAC prophylaxis:** 1,200 mg orally once weekly.
* *Note: Dosing can vary based on regional resistance patterns and specific site of infection; consult institutional guidelines.*
## Pediatric Dosing
* **General bacterial infections:** 10 mg/kg orally on Day 1 (max 500 mg), followed by 5 mg/kg once daily on Days 2–5 (max 250 mg/day).
* **Otitis media:** 30 mg/kg as a single dose OR 10 mg/kg once daily for 3 days.
* **Safety:** Not recommended for infants <6 months unless in life-threatening scenarios due to the risk of infantile hypertrophic pyloric stenosis (IHPS).
## Dose Adjustments
* **Renal Impairment:** No adjustment required for mild to moderate impairment (CrCl >10 mL/min). Use caution in severe impairment.
* **Hepatic Impairment:** Use with caution; may increase plasma concentrations, though specific dose adjustments are not standardized.
## Contraindications
* Hypersensitivity to azithromycin, erythromycin, or any macrolide.
* History of cholestatic jaundice or hepatic dysfunction associated with previous use of azithromycin.
## Adverse Effects
* **Gastrointestinal:** Nausea, vomiting, abdominal pain, diarrhea (very common).
* **Cardiac:** QT interval prolongation, risk of Torsades de Pointes.
* **Hepatic:** Potential for elevated liver enzymes and rarely, hepatotoxicity.
* **Dermatologic:** Serious skin reactions (SJS/TEN) are rare but possible.
## Key Drug Interactions
* **QT Prolonging Agents:** Additive risk of arrhythmias (e.g., amiodarone, ondansetron, fluoroquinolones).
* **Warfarin:** May potentiate anticoagulant effects; monitor INR closely.
* **Digoxin:** May lead to increased digoxin levels due to gut microbiome modification.
* **Statin (Statins metabolized by CYP3A4):** Potential for increased risk of myopathy.
## Monitoring
* **Cardiac:** Baseline ECG for patients with high risk of arrhythmias or pre-existing cardiovascular disease.
* **Hepatic:** Liver function tests if symptoms of jaundice or hepatotoxicity develop.
* **GI:** Monitor for persistent or bloody diarrhea (potential *C. difficile* colitis).
## Clinical Pearls
* **Administration:** Oral suspensions and tablets can be taken with or without food.
* **Tissue Distribution:** Azithromycin concentrates in macrophages and fibroblasts, leading to high intracellular levels, which explains the long post-antibiotic effect.
* **Resistance:** Increasing resistance in *Streptococcus pneumoniae* reduces its utility as monotherapy for severe pneumonia in some regions.
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**Disclaimer:** This information is for educational purposes only. Always verify dosages, contraindications, and drug interactions with the most current prescribing information (e.g., FDA label or Micromedex/Lexicomp) and institutional protocols before prescribing or administering medication.
