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# *Mycoplasma pneumoniae* (Pathogen)
## Overview
*Mycoplasma pneumoniae* is an atypical bacterium lacking a rigid cell wall, rendering beta-lactam antibiotics (penicillins, cephalosporins) completely ineffective. Treatment is targeted at inhibiting protein synthesis or DNA replication.
## Primary Indications
Community-acquired pneumonia (CAP), tracheobronchitis, and systemic infections caused by *M. pneumoniae*.
## Adult Dosing
* **Macrolide (Preferred):** Azithromycin 500 mg PO on Day 1, then 250 mg PO daily for Days 2–5.
* **Tetracycline:** Doxycycline 100 mg PO BID for 7–14 days.
* **Fluoroquinolone:** Levofloxacin 500 mg PO/IV daily for 7–14 days (reserve for severe cases or resistance).
## Pediatric Dosing
* **Macrolide:** Azithromycin 10 mg/kg (max 500 mg) on Day 1, then 5 mg/kg (max 250 mg) daily for Days 2–5.
* **Tetracycline:** Doxycycline (usually reserved for children ≥8 years due to tooth discoloration risk) 2.2–4.4 mg/kg/day divided BID (max 100 mg/dose).
* **Fluoroquinolone:** Levofloxacin (consult ID/Local Protocol for specific weight-based pediatric dosing; generally limited due to joint safety concerns but used for documented resistance).
## Dose Adjustments
* **Renal/Hepatic:** No routine adjustments required for short-term macrolide or tetracycline use. Fluoroquinolones require renal dose adjustment based on CrCl < 50 mL/min.
## Contraindications
* **Macrolides:** Hypersensitivity to macrolides; history of cholestatic jaundice.
* **Tetracyclines:** Pregnancy (second/third trimester), children <8 years (unless life-threatening infection), severe hepatic impairment.
* **Fluoroquinolones:** Hypersensitivity; peripheral neuropathy; history of tendon disorders.
## Adverse Effects
* **Macrolides:** QT prolongation, GI intolerance (nausea, diarrhea), hepatotoxicity.
* **Tetracyclines:** Photosensitivity, esophageal ulceration (take with full glass of water), teeth discoloration in pediatrics.
* **Fluoroquinolones:** Tendon rupture, QT prolongation, CNS effects (dizziness), hypoglycemia in diabetics.
## Key Drug Interactions
* **QT-Prolonging Agents:** Avoid concomitant use of fluoroquinolones or macrolides with other QT-prolonging drugs (e.g., ondansetron, amiodarone).
* **Cations:** Tetracyclines chelate with divalent/trivalent cations (calcium, magnesium, iron, aluminum, antacids); separate doses by 2–4 hours.
* **Warfarin:** Macrolides and doxycycline may increase INR; monitor closely.
## Monitoring
* **Clinical:** Resolution of fever and respiratory symptoms.
* **Safety:** Monitor ECG (if high-risk for QTc prolongation), monitor for signs of tendon pain (fluoroquinolones), and ensure hydration (doxycycline).
## Clinical Pearls
* **Resistance:** Macrolide resistance in *M. pneumoniae* is increasing globally; if a patient fails 48–72 hours of macrolide therapy, consider switching to a tetracycline or fluoroquinolone.
* **Lack of Cell Wall:** Because *Mycoplasma* lacks a peptidoglycan cell wall, penicillins, cephalosporins, and carbapenems have zero activity against this organism.
* **Doxycycline:** Doxycycline has proven effective for *M. pneumoniae* and is often favored to preserve macrolide efficacy.
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**Educational Disclaimer:** This information is for educational purposes only. Prescribing practices, local susceptibility patterns, and institutional guidelines vary significantly. Always verify doses, contraindications, and drug interactions against the most current primary literature and institutional protocols before prescribing.
