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# Mycoplasma pneumoniae (Pathogen)
## Overview
*Mycoplasma pneumoniae* is a common cause of "walking pneumonia" (atypical pneumonia) and tracheobronchitis. It lacks a cell wall, rendering beta-lactam antibiotics (e.g., penicillins, cephalosporins) completely ineffective. Treatment focuses on protein synthesis inhibitors.
## Primary Indications
* Community-acquired pneumonia (CAP)
* Tracheobronchitis
## Adult Dosing
* **Azithromycin:** 500 mg Day 1, followed by 250 mg daily for 4 days.
* **Doxycycline:** 100 mg orally every 12 hours for 5–7 days.
* **Levofloxacin:** 500 mg orally/IV daily for 7–10 days.
* **Moxifloxacin:** 400 mg orally/IV daily for 7–10 days.
## Pediatric Dosing
* **Azithromycin:** 10 mg/kg (max 500 mg) on Day 1, followed by 5 mg/kg (max 250 mg) daily for 4 days.
* **Doxycycline:** For children <8 years old, use only if benefits outweigh risks (potential for dental staining). Dose: 2.2 mg/kg per dose twice daily (max 100 mg/dose).
* **Levofloxacin:** 10 mg/kg/dose every 12 hours (age 6 mo–5 years) or every 24 hours (age ≥5 years).
## Dose Adjustments
* **Renal:** No routine adjustment needed for azithromycin or doxycycline. Fluoroquinolones require dose/frequency adjustments based on CrCl (refer to specific package inserts).
* **Hepatic:** Use caution with azithromycin in patients with severe hepatic impairment.
## Contraindications
* **Azithromycin/Macrolides:** History of cholestatic jaundice or hepatic dysfunction; known hypersensitivity.
* **Doxycycline:** Severe hepatic impairment; pregnancy (second/third trimester) or children <8 years unless benefit outweighs risks.
* **Fluoroquinolones:** History of tendon disorders; pregnancy/nursing; myasthenia gravis.
## Adverse Effects
* **Macrolides:** QTc prolongation, GI upset (diarrhea, nausea), hepatotoxicity.
* **Doxycycline:** Photosensitivity, esophageal ulceration (take with full glass of water, remain upright), tooth discoloration in young children.
* **Fluoroquinolones:** Tendonitis/tendon rupture, QTc prolongation, peripheral neuropathy, *C. difficile* infection, blood glucose disturbances.
## Key Drug Interactions
* **Azithromycin:** Warfarin (may increase INR), CYP3A4 inhibitors/inducers, drugs causing QTc prolongation.
* **Doxycycline:** Antacids, iron, calcium, or magnesium supplements (take 2 hours before or 4 hours after to prevent chelation).
* **Fluoroquinolones:** Multi-valent cations (chelation), warfarin, NSAIDs (increased risk of CNS stimulation).
## Monitoring
* Baseline and follow-up clinical assessment for pulmonary status.
* Monitor for signs of QTc prolongation if on concurrent high-risk medications.
* Watch for *C. difficile* symptoms (watery diarrhea).
## Clinical Pearls
* **Empiric Coverage:** Always assume *M. pneumoniae* if clinical presentation is "atypical" (slow onset, dry cough, malaise) and initial beta-lactams have failed.
* **Macrolide Resistance:** Increasing resistance in *M. pneumoniae* has been reported in certain geographic regions; consider tetracyclines or fluoroquinolones if clinical improvement is not seen within 48–72 hours.
* **Doxycycline Safety:** Modern literature suggests short-term use in children <8 years is unlikely to cause significant tooth discoloration.
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**Disclaimer:** This information is for educational purposes only. Always consult current institutional guidelines, local antibiograms, and official prescribing information (package inserts) before initiating therapy. Dosage may vary based on patient-specific factors, severity of infection, and local resistance patterns.
