Erythromycin

# Erythromycin ## Overview - **Classification**: Macrolide antibiotic. - **Mechanism**: Binds to the 50S ribosomal subunit, inhibiting bacterial protein synthesis. Bacteriostatic but can be bactericidal. ## Primary Indications 1. **Bacterial Infections**: Respiratory tract, skin/soft tissue, genitourinary. 2. **Pertussis (Whooping Cough)**: Treatment and post-exposure prophylaxis. 3. **Chlamydial Infections**: Ocular, genitourinary infections (alternative). 4. **Gastroparesis**: Prokinetic agent for impaired gastric emptying (off-label). ## Adult Dosing ### Standard Dosing **Bacterial Infections (e.g., Respiratory, Skin, Soft Tissue)** - **Dose**: **250 mg** to **500 mg** (as erythromycin base, stearate, or estolate) - **Frequency**: Every 6 hours (QID) or **333 mg** every 8 hours (TID) - **Route**: Oral (PO) - **Duration**: 7-14 days depending on infection. - **Maximum**: **4 g/day** **Pertussis (Whooping Cough)** - **Dose**: **500 mg** (as erythromycin base, stearate, or estolate) - **Frequency**: Every 6 hours (QID) - **Route**: Oral (PO) - **Duration**: 14 days **Chlamydial Infections** - **Dose**: **500 mg** (as erythromycin base or stearate) - **Frequency**: Every 6 hours (QID) - **Route**: Oral (PO) - **Duration**: 7 days **Gastroparesis (Prokinetic)** - **Dose**: **125 mg** to **250 mg** (as erythromycin base) - **Frequency**: Three times daily (TID) or four times daily (QID) 30 min before meals. - **Route**: Oral (PO) - **Special Considerations**: Use lowest effective dose for shortest duration due to tachyphylaxis. ### Dose Adjustments - **Renal Impairment**: No adjustment for mild-moderate impairment. - CrCl <10 mL/min: Consider dose reduction by **25-50%** or increased dosing interval. - **Hepatic Impairment**: Use with caution. Consider dose reduction in severe impairment. - **Elderly Patients**: No specific adjustment based on age alone. Monitor for QTc prolongation and drug interactions. ## Pediatric Dosing ### Neonates (0-28 days) - **Indication**: Systemic infections (e.g., chlamydia pneumonia). - **Dose**: **10-12.5 mg/kg/dose** - **Frequency**: Every 6 hours (QID) - **Maximum**: **250 mg/dose** - **Special Notes**: Associated with risk of infantile hypertrophic pyloric stenosis (IHPS), especially in first 2 weeks. Monitor closely for vomiting. ### Infants (1-12 months) - **Indication**: Bacterial infections (e.g., pertussis, chlamydia pneumonia). - **Dose**: **30-50 mg/kg/day** (in 3-4 divided doses) - **Frequency**: Every 6-8 hours - **Maximum**: **500 mg/dose** or **2 g/day** - **Special Notes**: Oral suspension preferred. Continue to monitor for IHPS, though risk decreases after neonatal period. ### Children (1-12 years) - **Indication**: Bacterial infections (e.g., pertussis, strep throat alternative). - **Dose**: **30-50 mg/kg/day** (in 3-4 divided doses) - **Frequency**: Every 6-8 hours - **Maximum**: **500 mg/dose** or **2 g/day** (not to exceed adult dose). - **Special Notes**: Oral suspension or chewable tablets available. ### Adolescents (13-18 years) - **Indication**: Bacterial infections. - **Dose**: Follow **adult dosing** guidelines. - **Frequency**: As per adult regimen. - **Maximum**: **4 g/day** - **Special Notes**: Counsel on proper administration (e.g., with food to minimize GI upset). ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to erythromycin or macrolides. - **Absolute**: Coadministration with pimozide, ergotamine, dihydroergotamine (life-threatening arrhythmias/vasoconstriction). - **Absolute**: Coadministration with colchicine (increased toxicity). - **Absolute**: History of cholestatic jaundice/hepatic dysfunction with erythromycin use. - **Absolute**: Congenital long QT syndrome or QTc prolongation. - **Absolute**: Concomitant use with HMG-CoA reductase inhibitors (statins) metabolized by CYP3A4 (e.g., simvastatin, lovastatin) due to rhabdomyolysis risk. ### Common Adverse Effects - **Very Common (>10%)**: Abdominal pain/cramping, nausea, vomiting, diarrhea. - **Common (1-10%)**: QTc prolongation, headache, rash, elevated LFTs. - **Serious but Rare**: Torsades de Pointes, cholestatic hepatitis, pseudomembranous colitis (C. difficile), ototoxicity (reversible), infantile hypertrophic pyloric stenosis (IHPS) in neonates. ### Key Drug Interactions - **CYP3A4 Substrates (Simvastatin, Lovastatin)**: Increased statin levels, rhabdomyolysis. **Contraindicated.** - **Pimozide, Ergotamine, Dihydroergotamine**: Increased toxicity, life-threatening events. **Contraindicated.** - **Colchicine**: Increased colchicine levels, risk of toxicity. **Contraindicated.** - **Warfarin**: Enhanced anticoagulant effect. Monitor INR closely. - **Antiarrythmics (e.g., Amiodarone, Quinidine)**: Increased risk of QTc prolongation and Torsades. - **Digoxin**: Increased digoxin levels. Monitor levels. - **Immunosuppressants (e.g., Cyclosporine, Tacrolimus)**: Increased levels, risk of toxicity. Monitor levels. - **Theophylline**: Increased theophylline levels, toxicity risk. ## Monitoring & Follow-up - **Before Treatment**: Review patient's medication list for drug interactions. Baseline LFTs for prolonged therapy or hepatic impairment. - **During Treatment**: - Monitor for GI intolerance (nausea, vomiting, diarrhea). - Monitor for signs of hepatotoxicity (jaundice, dark urine). - **Neonates/Infants**: Monitor closely for signs of IHPS (forceful vomiting, feeding intolerance). - **Prolonged use/IV**: Monitor LFTs, ECG for QTc prolongation (especially with risk factors). - **Clinical Signs**: Resolution of infection symptoms. Improvement in gastric emptying for gastroparesis. ## Clinical Pearls - 💡 **GI Upset**: Erythromycin frequently causes GI side effects. Taking with food may reduce symptoms but can reduce absorption of some forms. - 💡 **Formulations**: Dosing varies by salt form (base, stearate, estolate, ethylsuccinate). The **ethylsuccinate** form is typically better tolerated GI-wise but less reliably absorbed. - 💡 **CYP3A4 Inhibition**: Erythromycin is a potent CYP3A4 inhibitor, making drug interactions common and clinically significant. **Always check for interactions.** - 💡 **Taste**: Oral suspensions can be unpalatable; counsel patients/parents on administration. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.