Erythromycin is a macrolide antibiotic derived from *Streptomyces erythreus*. It is a broad-spectrum bacteriostatic agent, primarily used for treating infections caused by Gram-positive bacteria, atypical pathogens, and some Gram-negative organisms. It is a first-line alternative for patients allergic to penicillins. In the Indian context, it is widely used for respiratory, skin, and soft tissue infections, and for prophylaxis in rheumatic fever.
Adult: 250-500 mg orally every 6 hours, OR 333 mg every 8 hours, OR 500 mg every 12 hours (for specific formulations). For severe infections: Up to 4 g/day in divided doses. Typical dose: 250 mg QID.
Note: Oral tablet/capsule: Preferably taken on an empty stomach (1 hour before or 2 hours after meals) with a full glass of water to maximize absorption. Erythromycin ethylsuccinate and estolate may be taken with or without food. Do not crush or chew enteric-coated tablets. Complete the full prescribed course even if symptoms improve.
Erythromycin reversibly binds to the 50S subunit of the bacterial ribosome, specifically at the peptidyl transferase center. This binding inhibits the translocation step of protein synthesis, where tRNA moves from the A-site to the P-site. This prevents the addition of new amino acids to the growing peptide chain, thereby inhibiting bacterial protein synthesis.
Pregnancy: US FDA Category B. Erythromycin base and stearate are considered safe. Erythromycin estolate is contraindicated due to risk of hepatotoxicity in the pregnant patient. Use only if clearly needed.
Driving: Generally safe. Caution advised if dizziness, vertigo, or visual disturbances occur as rare side effects.
| Cisapride, Terfenadine, Astemizole | Increased risk of life-threatening ventricular arrhythmias (QT prolongation, Torsades de Pointes) | Contraindicated |
| Simvastatin, Lovastatin, Atorvastatin | Increased statin levels, significantly raising risk of myopathy and rhabdomyolysis | Major |
| Warfarin | Potentiates anticoagulant effect, increasing INR and risk of bleeding | Major |
| Carbamazepine | Increased carbamazepine levels leading to toxicity (dizziness, ataxia, nausea) | Major |
| Theophylline | Increased theophylline levels, risk of nausea, seizures, arrhythmias | Major |
| Digoxin | Increased digoxin bioavailability, risk of toxicity (nausea, bradycardia, arrhythmias) | Major |
| Cyclosporine, Tacrolimus | Increased immunosuppressant levels, risk of nephrotoxicity and neurotoxicity | Major |
| Midazolam, Triazolam | Increased sedation and prolonged effect | Major |
| Oral Contraceptives | Potential for reduced contraceptive efficacy; advise backup method | Moderate |
| Sildenafil | Increased sildenafil levels, risk of hypotension, visual disturbances | Major |
Same composition (Erythromycin (250mg)), different brands: