Usage
Erythromycin is prescribed for a wide range of bacterial infections including: upper and lower respiratory tract infections (e.g., pneumonia, bronchitis, pharyngitis, sinusitis, pertussis), skin and soft tissue infections (e.g., cellulitis, impetigo, erysipelas), sexually transmitted infections (e.g., syphilis, chlamydia, gonorrhea), gastrointestinal infections (e.g., Campylobacter enteritis), and other infections like diphtheria, Legionnaires’ disease, and rheumatic fever prophylaxis. It is also used as a prokinetic agent for gastroparesis and in bowel preparation.
Pharmacological Classification: Macrolide antibiotic.
Mechanism of Action: Erythromycin inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, thereby preventing the translocation of aminoacyl tRNA. This bacteriostatic action prevents bacterial growth and allows the body’s immune system to eliminate the infection.
Alternate Names
Erythromycin base, erythromycin ethylsuccinate, erythromycin estolate, erythromycin lactobionate, erythromycin stearate. Brand names include E-Mycin, Erythrocin, Ilosone, EryPed, and others.
How It Works
Pharmacodynamics: Erythromycin primarily exerts a bacteriostatic effect by inhibiting protein synthesis in susceptible bacteria.
Pharmacokinetics: Erythromycin is absorbed orally, though food can impair absorption of some formulations. It is widely distributed throughout the body, achieving high concentrations in tissues and fluids. It is primarily metabolized in the liver by CYP3A4 enzymes and excreted mainly in the bile, with a small fraction excreted in the urine.
Mode of Action: Binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting transpeptidation and translocation steps of protein synthesis.
Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Erythromycin acts on bacterial ribosomes and does not typically bind to human receptors or modulate neurotransmitters. It is a substrate and inhibitor of CYP3A4, which can lead to drug interactions.
Elimination Pathways: Primarily hepatic excretion via bile, with minor renal excretion.
Dosage
Standard Dosage
Adults:
- Oral: 250 mg every 6 hours, or 500 mg every 12 hours (for total daily doses not exceeding 1g). For severe infections, dosages may be increased up to 4 g/day in divided doses.
- IV: 15-20 mg/kg/day (up to 4g/day), divided and administered over 20-60 minutes every 6 hours.
Children:
- Oral: 30-50 mg/kg/day (up to 4 g/day) divided every 6-8 hours, depending on the severity of infection. Neonates: Dosage should be determined based on body weight and postnatal age.
- IV: Same as adult dose adjusted for weight.
Special Cases:
- Elderly Patients: Use with caution; dosage adjustments may be necessary for patients with hepatic or renal impairment. Higher doses (≥4g/day) may increase risk of hearing loss.
- Patients with Renal Impairment: Caution is advised in patients with severe renal impairment (CrCl < 10 mL/min); a maximum daily dose of 2 g is recommended. No adjustment necessary for mild to moderate impairment.
- Patients with Hepatic Dysfunction: Use with caution; dosage adjustment may be necessary. Serum level monitoring recommended.
- Patients with Comorbid Conditions: Exercise caution with other medications metabolized by CYP3A4, as erythromycin can inhibit their metabolism.
Clinical Use Cases
- Intubation/Surgical Procedures/Mechanical Ventilation/ICU Use: Prokinetic doses of 70-200 mg IV every 6-8 hours are often used, although oral administration is also utilized, typically at higher doses.
- Emergency Situations: Higher IV doses may be needed based on infection severity and patient response.
Dosage Adjustments:
Dosage adjustments are necessary for patients with hepatic or severe renal dysfunction. Consider reducing the dose or increasing the dosing interval. Therapeutic drug monitoring may be helpful.
Side Effects
Common Side Effects:
Nausea, vomiting, diarrhea, abdominal pain, loss of appetite.
Rare but Serious Side Effects:
Cholestatic jaundice, hepatotoxicity, hearing loss (especially at higher doses), cardiac arrhythmias including QT prolongation, allergic reactions (rash, itching, swelling).
Long-Term Effects:
Long-term use may result in antibiotic-associated colitis and the development of resistant bacterial strains.
Adverse Drug Reactions (ADR):
Severe allergic reactions (anaphylaxis), Stevens-Johnson syndrome, toxic epidermal necrolysis, drug-induced liver injury.
Contraindications
Hypersensitivity to erythromycin or any macrolide antibiotics. Concurrent use with terfenadine, astemizole, cisapride, and other drugs that prolong the QT interval. Use with caution in patients with liver disease, prolonged QT interval, or a history of cardiac arrhythmias. Infants under two weeks old should not be given erythromycin due to a possible association with infantile hypertrophic pyloric stenosis (IHPS).
Drug Interactions
Erythromycin is a CYP3A4 inhibitor and can interact with numerous medications, including: warfarin, theophylline, statins, some antihistamines, certain antifungals, immunosuppressants, and others. It can also interact with grapefruit juice and alcohol. These interactions can lead to increased levels of the co-administered drugs, potentially leading to toxicity.
Pregnancy and Breastfeeding
Pregnancy Category B. Erythromycin is generally considered safe during pregnancy, but the potential benefits should outweigh the risks. It is excreted in breast milk, but generally considered compatible with breastfeeding.
Drug Profile Summary
- Mechanism of Action: Inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit.
- Side Effects: Nausea, vomiting, diarrhea, abdominal pain, hepatotoxicity, QT prolongation, allergic reactions.
- Contraindications: Hypersensitivity to macrolides, concurrent use of QT-prolonging drugs, infants under two weeks old.
- Drug Interactions: CYP3A4 substrates, QT prolonging agents.
- Pregnancy & Breastfeeding: Category B; generally safe but weigh risks vs. benefits. Compatible with breastfeeding.
- Dosage: Adults: 250-500 mg q6-12h (up to 4g/day). Children: 30-50 mg/kg/day divided q6-8h.
- Monitoring Parameters: Liver function tests, ECG (for QT interval), signs of superinfection.
Popular Combinations
Erythromycin is sometimes combined with sulfisoxazole for certain infections.
Precautions
Assess for allergies to macrolides, liver or renal function, and concomitant use of QT-prolonging medications. Use with caution in patients with prolonged QT interval or those at risk for cardiac arrhythmias. Dosage adjustments may be needed in the elderly and in patients with hepatic or renal dysfunction. Avoid or use with caution in infants younger than two weeks due to the risk of IHPS.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Erythromycin?
A: Adults: 250 mg every 6 hours or 500 mg every 12 hours, up to 4 g/day for severe infections. Children: 30-50 mg/kg/day divided every 6-8 hours. Neonates: Dosage needs to be determined on a case-by-case basis.
Q2: What are the common side effects?
A: The most common side effects are gastrointestinal, including nausea, vomiting, diarrhea, and abdominal pain.
Q3: What are the serious side effects?
A: Serious side effects include cholestatic jaundice, hepatotoxicity, hearing loss, cardiac arrhythmias (QT prolongation), and allergic reactions.
Q4: What are the contraindications to using erythromycin?
A: Contraindications include hypersensitivity to macrolides, concurrent use of QT prolonging drugs, and use in infants under two weeks old.
Q5: What are the significant drug interactions with erythromycin?
A: Erythromycin inhibits CYP3A4 and can interact with numerous drugs including warfarin, theophylline, statins, some antifungals, and certain antihistamines, potentially increasing their levels and causing toxicity.
Q6: Can erythromycin be used in pregnant or breastfeeding women?
A: It is generally considered safe during pregnancy (Category B) but the benefits should outweigh the risks. It is excreted in breast milk but is considered compatible with breastfeeding.
Q7: What monitoring parameters are important when using erythromycin?
A: Liver function tests, ECG (for QT interval), and signs of superinfection should be monitored.
Q8: How should erythromycin be administered?
A: Oral erythromycin should be taken on an empty stomach, ideally 1-2 hours before or after a meal. IV erythromycin should be infused over 20-60 minutes.
Q9: Can erythromycin be used in patients with renal impairment?
A: Caution is advised in severe renal impairment. Dosage adjustments may be needed.
Q10: What is the role of erythromycin in intensive care settings?
A: In intensive care settings, erythromycin is sometimes used at lower doses (70-200 mg IV or 125-250 mg enterally) for its prokinetic effects to treat gastroparesis and promote gastric emptying.
