Erythromycin

1. Introduction

Erythromycin is a macrolide antibiotic used to treat various bacterial infections. It inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, making it effective against gram-positive and some gram-negative bacteria. Erythromycin also has prokinetic properties, which make it useful in specific gastrointestinal disorders.

2. Indications

  • Approved Indications:
    • Respiratory tract infections (e.g., pneumonia, bronchitis, pharyngitis).
    • Skin and soft tissue infections (e.g., cellulitis, impetigo).
    • Sexually transmitted infections (e.g., chlamydia, syphilis).
    • Whooping cough (pertussis).
    • Eye infections (e.g., conjunctivitis in neonates).
  • Off-Label Uses:
    • Gastroparesis (due to its prokinetic effects).
    • Acne vulgaris (topical use).

3. Dosage

  • Adults:
    • Infections: 250–500 mg orally every 6–12 hours (maximum: 4 g/day).
    • Gastroparesis: 125–250 mg orally three times daily before meals.
  • Children:
    • Infections: 30–50 mg/kg/day in divided doses every 6–8 hours.
    • Neonatal conjunctivitis: 50 mg/kg/day in divided doses every 6–12 hours.
  • Elderly:
    • No specific dose adjustment required, but monitor for gastrointestinal and cardiac side effects.

4. Administration

  • Oral forms: Take with or without food. If gastrointestinal upset occurs, take with food.
  • Extended-release tablets: Swallow whole, do not crush or chew.
  • IV infusion: Administer slowly to avoid vein irritation.
  • Topical and ophthalmic forms: Apply as directed by a healthcare provider.

5. Forms Available

  • Tablets: 250 mg, 500 mg.
  • Capsules: 250 mg, 500 mg.
  • Oral suspension: 200 mg/5 mL, 400 mg/5 mL.
  • Intravenous solution: 50 mg/mL.
  • Topical gel: 2%.
  • Ophthalmic ointment: 0.5%.

6. Side Effects

6.1. Common Side Effects

  • Nausea and vomiting.
  • Diarrhoea.
  • Abdominal pain or cramping.

6.2. Less Common Side Effects

  • Skin rash.
  • Loss of appetite.
  • Dizziness.

6.3. Rare but Serious Side Effects

  • Prolonged QT interval and arrhythmias (e.g., torsades de pointes).
  • Cholestatic hepatitis.
  • Severe allergic reactions (e.g., anaphylaxis).

7. Warnings

  • QT Prolongation: Increased risk of torsades de pointes, especially in patients with pre-existing cardiac conditions or when used with other QT-prolonging drugs.
  • Hepatotoxicity: Use cautiously in patients with liver impairment, as erythromycin may cause cholestatic hepatitis.
  • Clostridioides difficile-Associated Diarrhoea (CDAD): May occur during or after treatment; report persistent diarrhoea to a healthcare provider.

8. Precautions

  • Avoid use in patients with a history of macrolide allergy.
  • Use with caution in patients with myasthenia gravis, as it may worsen symptoms.
  • Monitor for drug interactions, as erythromycin is a strong inhibitor of CYP3A4.

9. Interactions

  • Drug-Drug Interactions:
    • CYP3A4 substrates (e.g., warfarin, simvastatin, midazolam): Increased plasma levels and toxicity.
    • QT-prolonging drugs (e.g., amiodarone, sotalol): Increased risk of arrhythmias.
    • Theophylline: Increased levels and toxicity.
    • Antacids: May reduce erythromycin absorption.
  • Drug-Food Interactions:
    • Absorption may be reduced by grapefruit juice.

10. Monitoring Parameters

  • Monitor for symptom improvement in infections.
  • Assess for gastrointestinal side effects, particularly diarrhoea.
  • Monitor ECG in patients at risk of QT prolongation.
  • Check liver function tests in long-term therapy or in patients with pre-existing liver conditions.

11. Use in Children

  • Safe and widely used in paediatric populations for infections and neonatal eye prophylaxis. Adjust doses based on weight.

12. Use in Pregnancy

  • Category B: Considered safe for use during pregnancy. Often used for chlamydia or syphilis in pregnant women.

13. Use in Elderly

  • Safe for use, but elderly patients are more prone to cardiac side effects, such as QT prolongation.

14. Use in Kidney Disease

  • No dose adjustment is required in renal impairment.

15. Use in Liver Disease

  • Use cautiously, as erythromycin is metabolised in the liver. Monitor liver function during therapy.

16. Patient Counselling Points

  • Take erythromycin as prescribed, completing the full course even if symptoms improve.
  • Report any signs of severe diarrhoea, abdominal pain, or unusual fatigue to your doctor.
  • Avoid grapefruit juice during treatment.
  • If prescribed for acne or rosacea, it may take several weeks to see improvement.
  • For topical or eye formulations, apply only as directed, and avoid contaminating the tip of the tube or bottle.

17. Table of Brand Names, Manufacturers, and Prices

Brand NameManufacturerPrice (USD)
ErythrocinAbbott$20–40 (30 tablets, 250 mg)
EES (Erythromycin Ethylsuccinate)Pfizer$25–50 (30 tablets, 400 mg)
Generic ErythromycinVarious$10–30 (30 tablets, 250 mg)

18. FAQs (15 Questions)

  1. What is erythromycin used for?
    It is used to treat bacterial infections such as respiratory infections, skin infections, and sexually transmitted infections.
  2. How does erythromycin work?
    It inhibits bacterial protein synthesis, preventing bacterial growth.
  3. What are the common side effects of erythromycin?
    Nausea, vomiting, diarrhoea, and abdominal cramps are common side effects.
  4. Can erythromycin cause heart problems?
    Yes, it can prolong the QT interval, increasing the risk of arrhythmias, especially in patients with pre-existing cardiac conditions.
  5. Can erythromycin be used in children?
    Yes, it is safe and effective for paediatric use, with doses adjusted based on weight.
  6. Can erythromycin be taken during pregnancy?
    Yes, it is considered safe during pregnancy (Category B).
  7. What should I do if I miss a dose of erythromycin?
    Take it as soon as you remember, but skip it if it’s close to the next dose. Do not double up.
  8. Does erythromycin interact with other medications?
    Yes, it interacts with CYP3A4 substrates, QT-prolonging drugs, and antacids.
  9. Can erythromycin be used for acne?
    Yes, it is used topically or orally for acne, though treatment may take several weeks.
  10. Is erythromycin effective against all bacterial infections?
    No, it is ineffective against resistant strains or certain gram-negative bacteria.
  11. Can erythromycin cause diarrhoea?
    Yes, it may cause diarrhoea, including serious conditions like Clostridioides difficile-associated diarrhoea.
  12. How should erythromycin be stored?
    Store at room temperature, away from light and moisture.
  13. Can I drink alcohol while taking erythromycin?
    Moderate alcohol consumption is generally safe, but excessive alcohol may worsen side effects.
  14. How long does it take for erythromycin to work?
    Symptom improvement is typically seen within a few days, but the full course should be completed.
  15. Can erythromycin cause liver problems?
    Rarely, it can cause cholestatic hepatitis, especially with prolonged use.