Macrolides: Erythromycin, Azithromycin & Clarithromycin for Respiratory & Atypical Infections

Macrolides like Erythromycin and Azithromycin treat respiratory and atypical infections. Learn mechanism, spectrum, uses, side effects, and interactions.

Introduction

Macrolides are bacteriostatic antibiotics that inhibit bacterial protein synthesis. They are great for respiratory infections, rare germs, and patients allergic to penicillin. Common prototypes include Erythromycin, Azithromycin, and Clarithromycin.

Medications in the Class

• Erythromycin (prototype)

• Azithromycin

• Clarithromycin

• Fidaxomicin (narrow spectrum, mainly Clostridioides difficile)

Mechanism of Action

Macrolides bind to the 50S ribosomal subunit, inhibiting protein elongation. This stops bacterial growth, making them bacteriostatic. High concentrations may be bactericidal against some organisms.

Spectrum of Activity

• Gram-positive bacteria: Streptococcus pneumoniae, Staphylococcus aureus (non-MRSA)

• Gram-negative bacteria: Haemophilus influenzae, Moraxella catarrhalis (moderate activity)

• Atypical pathogens: Mycoplasma pneumoniae, Chlamydia spp., Legionella spp.

• Not effective against: Enterobacteriaceae and most anaerobes

Indications (When Used)

• Community-acquired pneumonia

• Pharyngitis and tonsillitis

• Atypical infections (Mycoplasma, Chlamydia, Legionella)

• Skin and soft tissue infections

• Prophylaxis of Mycobacterium avium complex (MAC) in immunocompromised patients

Contraindications (When Not to Use)

• Known hypersensitivity to macrolides

• Severe hepatic impairment (dose adjustment needed)

• History of QT prolongation or cardiac arrhythmias

Side Effects

• Gastrointestinal upset: nausea, vomiting, diarrhea (common with Erythromycin)

• Hepatotoxicity (rare, mostly cholestatic)

• QT prolongation → risk of arrhythmias

• Allergic reactions: rash, urticaria

Drug Interactions

• CYP3A4 substrates: Clarithromycin and Erythromycin can increase the levels of drugs like statins, warfarin, and carbamazepine.

• Antiarrhythmics: increased risk of QT prolongation

• Theophylline, digoxin: may require monitoring

• Azithromycin has fewer CYP450 interactions compared to Erythromycin and Clarithromycin

Antidote

No specific antidote. Supportive management is used for overdose or severe reactions. Cardiac monitoring is essential for QT prolongation.

Monitoring of Potential Complications

• Liver function tests during prolonged therapy

• Cardiac monitoring in patients at risk for arrhythmias

• Observe for severe allergic reactions

• Monitor for superinfections in long-term therapy

Macrolides are flexible antibiotics. They treat respiratory, skin, and atypical infections. This is especially helpful for patients who are allergic to penicillin. Their safety and easy access make them popular. But, clinicians need to watch for drug interactions and heart effects.