What are safe antibiotics for a patient with myasthenia gravis (MG) who has pertussis?

Safe Antibiotics for Pertussis in Myasthenia Gravis Patients

Azithromycin is the preferred antibiotic for treating pertussis in patients with myasthenia gravis due to its better safety profile and lower risk of exacerbating myasthenia symptoms compared to other antibiotics. 1

First-Line Treatment

Azithromycin

• Recommended regimen for adults: 500 mg on day 1, followed by 250 mg daily for 4 days (5 days total) 1
• Recommended regimen for children: 10 mg/kg on day 1, followed by 5 mg/kg daily for 4 days (5 days total) 1
• Safety in MG: Azithromycin has fewer drug interactions and a better safety profile in myasthenia gravis patients compared to other macrolides 2
• Important precaution: The FDA label specifically mentions that "exacerbation of symptoms of myasthenia gravis and new onset of myasthenic syndrome have been reported in patients receiving azithromycin therapy" 2, but it remains the safest option among antibiotics for pertussis

Medication Considerations

Medications to Avoid in MG Patients with Pertussis

• Aminoglycosides (including topical formulations like tobramycin eye drops) can trigger or worsen MG symptoms 3
• Fluoroquinolones (e.g., moxifloxacin) have been associated with MG exacerbations 4
• Erythromycin has more drug interactions and gastrointestinal side effects than azithromycin 5, 1
• Penicillins (including amoxicillin) have been reported to cause MG exacerbations in some cases 6

Second-Line Options (if azithromycin cannot be used)

Trimethoprim-Sulfamethoxazole

• Can be considered as an alternative, but:
  • Contraindicated in pregnant women and nursing mothers 1
  • Has higher risk of adverse effects including rash and blood dyscrasias 1
  • Requires longer treatment duration

Erythromycin (use with caution)

• Adult dosing: 2 g per day in 4 divided doses for 14 days 5
• Cautions:
  • Inhibits cytochrome P450 enzyme system, leading to potentially serious drug interactions 1
  • Associated with more gastrointestinal side effects 5
  • Higher risk of exacerbating MG symptoms compared to azithromycin

Monitoring and Management

Close Monitoring Required

• All MG patients receiving antibiotics should be closely monitored for:
  • Worsening of muscle weakness
  • Respiratory compromise
  • Difficulty swallowing
  • Increased fatiguability

Management of Exacerbations

• If MG symptoms worsen after antibiotic initiation:
  • Consider discontinuing the antibiotic and switching to an alternative
  • Hospitalization may be necessary if respiratory function is compromised 7
  • Intensification of MG treatment may be required

Important Clinical Considerations

• Infections themselves can trigger MG exacerbations, so prompt treatment of pertussis is essential 7
• Patients with generalized MG are more vulnerable to drug-induced exacerbations than those with stable, limited disease 8
• Patients should be instructed to complete the full course of antibiotic therapy to prevent bacterial resistance 2
• Antacids containing aluminum or magnesium should not be taken simultaneously with azithromycin as they reduce absorption 2

By following these guidelines, clinicians can effectively treat pertussis in MG patients while minimizing the risk of triggering a myasthenic crisis.