Is amoxicillin safe to use in patients with myasthenia gravis?

Amoxicillin Safety in Myasthenia Gravis Patients

Amoxicillin should be used with caution in patients with myasthenia gravis due to reported cases of myasthenic exacerbations, though it is generally safer than fluoroquinolones, aminoglycosides, and macrolides. 1, 2

Safety Profile of Antibiotics in Myasthenia Gravis

High-Risk Antibiotics (Avoid)

• Fluoroquinolones: Strong evidence shows these can block neuromuscular transmission and cause potentially life-threatening exacerbations 3, 4, 5
• Aminoglycosides: Should be avoided due to risk of worsening myasthenic symptoms 3, 1
• Macrolides: Can exacerbate myasthenia and require dose reduction in renal impairment 3, 1

Preferred Antibiotics

• Penicillins (including amoxicillin): Generally considered safer options, but recent evidence suggests caution is warranted 1, 2
• Cephalosporins: Typically well-tolerated in myasthenia gravis patients 1
• Tetracyclines: Generally safe with normal renal function 1, 6

Amoxicillin-Specific Concerns

Recent evidence indicates that amoxicillin may not be as safe as previously thought:

• A 2020 case series reported six myasthenia gravis patients who developed acute symptom worsening after amoxicillin or amoxicillin/clavulanate treatment 2
• Exacerbations typically occurred within days of antibiotic administration
• All patients showed worsening on the Myasthenia Gravis Foundation of America (MGFA) clinical classification
• Most patients required therapeutic intervention with increased dosage of previous therapy or introduction of new drugs
• All patients eventually recovered to baseline within 1-2 months 2

Monitoring Recommendations

When using amoxicillin in myasthenia gravis patients:

1. Close monitoring for signs of worsening weakness after antibiotic initiation
2. Assessment of:
   • New or worsening muscle weakness
   • Respiratory function
   • Availability of rescue medications 1
3. Discontinue immediately if worsening of MG symptoms occurs
4. Consider alternative antibiotics from a different class if symptoms worsen
5. Consider increasing acetylcholinesterase inhibitor dose or using IVIG/plasmapheresis for severe exacerbations 1

Management Algorithm for Infections in MG Patients

1. First-line antibiotic choices:

   • Cephalosporins
   • Tetracyclines (if appropriate for the infection and with normal renal function)
   • Amoxicillin (with careful monitoring)

2. If amoxicillin must be used:

   • Treat infection promptly and aggressively
   • Monitor closely for 48-72 hours after initiation
   • Have rescue medications available
   • Prepare for possible need to increase acetylcholinesterase inhibitors

3. If exacerbation occurs:

   • Discontinue amoxicillin immediately
   • Switch to a safer alternative antibiotic
   • Consider IVIG or plasmapheresis for severe cases

Conclusion

While amoxicillin has traditionally been considered safer than other antibiotics for myasthenia gravis patients, emerging evidence suggests it may trigger exacerbations in some individuals. When treating infections in myasthenia gravis patients, cephalosporins may represent a safer first-line choice, with amoxicillin used cautiously and with close monitoring.