Is tigecycline (generic name) safe to use in patients with myasthenia gravis (MG)?

Tigecycline and Myasthenia Gravis

Tigecycline appears to be safe for use in patients with myasthenia gravis and may represent a preferred antibiotic option when treating infections in this population, particularly when other antibiotics known to exacerbate MG must be avoided.

Evidence Supporting Safety in MG

• A case report documented successful treatment of community-acquired pneumonia with tigecycline in an 85-year-old woman with myasthenia gravis who had previously experienced a myasthenic exacerbation after receiving moxifloxacin 1
• The patient responded well to tigecycline therapy without experiencing myasthenic crisis or worsening weakness, and was discharged on day 4 of hospitalization 1
• This case specifically highlights tigecycline as an addition to the therapeutic armamentarium for treating infections in MG patients presenting to the emergency department 1

Context: Antibiotics That Worsen MG

Understanding which antibiotics to avoid makes tigecycline's safety profile more clinically relevant:

• Fluoroquinolones are particularly problematic: They block neuromuscular transmission by decreasing miniature endplate potential amplitudes in a dose-dependent manner (12.5-100 mg/L) 2
• Fluoroquinolones should be used only with great caution in disorders that compromise the safety margin of neuromuscular transmission 2
• Multiple drug classes can trigger or exacerbate MG by interfering with neuromuscular transmission through various mechanisms affecting pre- or postsynaptic ion channels or acetylcholinesterase 3
• Even traditionally "safe" antibiotics like penicillins have documented cases of MG exacerbation, with six reported cases of acute worsening after amoxicillin or amoxicillin/clavulanate requiring therapeutic intervention 4

Clinical Decision-Making Algorithm

When selecting antibiotics for MG patients with infections:

1. Assess infection severity and pathogen: Determine if tigecycline provides adequate coverage for the suspected or confirmed organism 1

2. Evaluate patient-specific risk factors: Symptomatic MG patients with generalized disease are especially vulnerable to drug-induced exacerbations, while stable patients with few symptoms are at lower risk 3

3. Consider tigecycline-specific contraindications:

   • Use cautiously in patients with liver insufficiency 5, 6, 7
   • Reduce dose to 25 mg every 12 hours in severe hepatic impairment 7
   • Avoid for bloodstream infections due to low serum concentrations 7
   • Consider high-dose regimens for pneumonia 6

4. Monitor for tigecycline adverse effects unrelated to MG: Watch for nausea/vomiting (consider slower infusion rate or antiemetics), elevated liver enzymes, abdominal pain, and thrombocytopenia 5, 8

Important Caveats

• Not first-line for all infections: Tigecycline is primarily indicated for multidrug-resistant Gram-negative infections, particularly carbapenem-resistant organisms 6
• Limited efficacy data: Tigecycline is not recommended for bloodstream infections and has shown numerically lower efficacy than polymyxin-based therapy for some resistant infections 5, 6
• Newer alternatives may be preferred: For carbapenem-resistant Enterobacterales, newer agents like ceftazidime-avibactam, meropenem-vaborbactam, or cefiderocol are preferred when active in vitro 6

Monitoring Recommendations

• Closely monitor any MG patient receiving new antibiotics for possible increase in muscle weakness 3
• If deterioration occurs, withdraw the new treatment or reduce the dose 3
• Obtain baseline liver function tests and monitor if underlying liver disease exists 5, 7