Doxycycline Contraindicated in Myasthenia Gravis: Mechanism and Alternatives

Doxycycline (and all tetracyclines) is contraindicated in myasthenia gravis (MG).

Mechanism of Harm

• Tetracyclines block acetylcholine release from presynaptic nerve terminals at the neuromuscular junction (NMJ).
• They also competitively inhibit postsynaptic acetylcholine receptors.
• In MG, autoantibodies (anti-AChR, anti-MuSK) already reduce safety margin of neuromuscular transmission. Further blockade → profound weakness, respiratory failure, myasthenic crisis.

Clinical Evidence

• Case reports of MG exacerbation after single doses.
• FDA labeling: contraindicated.
• Other antibiotic classes also risky: aminoglycosides, fluoroquinolones, macrolides (azithromycin), polymyxins, clindamycin (less).

Safer Antibiotic Choices for MG Patients

• Penicillins (amoxicillin, ampicillin)
• Cephalosporins (ceftriaxone, cefazolin)
• Carbapenems (meropenem)
• Vancomycin
• Aztreonam
• Metronidazole

Always inform all prescribers of MG diagnosis. Carry medical alert. Preoperative antibiotic selection requires anesthesiology coordination.