Magnesium Repletion in Myasthenic Crisis

Introduction to Magnesium Repletion

• Magnesium should not be repleted in patients with myasthenic crisis as it can worsen neuromuscular weakness and potentially precipitate or exacerbate respiratory failure 1, 2

Evidence Against Magnesium Use in Myasthenia Gravis

• Clinical guidelines specifically list IV magnesium among high-risk medications to avoid in myasthenia gravis 1, 3, 2
• Immediately discontinue any medications that can worsen myasthenia, including beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolide antibiotics 3, 2

Management Recommendations for Myasthenic Crisis

• For severe myasthenic crisis (Grade 3-4), management should include hospital admission with ICU-level monitoring 4
• Corticosteroids (prednisone 1-1.5 mg/kg orally daily or methylprednisolone 2-4 mg/kg/day IV) should be administered 1, 4
• Frequent pulmonary function assessment and neurological monitoring should be performed 3

Electrolyte Management in Myasthenic Crisis

• If severe hypomagnesemia requires treatment in a patient with myasthenia gravis, consult neurology before administration 2

Oral Magnesium Dosing in Myasthenia Gravis

Dose Recommendations

• High oral magnesium regimens (approximately 600 mg – 6500 mg per day) have been described in the erythromelalgia literature, but these doses should not be extrapolated to patients with myasthenia gravis because they can precipitate or worsen neuromuscular weakness; consequently, such high‑dose oral magnesium is contraindicated in this population. Low‑quality evidence (observational report) 5