Magnesium Glycinate and Myasthenia Gravis
Magnesium glycinate is contraindicated in patients with myasthenia gravis and must be strictly avoided, as all forms of magnesium—particularly intravenous but also oral formulations—can precipitate life-threatening myasthenic crisis requiring mechanical ventilation. 1, 2
Why All Magnesium Forms Are Dangerous in MG
Magnesium acts at the neuromuscular junction through two mechanisms that directly worsen myasthenic weakness: it inhibits presynaptic acetylcholine release and desensitizes the postsynaptic membrane, both of which exacerbate the fundamental pathophysiology of myasthenia gravis. 3 While guidelines specifically emphasize the danger of intravenous magnesium, the same neuromuscular blocking mechanisms apply to oral magnesium supplements including magnesium glycinate. 1, 2, 4
Evidence of Harm
A documented case report demonstrates acute respiratory failure requiring intubation and prolonged ICU stay in a 62-year-old woman with myasthenia gravis following standard intravenous magnesium replacement, illustrating the severe and rapid deterioration that magnesium can trigger. 3
Multiple authoritative guidelines from the American Society of Clinical Oncology and American Academy of Neurology explicitly list magnesium among high-risk medications that must be absolutely avoided in MG patients. 1, 2, 5
Clinical Algorithm for Magnesium Avoidance
Before prescribing or recommending any magnesium supplement:
Review the patient's current MG severity using MGFA classification and assess respiratory function with vital capacity and negative inspiratory force measurements. 2
Consult neurology before initiating any magnesium-containing product in symptomatic or unstable MG patients. 2
If magnesium exposure occurs:
Immediately discontinue the magnesium supplement. 2
Urgently assess respiratory function (vital capacity, negative inspiratory force) to determine need for ICU-level monitoring. 2
For Grade 3-4 exacerbations (dysphagia, respiratory weakness, rapidly progressive symptoms): admit to ICU, initiate IVIG 2 g/kg over 5 days or plasmapheresis, and continue/initiate corticosteroids. 1, 2
For Grade 2 exacerbations (mild generalized weakness): optimize pyridostigmine dosing up to 120 mg four times daily and initiate prednisone 1-1.5 mg/kg daily. 1, 2
Other High-Risk Medications to Avoid
Patients with MG must also strictly avoid β-blockers (all formulations, especially IV), fluoroquinolones, aminoglycosides (tobramycin, gentamicin, amikacin), macrolides (erythromycin, azithromycin, clarithromycin), and barbiturates like butalbital. 1, 2, 5
Critical Caveat
Symptomatic MG patients with generalized disease are especially vulnerable to drug-induced exacerbations, though even stable patients with minimal symptoms can deteriorate with magnesium exposure. 6 The risk-benefit calculation for magnesium supplementation in MG is unequivocally unfavorable given the availability of alternative supplements and the potentially catastrophic consequences of myasthenic crisis.