Myasthenia gravis: What does a pharmacist need to know?

Myasthenia gravis (MG) is not commonly covered in pharmacy school curricula. However, many medications that have been reported to cause exacerbations of MG are among the top 200 most prescribed drugs. The purpose of this therapeutic update is to provide pharmacists with a general understanding of the pathophysiology and treatment of MG and describe common medications with the potential to cause new onset or acute worsening of this disease.

MG is an autoimmune disorder in which patients develop autoantibodies to a component of the neuromuscular junction, most frequently the acetylcholine receptor, resulting in impairment of skeletal muscle contraction. Although MG is not highly prevalent, there are up to 60,000 individuals with MG in the US, making it a disease that many pharmacists will likely encounter at least once in their career. Immunosuppressant medications and acetylcholinesterase inhibitors are the mainstays of treatment, although there is limited evidence as to which agents are most efficacious. Medications that activate the immune system, such as immune checkpoint inhibitors, may cause new onset of disease, while those with actions on the neuromuscular junction, such as macrolides and fluoroquinolones, can cause acute worsening of disease.

MG, although not frequently covered in pharmacy school curricula, is a disease state for which it is not uncommon for pharmacists to provide care. Treatment tends to be patient specific, and evidence is often weak. Many medications that cause new onset or worsening of MG are among the most prescribed. Key classes of medications to use with caution include macrolides, fluoroquinolones, β-blockers, and magnesium.