Adverse effect of verapamil in myasthenia gravis

Verapamil, a class IV anti‐arrhythmic drug that blocks voltage‐dependent calcium channels in cardiac and smooth muscle, also has effects on presynaptic and postsynaptic voltage‐dependent calcium channels at the neuromuscular junction. In a postoperative patient with pre‐existent myasthenia gravis, oral verapamil caused a marked exacerbation in myasthenic weakness.