Acute effects of intravenous injection of beta-adrenoreceptor- and calcium channel at antagonists and agonists in myasthenia gravis.

The effect of intravenous injection of propranolol, verapamil, terbutaline, calcium, and edrophonium on neuromuscular transmission has been studied with repetitive nerve stimulation and clinical tests in 10 patients with myasthenia gravis (MG). The drugs were given intravenously in doses commonly used in clinical practice. Only minor clinical effects were noted except for edrophonium. The mean decrement of the deltoid muscle was not significantly changed after injection of propranolol (before 31%, 15 min after injection 27%) and verapamil (before 29%, 15 min after injection 26%). Terbutaline applied after propranolol and calcium applied after verapamil improved the decrement substantially. Edrophonium applied after propranolol or verapamil also greatly improved the decrement. We conclude that there is no rapid deterioration of neuromuscular transmission in patients with moderately severe MG after injections with therapeutic doses of propranolol and verapamil. However, we do not know if the most severely disabled MG patient could have reacted otherwise. We consider that, in cardiovascular emergencies, propranolol and verapamil may be used even in severe MG but with resuscitation equipment as well as specific antidotes available.