A 59-Year-Old Man with a History of Type 1 Diabetes

A 59-year-old man with a history of type 1 diabetes mellitus and depression is brought to the emergency department because of increasing confusion and fever over the past 14 hours. Four days ago, he was prescribed metoclopramide by his physician for the treatment of diabetic gastroparesis. His other medications include insulin and paroxetine. His temperature is 39.9°C (103.8°F) , pulse is 118/min, and blood pressure is 165/95 mm Hg. Physical examination shows profuse diaphoresis and flushed skin. There is generalized muscle rigidity and decreased deep tendon reflexes. His serum creatine kinase is 1250 U/L. The antidote for this patient's current condition most likely has which of the following mechanisms of action?

A) Activation of presynaptic voltage-gated calcium channels of motor neurons
B) Antagonism of peripheral and central serotonin receptors
C) Blockade of central dopamine D2 receptors
D) Inhibition of acetylcholinesterase at the neuromuscular junction
E) Inhibition of calcium ion release from sarcoplasmic reticulum of skeletal muscle