This drug antagonizes the RYR1 receptors of the sarcoplasmic reticulum, decreasing calcium release and is used to treat malignant hyperthermia.

• A. Ethosuximide
• B. Nimodipine
• C. Biphosphonates
• D. Dantrolene

Answer: (D)

Malignant hyperthermia is driven by uncontrolled calcium release from the skeletal muscle sarcoplasmic reticulum through the ryanodine receptor type 1 (RYR1). Blocking this channel lowers calcium in the muscle cell, which decreases excitation–contraction coupling, reduces heat production, and helps reverse the hypermetabolic crisis. Dantrolene does exactly this: it binds to the ryanodine receptor and inhibits calcium release, stabilizing intracellular calcium and mitigating MH symptoms. The other drugs act on different targets: ethosuximide modulates T-type calcium channels in the thalamus for absence seizures; nimodipine blocks L-type calcium channels to prevent cerebral vasospasm; biphosphonates slow bone resorption by osteoclasts. None address calcium release from the sarcoplasmic reticulum in skeletal muscle, so they don’t treat malignant hyperthermia.