Question

Dantrolene is used to treat malignant hyperthermia caused by succinylcholine because dantrolene

• A. Blocks calcium release from sarcoplasmic reticulum
• B. Induces contraction of skeletal muscle
• C. Increases the rate of succinylcholine metabolism
• D. Inhibits succinylcholine binding to nicotinic receptors

Hint:

Malignant hyperthermia is a dangerous reaction (often triggered by succinylcholine or certain anaesthetics) in which skeletal muscles release too much calcium, causing sustained muscle contraction, a sharp rise in body t

Answer 1

The Correct Option is A

Step 1: What is malignant hyperthermia?
Malignant hyperthermia (MH) is a life-threatening reaction triggered by certain anaesthetic agents, especially succinylcholine (a depolarising neuromuscular blocker). It causes uncontrolled skeletal muscle contraction, extreme body temperature rise, acidosis, and can be fatal.

Step 2: What goes wrong in MH?
In genetically susceptible people, succinylcholine (or volatile anaesthetics like halothane) triggers abnormal, massive release of calcium ions from the sarcoplasmic reticulum (SR) of skeletal muscle cells. This is due to a mutation in the ryanodine receptor (RYR1). The excess calcium causes sustained, uncontrolled muscle contraction, generating enormous heat.

Step 3: How dantrolene works.
Dantrolene is a hydantoin derivative. It acts directly on skeletal muscle. It blocks the ryanodine receptor (RYR1) on the sarcoplasmic reticulum, preventing the abnormal release of calcium. With less calcium available, muscle contraction stops and temperature normalises.

Step 4: Eliminate the wrong options.
Option 2: Dantrolene does not induce contraction; it stops it. Option 3: Dantrolene does not affect succinylcholine metabolism (that is pseudocholinesterase). Option 4: Dantrolene does not act on nicotinic receptors; it acts downstream on the sarcoplasmic reticulum.

Step 5: Conclusion.
Dantrolene specifically blocks calcium release from the sarcoplasmic reticulum via the ryanodine receptor, stopping the uncontrolled muscle contraction of malignant hyperthermia.


Answer: Option (1) — Blocks calcium release from sarcoplasmic reticulum