Ans. b. SuxamethoniumSuxamethonium is the drug most commonly responsible for causing malignant hyperthermia.'Drugs causing malignant hyperthermia are- succinylcholine (most common cause), halothane (MC inhalational agent), iso/des/sevo/methoxy- fluranes, lignocaine, TCA, MAO inhibitors and phenothiazines.''Thiopentone and pancuronium are protective drugs for malignant hyperthermia, as these raise the triggering threshold.''In malignant hyperthermia susceptible patients, safe anesthetics are N2O, Non-depolarizing muscle relaxants (atracurium), opiates, tranquilizers, etomidate, barbiturates (thiopentone) and propofol.'Malignant Hyperthermia* Autosomal dominant genetic disorder of skeletal muscle* Occurs in susceptible individuals due to exposure to some triggering agents, typically Suxamethonium or volatile agents, which cause an abnormal increase in intracellular calcium.* It is caused by dysregulation of excitation-contraction coupling in skeletal muscle.Triggering Agents:* Succinylcholine (most common cause)* Halothane (MC inhalational agent)* Halogenated Anesthesia:- Fluranes: Isoflurane, desflurane, sevoflurane. methoxy-flurane- Ether- Cyclopropane* Lignocaine* TCA* MAO inhibitors* PhenothiazinesClinical Features:* Rise in end tidal CO2 (1st sign)* Masseter muscle rigidity (MMR) and tachycardia are earliest sign* Hypermetabolic features, metabolic acidosis, fever, hyperthermia* Sympathetic over activity: Tachycardia, arrhythmia, unstable BP. initial hypertension* Muscle damage: Masseter muscle spasm, generalized rigidity, hyperkalemiaTretment:* Triggering agent must be stopped and hyperventilate with 100% oxygen* The mainstay of therapy is immediate administration of IV dantrolene.* Dantrolene is the only drug effective in reversing the symptoms and preventing the episode.