PH2.4 | PH2.4 | Skeletal Muscle Relaxants — SDL Guide — Summary & Reflection

KEY TAKEAWAYS

Skeletal muscle relaxants fall into two classes: neuromuscular blocking drugs (NMBDs) acting at the NMJ, and centrally acting spasmolytics acting on spinal interneurons or peripheral Ca²⁺ release. NMBDs include succinylcholine (depolarising — fastest onset 60 sec, 10–15 min duration, hydrolysed by BChE, contraindicated in burns/SCI/crush injury/hyperkalaemia/MH susceptibility) and non-depolarising agents (competitive, reversed by neostigmine or sugammadex — rocuronium preferred for RSI when succinylcholine contraindicated; atracurium/cisatracurium for organ failure patients via Hofmann elimination). Sugammadex reverses rocuronium at any depth (2/4/16 mg/kg for routine/deep/emergency reversal). Centrally acting spasmolytics: baclofen (GABA-B, spinal cord, MS/SCI), diazepam (GABA-A, acute spasm), tizanidine (central α2, spasticity), dantrolene (peripheral RyR1 block — malignant hyperthermia and NMS; 2.5 mg/kg IV up to 10 mg/kg). Malignant hyperthermia is triggered by volatile anaesthetics + succinylcholine in susceptible patients; treatment is dantrolene IV + stop trigger + cooling.

REFLECT

The RSI hook scenario at the start was not hypothetical — crush injury + succinylcholine-induced hyperkalaemic cardiac arrest has been documented in emergency medicine literature. In your internship, you may be asked to prepare drugs for RSI. How confident are you now about the succinylcholine contraindications and the rocuronium RSI alternative? Think also about dantrolene: hospitals in India vary in whether dantrolene is stocked in the theatre. What would you do if you suspected MH in a facility without dantrolene? And more broadly — what systematic gaps in drug availability create patient safety hazards in your future practice environment, and what can you do about them as a clinician?