# Neuromuscular Blockers and Reversal

> Neuromuscular blockers and reversal for NEET-PG Pharmacology: succinylcholine hyperkalaemia, rocuronium, sugammadex doses and malignant hyperthermia.

- Canonical URL: https://prepelephant.com/topics/neet-pg/pharmacology/neuromuscular-blockers-and-reversal
- Exam / course: NEET-PG · Subject: Pharmacology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Neuromuscular Blockers and Reversal", PrepElephant, https://prepelephant.com/topics/neet-pg/pharmacology/neuromuscular-blockers-and-reversal

## Direct answer

Succinylcholine (1-1.5 mg/kg) remains the fastest route to a paralysed, intubatable airway — onset in 45-60 seconds, offset in 6-10 minutes — but its depolarising mechanism makes potassium leak from muscle, so burns beyond 72 hours, crush injury, denervation, prolonged immobilisation and muscle dystrophies contraindicate it through dangerous hyperkalaemia. Rocuronium 0.6-1.2 mg/kg matches it for rapid sequence induction when reversal matters less, and sugammadex — 2 mg/kg at two twitches on train-of-four, up to 16 mg/kg for immediate reversal — encapsulates rocuronium or vecuronium specifically, reversing them cleanly with no cholinergic storm. Neostigmine 0.05 mg/kg with glycopyrrolate reverses any competitive block but demands some spontaneous recovery first; it does nothing for succinylcholine, which must fade on its own or, in malignant hyperthermia, be fought with dantrolene.

## What you must remember

- **Succinylcholine numbers:** 1-1.5 mg/kg intravenously, intubating conditions in 45-60 seconds, apnoea for 6-10 minutes; metabolised by plasma cholinesterase — prolonged apnoea in genetically deficient patients.
- **The hyperkalaemia list:** burns (beyond 24-72 hours), crush injury, denervation or stroke with immobility, muscular dystrophies — up-regulated extrajunctional nicotinic receptors open to potassium efflux.
- **Malignant hyperthermia:** succinylcholine plus volatile agents; rigidity, hypercarbia, hyperthermia, rhabdomyolysis — dantrolene 2.5 mg/kg intravenously, repeated as needed, with active cooling and stopping the trigger.
- **Rocuronium:** 0.6 mg/kg for routine intubation, 1.0-1.2 mg/kg for rapid sequence; intermediate duration; no histamine release; the sugammadex partner.
- **Sugammadex selectivity:** a cyclodextrin that encapsulates rocuronium and vecuronium only — useless for succinylcholine, atracurium or cisatracurium; doses 2 mg/kg at second-twitch recovery, 4 mg/kg in deep block, 16 mg/kg for immediate reversal three minutes after rocuronium.
- **Neostigmine plus glycopyrrolate:** 0.05 mg/kg with 0.01 mg/kg respectively; requires visible recovery (at least two to four twitches), and under-dosing in obesity leaves residual block — a cause of postoperative hypoxia.
- **Cisatracurium:** Hofmann elimination independent of liver and kidney — the organ-failure choice; its precursor atracurium releases histamine.
- **Monitoring craft:** train-of-four ratio above 0.9 before extubation; qualitative observation of four equal twitches is not sensitive enough for deep residual blockade.

## A worked airway decision

A 30-year-old with 40% burns from a house fire three days ago needs emergency laparotomy. The burns are beyond 72 hours old — the up-regulation window — so succinylcholine is off the table entirely, whatever the airway urgency. Rapid sequence induction proceeds with rocuronium 1.2 mg/kg and cricoid pressure; the intubating conditions arrive nearly as fast, the price being an hour of paralysis rather than ten minutes. At closure, train-of-four shows two twitches: sugammadex 2 mg/kg restores the ratio above 0.9 within minutes, without the bradycardia, secretions or bowel cramping of an anticholinesterase — and with no dependence on the patient's cholinesterase genotype or kidney function being perfect.

The contrast case is the theatre emergency every trainee must know cold: masseter spasm, rising end-tidal carbon dioxide despite constant ventilation, temperature climbing, urine turning dark. Malignant hyperthermia: volatile agent off, hundred percent oxygen, dantrolene drawn and given at 2.5 mg/kg with repeat dosing until rigidity melts, active cooling, and treatment of hyperkalaemia — the pharmacology of two drugs colliding, and the reason succinylcholine's speed never earns it an unconditional pass.

## Where examiners probe

Three probes recur. First, the hyperkalaemia vignette: a stem with "burned three days ago" or "crush injury" exists solely to exclude succinylcholine — the timing qualifier (not fresh burns, but burns older than a day or two) is the discriminator candidates miss. Second, sugammadex specificity: "which block can sugammadex not reverse?" — succinylcholine and the benzylisoquinoliniums; and the mechanism word "encapsulation" earns more than "antagonism". Third, residual block: why neostigmine fails when given too early or dosed on ideal rather than actual body weight, and why train-of-four above 0.9 — not "four twitches present" — is the extubation standard. Indian context: sugammadex's cost keeps neostigmine-glycopyrrolate the default in most government theatres, so knowing both regimens — and the monitoring that makes the cheap one safe — is the practical exam answer, not a footnote.

## Frequently asked questions

### Why is succinylcholine avoided in patients with burns or crush injury?

Extrajunctional receptor proliferation makes the depolarising block release large amounts of potassium, risking fatal arrhythmia from about 24-72 hours after injury onward.

### Which neuromuscular blockers can sugammadex reverse?

Only rocuronium and vecuronium — it encapsulates these aminosteroids and has no effect on succinylcholine or cisatracurium.

### What dose of sugammadex reverses rocuronium at two twitches?

2 mg/kg, with 4 mg/kg in deep block and 16 mg/kg for immediate reversal given three minutes after intubating-dose rocuronium.

### Why must neostigmine wait for spontaneous recovery?

It inhibits acetylcholinesterase to tilt the competition at the junction; with no acetylcholine transmission yet present, it merely produces bradycardia and secretions without reversal.

### What is the malignant hyperthermia regimen?

Stop volatile agents and succinylcholine, give dantrolene 2.5 mg/kg intravenously with repeats, hundred percent oxygen, active cooling and hyperkalaemia treatment.