Pharmacology - Muscle Relaxants
Below is a summary of agents commonly used for inducing and reversing muscle relaxation. Note that some agents are often used for multiple indications. Doses are IV, unless indicated. Also note that less common agents are detailed in the AFMS manual.
The agents are listed with the generic name followed by the trade name in brackets.
Rocuronium (Zemuron)
- Mechanism
- Nicotinic Ach receptor antagonist
- Indication
- Neuromuscular blockade
- Dosing
- 0.6 mg/kg
- Considerations
- May double dose (1.2 mg/kg) for Rapid Sequence Induction (RSI)
- Non-depolarizing intermediate acting neuromuscular blocker
- Another intermediate acting agent, Cisatracurium, is safer in cirrhotic patients given its Hoffman (non-enzymatic) elimination
- Effect terminated by diffusion out of Neuromuscular Junction (NMJ)
- Increased risk of acute postoperative respiratory complications with residual blockade mandates reversal agent
- Most common cause of anaphylaxis under anesthesia
Succinylcholine (Anectine)
- Mechanism
- Overactivation of nicotinic Ach receptor
- Indication
- Neuromuscular blockade
- Dosing
- 1-1.5 mg/kg
- Considerations
- Depolarizing short-acting neuromuscular blocker
- Expect paralysis after brief fasciculations/rigidity (Phase 1)
- Preferred option for rapid sequence induction given faster onset (30-60s).
- Effect terminated within 10 min by pseudocholinesterase
- Contraindicated in patients at risk of hyperkalemia (stroke, burn, neuromuscular disease), prior or family hx of malignant hyperthermia, or pseudocholinesterase deficiency, dysrhythmias
- Check muscle twitch before extending effect with rocuronium to not miss pseudocholinesterase deficiency diagnosis or poor succinylcholine elimination.
- Risk of bradycardia with repeat doses
Neostigmine
- Mechanism
- Acetylcholinesterase inhibition
- Indication
- Reversal agent
- Dosing
- 0.04–0.07 mg/kg or 2.5 mg
- Considerations
- Requires at least 2 twitches on TOF or obvious movement. Optional if ≥3 twitches on TOF.
- Combination with anticholinergic is required to reduce its side effects of increased airway secretions and bradycardia
Glycopyrrolate
- Mechanism
- Muscarinic Ach receptor antagonist
- Indication
- Reversal agent/Anticholinergic Agent
- Dosing
- 8 mcg/kg or 0.4 mg
- Considerations
- Compared to Atropine, causes less tachycardia and does not cross blood brain barrier
Atropine
- Mechanism
- Muscarinic Ach receptor antagonist
- Indication
- Reversal agent/Anticholinergic Agent
- Dosing
- 20 mcg/kg or 0.6 mg
- Considerations
- Also used in ACLS for bradycardi
Sugammadex (Bridion)
- Mechanism
- Selective relaxant-binding (works with Rocuronium)
- Indication
- Reversal agent
- Dosing
- 2-16 mg/kg
- Considerations
- Can reduce deep neuromuscular blockade (e.g. no twitches on TOF).
- Does not require coadministration of anticholinergics as no effect on cholinergic transmission.
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