Cisatracurium, Rocuronium and Vecuronium

Mechanism

Mechanism of action

Nondepolarizing blockers competitively bind to one or both α₁ subunits of the nicotinic acetylcholine receptor of the muscle neuromuscular plate without activating the ion channel. Immobility occurs when approximately 70% - 80% of the junctional receptors are blocked. To completely abolish the neuromuscular response to train-of-four (TOF) stimulation, blockade of more than 90% of active receptors is required.

🧬 Cisatracurium

• Class: Benzylisoquinoline (pure stereoisomer of atracurium).
• Hofmann elimination: Spontaneous chemical degradation independent of hepatic or renal function.
• Does not induce systemic release of histamine at usual clinical doses, offering exceptional cardiovascular stability.

💊 Rocuronium

• Class: Aminosteroid with rapid onset of action.
• Onset of action: 60 - 90 seconds at a dose of 1.2 mg/kg (preferred alternative to succinylcholine for RSI).
• Clearance effect dependent on metabolism and hepatic bile transport.

Pharmacokinetics

Pharmacokinetics of Representative Agents

Indicators and dose

Clinical Management and Adjustments in Special Populations

• Chronic Renal and Liver Failure: Cisatracurium is the absolute relaxant of choice due to its spontaneous elimination, avoiding the accumulation of free drug observed with vecuronium or rocuronium in cirrhotic patients or patients with end-stage renal failure.
• Neuromuscular Relaxation Monitoring (TOF): It is performed through electrical stimulation of the ulnar or facial nerve. The presence of 4 identical responses indicates the recovery of 70% of the recipients; 1 or 2 responses indicate optimal surgical block for intraoperative surgical maintenance.

Security

The Hofmann Reaction of Cisatracurium

Hofmann elimination is a spontaneous non-enzymatic chemical elimination reaction that occurs biologically in plasma and tissues at physiological body temperature and pH:

Cisatracurium pH 7.40, Temp 37^ Laudanosine + Monoquaternary Metabolite

The rate of chemical degradation depends solely on the systemic pH and the patient's temperature. Extreme acidosis (pH < 7.15) or severe hypothermia (Temp < 32^) reflexively slows the rate of spontaneous degradation, significantly prolonging the clinical duration of muscle relaxation in the operating room.