Cisatracurium

A structured viva answer should cover class/structure, elimination, and side-effect profile.

• Class: non-depolarising NMBA; benzylisoquinolinium.
• Structure: a single stereoisomer of atracurium (more potent).
• Elimination: Hofmann elimination + ester hydrolysis → relatively organ-independent.
• Adverse effects: less histamine release and less laudanosine production than atracurium → more haemodynamically stable.

This is a common FRCA pharmacology viva theme: define the pathway and state clinical consequences.

• Hofmann elimination is a non-enzymatic chemical degradation that depends on physiological pH and temperature.
• Acidosis slows degradation → prolonged neuromuscular block.
• Hypothermia slows degradation → prolonged block (important in ICU/major surgery).
• Alkalosis and hyperthermia accelerate degradation → shorter duration.

• Intubation: 0.15–0.2 mg/kg IV (≈3×ED95).
• Maintenance bolus: ~0.03 mg/kg IV; infusion often ~1–3 micrograms/kg/min titrated to monitoring.
• Onset: typically slower than rocuronium; intubating conditions often around 2–3 minutes after an intubating dose.

• Generally haemodynamically stable with minimal direct cardiovascular effects at clinical doses.
• Minimal histamine release compared with atracurium; histamine effects (flushing, hypotension, bronchospasm) are uncommon but can occur with rapid large bolus.

• Reversal: neostigmine with an antimuscarinic (e.g., glycopyrrolate/atropine) once there is evidence of recovery (e.g., TOF count ≥2).
• Endpoint: quantitative TOF ratio ≥0.9 prior to extubation to reduce residual paralysis complications.
• Sugammadex has no role (does not encapsulate cisatracurium).

• Preferred because elimination is largely organ-independent (Hofmann elimination/ester hydrolysis) → more predictable in renal failure than many alternatives.
• ICU factors that prolong effect: hypothermia, acidosis, drug interactions (e.g., magnesium, aminoglycosides), and reduced muscle perfusion/critical illness.
• Prolonged infusions can lead to metabolite accumulation (laudanosine), though less than atracurium.

• Laudanosine is a metabolite produced during degradation of atracurium/cisatracurium.
• It is a CNS stimulant in high concentrations (historically associated with seizure concerns in prolonged high-dose infusions).
• Cisatracurium produces less laudanosine than atracurium; clinical relevance is mainly in prolonged ICU infusions, especially if other risk factors for seizures exist.

• Higher potency means fewer molecules are administered for a given effect; a smaller concentration gradient to the NMJ can slow equilibration and receptor occupancy.
• Cisatracurium is more potent than atracurium and typically has a slower onset than less potent agents like rocuronium (dose and circulation time also matter).

• Potentiators: volatile anaesthetics, magnesium, aminoglycosides, clindamycin, lithium, local anaesthetics, some antiarrhythmics.
• Management: reduce dose, use quantitative monitoring, anticipate prolonged recovery, and ensure appropriate reversal strategy.

• Myasthenia gravis increases sensitivity to non-depolarising NMBAs due to reduced functional post-synaptic ACh receptors.
• Use markedly reduced doses and titrate to effect with quantitative monitoring; avoid long-acting paralysis and ensure full recovery before extubation.

• Non-depolarising block produces TOF fade because pre-synaptic nicotinic receptors involved in mobilising ACh during repetitive stimulation are inhibited.
• Less ACh is released with successive stimuli → progressively smaller twitch responses.

• Confirm indication (e.g., severe ventilator dyssynchrony, refractory hypoxaemia, raised ICP with shivering) and ensure deep sedation/analgesia first.
• Start with a bolus if needed then infusion (e.g., ~1–3 micrograms/kg/min) and titrate to lowest effective block using TOF.
• Monitor: quantitative or at least peripheral nerve stimulator, ventilator parameters, temperature, acid–base, electrolytes (Mg2+), and drug interactions.
• Prevent complications: eye care, pressure area care, DVT prophylaxis, physiotherapy planning, daily interruption/assessment where appropriate.

A high-scoring structure: classification → mechanism → PK (Hofmann) → PD (CV/histamine) → dosing → interactions → reversal/monitoring → special situations.

• Classification/structure: non-depolarising benzylisoquinolinium; atracurium stereoisomer; quaternary ammonium.
• Mechanism: competitive Nm antagonist → fade on TOF.
• PK: Hofmann elimination (pH/temperature dependent) + ester hydrolysis; relatively organ-independent; laudanosine (less than atracurium).
• PD: minimal histamine release; stable haemodynamics; no sedation/analgesia.
• Clinical: dosing, onset/duration, monitoring (TOF ratio ≥0.9), reversal with neostigmine; no sugammadex.

• Both: benzylisoquinoliniums; non-depolarising; Hofmann elimination; produce laudanosine; can be used in organ failure.
• Cisatracurium: more potent, typically slower onset; less histamine release; less laudanosine; often more haemodynamically stable.
• Atracurium: more histamine-related effects at higher/rapid doses; more laudanosine production; may be cheaper/used where available.

• Acidosis + hypothermia slow Hofmann elimination → prolonged paralysis and delayed recovery.
• ICU implications: frequent reassessment, avoid unnecessary deep block, correct reversible contributors (temperature, pH, magnesium), and use quantitative monitoring where possible.