Pharmacokinetics and Pharmacodynamics Flashcards

Ketamine's dissociative anesthetic effect is mediated primarily by:

Answer: Non-competitive NMDA receptor antagonism

Ketamine produces dissociative anesthesia by non-competitive antagonism of NMDA (N-methyl-D-aspartate) glutamate receptors, blocking the ion channel in an open-channel fashion.

The volume of distribution (Vd) of a highly lipophilic drug is characteristically:

Answer: Much greater than total body water, often >10 L/kg

Highly lipophilic drugs distribute extensively into fat and tissue, resulting in very large apparent volumes of distribution often many times greater than actual body volume.

Zero-order kinetics describes drug elimination where:

Answer: A constant amount of drug is eliminated per unit time regardless of concentration

Zero-order kinetics occurs when elimination pathways are saturated, so a fixed amount (not fraction) of drug is eliminated per unit time, as seen with ethanol and high-dose aspirin.

Which property of local anesthetics is most responsible for their ability to cross nerve sheaths and reach the axon membrane?

Answer: pKa close to physiologic pH allowing significant un-ionized fraction

Local anesthetics with pKa close to 7.4 have a larger un-ionized (lipid-soluble) fraction at physiologic pH, allowing better membrane penetration to reach the axon.

A competitive antagonist shifts the agonist concentration-response curve:

Answer: To the right in a parallel fashion, without reducing Emax

A competitive antagonist causes a parallel rightward shift of the agonist dose-response curve (increased EC50) without reducing Emax because its effect is surmountable by excess agonist.

During cardiopulmonary bypass at 28°C, the pharmacokinetics of fentanyl will be most affected by:

Answer: Reduced hepatic blood flow and metabolic enzyme activity

Hypothermia during CPB reduces hepatic blood flow and CYP enzyme activity, significantly decreasing fentanyl clearance and prolonging its effect.

Which neuromuscular blocking agent is most appropriate for a patient with both hepatic and renal failure?

Answer: Cisatracurium

Cisatracurium undergoes organ-independent Hofmann elimination and ester hydrolysis, making it the NMB of choice in combined hepatorenal failure.