Pharmacology Fundamentals Flashcards

Ketamine's analgesic and dissociative effects are primarily mediated by:

Answer: Non-competitive NMDA receptor antagonism

Ketamine blocks the open channel of NMDA receptors in a non-competitive, use-dependent manner, producing dissociation and analgesia.

A patient receiving a continuous infusion of noradrenaline develops progressive peripheral ischaemia. Which agent is most appropriate to add to improve limb perfusion?

Answer: Phentolamine infused intra-arterially

Phentolamine, a competitive alpha-adrenoceptor antagonist, can be infused intra-arterially or subcutaneously to reverse catecholamine-induced vasospasm and tissue ischaemia.

Which change in critical illness most commonly increases the volume of distribution of hydrophilic antibiotics?

Answer: Capillary leak and third spacing expanding the extravascular fluid compartment

Sepsis-related endothelial dysfunction causes capillary leak, dramatically expanding the extravascular space and increasing Vd for hydrophilic drugs like aminoglycosides and beta-lactams.

The Emax model of pharmacodynamics predicts that doubling the dose above the EC90 will:

Answer: Yield minimal additional effect as the response approaches the maximum

The sigmoidal Emax model plateaus near the maximum effect; above EC90, the dose–response curve is nearly flat and large dose increases produce little additional benefit.

Heparin resistance in a critically ill patient is most often caused by:

Answer: Antithrombin III deficiency reducing heparin binding

Heparin exerts its anticoagulant effect by binding and potentiating antithrombin III; deficiency (from consumption, liver disease, or nephrotic syndrome) renders heparin ineffective.

Which statement correctly describes the pharmacology of dexmedetomidine?

Answer: It is a selective alpha-2 agonist producing sedation, analgesia, and sympatholysis without respiratory depression

Dexmedetomidine selectively agonises central and peripheral alpha-2 adrenoceptors, producing a state of cooperative sedation and analgesia while largely preserving respiratory drive.

A patient prescribed fluconazole for candidaemia is also receiving fentanyl PCA. Which interaction should be anticipated?

Answer: Increased fentanyl plasma levels due to CYP3A4 inhibition by fluconazole

Fluconazole is a potent CYP3A4 and CYP2C9 inhibitor; CYP3A4 is the primary enzyme metabolising fentanyl, so co-administration increases fentanyl exposure and risk of opioid toxicity.