FANZCA FANZCA Clinical Pharmacology and Anesthesia 2 — Questions and Answers
Question 1: Which pharmacodynamic parameter describes the concentration of a drug required to produce 50% of its maximum effect?
- LD50
- EC50 (Correct answer)
- Vd
- Tmax
Correct answer: EC50
The EC50 (effective concentration 50%) represents the drug concentration at which 50% of the maximum pharmacological effect is achieved, reflecting potency.
Question 2: What is the primary mechanism by which ketamine produces dissociative anesthesia?
- GABA-A receptor potentiation
- NMDA receptor antagonism (Correct answer)
- Alpha-2 adrenoceptor agonism
- Mu-opioid receptor agonism
Correct answer: NMDA receptor antagonism
Ketamine primarily acts as an NMDA receptor antagonist, blocking glutamate-mediated excitation to produce its characteristic dissociative state, analgesia, and bronchodilation.
Question 3: Which inhalational agent is contraindicated in patients with a known or suspected genetic predisposition to malignant hyperthermia?
- Nitrous oxide
- Xenon
- Sevoflurane
- All potent volatile halogenated agents (Correct answer)
Correct answer: All potent volatile halogenated agents
All potent volatile halogenated agents (halothane, isoflurane, sevoflurane, desflurane) are triggers for malignant hyperthermia and must be avoided in susceptible patients.
Question 4: What is the clinical significance of the context-sensitive half-time in intravenous anesthetic pharmacokinetics?
- It predicts how fast a drug is absorbed from the gut
- It describes the time to peak plasma concentration after a bolus
- It represents the half-life of a drug after infusion ceases, which increases with longer infusions for many drugs (Correct answer)
- It reflects the drug's volume of distribution at steady state
Correct answer: It represents the half-life of a drug after infusion ceases, which increases with longer infusions for many drugs
Context-sensitive half-time is the time for plasma concentration to fall by 50% after stopping an infusion; for drugs like fentanyl, this lengthens considerably with prolonged infusions.
Question 5: Which drug class used in anesthesia acts by inhibiting cyclooxygenase enzymes to provide multimodal analgesia as part of an opioid-sparing strategy?
- Benzodiazepines
- NSAIDs (Correct answer)
- Alpha-2 agonists
- N-methyl-D-aspartate antagonists
Correct answer: NSAIDs
NSAIDs reduce prostaglandin synthesis by inhibiting COX-1 and COX-2 enzymes, providing anti-inflammatory analgesia that reduces opioid requirements perioperatively.
Question 6: What is the pharmacological rationale for using dexmedetomidine as a sedative in the ICU or as an adjunct in anesthesia?
- It enhances GABA-mediated inhibition in the cortex
- It selectively activates alpha-2 adrenoceptors to produce sedation, analgesia, and anxiolysis without significant respiratory depression (Correct answer)
- It blocks dopamine D2 receptors to reduce agitation
- It inhibits histamine H1 receptors causing sedation
Correct answer: It selectively activates alpha-2 adrenoceptors to produce sedation, analgesia, and anxiolysis without significant respiratory depression
Dexmedetomidine's selective alpha-2 agonism in the locus coeruleus and spinal cord produces cooperative sedation and analgesia while preserving respiratory drive.
FANZCA FANZCA Clinical Pharmacology and Anesthesia 2
Which pharmacodynamic parameter describes the concentration of a drug required to produce 50% of its maximum effect?