Which of the following pairs of drugs was most likely administered?

Correct Answer: C

Rationale: The correct answer is C: Fentanyl and ketamine. Fentanyl is a potent opioid analgesic, while ketamine is a dissociative anesthetic. This combination is commonly used for procedures requiring analgesia and sedation. Fentanyl provides pain relief, and ketamine induces a dissociative state for anesthesia. Thiopental and midazolam (choice D) are both sedatives, not commonly used together. Fentanyl and thiopental (choice A) are both sedatives, but lacking in analgesic effects. Fentanyl and midazolam (choice B) offer sedation and anxiolysis, but lack the dissociative anesthesia provided by ketamine.

Correct Answer: C

Rationale: The correct answer is C: Lidocaine. Lidocaine is an amide-type local anesthetic that does not contain PABA, making it suitable for a patient with a history of anaphylactic reaction to PABA. Procaine (A) is an ester-type local anesthetic that metabolizes into PABA. Tetracaine (B) is also an ester-type local anesthetic that may cross-react with PABA. Benzocaine (D) is a para-aminobenzoic acid derivative and should be avoided in patients with a history of anaphylaxis to PABA.

Correct Answer: C

Rationale: The correct answer is C: Vecuronium. This drug was most likely administered to achieve muscle relaxation in the 74-year-old man with impaired hepatic and renal function undergoing abdominal surgery because it is primarily eliminated through the liver and does not require renal excretion. This makes it a safer choice in patients with impaired hepatic and renal function. Succinylcholine (A) can cause hyperkalemia in renal failure patients. Tubocurarine (B) is eliminated through the kidneys, which can be problematic in renal impairment. Mivacurium (D) is metabolized by plasma cholinesterase, which can be affected in liver dysfunction.

Correct Answer: A

Rationale: The correct answer is A: Tubocurarine. Tubocurarine is a non-depolarizing muscle relaxant that works by blocking the action of acetylcholine at the neuromuscular junction. In a patient with Tubocurarine deficiency of plasma cholinesterase, using Tubocurarine as a muscle relaxant would be contraindicated because it would exacerbate the deficiency and lead to prolonged effects. Summary of other choices: B: Cisatracurium - Not contraindicated in a patient with Tubocurarine deficiency of plasma cholinesterase. C: Baclofen - Acts on spinal cord neurons, not related to neuromuscular junction function. D: Mivacurium - A short-acting non-depolarizing muscle relaxant, not contraindicated in this scenario.

Correct Answer: D

Rationale: The correct answer is D: Inhibition of acetylcholine exocytosis from cholinergic terminals. Botulinum toxin works by blocking the release of acetylcholine at the neuromuscular junction, leading to muscle paralysis. This inhibition prevents the communication between nerve cells and muscles, resulting in the therapeutic effect. Choices A, B, and C are incorrect as they do not directly relate to the mechanism of action of botulinum toxin in blocking acetylcholine release.