Which of the following alfa receptor antagonists is useful in reversing the intense local vasoconstriction caused by inadvertent infiltration of norepinephrine into subcutaneous tissue during intravenous administration?

Correct Answer: B

Rationale: The correct answer is B: Phentolamine. Phentolamine is an alpha receptor antagonist that can rapidly reverse the vasoconstriction caused by local infiltration of norepinephrine. It works by blocking alpha receptors, leading to vasodilation and improved blood flow in the affected area. Propranolol (A) is a beta-blocker and not effective in reversing alpha receptor-mediated vasoconstriction. Tamsulosin (C) is an alpha-1 blocker primarily used for benign prostatic hyperplasia, not for acute vasoconstriction reversal. Ergotamine (D) is a vasoconstrictor used in treating migraines, which would exacerbate the problem in this scenario.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Valproate's mechanism of action involves multiple pathways. 1. Valproate facilitates GABA synthesis by inhibiting GABA breakdown enzyme and enhancing GABA accumulation. 2. It inhibits voltage-sensitive Na+ channels, reducing neuronal excitability. 3. It also inhibits low threshold (T-type) Ca2+ channels, further reducing neuronal excitability. These combined actions lead to increased GABAergic transmission and decreased excitatory neurotransmission, contributing to its antiepileptic and mood stabilizing effects. Other choices are incorrect because they do not encompass all the mechanisms involved in valproate's action.

Correct Answer: D

Rationale: The correct answer is D: All of the above. In the antinociceptive descending pathways, multiple endogenous opioids play a role in pain modulation. Beta-endorphin, met- and leu-enkephalin, and dynorphin all act as chemical mediators to inhibit pain signals. Each of these opioids bind to different opioid receptors in the central nervous system, contributing to the overall analgesic effect. Therefore, the correct answer includes all three options as they collectively participate in the antinociceptive pathways. Choices A, B, and C alone are not sufficient to fully explain the complexity of the pain modulation system, making option D the most comprehensive and accurate choice.

Correct Answer: D

Rationale: The correct answer is D: Acetaldehyde. Disulfiram inhibits the enzyme aldehyde dehydrogenase, leading to accumulation of acetaldehyde when alcohol is consumed. Acetaldehyde buildup causes unpleasant symptoms like flushing, nausea, and headache. Formaldehyde (A) is not directly related to this interaction. Acetate (B) is a product of alcohol metabolism, not affected by disulfiram. Formic acid (C) is associated with methanol toxicity, not disulfiram-alcohol reaction. Therefore, the correct answer is D, as it aligns with the mechanism of action of disulfiram.

Correct Answer: C

Rationale: The correct answer is C: Haloperidol. Haloperidol is preferable in patients with coronary and cerebrovascular disease due to its lower risk of causing cardiovascular adverse effects compared to the other options. Chlorpromazine (A) can cause orthostatic hypotension and prolong QT interval. Fluphenazine (B) can lead to QT prolongation and hypotension. Perphenazine (D) also carries a risk of QT prolongation and orthostatic hypotension. In contrast, Haloperidol has a more favorable cardiovascular safety profile, making it the preferred choice for patients with coronary and cerebrovascular disease.