Which of the following antidepressants is a selective short-acting MAO-A inhibitor?

Correct Answer: C

Rationale: The correct answer is C: Moclobemide. Moclobemide is a selective short-acting MAO-A inhibitor, which means it specifically targets the MAO-A enzyme, leading to increased levels of serotonin and norepinephrine. This helps alleviate symptoms of depression. Maprotiline (A) is a tetracyclic antidepressant, Amitriptyline (B) is a tricyclic antidepressant, and Selegiline (D) is a MAO-B inhibitor used for Parkinson's disease, not for depression. Therefore, C is the correct answer as it matches the criteria of being a selective short-acting MAO-A inhibitor.

Correct Answer: B

Rationale: Step 1: Diazepam is a benzodiazepine known for its high abuse potential due to its sedative and hypnotic effects. Step 2: Benzodiazepines like diazepam can lead to physical and psychological dependence. Step 3: Buspirone is a non-benzodiazepine anxiolytic with low abuse potential. Step 4: Phenobarbital is a barbiturate with significant abuse potential but generally less than benzodiazepines. Step 5: Zolpidem is a non-benzodiazepine sedative-hypnotic with lower abuse potential compared to benzodiazepines like diazepam.

Correct Answer: B

Rationale: The correct answer is B: The reflex mechanism. Cytiton acts by triggering a reflex mechanism, which involves a response to a stimulus that is automatic and involuntary. This mechanism is distinct from direct activation of the respiratory center (choice A) or a mixed mechanism (choice C). Choice D is incorrect as Cytiton does have a specific action mechanism. In summary, the correct choice is B because it accurately describes how Cytiton works through a reflex mechanism, while the other choices do not align with the known pharmacological action of Cytiton.

Correct Answer: D

Rationale: The correct answer is D: Sodium phosphate. Osmotic laxatives like sodium phosphate work by drawing water into the colon to soften the stool and stimulate bowel movements. Docusate sodium (A) is a stool softener, not an osmotic laxative. Bisacodyl (B) is a stimulant laxative that works by increasing muscle contractions in the intestines. Phenolphthalein (C) was previously used as a laxative but has been banned due to safety concerns.

Correct Answer: A

Rationale: Step 1: Digitalis increases vagal tone by enhancing parasympathetic activity. Step 2: This results in a decrease in heart rate and improved contractility. Step 3: Therefore, choice A is correct as it accurately states that digitalis increases vagal tone. Summary: Choices B, C, and D are incorrect because digitalis does increase vagal tone, which is a specific action of the medication.