The strong antiemetic effect of the phenothiazine derivatives is due to dopamine receptor blockade:

Correct Answer: A

Rationale: The correct answer is A because phenothiazine derivatives exert their strong antiemetic effect by blocking dopamine receptors in the chemoreceptor trigger zone of the medulla. This area is responsible for initiating the vomiting reflex. By blocking dopamine receptors here, phenothiazines prevent the activation of the vomiting reflex. Choices B and C are incorrect because phenothiazines primarily target the chemoreceptor trigger zone in the medulla, not the receptors in the stomach or the medullar vomiting centre. Choice D is also incorrect because the antiemetic effect is specifically due to dopamine receptor blockade in the chemoreceptor trigger zone, not all of the above options.

Correct Answer: A

Rationale: The correct answer is A: Triazolam. Triazolam has a short duration of action due to its rapid onset and short half-life. It is commonly used for the treatment of insomnia. Clorazepate (B), Prazepam (C), and Clordiazepoxide (D) have longer durations of action compared to Triazolam. Clorazepate is a long-acting benzodiazepine used for anxiety disorders, Prazepam is an intermediate-acting benzodiazepine, and Clordiazepoxide is a long-acting benzodiazepine used for alcohol withdrawal and anxiety. Triazolam's rapid onset and short duration make it suitable for managing acute insomnia.

Correct Answer: A

Rationale: The correct answer is A: Benzodiazepines. They are the drugs of choice for reversing withdrawal syndromes due to their ability to target the central nervous system and alleviate symptoms by acting on GABA receptors. Benzodiazepines help to reduce anxiety, seizures, and other withdrawal symptoms effectively. Neuroleptics (choice B) are not typically recommended for treating withdrawal symptoms as they may worsen certain symptoms. Antidepressants (choice C) are not the first-line treatment for reversing withdrawal syndromes as they mainly target mood disorders. Choice D is incorrect because not all the options are drugs of choice for reversing withdrawal syndromes.

Correct Answer: C

Rationale: Step-by-step rationale: 1. 5-lipoxygenase is an enzyme involved in leukotriene synthesis. 2. Zileuton is a specific 5-lipoxygenase inhibitor. 3. Budesonide and Beclometazone are corticosteroids, not 5-lipoxygenase inhibitors. 4. Sodium cromoglycate is a mast cell stabilizer, not a 5-lipoxygenase inhibitor. Summary: Choice C (Zileuton) is the correct answer as it directly inhibits 5-lipoxygenase, which is crucial in leukotriene production. Choices A, B, and D are incorrect as they are not 5-lipoxygenase inhibitors but belong to different classes of medications.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Folic acid is essential for DNA synthesis, crucial for red blood cell formation. 2. Megaloblastic anemia is characterized by large, immature red blood cells. 3. Folic acid deficiency can lead to megaloblastic anemia. 4. Therefore, folic acid supplementation is recommended for treating megaloblastic anemia. Summary: - Choice A is correct because folic acid is recommended for treating megaloblastic anemia due to its role in red blood cell formation. - Choice B is incorrect because folic acid is indeed recommended for megaloblastic anemia treatment. - Choice C is incorrect as it implies all choices are correct, which is not the case. - Choice D is incorrect as folic acid is recommended for megaloblastic anemia treatment.