Which of the following drug which directly inhibits HIV-reverse transcriptase without the need for intracellular activation by phosphorylation:

Correct Answer: B

Rationale: The correct answer is B: Nevirapine. Nevirapine is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that directly inhibits the HIV-reverse transcriptase enzyme without the need for intracellular activation by phosphorylation. It binds to a hydrophobic pocket near the enzyme's active site, thus preventing viral RNA from being converted to DNA. A: Nelfinavir is a protease inhibitor that works by blocking the activity of the protease enzyme, not directly inhibiting reverse transcriptase. C: Stavudine and D: Didanosine are nucleoside reverse transcriptase inhibitors (NRTIs) that require intracellular phosphorylation to become active and inhibit reverse transcriptase.

Correct Answer: B

Rationale: Step-by-step rationale for why Pyrantel pamoate (choice B) is the correct answer: 1. Pyrantel pamoate is a cholinergic agonist that acts on nematodes by stimulating nicotinic receptors, leading to spastic paralysis of the worms. 2. Its mechanism of action involves depolarizing the neuromuscular junction, causing sustained muscle contraction in the parasites. 3. This spastic paralysis makes the worms lose their ability to maintain attachment to the host's intestine, facilitating their expulsion from the body. 4. Piperazine (choice A) works by blocking the response of the worm's muscle cells to acetylcholine, causing flaccid paralysis. 5. Mebendazole (choice C) and Albendazole (choice D) are benzimidazole anthelmintics that inhibit microtubule formation, leading to impaired glucose uptake and energy depletion in the parasites, not acting as cholinergic agonists.

Correct Answer: C

Rationale: The correct answer is C: Clofazimine. Clofazimine is an antileprosy drug that is known to suppress both lepra reactions and reversal reactions. It has anti-inflammatory properties that help control and prevent leprosy reactions. Dapsone (A) is primarily used for leprosy treatment but does not specifically target lepra and reversal reactions. Rifampin (B) is effective against the leprosy bacteria but is not known for its role in managing lepra reactions. Minocycline (D) is another antibiotic used in leprosy treatment but does not have the same anti-inflammatory properties as clofazimine. Therefore, clofazimine is the correct choice for managing both lepra and reversal reactions in leprosy patients.

Correct Answer: B

Rationale: The correct answer is B: Testosterone. Dutasteride is a 5-alpha reductase inhibitor used to treat BPH by reducing DHT levels. Testosterone is converted to DHT by the enzyme 5-alpha reductase, so combining dutasteride with testosterone can potentially increase the risk of side effects related to low DHT levels. Tamsulosin is an alpha blocker and does not directly interact with dutasteride. Sildenafil is a phosphodiesterase inhibitor used for erectile dysfunction and does not have a known interaction with dutasteride. Hydrochlorothiazide is a diuretic and is unlikely to interact with dutasteride.

Correct Answer: C

Rationale: The correct answer is C: Nitroglycerin should be avoided in a patient taking sildenafil because both drugs can cause a significant drop in blood pressure leading to severe hypotension, syncope, or even cardiovascular collapse. Nitroglycerin is a potent vasodilator, and when combined with sildenafil (a phosphodiesterase type 5 inhibitor), the additive vasodilatory effects can result in dangerous hypotension. A: Amlodipine and B: Diltiazem are calcium channel blockers that are commonly used in combination with sildenafil for the treatment of hypertension and angina. They work through different mechanisms and do not have a significant interaction with sildenafil. D: Metoprolol is a beta-blocker that can be safely used with sildenafil. It helps in reducing heart rate and blood pressure, and its combination with sildenafil can have a beneficial effect in patients with angina.