The most frequent side effect of oral ampicillin is:

Correct Answer: A

Rationale: The correct answer is A: Nausea and vomiting. Ampicillin is a penicillin antibiotic that commonly causes gastrointestinal side effects such as nausea and vomiting due to its irritation of the stomach lining. This is the most frequent side effect reported with oral ampicillin use. Choices B (Loose bowel movements) and C (Constipation) are less common side effects associated with ampicillin use. Choice D (Urticaria) is a possible side effect of ampicillin, but it is less frequent compared to nausea and vomiting.

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: D

Rationale: The correct answer is D: Foscarnet. Foscarnet is a pyrophosphate analog that inhibits both DNA polymerase and reverse transcriptase, making it effective against cytomegalovirus (CMV) infection in AIDS patients. It is not a nucleoside analog like Acyclovir (A) and Valacyclovir (B) which target viral DNA polymerase. Amantadine (C) is an antiviral drug used for influenza A virus, not CMV. Foscarnet is specifically indicated for CMV infection in AIDS patients due to its unique mechanism of action, making it the correct choice.

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.