A 28 year old male patient present with a painless sore in his penis and blood test confirms Treponema pallidum. Which of the following agent is the treatment of choice that can be given as a single dose?

Correct Answer: A

Rationale: The correct answer is A: Benzathine penicillin. Benzathine penicillin is the treatment of choice for syphilis caused by Treponema pallidum. It is given as a single dose due to its long-acting nature, ensuring adequate treatment. Ceftriaxone (B) is not the first-line treatment for syphilis. Vancomycin (C) is not effective against Treponema pallidum. Aztreonam (D) is not used for the treatment of syphilis. Therefore, the most appropriate choice for this scenario is Benzathine penicillin.

Correct Answer: C

Rationale: The correct answer is C because amantadine exerts its antiviral action by interacting with the viral M2 protein. This protein is essential for viral replication by facilitating the release of viral genetic material into the host cell. By binding to the M2 protein, amantadine disrupts this process, preventing viral replication. Choice A is incorrect because amantadine does not inhibit viral protease enzyme activity. Choice B is incorrect because amantadine does not target viral RNA mediated DNA synthesis. Choice D is incorrect because amantadine does not interact with a virus-directed thymidine kinase, which is involved in the activation of certain antiviral drugs like acyclovir.

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.