Which of the following interferes with mycolic acid synthesis an essential component of mycobacterial cell walls for which resistance will develop rapidly if the drug is used alone?

Correct Answer: A

Rationale: The correct answer is A: Isoniazid. Isoniazid inhibits the synthesis of mycolic acid, a crucial component of mycobacterial cell walls. If used alone, resistance can develop rapidly due to its specific mechanism of action. Rifampicin (B) acts on RNA polymerase, not mycolic acid synthesis. Pyrazinamide (C) targets mycobacteria in acidic environments, not mycolic acid. Ethambutol (D) inhibits arabinosyltransferase, not mycolic acid synthesis.

Correct Answer: C

Rationale: The correct answer is Cefotaxime (C) because it is a third-generation cephalosporin with excellent penetration into the cerebrospinal fluid, making it effective against bacterial meningitis pathogens. Cefotaxime covers a broad spectrum of bacteria commonly causing meningitis, including Streptococcus pneumoniae and Neisseria meningitidis. A: Cefuroxime (A) is not the best choice as it has limited activity against some of the common pathogens causing meningitis. B: Cephalexin (B) is a first-generation cephalosporin with poor central nervous system penetration and limited activity against meningitis pathogens. D: Cefdinir (D) is a third-generation cephalosporin but is not the preferred choice for treating bacterial meningitis due to its inferior CNS penetration compared to cefotaxime.

Correct Answer: A

Rationale: The correct answer is A: Griseofulvin. Griseofulvin is the drug of choice for ringworm infection because it specifically targets the fungus that causes ringworm. It works by inhibiting fungal cell division, leading to the destruction of the fungus. Amphotericin B is an antifungal medication used for systemic fungal infections, not for ringworm. Nystatin is used to treat fungal infections of the skin, mouth, and intestines, but it is not the first-line treatment for ringworm. Neomycin is an antibiotic used to treat bacterial infections, not fungal infections like ringworm. Therefore, Griseofulvin is the most appropriate choice for treating ringworm.

Correct Answer: C

Rationale: The correct answer is C: Primaquine. Primaquine is used for clinical curative treatment of malaria, particularly for the eradication of hypnozoites in Plasmodium vivax and Plasmodium ovale infections. It is not used as a prophylactic drug due to its potential side effects, such as hemolysis in individuals with G6PD deficiency. Choice A (Pyrimethamine + sulfadoxine) is a combination used for both treatment and prophylaxis. Choice B (Proguanil) is used for prophylaxis and treatment. Choice D (Mefloquine) is used for both prophylaxis and treatment of malaria.

Correct Answer: C

Rationale: The correct answer is C: Amantadine. Amantadine is an antiviral medication that is specifically effective against influenza A virus. It works by blocking the viral ion channel, preventing the virus from entering the host cell. This inhibits viral replication and helps reduce the severity and duration of symptoms. Choice A, Cidofovir, is used to treat certain DNA viruses but is not effective against influenza A. Choice B, Famciclovir, is used to treat herpes viruses, not influenza A. Choice D, Ribavirin, is an antiviral medication used for respiratory syncytial virus and hepatitis C, but not as effective against influenza A. Therefore, the most appropriate choice in this scenario is Amantadine due to its specific activity against influenza A virus.