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: D

Rationale: Mycolic acid synthesis is inhibited by Ethambutol by targeting the enzyme arabinosyltransferase, essential for cell wall synthesis in mycobacteria. Resistance develops slowly with Ethambutol, unlike other choices which target different pathways (A: Isoniazid - inhibits mycolic acid synthesis by targeting InhA enzyme, B: Rifampicin - inhibits RNA polymerase, C: Pyrazinamide - disrupts membrane potential). Ethambutol is essential in combination therapy to prevent resistance.

Correct Answer: D

Rationale: The correct answer is D: Cefepime. Cefepime is a fourth-generation cephalosporin that has broad-spectrum activity, including against anaerobic gram-negative bacteria like Bacteroides fragilis. Its extended spectrum of activity is due to its increased stability against beta-lactamases produced by many bacteria. Choices A, B, and C (Cefdinir, Cefuroxime, Cefazolin) are not typically effective against anaerobic gram-negative bacteria. Cefdinir is primarily active against respiratory pathogens, Cefuroxime has limited anaerobic coverage, and Cefazolin is more effective against gram-positive bacteria.

Correct Answer: A

Rationale: Step-by-step rationale for choice A (Ganciclovir) being the correct answer: 1. Ganciclovir is a nucleoside analog that inhibits CMV DNA synthesis. 2. It is specifically approved for the treatment of CMV retinitis in immunocompromised patients. 3. Ganciclovir has a high specificity for CMV, making it an effective antiviral agent against CMV. Summary of why the other choices are incorrect: - Choice B (Foscarnet) is also active against CMV but is not as commonly used as Ganciclovir. - Choice C (Acyclovir) is not effective against CMV as it primarily targets herpes simplex virus and varicella-zoster virus. - Choice D ( ) is an incomplete choice and does not correspond to any known antiviral agent.

Correct Answer: B

Rationale: The correct answer is B: Lamivudine and zidovudine. Combivir is a combination therapy that consists of these two drugs. Lamivudine and zidovudine work together to inhibit the replication of the HIV virus. Lamivudine is a nucleoside reverse transcriptase inhibitor, while zidovudine is a nucleoside analog reverse transcriptase inhibitor. Both drugs target different stages of the HIV life cycle, making them effective when used in combination. Choice A (Lamivudine and stavudine) is incorrect because stavudine is not part of the Combivir combination therapy. Choice C (Abacavir and zidovudine) is incorrect because abacavir is not included in Combivir. Choice D (Abacavir and stavudine) is incorrect because stavudine is not part of the Combivir combination therapy.

Correct Answer: B

Rationale: The correct answer is B: Azithromycin. It has a long half-life allowing for once-daily dosing for 3 days. Azithromycin is effective against common ENT, respiratory, and genital infections. Rationale: A: Erythromycin requires more frequent dosing due to shorter half-life. C: Clarithromycin is not typically given once a day for 3 days. D: Roxithromycin is less commonly used for these infections and has a shorter half-life.