Which of the following drug adverse reactions precludes a patient from being given the same drug in the future?

Correct Answer: C

Rationale: The correct answer is C because Steven-Johnson syndrome is a severe and life-threatening skin reaction that can occur with certain medications like Trimethoprim/Sulfamethoxazole. Once a patient experiences this reaction, they should never be given the same drug again to avoid a potentially fatal outcome. The other choices, GI upset from Clarithromycin, skin rash from Ampicillin, and Clostridium difficile superinfection from Ofloxacin, are adverse reactions that can be managed or treated without completely excluding the drug from future use.

Correct Answer: C

Rationale: The correct answer is C: Trimethoprim/Sulfamethoxazole. This combination is the first-line treatment for Pneumocystis carinii pneumonia in patients with HIV-AIDS due to its efficacy against the organism. Trimethoprim inhibits dihydrofolate reductase, while sulfamethoxazole inhibits dihydropteroate synthase, both essential enzymes for folate synthesis in bacteria and protozoa like P. carinii. Metronidazole (A) is used for anaerobic infections, Carbenicillin (B) is a penicillinase-resistant penicillin used for Gram-negative infections, and Penicillin G (D) is a narrow-spectrum antibiotic mainly used for Gram-positive infections.

Correct Answer: A

Rationale: The correct answer is A: Two nucleoside reverse transcriptase inhibitors (NRTIs) + one protease inhibitor (PI). This regimen is typically reserved for advanced cases of AIDS or repeated treatment failures due to its high potency and effectiveness in suppressing HIV replication. NRTIs work by blocking the reverse transcriptase enzyme, while PIs inhibit the protease enzyme, both essential for HIV replication. Combining two NRTIs with a PI targets the virus at multiple stages, reducing the likelihood of resistance development. In contrast, the other choices (B, C, D) do not offer the same level of efficacy or resistance prevention as the combination in choice A. B: Three NRTIs may lead to increased toxicity without added benefit. C: Two NRTIs + one non-NRTI lacks the potency of a PI in advanced cases. D: One NRTI + one non-NRTI + one PI is not as effective as two NRTIs + one PI in suppressing

Correct Answer: A

Rationale: Acyclovir is an antiviral medication that specifically targets viruses that belong to the herpes virus family by inhibiting their replication. Herpes simplex Type 1 virus is most susceptible to acyclovir because it has a thymidine kinase enzyme that activates acyclovir into its active form, which then interferes with viral DNA synthesis. Herpes simplex Type 2 virus also has this enzyme, but it is not as effective against acyclovir compared to Type 1. Varicella-zoster virus and Epstein-Barr virus do not have the thymidine kinase enzyme necessary for acyclovir activation, making them less susceptible to the drug.

Correct Answer: B

Rationale: The correct answer is B, Tinidazole, for oral treatment of trichomonas vaginitis. Tinidazole is a nitroimidazole antibiotic that is effective against trichomonas. It has good oral bioavailability and is commonly used for this infection. Diiodohydroxyquin (A) is not indicated for trichomonas vaginitis. Clotrimazole (C) and Ketoconazole (D) are antifungal agents used for yeast infections, not trichomonas. Tinidazole is the most appropriate choice due to its effectiveness against trichomonas and its oral administration route.