A 40 year old man is HIV positive with CD4 count of 200/ cu.mm . After 2 months of therapy, he develops a peripheral WBC count of 1000 and hemoglobin of 9. Which of the following drugs most likely cause d this hematologic abnormality?

Correct Answer: A

Rationale: The correct answer is A: Zidovudine. Zidovudine is known to cause bone marrow suppression, leading to decreased white blood cell and red blood cell counts. In this case, the patient's peripheral WBC count of 1000 and low hemoglobin after starting therapy are indicative of hematologic abnormalities consistent with zidovudine use. Acyclovir, Foscarnet, and Amantadine do not typically cause bone marrow suppression and are not associated with the hematologic abnormalities seen in this patient.

Correct Answer: A

Rationale: The correct answer is A: Benzathine penicillin. Benzathine penicillin has the longest duration of action among the choices because it is formulated as a salt that releases the active drug slowly over an extended period. The benzathine salt forms a depot at the injection site, leading to a sustained release of penicillin into the bloodstream. This results in a prolonged therapeutic effect and less frequent dosing compared to other penicillin preparations. Summary: - Choice B: Sodium penicillin has a shorter duration of action as it gets rapidly absorbed and eliminated from the body. - Choice C: Potassium penicillin is not a standard form of penicillin and does not exist as a distinct preparation. - Choice D: Procaine penicillin has an intermediate duration of action compared to benzathine penicillin due to the addition of procaine for local anesthesia, but it is not as long-acting.

Correct Answer: D

Rationale: The correct answer is D because both statements (A and B) are accurate. A: Metronidazole is a first-line drug for amoebic dysentery and liver abscess due to its efficacy against Entamoeba histolytica. B: Metronidazole is a prodrug that gets activated to form nitro intermediates, which bind DNA and disrupt anaerobic microbial replication. Therefore, option D is correct as both A and B provide accurate information about metronidazole. Option C is incorrect as metronidazole is not specifically targeted to eradicating amoebic cysts from the colon.

Correct Answer: D

Rationale: The correct answer is D: Escherichia coli. E. coli is notorious for developing antimicrobial resistance rapidly due to its ability to acquire resistance genes through plasmid exchange and mutation. This bacterium is commonly found in the gut of humans and animals, leading to frequent exposure to antibiotics. On the other hand, choices A, B, and C are less likely to develop resistance as rapidly as E. coli due to their lower frequency of exposure to antibiotics and differences in genetic makeup. Streptococcus pyogenes is susceptible to penicillin, Meningococcus has shown susceptibility to several antibiotics, and Treponema pallidum has limited exposure to antibiotics due to its unique nature as the causative agent of syphilis.

Correct Answer: C

Rationale: Rationale: The correct answer is C: Hydrochlorothiazide. It is a thiazide diuretic that reduces calcium excretion, preventing stone formation. Furosemide (A) and spironolactone (B) do not target calcium excretion specifically. Acetazolamide (D) is a carbonic anhydrase inhibitor and not commonly used for calcium stones.