Indications for 1,25-dihydroxyvitamin D3 (calcitriol) administration are the following, EXCEPT:

Correct Answer: D

Rationale: The correct answer is D: Elevated skeletal turnover. 1,25-dihydroxyvitamin D3 (calcitriol) is administered for hypocalcemia in chronic renal failure, vitamin D-dependent rickets, and malabsorption of vitamin D. Elevated skeletal turnover is not an indication for calcitriol as it can exacerbate bone resorption. Administering calcitriol in such cases can lead to increased calcium release from bones and worsen the condition. Therefore, D is the correct answer.

Correct Answer: B

Rationale: The correct answer is B: Macrolides. Macrolides exert a bacteriostatic effect by inhibiting bacterial protein synthesis. They do not directly kill bacteria but rather prevent their growth and reproduction. Carbapenems (A), aminoglycosides (C), and cephalosporins (D) are examples of antibiotics that typically exhibit bactericidal effects, meaning they directly kill bacteria. Therefore, Macrolides are the only group among the options that demonstrate a bacteriostatic effect.

Correct Answer: B

Rationale: Rationale: Trimethoprim inhibits dihydropteroate reductase, an enzyme in the folate synthesis pathway in bacteria, disrupting DNA and protein synthesis. This leads to bacterial cell death. Cyclooxygenase (Choice A) is targeted by NSAIDs, not trimethoprim. Dihydropteroate synthase (Choice C) is targeted by sulfonamides, not trimethoprim. DNA gyrase (Choice D) is targeted by fluoroquinolones, not trimethoprim. Therefore, Choice B is correct for trimethoprim's mechanism of action.

Correct Answer: A

Rationale: The correct answer is A because niclosamide works by increasing cell membrane permeability for calcium in helminthes. This leads to paralysis, dislodgement, and ultimately death of the parasites. Choice B is incorrect because niclosamide does not work by blocking acetylcholine transmission at the myoneural junction. Choice C is incorrect as niclosamide does not inhibit microtubule synthesis or impair glucose uptake in helminthes. Choice D is incorrect as niclosamide does not inhibit oxidative phosphorylation in helminthes.

Correct Answer: B

Rationale: Step-by-step rationale: 1. Estrogens are contraindicated in most cancers due to their potential to promote cancer growth. 2. However, in prostate cancer, estrogens can be used as a form of androgen deprivation therapy. 3. Estrogen therapy in prostate cancer helps suppress testosterone production, slowing cancer growth. 4. Hence, the correct indication for estrogens in oncological practice is prostate cancer. Summary: A, C, and D are incorrect because estrogen therapy is not indicated in leukemia, endometrial cancer, or brain tumors due to the risk of promoting cancer growth. Prostate cancer is the exception where estrogens can be beneficial for treatment.