Commercially available analogs of 1,25-dihydroxyvitamin D3 (calcitriol) are:

Correct Answer: C

Rationale: Rationale: 1. Both Doxercalciferol (Hectoral) and Paricalcitol (Zemplar) are synthetic analogs of 1,25-dihydroxyvitamin D3. 2. Doxercalciferol is converted to calcitriol in the body. 3. Paricalcitol is a selective vitamin D receptor activator. Summary: A: Doxercalciferol is correct as it is a synthetic analog of calcitriol. B: Paricalcitol is correct as it is also a synthetic analog of calcitriol. C: Correct as both A and B are true. D: Incorrect as both A and B are commercially available analogs of calcitriol.

Correct Answer: B

Rationale: The correct answer is B: Cefaclor. Cefaclor belongs to the cephalosporin class of antibiotics, specifically a second-generation cephalosporin. Cephalosporins are beta-lactam antibiotics that inhibit bacterial cell wall synthesis. Streptomycin (A) is an aminoglycoside antibiotic, Phenoxymethylpenicillin (C) is a penicillin antibiotic, and Erythromycin (D) is a macrolide antibiotic. These choices do not belong to the cephalosporin class.

Correct Answer: D

Rationale: The correct answer is D: Rifampin. Rifampin is an antimycobacterial drug that is commonly used to treat tuberculosis and other mycobacterial infections. It works by inhibiting the RNA polymerase enzyme in mycobacteria, leading to the suppression of bacterial growth. Isoniazid (Choice A) is also used for tuberculosis treatment, but it is not classified as an antibiotic. PAS (Choice B) is an antimycobacterial drug but is not an antibiotic. Ethambutol (Choice C) is also used to treat tuberculosis, but it works by inhibiting cell wall synthesis rather than RNA polymerase. Therefore, the correct choice is Rifampin as it directly targets the mycobacterial RNA polymerase enzyme, making it an effective antibiotic for treating mycobacterial infections.

Correct Answer: A

Rationale: Niclosamide inhibits oxidative phosphorylation by blocking the electron transport chain in helminthes. It disrupts their energy production, leading to paralysis and death. Piperazine acts on GABA receptors, Praziquantel disrupts the parasite's tegument, and Mebendazole inhibits microtubule function. Therefore, Niclosamide is the correct choice for inhibiting oxidative phosphorylation in helminthes.

Correct Answer: A

Rationale: Flutamide is the correct answer as it is a known antiandrogen drug used to treat conditions like prostate cancer. It works by blocking the action of androgens in the body. Aminoglutethimide is not an antiandrogen but an aromatase inhibitor. Tamoxifen is a selective estrogen receptor modulator used in breast cancer treatment. Testosterone is a natural male hormone and not an antiandrogen. Therefore, Flutamide is the correct choice for an antiandrogen drug.