Route of administration of 1,25-dihydroxyvitamin D3 (calcitriol) is:

Correct Answer: D

Rationale: The correct route of administration for 1,25-dihydroxyvitamin D3 (calcitriol) is oral (Choice D). This is because calcitriol is a form of vitamin D that is typically taken orally for absorption in the intestine. When taken orally, it undergoes hepatic and renal hydroxylation to its active form. Subcutaneous (Choice A), intravenous (Choice B), and intranasal (Choice C) routes are not typically used for administering calcitriol as they may not provide the necessary absorption and metabolism required for its activation in the body.

Correct Answer: C

Rationale: Step-by-step rationale for why choice C (Aztreonam) is correct: 1. Monobactams are a class of antibiotics with a unique monocyclic beta-lactam ring structure. 2. Aztreonam is the only monobactam antibiotic listed among the choices. 3. Aztreonam is effective against aerobic Gram-negative bacteria. 4. It does not have cross-reactivity with beta-lactamases. Summary: A, B, and D are incorrect because they belong to different classes of antibiotics (penicillins, penicillin combinations, and carbapenems respectively), not monobactams.

Correct Answer: B

Rationale: The correct answer is B: PAS (para-aminosalicylic acid) because it is a second-line antimycobacterial drug used to treat drug-resistant tuberculosis. Isoniazid and rifampin are first-line agents, and streptomycin is an aminoglycoside antibiotic primarily used for treating bacterial infections, not specifically for mycobacterial infections. PAS is specifically indicated for multidrug-resistant tuberculosis cases, making it a second-line option.

Correct Answer: C

Rationale: The correct answer is C. Mebendazole inhibits microtubule synthesis in helminths, leading to irreversible impairment of glucose uptake. This disrupts the helminths' ability to maintain their structure and energy production, ultimately causing their death. A, B, and D are incorrect as mebendazole does not work by inhibiting oxidative phosphorylation, increasing cell membrane permeability for calcium, or blocking acetylcholine transmission. These mechanisms are not associated with mebendazole's mode of action.

Correct Answer: D

Rationale: The correct answer is D: Anastrozole. Anastrozole is an aromatase inhibitor that works by blocking the enzyme aromatase, which is responsible for converting androgens into estrogen. By inhibiting estrogen production, Anastrozole effectively reduces estrogen levels in the body. Leuprolide (A) is a gonadotropin-releasing hormone agonist that suppresses estrogen production indirectly. Tamoxifen (B) is a selective estrogen receptor modulator that blocks estrogen receptors. Flutamide (C) is an antiandrogen that blocks the effects of androgens, not estrogen.