Which of the following antivitamins prevent a vitamin A from exerting its typical metabolic effects?

Correct Answer: A

Rationale: The correct answer is A: Lipooxidase. Antivitamins are substances that interfere with the absorption, metabolism, or utilization of vitamins. In this case, antivitamin A would prevent vitamin A from exerting its typical effects. Lipooxidase is an antivitamin that inhibits the action of vitamin A by interfering with its metabolic pathways. Summary: - Oral contraceptives do not prevent vitamin A from exerting its effects. - Antibiotics do not prevent vitamin A from exerting its effects. - Therefore, the correct answer is A: Lipooxidase.

Correct Answer: C

Rationale: The correct answer is C: Oral. Dihydrotachysterol is a form of vitamin D used to treat hypoparathyroidism. The oral route is chosen for its optimal absorption in the gastrointestinal tract. Intravenous (A) and subcutaneous (B) routes are not commonly used for dihydrotachysterol administration due to potential adverse effects and lack of significant benefits. Intranasal (D) administration is not suitable for dihydrotachysterol as it is not designed to be absorbed through the nasal mucosa.

Correct Answer: D

Rationale: The correct answer is D: Spironolactone (Aldactone). Spironolactone has a steroid-like structure due to its chemical similarity to aldosterone, allowing it to competitively inhibit aldosterone receptors. This anti-androgenic effect is crucial in conditions like hirsutism and acne. Amiloride (A), Furosemide (B), and Hydrochlorothiazide (C) do not possess a steroid-like structure and do not exhibit anti-androgenic properties.

Correct Answer: A

Rationale: The correct answer is A: Doxycycline, as it belongs to the tetracycline class of antibiotics. Tetracyclines inhibit bacterial protein synthesis by binding to the bacterial ribosome. Streptomycin (B) is an aminoglycoside, Clarithromycin (C) is a macrolide, and Amoxicillin (D) is a penicillin; these do not belong to the tetracycline class.

Correct Answer: B

Rationale: The correct answer is B because isoniazid inhibits the synthesis of mycolic acids, a crucial component of the cell wall of Mycobacterium tuberculosis. By blocking mycolic acid synthesis, isoniazid disrupts the integrity of the bacterial cell wall, leading to cell death. Choices A, C, and D are incorrect because isoniazid does not affect protein synthesis, RNA synthesis, or ADP synthesis. These processes are not targeted by isoniazid in its mechanism of action against tuberculosis.