Mifepristone (RU-486) is:

Correct Answer: A

Rationale: The correct answer is A: Antiprogestin. Mifepristone is a synthetic steroid that acts as an antiprogestin by competitively binding to progesterone receptors, blocking the effects of progesterone. It is commonly used for medical abortion and in the treatment of conditions like Cushing's syndrome. Explanation for incorrect choices: B: Antiandrogen - Mifepristone does have some antiandrogenic properties, but its primary mechanism of action is as an antiprogestin. C: Antiestrogen - Mifepristone is not an antiestrogen; it does not block estrogen receptors. D: Androgen - Mifepristone is not an androgen; it is a synthetic steroid with antiprogestational activity.

Correct Answer: A

Rationale: The correct answer is A because vitamin-like compounds are a group of compounds that are essential for health but are not classified as vitamins. These compounds have specific roles in the body, particularly during periods of rapid growth and development. They are not inorganic nutrients (B) or organic substances needed in large quantities (C). They are also not products of endocrine gland secretion (D). The key is to understand that vitamin-like compounds are essential for certain stages of development and growth, making choice A the most appropriate answer.

Correct Answer: B

Rationale: Selegiline is the correct answer as it is a monoamine oxidase (MAO) inhibitor. MAO inhibitors block the breakdown of monoamine neurotransmitters such as dopamine, serotonin, and norepinephrine. Physostigmine is an acetylcholinesterase inhibitor, not an MAO inhibitor. Acetazolamide is a carbonic anhydrase inhibitor used in glaucoma and altitude sickness. Disulfiram is an aldehyde dehydrogenase inhibitor used in alcohol aversion therapy.

Correct Answer: D

Rationale: Gemfibrozil (Lopid) increases lipoprotein lipase (LPL) activity in adipose tissue. Firstly, it is a fibric acid derivative that specifically targets LPL, leading to increased breakdown of triglyceride-rich lipoproteins. This mechanism helps lower triglyceride levels in the blood. Cholestyramine (A) is a bile acid sequestrant that does not affect LPL activity. Lovastatin (B) is a statin that primarily works by inhibiting cholesterol synthesis in the liver. Nicotinic acid (C) mainly acts by reducing circulating levels of LDL cholesterol and triglycerides, not by enhancing LPL activity.

Correct Answer: D

Rationale: Step-by-step rationale for the correct answer (D): 1. Pamidronate is a bisphosphonate used to treat conditions involving excessive bone breakdown. 2. Hypercalcemia is a condition characterized by elevated calcium levels in the blood. 3. Pamidronate works by inhibiting bone resorption, which helps lower blood calcium levels in hypercalcemia. 4. Therefore, the indication for pamidronate administration is hypercalcemia. Summary of other choices: A: Failure of vitamin D formation in skin - Not related to pamidronate use. B: Hypoparathyroidism - Pamidronate is not indicated for hypoparathyroidism. C: Elevated skeletal turnover - While pamidronate is used for conditions involving high skeletal turnover, hypercalcemia is the primary indication for its administration.