Duration of action of:

Correct Answer: B

Rationale: The correct answer is B because chlorpropamide has a longer duration of action compared to tolbutamide. Chlorpropamide has a half-life of around 36 hours, whereas tolbutamide's half-life is about 5 hours. This means that chlorpropamide stays in the body and continues to lower blood sugar levels for a longer period of time compared to tolbutamide. Choices A and C are incorrect as they suggest that the durations of action are equal or that tolbutamide has a longer duration, which is not the case based on their pharmacokinetics. Choice D is also incorrect as it does not address the specific comparison between tolbutamide and chlorpropamide.

Correct Answer: D

Rationale: The correct answer is D: 19 hours. The half-life of a drug is the time it takes for the concentration of the drug in the body to reduce by half. Cyclosporine A has a half-life of approximately 19 hours, meaning that it takes 19 hours for the concentration of cyclosporine A in the body to decrease by half. This is the most accurate description of the half-life of cyclosporine A. Choice A (25-35 minutes) is too short for the half-life of cyclosporine A, as it typically stays in the body for a longer duration. Choice B (21 days) is too long for the half-life of cyclosporine A, as this is more commonly seen in drugs with very long half-lives. Choice C (4 - 16 hours) is closer to the correct answer, but 19 hours is a more precise estimate for the half-life of cyclospor

Correct Answer: A

Rationale: Rationale for Correct Answer (A): 1. Pernicious anemia is a condition caused by the inability of the stomach to absorb vitamin B12. 2. It is characterized by abnormally large red blood cells, gastrointestinal disturbances, and spinal cord lesions. 3. It predominantly affects elderly adults due to age-related decline in stomach acid production. 4. This choice accurately describes the key features and etiology of pernicious anemia. Summary of Incorrect Choices: B. This choice describes aplastic anemia, not pernicious anemia. C. This choice describes hypochromic anemia, not pernicious anemia. D. This choice is incorrect as only option A accurately describes pernicious anemia.

Correct Answer: B

Rationale: Correct Answer: B Rationale: 1. Nicotinic acid (Niacin) primarily works by inhibiting lipolysis in adipose tissue, leading to decreased free fatty acids and triglycerides. 2. Triglycerides and LDL cholesterol are reduced by Niacin due to its effect on lipid metabolism. 3. High doses of Niacin can indeed cause hepatic or pancreatic disturbances, leading to the discontinuation of doses higher than 3 gm/day. 4. Cutaneous flushing and itching are common side effects of Niacin, not directly related to the drug's effect on apoproteins synthesis.

Correct Answer: A

Rationale: Step 1: 25-hydroxyvitamin D3 (calcifediol) is a precursor to 1,25-dihydroxyvitamin D3 (calcitriol). Step 2: Calcitriol is the active form of vitamin D that stimulates intestinal calcium transport. Step 3: Calcifediol is converted into calcitriol in the kidneys. Step 4: Since calcifediol is less potent than calcitriol, it is less effective in stimulating intestinal calcium transport. Step 5: Therefore, hypercalcemia, a condition of high calcium levels in the blood, is less likely to occur with calcifediol compared to calcitriol. Summary: Choice A is correct because calcifediol is indeed less effective than calcitriol in stimulating intestinal calcium transport, leading to a lower risk of hypercalcemia. Choices B, C, and D are incorrect as they do not accurately reflect the relationship between