Pernicious anemia is:

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: 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

Correct Answer: A

Rationale: The correct answer is A: Intravenous. Plicamycin is a cytotoxic antibiotic that is administered intravenously to ensure direct delivery into the bloodstream for optimal absorption and distribution to target tissues. Subcutaneous and intranasal routes are not suitable for plicamycin due to its potency and potential irritation at the injection site. Oral administration is ineffective as plicamycin is poorly absorbed through the gastrointestinal tract and extensive first-pass metabolism would render it ineffective. Therefore, intravenous administration is the most appropriate route for plicamycin to achieve desired therapeutic effects.

Correct Answer: C

Rationale: The correct answer is C: Co-trimoxazole. Co-trimoxazole is a combination of sulfamethoxazole and trimethoprim, which are not antibiotics but rather antimicrobial agents. Streptomycin, Penicillin, and Chloramphenicol are all antibiotics that target and kill bacteria. Antibiotics specifically target bacterial infections, while antimicrobial agents can target a broader range of microbes. Therefore, Co-trimoxazole does not fall under the category of antibiotics, making it the correct answer.

Correct Answer: B

Rationale: Step-by-step rationale for Choice B being correct: 1. Trimethoprim inhibits bacterial dihydrofolate reductase. 2. Sulfonamides inhibit dihydropteroate synthetase. 3. Combination blocks sequential steps in folate synthesis. 4. Synergistic effect enhances antimicrobial activity. Summary: A: Incorrect. Combination does not decrease unwanted effects of sulfonamides. C: Incorrect. Combination does not decrease antimicrobial activity. D: Incorrect. Combination does not increase elimination of sulfonamides.