Indication for 25-hydroxyvitamin D3 (calcifediol) administration is:

Correct Answer: B

Rationale: The correct answer is B: Rickets. Calcifediol is administered for the treatment of vitamin D deficiency-related conditions like rickets, which is a bone disorder caused by a lack of vitamin D, leading to soft and weak bones. The other choices are incorrect because: A) Primary hyperparathyroidism is treated with medications that target the parathyroid gland, not vitamin D. C) Hypercalcemia is an excess of calcium in the blood and is not treated with calcifediol since it can exacerbate the condition. D) Failure of vitamin D formation in the skin is not an indication for calcifediol administration as it is used to treat vitamin D deficiency, not a failure in its formation.

Correct Answer: C

Rationale: The correct answer is C: Penicillins. Penicillins demonstrate bactericidal effects by interfering with bacterial cell wall synthesis, leading to cell lysis and death. Tetracyclines and macrolides are bacteriostatic, inhibiting bacterial growth but not directly killing them. Choice D is incorrect as not all antibiotics listed exhibit bactericidal effects.

Correct Answer: B

Rationale: Step-by-step rationale for choice B (Taking of drinks with alkaline pH) being correct: 1. Sulfonamides are more soluble in alkaline solutions, reducing the risk of precipitation. 2. Alkaline pH helps in preventing the formation of crystals in the urine. 3. Alkaline drinks can help maintain a higher urinary pH, minimizing the risk of crystalluria. 4. This approach is supported by medical literature and pharmacological principles. Summary: - Choice A (Taking of drinks with acid pH) is incorrect as it may exacerbate sulfonamide precipitation and crystalluria. - Choice C (Taking of saline drinks) is incorrect as it does not address the solubility issues of sulfonamides. - Choice D (Restriction of drinking) is incorrect as hydration is essential to prevent crystalluria.

Correct Answer: B

Rationale: The correct answer is B: Metronidazole. Metronidazole is the drug of choice for extraluminal amebiasis due to its high efficacy against Entamoeba histolytica. It is a nitroimidazole antibiotic that works by disrupting the DNA structure of the parasite. Other choices are incorrect because: A: Iodoquinol is mainly used for luminal amebiasis. C: Diloxanide is also used for luminal amebiasis. D: Tetracycline is not the first-line treatment for extraluminal amebiasis.

Correct Answer: A

Rationale: The correct answer is A: Inhibition of dihydrofolate reductase. Methotrexate inhibits dihydrofolate reductase, an enzyme involved in the synthesis of nucleotides. This leads to decreased production of DNA, RNA, and proteins, inhibiting cell proliferation. Choices B and C are incorrect as methotrexate does not activate cell differentiation or deplete serum asparagine. D is incorrect as methotrexate's mechanism of action is specifically through inhibiting dihydrofolate reductase, not all of the above.