Mechanism of action of I.V. IgG preparation is:

Correct Answer: D

Rationale: The correct answer is D because I.V. IgG preparations compete for Fc receptors with autoantibodies. This blocks the binding of autoantibodies to their target antigens, thereby preventing autoimmune reactions. Choice A is incorrect as I.V. IgG does not inhibit CD3 receptors. Choice B is incorrect as it does not inhibit calcineurin. Choice C is incorrect as I.V. IgG does not induce complement-mediated cytolysis of T lymphocytes.

Correct Answer: A

Rationale: The correct answer is A: TRUE. Cholesterol synthesis inhibitors, like statins, reduce cholesterol production in the liver, leading to an upregulation of LDL receptors on hepatocytes. This increases the clearance of LDL cholesterol from the plasma, ultimately lowering LDL levels. Therefore, the statement that cholesterol synthesis inhibitors increase the rate of clearance of LDL cholesterol from the plasma is true. Choices B, C, and D are incorrect because they do not accurately reflect the relationship between cholesterol synthesis inhibitors and LDL cholesterol clearance.

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: D

Rationale: The correct answer is D: Fludrocortisone. Fludrocortisone is a synthetic steroid that primarily exhibits mineralocorticoid activity. It is commonly used to treat adrenal insufficiency due to its potent mineralocorticoid effects. Hydrocortisone (A) is a natural steroid with both glucocorticoid and mineralocorticoid activity. Spironolactone (B) is a potassium-sparing diuretic that acts as an aldosterone antagonist, reducing the effects of aldosterone. Dexamethasone (C) is a synthetic steroid with potent anti-inflammatory and immunosuppressive properties but minimal mineralocorticoid activity.

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.