Indication for dihydrotachysterol administration is:

Correct Answer: A

Rationale: Step-by-step rationale for correct answer (A): 1. Dihydrotachysterol is a vitamin D analog used to treat parathyroid hormone resistance. 2. Parathyroid hormone resistance leads to impaired calcium absorption and bone mineralization. 3. Dihydrotachysterol helps increase calcium absorption and bone mineralization in these patients. Summary of incorrect choices: - B: Paget's disease is typically treated with bisphosphonates or calcitonin, not dihydrotachysterol. - C: Increased osteolysis is not a direct indication for dihydrotachysterol administration. - D: Hypophosphatemia is usually treated with phosphate supplements, not dihydrotachysterol.

Correct Answer: B

Rationale: The correct answer is B: Polymyxins. Polymyxins are antibiotics that work by altering the permeability of the bacterial cell membrane, leading to leakage of cellular contents and ultimately bacterial cell death. This mechanism of action is specific to polymyxins, making it the correct choice. Incorrect Choices: A: Glycopeptides - Glycopeptides work by inhibiting cell wall synthesis, not by altering cell membrane permeability. C: Tetracyclines - Tetracyclines inhibit protein synthesis in bacteria, they do not target cell membrane permeability. D: Cephalosporins - Cephalosporins interfere with cell wall synthesis, they do not directly affect cell membrane permeability.

Correct Answer: C

Rationale: Step-by-step rationale for choice C: 1. Ethambutol is known to cause retrobulbar neuritis, a condition that affects the optic nerve leading to vision changes. 2. The specific symptom of red-green color blindness is commonly associated with ethambutol toxicity. 3. This effect is due to the drug's direct impact on the optic nerve. 4. Regular monitoring of visual acuity and color vision is recommended during ethambutol treatment. Summary of other choices: A. Cardiotoxicity: Ethambutol is not known to cause direct cardiotoxic effects. B. Immunetoxicity: Ethambutol primarily affects the optic nerve, not the immune system. D. Hepatotoxicity: Ethambutol is generally well-tolerated by the liver and does not commonly cause hepatotoxicity.

Correct Answer: D

Rationale: The correct answer is D: Ivermectin. Ivermectin is the drug of choice for strongyloidiasis due to its high efficacy and low toxicity. It works by paralyzing and killing the parasites. Niclosamide (A) is used for tapeworm infections, Praziquantel (B) for schistosomiasis, and Bithionol (C) for fascioliasis. Therefore, D is the correct choice for treating strongyloidiasis.

Correct Answer: C

Rationale: The correct answer is C: Demeclocycline. This drug is specifically used to treat the condition of syndrome of inappropriate antidiuretic hormone secretion (SIADH), which is common in elderly patients. Demeclocycline works by inhibiting the action of antidiuretic hormone, thus promoting water diuresis. Desmopressin (choice A) is used to treat diabetes insipidus, the opposite of SIADH. Hydrochlorothiazide (choice B) and Amiloride (choice D) are diuretics commonly used for different conditions like hypertension and edema but are not indicated for SIADH.