A 60-year-old male is prescribed levothyroxine for hypothyroidism. Levothyroxine works by:

Correct Answer: B

Rationale: The correct answer is B: Replacing deficient thyroid hormone. Levothyroxine is a synthetic form of thyroid hormone used to treat hypothyroidism by supplementing the low levels of thyroid hormone in the body. It does not increase TSH production (Choice A), inhibit thyroid hormone synthesis (Choice C), or increase the metabolism of thyroid hormones (Choice D). By providing the missing thyroid hormone, levothyroxine helps restore normal thyroid function and alleviate symptoms of hypothyroidism.

Correct Answer: A

Rationale: The correct answer is A: Dry cough. Lisinopril, an ACE inhibitor, commonly causes a dry, persistent cough due to its effect on bradykinin levels. This side effect is distinct and prevalent compared to others like fatigue, weight gain, or hyperkalemia. Fatigue and weight gain are less common side effects of lisinopril, while hyperkalemia is a potential but less frequent adverse reaction associated with ACE inhibitors. Overall, the prevalence and mechanism of dry cough make it the most common side effect of lisinopril.

Correct Answer: A

Rationale: The correct answer is A because the therapeutic index (TI) is a measure of a drug's safety margin. A higher TI indicates a safer drug as it represents the ratio between the dose that produces therapeutic effects and the dose that causes toxicity. If the therapeutic dose is much lower than the toxic dose, it results in a higher TI, indicating a safer drug. Choice B is incorrect because a TI of 1 indicates that the therapeutic dose is equal to the toxic dose, which is not desirable. Choice C is incorrect as the presence of unwanted adverse effects does not necessarily impact the TI directly. Choice D is incorrect because the margin of safety for Digoxin is 0.8-2 ng/ml, so a level of 1.8 ng/ml would fall within the safe range, not pose a danger.

Correct Answer: D

Rationale: The correct answer is D: Diphenhydramine. Diphenhydramine is a first-generation antihistamine that can help prevent allergic reactions to contrast media. It works by blocking the action of histamine, which is released during allergic reactions. This drug is commonly used for pre-medication to prevent allergic reactions to contrast media in patients with a history of mild reactions. Choice A (Fluorocortisone) is a corticosteroid and is not typically used for preventing allergic reactions to contrast media. Choice B (Famotidine) is a histamine-2 blocker used for stomach acid reduction and is not indicated for preventing allergic reactions. Choice C (Zafirlukast) is a leukotriene receptor antagonist used for asthma and allergies, but it is not typically used for pre-medication before MRI with contrast media.

Correct Answer: D

Rationale: The correct answer is D because loratadine is a second-generation antihistamine that works by blocking the effects of histamine on peripheral tissues. This helps to alleviate symptoms of allergies such as pruritus and skin wheals. Option A is incorrect because loratadine does not block the release of histamine from mast cells. Option B is incorrect as loratadine does not prevent the antigen-antibody reaction. Option C is incorrect because loratadine does not elicit effects opposite to histamine; instead, it counteracts histamine effects.