A 40-year-old female with a history of depression is prescribed fluoxetine. Fluoxetine is classified as:

Correct Answer: A

Rationale: The correct answer is A: A selective serotonin reuptake inhibitor (SSRI). Fluoxetine falls under this class by specifically inhibiting the reuptake of serotonin, leading to increased serotonin levels in the brain. This mechanism helps alleviate symptoms of depression. Other choices are incorrect because fluoxetine is not an MAOI (B), TCA (C), or SNRI (D), as it does not primarily target monoamine oxidase enzymes, nor does it have the tricyclic structure or target both serotonin and norepinephrine reuptake.

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.

Correct Answer: B

Rationale: The correct answer is B: Trigeminal nerve. Sumatriptan is a serotonin receptor agonist that acts on serotonin receptors in the trigeminal nerve to reduce inflammation and pain associated with migraines. The trigeminal nerve is a key player in the pathophysiology of migraines, transmitting pain signals from blood vessels and meninges to the brain. The other choices (A: Nucleus accumbens, C: Vestibular nuclei, D: Chemoreceptor trigger zone) are not directly involved in the pathophysiology of migraines or the mechanism of action of sumatriptan. The nucleus accumbens is primarily associated with reward and motivation, the vestibular nuclei are involved in balance and spatial orientation, and the chemoreceptor trigger zone is related to the regulation of vomiting.