A 54-year-old woman suffering from initial insomnia was prescribed a hypnotic drug that increases the activity of a major neurotransmitter system in the brain. Which of the following neurotransmitter systems was most likely involved in the therapeutic action of that drug?

Correct Answer: D

Rationale: In the treatment of insomnia, drugs that enhance GABAergic activity are commonly prescribed as they help promote relaxation and sleep. GABA is the major inhibitory neurotransmitter in the brain, and increasing its activity can lead to sedative effects, making it a likely target for a hypnotic drug.

Correct Answer: A

Rationale: DES, a synthetic estrogen, causes deep vein thrombosis (choice A), feminization of male offspring (choice B), and miscarriages (choice C) in pregnancy, linked to historical congenital anomalies (e.g., vaginal adenocarcinoma). Virilization of female offspring (choice D) isn't reported; DES mimics estrogen, not androgens. This exception highlights its teratogenic risks, banning its use in pregnancy.

Correct Answer: C

Rationale: Carbimazole treats hyperthyroidism (choice A), Levothyroxine hypothyroidism (choice B), and Propylthiouracil is pregnancy-safe (choice D), all correct. Methimazole (choice C) isn't metabolized into carbimazole; carbimazole is a prodrug for methimazole, the active form, making this wrong. This clarifies thionamide metabolism, key for therapeutic accuracy.

Correct Answer: D

Rationale: Saxitoxin, produced by dinoflagellates, causes paralytic shellfish poisoning by blocking sodium channels.

Correct Answer: B

Rationale: Carbamazepine is a commonly used antiepileptic drug for the treatment of partial seizures. Given the patient's diagnosis and symptoms, Carbamazepine would be a likely choice for the neurologist to prescribe in this case.