A 54-year-old man had been receiving carbamazepine since he was diagnosed with complex partial seizures 5 years earlier. The drug was fully effective in controlling the seizures. Blockade of which of the following molecular targets most likely mediated the therapeutic effect of the drug in the patient's disease?

Correct Answer: D

Rationale: The correct answer is D: Na+ channels. Carbamazepine is an antiepileptic drug that works by blocking voltage-gated sodium channels, thus reducing neuronal excitability and preventing the generation of abnormal electrical discharges that lead to seizures. This mechanism of action is particularly effective in controlling partial seizures. A: Acetylcholine receptors - Carbamazepine does not directly interact with acetylcholine receptors. B: Glutamate receptors - Carbamazepine does not directly interact with glutamate receptors. C: Monoamine receptors - Carbamazepine does not directly interact with monoamine receptors. In summary, the therapeutic effect of carbamazepine in controlling seizures is mediated by its blockade of Na+ channels, which reduces neuronal excitability. Other choices are incorrect as carbamazepine does not target acetylcholine, glutamate, or monoamine receptors.

Correct Answer: A

Rationale: The correct answer is A: Carbamazepine. It is the most appropriate choice due to its efficacy in treating complex partial seizures. Carbamazepine is also less likely to worsen atrioventricular block compared to other antiepileptic drugs. Furthermore, it does not typically exacerbate nephrolithiasis. Phenytoin (B) can worsen atrioventricular block and does not specifically target complex partial seizures. Valproic acid (C) is contraindicated in patients with nephrolithiasis. Ethosuximide (D) is primarily used for absence seizures, not complex partial seizures.

Correct Answer: B

Rationale: The correct answer is B: Levodopa. Levodopa is a common medication used to treat Parkinson's disease. The symptoms described by the patient, such as facial grimacing, lip smacking, and rocking of the trunk, are characteristic of levodopa-induced dyskinesias, which can occur as a side effect of long-term levodopa therapy. Levodopa-induced dyskinesias usually develop after 1-2 hours of taking the medication, as seen in this case. Choice A: Selegiline is a selective MAO-B inhibitor and is less likely to cause the described adverse effects compared to levodopa. Choice C: Entacapone is a catechol-O-methyltransferase (COMT) inhibitor used in combination with levodopa, but it is not known to cause the specific dyskinesias described. Choice D: Amantadine is an antiviral agent with antiparkinsonian effects, but it is

Correct Answer: B

Rationale: The correct answer is B: Decreased acetylcholine release from cholinergic terminals. Acetylcholine release from cholinergic terminals contributes to the parasympathetic response, which can cause adverse effects such as bradycardia. By decreasing acetylcholine release, the parasympathetic response is reduced, leading to a more balanced autonomic control of the heart rate. Activation of cardiac dopamine receptors (choice A) and β receptors (choice C) would usually have positive effects on the heart, while blockade of cardiac M receptors (choice D) would exacerbate the adverse effects by blocking the already decreased parasympathetic response.

Correct Answer: D

Rationale: The correct answer is D: Clozapine. Clozapine is the most appropriate choice for a 29-year-old man with chronic paranoid schizophrenia at this stage due to its efficacy in treatment-resistant cases and lower risk of extrapyramidal side effects. It is often considered a last resort due to its potential side effects, such as agranulocytosis, which requires regular monitoring. A: Fluphenazine and B: Thioridazine are typical antipsychotics with a higher risk of extrapyramidal side effects and are less effective in treatment-resistant cases compared to Clozapine. C: Fluoxetine is an antidepressant and not typically used as a first-line treatment for schizophrenia. It is more commonly used for depressive symptoms that may co-occur with schizophrenia.