A 39-year-old man diagnosed with tonic-clonic seizures 2 years ago had been receiving a drug that exhibits dose-dependent elimination kinetics. Which of the following drugs did the patient most likely take?

Correct Answer: A

Rationale: Valproic acid is the correct answer because it exhibits dose-dependent elimination kinetics, meaning its clearance rate changes with dosage. In patients with epilepsy, maintaining steady drug levels is crucial for seizure control. Valproic acid's dose-dependent elimination allows for more predictable drug levels at higher doses. Lamotrigine, phenytoin, and topiramate do not exhibit this characteristic. Lamotrigine has time-dependent kinetics, phenytoin follows Michaelis-Menten kinetics, and topiramate has linear kinetics. Therefore, Valproic acid is the most likely drug taken by the patient.

Correct Answer: B

Rationale: The correct answer is B: Ethosuximide. In a 15-month-old with episodes of powerful muscle contractions, the most likely diagnosis is childhood absence epilepsy, which is characterized by brief, subtle seizures involving staring and muscle contractions. Ethosuximide is the first-line treatment for childhood absence epilepsy due to its efficacy and favorable side effect profile in young children. Carbamazepine (A) is not typically used for absence seizures. Phenytoin (C) and Phenobarbital (D) are not recommended for childhood absence epilepsy and may have more side effects in this age group.

Correct Answer: D

Rationale: Rationale: 1. Perampanel is a non-competitive antagonist of AMPA receptors, effective for partial seizures. 2. Lamotrigine is commonly used for partial seizures, making Perampanel a suitable add-on therapy. 3. Levetiracetam, Felbamate, and Topiramate are less commonly used or not as effective for partial seizures. Summary: Levetiracetam, Felbamate, and Topiramate are not the best choices due to their lower efficacy or different mechanisms of action compared to Perampanel, which is specifically effective for partial seizures and suitable as an add-on therapy in this case.

Correct Answer: B

Rationale: The correct answer is B because inhibiting the abnormally high cholinergic tone in the striatum can help reduce tremors. The striatum plays a key role in motor control, and an imbalance between cholinergic and dopaminergic signaling can lead to tremors. By inhibiting the excessive cholinergic activity, the balance is restored, resulting in reduced tremor. A: Inhibition of levodopa metabolism in the striatum wouldn't directly affect tremors as levodopa is a precursor to dopamine. C: Activation of dopaminergic receptors in the striatum may help with motor control but wouldn't specifically address the cholinergic imbalance causing tremors. D: Blockade of β adrenoceptors in skeletal muscle is unrelated to the striatum and cholinergic signaling involved in tremors.

Correct Answer: D

Rationale: The correct answer is D: Omeprazole. Omeprazole is a proton pump inhibitor used to reduce stomach acid production, which can cause nausea as a side effect. Carbidopa is used to treat Parkinson's disease, Benztropine is an anticholinergic used to treat Parkinson's symptoms, and Pramipexole is a dopamine agonist also used in Parkinson's disease. None of these drugs are known to commonly cause nausea as a side effect.