A 29-year-old woman presents to the nurse practitioner with a history of chronic migraine, including more than 15 headache days each month. Of the following, which is NOT considered first-line migraine prophylaxis treatment?

Choice A reason: Divalproex is an anticonvulsant approved for migraine prophylaxis. It modulates neurotransmitter activity and reduces neuronal excitability, making it effective for chronic migraine prevention. Choice B reason: Topiramate is another anticonvulsant with proven efficacy in migraine prophylaxis. It reduces frequency and severity by stabilizing neuronal firing and inhibiting cortical spreading depression. Choice C reason: Metoprolol is a beta-blocker commonly used for migraine prevention. It reduces sympathetic nervous system activity and stabilizes vascular tone, helping to prevent migraine attacks. Choice D reason: Sumatriptan is a triptan used for acute migraine treatment, not prophylaxis. It acts as a serotonin receptor agonist to abort migraine episodes but does not prevent their occurrence. Therefore, it is not considered first-line for prophylaxis.