B

If a benzodiazepine (e.g., buccal/IN midazolam) has already failed and an IV line is now in place, the next guideline-recommended step for ongoing convulsive seizures is a second-line intravenous antiseizure drug—traditionally IV phenobarbital or phenytoin; phenobarbital is one of the standard choices and is available in IV form, whereas carbamazepine is not and oral valproate is too slow for acute control [Loddenkemper & Goodkin, 2011, PMID 21956209; Eriksson & Kälviäinen, 2005, PMID 16274335].