**Core Concept**
The management of acute seizures involves the administration of benzodiazepines as first-line treatment, such as Lorazepam. However, in cases where seizures persist despite initial treatment, antiepileptic drugs (AEDs) are used to control the seizures and prevent further episodes.

**Why the Correct Answer is Right**
Phenytoin is a hydantoin-class AED that is effective in controlling seizures by stabilizing the voltage-gated sodium channels, which reduces the frequency of action potentials and subsequent neuronal excitation. It is particularly useful in treating generalized tonic-clonic seizures, complex partial seizures, and status epilepticus. Phenytoin is administered intravenously in the setting of acute seizures that are refractory to benzodiazepines, as in this case.

**Why Each Wrong Option is Incorrect**
* **Option A:** Fosphenytoin is a prodrug of phenytoin and is also used in the treatment of status epilepticus, but it is not the next step after Lorazepam.
* **Option B:** Midazolam is a benzodiazepine that can be used to control seizures, but it is not the next step after Lorazepam has been administered.
* **Option D:** Valproate is an AED that can be used in the long-term management of seizures, but it is not the immediate next step in the acute setting.

**Clinical Pearl / High-Yield Fact**
In the acute management of seizures, the goal is to control the seizures as quickly as possible, and AEDs like phenytoin are effective in achieving this goal.

**Correct Answer:** C. Phenytoin