Final Answer:
The appropriate generic substitution for Maxalt in this prescription is **C. Rizatriptan.**
Step-by-step explanation:
1. **Maxalt 5mg PO at first sign of migraine:** This part of the prescription indicates the specific medication (Maxalt) and the recommended dosage (5mg by mouth) to be taken at the initial signs of a migraine.
2. **Can repeat x 1 if migraine pain persists:** This part of the prescription allows for one additional dose if the migraine pain persists after the initial dose.
(C. Rizatriptan):
Rizatriptan is a triptan medication, like Maxalt, commonly prescribed for the acute treatment of migraines. It works by narrowing blood vessels in the brain, alleviating migraine symptoms. As the prescription specifies Maxalt, the appropriate generic substitution is Rizatriptan, making option C the correct choice.