Final answer:
The generic substitution for Imitrex, a migraine medication, is Sumatriptan. It works by constricting blood vessels in the brain and blocking pain pathways.
Step-by-step explanation:
The appropriate generic substitution for Imitrex, which is a brand name medication, is Sumatriptan. Imitrex is a triptan drug that is used for the treatment of migraines and its generic form is Sumatriptan. Triptans work by constricting blood vessels around the brain and blocking pain pathways in the brain. Each option listed (A. Almotriptan, B. Sumatriptan, C. Rizatriptan, D. Eletriptan, E. Zolmitriptan) represents a different triptan medication, but the one that is identical to Imitrex is Sumatriptan, choice B.