Final answer:
Imitrex (sumatriptan) is the drug among the listed options that is not used as a prophylactic product; it is instead used for treating migraine attacks after onset.
Step-by-step explanation:
The drug among the listed options which is not used as a prophylactic agent is b. imitrex. Prophylactic drugs are used to prevent diseases or conditions before they occur.
Amoxicillin is a prophylactic antibiotic used for the prevention of bacterial infections, norgestimate-ethinyl estradiol is a combination contraceptive used as a prophylactic measure to prevent pregnancy, and propranolol is a beta-blocker sometimes used prophylactically to prevent migraines. Imitrex (sumatriptan), on the other hand, is used for the treatment of migraine attacks after they have started and it's not used as prophylactic medication.