Flexeril 5mg tablets contain hydroxypropyl cellulose, hypromellose, lactose, magnesium stearate, starch, titanium dioxide, Yellow D&C #10 Aluminum Lake HT, and Yellow FD&C #6 Aluminum Lake.Flexeril 10mg tablets contain hydroxypropyl cellulose, hypromellose, iron oxide, lactose, magnesium stearate, starch, and titanium dioxide. Fact Table Formula C20H21N License US FDA Bioavailability 55% Legal status US: RX Only Chemical Name Cyclobenzaprine Elimination half-life 12 hours Dosage (Strength) 32 hours (extended-release, range 8-37 hours), 18 hours (immediate release, range 8–37 hours) Pregnancy Consult a doctor Brands Flexeril, Amrix, Fexmid Protein binding 93% PubChem CID 2895 MedlinePlus a682514 ChEBI 3996 ATC code M03BX08 DrugBank DB00924 KEGG D07758 Routes of administration By mouth