Hello, I Am Prescribed The Generic For Fiorinal + Codeine

Hello, I am prescribed the generic for Fiorinal + codeine (Butalbital etc.... / Quite often unless I use same Pharm every time the Pharm fills it as (generic for Fioicet w/cod. I have sensitivity to ascetamophen How can I insure that Rex is filled correctly is there a difference between “ASA”. vs. Compound ?