Basic drug compositions with enhanced bioavailability

A composition comprising a basic drug, a drug which forms a zwitterion, or a salt of either entity, admixed with a polymer selected from hydroxypropylmethylcellulose acetate succinate (HPMCAS), cellulose acetate trimellitate (CAT), cellulose acetate phthalate (CAP), hydroxypropylcellulose acetate phthalate (HPCAP), hydroxypropylmethyl-cellulose acetate phthalate (HPMCAP), and methylcellulose acetate phthalate (MCAP). The compositions having improved solubility, hence bioavailability, in the small intestine; Processes for testing such compositions, and methods of using such compositions. The compositions comprise the basic drug, zwitterion, or salt and one or more of the aforementioned polymers. The invention further relates to a method for increasing the bioavailability of a basic or a zwitterionic drug comprising co-administering the basic drug, the zwitterionic drug, or the salt, with one or more of the aforementioned polymers.