Fig. 1: Chemical structures of celecoxib (CEL) and the polymer excipients studied.

a CEL in neutral form with scheme showing the formation of the CEL anionic salt in the presence of NaOH or KOH. b Poly-(1-vinylpyrrolidone-co-vinyl-acetate) (PVP-VA). The polymer studied, PVP-VA 64, has a ratio of 6:4 by mass for the N-vinylpyrrolidone (VP) and vinyl acetate (VA) components. c Hypromellose acetate succinate (HPMCAS). The M-grade contains acetyl and succinoyl groups at 7–11% and 10–14% mass fractions along with methoxyl and hydroxypropoxyl groups at 21–25% and 5–9%66.