The Effect of HPMCAS Functional Groups on Drug Crystallization from the Supersaturated State and Dissolution Improvement

The inhibitory effect on drug crystallization in aqueous solution was evaluated using various forms of hydroxypropyl methylcellulose acetate succinate (HPMCAS). HPMCAS suppressed crystallization of carbamazepine (CBZ), nifedipine (NIF), mefenamic acid, and dexamethasone. The inhibition of drug crystallization mainly derived from molecular level hydrophobic interactions between the drug and HPMCAS. HPMCAS with a lower succinoyl substituent ratio strongly suppressed drug crystallization. The inhibition of crystallization was affected by pH, with the CBZ crystallization being inhibited at a higher pH due to the hydrophilization of HPMCAS derived from succinoyl ionization. The molecular mobility of CBZ in an HPMCAS solution was evaluated by 1D-(1)H NMR and relaxation time measurements. CBZ mobility was strongly suppressed in the HPMCAS solutions where strong inhibitory effects on CBZ crystallization were observed. The mobility suppression of CBZ in the HPMCAS solution was derived from intermolecular interactions between CBZ and HPMCAS leading to an inhibition of crystallization. The effect of HPMCAS on the drug dissolution rate was evaluated using an NIF/HPMCAS solid dispersion. The dissolution rate of NIF was increased when HPMCAS with a higher succinoyl substituent ratio was used.