Table 6. Coformers That Form Anhydrous and Hydrate Forms of Cocrystals with Theophylline.
| coformer | pKa value of coformer | anhydrous forma | hydrate formb |
|---|---|---|---|
| anthranilic acid | 2.108 | 2:378 | 3:2:4 and 2:1:478 |
| 2,4-dihydroxybenzoic acid | 3.32 | 1:179 | 1:1:180 |
| citric acid | 3.15 | 1:1c,81 | 1:1:181 |
a
Theophylline–acid stoichiometry in anhydrous form.
b
Theophylline–acid–water stoichiometry in hydrate form.
c
The theophylline–citric acid cocrystal formation was confirmed by a PXRD experiment, but it was not possible to grow a crystal for an SXRD measurement and so the 1:1 stoichiometry is hypothetical.