A hydrate of an acid addition bis-salt of an anthranilic acid derivative is produced by a process which comprises: (a) combining, in any order, the anthranalic acid derivative, a pharmaceutically acceptable organic solvent, an excess of water and a pharmaceutically acceptable strong acid to form a mixture; (b) warming the mixture until a clear solution forms; (c) filtering the solution while it is warm, to yield a filtrate; and (d) recovering the hydrate as defined above from the filtrate. The hydrate has a defined number of moles of water of crystallization and possesses better storage stability and dissolution characteristics than conventionally produced hydrates of such acid addition bis-salts.