The orthorhombic pseudopolymorph of tacrine hydrochloride.

Crystallization of tacrine hydrochloride, an acetylcholinesterase inhibitor used during treatment of mild to moderate Alzheimer's disease, from a water:ethanol solution has resulted in an orthorhombic pseudopolymorph. This orthorhombic form which occurs as a dihydrate shows columns of stacking acridines together with continuous Cl-Owater-Owater-Cl chains and ladder-like ribbons composed of squares and hexagons.