Extended release compositions comprising trihexyphenidyl

A pharmaceutical pellet composition comprising:

• a) a core comprising an organic acid;
• b) a first drug layer covering at least a portion of the core;
• and
• c) a functional coat covering at least a portion of the first drug layer,
• wherein the first drug layer comprises trihexyphenidyl hydrochloride and a nonionic water-soluble polymer,
• wherein the functional coat comprises a nonionic water-insoluble polymer and a pore former, wherein the nonionic water-insoluble polymer and the pore former are present in a weight ratio of between about 80:20 and about 98:2,
• wherein the functional coat has a coating weight gain of between about 10% w/w and about 40% w/w, based on the total weight of the pellet without the functional coat,
• wherein the trihexyphenidyl hydrochloride and the organic acid are present in a weight ratio of between about 1:5 and about 1:15,
• wherein the organic acid provides an acid microenvironment within the dosage form and improves the solubility of the trihexyphenidyl hydrochloride, in the portions of the GI tract with a pH of greater than or equal to 5, to maintain a minimum therapeutic plasma concentration of the trihexyphenidyl hydrochloride at such pH, and
• wherein the composition provides extended release of the trihexyphenidyl hydrochloride, with a Cmin:Cmax ratio of >0.4, for a period of at least about 16 hours.