Controlled release formulation

In a controlled release procainamide hydrochloride formulation in the form of a tablet which is adapted to approach zero order release of procainamide hydrochloride over an 8 to 12 hour or more period, which tablet is comprised of a core and a pharmaceutically acceptable coating therefor, said core comprising more than about 70% by weight of procainamide hydrochloride, the improvement which consists essentially of incorporating in said core, from at least about 5 to not more than 15% by weight of one or more primary hydrocolloid gelling agent composed of hydroxypropylmethyl cellulose having a methoxyl content of 28 to 30% having a viscosity of within the range of from about 1,000 to about 6,000 centipoises in 2% solution of 20.degree. C., from 0 to about 7.5% by weight of a secondary hydrocolloid gelling agent which is hydroxypropyl cellulose, from 0 to about 8% by weight of one or more non-swellable binders and/or from 0 to about 8% by weight of one or more wax binders, said non-swellable binder or wax binder being present when said medicament and hydrocolloid gelling agent are non-compressible and from about 1.1 to less than about 4% by weight water, all of said % being based on the weight of said core, and said coating permitting entry of water and hydration of the core, so that there is not a large initial surge in the release of medicament and essentially comprising as film formers a mixture of at least one hydrophobic polymer and at least one hydrophilic polymer in a weight ratio to each other of from about 4:1 to about 1:4.