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 containing procainamide hydrochloride and a pharmaceutically acceptable coating therefor, the improvement which comprises incorporating in said core from about 5 to about 15% by weight of one or more hydrocolloid gelling agents having a viscosity of within the range of from about 10,000 to about 200,000 centipoises in 2% solution of 20.degree. C. and are selected from the group consisting of cellulose ethers, cellulose alkyl hydroxylates, cellulose alkyl carboxylates, alkali metal salts of cellulose alkyl carboxylates, gum acacia, guar gum, gum tragacanth, gum xanthan, an alkali metal or alkaline earth metal carageenate, an alginate and mixtures thereof, from 0 to about 8% by weight of one or more non-swellable binders, and from 0 to about 8% by weight of one or more wax-binders and said coating comprises a mixture of at least one hydrophilic polymer and at least one hydrophobic polymer in a weight ratio to each other of within the range of from about 4:1 to about 1:4, and said procainamide hydrochloride is present in said core in an amount of from about 80 to about 95% by weight of the core, which represents an increase in procainamide hydrochloride tablet content of at least about 14% over prior known formulations, the combination of said core and coating providing substantially zero order release of said procainamide hydrochloride.