Theophylline tablets coated with aqueous latexes containing dispersed pore formers

Constant drug release was achieved from theophylline tablets coated with a multiporous membrane in an aqueous environment. The tablets were coated with an aqueous acrylic latex containing a dispersed pore-forming agent with pH-dependent solubility characteristics. The pore former, dibasic calcium phosphate, was insoluble in the latex but leached out rapidly in 0.1 M HCl. Theophylline was then released at a constant rate through the multiporous membrane. The drug release was a function of the level of the pore-forming agent and the membrane thickness, but independent of the pH of the dissolution medium and the degree of agitation.