Formulation and optimization of a modified microporous cellulose acetate latex coating for osmotic pumps

A cellulose acetate (CA) latex was modified for use as a microporous coating for osmotic devices. Potassium chloride core tablets were coated with a CA latex formulation containing a plasticizer (triacetin) and a pore-forming agent (urea). To promote the coalescence of the cellulose acetate latex beads into a film on the surface of the tablet, it was necessary to cure the coated tablets, hereafter referred to as devices, at elevated temperatures. The objectives were to determine the effect of four formulation variables (plasticizer level, pore former level, cure time, and cure temperature) on the in vitro KCl release rate and coat burst strength using a full 2(4) factorial experimental design. Burst strength was measured as the number of grams force a depleted device could support before bursting. The results indicated that urea content was the most important variable, followed by triacetin content and cure time. Cure temperature did not influence the results. Response surfaces generated with the experimental values were used to predict a formulation which would have both a high release rate and a high burst strength. This formulation was prepared and tested both in vitro and in vivo in dogs. The in vitro release rate and burst strength results agreed with those predicted by the model. The in vitro and in vivo release rates were not statistically significantly different as determined by ALQ analysis.