STUDIES ON DRUG-RELEASE FROM A CARBOMER TABLET MATRIX

The purpose of this investigation was to study the drug release mechanisms for tablet matrices of carbomer. Carbomer is a polymer of acrylic acid which is cross-linked with polyalkenyl polyether. The drug and the carbomer were blended and directly compressed into tablets using a laboratory Carver press. The influence of the level of carbomer, the type of drug, and the pH of dissolution media were investigated by measuring drug release kinetics. In general, the release of a relatively neutral molecule (e.g. theophylline) in the pH 7.2 phosphate buffer solution appears to exhibit nearly zero-order kinetics via a diffusion-controlled mechanism for all polymer levels studied (10-85%). The drug release process based on diffusion can be described by the general expression: M(t) = k(1)t(1/2) + k(2)t, where M(t) represents the amount of the drug released at time t, and k(1), k(2) are related to kinetic constants characteristic of the drug delivery systems. The release kinetics are modified when an ionic species, such as sodium salicylate, is incorporated into the tablet matrix.