Prolonged Release of Theophylline from Aqueous Suspensions

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Abstract
The dissolution of theophylline from aqueous suspensions was measured by the U.S.P. paddle method. Theophylline release was retarded in the presence of xanthan gum, 1%, sodium alginate, 0.5%, and equi-weight mixtures of gelatin type B and iota carrageenan, 1%. These suspensions formed gels in situ in Simulated Gastric Fluid, U.S.P. Diffusion cell studies suggested that theophylline transport within the formed matrix was due to diffusion through immobilized liquid water. Evidence in support of a diffusion controlled dissolution mechanism in these systems were linearity of the initial section of plots of dissolution against the square route of time, the lack of effect of theophylline particle size on dissolution rate, and the tendency for release from a particular system to become independent of polymer concentration once a sufficiently high concentration was reached.

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