NEW METHOD FOR DETERMINING THE DIFFUSION-COEFFICIENT OF DRUGS IN SEMISOLID VEHICLES FROM RELEASE DATA

Experimental data on release of benzocaine from a series of hydrophilic gels were used for the evaluation of a new method for determining the diffusion coefficient of drugs in semisolid vehicles. The values of D, the drug diffusivity in the vehicle, and of R, the diffusional resistance of the membrane interposed between releasing and receiving phase, resulted from a fit of the experimental release data to theoretical data generated by numerical analysis of a vehicle-membrane controlled diffusional model. Comparison of the computed D (and R) values with values obtained by different routes, or with literature data, showed the method to be conducive to rather accurate estimates of these parameters, in cases where the requirements of the theoretical model were fulfilled by the experimental system. The results are discussed in terms of validity, accuracy and applicability of the proposed method. Results obtained from systems not complying with the diffusional model are also discussed and evaluated. The computations were executed with the aid of an IBM 370/168 computer. © 1979.