The influence of polymer concentration on the 5-fluorouracil release rate from carbopol hydrogels

5-Fluorouracil (5-FU) release kinetics from Carbopol 940 hydrogels prepared at pH 5.5 and five different polymer concentrations (0.0010, 0.0015, 0.0020, 0.0025 and 0.0030 w/w) were determined using Franz diffusion cells. Higuchi's equation for release from solutions was used to calculate the diffusion coefficients of 5-FU in the hydrogels. An empirical equation was obtained for the estimation of diffusivity of 5-FU as a function of polymer concentration, which from a practical view point can be considered useful in preformulation studies. Furthermore, the values of viscosity for all hydrogels assayed were determined. The diffusivity-viscosity relationship resembles the Stokes-Einstein equation for small solutes in liquid phases and provides a factor indicative of additional resistance offered by the gelling agent for drug diffusion.