A series of polymers with wide ranges of water absorptivity were prepared and utilized as matrices for the controlled release of drugs. The drugs were introduced into the matrices by use of an appropriate organic solvent. Release rates of erythromycin and erythromycin estolate from hydrogel were analyzed kinetically and found to conform to Higuchi's equation, that is, Mt = A(2DtCsC0)1/2, where Mt is the accumulated amount of released drug at time t, A is the surface area, D is the diffusion coefficient, Cs is the solubility of drug in the hydrogel matrix, and Co is the initial drug content of the preparation in the swollen state. The relationship between the water content of hydrogel and the diffusion coefficient of erythromycin in hydrogel is expressed by the equation D = 3.03 × 10−10 W3.03 (cm2/sec), where W is the water content (%). The release rate of drug can be controlled quantitatively by adjustment of the water content of the hydrogel matrix. A guide to the design for the preparation is suggested. Copyright © 1979 John Wiley & Sons, Inc.
