Hydrogels for controlled drug delivery.

Physical properties such as number average molecular weight Mn, specific hydrates and changing diffusion coefficient of crystalline/rubbery hydrogels based on poly(ethylene glycol) Mn 3 000-8 000 which affect the diffusion of drugs through the water swollen matrix and across the polymer boundary are discussed. The advantage of starting with a dry, drug-impregnated polymer to obtain the desirable zero order release rate while the hydrogel absorbs water is illustrated. Drugs have been classified into five groups showing different release profiles. The effects of design and loading on the release profile, are described including the first clinical results of morphine loaded hydrogel suppositories.