Controlled drug release from polymeric delivery devices IV: in vitro--in vivo correlation of subcutaneous release of norgestomet from hydrophilic implants.

The in vitro and in vivo releases of norgestomet from hydrophilic implants were found to follow a matrix-controlled (Q - t1/2) process. The sorption of drug onto the implants was observed to obey the same mechanism but with a much smaller magnitide of the Q/t1/2 value. The effect of the extent of cross-linking on the magnitude of drug release (Q/t1/2) profiles was analyzed both theoretically and experimentally. The release of norgestomet from hydrophilic implants was found to be an energy-linked process. Two energy terms were calculated; the activation energy for matrix diffusion was 7.71 kcal/mole, and the heat of drug crystal solvation was 25-28.6 kcal/mole.