In vivo and in vitro release of macromolecules from polymeric drug delivery systems.

In vivo release rates of a macromolecule from an ethylene-vinyl acetate copolymer have been shown to be indistinguishable from those of identical implants tested in vitro. The studies were conducted for approximately 2 months, and two different techniques were used to assess release rates. One of these techniques, using [3H]inulin as a marker, may be particularly useful in future studies assessing in vivo release rates from drug delivery systems. The appearance of [3H]inulin in the urine of rats bearing implants allowed continuous monitoring of release. A histological evaluation of tissue sections surrounding polymer implanted for 7 months showed no inflammatory cell reaction.