In vitro controlled release of bupivacaine from albumin microspheres and a co-matrix formed by microspheres in a poly(lactide-co-glycolide) film.

Albumin microspheres cross-linked with glutaraldehyde and loaded with bupivacaine, a local anaesthetic, were synthesized (138 +/- 59 microm diameter). A matrix formed by bupivacaine-loaded microspheres in a poly(lactide-co-glycolide) film was prepared in order to improve the controlled release of the drug. In vitro release of the drug was determined in phosphate buffer at 37 degrees C in the absence and in the presence of protease type VIII to mimic a biological system. The effect of temperature and protease on bupivacaine as a function of time was examined; both of them cause a degradative effect on the drug. A rapid release (60 +/- 8% of the drug) takes place at 1 h, and maximum release is found at 50 +/- 6 h from microspheres with swelling. In the presence of protease, maximum release of bupivacaine from microspheres is found at 28 +/- 2 h; the microspheres disappear at 8 days. Inclusion of bupivacaine-loaded microspheres in a poly(lactide-co-glycolide) film causes a slower release of the drug, up to 18 days, with swelling. In the presence of protease, the polymer protects bupivacaine-loaded microspheres from degradation, which takes place at 20 days.