BIOAVAILABILITY OF THEOPHYLLINE FROM GLUTARALDEHYDE CROSS-LINKED CASEIN MICROSPHERES IN RABBITS FOLLOWING ORAL-ADMINISTRATION

Theophylline loaded bovine casein microspheres were prepared by the glutaraldehyde cross linking of an aqueous alkaline dispersion of the protein containing the drug in a non-aqueous dispersion medium. The cross-linking of the protein droplets was carried out via the organic phase by the addition of varying quantities of glutaraldehyde- saturated toluene. In vitro release of the drug was examined in simulated gastric fluid at 37 degrees C from spheres having three different cross-linking densities. The bioavailability of theophylline released from the microspheres of different cross-linking densities was studied in rabbits following single oral administration. Microspheres with higher cross-linking densities were found to sustain theophylline release even up to 24 h. The peak serum concentrations of such preparations were well within therapeutic limits. Determinations of in vitro/in vivo correlation based on the data showed that a fairly good relationship exists between in vitro and in vivo release. The study demonstrated the potential of cross-linked milk protein as a matrix for sustained release oral preparations.