BILIARY-EXCRETION OF POLYSTYRENE MICROSPHERES WITH COVALENTLY-LINKED FITC FLUORESCENCE AFTER ORAL AND PARENTERAL ADMINISTRATION TO MALE WISTAR RATS

To further our understanding of microspheres as a drug delivery system , the biliary excretion of covalently linked FITC fluorescence polysty rene microspheres of various diameters was investigated after oral and parenteral administration to male Wistar rats. About 36%, 16%, 3% and 1% of the dose was excreted into the bile after parenteral injection of 50 nm, 500 nm, 1 mu m and 3 mu m diameter microspheres, respectivel y, over 24 h. In addition, about 30%, 11%, 1%, and 1% of the dose, res pectively, was found in the blood at 24 h. After oral administration o f 50 nm, 500 nm, and 1 Fun microspheres, the recovery was about 18%, 8 % and 1% of the dose in the bile and about 9%, 1%, and 0% in the blood , respectively. No 3 mu m microspheres were detected in the bile or bl ood after oral administration. Particles were not detected in the urin e of any group tested. Thus, the present study demonstrated that bilia ry excretion plays an important role in the disposition of microsphere s administered by the oral or parenteral routes, and there is a size-r elated excretion of microspheres into the bile.