PRECORNEAL CLEARANCE OF MUCOADHESIVE MICROSPHERES FROM THE RABBIT EYE

The ocular disposition of hydrated In-111-labelled microspheres was in vestigated in the rabbit by gamma scintigraphy. Microspheres of cross- linked poly(acrylic acid) (Carbopol 907) were prepared by a w/o emulsi fication process. An in-vitro mucoadhesion test of prehydrated microsp heres showed that greater adhesion was achieved to a mucus gel at pH 5 .0 compared with pH 7.4. Clearance was a biphasic process with a rapid initial phase preceding a slower basal phase. When hydrated in pH 5.0 phosphate buffered saline, clearance during the basal phase was slowe r compared with a pH 7.4 buffered preparation. Both prehydrated prepar ations were retained on the preocular area during the basal phase for longer periods than non-hydrated microspheres. The retention on the oc ular surface of approximately 25% of the instilled dose would suggest this technology will have application for controlled ophthalmic drug d elivery.