GAMMA-SCINTIGRAPHY AS A NOVEL METHOD TO STUDY THE DISTRIBUTION AND RETENTION OF A BIOADHESIVE VAGINAL DELIVERY SYSTEM IN SHEEP

The distribution and the retention time of a novel bioadhesive intrava ginal delivery system based on HYAFF microspheres were studied in a sh eep model. In a preliminary experiment, the vagina of the ewe was outl ined by gamma scintigraphy following vaginal administration of a radio labelled gel and this data was used as a reference for subsequent eval uation of the distribution of bioadhesive vaginal formulations. Techne tium-labelled HYAFF microspheres were administered intravaginally, eit her as a dry powder or suspended in a vaginal pessary, and the intensi ty and distribution of radioactivity in the genital tract was determin ed for a period of 12 h. With both HYAFF formulations, the radiolabell ed microspheres were dispersed along the length of the vagina and were retained at this site for the duration of the study. Twelve hours aft er administration, between 60 and 80% of the radioactivity remained wi thin the vagina with retention of the microspheres being slightly high er for the dry powder formulation than for the vaginal pessary. Import antly, there was no indication of movement of the microspheres from th e vagina to the upper levels of the genital tract. These studies furth er demonstrated the potential of HYAFF microspheres as a long-acting i ntravaginal delivery system and illustrated the utility of the sheep m odel and the gamma-scintigraphy methodology for a direct assessment of the distribution, spreading and retention time of bioadhesive formula tions.