THE PLASMA CONCENTRATION OF A SYNTHETIC PROGESTIN, R 2323, RELEASED FROM POLYSILASTIC VAGINAL RINGS Lasse Viinikka, M.D.*' Arne Victor, M.D.*" Olli Jlnne, M.D.X2 Jean-Pierre Raynaud, Ph.D.%%* 'Steroid Research Laboratory, Department of Medical Chemistry, University of Helsinki, SF-00170 Helsinki 17, Finland, "*University Hospital, Department of Obstetrics and Gynaecology, S-750 12 Uppsala, Sweden XXXCentre de Recherches, Roussel-Uclaf, 93230 Romainville, France ABSTRACT The present study was undertaken to study the release of a synthetic progestin, R 2323 (13-ethy1-17-hydroxy-18,19-dinor-17~-pregna-4,9,11-trien- 20-yn-3-one), from polysiloxane vaginal rings. Fourteen healthy, normally menstruating women took part in the study. The vaginal rings containing lo,50 or 200 mg of R 2323 were inserted on the first day after menstrual bleeding had ceased and were left in the vagina for three weeks. Blood samples were taken at two-to five-day intervals and the plasma concen- tration of R 2323 was determined by radioinnnunoassay. The results show that the initial release of the steroid is rapid. The highest concentration measured was always in the first sample, usually taken on the first or second day after the insertion. After that the concentrations decreased rapidly. 'Present address: Department of Clinical Chemistry, University of Oulu, SF-90220 Oulu 22, Finland (Correspondence) 2 Present address: Department of Medicine, Division of Endocrinology, The Milton S. Hershey Medical Center, The Pennsylvania State University, Hershey, Pa 17033, U. S. A. Accepted for publication December 18, 1974 zyxwvutsrqponmlkjihgfedcbaZYX SEPTEMBER 1975 VOL. 12 NO. 3 309