The pharmacodynamics and efficacy of Implanon (R) - An overview of the data

Implanon(R) is a long-acting reversible contraceptive method, consisting of a single rod that is applied subdermally. Ovulation inhibition was determi ned by serum progesterone (P) levels and ultrasound scanning (USS) of the o varies. Ovarian function was further assessed by serum estradiol (E-2) leve ls. The effects of Implanon on serum gonadotropin levels (follicle-stimulat ing hormone [FSH] and luteinizing hormone [LH]) and on cervical mucus were also investigated, by means of Insler scores and sperm penetration tests. T he effect on the endometrium was assessed by endometrial biopsies and USS. The Pearl index was calculated over 13 studies performed according to Good Clinical Practice (GCP), including 1716 women using Implanon. Return of ovu lation after implant removal was determined by P levels and USS of the ovar ies. The contraceptive efficacy of Implanon was high, with zero pregnancies duri ng 53,530 cycles (4103 woman-years), resulting in a Pearl index of 0.0 (95% confidence interval, 0.00-0.09). This was achieved by inhibition of ovulat ion, which was reflected by suppressed P levels, as the primary mode of act ion. Ovulation was inhibited, but otherwise ovarian activity was still pres ent (follicle growth, E-2 synthesis). The FSH serum concentrations were onl y slightly lower than preinsertion levels and LH surges were prevented. The viscosity of the cervical mucus was increased. The endometrium was thin bu t not atrophic; it showed primarily inactive or weak proliferation. Return of ovulation after removal of Implanon was rapid. (C) 1998 Elsevier Science Inc. All rights reserved.