Suppression of follicular phase pituitary-gonadal function by a potent new gonadotropin-releasing hormone antagonist with reduced histamine-releasing properties (ganirelix).

OBJECTIVE: To determine if daily subcutaneous doses of ganirelix will suppress and maintain E2 < or = 30 pg/mL (conversion factor to SI unit, 3.671), the serum profiles of LH and FSH during and after cessation of treatment, the time-course of the resumption of normal ovarian function after ganirelix cessation, and to identify side effects of daily treatment.
DESIGN: Open-label nonrandomized clinical study.
SETTING: Normal human volunteers in an academic research center. PATIENTS: Women 21 to 45 years of age, with documented ovulatory menstrual cycles.
INTERVENTIONS: Ganirelix was administered subcutaneously daily for 8 days. Blood samples were obtained during dosing as well as before and after cessation of dosing. MAIN OUTCOME MEASURES: Changes in serum E2, LH, FSH, P, and ganirelix.
RESULTS: Ganirelix treatment rapidly decreased serum levels of gonadotropins and E2 after both 1 and 2 mg administration. Twenty-four hours after the first dose of ganirelix, E2 decreased from a mean +/- SEM of 50 +/- 8 and 67 +/- 11 pg/mL at baseline to 25 +/- 4 and 20 +/- 3 in the 1 mg and 2 mg groups, respectively. Estradiol remained suppressed (mean levels < 26 pg/mL) on all subsequent 7 days of ganirelix dosing in both groups. After the final dose of ganirelix, there was a rapid return of ovarian function in all volunteers. All women had P levels indicative of ovulation in the subsequent cycle, and the mean number of days from the final ganirelix dose to the next menses was 25.8 +/- 2.1 and 27.3 +/- 1.6 in the 1 and 2 mg groups, respectively.
CONCLUSIONS: Daily ganirelix administration is effective in suppressing the pituitary-gonadal axis and has a side effect profile that should be well tolerated.