title: Long-acting gonadotrophin releasing hormone agonist implant causes variable duration of suppression of ovarian steroid and inhibin secretion.
abstract: OBJECTIVE
  The duration of action of a gonadotrophin releasing hormone (GnRH) agonist implant designed to be effective for 3 months was investigated in women by monitoring drug release and ovarian hormone secretion. Serum inhibin secretion was measured to determine whether the secondary rise in serum FSH concentrations observed during long-term GnRH agonist treatment was attributable to changes in inhibin secretion.
  
  
  METHODS
  The implants of slowly biodegradable polylactide/glycolide (molar ratio 75:25) containing 3.3 mg buserelin, D-Ser (But)6-GnRH (1-9)-nonapeptide-ethylamide, in a rod 1 cm long and 0.13 cm diameter were injected s.c. in patients with endometriosis (3.3 mg buserelin in four patients, 6.6 mg buserelin in six patients).
  
  
  METHODS
  Urinary secretion of oestrone, pregnanediol, LH and buserelin were determined in daily samples collected for 2 cycles before treatment, during treatment, and for 2 recovery cycles. Oestradiol, progesterone, inhibin, LH and FSH were measured in serum collected once per week.
  
  
  RESULTS
  In all patients ovarian hormone secretion was suppressed successfully but considerable variability occurred in the length of time taken for ovarian function to recommence, time to return to ovulation being 100-194 days (median 118 days) (3.3 mg group) and 79-290 (median 178 days) (6.6 mg group). After implant injection, there was a rapid rise in the urinary buserelin excretion followed by an early fast phase of buserelin release, half life (t1/2) = 9 days for 3.3 mg implant and 11 days for 6.6 mg implant. This was followed by a second phase representing a plateau of release, t1/2 = 50 days (3.3 mg implant) and 90 days (6.6 mg implant). During this second phase, an excretion rate of greater than 0.2 nmol buserelin/mol Cr was associated with oestrone excretion at or below early follicular phase values. Once buserelin excretion fell below 0.1 nmol/mol Cr, ovarian function returned in all patients. The period for which buserelin secretion was maintained between 0.1 and 0.2 nmol/mol Cr corresponded to the time taken to recovery of ovulatory cycles in 8/10 of the women. In 9/10 patients serum immunoreactive inhibin concentrations declined at 2 weeks, along with the suppression of oestradiol, and remained suppressed throughout the period of anovulation. Recovery of FSH secretion began after 4-5 weeks.
  
  
  CONCLUSIONS
  While this implant should have important clinical application where chronic treatment is indicated, further work is needed on design of long-term implants so that such preparations can be used when precise return to ovarian activity is required. A fall in inhibin secretion may contribute to the secondary rise in FSH by withdrawal of negative feedback but these events are not closely correlated.
authors.affiliation: Centre for Reproductive Biology, Edinburgh, UK.
authors.forename: H M
authors.initials: HM
authors.lastname: Fraser
authors.forename: R
authors.initials: R
authors.lastname: Haining
authors.forename: G M
authors.initials: GM
authors.lastname: Cowen
authors.forename: J
authors.initials: J
authors.lastname: Sandow
authors.forename: K B
authors.initials: KB
authors.lastname: Smith
authors.forename: S K
authors.initials: SK
authors.lastname: Smith
mesh_terms: D000328:Adult; D002064:Buserelin / Q000008:administration & dosage* / Q000493:pharmacokinetics; D004343:Drug Implants; D004715:Endometriosis / Q000097:blood / Q000188:drug therapy* / Q000503:physiopathology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D006207:Half-Life; D006801:Humans; D007265:Inhibins / Q000378:metabolism; D010053:Ovary / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
chemical_list: D004343:Drug Implants; D007265:Inhibins; D005640:Follicle Stimulating Hormone; D002064:Buserelin