Cetrotide® (cetrorelix acetate for injection) is a synthetic decapeptide with gonadotropin-releasing hormone (GnRH) antagonistic activity. Cetrorelix acetate is an analog of native GnRH with substitutions of amino acids at positions 1, 2, 3, 6, and 10. The molecular formula is Acetyl-D-3-(2´-naphtyl)-alanine-D-4-chlorophenylalanine-D-3-(3´-pyridyl)-alanine- L-serine-L-tyrosine-D-citruline-L-leucine-L-arginine-L-proline-D-alanine-amide, and the molecular weight is 1431.06, calculated as the anhydrous free base. The structural formula is as follows:
Cetrotide® (cetrorelix acetate for injection) 0.25 mg or 3 mg is a sterile lyophilized powder intended for subcutaneous injection after reconstitution with Sterile Water for Injection, USP (pH 5-8), that comes supplied in either a 1.0 mL (for 0.25 mg vial) or 3.0 mL (for 3 mg vial) pre-filled syringe. Each vial of Cetrotide® 0.25 mg (multiple dose regimen) contains 0.26-0.27 mg cetrorelix acetate, equivalent to 0.25 mg cetrorelix, and 54.80 mg mannitol. Each vial of Cetrotide® 3 mg (single dose regimen) contains 3.12-3.24 mg cetrorelix acetate, equivalent to 3 mg cetrorelix, and 164.40 mg mannitol.
CLINICAL PHARMACOLOGY
GnRH induces the production and release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the gonadotrophic cells of the anterior pituitary. Due to a positive estradiol (E2) feedback at midcycle, GnRH liberation is enhanced resulting in an LH-surge. This LH-surge induces the ovulation of the dominant follicle, resumption of oocyte meiosis and subsequently luteinization as indicated by rising progesterone levels.
Cetrotide® competes with natural GnRH for binding to membrane receptors on pituitary cells and thus controls the release of LH and FSH in a dose-dependent manner. The onset of LH suppression is approximately one hour with the 3 mg dose and two hours with the 0.25 mg dose. This suppression is maintained by continuous treatment and there is a more pronounced effect on LH than on FSH. An initial release of endogenous gonadotropins has not been detected with Cetrotide®, which is consistent with an antagonist effect.
The effects of Cetrotide® on LH and FSH are reversible after discontinuation of treatment. In women, Cetrotide® delays the LH-surge, and consequently ovulation, in a dose-dependent fashion. FSH levels are not affected at the doses used during controlled ovarian stimulation. Following a single 3 mg dose of Cetrotide®, duration of action of at least 4 days has been established. A dose of Cetrotide® 0.25 mg every 24 hours has been shown to maintain the effect.
Pharmacokinetics
The pharmacokinetic parameters of single and multiple doses of Cetrotide® (cetrorelix acetate for injection) in adult healthy female subjects are summarized in Table 1.
Table 1: Pharmacokinetic parameters of Cetrotide® following 3 mg single or 0.25mg single and multiple (daily for 14 days) subcutaneous (sc) administration.
Single dose
Single dose
Multiple dose
3 mg
0.25 mg
0.25 mg
Geometric mean (95%CIln), †arithmetic mean, or * median (min-max)
tmax Time to reach observed maximum plasma concentration
t1/2 Elimination half-life
Cmax Maximum plasma concentration; multiple dose Css, max
AUC Area under the curve; single dose AUC0-inf, multiple dose AUCτ
CL Total plasma clearance
Vz Volume of distribution
a Based on iv administration (n=6, separate study 0013)
No. of subjects
12
12
12
tmax* [h]
1.5
1.0
1.0
(0.5 – 2)
(0.5 – 1.5)
(0.5 – 2)
t1/2* [h]
62.8
5.0
20.6
(38.2 – 108)
(2.4 – 48.8)
(4.1 – 179.3)
Cmax [ng/ml]
28.5
4.97
6.42
(22.5 – 36.2)
(4.17 – 5.92)
(5.18 – 7.96)
AUC [ng·h/ml]
536
31.4
44.5
(451 – 636)
(23.4 – 42.0)
(36.7 – 54.2)
CL† [ml/min·kg]
1.28a
Vz† [l/kg]
1.16a
Absorption
Cetrotide® is rapidly absorbed following subcutaneous injection, maximal plasma concentrations being achieved approximately one to two hours after administration. The mean absolute bioavailability of Cetrotide® following subcutaneous administration to healthy female subjects is 85%.
Distribution
The volume of distribution of Cetrotide® following a single intravenous dose of 3 mg is about 1 l/kg. In vitro protein binding to human plasma is 86%.
Cetrotide® concentrations in follicular fluid and plasma were similar on the day of oocyte pick-up in patients undergoing controlled ovarian stimulation. Following subcutaneous administration of Cetrotide® 0.25 mg and 3 mg, plasma concentrations of cetrorelix were below or in the range of the lower limit of quantitation on the day of oocyte pick-up and embryo transfer.
Metabolism
After subcutaneous administration of 10 mg Cetrotide® to females and males, Cetrotide® and small amounts of (1-9), (1-7), (1-6), and (1-4) peptides were found in bile samples over 24 hours.
In in vitro studies, Cetrotide® was stable against phase I- and phase II-metabolism. Cetrotide® was transformed by peptidases, and the (1-4) peptide was the predominant metabolite.
Excretion
Following subcutaneous administration of 10 mg cetrorelix to males and females, only unchanged cetrorelix was detected in urine. In 24 hours, cetrorelix and small amounts of the (1-9), (1-7), (1-6), and (1-4) peptides were found in bile samples. 2-4% of the dose was eliminated in the urine as unchanged cetrorelix, while 5-10% was eliminated as cetrorelix and the four metabolites in bile. Therefore, only 7-14% of the total dose was recovered as unchanged cetrorelix and metabolites in urine and bile up to 24 hours. The remaining portion of the dose may not have been recovered since bile and urine were not collected for a longer period of time.
Special Populations
Pharmacokinetic investigations have not been performed either in subjects with impaired renal or liver function, or in the elderly, or in children (see PRECAUTIONS). Pharmacokinetic differences in different races have not been determined. There is no evidence of differences in pharmacokinetic parameters for Cetrotide® between healthy subjects and patients undergoing controlled ovarian stimulation.
Drug-Drug Interactions
No formal drug-drug interaction studies have been performed with Cetrotide® (see PRECAUTIONS).
CLINICAL STUDIES
Seven hundred thirty two (732) patients were treated with Cetrotide® (cetrorelix acetate for injection) in five (two Phase 2 dose-finding and three Phase 3) clinical trials. The clinical trial population consisted of Caucasians (95.5%) and Black, Asian, Arabian and others (4.5%). Women were between 19 and 40 years of age (mean: 32). The studies excluded subjects with polycystic ovary syndrome (PCOS), subjects with low or no ovarian reserve, and subjects with stage III-IV endometriosis.
Two dose regimens were investigated in these clinical trials, either a single dose per treatment cycle or multiple dosing. In the Phase 2 studies, a single dose of 3 mg was established as the minimal effective dose for the inhibition of premature LH surges with a protection period of at least 4 days. When Cetrotide® is administered in a multidose regimen, 0.25 mg was established as the minimal effective dose. The extent and duration of LH-suppression is dose dependent.
In the Phase 3 program, efficacy of the single 3 mg dose regimen of Cetrotide® and the multiple 0.25 mg dose regimen of Cetrotide® was established separately in two adequate and well controlled clinical studies utilizing active comparators. A third non-comparative clinical study eva luated only the multiple 0.25 mg dose regimen of Cetrotide®. The ovarian stimulation treatment with recombinant FSH or human menopausal gonadotropin (hMG) was initiated on day 2 or 3 of a normal menstrual cycle. The dose of gonadotropins was administered according to the individual patient’s disposition and response.
In the single dose regimen study, Cetrotide® 3 mg was administered on the day of controlled ovarian stimulation when adequate estradiol levels (400 pg/mL) were obtained, usually on day 7 (range day 5-12). If hCG was not given within 4 days of the 3 mg dose of Cetrotide®, then 0.25 mg of Cetrotide® was administered daily beginning 96 hours after the 3 mg injection until and including the day of hCG administration.
In the two multiple dose regimen studies, Cetrotide® 0.25 mg was started on day 5 or 6 of COS. Both gonadotropins and Cetrotide® were continued daily (multiple dose regimen) until the injection of human chorionic gonadotropin (hCG).
Oocyte pick-up (OPU) followed by in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) as well as embryo transfer (ET) were subsequently performed. The results for Cetrotide® are summarized below in Table 2.
Table 2: Results of Phase 3 Clinical Studies with Cetrotide® (cetrorelix acetate for injection) 3 mg in a single dose (sd) regimen and 0.25 mg in a multiple dose (md) regimen.
