CLINICAL PHARMACOLOGY
The pulsatile release of GnRH stimulates the synthesis and secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The frequency of LH pulses in the mid and late follicular phase is approximately 1 pulse per hour. These pulses can be detected as transient rises in serum LH. At midcycle, a large increase in GnRH release results in an LH surge. The midcycle LH surge initiates several physiologic actions including: ovulation, resumption of meiosis in the oocyte, and luteinization. Luteinization results in a rise in serum progesterone with an accompanying decrease in estradiol levels.
Ganirelix Acetate acts by competitively blocking the GnRH receptors on the
pituitary gonadotroph and subsequent transduction pathway. It induces a rapid,
reversible suppression of gonadotropin secretion. The suppression of pituitary
LH secretion by Ganirelix Acetate is more pronounced than that of FSH. An initial
release of endogenous gonadotropins has not been detected with Ganirelix Acetate,
which is consistent with an antagonist effect. Upon discontinuation of Ganirelix
Acetate, pituitary LH and FSH levels are fully recovered within 48 hours.
Pharmacokinetics
The pharmacokinetic parameters of single and multiple injections of Ganirelix
Acetate Injection in healthy adult females are summarized in Table I. Steady-state
serum concentrations are reached after 3 days of treatment. The pharmacokinetics
of Ganirelix Acetate are dose-proportional in the dose range of 125 to 500 µg.
TABLE I: Mean (SD) pharmacokinetic parameters of 250 µg of
Ganirelix Acetate following a single subcutaneous (SC) injection (n=15) and
daily SC injections (n=15) for seven days.
|
tmax h |
t1/2 h |
Cmax
ng/mL |
AUC
ng•h/mL |
CL/F L/h |
Vd/F L |
Ganirelix Acetate single dose |
1.1 (0.3) |
12.8 (4.3) |
14.8 (3.2) |
96 (12) |
2.4 (0.2)† |
43.7 (11.4)† |
Ganirelix Acetate multiple dose |
1.1 (0.2) |
16.2 (1.6) |
11.2 (2.4) |
77.1 (9.8) |
3.3 (0.4) |
76.5 (10.3) |
tmax Time to maximum concentration
t1/2 Elimination half-life
Cmax Maximum serum concentration
AUC Area under the curve; Single dose: AUC0-&inifn;; multiple
dose: AUC0-24
Vd Volume of distribution
† Based on intravenous administration CL Clearance = Dose/AUC0-&inifn;
F Absolute bioavailability |
Absorption
Ganirelix Acetate is rapidly absorbed following subcutaneous injection with
maximum serum concentrations reached approximately one hour after dosing. The
mean absolute bioavailability of Ganirelix Acetate following a single 250 µg
subcutaneous injection to healthy female volunteers is 91.1%
Distribution
The mean (SD) volume of distribution of Ganirelix Acetate in healthy females
following intravenous administration of a single 250 µg dose is 43.7 (11.4)
liters (L). In vitro protein binding to human plasma is 81.9%.
Metabolism
Following single dose intravenous administration of radiolabeled Ganirelix Acetate to healthy female volunteers, Ganirelix Acetate is the major compound present in the plasma (50-70% of total radioactivity in the plasma) up to 4 hours and urine (17.1-18.4% of administered dose) up to 24 hours. Ganirelix Acetate is not found in the feces. The 1-4 peptide and 1-6 peptide of Ganirelix Acetate are the primary metabolites observed in the feces.
Excretion
On average, 97.2% of the total radiolabeled Ganirelix Acetate dose is recovered
in the feces and urine (75.1% and 22.1%, respectively) over 288 h following
intravenous single dose administration of 1 mg [14C]-Ganirelix Acetate.
Urinary excretion is virtually complete in 24 h, whereas fecal excretion starts
to plateau 192 h after dosing.
Special Populations
The pharmacokinetics of Ganirelix Acetate Injection (ganirelix) has not been determined
in special populations such as geriatric, pediatric, renally impaired and hepatically
impaired patients (see PRECAUTIONS).
Drug-Drug Interactions
Formal in vivo or in vitro drug-drug interaction studies have
not been conducted (see PRECAUTIONS). Since Ganirelix Acetate can suppress
the secretion of pituitary gonadotropins, dose adjustments of exogenous gonadotropins
may be necessary when used during controlled ovarian hyperstimulation (COH).
Clinical Studies
The efficacy of Ganirelix Acetate Injection (ganirelix) was established in two adequate
and well-controlled clinical studies which included women with normal endocrine
and pelvic ultrasound parameters. The studies intended to exclude subjects with
polycystic ovary syndrome (PCOS) and subjects with low or no ovarian reserve.
One cycle of study medication was administered to each randomized subject. For
both studies, the administration of exogenous recombinant FSH [Follistim®
(follitropin beta for injection)] 150 IU daily was initiated on the morning
of Day 2 or 3 of a natural menstrual cycle. Ganirelix Acetate Injection (ganirelix) was
administered on the morning of Day 7 or 8 (Day 6 of recombinant FSH administration).
The dose of recombinant FSH administered was adjusted according to individual
responses starting on the day of initiation of Ganirelix Acetate. Both recombinant
FSH and Ganirelix Acetate were continued daily until at least three follicles
were 17 mm or greater in diameter at which time hCG [Pregnyl® (chorionic
gonadotropin for injection, USP)] was administered. Following hCG administration,
Ganirelix Acetate and recombinant FSH administration were discontinued. Oocyte
retrieval, followed by in vitro fertilization (IVF) or intracytoplasmatic
sperm injection (ICSI), was subsequently performed.
In a multicenter, double-blind, randomized, dose-finding study, the safety
and efficacy of Ganirelix Acetate Injection (ganirelix) were evaluated for the prevention
of LH surges in women undergoing COH with recombinant FSH. Ganirelix Acetate
Injection doses ranging from 62.5 µg to 2000 µg and recombinant FSH were administered
to 332 patients undergoing COH for IVF (see TABLE II). Median serum LH on the
day of hCG administration decreased with increasing doses of Ganirelix Acetate.
Median serum E2 (17β-estradiol) on the day of hCG administration was 1475,
1110, and 1160 pg/mL for the 62.5, 125, and 250 µg doses, respectively. Lower
peak serum E2 levels of 823, 703, and 441 pg/mL were seen at higher
doses of Ganirelix Acetate 500, 1000, and 2000 µg, respectively. The highest
pregnancy and implantation rates were achieved with the 250 µg dose of Ganirelix
Acetate Injection as summarized in Table II.
TABLE II: Results from the multicenter, double-blind, randomized,
dose-finding study to assess the efficacy of Ganirelix Acetate Injection (ganirelix) to
prevent premature LH surges in women undergoing COH with recombinant FSH.
|
Daily dose (µg) of Ganirelix Acetate Injection |
62.5 µg |
125 µg |
250 µg |
500 µg |
1000 µg |
2000 µg |
No. subjects receiving Ganirelix Acetate |
31 |
66 |
70 |
69 |
66 |
30 |
No. subjects with ET† |
27 |
61 |
62 |
54 |
61 |
27 |
No. of subjects with LH rise ≥ 10 mIU/mL* |
4 |
6 |
1 |
0 |
0 |
0 |
Serum LH (mIU/mL) on day of hCG‡
5 th-95th percentiles |
3.6
0.6-19.9 |
2.5
0.6-11.4 |
1.7
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