Pharmacokinetics, bioavailability and metabolism of cligosiban, an antagonist of oxytocin receptor, in rat by liquid chromatography hyphenated with electrospray ionization tandem mass spectrometry.

Cligosiban is a highly-affinity nonpeptide oxytocin receptor antagonist. In this study, a simple an sensitive LC-MS/MS method was developed and validated for the determination of cligosiban in rat plasma. The plasma samples were pretreated with acetonitrile as precipitant and then separated on an ACQUITY BEH C18 column (2.1 × 50 mm, 1.7 µm) with 0.1% formic acid in water and acetonitrile as mobile phase. The analytes were monitored using selected reaction monitoring (SRM) mode with transitions at m/z 420.1→248.1 for cligosiban and m/z 304.1→161.1 for IS. The developed method showed good linearity over the concentration range of 1-1000 ng/mL with coefficient of correlation > 0.996. The lower limit of quantification (LLOQ) is 1 ng/mL. The method was validated for selectivity, precision, accuracy, recovery, and stability in accordance with FDA's guidance. The validated assay has been successfully applied to the pharmacokinetic study of cligosiban in rat plasma after intravenous and oral administration. According to the current results, the oral bioavailability of cligosiban was 63.82%. Furthermore, the metabolites present in rat liver microsomes (RLM), human liver microsomes (HLM) and rat plasma were analyzed by UHPLC-LTQ-Orbitrap-MS method, and four metabolites structurally identified based on their accurate masses, and fragment ions. The proposed metabolic pathways of cligosiban were demethylation and glucuronidation. This study is the first report on the pharmacokinetic and metabolic information of cligosiban, which would provide insights into the effectiveness and toxicity of cligosiban.

Elagolix Pharmacokinetic Profiles in Women With Renal or Hepatic Impairment.

The aim of these studies was to assess the safety and pharmacokinetics of elagolix, an oral nonpeptide gonadotropin-releasing hormone antagonist following oral administration in women with renal or hepatic impairment. Two phase 1 studies were conducted in adult women with normal renal function versus renal impairment (reduced study), and normal hepatic function versus hepatic impairment (full study design). All women received a single dose of elagolix 200 mg (renal) or 150 mg (hepatic). Intensive pharmacokinetic blood samples were collected. Elagolix exposures were comparable in women with normal renal function and those with moderate/severe renal impairment or end-stage renal disease. Elagolix exposures also appeared to be similar in women with normal hepatic function and women with mild hepatic impairment. Elagolix area under the curve in women with moderate hepatic impairment and with severe hepatic impairment was approximately 3-fold and 7-fold higher than in women with normal hepatic function. The adverse event incidence was low, with the main events being mild nausea and headache. No dosage adjustment was needed in women with renal impairment or women with mild hepatic impairment. Although an elagolix dose of 150 mg once daily may be used in women with moderate hepatic impairment for up to 6 months, this elagolix dose should not be used in women with severe hepatic impairment.

A single- and multiple-dose study to investigate the pharmacokinetics of epelsiban and its metabolite, GSK2395448, in healthy female volunteers.

An open-label single- and repeat-dose study was conducted to investigate the pharmacokinetics, safety, and tolerability of ascending doses of epelsiban in healthy female volunteers (n = 48). The pharmacokinetics of the epelsiban metabolite, GSK2395448, were also assessed. Epelsiban was readily absorbed and parent and metabolite readily appeared in plasma. The parent drug's median tmax was approximately 0.5 hours, and the metabolite's median tmax ranged from 0.5 to 1.0 hours post-parent dosing. Both epelsiban and GSK2395448 had rapid elimination half-lives, ranging between 2.66 and 4.85 hours. The metabolite:parent ratios for exposure (AUC and Cmax ) ranged from approximately 70% to greater than 100%, and therefore, GSK2395448 is considered a major metabolite of epelsiban. Mean epelsiban and GSK2395448 AUC values increased in a dose-proportional manner following both single-dose administration from 10 to 200 mg and repeat administration from 10 to 150 mg following twice daily or 4-times-daily dosing. Single-dose epelsiban pharmacokinetics in women was similar to single-dose pharmacokinetics previously observed in men. Epelsiban was generally well tolerated, and no events of clinical concern were observed in volunteers dosed in this study. The safety findings were consistent with the previous study in men, with headache the most commonly reported adverse effect.

Oil-based formulation as a sustained-released injection for a novel synthetic peptide.

In this study, sustained-release of GnRH antagonist peptide LXT-101 was realized through oil formulation, and their releasing characteristics in vitro and in vivo were investigated. In this formulation, the static interaction between cationic charged peptide LXT-101 and the negative charged phospholipid led to the formation of the phospholipid-peptide complex, by which LXT-101 was completely dissolved in oils. This formulation was prepared by mixing an aqueous solution of LXT-101 and empty SUV (small unilamellar liposomes) containing EPC (phosphatidylcholine) and DPPG (1, 2-dipalmitog-sn-glycero-3- phosphoglycerol) at an appropriate ratio, the mixture was subsequently lyophilized, and the resultant was dissolved in the oil to form a clear oily solution containing solubilized peptide LXT-101. With atomic force microscopy combined with Langmuir-Blodgett technology, the morphology of the particles in the oily solution were examined to be oval-shaped and the mean particle size was 150 nm in diameter. In pure water at 37°C, about 70~90 % of LXT-101 was released slowly from the oily formulation over 7 days. An effective sustained suppression of testosterone in beagle dogs could be achieved over a period of seven days with this LXT-101 oily formulation, by i.m. at a dose of 0.2 mg/kg (2 mg/ml). This formulation dramatically improved the bioactivity of LXT-101 compared to its aqueous solution. It was also found that when the concentration of peptide LXT-101 was up to or over 10 mg/ml in aqueous solution, there was no significant difference between the oily formulation and aqueous solution. This fact meant that LXT-101 itself could conduct sustained release in vivo by self-assembly of nanofibers.

Evidence of GnRH antagonist escape in obese women.

CONTEXT: Assisted reproductive technology (ART) cycle cancelation rates are increased among overweight and obese women; however, the reasons for this are not completely clear. Premature luteinization due to inadequate endogenous gonadotropin suppression is a possibility for this higher risk of cancellation. OBJECTIVE: The objective of the study was to investigate the impact of female obesity on the pharmacokinetics of cetrorelix (GnRH antagonist). DESIGN: This was an interventional study. SETTING: The study was conducted at a university clinical and translational research center. PARTICIPANTS: Regularly menstruating obese (n = 10) and normal-weight (n = 10) women participated in the study. INTERVENTIONS: A frequent blood sampling study was performed after a GnRH antagonist was administered, followed by recombinant LH. MAIN OUTCOMES MEASURED: Pharmacokinetics of cetrorelix in obese vs normal weight women were measured. RESULTS: Five of the obese women (50%) and none of the normal-weight women had a rebound of LH (defined as >50% increase in LH level from nadir) over the 14-hour postdose observation period. The obese group had a significantly decreased distributional half-life of cetrorelix compared with the normal-weight group (8.1 ± 1.6 vs 12.7 ± 6.2 hours, P = .02). The obese group exhibited increased clearance of cetrorelix compared with the normal-weight group (25.8 ± 6.8 vs 20.1 ± 8.3 L/h, P = .058). CONCLUSIONS: The altered pharmacokinetics of cetrorelix in obese women may lead to premature ovulation during ART, and this could be one of the mechanisms that results in increased cycle cancelation in this group of women. In accordance with the higher gonadotropin requirements for obese women undergoing ART, weight-based dosing of GnRH antagonists may be required.

Development and validation of an LC-MS/MS-ESI method for the determination of lorglumide, a CCK-1 antagonist in mouse plasma: application to a pharmacokinetic study.

A highly sensitive, rapid assay method was developed and validated for the estimation of lorglumide in mouse plasma using liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in positive-ion mode. The assay procedure involves extraction of lorglumide and phenacetin (internal standard, IS) from mouse plasma with simple protein precipitation. Chromatographic separation was achieved using an isocratic mobile (0.2% formic acid solution-acetonitrile, 20:80, v/v) at a flow-rate of 0.5 mL/min on an Atlantis dC18 column maintained at 40 °C with a total run time of 4.0 min. The MS/MS ion transitions monitored were 459.2 → 158.4 for lorglumide and 180.1 → 110.1 for IS. Method validation was performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.42 ng/mL and the linearity range extended from 0.42 to 500 ng/mL. The intra- and inter-day precisions were in the ranges of 1.47-10.9 and 3.56-7.53, respectively.

In vitro P-glycoprotein interactions and steady-state pharmacokinetic interactions between tolvaptan and digoxin in healthy subjects.

Interactions between tolvaptan and digoxin were determined in an open-label, sequential study where 14 healthy subjects received tolvaptan 60 mg once daily (QD) on days 1 and 12 to 16 and digoxin 0.25 mg QD on days 5 to 16. Mean maximal concentrations (C(max)) and area under the curve during the dosing interval (AUC(τ)) for digoxin with tolvaptan (day 16) were increased 1.27- and 1.18-fold compared with digoxin alone (day 11); mean renal clearance of digoxin was decreased by 59% (P < .05). Tolvaptan C(max) and AUC(0-24h) for a single dose with digoxin (day 12) were each increased about 10% compared with tolvaptan alone (day 1). Tolvaptan did not accumulate upon multiple dosing. After a single dose of tolvaptan (day 1, day 12), 24-hour urine volume was about 7.5 L. As expected, after 5 days of tolvaptan, 24-hour urine volume decreased about 20%. In vitro studies in control and MDR1-expressing LLC-PK1 cells indicate that tolvaptan is a substrate of P-glycoprotein. Tolvaptan (50 µM) inhibited basolateral to apical digoxin secretion to the same extent as 30 µM verapamil; the IC50 of tolvaptan was determined to be 15.9 µM. The increase in steady-state digoxin concentrations is likely mediated by tolvaptan inhibition of digoxin secretion.

Quantitative determination of oxytocin receptor antagonist atosiban in rat plasma by liquid chromatography-tandem mass spectrometry.

A kinetic study of atosiban was conducted following repeated intravenous administration in Wistar rats. Sample analysis was performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) following full validation of an in-house method. Eptifibatide, a cyclic peptide, was used as an internal standard (IS). The analyte and internal standard were extracted using solid phase extraction (SPE) method. Chromatographic separation was carried out using an ACE C18 5 microm 50 mm x 4.6 mm column with gradient elution. Mass spectrometric detection was performed using TSQ Quantum ultra AM. The lower limit of quantification was 0.01 microg/ml when 100 microl rat plasma was used. Plasma concentrations of atosiban were measured at 0 (pre-dose), 2, 15, 30, 45, 60, 120 min at the dosage levels of 0.125 mg/kg (low dose), 0.250 mg/kg (mid dose), and 0.500 mg/kg (high dose), respectively. Atosiban plasma concentration measured at Day 1 showed mean peak atosiban concentration (C(max)) 0.40, 0.57, 1.95 microg/ml for low, mid and high dose treated animals and mean peak concentration on Day 28 was 0.41, 0.88, 1.31microg/ml on Day 28 for low, mid and high dose treated animals.

V1/V2 Vasopressin receptor antagonism potentiates the renoprotection of renin-angiotensin system inhibition in rats with renal mass reduction.

Blockade of the renin-angiotensin system (RAS), the standard treatment for chronic proteinuric nephropathy, slows but may not halt progression of the disease, particularly when therapy is started late. Because vasopressin may also play a role in the progression of renal disease, we measured the effect of a dual V(1a) and V(2) vasopressin receptor antagonist (RWJ-676070) alone or combined with angiotensin-converting enzyme inhibition or angiotensin II type 1 receptor blockade on proteinuria and renal disease progression during overt nephropathy. Twenty-one days after renal mass reduction, a time of established injury, rats were given vehicle, RWJ-676070, enalapril, losartan, RWJ-676070 plus enalapril, or losartan in drinking water for an additional 39 days. RWJ-676070 returned the blood pressure to pre-treatment levels, which were significantly lower than those in vehicle-treated rats. Enalapril, losartan, and the combined therapies reduced blood pressure to a greater extent. RWJ-676070 afforded a partial antiproteinuric effect, which was enhanced by the addition of enalapril or losartan. Renal functional impairment, and glomerular and tubular changes were partially ameliorated by RWJ-676070; parameters significantly improved with either enalapril or losartan alone and improved to a greater extent with the combined therapies. Our findings suggest that vasopressin receptor antagonists could be of additional therapeutic value in the treatment of chronic proteinuric nephropathy.

Quantitative analysis of RU38486 (mifepristone) by HPLC triple quadrupole mass spectrometry.

A sensitive liquid chromatography-mass spectrometric method was validated for the quantification of RU38486 (mifepristone) in human and murine plasma. The analyte and internal standard (alfaxolone) were extracted by liquid-liquid extraction with diethyl ether, resolved on a C18 column using gradient elution with methanol and ammonium acetate and detected after positive electrospray ionization (m/z 430-->372; m/z 333-->297, respectively). Quantification was linear over the range 0.5-500ng (r(2)>0.997), precise and accurate (intra-assay RSD< or =7.2%, RME< or =8.2%; inter-assay RSD< or =15.7% RME< or =10.2%). The limit of quantification (LOQ) was 50pg injected on column, permitting reproducible analysis of RU38486 in small volumes of plasma.

Serum cetrorelix concentrations do not affect clinical pregnancy outcome in assisted reproduction.

OBJECTIVE: To analyze the potential association between serum cetrorelix levels and clinical pregnancy outcome in patients who had undergone assisted reproduction cycles with a GnRH antagonist cetrorelix acetate 3-mg injection. DESIGN: Retrospective case-control study. SETTING: University-affiliated private-assisted reproduction center. PATIENT(S): 130 IVF and intracytoplasmic sperm injection first cycles, treated with the same cetrorelix acetate protocol, in two matched groups according to whether the cycle resulted in clinical pregnancy (n = 56) or not (n = 74). INTERVENTION(S): Cetrorelix acetate administration at 3 mg in a sandwich protocol. MAIN OUTCOME MEASURE(S): Serum cetrorelix concentrations on the day of hCG administration with regard to clinical pregnancy outcome, pre- versus post-hCG percent change in serum E(2) levels and implantation rates. RESULT(S): The cetrorelix serum concentrations were in the range of 0.29 to 5.12 ng/mL. The comparisons between groups with and without clinical pregnancy revealed comparable serum cetrorelix levels. There was no significant correlation between the serum cetrorelix concentrations and percent change in pre- versus post-hCG serum E(2) levels. Serum cetrorelix levels were comparable among patients with various implantation rates. CONCLUSION(S): Although a wide range of serum cetrorelix levels could be detected during a GnRH antagonist cycle, these levels were comparable in patients with and without clinical pregnancies.

Peripherally administered non-peptide oxytocin antagonist, L368,899, accumulates in limbic brain areas: a new pharmacological tool for the study of social motivation in non-human primates.

Central administration of oxytocin (OT) antagonists inhibits maternal and sexual behavior in non-primates, providing the strongest experimental evidence that endogenous OT facilitates these behaviors. While there have been a few reports that ICV administration of OT increases social behaviors in monkeys, no studies to date have assessed the effects of OT antagonists. Therefore, we studied in rhesus monkeys whether L368,899, a non-peptide antagonist produced by Merck that selectively blocks the human uterine OT receptor, penetrates the CNS after peripheral administration and alters female maternal and sexual behavior. In two studies in four male monkeys, L368,899 was injected iv (1 mg/kg) after which (1) CSF samples were collected at intervals over 4 h and (2) brains were collected at 60 min. Assay of samples confirmed that iv-administered L368,899 entered CSF and accumulated in the hypothalamus, septum, orbitofrontal cortex, amygdala and hippocampus, but not other areas. An adult female monkey was tested for interest in either an infant or sexual behavior, receiving a different iv treatment prior to each test (1 or 3 mg/kg of L368,899 or saline). OT antagonist treatment reduced or eliminated interest in the infant and sexual behavior. These results, although preliminary, are the first to directly implicate endogenous OT in activation of primate maternal interest and sexual behavior. While it remains to be empirically demonstrated that peripherally administered L368,899 blocks central OT receptors, our behavioral findings suggest that this non-peptide antagonist may facilitate testing OT involvement in a variety of social and other behaviors in primates.

Dose-finding study of daily gonadotropin-releasing hormone (GnRH) antagonist for the prevention of premature luteinizing hormone surges in IVF/ICSI patients: antide and hormone levels.

BACKGROUND: The aim of this study was to define the minimal effective dose of antide (Iturelix) to prevent premature luteinizing hormone (LH) surges in in vitro fertilization (IVF) patients. METHODS: In a prospective, single centre study, 144 IVF/ICSI patients were stimulated with r-hFSH from cycle day 2 and from cycle day 6 onwards, cotreated with daily 2 mg/2 ml (n=30), 1 mg/ml (n=30), 0.5 mg/ml (n=31), 0.5 mg/0.5 ml (n=23) and 0.25 mg/ml (n=30) GnRH antagonist (antide). Serum samples were taken three times daily during antide administration to assess antide and hormone levels. The minimal effective dose was defined as the lowest dose group with <2 LH surges (LH >12.4 IU/l and progesterone >2 ng/ml). RESULTS: Serum antide levels, mean LH and E2 levels per day and their area under the curves were dose-related to antide. The bioavailability of antide almost doubled after dilution in larger volumes. Pre-injection LH levels gradually increased during GnRH antagonist treatment. LH surges occurred in the lowest dose groups 0.5 mg/ml (3.2%), 0.5 mg/0.5 ml (6.7%) and 0.25 mg/ml (13.3%). Hence, 0.5 mg/ml is considered to be the minimal effective dose. Antide was overall well tolerated and safe. CONCLUSIONS: 0.5 mg/ml antide is the minimal effective dose to prevent an untimely LH surge in IVF patients stimulated with r-hFSH.

Development of a radioreceptor assay for measuring an oxytocin antagonist in blood.

The purpose of the present study was to develop a radioreceptor assay to monitor the pharmacokinetics of the oxytocin antagonist, TT-235, in the blood of the pregnant rat and baboon. The receptors used for this assay were prepared from the pregnant rat uterus at delivery. The assay using blood from pregnant rats and baboons was performed on filter plates and analyzed for radioactivity in a gamma counter. The assay was sensitive to 10 pg/well with a range from 10 to 1,000 pg. The average recovery was 86%. A new radioreceptor assay was developed for the oxytocin antagonist, TT-235. TT-235 had a much longer half-life than oxytocin in the pregnant rat and baboon. This longer half-life may partially explain the prolonged in vivo tocolytic activity of TT-235 in these animals.

Phase II study of cetrorelix, a luteinizing hormone-releasing hormone antagonist in patients with platinum-resistant ovarian cancer.

OBJECTIVE: The goal of this work was to study the anticancer activity of cetrorelix, a decapeptide with LHRH receptor antagonist properties in patients with platinum-resistant ovarian cancer. About 80% of primary ovarian cancers and cell lines bear LHRH receptors. Cetrorelix has anticancer activity in in vitro and in vivo ovarian cancer models. METHODS: Eligible patients with ovarian or mullerian carcinoma resistant to platinum chemotherapy received cetrorelix 10 mg subcutaneously every day. Eligibility criteria included age > or = 18, PS < or = 2, measurable disease, chemistries and blood counts in normal range, no estrogen replacement for at least 2 weeks, and no known allergic reactions to extrinsic peptide. In patients volunteering for a biopsy, tissue was taken to perform a LHRH receptor assay. RESULTS: Seventeen patients were treated. Median age was 58 years. Median performance status was 0. Median number of prior chemotherapies was 3. Three patients had partial remissions lasting 9, 16, and 17 weeks. Toxicities effects included grade 4 anaphylactoid reaction (one patient) controlled by cortisol and cimetidine, grade 2 histamine reaction (two patients), grade 2 arthralgia (one patient) 20% cholesterol increase (two patients, who did not require specific treatment), minor hot flushes, headache, and local skin reaction at the injection site. Six of seven samples were LHRH receptor positive for mRNA and/or ligand assay. Two responding patients were LHRH receptor positive. The patient who had no receptor did not respond. CONCLUSION: Cetrorelix has activity against ovarian cancer in this refractory population, and has minimal toxicity, except for potential anaphylactoid reactions. Activity may be mediated through the LHRH receptor.

No influence of body weight on pregnancy rate in patients treated with cetrorelix according to the single- and multiple-dose protocols.

The question of whether adjustment to body weight is necessary in in-vitro fertilization (IVF) cycles using GnRH antagonists is currently under discussion. Therefore, a data analysis of five prospective studies using either the single- or the multiple-dose antagonist protocol with cetrorelix (Cetrotide) was performed. The influence of stimulation procedure, gonadotrophins and body weight on pregnancy rate was evaluated in a linear logit model. The effect of the stimulation procedure and body weight on the cumulus-oocyte complex (COC) and follicle number was explored in an ANOVA model. Cetrorelix plasma concentrations were tested for any correlation with body weight. Baseline and outcome parameters in different body weight groups (<50 kg, 50-59 kg, 60-69 kg, 70-79 kg, > or =80 kg) were assessed for human menopausal gonadotrophin and recombinant human FSH stimulation separately. Cetrorelix plasma concentrations were correlated with body weight, but no influence of the type of stimulation or body weight on pregnancy rate was found. Body weight did not influence cetrorelix plasma concentrations. In contrast, body weight significantly influenced the number of retrieved COC as well as the number of follicles on the day of human chorionic gonadotrophin administration. Body weight does not influence the outcome of treatment in cetrorelix cycles.

Transactivation assay for determination of glucocorticoid bioactivity in human serum.

We have developed a mammalian cell (COS-1) bioassay, which measures glucocorticoid bioactivity (GBA) directly from a small amount of human serum. The assay is based on the expression of human glucocorticoid receptor (GR) together with a coactivator protein and reporter plasmid containing GR response elements upstream of the luciferase gene. Ten microliters of human serum, in duplicate, are added directly to the cell culture medium, and GBA is derived from reporter gene activity. The assay differentiates between biopotencies of synthetic steroids, and importantly, mifepristone (RU486) is able to block glucocorticoid-induced response. The assay is sensitive (<15.6 nM cortisol in fetal calf serum) and precise, with the within- and between-assay coefficients of variation less than 8% and 10%, respectively. We measured serum GBA (bioassay) and cortisol (RIA) levels in 34 asthmatic children (age range, 5.7-14.2 yr) at baseline and after treatment with either inhaled budesonide (800 microg/d, n = 14), fluticasone propionate (500 microg/d, n = 14), or cromones (control group, n = 6). Pretreatment serum GBA and cortisol levels correlated strongly (r = 0.90, P < 0.0001, n = 34). Two months of treatment with inhaled budesonide resulted in excess GBA in circulation, which was not attributable to endogenous cortisol (P < 0.001). In the fluticasone propionate group, the presence of serum excess GBA was at the borderline of statistical significance (P < 0.08) after 2 months of inhalation therapy, and no excess GBA was detected in the cromone group. In conclusion, our bioassay enables measurement of mammalian cell response to bioactive glucocorticoids in circulation and provides a novel means to investigate patients receiving drugs acting through the GR.

Validation of a liquid chromatographic-tandem mass spectrometric method for the measurement of (R)-1-[2,3-dihydro-2-oxo-1-pivaloylmethyl-5-(2-pyridyl)-1H-1,4-benzodiazepin-3-yl]-3-(3-methylaminophenyl)urea (YF476) in human plasma.

A sensitive and specific liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method has been validated for the measurement of YF476 in human plasma. The method involves a simple liquid-liquid extraction procedure, chromatography of the extracts on a C(18) column, atmospheric pressure chemical ionisation and detection in the multiple reaction monitoring mode. The calibration line was linear over the concentration range 0.1 ng/ml (the limit of quantification) to 25.0 ng/ml. Intra- and inter-batch precision was <14% and intra- and inter-batch accuracy was <11% over the entire calibration range. The bioanalytical method is robust and has been used for the analysis of many samples from human subjects involved in early clinical studies (Phase I).

Carbon-11 labelled cholecystokininB antagonists: radiosynthesis and evaluation in rats.

Three cholecystokinin type B (CCKB) receptor antagonists were labelled with 11C and evaluated ex vivo in rat biodistribution studies. The CCKB antagonists were YF 476 and two other compounds of the basic 3-ureido-1,4-benzodiazepine class. Following tail-vein administration of [11C]-YF 476 exceedingly low levels of radioactivity were found in all brain regions from 5 to 60 min post-injection. Similar results were obtained using the other two 11C-labelled CCKB antagonists. In light of the very poor brain penetration of these compounds, reports on the central nervous system activity of this class of CCKB antagonists should be viewed with caution.

Pharmacodynamic effects and plasma pharmacokinetics of single doses of cetrorelix acetate in healthy premenopausal women.

OBJECTIVE: To investigate the pharmacodynamic effects and plasma pharmacokinetics of single subcutaneous doses of cetrorelix acetate in healthy premenopausal women. SETTING: Phase I clinical research unit. PATIENT(S): Healthy, premenopausal women aged 19 to 35 years. INTERVENTION(S): Single subcutaneous morning doses of cetrorelix acetate (1, 3, or 5 mg peptide base) were investigated in a randomized, single-blind, placebo-controlled, parallel-group design. After a control cycle, 36 women received cetrorelix acetate (12 per dose) and 12 received placebo on the eighth individual cycle day. Transvaginal ultrasound was performed, and blood samples for LH, FSH, E2 were collected during both cycles and for pharmacokinetics up to 168 hours after dosing. The serum hormone levels were determined by electrochemicoluminescence immunoassay and plasma cetrorelix concentrations by radioimmuno assay. RESULTS: Cetrorelix acetate administration led to a rapid, marked, and reversible suppression of serum LH, E2, and to a lesser extent FSH concentrations. The median intra-individual shifts between treatment and control cycle were -1.0, 4.0, 8.0, and 9.5 days for serum LH maximum and -1.0, 4.5, 7.0, and 10.0 days for ovulation following placebo or 1, 3, and 5 mg cetrorelix acetate, peptide base, respectively. The area under the concentration-time curve (AUC) and peak cetrorelix concentrations in plasma (Cmax) increased proportionally with dose. CONCLUSIONS: Cetrorelix acetate showed pronounced and reversible LH and E2 suppression and a dose-dependent postponement of LH surge and ovulation after single subcutaneous administrations to healthy premenopausal women. Dose proportionality over the range of 1 mg to 5 mg cetrorelix acetate, peptide base was demonstrated.