Comparing cervical mucus changes in response to an oral progestin or oestrogen withdrawal in ovarian-suppressed women: a clinical pilot.

Purpose: Prior studies evaluating the effect of administered progestogens on peak cervical mucus have not controlled for the influence of endogenous hormones. To address this, we treated women with a gonadotropin-releasing hormone (GnRH) agonist to suppress the hypothalamus-pituitary-ovarian (HPO) axis and used transdermal oestradiol replacement to stimulate peak cervical mucus and then evaluated the effects of an oral progestin or oestradiol withdrawal. Materials and methods: We used a crossover design to examine cervical mucus changes in women receiving transdermal oestradiol replacement following intramuscular administration of leuprolide acetate. After increasing oestradiol patches to mid-cycle levels, subjects were assigned to either 0.35 mg oral norethindrone with continuation of the patches (NET) or oestradiol withdrawal by patch removal (E2WD). We collected serum and cervical mucus samples at 0, 2, 4, 6, 22 and 24 h following the intervention. Results: We analysed 12 cycles (6 NET, 6 E2WD) from three subjects. Baseline cervical mucus scores were favourable to sperm penetration [NET median 11, interquartile range (9-12), E2WD 13 (12-13)]. Two hours after removal of oestradiol patch or administration of norethindrone, cervical mucus scores declined [NET 8.5 (4-9), E2WD 10.5 (10-12)]. Low cervical mucus scores persisted at 24 h with NET [8.0 (7-8)] but not E2WD [10.5 (8-11)]. Conclusions: We observed a rapid decline in cervical mucus Insler scores following administration of a single dose of oral norethindrone, and scores remained lower and unfavourable through 24 h. Oestradiol withdrawal did not result in similar unfavourable changes.

In Vivo Formation of Ethinylestradiol After Intramuscular Administration of Norethisterone Enantate.

It is known that a small fraction of orally administered norethisterone is metabolically converted to ethinylestradiol. This exploratory, open-label, nonrandomized study was conducted to investigate the systemic exposure to ethinylestradiol after intramuscular administration of norethisterone enantate in comparison with the exposure to ethinylestradiol after administration of a standard combined oral contraceptive. Sixteen healthy premenopausal women received an oral contraceptive (ethinylestradiol 30 µg/levonorgestrel 150 µg) once daily for 21 days and-after a 1-week washout period-a single intramuscular dose of 200 mg norethisterone enantate. Blood samples to determine ethinylestradiol in serum were taken over 24 hours after the last dose of ethinylestradiol/levonorgestrel and over 8 weeks after administration of norethisterone enantate. Oral equivalent doses of ethinylestradiol were estimated based on area under the concentration-time curves. The ethinylestradiol serum concentrations observed after administration of norethisterone enantate were relatively low: The mean maximum concentration was only 32% of the maximum observed after ethinylestradiol/levonorgestrel (90% confidence interval, 22.5%-44.7%). The maximum oral equivalent dose of ethinylestradiol was markedly lower than 30 µg ethinylestradiol per day (20.3 µg/day; 90% confidence interval, 14.8-28.0 µg/day). The same applied to the average oral equivalent dose of ethinylestradiol for the 8-week postdose interval (4.41 µg/day; 90% confidence interval, 3.57-5.46 µg/day). To conclude, the study results indicate that metabolic conversion of norethisterone to ethinylestradiol also occurs after intramuscular administration of 200 mg norethisterone enantate, but is associated with a lower exposure to ethinylestradiol than the use of a combined oral contraceptive containing 30 µg ethinylestradiol (plus 150 µg levonorgestrel).

Comparison of Measured and Predicted Bioconcentration Estimates of Pharmaceuticals in Fish Plasma and Prediction of Chronic Risk.

Evaluation of the environmental risk of human pharmaceuticals is now a mandatory component in all new drug applications submitted for approval in EU. With >3000 drugs currently in use, it is not feasible to test each active ingredient, so prioritization is key. A recent review has listed nine prioritization approaches including the fish plasma model (FPM). The present paper focuses on comparison of measured and predicted fish plasma bioconcentration factors (BCFs) of four common over-the-counter/prescribed pharmaceuticals: norethindrone (NET), ibuprofen (IBU), verapamil (VER) and clozapine (CLZ). The measured data were obtained from the earlier published fish BCF studies. The measured BCF estimates of NET, IBU, VER and CLZ were 13.4, 1.4, 0.7 and 31.2, while the corresponding predicted BCFs (based log Kow at pH 7) were 19, 1.0, 7.6 and 30, respectively. These results indicate that the predicted BCFs matched well the measured values. The BCF estimates were used to calculate the human: fish plasma concentration ratios of each drug to predict potential risk to fish. The plasma ratio results show the following order of risk potential for fish: NET > CLZ > VER > IBU. The FPM has value in prioritizing pharmaceutical products for ecotoxicological assessments.

Clinical drug-drug interaction assessment of ivacaftor as a potential inhibitor of cytochrome P450 and P-glycoprotein.

Ivacaftor is approved in the USA for the treatment of cystic fibrosis (CF) in patients with a G551D-CFTR mutation or one of eight other CFTR mutations. A series of in vitro experiments conducted early in the development of ivacaftor indicated ivacaftor and metabolites may have the potential to inhibit cytochrome P450 (CYP) 2C8, CYP2C9, CYP3A, and CYP2D6, as well as P-glycoprotein (P-gp). Based on these results, a series of clinical drug-drug interaction (DDI) studies were conducted to evaluate the effect of ivacaftor on sensitive substrates of CYP2C8 (rosiglitazone), CYP3A (midazolam), CYP2D6 (desipramine), and P-gp (digoxin). In addition, a DDI study was conducted to evaluate the effect of ivacaftor on a combined oral contraceptive, as this is considered an important comedication in CF patients. The results indicate ivacaftor is a weak inhibitor of CYP3A and P-gp, but has no effect on CYP2C8 or CYP2D6. Ivacaftor caused non-clinically significant increases in ethinyl estradiol and norethisterone exposure. Based on these results, caution and appropriate monitoring are recommended when concomitant substrates of CYP2C9, CYP3A and/or P-gp are used during treatment with ivacaftor, particularly drugs with a narrow therapeutic index, such as warfarin.

Increased exposure of norethindrone in HIV+ women treated with ritonavir-boosted atazanavir therapy.

OBJECTIVE: Pharmacokinetics of norethindrone in combination oral contraceptive regimen are well described among HIV+ women treated with ritonavir-boosted protease inhibitor therapies; however, such characterization is lacking in women using progestin-only contraception. Our objective is to characterize pharmacokinetics of norethindrone in HIV+ women using ritonavir-boosted atazanavir treatment during progestin-only contraceptive regimens. STUDY DESIGN: An open-label, prospective, nonrandomized trial to characterize the pharmacokinetics of norethindrone in HIV+ women receiving ritonavir-boosted atazanavir (n=10; treatment group) and other antiretroviral therapy known to not alter norethindrone levels (n=17; control group) was conducted. Following informed consent, women were instructed to take a single daily fixed oral dose of 0.35 mg norethindrone and 300 mg/100 mg atazanavir/ritonavir for 22 days. On day 22, serial blood samples were collected by venous catheter at 0, 1, 2, 3, 4, 6, 8, 12, 24, 48 and 72 h. Whole blood was processed to collect serum and stored at -20°C until later analysis using radioimmunoassay. Pharmacokinetic parameters were estimated using noncompartmental method. RESULTS: In the treatment group, compared to the control group, an increase in area under the curve0₋24 (16.69 h*ng/mL vs. 25.20 h*ng/mL; p<.05) and maximum serum concentration (2.09 ng/mL vs. 3.19 ng/mL; p<.05), decrease (25%-40%) in apparent volume of distribution and apparent clearance, and unaltered half-life were observed. CONCLUSION(S): Our findings suggest that progestin-only contraceptives, unlike combination oral contraceptives, benefit from drug-drug interaction and achieve higher levels of exposure. Further studies are needed to establish whether pharmacokinetic interaction leads to favorable clinical outcomes. IMPLICATIONS: Norethindrone-based progestin-only contraceptives, unlike combination oral contraceptives, exhibit greater drug exposure when co-administered with ritonavir-boosted atazanavir regimen and thus may not warrant a category 3 designation by the World Health Organization. Prospective studies are needed to confirm whether pharmacokinetic interaction results in favorable clinical outcomes.

Pharmacokinetic and pharmacodynamic interactions between the hepatitis C virus protease inhibitor, boceprevir, and the oral contraceptive ethinyl estradiol/norethindrone.

PURPOSE: The purpose of this study was to examine drug interactions between boceprevir, a hepatitis C virus NS3/4A protease inhibitor, and a combined oral contraceptive containing ethinyl estradiol (EE) and norethindrone (NE). METHODS: A single-center, open-label study was conducted in 20 healthy female volunteers. In three consecutive 28-day treatment periods, subjects received EE/NE (0.035 mg/1 mg; 21 days on, 7 days off). During period 3, subjects also received boceprevir (800 mg three times daily) for 28 days. RESULTS: Coadministration of boceprevir with EE/NE did not affect NE AUC0-24 but slightly reduced NE C max. Geometric mean ratios (GMRs) for NE AUC0-24 and C max with EE/NE alone and EE/NE plus boceprevir were 0.96 (90% confidence interval (CI), 0.87-1.06) and 0.83 (90% CI, 0.76-0.90). Coadministration of boceprevir with EE/NE reduced EE AUC0-24 and C max by 26 and 21%, with GMRs of 0.74 (90% CI, 0.68-0.80) and 0.79 (90% CI, 0.75-0.84). Boceprevir had no effect on mid-cycle luteinizing hormone (LH), follicle-stimulating hormone (FSH), or sex hormone-binding globulin levels, and progesterone concentrations remained <1 ng/ml during the luteal phase. Adverse events reported in this study were consistent with the well-established safety profile of boceprevir. CONCLUSION: Serum progesterone, LH, and FSH levels indicate that ovulation was suppressed during coadministration of boceprevir with EE/NE. Coadministration of boceprevir with combined oral contraceptives containing EE and ≥1 mg of NE is therefore unlikely to alter contraceptive effectiveness. The ovulation suppression activity of oral contraceptives containing lower doses of NE, and of other forms of hormonal contraception during coadministration with boceprevir, has not been established.

Synergistic effects of E2MATE and norethindrone acetate on steroid sulfatase inhibition: a randomized phase I proof-of-principle clinical study in women of reproductive age.

The combination of a progestin such as norethindrone acetate (NETA) reducing the ovarian estrogen production with a steroid sulfatase (STS) inhibitor (STS-I) decreasing the local estrogen production could result in a new treatment option for endometriosis. The study reported was a randomized, double-blind, and placebo-controlled study to investigate the pharmacodynamics, pharmacokinetics, and safety of the STS-I PGL2001 (E2MATE) and NETA. A total of 24 healthy women of reproductive age were treated with weekly doses of PGL2001 or daily doses of NETA or a combination of both compounds for 4 weeks. Four weeks of treatment with PGL2001 or PGL2001 + NETA reduced the STS activity in the endometrium by 91% (±3%) and 96% (±4%), respectively, and comparable values were observed 1 month after the treatment was stopped. The combined treatment of PGL2001 + NETA led to significantly higher STS inhibition at both times (P < .01 and P < .05, respectively). This study showed that administration of PGL2001 alone at 4 mg/week or combined with NETA to healthy women of reproductive age led to STS inhibition and changes in functional STS biomarkers in the endometrium, resulting in synergistic effects of PGL2001 and NETA on STS activity.

Effect of protease inhibitors on steady-state pharmacokinetics of oral norethindrone contraception in HIV-infected women.

OBJECTIVE: Pharmacokinetic interactions exist between combined oral contraceptives and protease inhibitors (PI). However, such information is lacking for progestin-only oral contraception. We sought to define the steady-state pharmacokinetic interaction between norethindrone (NET) and PI in HIV-infected women. METHODS AND DESIGN: We conducted an open-label, prospective, nonrandomized trial to characterize the steady-state pharmacokinetics of serum NET in HIV-infected women receiving PI compared with a control group of HIV-infected women receiving other noninteracting drugs. After 21 days of 0.35 mg of NET ingestion once daily, serial serum samples were obtained at 0, 1, 2, 3, 4, 6, 8, 12, 24, 48, and 72 hours. The area under the curve between 0 and 72 hours after ingestion was calculated by trapezoidal approximation. RESULTS: Thirty-five women were enrolled, 2 withdrew. Sixteen women in the PI group and 17 controls completed the study. NET half-life and maximum concentration were not significantly different between the 2 groups. Minimum concentration of NET was significantly higher in the PI group (P = 0.01). The ratio of the geometric mean NET area under the curve in the PI group compared with controls was 1.5 (90% confidence interval: 1.21 to 1.86). NET serum concentrations were significantly higher in HIV-infected women taking a PI compared with controls (P = 0.004). CONCLUSIONS: Coadministration of PI inhibits NET metabolism as shown by higher serum NET area under the curve levels, a surrogate marker for therapeutic contraceptive efficacy. This study supports the increased utilization of progestin-only pills in HIV-infected women receiving certain PI regimens.

Comparison of serum and cervical mucus hormone levels during hormone-free interval of 24/4 vs. 21/7 combined oral contraceptives.

BACKGROUND: This study analyzes levels of progesterone, estradiol, norethindrone (NET) and ethinyl estradiol (EE) in serum and levels of NET in cervical mucus on the last day of the hormone-free interval (HFI) in users of 24/4 [norethindrone acetate (NETA)/EE-24] vs. 21/7 (NETA/EE-21) regimens. STUDY DESIGN: This was a randomized controlled, crossover, equivalency trial. Subjects were randomized to receive NETA/EE-24 or NETA/EE-21 for 2 months and then switched between study drugs. Blood and cervical mucus samples were obtained on Days 12-16 and on the last day of the HFI. RESULTS: From April 2010 to November 2011, 32 subjects were enrolled with 18 subjects completing all study visits. There were no statistically significant differences in either day 12-16 (p=.54) or last hormone-free day (p=.33) cervical mucus NET concentrations between the regimens. On the last day of the HFI, median serum progesterone levels did not differ significantly; however, users of NETA/EE-24 had higher levels of serum NET (p<.001) and users of NETA/EE-21 had higher levels of serum estradiol (p=.01). CONCLUSION: This data supports the fact that inhibition of the pituitary-ovarian axis occurs during oral contraceptive use and during the HFI. We demonstrated that a reduced HFI of 4 days resulted in better suppression of the ovarian hormone production, thereby reducing the risk of ovulation and potential contraceptive failure.

Testosterone-induced prostate growth is blocked by co- and preadministration of norethisterone enanthate in castrated cynomolgus monkeys.

INTRODUCTION: Prostate size and function are regulated by testosterone. However, the progesterone receptor is expressed in the primate prostate. Progestins affect the prostate by endocrine suppression, but can also act directly. Examining the role of progestins, we studied the effects of norethisterone (NET) on testosterone undecanoate (TU)-induced prostate growth in castrated macaques. MATERIALS AND METHODS: Two groups (n = 6 for each group) received TU every 9 weeks. Using a crossover setting, group I received norethisterone enanthate (NETE) 3 times at 3-week intervals, while group II received placebo. After 9 weeks, placebo was administered to group I, and group II received NETE. RESULTS: In group II, the prostate grew under TU and placebo over the first period. In group I, coadministered with NETE, the increase was lower. After the crossover, prostates of animals previously treated with NETE did not increase to normal values under placebo. Prostates of animals treated with TU and placebo in the first period shrank following NETE administration after the crossover. The long half-life of NET can explain the lack of a TU effect on animals coadministered with NETE after the crossover. CONCLUSIONS: Pre- and coadministration of NET reduces testosterone-induced prostate growth with possible implications for the treatment of benign prostate hyperplasia and hormonal male contraception.

Simple and rapid determination of norethindrone in human plasma by supported liquid extraction and ultra performance liquid chromatography with tandem mass spectrometry.

We report for the first time an ultra performance liquid chromatographic method with tandem mass spectrometric detection (UPLC/MS/MS) for the determination of norethindrone alone in human plasma over the concentration range of 50.0-25000 pg mL(-1) using a sample volume of 0.250 mL. Norethindrone and its internal standard (ISTD), norethindrone-(13)C(2), were extracted from human plasma by supported liquid extraction (SLE). After evaporation of the organic solvent, samples were reconstituted and analyzed on an UPLC/MS/MS system. The UPLC system used a Waters BEH C18 (100 mm × 2.1mm, 1.7 µm) column with mobile phase A of 0.05% formic acid in water:acetonitrile (65:35, v/v) and mobile phase B of 0.05% formic acid in methanol:acetonitrile (50:50, v/v). The flow rate was 0.500 mL min(-1). The method was fully validated. The inter-run accuracy and precision at the lower limit of quantitation (LLOQ), low, mid and high quality control (QC) concentration levels were 99.2-108.4% with a <8.1% CV (coefficient of variation), respectively. The validated method has been successfully applied to analysis of thousands of pharmacokinetic samples.

The pharmacokinetic interaction between an oral contraceptive containing ethinyl estradiol and norethindrone and the HCV protease inhibitor telaprevir.

BACKGROUND: Telaprevir is a hepatitis C virus protease inhibitor that is both a substrate and an inhibitor of CYP3A. STUDY DESIGN: The effect of steady-state telaprevir (administered 750 mg every 8 hours) on the steady-state pharmacokinetics of ethinyl estradiol (EE) and norethindrone (NE) was evaluated in 24 healthy women receiving oral contraceptives (OC) containing 0.5 mg NE and 0.035 mg EE for at least 3 months at the time of screening. This was a phase 1, open-label, single-center, nonrandomized study that included a cycle 1 (OC only for 21 days, followed by no OC for 7 days), cycle 2 (OC plus telaprevir for 21 days, followed by telaprevir alone for 7 days), and a follow-up period. RESULTS: When administration with or without telaprevir was compared, the least-squares mean ratios (90% confidence limits) for EE were 0.74 (0.68; 0.80) for C(max), 0.67 (0.63; 0.71) for C(min), and 0.72 (0.69; 0.75) for AUC; neither NE nor telaprevir exposure was affected. CONCLUSIONS: The efficacy of the OC may be compromised by the 26% to 33% reduction in EE exposure. Therefore, alternative methods of nonhormonal contraception should be used when hormonal contraceptives are coadministered with telaprevir and for up to 2 weeks following cessation of telaprevir.

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, does not affect the pharmacokinetics of ethinyl estradiol or norethindrone in healthy female subjects.

Sitagliptin is a dipeptidyl peptidase-IV (DPP-4) inhibitor used for the treatment of patients with type 2 diabetes mellitus. This randomized, placebo-controlled, 2-period, crossover study evaluated the effect of sitagliptin on the pharmacokinetics of 17 α-ethinyl estradiol (EE(2)) and norethindrone (NET) in healthy female subjects who were receiving oral contraceptives for >3 months prior to enrollment. A total of 18 subjects with normal menstrual cycles received the oral contraceptive pill ORTHO-NOVUM(®) 7/7/7 on days 1 to 28 for 2 successive cycles, and on days 1 to 21 were randomly assigned to receive sitagliptin 200 mg/day (2 × 100 mg tablets) or placebo using a computer-generated allocation schedule. Blood samples for determination of plasma EE(2) and NET concentrations were collected predose and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 18, and 24 hours postdose on day 20 or 21 of each treatment period. The GMRs (90% confidence interval [CI]) for the AUC(0-24 hr) of EE(2) and NET were 0.99 (0.93, 1.06) and 1.03 (0.97, 1.09), respectively, and for C(max) were 0.97 (0.86, 1.10) and 0.98 (0.89, 1.07), respectively. The coadministration of sitagliptin 200 mg/day with an oral contraceptive for 21 days did not lead to clinically meaningful alterations in the pharmacokinetics of EE(2) and NET.

Development of a high-performance liquid chromatographic method for the determination of mifepristone in human plasma using norethisterone as an internal standard: application to pharmacokinetic study.

OBJECTIVE: The objective of this study was to develop a simple, sensitive, stable and validated HPLC method for the determination of mifepristone levels in human plasma. METHODS: Solid-phase extraction cartridges were used to extract plasma samples. Separation was carried out on a C(18) column maintained at 20 degrees C with acetonitrile-water (80:20, v/v) as mobile phase at a flow rate of 0.6 mL/min. Norethisterone was employed as the internal standard. Dual wavelength mode was used, with mifepristone monitored at UV 302 nm and norethisterone at 240 nm. RESULTS: The calibration curve was linear in the concentration range of 5-10000 ng/mL, with linear correlation coefficient r being 0.9999. The limit of detection for the assay was 3 ng/mL. The inter-day accuracy ranged from 92.4% to 98.4% and precision 3.6% to 11.4%. The intra-day accuracy ranged from 92.1% to 100.6% and precision 4.7% to 12.2%. The absolute recovery was 91.7-100.1%. Plasma samples were stable for at least 1 month if stored at -20 degrees C. This validated HPLC method was successfully applied to pharmacokinetic study of mifepristone in human plasma samples collected from volunteers after oral administration of 10 mg mifepristone. CONCLUSION: The simple, accurate and stable method allows the sensitive determination of mifepristone in human plasma at the nanogram level. It could be applied to assess the plasma level of mifepristone in women up to 5 days after oral administration of 10 mg mifepristone.

A semi-automated 96-well plate method for the simultaneous determination of oral contraceptives concentrations in human plasma using ultra performance liquid chromatography coupled with tandem mass spectrometry.

Two semi-automated, relatively high throughput methods using ultra performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) were developed for the simultaneous determination of ethinyl estradiol (EE) in combination with either 19-norethindrone (NE) or levonorgestrel (LN) in human plasma. Using 300 microL plasma, the methods were validated over the concentration ranges of 0.01-2 ng/mL and 0.1-20 ng/mL for EE and NE (or LN), respectively. The existing methods for the determination of the oral contraceptives in human plasma require large volumes of plasma (> or =500 microL), and sample extraction is labor-intensive. The LC run time is at least 6 min, enabling analysis of only about 100 samples a day. In the present work the throughput was greatly improved by employing a semi-automated sample preparation process involving liquid-liquid extraction and derivatization with dansyl chloride followed by UPLC separation on a small particle size column achieving a run time of 2.7 min. The validation and actual sample analysis results show that both methods are rugged, precise, accurate, and well suitable to support pharmacokinetic studies where approximately 300 samples can be extracted and analyzed in a day.

Testosterone inhibits estrogen/progestogen-induced breast cell proliferation in postmenopausal women.

OBJECTIVE: During the past few years serious concern has been raised about the safety of combined estrogen/progestogen hormone therapy, in particular about its effects on the breast. Several observations suggest that androgens may counteract the proliferative effects of estrogen and progestogen in the mammary gland. Thus, we aimed to study the effects of testosterone addition on breast cell proliferation during postmenopausal estrogen/progestogen therapy. DESIGN: We conducted a 6-month prospective, randomized, double-blind, placebo-controlled study. A total of 99 postmenopausal women were given continuous combined estradiol 2 mg/norethisterone acetate 1 mg and were equally randomly assigned to receive additional treatment with either a testosterone patch releasing 300 microg/24 hours or a placebo patch. Breast cells were collected by fine needle aspiration biopsy at baseline and after 6 months, and the main outcome measure was the percentage of proliferating breast cells positively stained by the Ki-67/MIB-1 antibody. RESULTS: A total of 88 women, 47 receiving active treatment and 41 in the placebo group, completed the study. In the placebo group there was a more than fivefold increase (P<0.001) in total breast cell proliferation from baseline (median 1.1%) to 6 months (median 6.2%). During testosterone addition, no significant increase was recorded (1.6% vs 2.0%). The different effects of the two treatments were apparent in both epithelial and stromal cells. CONCLUSIONS: Addition of testosterone may counteract breast cell proliferation as induced by estrogen/progestogen therapy in postmenopausal women.

Pharmacokinetic interaction between bosentan and the oral contraceptives norethisterone and ethinyl estradiol.

OBJECTIVE: Bosentan has been shown in vitro and in vivo to induce the cytochrome P450 enzymes CYP2C9 and CYP3A4. The present study was conducted to investigate the effect of bosentan on the pharmacokinetics of a combined oral contraceptive. SUBJECTS AND METHODS: In a randomized, 2-way crossover study, 20 healthy female subjects received Treatments A and B. Treatment A consisted of a single dose of OrthoNovum containing 1 mg norethisterone (norethindrone) and 35 microg ethinyl estradiol. Treatment B consisted of bosentan, 125 mg b.i.d. for 7 days plus concomitant norethisterone and ethinyl estradiol on Day 7. Plasma concentrations of norethisterone and ethinyl estradiol were measured on days of oral contraceptive administration. RESULTS: In the absence of bosentan, the pharmacokinetics of norethisterone and ethinyl estradiol were characterized by Cmax and AUC0-infinity values (95% CI) of 9.8 (8.1, 11.9) ng/ml and 72.9 (57.0, 93.1) ng x h/ml, and 53.0 (47.0, 59.9) pg/ml and 758 (655, 878) pg x h/ml, respectively. Concomitant bosentan did not affect the Cmax but significantly decreased the AUC of norethisterone and ethinyl estradiol by 13.7% (-23.5, -2.6) and 31.0% (-40.5,-20.2), respectively. The maximum decrease in AUC of norethisterone and ethinyl estradiol in an individual subject was 56% and 66%, respectively. CONCLUSIONS: Bosentan decreases the AUC of norethisterone and ethinyl estradiol in healthy female subjects. In patients treated with bosentan, reduced efficacy of hormonal contraceptives should be considered.

Simultaneous determination of norethindrone and ethinyl estradiol in human plasma by high performance liquid chromatography with tandem mass spectrometry--experiences on developing a highly selective method using derivatization reagent for enhancing sensitivity.

In the present work, for the first time, a liquid chromatographic method with tandem mass spectrometric detection (LC-MS/MS) for the simultaneous analysis of norethindrone, and ethinyl estradiol, was developed and validated over the concentration range of 50-10000pg/ml and 2.5-500pg/ml, respectively, using 0.5 ml of plasma sample. Norethindrone, ethinyl estradiol, and their internal standards norethindrone-(13)C2, and ethinyl estradiol-d4, were extracted from human plasma matrix with n-butyl chloride. After evaporation of the organic solvent, the extract was derivatized with dansyl chloride and the mixture was injected onto the LC-MS/MS system. The gradient chromatographic elution was achieved on a Genesis RP-18 (50 mm x 4.6 mm, 3 microm) column with mobile phase consisted of acetonitrile, water and formic acid. The flow rate was 1.0 ml/min and the total run time was 5.0 min. Important parameters such as sensitivity, linearity, matrix effect, reproducibility, stability, carry-over and recovery were investigated during the validation. The inter-day precision and accuracy of the quality control samples at low, medium and high concentration levels were <6.8% relative standard deviation (RSD) and 4.4% relative error (RE) for norethindrone, and 4.2% RSD and 5.9% RE for ethinyl estradiol, respectively. Chromatographic conditions were optimized to separate analytes of interest from the potential interference peaks, arising from the derivatization. This method could be used for pharmacokinetic and drug-drug interaction studies in human subjects.

Biowaivers for oral immediate-release products: implications of linear pharmacokinetics.

Bioequivalence of drug formulations plays an important role in drug development. Recently, the Biopharmaceutical Classification System (BCS) has been implemented for the purpose of waiving bioequivalence studies on the basis of the solubility and gastrointestinal permeability of drug substance. Using the rationale of the BCS, it can be argued that biowaivers can, however, also be granted on the basis of standard pharmacokinetic data. If a drug exhibits dose-linear pharmacokinetics and a sufficiently fast dissolution profile, it can be concluded that this drug appears to pose no problem with respect to absorption. It should be noted that a change of an immediate-release tablet formulation can only lead to a deviating rate and/or extent of absorption when release of the drug from the formulation is altered. Logically, the dissolution profiles of the different formulations should be equal to guarantee bioequivalency. Thus, both BCS and the alternative linear pharmacokinetics approach require an evaluation of dissolution profiles. The justification of BCS is found in the permeability classification of the compound, while those of the linear pharmacokinetics lie in the apparent lack of a permeability problem. For example, in this context P-glycoprotein-transported drugs form an interesting class of compounds, which may be treated likewise when complying to the aforementioned requirements. Furthermore, poorly soluble compounds may be less troublesome than expected. It is shown that linear kinetics can be explained by the solubilising activity of, for example, bile salts. In this instance, linear pharmacokinetics shows that elevated doses do not appear to exhibit a limiting role on the dissolution. Hence, a change in formulation without any effect on the dissolution profile is not expected to cause a change in availability. It is clear that the formulations to be compared should not contain excipients that display an effect on (presystemic) drug metabolism.

Effect of zonisamide on the pharmacokinetics and pharmacodynamics of a combination ethinyl estradiol-norethindrone oral contraceptive in healthy women.

BACKGROUND: Several antiepileptic drugs have clinically significant pharmacokinetic interactions with oral contraceptives (OCs) that may result in contraceptive failure. OBJECTIVE: The aim of this study was to assess the effect of zonisamide on the pharmacokinetics of the individual components of a combination OC (ethinyl estradiol [EE] 0.035 mg and norethindrone [NOR] 1 mg) and on pharmacodynamic variables that may be increased in the event of reduced contraceptive efficacy (concentrations of serum luteinizing hormone [LH], follicle-stimulating hormone [FSH], and progesterone). METHODS: This was a single-center, open-label, 1-sequence, crossover study. Healthy, premenopausal women received the combination OC for three 28-day cycles (combination OC for 21 days, followed by placebo for 7 days). Following stabilization on the OC during the first cycle, blood was collected during cycle 2 for the determination of serum EE and NOR profiles (day 14) and serum LH, FSH, and progesterone concentrations (days 13-15). Starting on day 15 of cycle 2, zonisamide was administered orally at 100 mg/d and titrated to a target dose of 400 mg/d. EE and NOR profiles and serum LH, FSH, and progesterone concentrations were obtained again in cycle 3 (in the presence of zonisamide) and compared with those from cycle 2 (in the absence of zonisamide). RESULTS: Thirty-seven healthy premenopausal women (mean age, 26.1 years [range, 18-51 years]; mean body weight, 65.5 kg [range, 50.4-93.1 kg]; mean height, 165.8 cm [range, 152.4-182.9 cm]) received > or =1 dose of zonisamide. Of the 33 subjects (89.2%) who completed the study, 26 (78.8%) underwent titration to a stable zonisamide dose of 400 mg/d. For EE, the mean (SD) AUC over a 24-hour dosing interval (AUC(tau)) was 1139 (317) pg.h/mL in cycle 2 and 1143 (312) pg.h/mL in cycle 3; the mean C(max) in the respective cycles was 133 (39) and 141 (46) pg/mL. For NOR, the corresponding values were 140 (48) and 159 (46) ng.h/mL for AUC(tau) and 21 (5.4) and 23 (6.7) ng/mL for C(max). The 90% Cls for the geometric mean ratios (cycle 3:cycle 2) for AUC(tau) and C(max) fell within the accepted range for lack of interaction (0.80-1.25). There were no increases in LH, FSH, or progesterone concentrations between cycle 2 and cycle 3. CONCLUSIONS: In these healthy volunteers, steady-state zonisamide dosing had no clinically significant effect on the pharmacokinetics of EE or NOR. There was no pharmacodynamic evidence that zonisamide is likely to reduce the contraceptive effectiveness of OCs containing EE and NOR.