The effect of etoricoxib on the pharmacokinetics of oral contraceptives in healthy participants.

The pharmacokinetics of oral contraceptive (OC) components, ethinyl estradiol (EE) and norethindrone (NET), were evaluated after coadministration with etoricoxib in 3 double-blind, randomized, 2-period crossover studies of healthy women. There were 16, 39, and 24 participants enrolled in studies 1 (part I, part II), and 2, respectively. Each participant received triphasic OC (EE 35 microg/NET 0.5 mgx7 days, 0.75 mgx7 days, 1.0 mgx7 days) throughout each 28-day period. OC was coadministered with 21 days of etoricoxib daily followed by placebo for 7 days; the alternate period followed the reverse regimen (placebo to etoricoxib). Study 1 (part I) examined concurrent (morning) administration of OC/etoricoxib 120 mg, study 1 (part II) examined staggered (morning/night) administration of OC/etoricoxib 120 mg, and study 2 examined concurrent (morning) administration of OC/etoricoxib 60 mg. Coadministration of OC and etoricoxib 120 mg once daily was associated with a approximately 50% to 60% increase in EE concentrations, whereas etoricoxib 60 mg once daily was associated with a approximately 37% increase in EE concentrations. Coadministration of OC and etoricoxib was generally well tolerated. A clinically important change in NET AUC0-24 h was not observed. Adverse events included dyspepsia, diarrhea, headache, nausea, fatigue, loss of appetite, and taste disturbance.

The interaction between St John's wort and an oral contraceptive.

OBJECTIVES: The popular herbal remedy St John's wort is an inducer of cytochrome P450 (CYP) 3A enzymes and may reduce the efficacy of oral contraceptives. Therefore we evaluated the effect of St John's wort on the disposition and efficacy of Ortho-Novum 1/35 (Ortho-McNeil Pharmaceutical, Inc, Raritan, NJ), a popular combination oral contraceptive pill containing ethinyl estradiol (INN, ethinylestradiol) and norethindrone (INN, norethisterone). METHODS: Twelve healthy premenopausal women who were using oral contraception (>3 months) received a combination oral contraceptive pill (Ortho-Novum 1/35) for 3 consecutive 28-day menstrual cycles. During the second and third cycles, the participants received 300 mg St John's wort 3 times a day. The serum concentrations of ethinyl estradiol (day 7), norethindrone (day 7), follicle-stimulating hormone (days 12-16), luteinizing hormone (days 12-16), progesterone (day 21), and intravenous and oral midazolam (days 22 and 23) were determined in serial blood samples. The incidence of breakthrough bleeding was quantified during the first and third cycles. RESULTS: Concomitant use of St John's wort was associated with a significant (P <.05) increase in the oral clearance of norethindrone (8.2 +/- 2.7 L/h to 9.5 +/- 3.4 L/h, P =.042) and a significant reduction in the half-life of ethinyl estradiol (23.4 +/- 19.5 hours to 12.2 +/- 7.1 hours, P =.023). The oral clearance of midazolam was significantly increased (109.2 +/- 47.9 L/h to 166.7 +/- 81.3 L/h, P =.007) during St John's wort administration, but the systemic clearance of midazolam was unchanged (37.7 +/- 11.3 L/h to 39.0 +/- 10.3 L/h, P =.567). Serum concentrations of follicle-stimulating hormone, luteinizing hormone, and progesterone were not significantly affected by St John's wort dosing (P >.05). Breakthrough bleeding occurred in 2 of 12 women in the control phase compared with 7 of 12 women in the St John's wort phase. The oral clearance of midazolam after St John's wort dosing was greater in women who had breakthrough bleeding (215.9 +/- 66.5 L/h) than in those who did not (97.5 +/- 37.2 L/h) (P =.005). CONCLUSION: St John's wort causes an induction of ethinyl estradiol-norethindrone metabolism consistent with increased CYP3A activity. Women taking oral contraceptive pills should be counseled to expect breakthrough bleeding and should consider adding a barrier method of contraception when consuming St Johns wort.

Effect of topiramate or carbamazepine on the pharmacokinetics of an oral contraceptive containing norethindrone and ethinyl estradiol in healthy obese and nonobese female subjects.

PURPOSE: To study the pharmacokinetics of a combination oral contraceptive (OC) containing norethindrone and ethinyl estradiol during OC monotherapy, concomitant OC and topiramate (TPM) therapy, and concomitant OC and carbamazepine (CBZ) therapy in order to comparatively evaluate the pharmacokinetic interaction, which may cause contraceptive failure. METHODS: This randomized, open-label, five-group study included two 28-day cycles. Five groups of female subjects received oral doses of ORTHO-NOVUM 1/35 alone (cycle 1) and then concomitant with TPM or CBZ (cycle 2). The treatment groups were group 1, TPM, 50 mg/day; group 2, TPM, 100 mg/day; group 3, TPM, 200 mg/day; group 4, TPM, 200 mg/day (obese women); and group 5, CBZ, 600 mg/day. Group 4 comprised obese women whose body mass index (BMI) was between 30 and 35 kg/m(2). The BMI of the remaining four groups was < or =27 kg/m2. RESULTS: Coadministration of TPM at daily doses of 50, 100, and 200 mg (nonobese) and 200 mg (obese) nonsignificantly (p > 0.05) changed the mean area under the curve (AUC) of ethinyl estradiol by -12%, +5%, -11%, and -9%, respectively, compared with OC monotherapy. A similar nonsignificant difference was observed with the plasma levels and AUC values of norethindrone (p > 0.05). CBZ (600 mg/day) significantly (p < 0.05) decreased the AUC values of norethindrone and ethinyl estradiol by 58% and 42%, respectively, and increased their respective oral clearance by 69% and 127% (p < 0.05). Because CBZ induces CYP 3A-mediated and glucuronide conjugation metabolic pathways, the significant increase in the oral clearance of ethinyl estradiol and norethindrone was anticipated. CONCLUSIONS: TPM, at daily doses of 50-200 mg, does not interact with an OC containing norethindrone and ethinyl estradiol. The lack of the TPM-OC interaction is notable when it is compared with the CBZ-OC interaction.

Evaluation of interaction between fluconazole and an oral contraceptive in healthy women.

OBJECTIVE: To evaluate the potential pharmacokinetic interaction between 2 x 150 mg fluconazole administered once weekly and an oral contraceptive (OC) containing ethinyl estradiol and norethindrone. METHODS: A placebo-controlled, double-masked, randomized, two-way crossover study was used to investigate the pharmacokinetic interaction between 300 mg fluconazole once weekly and the OC Ortho Novum 7/7/7 (Ortho-McNeil Pharmaceutical, Inc., Raritan, NJ) in 26 healthy women, 18-36 years old. In the first cycle (28 days), subjects received OC only. In the second cycle, subjects were assigned randomly to receive OC-fluconazole or OC-placebo. In the third cycle, subjects were crossed over to the opposite treatment. RESULTS: Data for 21 subjects who completed the study were included in the pharmacokinetic analysis; data for all 26 subjects were included in the safety analysis (26 OC only; 24 OC-fluconazole; 23 OC-placebo). Treatment with OC-fluconazole resulted in small but statistically significant increases in 0-24 hour area under the plasma concentration-time curve (AUC(0-24)) for both ethinyl estradiol (mean 24%, 95% confidence interval [CI] 18%, 31%) and norethindrone (mean 13%, 95% CI 8%, 18%) as compared with treatment with OC-placebo. Ethinyl estradiol maximum plasma concentration (C(max)) was slightly (mean 8%, 95% CI 2%, 15%) though statistically significantly higher for OC-fluconazole treatment as compared with OC-placebo treatment. Norethindrone C(max) was not different (95% CI -6%, 11%) between the two treatment groups. No adverse events related to treatment were seen in the fluconazole treatment group. CONCLUSION: The concomitant administration of 300 mg fluconazole once weekly, twice the recommended dose for vaginal candidiasis, to women using OCs results in a slight increase in OC concentrations. Therefore, it appears that there is no threat of contraceptive failure because of concomitant fluconazole administration.

A double-blind, placebo-controlled evaluation of the effect of oral doses of rizatriptan 10 mg on oral contraceptive pharmacokinetics in healthy female volunteers.

Rizatriptan (MAXALT), a potent, oral 5-HT1B/1D agonist with a rapid onset of action, is available now for the acute treatment of migraine. This study examined the pharmacokinetic and clinical interaction between rizatriptan 10 mg and the components (ethinyl estradiol [EE] 35 micrograms and norethindrone [NET] 1.0 mg) of a well-established oral contraceptive combination product, ORTHO-NOVUM 1/35. Levels of sex hormone binding globulin (SHBG), a protein increased by EE to which NET binds, were also examined. In this two-period crossover study, 20 healthy young female subjects received a coadministration of 8 days of rizatriptan treatment (6 days of single-dose 10 mg rizatriptan and 2 days of multiple-dose rizatriptan, 10 mg q 4 hours for three doses, giving a total daily dose of 30 mg on Days 7 and 8) or matching placebo along with their daily dose (one tablet) of ORTHO-NOVUM 1/35 within their oral contraceptive cycle. Plasma was sampled for EE, NET, and SHBG concentrations. Safety evaluations included routine laboratory safety studies, physical examinations, and monitoring for ECG, vital signs, and adverse events. There were no statistically significant differences in any of the pharmacokinetic parameters of EE or NET between the rizatriptan and placebo treatment periods, thus indicating that rizatriptan had no meaningful effect on the disposition of either the EE or the NET component of ORTHO-NOVUM 1/35. The SHBG concentration did not change throughout the entire study. Clinically, coadministration of rizatriptan with ORTHO-NOVUM 1/35 was well tolerated. Blood pressure, heart rate, and temperature showed no consistent trend or clinically important changes. Adverse events following coadministration of rizatriptan with ORTHO-NOVUM 1/35 were similar to those reported when placebo was given with ORTHO-NOVUM 1/35. The findings of this study indicate that there is little potential for dosages as high as 30 mg/day, the maximum recommended dosing schedule, of rizatriptan to alter the plasma concentrations of oral contraceptives.

Biotransformation of mestranol to ethinyl estradiol in vitro: the role of cytochrome P-450 2C9 and metabolic inhibitors.

Mestranol, the estrogen component of some oral contraceptive formulations, must be demethylated to its active metabolite, 17 alpha-ethinyl estradiol, to produce estrogenic activity. To investigate the transformation of mestranol to ethinyl estradiol, an in vitro assay was used with human liver microsomes from four different donors. Incubation of a fixed concentration of mestranol (3 mumol/L) with varying concentrations of CYP inhibitors revealed strong inhibition of ethinyl estradiol formation by sulfaphenazole, a specific CYP2C9 inhibitor, with an average inhibitor concentration at one half of Emax (IC50) of 3.6 mumol/L (range, 1.8-8.3 mumol/L) and an average maximal inhibitory capacity (Emax) of 75% (range, 60-91%). Troleandomycin (a CYP3A3/4 inhibitor) and quinidine (a CYP2D6 inhibitor), however, produced no substantial inhibitory activity. alpha-Naphthoflavone (a CYP1A1/2 inhibitor only at concentrations < 2 mumol/L and a CYP2C9 inhibitor at higher concentrations) had a weak inhibitory effect on ethinyl estradiol formation (< 20% decrease in mestranol demethylation activity). Of the three antifungal azoles tested, miconazole strongly inhibited mestranol demethylation, with an average IC50 of 1.5 mumol/L (range, 0.7-3.2 mumol/L) and an average Emax of 90% (range, 77-100%), whereas fluconazole displayed relatively weak inhibition only at the highest concentration of 50 mumol/L (mean reduction in demethylation activity was 29%). Itraconazole produced no meaningful inhibition. Strong inhibition of ethinyl estradiol formation by sulfaphenazole suggests a major contribution of CYP2C9 to this reaction.

Are low-dose oral contraceptives safer and better?

It is widely believed that the use of low-dose oral contraceptives decreases thrombotic risks, compared with higher-dose oral contraceptives. Two recent epidemiologic studies infer a lower risk with 30 to 35 mcg than with 50 mcg estrogen oral contraceptives. However, as with prior studies from which similar conclusions were drawn, these studies have major flaws, the worst being that all 50 mcg oral contraceptives are lumped together, whereas 50 mcg mestranol oral contraceptives are actually bioequivalent to 35 mcg ethinyl estradiol oral contraceptives, thus confounding all such studies. Moreover, while rare thrombotic events have received inordinate attention, the major protective effect against endometrial and ovarian cancer that has been shown in older studies among users of oral contraceptives containing > or = 50 mcg ethinyl estradiol or > or = 80 mcg mestranol are almost totally ignored. The theoretical benefits of using lower-dose oral contraceptives have not been demonstrated, whereas the protection against these types of reproductive cancer have been shown repeatedly with high-dose oral contraceptives but not, to date, with lower-dose oral contraceptives. Such protection may be diminished by lowering the oral contraceptive dosage. Should every woman of reproductive age use high-dose oral contraceptives for 2 years? Are we throwing out the baby with the bath water?

Pharmacokinetics of ethinyl estradiol and mestranol.

Pharmacokinetally, a 50 micrograms oral dose of mestranol (which itself is inactive) is bioequivalent to a 35 micrograms dose of ethinyl estradiol. Physiologically, mestranol ranges from 50% to 100% of the activity of ethinyl estradiol, depending on the endpoint chosen. Compounds such as these, which are metabolized with a first-pass effect and are enterohepatically recirculated, demonstrate large interindividual and intraindividual variability in their pharmacokinetics. Thus a given dose of ethinyl estradiol in one person may produce an effect equivalent to a substantially larger (or smaller) dose in another person. This wide variability confounds efforts to establish tight dose-response relationships, a point rarely considered in clinical or epidemiologic studies of these compounds. The circulating levels of ethinyl estradiol sulfates may be higher than those of free ethinyl estradiol itself. It has been thought that these sulfates represent a "reservoir" of ethinyl estradiol. Our studies show that this idea is untenable because the half-life of the sulfates is not long enough for such an effect. Differences in the pharmacokinetics of ethinyl estradiol and mestranol have been observed in studies of various populations. The reality of these group differences is affirmed by analyses of urinary metabolite patterns.

Selected aspects of the pharmacokinetics and metabolism of ethinyl estrogens and their clinical implications.

Careful studies in an adequate sample of subjects show a very marked degree of variability in the pharmacokinetics of ethinyl estradiol--specifically, in parameters such as area under the curve, half-life, and time to peak. This variability is seen in differences between different populations, as well as from one individual to another. These studies also show variability in area under the curve and other parameters in the same person from time to time. Such differences may equal or exceed the differences between low dose (35 micrograms) and high-dose (50 micrograms) formulations. The levels of plasma ethinyl estradiol produced by a 50 micrograms dose of mestranol are similar to those from 35 micrograms of ethinyl estradiol. Thus a high-dose pill may be no higher than a low-dose pill if the nature of the estrogen is not kept in mind. Qualitative differences in the oxidative metabolites of estrogens may be of significance with respect to oncogenic potential.

PIP: The variability in the pharmacokinetics of ethinyl estradiol (EE) is pronounced, especially regarding such parameters as area under the curve, half-life, and time to peak. This variability shows up in different populations, different individuals, or in the same individual, and can even exceed the differences between low dose (35 mcg) and high- dose (50 mcg) formulations. 50 mcg of mestranol and 35 mcg of ethinyl estradiol both produce similar plasma EE levels. Qualitative differences in the oxidative metabolites of estrogens may be of significance with respect to oncogenic potential. The pharmacokinetic differences of EE whether caused by dietary, ethnic, or other factors are not merely differences in gastric absorption or renal excretion. Studies on kinetics and bioavailability showed that after oral administration of EE 3-sulfate only about 20% appeared as free EE in the blood, while EE 17-sulfate produced about half this amount. Individual variation showed a large spread both for plasma total EE sulfate levels and free EE. The pharmacokinetics of three 1 mg norethindrone/35 mcg EE and three 1 mg norethindrone/50 mcg mestranol formulations were analyzed and the mean values, standard deviations, and highest and lowest individual plasma patterns of the 3 EE preparations were indistinguishable. The administration of 50 mcg of mestranol resulted in an average area under the curve EE of 963 +- 544, whereas the dose 35 mcg of EE produced an area under the curve of 1036 +- 483, thus 35 mcg of EE proved to be a stronger dose than 50 mcg of mestranol. Inter- and intraindividual variability was demonstrated in a study: 24 patients received 35 mcg EE formulations and 27 others received 50 mcg mestranol agents. 3 identical formulations by different manufacturers proved to be bioequivalent. Extreme values ranged from -79% to +134% of the mean of the 3 determinations per individual. Clinical implications of these findings are that plasma EE levels engendered by 35 mcg EE may be indistinguishable from those produced by 50 mcg in another person. 2 to 3 mcg of moxestrol (the 11 beta-methoxy derivative of EE) is an effective contraceptive, as it is 10 times as potent as EE. Exposure of certain cell clones to estradiol, EE, and stilbestrol causes formation in vitro to foci of transformed (neoplastic) cells. However, moxestrol did not produce such cell transformation and these oxidative metabolites increased with estradiol or EE but not with moxestrol. This does not prove the oncogenic role of estrogens in humans, but it offers a new approach in the development of safer estrogens.

Bioequivalence of two oral contraceptive drugs containing norethindrone and ethinyl estradiol.

Two oral contraceptive drugs, Formulation A and Formulation B, both of similar hormonal content, were compared with each other to determine if they were bioequivalent. Both drugs contain 1 mg of norethindrone (NET) and 0.035 mg of ethinyl estradiol (EE). Application of an interval test for the ratio of the computed parameter means demonstrated equivalence for the two formulations with respect to the 0-24 hour area under the plasma level versus time curve (AUC24), the total area under the curve (AUCtot) and for the maximum plasma concentration (Cmax) for both ethinyl estradiol and norethindrone. The data support the hypothesis for bioequivalence of the two formulations with respect to total absorption.

Pharmacokinetics of three bioequivalent norethindrone/mestranol-50 micrograms and three norethindrone/ethinyl estradiol-35 micrograms OC formulations: are "low-dose" pills really lower?

We have examined the pharmacokinetic parameters derived from the analysis of plasma ethinyl estradiol (EE) and norethindrone levels after administration of a single dose of three bioequivalent norethindrone-1mg/mestranol (ME)-50 micrograms formulations (Ortho-NovumR 1/50, NorinylR 1/50 and Norcept-MR 1/50) and three norethindrone-1mg/ethinyl estradiol-35 micrograms formulations (Ortho-Novum 1/35R, NorinylR 1/35, Norcept-ER 1/35) in a randomized crossover design involving 24 women for the 35 micrograms and 27 women for the 50 micrograms agents. Differences between the AUC-EE of pairs from the same manufacturer (1 + 35 and 1 + 50) were not significantly different, indicating that 50 micrograms of mestranol was equivalent to 35 micrograms ethinyl estradiol with respect to this pharmacokinetic parameter. The Cmax values were also similar. Inter-individual coefficients of variation (C.V.) for the AUC-EE were 47% and 57% for the 1 + 35 and 1 + 50 agents, respectively. Intra-individual C.V.s were 41% and 42%, respectively. For norethindrone, the AUC was larger with the 1 + 50 formulations than with the 1 + 35 group (87.9 vs. 72.8 pg hr/ml). Additionally, the Cmax values were larger for the 1/50 group (17.7 vs. 14.0). Since the amount of norethindrone in the two dosage groups was the same, this difference in the pharmacokinetics between the 35 micrograms EE and the 50 micrograms ME formulations remains unexplained. The inter-individual C.V. averaged 56% for both dosage groups. The intra-individual C.V.s were 17% and 46% for the 1 + 35 and 1 + 50 groups, respectively. The large variation in blood levels of ethinyl estradiol and norethindrone between and within individuals may overshadow clinical differences attributable to differences in dosage.

Assessment of a new low-dose once-a-month injectable contraceptive.

Norethisterone (NET) in combination with mestranol (ME), in a macrocrystalline aqueous suspension that provides sustained release of steroids, was assessed as a once-a-month injectable contraceptive in ten healthy women of reproductive age. The ovarian function was studied before and after the intramuscular administration of 12mg NET plus 1.2mg ME, delivered as crystals of 150 micron average size. Serial blood samples were taken throughout the injection intervals in all women to measure serum progesterone (P), estradiol (E2), and NET. The NET/ME preparation effectively inhibited ovulation in 23 out of the 25 injection intervals studied. The administration of this formulation induced in some women a small degree of follicular maturation not followed by luteal activity. The endometrial bleeding patterns after each injection showed a bleeding-free period of two to three weeks. The overall data demonstrate that the parenteral administration of a macrocrystalline steroid preparation of NET/ME can bring about a sustained release contraceptive system at a substantially lower dose than those currently employed in once-a-month injectable contraception.

Effects of serum from oral contraceptive users on the metabolism of low density lipoprotein.

The metabolism of radiolabeled 125I-low density lipoprotein (LDL) was studied in cultured human aortic smooth muscle cells (SMC) to investigate potential mechanisms contributing to heart attack and stroke in young women taking oral contraceptive (OC) preparations. No consistent difference was discerned in the capacity of these cells to bind and internalize LDL following 24-hour exposure to pooled lipoprotein-poor (d greater than 1.25 gm/ml) serum from nonsmoking OC users and controls. However, significantly (p greater than 0.01) less soluble radioactive material was released into the media from dishes containing SMC incubated with OC serum, indicating that their capacity to degrade LDL was impaired. Increased amounts of both cholesterol and cholesterol ester and electron microscopic evidence of lipid accumulation were found in SMC grown for 12 days under standard culture conditions with 10% OC serum. This combination of in vitro findings suggests that OC use may accelerate the development of cardiovascular disease in some women by modifying the metabolism of LDL by cells of the arterial wall.