Assay of ethynyloestradiol in human serum and its binding to plasma proteins

Pharmacokinetic Drug Interactions Involving 17??-Ethinylestradiol

17alpha-Ethinylestradiol (EE) is widely used as the estrogenic component of oral contraceptives (OC). In vitro and in vivo metabolism studies indicate that EE is extensively metabolised, primarily via intestinal sulfation and hepatic oxidation, glucuronidation and sulfation. Cytochrome P450 (CYP)3A4-mediated EE 2-hydroxylation is the major pathway of oxidative metabolism of EE. For some time it has been known that inducers of drug-metabolising enzymes (such as the CYP3A4 inducer rifampicin [rifampin]) can lead to breakthrough bleeding and contraceptive failure. Conversely, inhibitors of drug-metabolising enzymes can give rise to elevated EE plasma concentrations and increased risks of vascular disease and hypertension. In vitro studies have also shown that EE inhibits a number of human CYP enzymes, such as CYP2C19, CYP3A4 and CYP2B6. Consequently, there are numerous reports in the literature describing EE-containing OC formulations as perpetrators of pharmacokinetic drug interactions. Because EE may participate in multiple pharmacokinetic drug interactions as either a victim or perpetrator, pharmaceutical companies routinely conduct clinical drug interaction studies with EE-containing OCs when evaluating new chemical entities in development. It is therefore critical to understand the mechanisms underlying these drug interactions. Such an understanding can enable the interpretation of clinical data and lead to a greater appreciation of the profile of the drug by physicians, clinicians and regulators. This article summarises what is known of the drug-metabolising enzymes and transporters governing the metabolism, disposition and excretion of EE. An effort is made to relate this information to known clinical drug-drug interactions. The inhibition and induction of drug-metabolising enzymes by EE is also reviewed.

The effect of phytoestrogens on the female genital tract

Environmental oestrogens have been implicated in the pathogenesis of hormonally treated cancers (such as breast and prostate cancer), male infertility, and abnormalities of the male and female reproductive tracts. They may be derived from plants (phytoestrogens), pharmaceuticals, or other synthetic compounds not originally intended to have oestrogenic activity (including soy based infant formulas). This review will discuss the evidence from both animal studies and humans for an effect of these ubiquitous compounds on the development of the human female genital tract, in addition to prolonging the menstrual cycle, alleviating symptoms of the menopause, and protecting against the development of endometrial carcinoma.

Determination of bisphenol A in blood using high-performance liquid chromatography-electrochemical detection with solid-phase extraction

A method for the determination of bisphenol A (BPA) in blood was investigated using high-performance liquid chromatography-electrochemical detection (HPLC-ED) with solid-phase extraction. When BPA at the concentrations of 25-100 ng/ml were added to whole blood, BPA recoveries were 26-48%. When BPA was added to water, plasma or hemolyzed red blood cells (H-RBC), BPA recoveries in water and plasma were almost similar (94%). However, the recovery in H-RBC was very low (36-46%). When BPA and plasma were added to H-RBC, the recovery was 70-85%. In authentic bovine metHb solution, BPA decreased depending on the metHb concentration, however, BPA recovery in the solution added with more than 17% plasma was higher than that in metHb only. These suggest that metHb influences the BPA recovery in whole blood. However, an accurate determination of BPA using HPLC was easily made possible by separating RBC from plasma.

Altered prostate growth and daily sperm production in male mice exposed prenatally to subclinical doses of 17alpha-ethinyl oestradiol

Approximately 2 million women in the USA and Europe continue taking oral contraceptives each year during undetected pregnancy due primarily to non-compliance and also to individual variation in sensitivity to hormones in the contraceptives. Prenatal exposure to oral contraceptives containing 17alpha-ethinyl oestradiol (EE) has generally not been associated with an increased incidence of externally observable malformations at birth. The purpose of this study was to assess effects on reproductive organs in adult male mice that had been exposed during gestation day 0 through 17 (equivalent to gestation week 16 in humans) to clinically relevant (approximately 0.5 microg/kg/day) and lower doses of EE. Doses used in this study ranged from 0.002 to 2 microg/kg/day. By 5 months of age, prostate weight was significantly (P < 0.05) higher than controls in most treatment groups of EE (0.02-2 microg/kg). Prostatic androgen receptor populations were significantly elevated only in the 0.02 microg/kg group, suggesting different mechanisms for the increase in prostate weight at different doses. Daily sperm production (DSP) and DSP per gramme of testis were reduced in all treatment groups during adolescence, but not later in adulthood. These findings are consistent with prior studies showing that prenatal exposure of mice to very low doses of a number of oestrogenic chemicals can alter the adult male reproductive system without causing gross external malformations.

Developmental effects of estrogenic chemicals are predicted by an in vitro assay incorporating modification of cell uptake by serum

Many estrogenic chemicals found in the environment (xenoestrogens) show a lower affinity for plasma estrogen binding proteins relative to the natural estrogens such as estradiol. These binding proteins, which include alphafetoprotein in rats and mice, sex hormone binding globulin in humans, and albumin in all species, regulate estrogen uptake into tissues. Therefore, the in vivo estrogenic potency relative to estradiol of xenoestrogens that show lower binding to these serum proteins will thus be underestimated in assays that compare the potency of xenoestrogens to estradiol and do not take serum binding into account. We have examined the effects of the binding components in serum on the uptake of a number of xenoestrogens into intact MCF-7 human breast cancer cells. Since most estrogenic chemicals are not available in radiolabeled form, their uptake is determined by competition with [3H]estradiol for binding to estrogen receptors (ER) in an 18-h assay. Serum modified access (SMA) of cell uptake of xenoestrogens is calculated as the RBA in serum-free-medium divided by the RBA in serum, and the bioactive free fraction of xenoestrogen in serum is then also calculated. We predicted the concentration of two xenoestrogens, bisphenol A and octylphenol, required to alter development of the prostate in male mouse fetuses. Whereas octylphenol was predicted to be a more potent estrogen than bisphenol A when tested in serum-free medium, our assay predicted that bisphenol A would be over 500-times more potent than octylphenol in fetal mice. The finding that administration of bisphenol A at a physiologically relevant dose predicted from our in vitro assay to pregnant mice from gestation day 11 to 17 increased adult prostate weight in male offspring relative to controls (similar to the effect of estradiol), while the same doses of octylphenol did not alter prostate development, provided support for our hypothesis.

Absence of an effect of high vitamin C dosage on the systemic availability of ethinyl estradiol in women using a combination oral contraceptive

Previous studies in small numbers of women have suggested that the administration of gram quantities of ascorbic acid interferes with the conversion of ethinyl estradiol (EE2) to its sulfates, leading to higher blood levels of EE2. The possibility of such potentiation has been investigated in 37 women using a combination monophasic oral contraceptive (30 micrograms EE2 and 150 micrograms levonorgestrel) for two consecutive cycles. Concomitant daily administration of 1 g ascorbic acid taken 1/2 hour before OC intake, was randomly assigned to the first or second cycle of OC use. On the first and 15th day of OC intake, blood samples were drawn 11 times over a 12-hour interval and Cmax and AUC(0-12 h) calculated. On pill days 10 and 21, only 6-hour post-intake samples were obtained. Samples were analyzed for levels of ascorbic acid, free and sulfated ethinyl estradiol (and a number of other parameters). Cmax and AUC values for EE2 and EE2-sulfate in cycles with and without ascorbic acid were evaluated statistically by the Grizzle model for days 1 and 15 and the ratios of day 15/day 1 for each of the substances. No effect of ascorbic acid was observed (alpha = 0.05, 1-beta = 0.9). Only on day 15 was there a significantly lower AUC for EE2-sulfate in the presence of ascorbic acid intake. Thus, the competition between ascorbic acid and EE2 for sulfation does not lead to an increased systemic availability of EE2 and is, therefore, unlikely to be of any clinical importance. Ascorbic acid can, therefore, be removed from the list of drugs interfering with the pharmacokinetics of ethinyl estradiol.

Rapid high-performance liquid chromatographic assay of ethynyloestradiol in rabbit plasma

A method for the determination of ethynyloestradiol in samples of rabbit plasma containing pentobarbital and heparin, the former used as an anaesthetic and the latter as an anticoagulant, has been developed. Quantification was carried out using a reversed-phase high-performance liquid chromatographic (HPLC) method in isocratic mode at room temperature, with electrochemical detection at an applied potential of +1 V vs. Ag/AgCl. Under these conditions, the retention time for ethynyloestradiol was ca. 2.9 min, the average recovery from plasma was 74.5%, and the limit of detection was 10 pg, corresponding to a plasma concentration of 50 pg/ml using 1 ml of plasma. Natural oestrogens, oestriol, oestradiol and oestrone showed peaks that did not interfere with ethynyloestradiol, and retention times of ca. 0.8, 2.4 and 3.4 min, respectively.

25 mg oestradiol implants--the dosage of first choice for subcutaneous oestrogen replacement therapy?

OBJECTIVE

To assess the oestrogen concentrations and symptom relief obtained with 25 mg oestradiol implants.

DESIGN

Open, observational study.

SUBJECTS

Twelve symptomatic, post-menopausal women seen in a designated menopause clinic.

INTERVENTION

A 25 mg oestradiol pellet was inserted subcutaneously, blood samples were obtained before implantation and at regular intervals (2-4 weeks) until symptoms refused as hypoestrogenaemia developed.

MAIN OUTCOME MEASURES

Change in symptom score following implant treatment. Concentrations of oestrogens and their metabolites before and during low dose subcutaneous oestradiol therapy.

RESULTS

Ten of the 12 women had excellent symptom relief, associated with oestradiol concentrations in the follicular range for between 28 and 35 weeks. The ratio of circulating oestrogen metabolites remained physiological, despite the oestradiol concentrations being substantially higher on treatment.

CONCLUSIONS

We suggest that 25 mg pellets should be used as the initial dose for subcutaneous oestrogen treatment, and a combination of return of symptoms and weeks since insertion used to judge the timing of reimplantation.

Intrasubject variability in the pharmacokinetics of ethynyloestradiol

Intrasubject and intersubject variability in the metabolism of ethynyloestradiol (EE) was assessed in a cross-over randomized study of 6 women who each received 3 months treatment with 50 micrograms EE and 50 micrograms EE with 250 micrograms levonorgestrel (LNG). Blood samples were collected at the end of each treatment month, assayed for EE and the half-life of elimination (Tel) and bioavailability (area under the serum concentration-time curve, AUC) calculated. Intrasubject variability for Tel and AUC varied markedly; the variability was random and not correlated with the formulation administered. The intrasubject variability for Tel and AUC was 31 and 17%, respectively, and intersubject variability 66 and 95%. The intersubject range of values was more than 3-fold for both Tel and AUC and the intrasubject range about 2-fold. The pharmacokinetics of EE were not influenced by LNG; mean values for Tel and AUC were 17.3 +/- 5.5 h and 11.1 +/- 3.8 ng/ml/h, respectively, when EE was administered alone compared with 16.4 +/- 4.8 h and 12.5 +/- 3.9 ng/ml/h when given with LNG. However, EE influenced the metabolism of LNG; Tel for LNG was 19.3 +/- 4.2 h when administered alone and significantly higher (30.0 +/- 11.2 h) when given with EE. There was no correlation between the rate of metabolism of EE and that of LNG. The intrasubject variability shown in this and other studies suggests that genetic factors are less important in intersubject variability than previously thought. Some implications of intrasubject variability are discussed.

A pharmacodynamic and pharmacokinetic study of the Chinese No. 1 pill

A pharmacodynamic and pharmacokinetic study of the Chinese No. 1 pill, a combined oral contraceptive containing 35 micrograms ethynyloestradiol (EE) and 600 micrograms norethisterone (NET), was performed in 29 women over a period of six months. Blood samples for analysis were taken during a pretreatment cycle, the first and 6th treatment cycles and post-treatment. Minor changes in carbohydrate metabolism occurred and these were particularly noticeable when the incremental areas under the serum concentration-time curves for both glucose and insulin in response to a glucose tolerance test were calculated. No changes occurred in the serum glycosylated haemoglobin levels. The serum concentrations of all the lipids measured (total cholesterol, triglycerides, LDL-C, HDL-C and apolipoproteins AI, AII and B) were significantly increased on treatment as were levels of Factor X, SHBG and caeruloplasmin whereas antithrombin III decreased. In 38 of the 40 treatment cycles, ovulation was suppressed. In one cycle serum oestradiol and progesterone levels showed a typical ovulatory pattern and in another there was evidence of follicular activity without ovulation. Serum EE concentrations showed a similar pattern in both treatment cycles showing that co-administration of NET did not affect EE metabolism. Serum NET levels were higher in the 6th than in the first treatment cycles. On comparing pharmacodynamic and pharmacokinetic parameters, the only statistically significant correlations were between the percentage change in triglycerides and SHBG and serum NET, but not EE concentrations, and between apolipoproteins AI and serum EE.

Protein binding of the contraceptive steroids gestodene, 3-keto-desogestrel and ethinylestradiol in human serum

The protein binding of ethinylestradiol (EE2), gestodene (GEST) and 3-keto-desogestrel (KDG) has been determined by ultrafiltration in the serum of women who had either taken a gestodene (n = 37) or desogestrel (n = 28) containing oral contraceptive for a time period of at least 3 months. GEST and KDG were analyzed in individual serum pools whereas EE2 was repeatedly measured in two serum pools, each one representing one treatment group. The respective free fractions of the three steroids were 0.6 +/- 0.1% (GEST), 2.5 +/- 0.2% (KDG), 1.7 +/- 0.6% (EE2, in the gestodene-group) and 1.5 +/- 0.2% (EE2, in the desogestrel-group). EE2 was exclusively bound to albumin, whereas GEST and KDG were also bound to sex-hormone-binding globulin (SHBG). The distribution of the two progestins over the serum binding proteins was determined after heat-treatment of serum samples. For GEST, the contribution of albumin and SHBG was 24.1 +/- 9.1 and 75.3 +/- 9.1%, respectively and for KDG it was 65.9 +/- 11.9 and 31.6 +/- 12.0%, respectively. SHBG and corticosteroid-binding globulin (CBG) concentrations were measured in the serum samples obtained from both treatment groups. In the gestodene-group 180 +/- 61 nmol/l (SHBG) and 89 +/- 13 mg/l (CBG) were measured, the corresponding values in the desogestrel-group were 226 +/- 64 nmol/l (SHBG) and 93 +/- 14 mg/l (CBG). SHBG concentrations were correlated with the total concentration of GEST and its free fraction and a positive (r = 0.395) and negative (r = -0.491) correlation respectively was found. Only a weak negative correlation (r = -0.291) was found for SHBG and the free fraction of KDG in the serum. These data demonstrate that the three contraceptive steroids EE2, GEST and KDG were all bound extensively to serum proteins, however, with pronounced differences concerning their distribution over the various binding proteins.

Interaction with the pharmacokinetics of ethinylestradiol and progestogens contained in oral contraceptives

The serum concentrations of ethinylestradiol (EE) during the first 4 h and 24 h after intake of an oral contraceptive containing 30 micrograms EE and 75 micrograms gestodene (EE/GSD) were compared to those after intake of a preparation containing the same EE dose and 150 micrograms desogestrel (EE/DG) in each of 11 women on days 1, 10, and 21 of their 1st, 3rd, 6th, and 12th cycles. There were great interindividual variations, but during treatment with EE/GSD the EE levels were higher and the EE peaks occurred by 30 min later than during treatment with EE/DG. The areas under the EE serum concentration-versus-time curves (AUC) between 0 and 4 h were higher by 37% (p less than 0.03) and between 0 and 24 h higher by 70% (p less than 0.002) during treatment with EE/GSD. During each treatment cycle, the EE levels rose between day 1 and 10. The serum levels of corticosteroid-binding globulin (CBG), which is known to be influenced only by the estrogenic component of the combination pill, increased significantly (p less than 0.01) during each treatment cycle. CBG was elevated on day 21 of the 6th and 12th cycle by 150 to 155% and by 120 to 130% with EE/GSD and EE/DG, respectively. The difference between the two drugs was significant (p less than 0.02). During the pill-free intervals of 7 days between the treatment cycles, the CBG levels decreased but were still elevated by 85% with EE/GSD and 50% with EE/DG at the beginning of the following cycle as compared to the control cycle. The serum levels of cortisol were also significantly more elevated (p less than 0.05) during treatment with EE/GSD as compared to EE/DG. Despite the same EE dose during treatment, the higher EE levels with EE/GSD as compared to EE/DG seem to be due to a retardation of the inactivation and elimination of EE caused by the progestogen component. The rise in the EE levels during each cycle seems to be due to a reduction in the oxidative metabolism by EE itself.

The pharmacokinetics and metabolism of ethinyl estradiol and its three sulfates in the baboon

Ethinyl estradiol sulfates are major circulating metabolites of ethinyl estradiol (EE2); this is a relationship analogous to that of endogenous estrone and estrone sulfate. Because of the wide use of contraceptives containing EE2, the pharmacokinetics of its sulfate conjugates are of some importance. In previous studies of the intermediate metabolism of ethinyl estrogens we have shown that the baboon is an appropriate animal model. Accordingly, oral and/or intravenous doses of EE2 or each of its three sulfates were administered to castrate female baboons, and plasma levels of EE2 and its sulfates were studied by specific radioimmunoassay or radioisotope counting. After intravenous administration of EE2, the 3-sulfate and the 3,17-disulfate are the major circulating metabolites. After oral dosage administration, the 3-glucuronide and, in some cases, the 3,17-diglucuronide also become important. After intravenous administration, about twice as much of the drug exists in the sulfate as in the free form, as reflected by the areas under the plasma level curves. The bioavailability of orally administered EE2 was about 60%, confirming the presence of a substantial first-pass effect. Hydrolysis at the 17-position occurs when EE2-17-sulfate is administered orally but appears not to occur with intravenous administration. EE2 and the three sulfates, given intravenously, exhibited two-compartment open-model kinetics. The elimination phase half-lives of all four compounds were similar, ranging from 8.8 to 11.2 hours. The area under the plasma level curve of EE2 resulting from the intravenous administration of the 3-sulfate was approximately 8% of the total area under the plasma level curve of both EE2 and EE2 sulfates. The ratio of the area under the plasma level curve of sulfates resulting from 3-sulfate administration compared to the other two sulfates was approximately 0.3, reflecting the existence of other metabolic pathways for its disposition.

Binding capacity of testosterone-estradiol-binding globulin (TeBG), total and calculated unbound concentrations of testosterone in patients with carcinoma of the prostate treated with orchidectomy or estrogens

Testosterone-estradiol-binding globulin (TeBG) binding capacity, total estradiol-17 beta and total testosterone were measured in patients with carcinoma of the prostate treated with orchidectomy or estrogens. Comparisons were made with a control group. There was a significant increase in TeBG binding capacity in the group treated with estrogens. Both orchidectomy and estrogen-treatment decreased total testosterone significantly and to the same degree. The concentration of free testosterone was calculated using a new method, and was found to be lower in orchidectomized and estrogen treated patients when compared with the control group. When the two groups under treatment were compared, the calculated free testosterone concentration was significantly lower in the estrogen treated group.

Pharmacokinetics of oral contraceptive steroids after morning or evening administration

An oral contraceptive containing ethynyloestradiol and norethisterone was administered to six women in the morning and in the evening using a cross-over design. Serum levels of ethynyloestradiol and norethisterone were measured at various times after administration. There was no significant difference in a number of pharmacokinetic parameters between the two times of administration, suggesting that morning or evening administration of the contraceptive are equally effective.

Transfer of contraceptive steroids in milk of women using long-acting gestagens

Levels of norethisterone and medroxyprogesterone acetate were measured in serum and milk of women receiving the injectable contraceptive formulations Norigest and DepoProvera, respectively, throughout complete injection intervals. In 5 of 10 women receiving Norigest, serum norethisterone levels were undetectable by 8 weeks after injection and only 2 women had detectable levels of norethisterone in milk at this time. In contrast, 8 of 10 women receiving DepoProvera had detectable levels of medroxyprogesterone acetate in both serum and milk 12 weeks after injection. The ratio of the milk:serum concentrations of norethisterone varied from 0.12 to 0.92 (mean 0.34) and for medroxyprogesterone acetate from 0.12 to 2.60 (mean 0.88). It is unlikely that these differences between the two formulations are due entirely to differences between the binding of norethisterone and medroxyprogesterone acetate to serum proteins. The area under the curve of serum steroid concentrations plotted against time was only 50% higher for women injected with DepoPovera than for those injected with Norigest but the area under the curve for milk values was 400 times higher. Assuming the infant ingests 600 ml daily, the daily intake of steroids in the first week after injection would be 0.5 to 2.4 micrograms for norethisterone and 1 to 13 micrograms for medroxyprogesterone acetate. By 8 weeks after injection, the amount of norethisterone ingested would be small but that of medroxyprogesterone acetate would still be significant.

Plasma levels of ethinylestradiol (EE) during cyclic treatment with combined oral contraceptives

The purpose of the present study was to extend the still limited data concerning ethinylestradiol (EE) plasma levels after repeated daily ingestion of a combination pill during the course of classical cyclic treatment. Plasma EE levels were followed in 13 volunteers throughout, in total, 19 treatment cycles with either a 50 ug EE (+ 125ug d-norgestrel) or a 30 ug (+ 150ug d-norgestrel) containing oral contraceptive. In addition, single plasma EE determinations were performed in 110 chronic oral contraceptive users. Whereas different patterns in plasma EE levels (sampling 24 hours following last pill ingestion) were observed among the different volunteers, the mean levels increased progressively during treatment and reflected closely the differences in dosage. The values obtained in the volunteers at the end of the treatment cycle showed important interindividual variations. The findings during a first treatment cycle or during the following ones were similar and for different treatment cycles in the same patient, the patterns in plasma EE levels were consistent. The results for single plasma determinations in chronic contraceptive users (sampling between 8th and 21st day of treatment cycle, 9 to 24 hours since last pill ingestion) showed more pronounced interindividual variations, the individual EE levels being not correlated to parameters such as body weight, body surface, months of oral contraception prior to the study, sex hormone binding capacity or day of the cycle. However, significant differences in mean plasma EE levels were noticed for patients treated with different commercial preparations with identical EE content, suggesting the existence of differences in bioavailability. The relevancy of plasma EE determinations is discussed and from the results of the present study, it is concluded that a strictly standardized time of sampling is an absolute condition for obtaining interpretable results.

Pharmacokinetics of ethynyloestradiol in women for different populations

The pharmacokinetics of a dose of 50 microgram ethynyloestradiol administered orally was studied in fourteen centres. Absorption was rapid and the highest serum concentrations of total ethynyloestradiol were found in most subjects at 1 h and by 24 h concentrations were less than 250 pg/ml. Calculation of the half-lives for absorption, distribution and elimination showed wide variations between subjects, the half-life of elimination varying from 2.5 h to more than 30 h. Bioavailability as measured by the area under the serum ethynyloestradiol concentration-time curve also showed more than a ten-fold variation. Intra-centre differences in the various parameters measured were as large as the inter-centre differences.