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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:3071-3078.)
© 1997 American Heart Association, Inc.

Articles

Effects of Oral and Transdermal Estrogen/Progesterone Regimens on Blood Coagulation and Fibrinolysis in Postmenopausal Women

A Randomized Controlled Trial

Pierre-Yves Scarabin; Martine Alhenc-Gelas; Geneviève Plu-Bureau; Pascale Taisne; Rachid Agher; ; Martine Aiach

From the INSERM-Cardiovascular Epidemiology Unit U258 (P.-Y. S., G.P.-B., R.A.) and Laboratory of Haemostasis and INSERM Unit 428 (M.A.-G., P.T., M.A.), Hôpital Broussais, Paris, France.

Correspondence to Dr P.-Y. Scarabin, INSERM - Cardiovascular Epidemiology Unit U258, Hôpital Broussais, 96, rue Didot, Paris, France. E-mail epicv{at}hbroussais.fr

	Abstract

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Abstract Postmenopausal hormone replacement therapy is associated with a reduction in the incidence of coronary heart disease. However, inconclusive results have been reported with respect to the risk of stroke, and recent studies consistently showed an increased risk of venous thromboembolism in postmenopausal women using oral estrogen. There are surprisingly few interventional studies to assess the true effects of estrogen-progestin regimens on blood coagulation and fibrinolysis, and the impact of the route of estrogen administration on hemostasis has not been well documented. Therefore, we investigated the effects of oral and transdermal estradiol/progesterone replacement therapy on hemostatic variables. Forty-five healthy postmenopausal women, aged 45 to 64 years, were assigned randomly to one of the three following groups: cyclic oral or transdermal estradiol, both combined with progesterone, or no hormonal treatment. Hemostatic variables were assayed at baseline and after a 6-month period. Pairwise differences in the mean change between the three groups were compared using nonparametric tests. Oral but not transdermal estradiol regimen significantly increased the mean value of prothrombin activation peptide (F1+2) and decreased mean antithrombin activity compared with no treatment. Differences in fragment F1+2 levels between active treatments were significant. The oral estrogen group was associated with a significant decrease in both mean tissue-type plasminogen (t-PA) concentration and plasminogen activator inhibitor (PAI-1) activity and a significant rise in global fibrinolytic capacity (GFC) compared with the two other groups. A transdermal estrogen regimen had no significant effect on PAI-1, t-PA, and GFC levels. There were no significant changes in mean values of fibrinogen, factor VII, von Willebrand factor, protein C, fibrin D-dimer, and plasminogen between and within the three groups. We conclude that oral estrogen/progesterone replacement therapy may result in coagulation activation and increased fibrinolytic potential, whereas opposed transdermal estrogen appears without any substantial effects on hemostasis. Whereas these results may account for an increased risk of venous thromboembolism in users of oral postmenopausal estrogen, they emphasize the potential importance of the route of estrogen administration in prescribing hormone replacement therapy to postmenopausal women, especially to those at high risk of thrombotic disease.

Key Words: menopause • hormone replacement therapy • hemostasis

	Introduction

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Cardiovascular diseases are the leading cause of morbidity and mortality among women in developed countries. The incidence of coronary heart disease (CHD) rises dramatically after the menopause¹ and observational studies suggest that hormone replacement therapy (HRT) reduces the CHD risk.^2,3 However, inconclusive results have been reported with respect to the risk of stroke,^2,3 and HRT has long been believed to have little effect on the risk of venous thromboembolism.⁴ Most of these studies were performed in the United States among women using oral estrogen alone or combined with progestin. Parenteral estrogen is used widely in European countries, especially in France, but little relevant information on the cardiovascular effects of this hormone regimen is available. The apparent cardioprotective effect of HRT is believed to be largely mediated through favorable effects on both plasma lipoproteins profile and arterial wall.⁵ Despite some evidence that HRT may inhibit the development of atherosclerosis,⁶ the indications for HRT in postmenopausal women remain a subject of debate, and the effects of different formulations on both venous and arterial thrombotic process have not yet been a mainstream subject for investigation.

Some specific regimens or doses of estrogen are likely to be thrombogenic. Combined oral contraceptives are associated with an increased risk of venous thromboembolism,⁷ and low-estrogen preparations may still have adverse effects on blood coagulation.⁸ High-dose conjugated equine estrogens have been shown to be associated with a rise in incidence of myocardial infarction in both men⁹ and postmenopausal women.² Several recent case-control studies have showed consistent associations between current users of HRT and an increased risk of venous thromboembolism in postmenopausal women.^10-12 However, the findings were restricted to women who used oral estrogen alone or combined with progestagens. One of these studies¹⁰ stated that only a few women used transdermal therapy, and a nonsignificant increase in the thrombotic risk was found in this subgroup.

There are surprisingly few interventional studies that assess the true effects of HRT regimens on blood coagulation and fibrinolysis. Furthermore, the impact of the route of estrogen administration on hemostasis is not well documented. Therefore, we investigated the effects of oral and transdermal estradiol/progesterone regimens on hemostatic variables in a randomized controlled clinical trial.

	Subjects and Methods

Top Abstract Introduction Subjects and Methods Participants Study Design and Treatments Informed Consent Follow-up and Measurements Statistical Analysis Results Discussion References

 

	Participants

Top Abstract Introduction Subjects and Methods Participants Study Design and Treatments Informed Consent Follow-up and Measurements Statistical Analysis Results Discussion References

 
Subjects were recruited through six gynecologist practitioners in Paris between September 1992 and June 1995. Healthy women aged 45 to 64 years, with an intact uterus, were invited to participate in the trial. Two screening visits were scheduled to evaluate eligibility. Women were required to be naturally menopausal (no menstrual period for at least 6 months, follicle-stimulating hormone (FSH) level greater than 40 IU/L, and serum estradiol level lower than 30 pg/mL). Normal baseline results of mammography were also required. Women had to be free of cardiovascular diseases (including blood pressure greater than or equal to 160 mm Hg systolic or 95 mm Hg diastolic), diabetes, and cancer. Subjects taking antihypertensive medication, cholesterol-lowering drugs, and/or antithrombotic treatment were not eligible. Women who had used HRT or other hormone therapy within 3 months were excluded, as were women who had severe menopausal symptoms. Women who had total cholesterol level higher than 6.72 mmol/L were also excluded. Other exclusion criteria included abnormal vaginal bleeding and previous history of breast or endometrial cancer.

	Study Design and Treatments

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This study was an open, randomized, controlled trial aimed to assess the effects of oral and transdermal cyclic (25 days/month) 17-ß estradiol (E2) combined with progesterone on hemostatic variables. Women were randomly assigned in equal numbers to one of the three following groups: oral E2 valerate (2 mg/d) or transdermal E2 (2.5 mg/d), both combined with micronized progesterone (200 mg/d from days 14 to 25), or no hormonal treatment. Transdermal E2 was given in the form of gel as described.¹³ Women were requested to take the active drugs at bedtime. The HRT regimens were those currently used in France, and micronized progesterone was chosen because it is likely to have little effect on blood coagulation. A blocked randomization was used to assign women in equal numbers to one of the three treatment groups. Treatment allocation was stratified by clinical investigator. The study was not designed to be double-blind because of regular bleeding in the two active treatment groups. To assess the compliance to treatment, clinical data and biolological measurements (serum E2 and FSH level) were used.

With a two-sided =0.05, the study was expected to have a 80% statistical power to detect a difference between groups of about 1 standard deviation for a normally distributed variable. Based on a previous study of menopause-related changes in hemostatic variables,¹⁴ it was estimated that sample size would be large enough to detect relative changes of about 20% and 16% in plasma fibrinogen concentration and factor VII activity, respectively (eg, absolute difference of about 0.50g/L and 0.17 IU/mL, respectively).

	Informed Consent

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Each clinical investigator as well as a local ethics committee approved the study protocol and consent forms. Information on study design was provided to all participants, who gave written informed consent for the trial.

	Follow-up and Measurements

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All the potential participants were asked to attend a central laboratory of hemostasis (Hôpital Broussais, Paris) at the first screening visit and 6 months after randomization. Fasting blood samples were obtained beween 8 and 10 AM, and women under active treatment were required to schedule the 6-months visit between day 13 and day 21. Systematic biological measurements included hemostatic variables, plasma lipids and lipoproteins, and serum hormones. Blood pressure was also measured using standardized procedure.

With regard to hemostatic tests, venous blood (9 volumes) was collected into siliconized tubes (Vacutainer, Becton Dickinson) containing 0.11 mol/L trisodium citrate (1 volume). Platelet-poor plasma was obtained by two centrifugation steps at 2500g and 12°C for 15 mn. Without delay, aliquots of plasma were transferred to plastic tubes, quickly frozen, and stored at -50°C. At the time of assay, plasma samples were transferred to a water-bath at 37°C for 5 minutes and then handled at room temperature. Baseline and 6-months samples from the same subject were analyzed within the same batch to minimize measurement error. All hemostatic tests were performed within a 1-year period following blood collection.

Fibrinogen was measured according to the method of Clauss¹⁵ using Fibrinomat (Biomérieux, Marcy l'Etoile, France) as reagent. Coagulant factor VII activity (factor VIIc) was assayed in a regular one-stage system using rabbit thromboplastin (Thrombomat, Biomerieux) and factor VII-deficient substrate plasma (Diagnostica Stago, Asnières, France). Activated factor VII (factor VIIa) was determined with a clot-based assay using a soluble, recombinant, truncated tissue factor (Staclot FVIIa-rTF, Diagnostica Stago) as described.¹⁶ Antithrombin and protein C activities were measured by automated amidolytic method using commercially available kits (Hemolab AT Chrom and Hemolab PC Chrom, respectively, Biomerieux). PAI-1 activity was measured by a two-stage amidolytic method using the Spectrolyse pl (V1 to 1) kit (Biopool, Umea, Sweden). Plasminogen activity was measured using the kit Berichrom plasminogen (Behring, Marburg, Germany). Commercially available kits based on ELISA methods were used for determining factor VII antigen (Asserachrom FVIIag, Diagnostica Stago), prothrombin fragments F1+2 (Enzygnost F1+2 micro, Behring), D Dimer (Fibrinostika FBDP, Organon Teknika, Fresnes, France), von Willebrand factor (Asserachrom vWF, Diagnostica Stago), PAI-1 antigen (Tint Elize PAI1, Biopool), and t-PA antigen (Tint Elize tPA, Biopool). Global fibrinolytic capacity (GFC) was determined with an assay based on the ability of plasma to degrade a standardized fibrin clot at 37°C in the presence of purified t-PA.¹⁷ Results were expressed as the amount of D Dimer generated for 1 hour.

Several internal quality control materials were used during the study. A normal plasma pool from 15 healthy sujects was used for PAI-1 antigen, D Dimer, and von Willebrand factor. A single batch of lyophilized control plasmas was used for each of other hemostatic variables. Coag Norm (Diagnostica Stago) and/or Uniplasmatrol Index P (Biomérieux) control plasmas were used for factor VIIc, factor VIIag, fibrinogen, antithrombin, and protein C activities. PAI activity and t-PA antigen control plasma sets (Biopool) were used for PAI-1 activity and t-PA antigen, respectively. Control plasma P (Behring) was used for plasminogen. Plasma controls were available in the factor VIIa and prothrombin fragment 1+2 kits.

All the hemostatic tests were performed in duplicate, and coefficients of variation for laboratory procedures were ranged from 3% (fibrinogen) to 12% (PAI activity).

	Statistical Analysis

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Statistical analysis used procedures available in the Statistical Analysis System (SAS) software (SAS Institute, Inc., Cary, N.C.). The distributions of PAI activity and antigen were positively skewed, and these variables were logarithmically transformed. Geometric means and approximate standard deviations are given in the tables for these measurements. Linear rank statistics were used for all hypothesis testing. Wilcoxon signed-rank tests were used for within-group comparisons and results are presented for descriptive purposes only. Assessment of treatment effects were based on the mean changes from the baseline. Wilcoxon sum-rank tests were used to assess pairwise differences between the three treatment groups. The 95% confidence intervals for between groups differences were estimated according to the method of Bonferroni. A two-tailed P value <.05 was considered statistically significant.

	Results

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A total of 65 women were eligible for the first screening visit and attended the central laboratory of hemostasis. Of these, 11 women were excluded because of either high serum cholesterol concentration (8 women) or elevated plasma estradiol levels (3 women), and 54 women (83%) entered the trial. Of these 54 women, 45 (83%) completed the trial and nine (17%) dropped out. The reasons for withdrawal from the study were concern about HRT (2 women), abnormal bleeding (2 women), discomfort during treatment (2 women), lack of time for participation (2 women), and weight gain (1 woman). The number of women who were lost to follow-up was approximately equal in the three groups. Two women were not within the treatment period at the 6-month visit, and they were excluded from analysis.

Table 1 summarizes the baseline values for the clinical data among the three randomly assigned treatment groups. There was no significant imbalance between the groups with respect to these general characteristics. Table 2 shows the mean changes in sex hormone level by treatment groups. Both active treatments increased the mean values of plasma estradiol substantially, with a further rise associated with the transdermal estradiol regimen, and clearly decreased the mean levels of FSH. Mean values of E2 and FSH remained at similar level in untreated group.

View this table: [in this window] [in a new window]   Table 1. Clinical Data by Treatment Groups

View this table: [in this window] [in a new window]   Table 2. Plasma E2 and FSH at Baseline and After 6 Months by Treatment Groups

Table 3 gives the values of hemostatic variables by treatment groups at baseline and after 6 months of follow-up. There was no significant difference between groups in baseline levels for the main outcome variables. Highly significant changes were detected in the oral estradiol group. Mean levels of F1+2 prothrombin fragment and global fibrinolytic capacity increased by about 15% and 60% respectively, whereas the mean values of antithrombin, PAI activity, and t-PA antigen decreased by about 10%, 50%, and 20% respectively.

View this table: [in this window] [in a new window]   Table 3. Hemostatic Variables at Baseline and After 6 Months of Treatment

Table 4 shows the differences in the mean changes between the treatment groups; Fig 1 depicts only the significant effects. Oral but not transdermal estradiol regimen increased mean value of prothrombin activation peptide (F1+2) significantly and decreased mean antithrombin activity compared with no treatment. Differences in F1+2 levels between active treatments were significant. The oral estrogen group was associated with a significant decrease in both mean t-PA concentration and PAI-1 activity and with a significant rise in GFC compared with the two other groups. Transdermal estrogen regimen had no significant effect on PAI-1, t-PA, and GFC levels. There were no significant changes in mean values of fibrinogen, factor VII, von Willebrand factor, protein C, fibrin D-Dimer, and plasminogen between the three groups.

View this table: [in this window] [in a new window]   Table 4. Comparison of Treatment Effects on Hemostatic Variables

View larger version (20K): [in this window] [in a new window]   Figure 1. Bar graphs show the mean changes in F1+2 levels (a), antithrombin activity (b), PAI-1 activity (c), t-PA antigen (d), and global fibrinolytic capacity (e) by treatment groups. Only significant between-group differences are shown. E: estrogen, P: progesterone.

	Discussion

Top Abstract Introduction Subjects and Methods Participants Study Design and Treatments Informed Consent Follow-up and Measurements Statistical Analysis Results Discussion References

 
This trial provide experimental evidence for an increase in both the amount of thrombin generated in vivo and the fibrinolytic potential in postmenopausal women who use cyclic oral estrogen/progesterone. By contrast, our results show no significant change in hemostatic variables in transdermal estrogen users. Furthermore, the two routes of estrogen administration differ significantly with respect to blood coagulation and fibrinolysis.

Some clotting factors may play an important role in the pathogenesis of CHD.¹⁸ Plasma fibrinogen level is a powerful predictor of CHD in men and women.¹⁹ Raised factor VII coagulant activity has been found to be associated with an increased risk of myocardial infarction.²⁰ Population-based studies consistently showed higher levels of fibrinogen^21-25 and factor VII^22-24,26 in postmenopausal than in premenopausal women of the same age. Recent cross-sectional data suggested that HRT could lower plasma fibrinogen^27-30 and reverse the menopause-related changes in factor VII.¹⁷

Our study fails to detect any changes in either plasma fibrinogen or factor VII levels between treatment groups. The extensive postmenopausal estrogen/progestin interventions (PEPI) in the United States showed recently that placebo resulted in a significantly greater increase in mean fibrinogen than any active treatments.³¹ In the PEPI trial, HRT was given as continuous conjugated equine estrogen (0.625 mg per day) alone or in combination with medroxyprogesterone (cyclic or consecutive) or cyclic micronized progesterone. The magnitude of the effects was relatively small (0.04 to 0.12g/L), and the number of subjects included in our trial may have not been large enough to detect such differences. One smaller placebo-controlled study did not find any significant changes in fibrinogen among postmenopausal women using cyclic oral estradiol (1 or 1.5 mg per day) combined with nomegestrol acetate.³² Two randomized comparisons failed to detect significant differences in fibrinogen levels between transdermal estradiol (continuous or cyclic 50 µg per day) alone or combined with medroxyprogesterone and oral conjugated equine estrogen (0.625 mg per day) alone or in combination with medroxyprogesterone.^33,34 In a recent placebo-controlled study,³⁵ continuous transdermal estradiol (50 µg per day) combined with sequential medroxyprogesterone significantly decreased fibrinogen concentration. All these results are consistent with a small HRT-induced decrease in fibrinogen level or no HRT effect.

With regard to factor VII, conflicting results have been reported. A rise in factor VII has been found in postmenopausal women using unopposed oral conjugated equine estrogen (0.625 mg per day) or transdermal estradiol³³ or oral estradiol valerate (2 mg per day) alone.³⁶ No significant change in factor VII was detected in women receiving opposed cyclic oral estrogen^32,34 as well as trandermal estradiol.³⁴ One placebo-controlled study showed that continuous transdermal estrogen (50 µg per day) resulted in decreased factor VII activity.³⁵ Interestingly, a randomized trial reported higher factor VII activity attributable to oral conjugated equine estrogen (0.625 mg/day) alone compared with estrogen combined with a progestogen norgestrel.³⁷ Our data suggest that opposed oral or transdermal estrogen does not affect substantially factor VII levels. Cross-sectional data recently suggested that HRT could lower activated factor VII.³⁸ Our results do not support this finding.

Antithrombin III and protein C are important inhibitors of coagulation. The present study shows that oral, but not transdermal, estrogen significantly decreases antithrombin activity as reported with oral estradiol (2 mg/day)^13,39 as well as conjugated equine estrogen.^33,40 No significant change is observed with respect to protein C. A placebo-controlled study reported a significant rise in protein C in postmenopausal women receiving high-dose oral conjugated equine estrogen (1.25 mg per day) but not in those using conventional 0.625 mg dosage.⁴⁰ Other trials failed to detect any significant changes in proteine C among women receiving oral conjugated estrogen (0.625 mg per day) or transdermal estradiol (50 µg per day) combined or not combined with medroxyprogesterone.^33,35

The effects of HRT on markers of hemostatic system activation are not well documented. Our results show higher F1+2 levels in the oral estrogen group than in both untreated and transdermal groups. Consistent with this finding, a dose-dependent increase in mean values of F1+2 and fibrinopeptide A has been reported in a randomized, placebo-controlled trial of unopposed conjugated equine estrogen at 0.625 mg or 1.25 mg per day.⁴⁰ However, transdermal estrogen use was not investigated in this study. Another clinical trial³³ reported high F1+2 levels in postmenopausal women using unopposed oral conjugated estrogen (0.625 mg per day). No significant change in F1+2 concentration was detected recently in a randomized, placebo-controlled trial of cyclic oral estradiol (1 or 1.5 mg per day) combined with nomegestrol acetate, but the sample size was small.³² Reliable assays for F1+2 measurement have been developed to monitor factor Xa action on prothrombin, and we used the basal concentration of this peptide activation as an indicator of hypercoagulable state.⁴¹ Elevated plasma F1+2 levels are found during acute thombotic events⁴² as well as in subjects with increased risk of venous thromboembolism.⁴³ Furthermore, increased levels of plasma F1+2 in men at high risk of myocardial infarction have been recently reported.⁴⁴

A reduction in fibrinolytic activity attributable to increased PAI-1 activity has recently emerged as a novel putative risk factor for CHD.⁴⁵ High PAI-1 levels have been reported consistently in postmenopausal women not receiving HRT compared with premenopausal women.^46-48 Observational studies suggested an association between HRT and increased fibrinolytic potential,^17,30,47,48 but experimental data are scarce. Our study demonstrates that oral, but not transdermal, estrogen/progesterone significantly decreases both PAI activity and t-PA concentration, and significantly increases global fibrinolytic activity. Two clinical trials are consistent with our findings. A fall in PAI-1 activity associated with unopposed oral conjugated estrogens (0.625 mg per day), but not with transdermal estradiol (50 µg per day), has been reported,³³ and another study³⁵ showed no significant change in PAI-1 activity in postmenopausal women receiving cyclic or continuous transdermal estradiol (50 µg per day) combined with medroxyprogesterone. In the present study, t-PA antigen was positively correlated with PAI-1 activity and antigen (r>.6, P<.001) as reported.^47,48 In addition, t-PA antigen was negatively correlated with global fibrinolytic activity (r=.64, P <.01). Therefore, t-PA antigen assay probably detect circulating complexes of inactive t-PA and PAI-1, and a rise in t-PA antigen may be an indicator of reduced fibrinolysis, which can result in an increased CHD risk.^49,50 However, recent data emphasized differences between PAI-1 and t-PA antigen with respect to their biological significance as CHD risk markers.⁵¹

Our results show no significant difference in fibrin D Dimer concentrations within and between groups, and no significant correlation was detected between the mean changes in fibrinolytic variables and F1+2 levels. Therefore, the oral estrogen-related changes in fibrinolytic system do not appear as a compensatory effect in response to increased hemostatic system activation. An increased fibrinolytic activity induced by oral estrogen should theorically protect against the atherothrombotic process, but this potential benefit is somewhat puzzling when allowance is made for blood coagulation activation and the clinical relevance of increased fibrinolytic potential in postmenopausal women using oral estrogen remains unclear. However, although no significant change in D Dimer concentration was detected in postmenopausal women using oral estrogen, the pattern of effects on blood coagulation and fibrinolysis is close to those observed in oral contraceptive users.⁵² It should be emphasized that use of oral contraceptives containing a low dose of ethynil estradiol is still associated with an increased risk of venous thromboembolism.⁷

The mechanisms underlying the effects of oral estrogen replacement therapy on hemostatic variables remain speculative. It is unlikely that an estrogen-related decrease in the clearance of prothrombin peptide activation will explain the rise in F1+2 levels in women receiving oral estrogen. Oral, but not trandermal, estrogen administration leads to high hormone concentrations in the liver. This so-called first-pass effect may result in impaired hepatic biosynthesis and secretion of a number of proteins that may be responsible for changes in blood coagulation and fibrinolysis.⁵³ These effects may be mediated through estrogen receptors that modulate transcription of target genes.⁵⁴ With regard to fibrinolytic system, t-PA is mainly released by vascular endothelium, whereas PAI-1 is producted by a number of cells, including hepatocytes and endothelial cells.⁴⁵ The absence of significant change in vWF levels suggests that estrogen does not alter endothelial function. Therefore, decreased t-PA antigen in women using oral estrogen could be a consequence of low levels of PAI-1 and inactive t-PA/PAI-1 complex. Plasma triglycerides and insulin levels are strongly and positively correlated with PAI-1 activity.⁴⁵ Oral estrogen use increases triglycerides levels and appears without any substantial effect on insulin levels.³¹ Therefore, reduction in insulin resistance is unlikely to explain the oral estrogen-induced changes in fibrinolysis.

The effects of progestogens on the hemostatic system is not well documented. Recent data suggested that users of oral contraceptives containing a third-generation progestogen (desogestrel or gestoden) had higher risk of venous thromboembolic disease than did users of the first (norethindrone type) and second (norgestrel group) generations.⁷ In addition, third-generation oral contraceptives may have more pronounced adverse effects on hemostasis than other preparations.⁵² However, these new progestogens have not yet been used in current HRT practice. In a recent case-control study,¹⁰ there was no significant difference in the risk of venous thromboembolic disease between HRT with estrogen alone or combined with progestogens. Two randomized trials have investigated the effects of estrogen versus estrogen plus progestogen on CHD risk markers. There was little difference between conjugated equine estrogen (0.625 mg per day) alone and the same regimen of estrogen combined with cyclic norgestrel (150 µg per day) in their lipid and hemostatic effects.³⁷ In the PEPI trial in the U.S.,³¹ actively treated women were receiving conjugated equine estrogen (0.625 mg per day) alone or combined with either cyclic or continuous medroxyprogesterone acetate (10 mg or 2.5 mg per day, respectively) or cyclic micronized progesterone (200 mg per day). There was no significant difference in plasma fibrinogen concentration between active treatments. In our study, the two estrogen/progesterone regimens differed only on the route of estrogen administration. Therefore, natural progesterone is unlikely to explain the oral estrogen-induced changes in the hemostatic system.

Our results appear of great relevance to clinical findings and may have implications for the management of menopause in current medical practice. While it is doubtful that the cardioprotective effect of HRT, if any, might be mediated through favorable changes in coagulation cascade, a hypercoagulable state may explain an increased risk of arterial thrombosis in women who use high dose of oral estrogen.^2,3 Furthermore, a rise in the amount of thrombin generated in vivo may account for an increased risk of venous thromboembolism in postmenopausal women receiving oral estrogen as recently reported.^10-12 Inconclusive results are available with respect to the route of estrogen administration. Among the recent data, only one case-control study showed a nonsignificant increase in the thrombotic risk in women using transdermal therapy, but this finding was based on only five cases of women who were current HRT users.¹⁰ Until the results of clinical end-point trials are available,⁵⁵ our data suggest that indications for oral estrogen should be restricted to postmenopausal women without any increased risk of thrombotic disease, whereas transdermal estrogen appears safe with respect to hemostatic system. Pending the results of other trials, our findings emphasize the potential importance of the route of estrogen administration in prescribing HRT to postmenopausal women, especially to those at high risk of thrombotic disease.

The main limitation of this randomized clinical trial deals with the statistical power. The sample size may not have been large enough to detect small differences in clotting factors between treatment groups, and confidence intervals of estimates are large. Another drawback arises from the menopausal status of the women enrolled in the trial. In some cases, HRT was given in an early stage of menopause, and the effect of treatments on hemostatic variables may have been attenuated. The long-term effects of HRT, as well as the dose of estrogen and the impact of progestins on the hemostatic system, require further investigation.

	Acknowledgments

 
Clinical investigators: Dr M. Cochard, Dr E. Delavoipiere, Dr M. Detoeuf, Dr M.C. Lebrun, Dr M. Scarabin, Dr P. Touraine. Coordinating center: Institut National de la Santé et de la Recherche Medical (INSERM), U 258: P.-Y. Scarabin, MD (Principal Investigator), G. Plu-Bureau, MD, R. Agher, Msc (Statistical analysis). Hemostasis laboratory: M. Aiach, PhD, M. Alhenc-Gelas, PhD, P. Taisne, and Biochemistry Laboratory: N. Moatti, PhD, M. Cambillaud, PhD. Hôpital Broussais, Paris. This work was supported by grants from INSERM, Mutuelle Générale de l'Education Nationale (MGEN), and Laboratoires Besins-Iscovesco, Paris. We thanks Stago Group (Asnières, France) for determining global fibrinolytic activity.

Received October 2, 1996; accepted February 7, 1997.

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Top Abstract Introduction Subjects and Methods Participants Study Design and Treatments Informed Consent Follow-up and Measurements Statistical Analysis Results Discussion References

 

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