Transdermal hormone replacement therapy is associated with the lowest risk of venous thromboembolism, yet still is relatively underused compared to oral preparations, researchers say.
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Writing in the BMJ, Yana Vinogradova, PhD, of the University of Nottingham (England) and her associates reported the results of two nested case-control studies of hormone replacement therapy (HRT) and venous thromboembolism (VTE) from Jan. 1998 to Feb. 2017 that altogether included 80,396 women aged 40-79 years with a primary diagnosis of VTE matched to 391,494 female controls.
Overall, 7% of the women with VTE had been exposed to HRT in the 90 days before the index date versus 5.5% of controls.
The greatest increase in risk of VTE, compared with no exposure, was seen with oral conjugated equine estrogen with medroxyprogesterone acetate, which was associated with a more than twofold increase in risk (odds ratio, 2.10; 95% confidence interval, 1.92-2.31; P less than .01).
However transdermal HRT use was not associated with any increase in risk, compared with no HRT exposure. The data even pointed to a slight decrease in risk, which the authors suggested may be the result of some residual confounding or indication bias.
Oral HRT generally was associated with a 58% increased risk of VTE, which amounted to a number needed to harm of 1,076 and nine extra cases of VTE per 10,000 women taking oral HRT.
Dr. Vinogradova and her colleagues noted that the vast majority of women in the study were being prescribed oral HRT for menopausal symptoms despite previous studies showing transdermal HRT has much lower risk.
“When women with menopausal symptoms already have an increased VTE risk because of comorbidities or obesity, these women and their doctors should give greater consideration to transdermal HRT,” they wrote.
Lubna Pal, MBBS, director of the menopause program and professor of obstetrics, gynecology, and reproductive sciences at Yale University, New Haven, Conn., commented in an interview, “These data are tremendously reassuring. The reported findings are: 1) reaffirm what we have already known , i.e. that advancing age, higher body mass index, and higher doses of exogenous systemic estrogen therapy are associated with increased risk for VTE; 2) offer greater granularity in risk for VTE with different formulations of estrogens and progestins and different regimens than understood thus far, 3) reaffirm that, unlike oral estrogen, transdermal estrogen formulations in doses commonly utilized in clinical practice are not associated with VTE risk, and 4) provide reassurance that the absolute risk, while exaggerated with oral estrogen or combination estrogen and progestin use, is nonetheless small as reflected in the number needed to harm with oral hormone therapy being 1,076, and the number of extra VTE cases attributable to oral HT being 9 per 10,000 woman years.
“The authors are to be commended on this massive analytic undertaking that allows an improved understanding of HRT-related risk for VTE and offers meaningful guidance to the practitioner,” said Dr. Pal, who was not involved in the study.*
Estrogen-only preparations had a 40% higher risk and combined preparations had a 73% higher risk, compared with no exposure.
In estrogen-only preparations, the lowest risk was seen with estradiol, compared with conjugated equine estrogens or combined preparations.
The lowest risk of VTE among oral preparations was seen with estradiol plus dydrogesterone, which only showed a nonsignificant 18% increase in risk.
In an attempt to account for possible increased risk of VTE, the authors conducted a sensitivity analysis in a subgroup of women who had not previously used anticoagulants, but they found similar results to the main analysis.
“This sensitivity analysis indicates that most of the excluded women had probably used anticoagulants because of atrial fibrillation or hip replacement operations rather than an earlier unrecorded VTE,” they wrote.
One author declared directorship of a clinical software company, but no other conflicts of interest were declared. There was no external funding. Dr. Pal reported that she was a coinvestigator in the Kronos Early Estrogen Prevention Study and on an AMAG Pharmaceuticals advisory board and member of their speaker’s bureau.
SOURCE: Vinogradova Y et al. BMJ. 2019 Jan 9. doi: 10.1136/bmj.k4810.
*This article was updated 1/11/19.