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A journal club style critical review of current publications in evidence-based transgender medical care.

Wednesday, May 30, 2012

Transdermal Estradiol Reduces Risk of Venus Thromboembolism in Menopausal Hormone Replacement Therapy

Matched cohort study looks at risk reduction of using transdermal estrogen vs. oral in menopausal hormone therapy. (1) 

     In this matched cohort study of incidence of VTE in women using menopausal HRT, investigators attempted to quantify the risk reduction for VTE events associated with transdermal relative to oral estrogens.  Claims records from a health insurance database of 30 million people living in the US were reviewed over the period of January 2002 - October 2009 for patients who had received at least two dispensings of a transdermal or oral estradiol and were over age 35.  Users of other estrogens such as vaginal or injections and those with a prior VTE were excluded.  At total of 27,018 women were enrolled in each cohort.  Interestingly while only 22.4% of women in each cohort had undergone hysterectomy, a minority of the women were using a progestagen.  Primary outcome measures were the overall VTE risk as well as hospitalization-related VTE, as measured by incidence rate.

     Mean drug exposure times were 391 days for transdermal estrogen and 401 days for oral estrogens.    A total of 115 VTE events were encountered in the transdermal group vs. 164 in the oral group; a statistically significant difference.  Further analysis revealed more pronounced statistically significant reductions in VTE incidence among hospitalized women and reductions in PE incidence.

     Yet another study highlighting the likely benefits of transdermal HRT with respect to VTE risk.  While this study did not compare incidence to a control population, overall VTE incidence in both cohorts was slightly higher than reported baseline incidences.  This raises the possibility of an overall skewing of the sample population, though it may not affect internal validity of the results.  It is noteworthy that the average times on HRT was just over 1 year in both cohorts;  given that the risk of VTE is highest in the first year of HRT, this may explain such skewing.  Further studies should compare oral vs. transdermal VTE incidences in those on longer term HRT when the overall VTE risk is lower, and specifically in transgender populations.  

     It is possible that there might be a skewing of results toward higher incidences of VTE as the investigators included all oral estrogen forms including conjugated equine estrogens in the oral therapy arm.

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