Safety of nonoral estrogen therapy. Administration of nonoral estrogen is associated with avoidance of hepatic first-pass metabolism and a resulting lower impact on hepatic proteins. Thus, data indicate a potentially lower risk for venous thromboembolic events with transdermal estrogen compared to oral estrogen.1 Since the publication of the results of the WHI trials, prescribing patterns in the United States indicate a general decline in the proportion of oral hormones, while transdermal prescription volume has remained steady, and the use of vaginal formulations has increased.2
Topical estrogen formulations. Transdermal or topical delivery of estrogen can be achieved through various formulations, including patches, gels, and a spray. While patches are simple to use, some women display hypersensitivity to the adhesive. Use of gel and spray formulations avoids exposure to adhesives, but these pose a risk of transfer of hormonal ingredients that are not covered by a patch. This risk is amplified by the relative accessibility of the product-specific application sites, which include the arms or thighs. Each manufacturer recommends careful handwashing after handling the product, a specific drying time before the user covers the site with clothing, and avoidance of contact with the application site for a prescribed period of time, usually at least 1 to 2 hours.3-6
Our patient. This case illustrates the importance of discussing the risk of medication transfer to both humans and animals when prescribing individualized hormone therapy. While the Evamist prescribing information specifically addresses the risk of unintentional medication transfer to children, it does not discuss other contact risks.6 In the literature, there have been a limited number of reports on the adverse effects from transdermal or topical human medication transfer to pets. Notably, the American Pet Products Association estimates that in the United States, approximately 90 million dogs and 94 million cats are owned as a pet in 67% of households.7
THE TAKEAWAY
Use of HRT, including transdermal or topical estrogen formulations, is common. Given the large number of companion animals in the United States, physicians should consider that all members of a patient’s household—including pets—may be subject to unintentional secondary exposure to topical estrogen formulations and that they may experience adverse effects. This presents an opportunity for patient education, which can have a larger impact on all occupants of the home.
CORRESPONDENCE
Shannon Scott, DO, FACOFP, Clinical Associate Professor, Arizona College of Osteopathic Medicine, 19389 North 59th Avenue, Glendale, AZ 85308; sscott1@midwestern.edu.