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Route of estrogen administration may influence venous thromboembolism risk

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22nd Annual Meeting of NAMS

WASHINGTON, D.C. — An estradiol transdermal system bested oral estrogen-only hormone therapy agents in terms of reducing risk for and decreasing incidence of venous thromboembolism, researchers reported here.

In a study sponsored by Novartis, Eric Beresford, PharmD, and colleagues searched health insurance claims from the Thomson Reuters MarketScan Database from 2002 to 2009 for cases of venous thromboembolism among women who newly initiated treatment with a transdermal estradiol system (Vivelle-Dot, Novartis) or oral estrogen-only HT. All patients included in the study were aged at least 35 years and had received two or more dispensings of either form of HT. Estradiol transdermal system dosage strength ranged from 0.025 mg to 0.1 mg daily. To assess the impact of dosage strength, subgroup analyses of women initiating high-dose estradiol transdermal system based on two definitions — 0.075 mg daily or 0.1 mg daily and 0.1 mg daily — were reported. Of the 30,457 women treated with the estradiol transdermal system and 159,281 receiving oral estrogen-only therapy, 27,018 patients from each group were matched for the study.

The incidence of venous thromboembolism was lower in the transdermal group, Beresford said at a presentation here. He said 115 cases occurred in transdermal users compared with 164 cases in the oral administration group (incidence rate ratio=0.72; 95% CI, 0.57-0.91).

In addition, risk for venous thromboembolic events remained significantly lower in women using the high-dose estradiol transdermal system than in those using oral formulation, according to Beresford. Among the women who initiated the estradiol transdermal treatment at 0.075 mg or 0.1 mg daily, only 45 women developed venous thromboembolism vs. 80 women in the oral therapy group (incidence rate ratio=0.58; 95% CI, 0.4-0.84). In the group in which high dose was defined as 0.1 mg daily, 32 transdermal users and 65 oral estrogen-only users had VTE events (incidence rate ratio=0.52; 95% CI, 0.34-0.8)

“[These results suggest] that women receiving estrogen transdermal systems had a significantly lower incidence rate of venous thromboembolism and hospitalizations related to venous thromboembolisms than women receiving oral estrogen-only HT,” Beresford said. “Data from this study have also shown a lower risk of venous thromboembolisms associated with transdermal systems that remains significant in women initiating both high-dose and lower-dose estradiol transdermal system relative to matched oral estrogen-only women.” – by Melissa Foster

For more information:

• Kahler KH. S-4. Presented at: the 22nd Annual Meeting of the North American Menopause Society; Sept. 21-24, 2011; Washington, D.C.

Disclosure: Dr. Beresford is an employee of Novartis.

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