The first transdermal contraceptive patch was approved by the US Food and Drug Administration (FDA) in 2001.1 A 2018 survey revealed that 5% of women in the United States between the ages of 15 and 49 years reported the use of a short-acting hormonal contraceptive method (ie, vaginal ring, transdermal patch, injectable) within the past month, with just 0.3% reporting the use of a transdermal patch.2 Transdermal contraceptive patches are an effective form of birth control that may be a convenient option for patients who do not want to take a daily oral contraceptive pill but want similar efficacy and tolerability. Typical failure rates of patches are similar to that of combined oral contraceptives (COCs).1,3
While transdermal hormone delivery results in less peaks and troughs of estrogen compared with COCs, the total estrogen exposure is higher than with COCs; therefore, the risk for venous thromboembolism (VTE) with previously available patches is about twice as high.1 Twirla (Agile), an ethinyl estradiol (EE)/levonorgestrel (LNG) patch, delivers a low and consistent daily dose of hormones over 3 patches replaced once weekly, with no patch on the fourth week.3 Twirla contains 120 μg/day LNG and 30 μg/day EE. OrthoEvra, FDA approved in 2001 as mentioned, contains 150 μg/day norelgestromin and 35 μg/day EE.1 A reduction of the EE dose in COCs has been associated with lower risk for VTE.4
The addition of Twirla to the market offers another contraceptive option for patients who opt for a weekly, self-administered method.
How much lower is the VTE risk?
OBG Management: Can you define what is the reduction in VTE risk for the EE dose in Twirla versus Ortho Evra (a norelgestromin/EE patch) and similar contraceptive patches already available?
Barbara Levy, MD: The reality is we can’t designate a reduction of risk, except, in general, when the dose of ethinyl estradiol is lower, we think that the VTE risk is lower. There has not been a head-to-head comparison in a large enough population to be able to say that the risk is reduced by a certain factor. We just look at the overall exposure to estrogen and say, “In general, for VTE risk, a lower dose is a better thing for women.”
That being said, look at birth control pills, like COCs. We don’t have actual numbers to say that a 30-μg pill is this much less risky than a 35-μg pill. We just put it into a hierarchy, and that’s what we can do with the patch. We can say that, in general, lower is better for VTE risk, but no one can provide absolute numbers.
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