Transdermal Patch (EVRA)
How They Work; Pros and Cons
The contraceptive patch (Evra®) has been available in Canada since January 2004. It is a 4 x 4 cm beige patch that sticks to a woman’s skin and continuously releases 20µg of ethinyl estradiol and 150µg of the progestin norelgestromin (the primary metabolite of norgestimate) per day. (These transdermal doses cannot be directly compared to oral doses.)
Mechanism of Action
Similar to the combined oral contraceptive, the patch’s primary mechanism of action is to prevent ovulation by suppressing gonadotropin secretion. Likewise, it can also thicken the cervical mucus, cause endometrial atrophy and possibly impair tubal transport.
Each patch is worn for seven days. A patch is applied to clean, dry, intact skin on the shoulder, abdomen, buttocks or torso (not on the breasts) on the first day of the menstrual period. This becomes the “Patch Change Day”. A patch is applied weekly on the patch change day for three weeks. The fourth week is patch-free, allowing for menses. Alternately, the patch can be used semi-continuously like the oral contraceptive pill, by eliminating the patch-free week to skip menses.
Like the combined oral contraceptive, the patch has a failure rate of 0.3% per year when used perfectly, with about a 3% failure rate for typical users. It may be less effective in women who weigh more than 90 kg (198 pounds). The patch may work better than the combined OCP in women who have trouble remembering to take a pill every day. One study showed 88% perfect use of the patch, regardless of the woman’s age, while only 78% of women overall used the pill perfectly (and adherence decreased with younger age).
- Effective birth control that only needs to be remembered once per week
- Continual release gives steady serum hormone levels; no fluctuations
- Avoids the gastrointestinal tract and the “first pass effect”
- Cycle control; timed, lighter periods
- Reversible; no delay to fertility
- Other non-contraceptive benefits are assumed to be similar to the combined oral contraceptive.
- Does not protect against sexually transmitted infections or HIV.
- Costs slightly more than the Pill (cost to pharmacies is $14 per month versus ~$12 per month for OCP), and may not yet be covered by all drug plans.
- Same contraindications as the combined oral contraceptive.
- Nuisance side effects when starting can include breakthrough bleeding, breast tenderness, headaches, or nausea, similar to the combined oral contraceptive. Initially, breast tenderness and breakthrough bleeding may be more common with the patch than the pill, but these symptoms usually resolve after the first few months.
- Skin irritation from the strong adhesive of the patch is common (20%) but only 2% of users discontinued it for this reason. Rotating the site is recommended.
How to start
The first patch should be applied on the first day of bleeding. Women switching from a combined oral contraceptive should also start on their first day of bleeding (not when they would have started the next pack of pills) because of the delayed rise to therapeutic serum levels. If the patch is applied after the first day of the period, the woman may not be protected from pregnancy and should use a back-up method of contraception if she has intercourse in the first 7 days of the cycle.
An alternative is the “Quick Start” method, which is useful if contraception is needed quickly. After excluding pregnancy, the first patch can be applied at the office visit, regardless of where the patient is in her cycle. Back-up contraception is needed for 7 days.
The woman should check each day to make sure the patch is still well applied.
If the edges come loose
She can try to smooth it back on by pressing with her hand for 10 seconds. If it does not stick back on, or comes off completely, she should apply a new patch. (The principle is that the hormones are only being absorbed if the patch is “sticking” adequately.) She would still have the same patch change day and is still protected against pregnancy.
If the patch falls off for more than 24 hours
A new patch should be applied as soon as possible, and a new four-week cycle started. She will have a new patch change day and will need to use a back-up method of birth control for the next week.
Forgotten patch change (2 days or less)
She should apply a new patch when she remembers, is still protected against pregnancy. She can either keep the same patch change day or adopt the new one. If she is more than 2 days late in changing the patch, she should start a new four-week cycle as soon as possible. The patch change day will change, and she will need to use a back-up method of birth control for the first week.
Forgotten patch removal at the start of the patch-free week
The patch should be removed when remembered and the next cycle started on the usual day.
Prolonged patch-free interval
If the patch-free interval is longer than 7 days, there is a risk of pregnancy. She should begin the new cycle as soon as possible as long as pregnancy is excluded (consider emergency contraception if necessary). She will need to use back up birth control for the first week of the new cycle.