New Method Is as Effective As Levonorgestrel After Unprotected Intercourse
A new emergency contraceptive that was approved for use in Europe in 2009 is at least as effective as levonorgestrel, according to a study comparing the two methods.1 Among a sample of women who visited family planning clinics in the United Kingdom, Ireland and the United States in 2007–2009, and who took either ulipristal acetate or levonor-gestrel within 72 hours of unprotected intercourse, similar proportions of each group (1.8–2.6%) became pregnant. Furthermore, among women who had taken the drug 73–120 hours after unprotected sex, no pregnancies occurred in the ulipristal acetate group, whereas three occurred in the levonorgestrel group. Adverse events were reported by 54–56% of women in each treatment group; most were rated mild or moderate. In a meta-analysis combining data from this and an earlier study, ulipristal acetate was more effective than levonorgestrel whether taken within 24, 72 or 120 hours after unprotected intercourse.
The study was conducted among 2,221 women who had sought emergency contraception at one of 35 family planning clinics within 120 hours of having unprotected intercourse. To be eligible, women had to have a regular menstrual cycle (24–35 days) and be at least 16 years old (in the United Kingdom) or 18 (in Ireland and the United States). Women who were pregnant, breast-feeding, sterilized, or using an IUD or a hormonal contraceptive, or whose partner was sterilized, were excluded from the study.
Participants were randomly assigned to receive either 30 mg of ulipristal acetate or 1.5 mg of levonorgestrel during the clinic visit, and were asked to keep a daily diary of subsequent acts of intercourse, contraceptive use, vaginal bleeding, medication use and adverse events. Pregnancy tests were conducted 5–7 days after the expected onset of next menses, and women with delayed menses were tested for up to 60 days after treatment; pregnancies judged to have predated the use of emergency contraception were excluded. The two drugs were compared in a logistic regression model that incorporated the probability of conception as a cofactor. To increase the generalizability of the results, the researchers conducted a meta-analysis, combining their data with those from a similar study, and used a nominal logistic regression model that controlled for study and treatment factors, as well as significant covariates, to calculate the magnitude of the treatment effect.
The two treatment groups had similar background characteristics. Women were, on average, 25 years old; three-quarters were white, and most of the rest were black. Half had been pregnant before, and half had previously used an emergency contraceptive; the reasons for seeking emergency contraception were contraceptive nonuse (55–56%), condom failure (38–39%) and failure of another method (5–6%). Finally, 33–35% had sought treatment within 24 hours of unprotected sex, 34–35% within 25–48 hours, 20–22% within 49–72 hours and 11% of each group within 73–120 hours.
Efficacy analysis was limited to the 1,899 participants who were younger than 35, were first-time study enrollees and had their pregnancy status after treatment determined. Among those who received treatment within 72 hours of unprotected intercourse, 15 pregnancies occurred in the ulipristal acetate group and 22 in the levonorgestrel group. The corresponding pregnancy rates of 1.8% and 2.6%, respectively, were significantly lower than the expected rates (5.5% and 5.4%); they did not differ from each other in the regression analysis. Three pregnancies occurred among participants who received treatment 73–120 hours after unprotected sex, all in the levonorgestrel group; significantly more pregnancies were prevented in the ulipristal acetate group than in the levonorgestrel group during this treatment period.
Fifty-four percent of women who had taken ulipristal acetate reported an adverse event, as did 56% of those who had taken levonorgestrel; 94% of women in each group rated these events as mild or moderate. Both groups reported similar rates of all events; headache, dysmenorrhea and nausea were the most common. Only two serious events were reported that may have been related to treatment: one case of dizziness in a woman who received ulipristal acetate, and a molar pregnancy (a form of miscarriage that involves the growth of abnormal pregnancy tissue in the uterus) in a woman who received levonorgestrel.
On average, onset of next menses after treatment was 2.1 days later than expected among women in the ulipristal acetate group and 1.2 days earlier than expected in the levonorgestrel group. Among participants who reported data on their cycle length, menses occurred within seven days of the expected time for 76% of women in the ulipristal acetate group and 71% of those in the levonorgestrel group. Duration of bleeding was not affected by either treatment.
In the meta-analysis, the likelihood of getting pregnant was lower among women who had received ulipristal acetate than among those who had received levonorgestrel within 24 hours, 72 hours or 120 hours after unprotected intercourse (odds ratios, 0.4–0.6).
The researchers note several limitations of the study: It was restricted to countries in which emergency contraceptives are now dispensed predominantly without a prescription; women who were current or recent users of hormonal methods were excluded; and participants were advised to abstain from intercourse or to use barrier methods for the remainder of their menstrual cycles, even though many health care providers advise women to start taking continuous hormonal contraceptives immediately following use of an emergency method. Nonetheless, the authors believe that because ulipristal acetate is licensed for use up to 120 hours after unprotected sex and was significantly more effective than levonorgestrel over this period, the method offers women and providers a valuable alternative for emergency contraception.
1. Glasier AF et al., Ulipristal acetate versus levonor-gestrel for emergency contraception: a randomised non-inferiority trial and meta-analysis, Lancet, 2010, 375(9714):555–562.