Mechanism of action of emergency contraceptive pills

Population-based evaluation of the effectiveness of two regimens for emergency contraception

OBJECTIVE

To estimate and compare the effectiveness of the levonorgestrel and Yuzpe regimens for hormonal emergency contraception in routine clinical practice.

METHODS

A retrospective population-based study included women who accessed emergency contraceptives for immediate use prescribed by community pharmacists in British Columbia, Canada, between December 2000 and December 2002. Linked administrative healthcare data were used to discern the timings of menses, unprotected intercourse, and any pregnancy-related health services. A panel of experts evaluated the compatibility of observed pregnancies with the timing of events. The two regimens were compared with statistical adjustments for potential confounding.

RESULTS

Among 7493 women in the cohort, 4470 (59.7%) received levonorgestrel and 3023 (40.3%) the Yuzpe regimen. There were 99 (2.2%) compatible pregnancies in the levonorgestrel group and 94 (3.1%) in the Yuzpe group (P=0.017). The estimated odds ratio for levonorgestrel compared with the Yuzpe regimen after adjusting for potential confounders was 0.64 (95% confidence interval 0.47-0.87). Against an expected pregnancy rate of approximately 5%, the relative and absolute risk reductions were 56.0% and 2.8%, respectively, for levonorgestrel and 36.7% and 1.8% for the Yuzpe regimen.

CONCLUSION

The levonorgestrel regimen is more effective than the Yuzpe regimen in routine use. The data suggest that both regimens are less effective than has been observed in randomized trials.

Does levonorgestrel emergency contraceptive have a post-fertilization effect? A review of its mechanism of action

BACKGROUND

Recent studies have identified that levonorgestrel administered orally in emergency contraception (LNG-EC) is only efficacious when taken before ovulation. However, the drug does not consistently prevent follicular rupture or impair sperm function.

OBJECTIVE

The present systematic review is performed to analyze and more precisely define the extent to which pre-fertilization mechanisms of action may explain the drug's efficacy in pregnancy avoidance. We also examine the available evidence to determine if pre-ovulatory drug administration may be associated with post-fertilization effects.

CONCLUSION

The mechanism of action of LNG-EC is reviewed. The drug has no ability to alter sperm function at doses used in vivo and has limited ability to suppress ovulation. Our analysis estimates that the drug's ovulatory inhibition potential could prevent less than 15 percent of potential conceptions, thus making a pre-fertilization mechanism of action significantly less likely than previously thought. Luteal effects (such as decreased progesterone, altered glycodelin levels, and shortened luteal phase) present in the literature may suggest a pre-ovulatory induced post-fertilization drug effect.

LAY SUMMARY

Plan B is the most widely used emergency contraceptive available. It is important for patients and physicians to clearly understand the drug's mechanism of action (MOA). The drug was originally thought to work by preventing fertilization. Recent research has cast doubt on this. Our review of the research suggests that it could act in a pre-fertilization capacity, and we estimate that it could prevent ovulation in only 15 percent or less of cases. The drug has no ability to alter sperm function and limited ability to suppress ovulation. Further, data suggest that when administered pre-ovulation, it may have a post-fertilization MOA.

Ectopic Pregnancy After Plan B Emergency Contraceptive Use

BACKGROUND

Pregnancy outcomes after emergency contraceptive use has been debated over time, but review of the literature includes mechanisms by which these medications may increase the chance of an ectopic pregnancy. Such cases are infrequently reported, and many emergency providers may not readily consider this possibility when treating patients.

CASE REPORT

This is a case presentation of ectopic pregnancy in a patient who had recently used Plan B (levonorgestrel) emergency contraceptive. She presented with abdominal pain and vaginal spotting, and was evaluated by serum testing and pelvic ultrasound. She was discovered to have a right adnexal pregnancy. She was treated initially with methotrexate, though she ultimately required surgery for definitive treatment. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This case report aims to bring a unique clinical case to the attention of emergency providers. The goal is to review research on the topic of levonorgestrel use and the incidence of ectopic pregnancies. The mechanism of action of this emergency contraceptive is addressed, and though no definite causal relationship is known between levonorgestrel and ectopic pregnancies, there is a pharmacologic explanation for how this event may occur after use of this medication. Ultimately, the emergency provider will be reminded of the importance of educating the patient on the possible outcomes after its use, including failure of an emergency contraceptive and the potential of ectopic pregnancy.

Preferential Cyclooxygenase 2 Inhibitors as a Nonhormonal Method of Emergency Contraception: A Look at the Evidence

OBJECTIVE

To review the literature surrounding the use of preferential cyclooxygenase 2 (COX-2) inhibitors as an alternative form of emergency contraception.

DATA SOURCES

MEDLINE (1950 to February 2014) was searched using the key words cyclooxygenase or COX-2 combined with contraception, emergency contraception, or ovulation. Results were limited to randomized control trials, controlled clinical trials, and clinical trials.

STUDY SELECTION AND DATA EXTRACTION

Human trials that measured the effects of COX inhibition on female reproductive potential were included for review.

DATA SYNTHESIS

The effects of the COX-2 inhibitors rofecoxib, celecoxib, and meloxicam were evaluated in 6 trials. Each of which was small in scope, enrolled women of variable fertility status, used different dosing regimens, included multiple end points, and had variable results.

CONCLUSIONS

Insufficient evidence exists to fully support the use of preferential COX-2 inhibitors as a form of emergency contraception. Although all trials resulted in a decrease in ovulatory cycles, outcomes varied between dosing strategies and agents used. A lack of homogeneity in these studies makes comparisons difficult. However, success of meloxicam in multiple trials warrants further study. Larger human trials are necessary before the clinical utility of this method of emergency contraception can be fully appreciated.

Knowledge and beliefs about mechanism of action of birth control methods among European women

BACKGROUND

Adequate knowledge is essential for making informed decisions. We attempted to determine the level of knowledge about mechanisms of action of birth control methods in five representative samples of European women.

STUDY DESIGN

Randomly selected women, aged 18-49 years, completed an anonymous survey in Germany, France, the UK, Sweden and Romania (N=1137). Participants were asked about how contraceptive methods work and if providers should inform them about this issue. Multiple linear regression was used to evaluate women's characteristics associated with their knowledge of mechanisms of action.

RESULTS

The majority of women identified the unequivocal mode of action of condoms, sterilization and abortion. Fewer than 2% identified all possible mechanisms of action of hormonal contraceptives and intrauterine devices. Highly educated women correctly identified the mechanism or mechanisms of action of more methods than less educated women (β=0.22, 95% confidence interval 0.01-0.43). Regardless of their sociodemographic characteristics and their belief about when human life begins, most women (75%) stated that the provider should inform them about possible postfertilization effects.

CONCLUSIONS

European women have low knowledge about mechanisms of action of several contraceptive methods. The majority want to be informed about possible postfertilization effects. Since adequate knowledge is essential for making informed decisions, providers are encouraged to inform women about all possible mechanisms of action of contraceptives.

Women's attitudes towards mechanisms of action of family planning methods: survey in primary health centres in Pamplona, Spain

Background

Informed consent in family planning includes knowledge of mechanism of action. Some methods of family planning occasionally work after fertilization. Knowing about postfertilization effects may be important to some women before choosing a certain family planning method. The objective of this survey is to explore women's attitudes towards postfertilization effects of family planning methods, and beliefs and characteristics possibly associated with those attitudes.

Methods

Cross-sectional survey in a sample of 755 potentially fertile women, aged 18–49, from Primary Care Health Centres in Pamplona, Spain. Participants were given a 30-item, self-administered, anonymous questionnaire about family planning methods and medical and surgical abortion. Logistic regression was used to identify variables associated with women's attitudes towards postfertilization effects.

Results

The response rate was 80%. The majority of women were married, held an academic degree and had no children. Forty percent of women would not consider using a method that may work after fertilization but before implantation and 57% would not consider using one that may work after implantation. While 35.3% of the sample would stop using a method if they learned that it sometimes works after fertilization, this percentage increased to 56.3% when referring to a method that sometimes works after implantation. Women who believe that human life begins at fertilization and those who consider it is important to distinguish between natural and induced embryo loss were less likely to consider the use of a method with postfertilization effects.

Conclusion

Information about potential postfertilization effects of family planning methods may influence women's acceptance and choice of a particular family planning method. Additional studies in other populations are necessary to evaluate whether these beliefs are important to those populations.

Effectiveness of levonorgestrel emergency contraception given before or after ovulation--a pilot study

BACKGROUND

Although widely used, the mechanisms of action of the levonorgestrel emergency contraceptive pill (LNG ECP) are still unclear. There are increasing data to indicate that LNG is particularly effective as an ECP by interrupting follicular development and ovulation. An important outstanding question is whether it has any effect on fertilization or implantation.

METHOD

Ninety-nine women participated; they were recruited at the time they presented with a request for emergency contraception. All women took LNG 1.5 mg in a single dose during the clinic consultation. A blood sample was taken immediately prior to ingestion of the ECP for estimation of serum LH, estradiol and progesterone levels to calculate the day of ovulation. The specimens were analyzed in a single batch. Based on these endocrine data, we estimated the timing of ovulation to be within a +/-24-h period with an accuracy of around 80%. Women were followed up 4-6 weeks later to ascertain pregnancy status. The effectiveness of ECP when taken before and after ovulation was determined.

RESULTS

Three women became pregnant despite taking the ECP (pregnancy rate, 3.0%). All three women who became pregnant had unprotected intercourse between Days -1 and 0 and took the ECP on Day +2, based on endocrine data. Day 0 was taken as ovulation day. Among 17 women who had intercourse in the fertile period of the cycle and took the ECP after ovulation occurred (on Days +1 to +2), we could have expected three or four pregnancies; three were observed. Among 34 women who had intercourse on Days -5 to -2 of the fertile period and took ECP before or on the day of ovulation, four pregnancies could have been expected, but none were observed. We found major discrepancies between women's self-report of stage of the cycle and the dating calculation based on endocrine data.

CONCLUSION

These data are supportive of the concept that the LNG ECP has little or no effect on postovulation events but is highly effective when taken before ovulation.