Hormonal consequences of "missing the pill"

U.S. Selected Practice Recommendations for Contraceptive Use, 2024

The 2024 U.S. Selected Practice Recommendations for Contraceptive Use (U.S. SPR) addresses a selected group of common, yet sometimes complex, issues regarding initiation and use of specific contraceptive methods. These recommendations for health care providers were updated by CDC after review of the scientific evidence and a meeting with national experts in Atlanta, Georgia, during January 25-27, 2023. The information in this report replaces the 2016 U.S. SPR (CDC. U.S. Selected Practice Recommendations for Contraceptive Use, 2016. MMWR 2016;65[No. RR-4]:1-66). Notable updates include 1) updated recommendations for provision of medications for intrauterine device placement, 2) updated recommendations for bleeding irregularities during implant use, 3) new recommendations for testosterone use and risk for pregnancy, and 4) new recommendations for self-administration of injectable contraception. The recommendations in this report are intended to serve as a source of evidence-based clinical practice guidance for health care providers. The goals of these recommendations are to remove unnecessary medical barriers to accessing and using contraception and to support the provision of person-centered contraceptive counseling and services in a noncoercive manner. Health care providers should always consider the individual clinical circumstances of each person seeking contraceptive services. This report is not intended to be a substitute for professional medical advice for individual patients; when needed, patients should seek advice from their health care providers about contraceptive use.

Effect of missed combined hormonal contraceptives on contraceptive effectiveness: a systematic review

BACKGROUND

Combined hormonal contraceptives (CHCs) are popular methods of reversible contraception in the United States, but adherence remains an issue as reflected in their lower rates of typical use effectiveness. The objective of this systematic review was to evaluate evidence on the effect of missed CHCs on pregnancy rates as well as surrogate measures of contraceptive effectiveness (e.g., ovulation, follicular development, changes in hormone levels, cervical mucus quality).

STUDY DESIGN

We searched the PubMed database for peer-reviewed articles published in any language from database inception through April 2012. We included studies that examined measures of contraceptive effectiveness during cycles with extended hormone-free intervals or nonadherence (e.g., omission of pills, delayed patch replacement) on days not adjacent to the hormone-free interval. We used standard abstract forms and grading systems to summarize and assess the quality of the evidence.

RESULTS

The search strategy identified 1387 articles, of which 26 met our study selection criteria. There is wide variability in the amount of follicular development and risk of ovulation among women who extended the pill-free interval to 8-14 days; in general, the risk of ovulation was low, and among women who did ovulate, cycles were usually abnormal (i.e., low progesterone levels, small follicles and/or poor cervical mucus) (Level I, good, indirect to Level II-3, fair, indirect). Studies of women who missed one to four consecutive pills or 1-3 consecutive days of delay before patch replacement at times other than adjacent to the hormone-free interval reported little follicular activity and low risk of ovulation (Level I, fair, indirect to Level II-3, poor, indirect). Studies comparing 30 mcg versus 20 mcg mc ethinyl estradiol pills showed more follicular activity when 20 mcg ethinyl estradiol pills were missed (Level I, good, indirect).

CONCLUSION

Most of the studies in this evidence base relied on surrogate measures of pregnancy risk and ranged in quality. For studies providing indirect evidence on the effects of missed CHCs, it is unclear how differences in surrogate measures correspond to pregnancy risk. Fewer studies examined the transdermal patch and vaginal ring than combined oral contraceptives.

Menstrual suppression for adolescents with developmental disabilities

The approach to menstrual suppression for adolescents with developmental disabilities has evolved considerably over the years due to changing philosophies and evolving treatment options. We review the medical management options available for menstrual suppression with a focus on the needs and treatment of adolescents with developmental disabilities.

Missed hormonal contraceptives: new recommendations

OBJECTIVE

To provide evidence-based guidance for women and their health care providers on the management of missed or delayed hormonal contraceptive doses in order to prevent unintended pregnancy.

EVIDENCE

Medline, PubMed, and the Cochrane Database were searched for articles published in English, from 1974 to 2007, about hormonal contraceptive methods that are available in Canada and that may be missed or delayed. Relevant publications and position papers from appropriate reproductive health and family planning organizations were also reviewed. The quality of evidence is rated using the criteria developed by the Canadian Task Force on Preventive Health Care.

BENEFITS, HARMS, AND COSTS

This committee opinion will help health care providers offer clear information to women who have not been adherent in using hormonal contraception with the purpose of preventing unintended pregnancy.

SPONSORS

The Society of Obstetricians and Gynaecologists of Canada. SUMMARY STATEMENTS: 1. Instructions for what women should do when they miss hormonal contraception have been complex and women do not understand them correctly. (I) 2. The highest risk of ovulation occurs when the hormone-free interval is prolonged for more than seven days, either by delaying the start of combined hormonal contraceptives or by missing active hormone doses during the first or third weeks of combined oral contraceptives. (II) Ovulation rarely occurs after seven consecutive days of combined oral contraceptive use. (II) RECOMMENDATIONS: 1. Health care providers should give clear, simple instructions, both written and oral, on missed hormonal contraceptive pills as part of contraceptive counselling. (III-A) 2. Health care providers should provide women with telephone/electronic resources for reference in the event of missed or delayed hormonal contraceptives. (III-A) 3. In order to avoid an increased risk of unintended pregnancy, the hormone-free interval should not exceed seven days in combined hormonal contraceptive users. (II-A) 4. Back-up contraception should be used after one missed dose in the first week of hormones until seven consecutive days of correct hormone use are established. In the case of missed combined hormonal contraceptives in the second or third week of hormones, the hormone-free interval should be eliminated for that cycle. (III-A) 5. Emergency contraception and back-up contraception may be required in some instances of missed hormonal contraceptives, in particular when the hormone-free interval has been extended for more than seven days. (III-A) 6. Back-up contraception should be used when three or more consecutive doses/days of combined hormonal contraceptives are missed in the second and third week until seven consecutive days of correct hormone use are established. For practical reasons, the scheduled hormone-free interval should be eliminated in these cases. (II-A) 7. Emergency contraception is rarely indicated for missed combined hormonal contraceptives in the second or third week of the cycle unless there are repeated omissions or failure to institute back-up contraception after the missed doses. In cases of repeated omissions of combined hormonal contraceptives, emergency contraception may be required, and back-up contraception should be used. Health care professionals should counsel women in these situations on alternative methods of contraception that do not demand such stringent compliance. (III-A).

Effective use of hormonal contraceptives

This systematic review examines evidence regarding when during the menstrual cycle a woman can initiate combined oral contraceptive (COC) use and what can be done if a woman misses COCs. We searched the MEDLINE and EMBASE databases for articles published from 1966 to March 2005 related to COC initiation and to the effects of late or missed COCs. We identified 11 studies related to COC initiation and 25 studies related to the effects of missed pills. Evidence from these studies suggested that taking hormonally active pills for 7 consecutive days prevents normal ovulation and that initiating COCs through Day 5 of the menstrual cycle suppresses follicular activity. Studies on the effects of missed COCs generally showed that the risk of ovulation is greatest when the pill-free interval lasts >7 days. Limitations of this body of evidence include small sample sizes that may not reflect variation in larger populations, lack of a standard measurement of ovulation and difficulty in discerning how ovulation resulting from late or missed COCs corresponds to the risk of conception.

Modeling and simulation of adherence: approaches and applications in therapeutics

Partial adherence with a prescribed or randomly assigned dose gives rise to unintended variability in actual drug exposure in clinical practice and during clinical trials. There are tremendous costs associated with incomplete and/or improper drug intake-to both individual patients and society as a whole. Methodology for quantifying the relation between adherence, exposure and drug response is an area of active research. Modeling and statistical approaches have been useful in evaluating the impact of adherence on therapeutics and in addressing the challenges of confounding and measurement error which arise in this context. This paper reviews quantitative approaches to using adherence information in improving therapeutics. It draws heavily on applications in the area of HIV pharmacology.

Faculty Statement from the CEU on a New Publication: WHO Selected Practice Recommendations for Contraceptive Use Update Missed pills: new recommendations

The World Health Organisation Selected Practice Recommendations for Contraceptive Use (WHOSPR) was first published in 2002 and provides evidence-based recommendations on how to use contraception effectively. The WHOSPR was adapted for UK use by the Faculty of Family Planning and Reproductive Heath Care (FFPRHC). The UK version is available on the FFPRHC website (www.ffprhc.org). Extensive field experience with the first edition of the WHOSPR highlighted to the WHO the need for revised recommendations for missed combined oral contraceptive pills (COCs). The WHOSPR was updated in 2004 and revised guidance on missed pills published. This guidance is now available on the WHO website (www.who.int/reproductive-health). The FFPRHC endorses the new recommendations from WHO on missed COCs for the following reasons: There is new evidence on which to base guidance. The WHOSPR follow a published and rigorous process for assessing the available evidence. The recommendations were developed by an international expert panel, with UK representation. Field experience shows a need for simple, harmonised guidance. This Statement summarises the revised WHOSPR evidence-based 'missed pill rules' in formats which we hope clinicians will find useful. We recognise that different individuals favour different styles for the presentation of information. Thus, both tabular and flow chart styles of summary are provided; these convey the same information but in different ways. The FFPRHC considers that the following statements may also serve as useful aides memoir for the 'missed pill rules': Whenever a woman realises that she has missed pills, the essential advice is 'just keep going'. She should take a pill as soon as possible and then resume her usual pill-taking schedule. Also, if the missed pills are in week three, she should omit the pill-free interval. Also, a back-up method (usually condoms) or abstinence should be used for 7 days if the following numbers of pills are missed: 'Two for twenty' (ie if two or more 20 microgram ethinylestradiol pills are missed). 'Three for thirty' (ie if three or more 30-35 microgram ethinylestradiol pills are missed). The fpa (Family Planning Association) has produced a revised COC user information sheet to reflect these changes; available from April 2005.

Follicular growth during contraceptive pill or vaginal ring treatment depends on the day of ovulation in the pretreatment cycle

BACKGROUND

The aim of this study was to investigate whether the day of ovulation and the duration of a pretreatment cycle were related to the degree of follicular growth during subsequent contraceptive treatment.

METHODS

This randomized, open-label study was performed in 40 healthy female volunteers, who were randomized by a computer-generated list after stratification for the ovulation day in a pretreatment cycle. They received two cycles of NuvaRing (21 subjects) or a combined oral contraceptive (COC) containing 30 microg ethinylestradiol and 150 microg levonorgestrel (19 subjects). Follicular diameter and serum hormone concentrations (FSH, LH, 17beta-estradiol, progesterone) were measured every third day. Data from treatment day 20 onwards were used for analysis.

RESULTS

In the NuvaRing users, subjects with short cycles and early ovulations in the pretreatment cycle developed larger follicles during treatment than subjects with longer cycles and late ovulations. In the COC users, subjects with early ovulations in the pretreatment cycle developed larger follicles during treatment.

CONCLUSIONS

The degree of follicular growth during treatment with a combined hormonal contraceptive is influenced by the duration of the pretreatment cycle and particularly by the duration of the follicular phase.

Ovarian follicular development is initiated during the hormone-free interval of oral contraceptive use

We evaluated ovarian follicular development in women during compliant use of oral contraceptives (OC). Thirty-six healthy women received: [35 microg ethinyl estradiol (21)/180 microg norgestimate (7), 215 microg norgestimate (7), 250 microg norgestimate (7)]; [30 microg ethinyl estradiol (21)/150 microg desogestrel (21)]; or [20 microg ethinyl estradiol (21)/100 microg levonorgestrel (21)] for 3 consecutive 28-day cycles. Transvaginal ultrasonography was performed every third day to monitor follicular development. If a follicle reached > or = 14 mm, ultrasonography was performed daily and blood drawn every other day to determine estradiol-17beta concentrations. Seventeen of 36 women (47%) grew follicles > or = 10 mm. Nine of the 17 women (53%) grew follicles > or = 14 mm, in association with increased serum concentrations of estradiol-17beta. Thirty-seven of 43 follicles > or = 10 mm (86%) emerged during the hormone-free interval (HFI). No ovulations were observed. Our results supported the hypothesis that follicular development to an ostensibly ovulatory diameter occurs during compliant OC use, in association with loss of endocrine suppression during the HFI.

Plasma concentrations of endogenous hormones during one regular treatment cycle with a low-dose oral contraceptive and during two cycles with deliberate omission of two tablets

In this open, prospective, phase-I study we closely monitored levels of endogenous progesterone, 17beta-estradiol, luteinizing hormone (LH) and follicle stimulating hormone in six healthy women. We determined plasma concentrations every 1-3 days during one untreated baseline cycle and during the first treatment cycle with regular pill intake of an oral contraceptive containing 30 microg ethinylestradiol plus 75 microg gestodene. During the following two treatment cycles, two tablets were deliberately omitted (in cycle 2 on days 6/7 and in cycle 3 on days 11/12). All but possibly one volunteer ovulated in the untreated pre-cycle, as concluded from LH peaks followed by marked increases of progesterone. During the regular first treatment cycle and even after deliberate omission of two tables in treatment cycles 2 and 3, the progesterone and estradiol levels remained low, so that we concluded that no ovulation took place. However, two volunteers showed some sort of LH peak in the first regular treatment cycle and all women showed LH increases of > 40 microg/ml in at least one omission cycle. In ten out of 12 cycles, omissions of pill intake were followed by an episode of intermenstrual bleeding. In conclusion, we have shown that, after omission of two consecutive oral contraceptive tables, the endogenous hormone parameters did not provide evidence for ovulation. Although this provides confirmation of the robustness of this oral contraceptive towards non-compliance, the widely published practical recommendations should be followed.

Ovarian follicular development during the use of oral contraception: a review

Over the past 40 years, alterations to the composition of oral contraceptives (OCs) have been made in attempts to reduce adverse effects and to improve patient compliance while maintaining contraceptive efficacy. However, there is growing evidence to indicate that reducing the estrogen dose to minimize adverse effects may have compromised the degree of hypothalamo-pituitary-ovarian suppression, particularly during the hormone-free interval (HFI) or following missed doses. Follicle development during OC use appears to occur in association with a loss of endocrine suppression during the HFI. This information provides a rationale for reducing or eliminating the HFI in OC regimens. There is also evidence for an increased risk of follicle development and ovulation in women who use delayed OC initiation schemes, such as the "Sunday Start" method. It is not currently known why some follicles ovulate during OC use while others regress or form anovulatory follicle cysts. Continued research about follicle development during OC use would provide insight into understanding the precise mechanisms of action underlying combined OCs, as well as those of continuous OC formulations and emergency contraceptive regimens.

Long-Cycle Treatment with Oral Contraceptives

The conventional regimen of oral contraceptive (OC) use mimics the natural cycles by causing regular withdrawal bleeding, which can be avoided by omission of the hormone-free interval of 7 days. Consequently, long-cycle regimens with continuous administration of OCs for 3 or 6 months followed by a hormone-free interval of 7 days may reduce the frequency of menstruations and cycle-dependent complaints. Surveys have revealed that, despite a higher rate of irregular bleeding, the majority of women prefer the long-cycle regimen to the conventional OC regimen with regular bleeds every 4 weeks because it may improve quality of life. As this regimen increases the contraceptive efficacy to a large degree, continuous treatment with OCs may prevent unintended pregnancies in women who miss a pill or are concomitantly treated with drugs that are able to impair the efficacy of OCs. Postponement of withdrawal bleeding may also reduce or prevent menses-associated disorders such as hypermenorrhoea and dysmenorrhoea, and have beneficial effects in patients with haemorrhagic diathesis, endometriosis, uterine leiomyoma and polycystic ovary syndrome. Continuous use of OCs prevents the cyclic fluctuations of serum levels of ethinylestradiol and progestogen and, hence, the cyclic variations of metabolic serum parameters. Although the long-cycle regimen is initially associated with an elevated rate of irregular bleeding, the total number of bleeding days that require sanitary product protection is lower than during conventional OC treatment. Many physicians tend to prescribe extended OC cycles for postponement of menstruation or reduction of frequency of regular bleeding. This review summarises and examines the available data on OC long-cycle regimens. The data suggest that the rate of treatment-related side effects with OCs according to the long-cycle regimen is similar to that of conventional OC regimens. However, clinical trials are necessary to assess the impact of long-term OC long cycles on safety, particularly the risk of cancer and cardiovascular disease, and fertility after discontinuation of treatment.

The effect of tolterodine on the pharmacokinetics and pharmacodynamics of a combination oral contraceptive containing ethinyl estradiol and levonorgestrel

BACKGROUND

Tolterodine is an antimuscarinic agent for the treatment of overactive bladder, a chronic condition that is particularly common in women. Given the prevalence pattern of overactive bladder and the widespread use of oral contraception, circumstances are likely to arise in which physicians may wish to prescribe tolterodine for patients already taking oral contraceptives. Based on a search of MEDLINE from 1990 to 2001, there have been no studies of whether concomitant use of these agents entails a risk of drug-drug interaction or conception.

OBJECTIVE

This study investigated the effects of tolterodine on the pharmacokinetics and pharmacodynamics of a low-dose combination oral contraceptive (ethinyl estradiol 30 microg/levonorgestrel 150 microg).

METHODS

This was an open-label, randomized, 2-period crossover study in healthy women. Oral contraception was given for 21 days either alone or in combination with oral tolterodine 2 mg BID (on days 1-14) over two 28-day contraceptive cycles. Pharmacokinetic assessments were performed on day 14 based on plasma levels of ethinyl estradiol and levonorgestrel up to 24 hours after dosing and serum tolterodine levels at 1 to 3 hours after dosing. The potential for pharmacodynamic interaction was assessed in terms of the risk of failure of suppression of ovulation based on serum levels of estradiol and progesterone measured throughout each cycle.

RESULTS

Twenty-four healthy women (age, 23-41 years [mean, 30 years]; height, 155-178 cm [mean, 167 cm]; body weight, 51-75 kg [mean, 64 kg]) participated in the study. There was no evidence of a pharmacokinetic interaction between tolterodine and the steroid hormones in the oral contraceptive used, nor did the oral contraceptive show any relevant pharmacokinetic interaction with tolterodine. Serum levels of estradiol and progesterone indicated suppression of ovulation in both treatment periods.

CONCLUSION

In this selected population. coadministration of tolterodine did not affect the contraceptive efficacy of a low-dose combination oral contraceptive containing ethinyl estradiol and levonorgestrel.

Ovulatory potential of preovulatory sized follicles during oral contraceptive treatment

The ovulatory potential of preovulatory follicles was studied in five women taking monophasic gestodene pills containing 20 micrograms of ethinyl estradiol. After one normal pill cycle, follicles were allowed to grow to 16 mm in diameter by deliberate extension of the pill-free period. Once the size of the leading follicle reached 16 mm, the women resumed oral contraceptives for the following 21 days to investigate whether ovulation can be inhibited by late onset of the pill. In addition, 100 micrograms of gonadotropin releasing hormone analog was given intravenously on the third pill day to induce ovulation. Follicular growth and activity were monitored by ultrasonography and by serum concentrations of ethinyl estradiol, progesterone, luteinizing hormone, and follicle stimulating hormone from the last pill day of the first cycle until the end of the second pill intake of 21 days. An increase in luteinizing hormone secretion started before intravenous administration of a gonadotropin releasing hormone analog in all women, eventually leading to ovulation in four of five women. One woman developed an unruptured follicle. Thus, the ovulatory potential of a 16-mm functional follicle cannot be inhibited by reintroduction of pills containing 20 micrograms ethinyl estradiol and 75 micrograms of gestodene.

Omitting the first oral contraceptive pills of the cycle does not automatically lead to ovulation

OBJECTIVE

Our purpose was to test the hypothesis that omitting the first three pills of the contraceptive cycle leads to ovulation.

STUDY DESIGN

Ninety-nine women, randomly assigned to 1 of 3 treatments of combined oral contraceptives, completed the study. Treatments contained ethinyl estradiol and either monophasic gestodene, triphasic gestodene, or monophasic desogestrel. Pituitary-ovarian activity was monitored by ultrasonography of the ovaries and assay of serum concentrations of estradiol, progesterone, and follicle-stimulating hormone over 1 normal cycle (study period 1) and 1 cycle after an extended pill-free interval of 10 days (study period 2).

RESULTS

None of the women experienced normal ovulation as evaluated by ultrasonography and serum progesterone concentrations. However, follicle-stimulating hormone reached a maximal serum concentration in most women during the first 7 pill-free days, indicating complete pituitary recovery, and increases in serum estradiol concentrations were seen in each woman although with marked interindividual variation. During study period 2 we found follicles of >18 mm in 24%, 24%, and 40% of the monophasic gestodene, triphasic gestodene, and monophasic desogestrel groups, respectively.

CONCLUSIONS

Follicular growth up to preovulatory size is common in women missing the first one to three pills of their contraceptive cycle. Although this creates the prerequisite for ovulation, normal ovulation did not occur when pill omissions were limited to only 3 days.

The pharmacodynamic effects of an oral contraceptive containing 3 mg micronized 17 beta-estradiol and 0.150 mg desogestrel for 21 days, followed by 0.030 mg desogestrel only for 7 days

During oral treatment with 3 mg micronized 17 beta-estradiol and 0.150 mg desogestrel for 21 days followed by 0.030 mg (A) desogestrel (15 women) or placebo (B) (14 women) for 7 days, ovarian function, bleeding pattern and estradiol levels were evaluated. The study was performed in a group-comparative, double-blind fashion. During a pre-treatment control cycle, using ultrasound scan, follicular diameter was measured on cycle days 10-16 and endometrial thickness on one of cycle days 22-26. Estradiol was measured at the time of ultrasound scan and progesterone three times in the luteal phase. During three treatment cycles, follicular diameter and endometrial thickness were monitored three times weekly and at the same time, estradiol and progesterone were measured. Treatment resulted in anovulation in all women. Maximum and mean estradiol levels were approximately 900 pmol/l and 550 pmol/l during treatment, respectively, and approximately 200 pmol/l during the estradiol-free weeks in both groups. Ten women showed ovarian activity (follicle size > or = 15 mm) during treatment, seven in group A and three in group B. Endometrial thickness decreased approximately 3 mm during treatment in both groups. The incidence of breakthrough bleeding and spotting was higher in group A when compared to group B. The study indicates that the combination of 3.0 mg micronized estradiol and 0.150 mg desogestrel is an effective and safe contraceptive, offering an acceptable cycle control. The addition of a low dose of desogestrel during the pill-free period did not further suppress ovarian activity nor improve the bleeding pattern. The results of this study should be interpreted with great care, since the number of women studied is relatively small.

Shorter pill-free interval in combined oral contraceptives decreases follicular development

The objective of the study was to determine the suppressive effect on ovarian activity of 20 micrograms ethinylestradiol plus 75 micrograms gestodene administered for 21 or 23 days. The study was designed as a double-blind, randomized, multicenter trial in 60 women. A pre-treatment cycle, three treatment cycles and a post-treatment period were monitored by ovarian ultrasound and by LH, FSH, 17 beta-estradiol and progesterone measurements every other day. No ovulation and no luteinized, unruptured follicle were observed. Suppression of ovarian activity was more pronounced by the 23-day regimen. 17 beta-Estradiol serum levels during the last six days of a cycle and during the first six days of the next cycle were significantly less (p < 0.05) in the 23-day regimen. The superiority of the 23-day regimen in comparison to the 21-day regimen with regard to the suppression of ovarian activity was shown in this study. The observed differences in the 17 beta-estradiol levels and follicular development between a 21-day and 23-day preparation combine to suggest that shortening the pill-free interval in combined oral contraceptives may increase the contraceptive safety margin in women on low-dose formulations.

Risk for ovulation in women taking a low-dose oral contraceptive (Microgynon) when receiving antibacterial treatment with a fluoroquinolone (ofloxacin)

The possibility of escape ovulation in women using a fluoroquinolone ofloxacin for antibacterial treatment at a dose of 200 mg twice daily for 7 days when taking a combined oral contraceptive (Microgynon, 150 micrograms levonorgestrel and 30 micrograms ethinyl estradiol) was studied in 20 women. By using a placebo-controlled, randomized, cross-over design 6 contraceptive pill cycles were followed. Follicle-stimulating hormone and estradiol concentrations were measured on tablet days 5-8, 19-21; progesterone was assayed on days 19-21 during treatment with ofloxacin or placebo. Ultrasonographical investigations for measurements of the number and diameter of ovarian follicles were performed on one of days 5-10, 11-17, 18-24, 25-28. No indications of ovulation during ofloxacin medication were detected. It is concluded that alternative contraceptive precautions should not be needed when ofloxacin is prescribed for patients taking oral contraceptives.

The combined oral contraceptive pill: what advice should we give when tablets are missed?

Despite more than 30 years' experience with the pill, being by far the most thoroughly studied drug ever, we must conclude that there still is a remarkable paucity of data that would allow us to assess unambiguously its margins of efficacy. The physiological studies on which we must rely encompass limited numbers of subjects and are unlikely to include sufficient representatives of the vulnerable minority of women that really matter. Even though we realise that this vulnerable minority is there, we still cannot do better than to hypothesise about their characteristics, let alone identify them in advance. This lack of knowledge has contributed to the existence of diverging views on how to advise the general population of pill takers about missed tablets. Against this background, we felt there was a need to make an inventory of the existing data and, subsequently, to incorporate them in advice that in our opinion is most appropriate in the current state of knowledge. We have come to the conclusion, in contrast to what is often held, that it is not the number of tablets missed, but rather the timing relative to the pill-free interval that determines the impact of noncompliance. We further conclude that shortening of the pill-free interval to five or six days could substantially improve the efficacy of the pill: at the low doses currently used in oral contraceptives the total steroid burden would not be substantially increased, while still allowing withdrawal bleeding to occur.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of patient compliance in clinical pharmacokinetics. A review of recent research

Until 1986 to 1987, the estimation of patient compliance with prescribed drug regimens in ambulatory care relied on methods that were biased either by their subjectivity or by the improvement in compliance that commonly occurs during the day or two prior to a scheduled examination, so called 'white-coat compliance'. In 1986 to 1987, 2 objective methods were developed: electronic monitoring and low-dose, slow-turnover chemical markers (digoxin or phenobarbital [phenobarbitone]) incorporated into dosage forms. While neither method is without limitations, both have enabled major advances in the understanding of patients' compliance with dosage regimens and, thus, the spectrum of drug exposure in ambulatory care. The new methods have also triggered not only a revival of interest in patient compliance and its determinants, but also new statistical approaches to interpreting the clinical correlates of widely variable drug administration, and thus drug exposure, in drug trials. The marker methods prove dose ingestion during the 3 to 7 days prior to blood sampling, but do not reveal the timing of doses. The electronic monitoring methods, i.e. time and date-stamping microcircuitry incorporated into drug packages, provide a continuous record of timing of presumptive doses throughout periods of many months, but do not prove dose ingestion. The electronic record has been judged robust enough to detect certain types of investigator fraud, and to support modelling projections of the complete time course of the plasma drug concentration during a trial. Both marker and electronic methods show that the predominant errors are those of omission, i.e. delays or omissions of scheduled doses. Patient interviews, diaries, and counts of returned, untaken doses have been shown by both marker and electronic monitoring methods to consistently and substantially to overestimate compliance. Monitoring of plasma drug concentrations also overestimates compliance, because white-coat compliance is prevalent, and the pharmacokinetic turnover of most drugs is rapid enough that measured concentrations of drug in plasma reflect only drug administration during the period of white-coat compliance. Thus, compliance is a great deal poorer in clinical trials than has been revealed by the older methods. The long-standing underestimation of poor compliance in drug trials has many implications for the interpretation of drug trials, for optimal dose estimation, for the interpretation of failed drug therapy, and for accurate labelling of prescription drugs.

The effect of follicular growth and luteal function of "missing the pill". A comparison between a monophasic and a triphasic combined oral contraceptive

The effects of follicular growth and hormonal indices of the deliberate omission of two low-dose combined oral contraceptives, a monophasic 130 micrograms ethinylestradiol + 150 micrograms desorgestrel) and a triphasic (30 micrograms ethinylestradiol + 50 micrograms levonorgestrel for 6 days, followed by 40 micrograms ethinylestradiol + 75 micrograms levonorgestrel for 5 days and 30 micrograms ethinylestradiol + 125 micrograms levonorgestrel for 10 days) combination during the first three days of one contraceptive pill cycle was studied in two groups of 10 women each. Follicular growth was followed by ultrasound scanning and plasma levels of estradiol, and progesterone were measured every other day until day 19 of the contraceptive pill cycle. In each group, ovulation occurred in one subject and 4 women reacted with follicular activity only, while 5 women on the monophasic and 3 on the triphasic formulation exhibited complete ovarian suppression. Two subjects on the triphasic preparation showed follicular growth followed by insufficient luteal function. Thus, the risk of escape ovulation when the pill-free interval is prolonged to 10 days in women taking low-dose combined oral contraceptive pills, is low (1/10).

Gonadotropin and estradiol secretion during the week of placebo therapy in oral contraceptive pill users

The changes in the hypothalamic-pituitary-ovarian axis during the placebo week in oral contraceptive pill users were assessed. Fifteen women using the combined oral contraceptive pill were studied for eight hours at the start and at the end of the placebo week and gonadotropin secretion and estradiol concentrations were compared with those in control women in the follicular phase of an unmedicated menstrual cycle. Both gonadotropin and estradiol concentrations were suppressed at the start of the placebo week. By day 7 of placebo, gonadotropin concentrations and pulse patterns were indistinguishable from those of the control subjects although estradiol concentrations were still significantly lower.

Pharmacokinetics and biotransformation of orally administered oestrone sulphate and oestradiol valerate in post-menopausal women

The pharmacokinetic properties and biotransformation of two orally active oestrogens, piperazine oestrone sulphate (PE1S, 2.5 mg/day) and oestradiol valerate (E2V, 2.0 mg/day), given alone or in combination with levonorgestrel (LNG, 250 micrograms/day) were compared in 8 post-menopausal women, using a randomized cross-over design. The end points measured in peripheral plasma included oestrone (E1), oestradiol (E2), oestriol (E3), oestrone sulphate (E1S), oestradiol sulphate (E2S) and oestriol sulphate (E3S). In addition, LNG and sex-hormone-binding globulin SHBG concentrations were also assessed. The plasma levels of E3 were invariably below the detection limit (220 pmol/l). The levels of all the other oestrogens analyzed were consistently higher and the area under the curve significantly greater (except in the case of E3S) following PE1S administration than those recorded after E2V ingestion. The terminal half-lives of the circulating oestrogens measured after PE1S administration did not differ from those found after E2V administration. After 21 days of PE1S administration (in combination with LNG for the last 10 days), the maximum levels of all the oestrogens (except those of E2) were significantly higher than those seen after the first dose. No such difference was observed after E2V administration. There was no difference between the effects of the two treatment regimens with regard to the E1/E2 ratios, but the E1/E1S ratios were significantly lower after PE1S treatment than after E2V administration. It is concluded that, compared with an equivalent dose of PE1S, daily repeated oral administration of E2V yields consistently lower peripheral plasma levels of E2 and its principal metabolites. However, in contrast to PE1S therapy, prolonged administration of E2V does not result in an accumulation of the circulating oestrogens measured.

A comparative study of Norinyl 1/35 versus Lo-Ovral in Ile-Ife Nigeria

A comparative analysis of those women on Norinyl 1/35 versus those on Lo-Ovral showed those on Norinyl 1/35 were significantly (P less than or equal to 0.05) older than women in the Lo-Ovral group. There were no significant differences (P greater than or equal to 0.05) between the groups for other characteristics at admission. There were no significant differences (P greater than or equal to 0.05) between the groups at follow-up in the number of women reporting serious complications, menstrual complaints or other pill-related problems. The continuation rates at 12 months were 79.4 for the Norinyl 1/35 group and 76.7 for the Lo-Ovral groups. There were no pregnancies reported during the study period.

Clearance of levonorgestrel from the circulation following removal of NORPLANT subdermal implants

The disappearance of levonorgestrel from plasma after the removal of NORPLANT subdermal implants was studied in 12 women who had been treated from 5.5 to 78 months. The existence of one or two half-lives for the rate of disappearance was assessed. The influence of body weight, body fat and length of treatment upon levonorgestrel clearance was studied through stepwise regression analysis. It was found that the levonorgestrel decay rate after implant removal can be entirely accounted assuming one half-life of 42 +/- 16 h (mean +/- SD; range 13 to 62 h). Stepwise regression analysis showed that levonorgestrel half-life is positively correlated with body weight and not significantly correlated with the length of treatment or body fat. It is concluded that, after long-term administration of levonorgestrel via subdermal implants, the major part of the steroid is cleared from plasma within 96 h and that only trace amounts are detected in the following days.

Plasma levels of levonorgestrel and free levonorgestrel index in women using NORPLANT implants or two covered rods (NORPLANT-2)

Plasma levels of levonorgestrel, sex hormone binding globulin (SHBG) and estradiol were studied during four years in 283 healthy women using either NORPLANT implants or two covered rods (NORPLANT-2). The women were randomized to use either type of implant. Both implant systems have previously been shown to have similar release rates of levonorgestrel. In both groups plasma levels of levonorgestrel decreased throughout the study, and there were no statistically significant differences between the two groups in mean plasma levels of levonorgestrel. During the study 8 women became pregnant. All pregnancies but one occurred after 35 months of implant use and only in women using the covered rods. No significant differences were seen between the women who became pregnant and the rest of the group using two covered rods with respect to plasma levels of levonorgestrel. SHBG capacity tended to be somewhat higher in women using the two covered rods. As levonorgestrel is to a great extent bound to SHBG, and in that form not biologically active, a "free levonorgestrel index" was calculated as a ratio between levonorgestrel and SHBG. This index was significantly lower in users of two covered rods than in users of NORPLANT implants at 1, 12 and 48 months of use. Women who became pregnant had significantly lower "free levonorgestrel index" than had the rest of the group. It is postulated that the difference in "free levonorgestrel index" between users of the two implant systems reflect differences in release rate, the covered rods having a lower release rate of levonorgestrel than NORPLANT throughout the observation period. It is concluded that "free levonorgestrel index" is a better parameter than levonorgestrel plasma levels to describe implant function, and to discriminate women who are at risk of pregnancy.

The effect of deliberate omission of Trinordiol or Microgynon on the hypothalamo-pituitary-ovarian axis

The effect of deliberate omission of a phased formulation pill, Trinordiol (ethinyl estradiol 30 micrograms + levonorgestrel 50 micrograms: 6 tablets; ethinyl estradiol 40 micrograms + levonorgestrel 75 micrograms: 5 tablets; ethinyl estradiol 30 micrograms + levonorgestrel 125 micrograms: 10 tablets) or a low-dose, combined, oral contraceptive pill, Microgynon (ethinyl estradiol 30 micrograms + levonorgestrel 150 micrograms: 21 tablets) on the hypothalamo-pituitary-ovarian axis were studied. Thirty-six women were recruited to the study and divided equally between the two types of pill. Medication was begun on the 8th pill-free day of the cycle and continued for 7 days (Group 1), 14 days (Group 2) or 21 days (Group 3). Levels of FSH, LH, estradiol (E2) and progesterone (P) were measured in plasma on alternate days during the final week of pill therapy, and daily for the 7 days after stopping the pill. For the first 2 weeks of pill therapy, follicular activity, as judged by plasma levels of E2, was greater in women taking Trinordiol than in those taking Microgynon, but was similar in both groups by the third week of pill treatment. Five women taking Trinordiol (2 in Group 1 and 3 in Group 2) had plasma levels of E2 in excess of 500 pmol/l whilst taking the pills, and only 1 patient achieved this degree of follicular activity after stopping the tablets. One woman who had taken 7 days of Trinordiol (Group 1) showed a rise of plasma levels of P to 6.8 nmol/l, but luteinization did not occur in any of the remaining 35 women who took Trinordiol or Microgynon. These findings suggest that follicular activity is less completely suppressed by Trinordiol than Microgynon, at least in the first 2 weeks of pill therapy, but that normal ovulation is still a rare event in the week after cessation of either of these pills, even if only 7 days of medication have been taken.

Hormonal consequences of missing the pill during the first two days of three consecutive artificial cycles

The hormonal effects of the deliberate omission of a low-dose combined oral contraceptive pill (30 micrograms ethinyl estradiol + 150 micrograms levonorgestrel) during the first two days of three consecutive artificial cycles were studied in 10 women. The plasma levels of estradiol, progesterone, levonorgestrel and--whenever justified--of LH were measured three times weekly (Mondays, Wednesdays and Fridays) throughout a 90-day period, and the ovarian reaction to the prolongation of the pill-free period from 7 to 9 days was assessed. One subject (with a premature LH surge) showed a marked follicular and an inadequate luteal activity in 2 of 3 cycles. The remaining cycles were characterized by a varying degree of follicular activity associated with the absence of any luteal function. None of the subjects exhibited peripheral steroid levels indicating a normal ovulatory cycle. The results are interpreted as suggesting that repeated prolongation of the pill-free period from 7 to 9 days might result in a gradual increase in ovarian activity.

Why do inadvertent pregnancies occur in oral contraceptive users? Effectiveness of oral contraceptive regimens and interfering factors

Inadvertent pregnancies in combined pill users are not uncommon, and are usually due to errors of tablet taking. However, many factors may contribute to 'pill failure'. In this review the endocrine pharmacology of pill use and the changes reported with missed pills have been considered in detail. The influences of other factors including drug interactions have been reviewed and a series of recommendations made for reducing the risk of pregnancy in each of these circumstances.