Pharmacokinetic and pharmacodynamic effects of small doses of norethisterone released from vaginal rings continuously during 90 days

"Per vaginam" topical use of hormonal drugs in women with symptomatic deep endometriosis: a narrative literature review

PURPOSE

We aim to provide a comprehensive overview of the role of the vagina as a route for drug delivery and absorption, with a particular focus on the use of vaginal hormonal compounds for the treatment of deep infiltrating symptomatic endometriosis.

METHODS

A MEDLINE search through PubMed was performed to identify all published studies in English language on vaginal hormonal treatments for symptomatic endometriosis.

RESULTS

Main advantages of the vaginal route include avoidance of the hepatic-first pass metabolic effect, the possibility of using lower therapeutic dosages, and the reduction of side effects compared with the oral administration. Studies on endometriosis treatment mainly focused on the use of vaginal danazol (n = 6) and the contraceptive vaginal ring (n = 2). One pilot study evaluated the efficacy of vaginal anastrozole in women with rectovaginal endometriosis. Most investigations evaluated the vaginal use of hormonal agents in women with deep infiltrating endometriosis/rectovaginal endometriosis. Overall, a substantial amelioration of pelvic pain symptoms associated with endometriosis was observed, particularly of dysmenorrhea. A significant reduction in rectovaginal endometriotic nodule dimensions measured at ultrasound examination was detected by some but not all authors.

CONCLUSIONS

The vaginal route represents a scarcely explored modality for drug administration. High local hormonal concentrations might achieve a greater effect on endometriotic lesions compared with alternative routes. Future studies should focus on the use of the vagina for delivering target therapies particularly in patients with deeply infiltrating rectovaginal lesions.

Intravaginal rings as delivery systems for microbicides and multipurpose prevention technologies

There is a renewed interest in delivering pharmaceutical products via intravaginal rings (IVRs). IVRs are flexible torus-shaped drug delivery systems that can be easily inserted and removed by the woman and that provide both sustained and controlled drug release, lasting for several weeks to several months. In terms of women's health care products, it has been established that IVRs effectively deliver contraceptive steroids and steroids for the treatment of postmenopausal vaginal atrophy. A novel application for IVRs is the delivery of antiretroviral drugs for the prevention of human immunodeficiency virus (HIV) genital infection. Microbicides are antiviral drugs delivered topically for HIV prevention. Recent reviews of microbicide IVRs have focused on technologies in development and optimizing ring design. IVRs have several advantages, including the ability to deliver sustained drug doses for long periods of time while bypassing first pass metabolism in the gut. IVRs are discreet, woman-controlled, and do not require a trained provider for placement or fitting. Previous data support that women and their male sexual partners find IVRs highly acceptable. Multipurpose prevention technology (MPT) products provide protection against unintended/mistimed pregnancy and reproductive tract infections, including HIV. Several MPT IVRs are currently in development. Early clinical testing of new microbicide and MPT IVRs will require a focus on safety, pharmacokinetics and pharmacodynamics. Specifically, IVRs will have to deliver tissue concentrations of drugs that are pharmacodynamically active, do not cause mucosal alterations or inflammation, and do not change the resident microbiota. The emergence of resistance to antiretrovirals will need to be investigated. IVRs should not disrupt intercourse or have high rates of expulsion. Herein, we reviewed the microbicide and MPT IVRs currently in development, with a focus on the clinical aspects of IVR assessment and the challenges facing microbicide and MPT IVR product development, clinical testing, and implementation. The information in this review was drawn from PubMed searches and a recent microbicide/MPT product development workshop organized by CONRAD.

Vaginal delivery of contraceptives

Although a steady increase in contraceptive use has been observed both in developed and less-developed countries, the large number of unplanned pregnancies may indicate that the contraceptive needs of a significant percentage of couples have so far not been met. Several new contraceptive products have reached the market during the last 2 years. Among these is a new contraceptive vaginal ring, which has become available for prescription. This new female method has been developed to expand the contraceptive choices available to couples. This review will address the specifics of the vaginal route for delivering contraceptive steroids and describe the various systems available or under evaluation.

Why consider vaginal drug administration?

OBJECTIVE

To review the anatomy and physiology of the vagina, the merits of vaginal drug administration, and the currently available vaginal drug-administration systems.

DESIGN

Review of basic and clinical research.

RESULT(S)

Although clinicians commonly use topically administered drugs in the vagina, this route for systemic drug administration is somewhat novel. Experience with a variety of products demonstrates that the vagina is a highly effective site for drug delivery, particularly in women's health. The vagina is often an ideal route for drug administration because it allows for the administration of lower doses, steady drug levels, and less frequent administration than the oral route. With vaginal drug administration, absorption is unaffected by gastrointestinal disturbances, there is no first-pass effect, and use is discreet. Knowledge of anatomy, physiology, histology, and immunology of the vagina should allow clinicians to reassure their patients concerning this mode of delivery. Greater understanding and experience by clinicians should lead to increased use and acceptance of the vagina as a route for drug administration.

CONCLUSION(S)

The safety and efficacy of vaginal administration have been well established. The vaginal route of drug delivery is acceptable and may even be a preferable route of administration for many drugs, particularly hormones, whether for contraception or postmenopausal estrogen therapy.

Progesterone and ovulation

The role of progesterone (P) in the mechanism of ovulation is controversial at best. The contraceptive application of P was established in rodents in 1936 and with orally absorbed progestogenes was put to human use. There were hints on the proovulatory actions of P administered before the time of ovulation in rats by 1948. Similarly, in 1954 the observation of high P level in the preovulatory follicle pointed to a role in ovulation. Neither of these two observations was further investigated and the positive feedback effect of P exerted on gonadotropins was described in 1968. Still the positive feedback between P and gonadotropins were not recognized as a physiologic mechanism, much less utilized pharmacologically. The apparent contradiction between these two different actions of P continues upto now. The paper sets out to expose this controversy and tries to resolve it using extensive literary data and the author's experiences with synthetic progestogenes in contraception, in the treatment of infertility and with the antigestagen mifepristone in blocking ovulation. The precise mechanisms lying behind these applications are explored and discussed in detail. The putative role of oestradiol (E2) in the mechanism of eliciting the gonadotropin surge is extensively discussed but refuted as the ovulatory signal. The time sequence between the rise of P and gonadotropins contradicts the common wisdom of LH causing luteinization. The positive feedback effect of P on the E2 sensitized ovulatory axis on the hypothalamic and pituitary level is discussed and its local role in the mechanism of follicular rupture is also taken into account. The final proof seems to be the antiovulatory effect of mifepristone, which blocked both GnRH pulsatility, pituitary sensitivity to GnRH and follicular rupture in several experiments. Thus, the dogma of LH peak causing follicular rupture and subsequent luteinization seems questionable, the putative role of E2 to initiate the ovulatory cascade has to be discarded and P's role as a trigger of the physiological mechanisms leading to ovulation should be firmly recognized.

Effect of a combined oral contraceptive containing 3 mg of drospirenone and 30 microg of ethinyl estradiol on the human endometrium

OBJECTIVE

To provide an in-depth assessment of the effects of the combined oral contraceptive containing 30 microg of ethinyl estradiol and 3 mg of drospirenone (Yasmin, Schering AG, Berlin) on the endometrium by means of endometrial morphometry in comparison to an untreated cycle.

DESIGN

The open, multicenter study consisted of one untreated precycle and 13 treatment cycles.

SETTING

Four gynecologic clinics in Belgium, The Netherlands, and Switzerland were involved.

PATIENT(S)

Forty women with a history of regular menstrual cycles.

INTERVENTION(S)

Before the commencement of the trial, 3 months without any hormonal intake was obligatory. The first endometrial sample was done in the untreated precycle, adjusted to the day of LH peak plus 5 to 6 days. During the medication phase, endometrial samples were taken at cycle 3, 6 and 13.

MAIN OUTCOME MEASURE(S)

Primary outcome measure of the study was the morphologic assessment of the endometrium with measures such as glandular diameter, glandular epithelial height, and number of vacuolated cells per 1,000 glandular cells. Furthermore, the endometrial thickness was measured by ultrasound.

RESULT(S)

After 13 cycles of medication use the endometrium had an atrophic appearance in 63% of the subjects. The size of the glands, the glandular epithelial height, and the number of glands per square millimeter were already significantly reduced after 3 months' use. Histological and ultrasonographical evaluation of the endometrium indicated a suppression of the proliferative activity of the endometrium.

CONCLUSION(S)

The combination of 30 microg of ethinyl estradiol with 3 mg of drospirenone induces changes of the endometrium that are comparable with other combined oral contraceptives and exhibits a marked antiproliferative effect on the endometrium. The medication was proven to be an effective oral contraceptive and revealed good cycle control characteristics.

Morphometric study of the human endometrium following continuous exposure to levonorgestrel released from vaginal rings during 90 days

The effects of vaginal devices releasing levonorgestrel (LNG) at a constant rate of approximately 20 micrograms/24 hrs on the human endometrium were studied in a group of 69 normally menstruating women during a period of 90 days of continuous use. Peripheral blood samples were withdrawn three times weekly starting at day 10 of a pretreatment (control) cycle and then three times weekly from day 60 to 90 of the treatment period. The levels of LNG, estradiol, progesterone and sex hormone binding globulin (SHBG) were analyzed by radioimmunoassay techniques. Endometrial biopsies were obtained in the luteal phase of the pretreatment cycle and on day 84-87 of the treatment period. Increased bleeding occurred in most subjects exposed to the LNG-releasing device; the mean number of bleeding and spotting days was 26.4 +/- 8.9 S.D. which exceeded that found in their control cycle. Morphometric analyses of the endometrial biopsies using 9 quantitative indices, revealed highly significant changes in glands and stroma following the use of the LNG-releasing vaginal device. Irrespective of the circulating steroid levels, the administration of LNG significantly diminished the glandular diameter (p less than 0.001), reduced the volume density of the glands (p less than 0.001) and of the glandular epithelium (p less than 0.001). and modified the ratio glandular epithelium: glands (p less than 0.001). It is concluded that levonorgestrel released at a rate of 20 micrograms/24 hrs, induces characteristic changes in the histologic structure of the human endometrium. Although no simple correlation has been found between any of the endometrial indices and the numbers of bleeding/spotting days or bleeding days, the changes as such may represent biochemical alterations which could be predisposing factors for intermenstrual bleeding and spotting. To prove a causal relationship between morphological and biochemical changes and changes in bleeding patterns, further in-depth studies may be required.

Pharmacokinetics of 3-keto-desogestrel and ethinylestradiol released from different types of contraceptive vaginal rings

Pharmacokinetics of 3-keto-desogestrel and ethinylestradiol released from contraceptive vaginal rings (CVRs) with different release rates (75/15, 100/15 and 150/15 micrograms 3-keto-desogestrel/ethinylestradiol daily) were investigated in two studies in young healthy female volunteers. As reference, an oral preparation containing 150 micrograms desogestrel and 30 micrograms ethinylestradiol (MarvelonR tablets) was also administered to the volunteers. To assess the disposition parameters of 3-keto-desogestrel and ethinylestradiol, some of the volunteers were additionally given an i.v. preparation containing 150 micrograms 3-keto-desogestrel and 30 micrograms ethinylestradiol. Serum levels obtained with CVRs showed an initial increase during the first three days, followed by a plateau decreasing only slightly during the remainder of the treatment period. Mean plateau levels (+/- s.d.) of 3-keto-desogestrel were 2.3 +/- 0.9, 2.8 +/- 1.1 and 3.8 +/- 1.1 pmol/ml for CVR 75/15, 100/15 and 150/15, respectively. Mean plateau levels of ethinylestradiol were 184 +/- 75, 262 +/- 102 and 233 +/- 102 pmol/l, respectively. The in vivo release rates of 3-keto-desogestrel and ethinylestradiol from the CVRs were in good agreement with the in vitro release rates. For both steroids the bioavailability from the CVRs was approximately 1.2 times higher than that from the tablets. The 3-keto-desogestrel serum levels were found directly proportional to the release rates within the range studied (75-150 micrograms/day). For ethinylesteradiol the intra-individual variation in steady-state levels was too large to draw pertinent conclusions.

Effects on the endometrium, endo- and exocervix following the use of local progestogen-releasing delivery systems

Some conflicting reports have appeared in the literature as to the effect of progestogens on the endometrium and on the endo- and exocervix in animals and humans. Hyperplasia of the endometrial and endocervical epithelium has been reported in some non-human primates following the administration of progestogens. In other studies no evidence has been found for such changes. In women using combined oral contraceptives, it has been claimed that the progestogen component causes adenomatous hyperplasia of the endocervix and that this hyperplastic transformation could be a precursor to adenocarcinoma of the cervix. So far, there is, however, no evidence in the literature to confirm this hypothesis. In view of the development of new delivery systems with a constant release of small amounts of progestogens, previous reports in the literature on hyperplasia and potential malignant transformation of the endometrium and the endocervix have been a matter of concern. The aim of the present study is therefore to review results from studies in animals and humans in particular with reference to the effect of a local release of various progestogens on the endometrium and the endo- and exocervix.

The in vivo release characteristics of a multi-compartment vaginal ring releasing 3-keto-desogestrel

The results of a stage I study of a new vaginal ring releasing 3-keto-Desogestrel [3kDOG] is reported. The study design consisted of one study cycle, where the ring was used continuously for 21 days and then removed. Twenty healthy volunteers were randomly allocated to each of two study groups. On day 5 of the menstrual cycle, group A used a vaginal ring releasing 30 micrograms 3kDOG per 24 hours and group B used a 15 micrograms 3kDOG per 24 hours ring. After initial absorption of the 3kDOG a plateau phase was reached in 46 hours [group A] and 49 hours [group B]. On reaching the plateau phase, the overall decline in plasma levels during the 21 days of use was 5.24% for group A and 5.27% for group B. This represents a daily decline in plasma levels of 0.27% and 0.28% for the 30 micrograms and 15 micrograms per 24 hours rings, respectively. The plasma levels achieved by the rings were significantly different throughout (p = 0.011). On removal after 21 days, the mean removal half-life for both ring types was similar at 20.9 hours for group A and 21.1 hours for group B. It is concluded that the characteristics of the delivery system are worthy of further study as a potential means of contraception using 3kDOG delivered from a vaginal ring.

The effect of intrauterine devices, the stainless steel ring, the copper T220, and releasing levonorgestrel, on the bleeding profile and the morphological structure of the human endometrium--a comparative study of three IUDs. A morphometric study of 96 cases

Thirty-four women using the stainless steel ring (SS), 43 women using the Copper T220 (TCu), and 19 women using levonorgestrel-releasing intrauterine devices (LNG) were admitted to the study. The light microscopic biopsy material was subjected to morphometric studies including 8 indices of endometrial activity before (Control) and after 24 months of exposure to the SS and TCu device and 3-10 months of exposure to the LNG device. The women were grouped into subjects with and without intermenstrual and prolonged bleeding. The results revealed that there were highly significant differences between the IUDs at the endometrial level as displayed by morphometry. However, the difference between bleeders and non-bleeders was not significant in any of the three types of IUDs. Although the mode of action of these IUDs at the endometrial level is different, the mechanism responsible for the irregular endometrial bleeding needs to be further investigated.

Pharmacodynamics of a contraceptive vaginal ring releasing 3-keto-desogestrel

The pharmacodynamic effects of a new type of 3-keto-Desogestrel [3kDOG] releasing vaginal ring was studied in a group of 20 normally ovulating women during a period of 21 days continuous use. Peripheral blood samples were taken for the estimation of progesterone and oestradiol levels, ultrasound tracking for follicular growth and cervical mucus sampling for scoring [modified Insler] and sperm penetration testing during a control, treatment and recovery period. Additional blood samples were taken for the estimation of 3kDOG levels during the treatment period. After a control cycle, twenty normally ovulating women were selected and randomly divided into two groups. Group A were given a vaginal ring on day 5 of the menstrual cycle releasing 30 ug/24 hours of 3kDOG and group B a similar ring releasing 15 ug/24 hours of kDOG. Of the treatment cycles, none showed an ovulatory pattern in group A and there was only one in group B, the respective mean plasma levels of 3kDOG were 0.38 and 0.25 pmol/ml. The formation of "cysts" or persistent follicles was common to both groups, 6 out of 10 subjects in group A and 8 out of 10 subjects in group B had "cysts" greater than 25mm in diameter in the treatment cycle, this had become 5 out of 10 and 8 out of 10, respectively, in the recovery cycle. A comparison of the cervical mucus scores and sperm penetration of cervical mucus showed a significant reduction between the control and treatment groups but no significant difference between the two groups. The bleeding profiles showed an increase in percentage of bleeding days in both treatment groups to 25% in group A and 21.7% in group B [cf, 17.1%, 15.9%, respectively, in control month]; there being no statistical difference between groups. In conclusion, it is believed that given the efficacy demonstrated and the low level of menstrual disturbances found, this system warrants further investigation as a means of contraception as it appears to offer a better compromise than previous vaginal ring systems.

Norethisterone-cholesterol eutectic mixture as an oral sustained-release hormonal preparation: bioequivalence study in humans

A solid dispersion of norethisterone and cholesterol (NET:CHOL; eutectic 1:4 w/w) was prepared by melting and rapid cooling. The fused material was then mixed with lactose as vehicle. Soft gelatin capsules were filled with 55 mg of the final mixture to give 0.35 mg of NET. One control formulation prepared with fused NET and lactose (NET:LAC) was capsuled with the same NET dosage, and one commercial tablet (Dianor, Syntex) with 0.35 mg NET were used as reference formulations. In a cross-over study, five female volunteers received, one month apart, in fasting state, each one of the three formulations. Blood samples were drawn at O,O.5,1,1.5,2,4,8,12,24 and 36 hours after dosing. Immunoreactive plasma NET was measured by RIA to assess pharmacokinetic parameters. The NET:CHOL formulation showed a greater area under the serum concentration-time curve, lower peak concentrations and a smaller release rate constant as compared to the reference preparations. It is concluded that the NET:CHOL eutectic mixture is a modified release dosage form and a sound approach in regulating the drug access rate to the body's central compartment.

Comparative pharmacokinetics of levonorgestrel and ethinyloestradiol following intravenous, oral and vaginal administration

The plasma concentrations of levonorgestrel (LNG) and ethinyloestradiol (EE2) have been measured in a random crossover study in five healthy female volunteers given a combination oral contraceptive tablet (250 micrograms LNG and 50 micrograms EE2) by the oral route and per vaginum and also receiving the same dose intravenously. The fractional bioavailability of LNG after oral administration was 1.00 +/- 0.16 (mean +/- S.D.) and after vaginal insertion 0.88 +/- 0.16. The time to peak (tmax) was significantly longer and the peak concentration (Cmax) significantly reduced following vaginal administration. The fractional bioavailability of EE2 after oral dosing was 0.62 +/- 0.11 and after vaginal insertion 0.74 +/- 0.16; tmax was prolonged, hence absorption was slower from the vagina. The reduced rate of absorption was evident in the differences seen in the area under the curve for early time periods for both steroids. However, overall bioavailability is not reduced for either steroid when a single tablet is inserted into the vagina.

A clinical pharmacological study of a new type of vaginal delivery system for levonorgestrel

The pharmacokinetic and pharmacodynamic effects of a new type of levonorgestrel-releasing vaginal device (with an in vitro release rate of 25 micrograms/24 h) were studied in a group of 18 normally menstruating women during a period of 90 days of continuous use. Peripheral blood samples were drawn three times weekly (Mondays, Wednesdays, Fridays) during a pretreatment (control) cycle and during the 90 days (3 segments) of exposure to levonorgestrel and the levels of levonorgestrel, progesterone and estradiol were analyzed. Blood samples were also drawn at frequent intervals during the first day and daily during the first week with the devices in situ. In addition, endometrial biopsy specimens were obtained during days 20-22 of the control cycle and then 6 and 10 weeks following the insertion of the devices for morphometric analysis and for the assay of progesterone and estradiol levels. Following insertion of the devices, plasma levels rapidly rose to 1 nmol/l in 12 hours; a plateau of approximately 1.6 nmol/l was reached in 3-4 days, after which the plasma levels declined in a linear fashion with a daily average rate of 7.4 pmol/l to 60% of the initial level in 90 days' time. Of the 54 treatment segments of 30 days, 68% were anovulatory and 24% showed normal, ovulatory-like estradiol and progesterone levels. A complete set of three biopsies were obtained from 15 of the 18 subjects. Of the biopsies obtained during exposure to levonorgestrel only one exhibited signs of atrophy, 80% showed suppressed or arrested proliferation, and 10% had a normal cyclic appearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic and pharmacodynamic studies of vaginal rings releasing low-dose levonorgestrel

Pharmacokinetic and pharmacodynamic effects of a vaginal ring releasing 20 micrograms/day levonorgestrel (L-NOG) have been studied in 15 women. Serum levels of L-NOG, estradiol and progesterone were measured three times a week in a control menstrual cycle and a treatment period of 3 months after the insertion of the first vaginal ring. All control cycles were normal ovulatory. Among the 36 treatment cycles 13 were ovulatory (36%), 5 ovulatory with inadequate luteal function (14%), 14 anovulatory but with marked follicle activity (39%) and 4 anovulatory (11%). In the groups with ovulatory reaction the serum levels of L-NOG showed a decline of 54% of the initial level at the end of the treatment period, calculated according to the linear regression equation of Y = 0.903-0.0142X, while in the groups without ovulation the L-NOG levels were higher and the decline was 24% of the initial level (Y = 1.034-0.0086X). There were distinct individual differences in the levels of L-NOG and ovarian reactions. Marked follicle activity with very high estradiol levels were found in correlation with high L-NOG in 7 treatment cycles, particularly in the B type of reaction (B = anovulatory cycle with marked follicle activity). More intermenstrual bleeding and spotting occurred in the second treatment cycles, particularly in those with anovulatory reactions.

Pharmacodynamic effects of ethinyl estradiol in women using vaginal devices releasing small doses of levonorgestrel at a constant rate

Eight normally menstruating women were provided with vaginal devices releasing levonorgestrel (NOG)4) at a constant rate of 20 micrograms/24 h. On day 71 or 72 following the insertion of the device, oral doses of 50 micrograms of ethinyl estradiol (EE) were administered daily for one week. Peripheral blood samples were drawn three times weekly during a pretreatment (control) cycle and from day 29 of the treatment period. The levels of progesterone (P), estradiol (E2) and NOG were measured by radioimmunoassay, sex hormone binding globulin (SHBG) by a steady state polyacrylamide gel electrophoresis and the percentage of binding of NOG, testosterone (T) and E2 by equilibrium dialysis of diluted plasma. An endometrial smear and a biopsy were taken from each subject on 3 occasions, viz. during the control cycle (cycle day 20-22), during the period with the NOG-releasing device in situ (44-50 days after the insertion of the device), and on the 7th day of concomitant EE administration.

Pharmacokinetic and pharmacodynamic investigations with vaginal devices releasing levonorgestrel at a constant, near zero order rate

The pharmacokinetic and pharmacodynamic effects of vaginal devices releasing levonorgestrel (L-NOG) at a constant rate (in vitro release: approximately 20 micrograms/day) were studied in a group of 20 normally menstruating women during a period of 90 days of continuous use. Peripheral blood samples were withdrawn two or three times (in the great majority of subjects, on Mondays, Wednesdays and Fridays) during a pretreatment (control) cycle, during 90 days of exposure and during the first week following the removal of the device, and the levels of L-NOG, estradiol and progesterone were analyzed by radioimmunoassay techniques. In 8 of these subjects, endometrial biopsies were also taken during days 23 to 25 of the control cycle, and then 6 and 10 weeks following the insertion of the devices. In addition, the initial absorption rate and removal half-life of L-NOG were assessed in 7 subjects using the devices for a period of 8 days only. Following insertion of the devices, the levels of L-NOG rose very rapidly, and reached the final "plateau" in some 30 minutes' time. This was followed by a limited period of "burst" with doubling the levels for a few hours, after which the levels remained stable and diminished very slowly in a linear fashion with an average decline of 23-26% during 90 days, corresponding to a daily decrease of 0.2 to 0.3 per cent. The removal half-life (first compartment) after 90 days of exposure in 19 subjects was 16.1 (13.7-18.6) hours. Sixty-nine treatment segments of 30 days were studied with frequent hormone assays; of these, 20 (or 29%) were anovulatory, 13 (19%) exhibited inadequate luteal function, and 32 (52%) had normal ovulatory-like cycles. All endometrial biopsies obtained during the pretreatment cycle were normal secretory; of the 16 biopsies obtained during treatment, 4 were suppressed, 2 proliferative, 6 secretory, and 4 could not be dated because of bleeding. An assessment of the bleeding profiles during exposure to L-NOG revealed almost a doubling of the number of days with bleeding and spotting (35% compared to 18% during the pretreatment cycle). However, significantly more frequent bleeding was found in the 20 anovulatory segments (37.3%) than in the 36 normal ovulatory-like ones (27.7%). It is concluded that differences in the frequency of bleeding and spotting with low-dose progestogens may reflect differences in the frequency of ovulation inhibition just as much as differences in the hormonal profiles of the compounds administered.