Ovulation inhibition with different doses of levonorgestrel and other progestogens: clinical and experimental investigations

Pharmacodynamics of combined estrogen-progestin oral contraceptives 3. Inhibition of ovulation

INTRODUCTION

Following a historical overview, the ovulation-inhibiting effect of various orally administered estrogen-progestin combinations (combined oral contraceptives [COCs]) are examined for their components alone or in the various combined formulations. Special emphasis is given to products containing natural estrogens. Areas covered: Inhibition of ovulation with progestins alone; estrogens alone; various progestins in combination with ethinyl estradiol; various progestins in combination with natural estrogens (estradiol, estradiol valerate, and estetrol). Expert commentary: The original idea to achieve ovulation blockage through the administration of steroid hormones involved the use a progestogen (both progesterone and its synthetic homologous). The ability of a progestin to inhibit ovulation depends on the type of compound and on its dosage and a difference of more than 20-fold in activity exists between compounds utilized today in COCs. Initially, the estrogenic component was present only because it contaminated the first progestin utilized. It was soon found that an estrogen is necessary for proper cycle control. It was also found that the estrogen acts synergistically in inhibiting ovulation. For almost half a century, most COCs contained ethinyl estradiol. Today, also natural estrogens are being employed. Inhibition of ovulation was complete with all early high dose preparations. Decreasing dosage allowed some ovarian activity to occur, occasionally leading to a mature follicle. Even in this situation, defective corpus luteum formation assured contraceptive protection.

Postcoital treatment with levonorgestrel does not disrupt postfertilization events in the rat

Levonorgestrel (LNG), a progestin widely used for regular hormonal contraception, is also used for emergency contraception (EC) to prevent pregnancy after unprotected intercourse. However, its mode of action in EC is only partially understood. One unresolved question is whether or not EC prevents pregnancy by interfering with postfertilization events. Here, we report the effects of acute treatment with LNG upon ovulation, fertilization and implantation in the rat. LNG inhibited ovulation totally or partially, depending on the timing of treatment and/or total dose administered, whereas it had no effect on fertilization or implantation when it was administered shortly before or after mating, or before implantation. It is concluded that acute postcoital administration of LNG at doses several-fold higher than those used for EC in women, which are able to inhibit ovulation, had no postfertilization effect that impairs fertility in the rat.

Influence of the substitution of 11-methylene, delta(15), and/or 18-methyl groups in norethisterone on receptor binding, transactivation assays and biological activities in animals

The profile of norethisterone and newly developed derivatives thereof were assessed by in vitro binding and transactivation assays on progesterone (PR) as well as on androgen (AR) receptors and by subcutaneous treatment in in vivo models. The following in vivo models were performed: A McPhail test for progestational activity in immature rabbits, an ovulation inhibition test in cycling rats and a Hershberger test for androgenic activity in immature orchidectomised rats. The compounds tested were: norethisterone (NET), 11-methylene-NET (11-NET), Delta(15)-NET (15-NET), 18-methyl-NET (18-NET, Levonorgestrel, LNG), 11-methylene-Delta(15)-NET (11, 15-NET), 11-methylene-18-methyl-NET (11,18-NET, 3-keto-desogestrel, Etonogestrel, ETG), (Delta(15)-18-methyl-NET (15,18-NET, Gestodene, GSD) and 11-methylene-Delta(15)-18-methyl-NET (11,15,18-NET). Compared to the non-substituted compound NET, the binding to and agonistic activity via PR was increased for all the three mono-substituted compounds, although the stimulatory effect of 15-NET was only twofold. Compounds with 18-methyl in combination with Delta(15) (GSD), with 11-methylene (ETG) or with both combined showed clear synergistic effects, leading to equipotent compounds. If the 18-methyl group was lacking as in 11,15-NET, potency was lower than for ETG or GSD, but higher than for 18-NET (LNG). A correlation coefficient of 0.9 was found between binding affinity and agonistic potency. With respect to the AR binding and transactivation activities, the 18-methyl group potentiated androgenic in vitro activity (LNG). The 11-methylene group increased relative binding affinity in NET, but reduced androgenic activity clearly when also other substituents were present (11,15-NET, ETG and 11,15,18-NET). The Delta(15) bond alone did not change the binding in NET, but decreased androgen binding, induced by the 18-methyl substituent, in GSD and 11,15,18-NET. Transactivation activity was also diminished in the compounds having a Delta(15) bond. In the McPhail test mono-substitution of NET increased the progestagenic in vivo activity three to five times. Bi- and tri-substitution enhanced the activity further. With respect to ovulation inhibition mono-substitution of NET resulted in three to nine times more potent compounds, whereas bi- and tri-substitution increased potency further, except for 11,15-NET, which was as active as 11-NET. The relative progestagenic potencies in the McPhail and ovulation inhibition tests, correlated significantly with those of the relative binding affinity values (correlation coefficient of 0. 91 and 0.93, respectively) and relative transactivation activity values (0.88 and 0.81) for the PR. In the Hershberger test, all the compounds increased androgenic activity with respect to growth of ventral prostate weight compared to NET, with the exception of 11, 15-NET and 11,15,18-NET. The androgenic activity was negligible for these latter compounds. The androgenicity of both 18-NET (LNG) and 15,18-NET (GSD), on the other hand, was significantly higher than that of 11,18-NET (ETG). The results of this in vivo test are in line with the AR binding and transactivation activity values (correlation coefficients of 0.86 and 0.88). In addition, selectivity indices were calculated by dividing the progestational potencies by androgenic potencies for both in vitro and in vivo assays. ETG and GSD had clearly higher in vitro and in vivo indices than the other compounds with NET and LNG having the lowest indices. Because the androgenicity of 11,15-NET and 11,15,18-NET was very low, no exact selectivity ratios could be calculated for these compounds. From these experiments we may conclude that small structural modifications exert enhancement of progestational activity and a clear reduction in androgenicity leading to very selective progestagenic compounds. The influence of bi-substitution is additive over mono-substitution, whereas tri-substition is not additive. (ABSTRACT TRUNCATED)

Inhibition of ovulation by an oral contraceptive containing 100 micrograms levonorgestrel in combination with 20 micrograms ethinylestradiol

Twenty-four healthy female volunteers with normal ovulatory cycles, aged between 20 and 34 years (27.5 +/- 4.3), were included in a single-center, non-comparative study to investigate the effect on inhibition of ovulation of an oral contraceptive containing 20 micrograms ethinylestradiol in combination with 100 micrograms levonorgestrel. At baseline, during three treatment cycles and post-treatment, ultrasonography was used to examine the ovaries, to measure follicular size, and to measure the thickness of the endometrium. Serum levels of LH, FSH, estradiol, progesterone, total testosterone, free testosterone, SHBG, and CBG were also measured. Compared with treatment cycle 1, an increase in residual ovarian activity (follicle grades 4-5) was observed in cycles 2 and 3. Mean levels of LH, FSH, 17 beta-estradiol and progesterone remained suppressed during treatment. No escape ovulation was observed during the treatment phase of the study and there were no pregnancies. Ovulation was noted to return rapidly in the posttreatment cycle. Subjective and objective tolerance of the present regimen was noted to be good. Results indicate that the monophasic oral contraceptive containing 100 micrograms levonorgestrel combined with 20 micrograms ethinylestradiol effectively inhibits ovulation, providing adequate suppression of ovarian activity.

Androgenic effects of oral contraceptives: implications for patient compliance

Androgenic disorders have many negative physical effects. These effects may be caused by excess androgen (exogenous or endogenous) or by end-organ sensitivity to normal levels of androgens. Historically, androgenic progestins in oral contraceptives have also been associated with some of these negative effects. The most apparent signs of androgen excess are the external manifestations, including oily skin, acne, hirsutism, android obesity, and androgenic alopecia. Of equal concern are the potential metabolic disturbances associated with hyperandrogenicity. Unfavorable lipid profiles and increased incidence of diabetes and hypertension are very real threats to long-term health. In oral contraceptive users, external manifestations of androgenicity often lead to poor compliance, decreased efficacy, and discontinuation of oral contraceptive use, especially in the younger patient. With the introduction of the newer oral contraceptive formulations containing less androgenic progestins (norgestimate, desogestrel, gestodene), androgen-related effects have been reduced and better compliance is anticipated.

Characterization of the novel progestin gestodene by receptor binding studies and transactivation assays

Gestodene is a novel progestin used in oral contraceptives with an increased separation of progestogenic versus androgenic activity and a distinct antimineralocorticoid activity. This specific pharmacological profile of gestodene is defined by its pattern of binding affinities to a variety of steroid hormone receptors. In the present study the affinity of gestodene to the progesterone receptor (PR), the androgen receptor (AR), the glucocorticoid receptor (GR), the mineralocorticoid receptor (MR) and the estrogen receptor (ER) was re-evaluated by steroid binding assays and compared to those obtained for 3-keto-desogestrel and progesterone. The two synthetic progestins displayed identical high affinity to rabbit PR and similar marked binding to rat AR and GR, while progesterone showed high affinity to PR but only low binding to AR and GR. Furthermore, 3-keto-desogestrel exhibited almost no binding to MR, whereas gestodene, similar to progesterone, showed marked affinity to this receptor. In addition to receptor binding studies, transactivation assays were carried out to investigate the effects of gestodene on AR-, GR- and MR-mediated induction of transcription. In contrast to progesterone, which showed antiandrogenic activity, gestodene and 3-keto-desogestrel both exhibited androgenic activity. Furthermore, all three progestins exhibited weak GR-mediated antagonistic activity. In contrast to progesterone, which showed almost no glucocorticoid activity, gestodene and 3-keto-desogestrel showed weak glucocorticoid action. In addition, gestodene inhibited the aldosterone-induced reporter gene transcription, similar to progesterone, whereas unlike progesterone, gestodene did not induce reporter gene transcription. 3-Keto-desogestrel showed neither antimineralocorticoid nor mineralocorticoid action.

Sex hormone receptor binding, progestin selectivity, and the new oral contraceptives

The desired biologic effect of progestins used in OCs is progestational activity. Undesired pharmacologic properties such as androgenic activity are not necessary for contraception and increase the potential for adverse effects. A selective progestin has progestational effects at relatively low concentrations or doses and androgenic effects at only relatively high concentrations or doses. The degree to which progestational activity is maximized and androgenic activity is minimized is a measure of a progestin's selectivity. The ratio of its affinity for progesterone receptors to its affinity for androgen receptors is the selectivity index. To minimize the androgenic side effects associated with the older progestins, the doses used in OCs have been reduced over the years. These dose reductions have decreased the potential for undesired androgenic effects but also have negatively affected cycle control. Three new progestins, norgestimate, desogestrel, and gestodene, have relatively greater affinity for progesterone receptors than for androgen receptors when compared with the older agents, permitting a reduction in androgenic side effects without the need for further dose reduction. Preclinical receptor-binding studies and animal pharmacologic studies have documented the higher selectivity indexes of these new progestins. Their higher ratios of progestational to androgenic activity provide the basis for the reduction in androgenic adverse effects observed with their clinical use.

Inhibition of ovulation by a triphasic gestodene-containing oral contraceptive

The minimal effective dose of gestodene for inhibition of ovulation was studied in 30 female volunteers. Daily doses of 10 micrograms to 50 micrograms gestodene were given orally for 21 days. A control cycle prior to treatment and a treatment cycle were monitored for LH, FSH, estradiol, progesterone and cervical score. At a daily dose of 40 micrograms of gestodene, 6/7 volunteers exhibited inhibition of ovulation and 1/7 had a cycle with luteal insufficiency. Ovulation was inhibited in all volunteers on 50 micrograms gestodene, suggesting that the minimum dose required to inhibit ovulation was 40 micrograms gestodene. Cervical score was blunted even at 10 micrograms gestodene. Similarly, 20 volunteers were treated with coated tablets containing ethinylestradiol/gestodene at 30/50 micrograms for 6 days, 40/70 micrograms for 5 days and 30/100 micrograms for 10 days. This triphasic gestodene-containing preparation inhibited ovulation in all 20 females. In one cycle in which follicle development was observed only 43 pg estradiol/ml was secreted. Data from this investigation suggest that this triphasic gestodene-containing OC has a high contraceptive efficacy.

A multicenter comparative trial of triphasic and monophasic, low-dose combined oral contraceptives

A comparative multicenter clinical trial of two combined oral contraceptives (OCs) was conducted at clinics located in the Sudan, Sri Lanka, Chile, the Dominican Republic and Ecuador. The trial was designed to determine if there were differences in efficacy, safety and acceptability between a triphasic and a low-dose monophasic OC. This report includes analysis of 1088 women. At each center, subjects were randomly allocated to one of the two OCs. Follow-up visits were scheduled at 1, 4, 8 and 12 months after admission. There were two accidental pregnancies attributed to user failure reported during the study period; one in the triphasic group and one in the monophasic group. Adverse experiences were mainly minor with headaches and dizziness being the most common complaints; frequency of reports was similar in both groups. Cycle control was good in both groups with women in the triphasic group reporting fewer complaints of intermenstrual bleeding. Both OCs were safe and effective.

Clinical and metabolic effects of a triphasic pill containing gestodene

The clinical and metabolic effects of a low-dose triphasic oral contraceptive containing gestodene were investigated in 42 healthy women during 6 months of treatment. No pregnancies and no severe side effects occurred during the study. The pill exerted good cycle control and the incidence of irregular bleeding was very low. As for the coagulatory system, there was an increase in prothrombin activity and in fibrinopeptide A plasma levels, and a decrease in activated partial thromboplastin time. Antithrombin III activity, fibrinogen concentration and platelets count did not change during pill intake. No significant modifications in plasma total-cholesterol, low density lipoprotein-cholesterol or in the subfraction high density lipoprotein2-cholesterol (HDL2-CH) were observed. Serum triglycerides, HDL-CH and HDL3-CH levels were significantly higher at the end of treatment. The pill did not alter fasting insulin and glucose levels or their response to an oral glucose tolerance test. These minimal effects on metabolism, combined with its high efficacy and acceptability, may suggest that this triphasic formulation with gestodene seems to be a safe and reliable contraceptive agent.

Desogestrel: using a selective progestogen in a combined oral contraceptive

Desogestrel is the most selective progestogen used in oral contraceptives (OCs). The clinical characteristics of the monophasic combined OC containing 150 micrograms desogestrel and 30 micrograms EE per tablet (Marvelon) are in accordance with the strong progestogenic and minimal androgenic effects of desogestrel: a very high contraceptive efficacy is combined with minimal and, in the case of lipid metabolism, even potentially positive effects on metabolic parameters. Through increasing the plasma levels of sex hormone binding globulin, and thereby decreasing the plasma levels of free testosterone, the desogestrel-containing OC also has substantial beneficial effects on acne.

Clinical and metabolic effects of a pill containing 30 mcg ethinylestradiol plus 75 mcg gestodene

The clinical and metabolic effects of a short-term treatment with a combination contraceptive pill containing 30 mcg ethinylestradiol and 75 mcg gestodene were evaluated in a group of 31 healthy women. The pill exerted good cycle control and the incidence of irregular bleeding was low. Side effects rarely occurred, and an improvement in premenstrual symptoms was reported during pill intake. Among the different biochemical parameters tested to monitor the coagulatory system, the only modification observed was an increase of fibrinopeptide A plasma levels, confirming that low-dose pills have less effects on the haemostatic system than oral contraceptives with a higher estrogen content. No significant modification in plasma total cholesterol, triglycerides, high density lipoprotein-cholesterol (HDL-CH), HDL2-CH, nor low density lipoprotein-cholesterol were observed. HDL3-CH levels were significantly increased. Moreover, the pill did not significantly alter the fasting insulin and glucose levels nor their response to an oral glucose tolerance test. It may be suggested that this new formulation has high efficacy and clinical acceptability, primarily due to the total absence of any adverse metabolic effect.

Comparison of contraceptive acceptability of levonorgestrel and ethinyl oestradiol administered in one three-phasic (Trionetta) and one monophasic (Neovletta) version

In a Swedish multicenter study, a total number of 835 women completed a total of 6472 treatment cycles. Half of them were allotted at random to use the monophasic oral contraceptive Neovletta, also known as Microgynon 30 (30 micrograms ethinyl oestradiol + 150 micrograms levonorgestrel in each tablet). The second half was allotted to Trionetta, also known as Triquilar, Trigynon and Logynon (6 tablets with 30 micrograms ethinyl oestradiol + 50 micrograms levonorgestrel, 5 tablets with 40 micrograms ethinyl oestradiol + 75 micrograms levonorgestrel and 10 tablets with 30 micrograms ethinyl oestradiol + 125 micrograms levonorgestrel). The latter version was also present in a 28-day version containing in addition 7 "placebo" tablets to be used in the otherwise tablet-free interval. The contraceptive reliability was excellent although one pregnancy occurred in the three-phase version. It could be attributed to patient failure. In all aspects of bleeding control, the three-phasic pill proved to be superior to the reference monophasic preparation. The extreme low incidence of missed withdrawal bleeding and stability already during the first months of use are noteworthy features. For both preparations, continuation rate was at six months of use about 85% and at 12 months it was a similar figure. The most common reason for withdrawal was bleeding, about 5% each for both preparation. No serious side-effects were reported. The study clearly indicates that the three-phasic version is a major improvement in spite of a considerably decreased total dose of the gestagen.