Aromatization of norethindrone to ethinyl estradiol by human placental microsomes.

The interaction of 19-norethindrone [4-estren-17 alpha-ethinyl-17 beta-ol,3-one (NET)] with human placental microsomes was investigated using enzymatic and spectral techniques. The incubation of [6,7-3H]norethindrone with human placental microsomes, NADPH, and molecular oxygen resulted in the production of ethinyl estradiol [1,3,5-(10)estratrien-17 alpha-ethinyl-3,17 beta-diol (EE)]. The reaction was linear with respect to time and protein concentration. Androstenedione inhibited the enzymatic aromatization of NET to EE. The product was identified by thin layer chromatography, recrystallization to constant specific activity, and derivative formation. No acid or base was used in any step of product identification. To ensure that spontaneous aromatization of metabolites of NET did not contribute to our results, representative samples were treated with sodium borohydride before processing. Sodium borohydride reduces the 4-en-3-one grouping of the A-ring, thereby preventing chemical aromatization. Sodium borohydride treatment did not reduce our observed yields of EE from NET. The addition of NET to a preparation of solubilized, partially purified placental microsomal cytochrome P-450 yielded a type I cytochrome P-450 binding spectrum. The apparent spectral dissociation constant for NET binding to cytochrome P-450 was 28 microM. These results suggest that NET is enzymatically aromatized to EE by human placental microsomes.

The effects of rifampin and rifabutin on the pharmacokinetics and pharmacodynamics of a combination oral contraceptive.

BACKGROUND: Rifampin (INN, rifampicin), a CYP34A inducer, results in significant interactions when coadministered with combination oral contraceptives that contain norethindrone (INN, norethisterone) and ethinyl estradiol (INN, ethinylestradiol). Little is known about the effects of rifabutin, a related rifamycin. OBJECTIVES AND METHODS: The relative effects of rifampin and rifabutin on the pharmacokinetics and pharmacodynamics of ethinyl estradiol and norethindrone were evaluated in a prospective, randomized, double-blinded crossover study in 12 premenopausal women who were on a stable oral contraceptive regimen that contained 35 microg ethinyl estradiol/1 mg norethindrone. Subjects were randomized to receive 14 days of rifampin or rifabutin from days 7 through 21 of their menstrual cycle. After a 1-month washout period (only the oral contraceptives were taken), subjects were crossed over to the other rifamycin. RESULTS: Rifampin significantly decreased the mean area under the plasma concentration-time curve from time 0 to 24 hours [AUC(0-24)] of ethinyl estradiol and the mean AUC(0-24) of norethindrone. Rifabutin significantly decreased the mean AUC(0-24) of ethinyl estradiol and the mean AUC(0-24) of norethindrone. The effect of rifampin was significantly greater than rifabutin on each AUC(0-24). Despite these changes, subjects did not ovulate (as determined by progesterone concentrations) during the cycle in which either rifamycin was administered. Levels of mean follicle-stimulating hormone increased 69% after rifampin. CONCLUSION: In this study, rifampin (600 mg daily) was a more significant inducer of ethinyl estradiol and norethindrone clearance than rifabutin (300 mg daily), but neither agent reversed the suppression of ovulation caused by oral contraceptives. The carefully monitored oral contraceptive administration and the limited exposure to rifamycins may restrict the application of this study to clinical situations.

PIP: The relative effects of rifampin and rifabutin (a related rifamycin) on the pharmacokinetics and pharmacodynamics of ethinyl estradiol (EE) and norethindrone were evaluated in a prospective, randomized, double-blinded crossover study in 12 premenopausal women who were on a stable oral contraceptive regimen that contained 35 mcg EE and 1 mg norethindrone. Subjects were randomized to receive 14 days of rifampin or rifabutin from days 7 through 21 of their menstrual cycle. After a 1-month washout period (only the oral contraceptives were taken), subjects were crossed over to the other rifamycin. Findings showed that rifampin significantly decreased the mean area under the plasma concentration-time curve from time 0 to 24 hours [AUC (0-24)] of EE and the mean AUC (0-24) of norethindrone. Rifabutin significantly decreased the mean AUC (0-24) of EE and the mean AUC (0-24) of norethindrone. The effect of rifampin was significantly greater than rifabutin on each AUC (0-24). Despite these changes, subjects did not ovulate (as determined by progesterone concentrations) during the cycle in which either rifamycin was administered. Levels of mean follicle-stimulating hormone increased 69% after rifampin. This study suggests that rifampin (600 mg daily) was a more important inducer of EE and norethindrone clearance than rifabutin, but none of these agents were able to reverse the suppression of ovulation done by oral contraceptives.

Gabapentin does not interact with a contraceptive regimen of norethindrone acetate and ethinyl estradiol.

Anticonvulsants that induce hepatic metabolism increase clearance of oral contraceptive hormones and thereby cause contraceptive failure. Gabapentin is not metabolized in humans and has little liability for causing metabolic-based drug-drug interactions. In healthy women receiving 2.5 mg norethindrone acetate and 50 microg ethinyl estradiol daily for three consecutive menstrual cycles, concurrent gabapentin administration did not alter the steady-state pharmacokinetics of either hormone. Thus, gabapentin is unlikely to cause contraceptive failure.

PIP: Anticonvulsants that induce hepatic metabolism increase the clearance of synthetic estrogens and progestogens used in oral contraceptives (OCs), thereby potentiating contraceptive failure. In contrast, the anticonvulsant drug gabapentin is not metabolized in humans and has little liability for metabolic-based drug interactions. The present study sought to confirm whether concurrent administration of gabapentin would alter the pharmacokinetics of norethindrone acetate (2.5 mg) and ethinyl estradiol (50 mcg) in healthy US women. A total of 13 women were enrolled for three menstrual cycles each. Pharmacokinetic values did not change appreciably as a result of the addition of gabapentin. The rate and extent of absorption of both hormones were unaffected by the anticonvulsant. Gabapentin plasma concentration time profiles and pharmacokinetic values from this study were similar to historical values after administration of gabapentin alone. The observed lack of interaction between gabapentin and norethindrone acetate or ethinyl estradiol is consistent with the fact that gabapentin is not metabolized, is not an inducer or inhibitor of hepatic drug metabolizing enzymes, is absorbed via a specific transport system for amino acids, and is not bound to plasma proteins. Anticonvulsant drugs that do not interact with OCs should be considered for the treatment of epileptic women of childbearing age who are using this method of fertility control.

Influence of nutritional status on pharmacokinetics of contraceptive progestogens.

PIP: In response to recent studies from India suggesting that malnutrition, as assessed by anthropometric indexes, affects metabolism of oral progestogens, this study administered a mini-pill containing .35 mg of norethindrone (NET) and combination pills containing 250 or 150 mcg of d-norgestrel (d-NG) and either 50 or 30 mcg ethinyl estradiol as a single dose for fasting women of high and low income. Blood samples were collected for up to 24 hours for NET and 80 hours for the combination pills. Pharmacokinetics were evaluated by a least-squares method. Anthropometric measurements were also made. Peak NET levels occurred within 1-2 hours; half-life of plasma NET was shorter among low income, malnourished women compared with high income, well-nourished women. A direct correlation between weight/height and half-life of the drug suggests that malnutrition enhanation rate and reduces NET's half-life. Peak levels for d-NG also were reached between 1 and 2 hours after dosing. In well-nourished women, the decline in plasma d-NG was tri-exponential; malnourished women showed a biphasic curve with a neglible alpha-phase. Therefore, the lower the nutrition status, the faster the plasma clearance of these 2 orally administered compounds. Studies inn rabbits designed to elucidate this connection showed a significant elevation in specific activities of liver microsomal glucuronyl transferase and cytochrome-p450 in undernourished compared with control animals. There was also an increase in the amount (but not affinity) of uterine progesterone receptors in undernourished animals. Another study of a small group of Thai and Indian women showed positive correlation between anthropometric indexes and post peak plasma NET levels; however, an obesity study of Thai women found no such correlation.^ieng

Contraceptive efficacy, pharmacokinetics, and safety of Annuelle biodegradable norethindrone pellet implants.

OBJECTIVE: To evaluate the contraceptive efficacy, pharmacokinetics, and safety of two formulations of Annuelle (Endocon, Inc., South Walpole, MA) biodegradable norethindrone (NET) SC pellet implants. DESIGN: Prospective observational study. SETTING: Two clinical sites in the United States. PATIENT(S): Thirty-nine healthy, fertile, sexually active women. INTERVENTION(S): Nineteen women received a four-pellet system containing 174 mg NET; 20 women received a five-pellet system containing 266.5 mg NET. MAIN OUTCOME MEASURE(S): Contraceptive efficacy, median serum NET levels, adverse events. RESULT(S): No pregnancies were observed in 293 woman-months in the four-pellet group or in 375 woman-months in the five-pellet group. An initial burst in median serum NET levels occurred in the first 24 hours postinsertion followed by a steady decline over the next 3 years. Norethindrone levels varied considerably among women. The main side effect was bleeding abnormalities, which persisted in half the participants for up to 2 years. No serious adverse events were reported that were related to the pellets. Pellet insertion and removal generally were uncomplicated. CONCLUSION(S): Annuelle shows potential as an effective, safe contraceptive with distinct advantages over other long-acting agents, because it is biodegradable but can be removed if problems arise or if fertility is desired.

PIP: The contraceptive efficacy, pharmacokinetics, bleeding profiles, and safety of two formulations of the Annuelle contraceptive implant system were investigated in a prospective study conducted at two clinical sites in the US. 19 women received a four-pellet system containing 174 mg of norethindrone (NET) and 20 women received a five-pellet system containing 266.5 mg of NET. Participants were followed quarterly for up to 39 months. No pregnancies were recorded during 293 woman-months in the four-pellet group and 375 woman-months in the five-pellet group. Most women exhibited a burst in NET levels (values equal to or exceeding 2 ng/ml) 24 hours after pellet insertion, followed by a steady decline over the next 3 years. Ovulation was inhibited in most participants in both groups at 9 months after insertion, and this protective effect persisted as long as 2 years in 16 of the 39 subjects. More than 80% of women in both groups had at least one clinically important bleeding pattern (e.g., frequent, irregular, or prolonged bleeding) in the first 90-day interval; this percentage dropped over time, but persisted in half the participants for up to 2 years. Serum levels of total cholesterol, low density lipoproteins, and triglycerides dropped substantially after pellet insertion in both groups, while high density lipoprotein levels remained fairly constant. Overall, the Annuelle system is considered to have potential as a safe, long-acting contraceptive agent capable of being surgically removed before complete absorption. Of concern, however, is the relatively long period during which the product releases detectable amounts of NET but may no longer be a fully effective contraceptive agent.

Sequential regimen of the antiprogesterone RU486 and synthetic progestin for contraception.

OBJECTIVE: To examine the effect of sequential use of the antiprogesterone RU486 and synthetic progestin on ovarian function of healthy women. DESIGN: Healthy women were given a sequential antiprogesterone-progestin treatment. Blood samples were taken twice a week during one control cycle and one to three treatment cycles; prospective analysis. SETTING: The outpatient clinic of the Helsinki City Maternity Hospital, Helsinki, Finland, and Steroid Research Laboratory, Department of Medical Chemistry, University of Helsinki, Helsinki, Finland. PATIENTS: Eleven healthy women, volunteers, 20 to 34 years of age. INTERVENTIONS: A dose of 25 mg/d of RU486 was given during cycle days 1 to 21, and synthetic progestin (5 mg of norethisterone to six and 5 mg of medroxyprogesterone acetate to five women) during cycle days 22 to 31. MAIN OUTCOME MEASURES: Serum P, E2, FSH, and LH were measured from serum samples. RESULTS: In 20 of the 24 treatment cycles analyzed the serum concentrations of P were anovulatory. In the remaining 4 cycles, P levels rose above 3 ng/mL, suggestive of ovulation. Folliculogenesis was not completely inhibited, but serum E2 profiles were subnormal and delayed. Bleeding control was satisfactory. CONCLUSIONS: Antiprogesterone RU486 hampers or delays follicular development, suggesting a possible use as an estrogen-free oral contraceptive. However, the synthetic progestins used in this regimen induced serum P rises in some cycles. The synthetic progestin provides the cycle control, but its possible effect on the reliability of the method remains to be evaluated.

PIP: To assess the effectiveness of an estrogen-free oral contraceptive (OC) involving the sequential administration of an antiprogesterone and synthetic progestin, 11 healthy Finnish women 20-34 years of age were enrolled in a prospective investigation for 1-3 cycles. 25 mg of RU-486 was administered for the first 21 days of the cycle, followed by 5 mg of norethisterone or medroxyprogesterone acetate for the next 10 days. It was hypothesized that prolonged RU-486 administration would prevent the follicle from surviving for ovulation. During the RU-486 phase, P increases above 3 ng/ml (suggestive of ovulation) were recorded in only four of the 24 treatment cycles analyzed. Mean serum estradiol concentrations were 147 pg/ml in ovulatory women and 72 pg/ml in anovulatory women, indicating that follicle development was subnormal and delayed, but not completely inhibited. Baseline secretion of luteinizing hormone (LH) increased during RU-486 administration, while an LH surge greater than 100% over baseline was recorded in the majority of cycles during progestin administration. No significant changes occurred in follicle-stimulating hormone levels. Menstrual bleeding began 1-5 days after progestin discontinuation; women who took norethisterone experienced no breakthrough bleeding or spotting during treatment. It is concluded that the main antiovulatory effect of RU-486 is attributable to its antiprogestational effect on the preovulatory P rise.

Pharmacokinetics of oestrogens and progestogens.

There are large inter- and intra-individual variations in the serum concentrations of natural and synthetic sex steroids irrespective of the route of administration. Oral ingestion of steroids has a stronger effect on hepatic metabolism than parenteral administration, as the local concentration in liver sinusoids are 4-5 times higher during the first liver passage. Oestradiol and oestrone are interconvertible, dependent on the local concentrations in liver and target organs, and oestrone sulphate serves as a large reservoir. The oestrone/oestradiol ratio has no physiological significance, as oestrone is only a weak oestrogen. Oestrone is both a precursor and a metabolite of oestradiol. Oestriol is extensively conjugated after oral administration. Therefore, the oestriol serum levels are similar after oral intake of 10 mg and after vaginal application of 0.5 mg oestriol resulting in similar systemic effectiveness. Conjugated oestrogens can easily enter the hepatocytes but are hormonally active only after hydrolyzation into the parent steroids. Ethinylestradiol which exerts strong effects on hepatic metabolism and inhibits metabolizing enzymes, should not be used for hormone replacement therapy. Among the progestogens, the progesterone derivatives have less effects on liver metabolism than the norethisterone derivatives (13-methyl-gonanes and 13-ethyl-gonanes). The highly potent 13-ethyl-gonanes are effective at very low doses, because of a slow inactivation and elimination rate due to the ethinyl group.

Animal toxicity studies performed for risk assessment of the once-a-month injectable contraceptive Mesigyna.

Results from toxicity studies performed for risk assessment of the combined injectable hormonal preparation Mesigyna are reviewed. Both components of Mesigyna, i.e., estradiol valerate (E2Val) and norethisterone enanthate (NET-EN), have been thoroughly investigated as individual compounds and some limited toxicity data have been obtained for the combination. Most findings which were gathered in these studies from different animal species occurred in the gonads, accessory genital and endocrine organs and can be related to the known species-specific pharmacological activity of a typical estrogen or progestin, respectively. No additional or unexpected information which might indicate a possible estrogen/progestin interaction was gained from the administration of the combined preparation to animals. Based on the results from toxicity testing, there were no objections to the long-term therapeutic use of Mesigyna for hormonal contraception. The predictive value of the effects (including the tumorigenicity) observed in the common laboratory animals with regard to human safety is critically discussed, taking the vast amount of previous experience with hormonal contraceptives into consideration. The conclusion is drawn that there is no animal model for safety assessment of sex steroids that adequately represents the human situation. Quantitative extrapolations from animal toxicity findings to humans, therefore, are not possible. Especially, the value of long-term studies and of toxicity studies on estrogen/progestin combinations is put into question. Like endocrine pharmacology studies, the toxicity studies with these steroid hormones are useful for the characterization of the possible endocrine pharmacological profile only.

PIP: Considerable research has been conducted on the 2 steroid components of the once-a-month injectable contraceptive, Mesigyna. These steroids are estradiol valerate and norethisterone enanthate. Most findings from the limited toxicity studies of the combined injectable in different animal species were limited to the gonads and accessory genital and endocrine organs. The steroids have a toxicological activity profile in each of the species, which indicate that they act as a typical steroidal estrogen or progestin. They are no different than comparable compounds as used in oral contraceptives. Other than these findings, researchers did not acquire any more or unexpected information that would suggest a possible estrogen/progestin interaction from administering the combined preparation to animals. The findings of the toxicity testing do not suggest problems with the long-term use of Mesigyna for hormonal contraception. Yet, the fundamental species differences in endocrinology, metabolism of compounds, and pharmacokinetics make it virtually impossible to quantitatively extrapolate from findings of animal toxicity studies to human, e.g., those on tumorigenicity. A critical review of in vitro and animal toxicity studies of both compounds individually and combined lead to the conclusion that no animal model for safety assessment of sex steroids exists that correctly replicates the human environment. Toxicologists with Schering AG even question the value of long-term studies and toxicity studies on estrogen/progestin combinations. Animal models can be used, however, to characterize a possible endocrine pharmacological profile of newly developed steroids. Any such animal studies need not last any longer than 6 months.

Pharmacokinetics of norethisterone in humans.

The pharmacokinetics of a dose of 1mg norethisterone administered with 50 micrograms ethynyloestradiol was studied in 83 subjects. The dose was rapidly absorbed and there were wide variations in the serum NET concentrations at any particular time after dosing; the concentrations at 24 h varied from 100 to 1700 pg/ml. There was a significant negative correlation between the serum NET concentration and the time after dosing in all women. There were large inter-subject variations in the pharmacokinetic parameters, the elimination half-life and bioavailability showing 3- and 5- fold variability, respectively. Mean values for the parameters were t1/2, 7.6 h; bioavailability, 53.6 ng/ml/h; C max, 4.63 ng/ml; clearance, 22.6 l/h; and Vd 2361. There were a number of statistically significant correlations between the pharmacokinetic parameters and analysis of the correlations suggested that clearance was an important determinant of the bioavailability and of C max whereas the elimination half-life was the determinant of the NET concentration at 24 h. The pharmacokinetics of NET are compared with those of ethynyloestradiol. The wide variation in pharmacokinetics is likely to be important in determining inter-subject variations in efficacy and, particularly, side-effects of oral contraceptives especially now that low-dose formulations are widely used.

PIP: The pharmacokinetics of a dose of 1 mg norethisterone administered with 50 mcg ethinyl estradiol was studied in 83 subjects. There were marked variations in age, height, and weight between subjects in the 14 centers, but few of the differences were statistically significant. Table 1 shows the mean values for the serum norethisterone (NET) concentration in samples from each center. Variations between the values observed at any particular time both between the subjects recruited in any 1 center and between subjects in different centers were considerable. Considering only mean values, there was a 2-3-fold variation between the centers at any 1 time. Absorption was quick in most of the 83 subjects. The peak serum concentration occurred within 1 hour in 10 women, between 1-2 hours in 47 women, and between 2-4 hours in 25 women. Elimination was slow, and in only 4 of the 83 subjects had the serum NET concentration declined to 100 pg/ml by 24 hours. Thus, in the majority of women, significant concentrations of NET still were present 24 hours after administration of the dose. For the elimination phase (2-24 hours), there was a significant negative correlation between the logarithm of the serum NET concentration and time after administration of the dose, the correlation coefficient being greater than 0.9 in all but 2 of the 83 women. Due to the large inter-subject variation and the small number of subjects studied in each center, few of the correlations between the pharmacokinetic parameters or of the parameters with the ponderal index in each center were significant although in 10 of the 14 centers there was a significant correlation of the serum NET concentration at 24 hours with the elimination half-life. There was a 3-fold variation between the lowest and highest values for the half-life and a 5-fold variation for area under the curve. In no subject were undetectable NET levels reached in less then 20 hours, and only in 18.5% had the levels decrease below 400 pg/ml. In 63% of the women, a time of 30-50 hours was necessary for serum NET levels to become undetectable, but in 22.2% of the subjects detectable levels were still present at more than 50 hours after administration of the dose. The wide variation in pharmacokinetics is likely to be important in determining inter-subject variations in efficacy and, particularly, side-effects of oral contraceptives.

Use of norethisterone and estradiol in mini doses as a contraceptive in the male. Efficacy studies in the adult male bonnet monkey (Macaca radiata).

Administration of norethisterone (NET) or NET + estradiol benzoate using an Alzet minipump or as once-a-month intramuscular injection of their depot forms, NET-enanthate (NET-EN) and estradiol valerate (E-val), resulted in azoospermia in all monkeys (n = 13) within 60 to 150 days of treatment. Although addition of depot form of testosterone (T, 20 mg/month) to the regimen restored the behavioral response typical of a normal male, it did not reverse the azoospermic state. Serum T (heightened nocturnal) levels were significantly reduced (> 85%, p < 0.001) in all the treated groups. Evidence for blockade in spermatogenesis following treatment was obtained by DNA flow cytometry. Following withdrawal of treatment, the T level was restored to normalcy within 15 days but 120 days more were required for the animals to exhibit normal sperm counts. In conclusion, the efficacy of once-a-month injection of relatively low doses of NET-EN + E-Val to bring about azoospermia in monkeys, in a relatively short time, has been demonstrated. As the results are uniform and reproducible, it appears desirable that this steroid regimen be tested in man for its contraceptive efficacy.

PIP: Monthly intramuscular injection with an Alzet minipump of depot norethisterone enanthate and estradiol valerate (E-val) produced azoospermia in 13 adult male bonnet monkeys within 60-150 days. Although azoospermia was achieved earlier when E-val was added to the injection, this agent can be eliminated once azoospermia occurs. Addition of the depot form of testosterone (20 mg/month) restored the sexual behavioral response but did not reverse azoospermia. Serum testosterone levels were significantly reduced in all treatment groups. DNA flow cytometry revealed evidence for blockade in spermatogenesis after treatment. There were no changes in the serum lipid profile. The testosterone level returned to normal within 15 days after the end of treatment, but normal sperm counts were not observed for another 120 days. Since the steroid formulation investigated in this study has been used effectively in women for over a decade, tests of its contraceptive efficacy in men now seem warranted.

Phase I clinical trial of two contraceptive preparations. Norethisterone enanthate (NEN) and norethisterone acetate (NET).

A Phase I Clinical Trial was conducted in 20 fertile Cuban women using for contraception: Norethisterone Enanthate injectable (NEN) and Norethisterone Acetate minipill (NET). Women had daily blood sampling during a control cycle and during the second month of treatment with either drug. Discontinuation rate was very low (1/20). The preovulatory LH and FSH peaks were abolished in all treated women, basal levels remaining unchanged. The incidence of menstrual disorders as amenorrhea, spotting and inter-menstrual bleeding was greater in subjects using NEN than in those on NET. No pregnancy was reported. Blood pressure was unaltered. Renal, hepatic and thyroid function were unchanged. Cholesterol levels were unchanged and triglycerides significantly decreased with both preparations. Women on either NEN or NET underwent OGTT before and after 2 months treatment. In NEN group glycemia was unchanged but insulin levels increased significantly at 120 minutes. In NET group glycemia and insulin levels were significantly increased at all times during post-treatment OGTT. Both forms of Norethisterone were well accepted by this group of women despite menstrual irregularities. Significant changes were found in the group using NET with regard to carbohydrate metabolism.

PIP: A clinical trial was conducted with 2 types of progestogen-only contraceptives in 20 fertile Cuban women. 1/2 the group was administered NEN (norethisterone enanthate) injectable; the other 1/2 was given NET (norethisterone acetate) minipill. Daily blood samples were taken and complicated laboratory procedures followed to measure pharmacological effects and gonadotropin secretion. Although preovulatory LH (luteinizing hormone) and FSH peaks were abolished, basal levels of these 2 hormones remained constant. 8 of the 10 women on NEN had some type of menstrual disorder; 5 of those on NET experienced menstrual disorders. Despite the menstrual irregularities, both drugs were highly acceptable and the continuation rate was high. No pregnancy was reported in either group. Blood pressure, renal, hepatic, and thyroid function remained unchanged. Cholesterol levels were unchanged. Both drugs significantly reduced triglycerides. The NET group registered significant changes in their carbohydrate metabolism.

Pharmacokinetics of norethisterone oenanthate in humans.

The pharmacokinetics of a dose of 200 mg NET-OEN were studied after intramuscular injection into nine subjects. Blood levels of NET and NET-OEN increased rapidly, reaching peaks in most subjects within seven days. At all times after injection, serum levels of NET exceeded those of NET-OEN. The half-life of absorption varied from 5.4 to 22.3 days and the half-life of elimination varied from 7.5 to 22.5 days; there was a significant correlation (R = 0.78) between these two half-lives. There were significant correlations between the absorption half-lives and the peak values of NET and NET-OEN, the time to reach peak values and the time for which NET was detectable in serum. In all subjects NET was detectable in the circulation for a longer time after injection (mean value 74 days) than NET-OEN (mean value 43 days). The time for which the two steroids were detectable in the circulation showed a significant correlation with the elimination half-lives but there was no correlation with the peak values attained, the time taken to reach peak values and bioavailability. There was a two-fold variation between the subjects in the bioavailability of NET, less than 5% of the bioavailable NET was released after day 60.

Serum levels and pharmacokinetics of norethisterone after ingestion of lynestrenol: its relation to dose and stage of the menstrual cycle.

The peak concentration, peak time, the area under the serum concentration time curve (AUC) and half-life of serum norethisterone (NET) after a single application of lynestrenol (LYN) to female volunteers demonstrated that 0.7 mg NET is bioequivalent to 1 mg LYN which is rapidly converted to NET. There was a decrease of the peak values and an increase of half-life of NET during the periovulatory and luteal phase which was, however, not significant due to the great individual differences. The shift of the peak time to longer intervals and the increase of half-life of NET after ingestion of higher LYN doses indicate a certain limitation of the metabolic capacity of the liver. One of the volunteers who complained of nausea and vertigo after the administration of 5 mg LYN, showed the highest serum values of NET. The large interindividual variations of the serum levels of synthetic steroids demonstrate a possible risk of contraceptive safety in women with low steroid levels and possibly a coherence between extremely high serum levels of synthetic steroids and side effects.

A morphometric study of the effect of oral norethisterone or levonorgestrel on endometrial blood vessels.

A morphometric study was undertaken to quantitate vessel numbers in uterine biopsies from a control group of patients, patients with dysfunctional uterine bleeding and patients taking low dose norethisterone or levonorgestrel. Vessels were counted at the endometrial/myometrial junction and in the functional endometrium just below the surface epithelium. The number of arteries at the endometrial/myometrial junction was found to be decreased in patients taking norethisterone and levonorgestrel. An increase was found in the total number of veins and in the number of dilated veins in the functional endometrium of the progestogen-treated specimens. Dilated veins were frequently found close to the endometrial surface and it is possible that they may be the major cause of the irregular bleeding associated with low dose oral progestogens.

PIP: A morphometric study undertaken to quantitate vessel numbers in uterine biopsies from a control group of patients, patients with dysfunctional uterine bleeding and patients taking low dose norethisterone or levonorgestrel, in Dublin, Ireland. Vessels were counted at the endometrial/myometrial junction and in the functional endometrium just below the surface epithelium. The number of arteries at the endometrial/myometrial junction was found to be decreased in patients taking norethisterone and levonorgestrel. An increase was found in the total number of veins and in the number of dilated veins in the functional endometrium of the progestogen-treated specimens. Dilated veins were frequently found close to the endometrial surface and it is possible that they may be the major cause of the irregular bleeding associated with low dose oral progestogens.

A comparative study on the return to ovulation following chronic use of once-a-month injectable contraceptives.

A comparative study was undertaken involving 21 Mexican women who discontinued the use of medroxyprogesterone acetate 25 mg plus oestradiol cypionate 5 mg (Cyclofem) and norethisterone enanthate 50 mg plus oestradiol valerate 5 mg (Mesigyna) to assess the time required for the return to menses and ovulation. All subjects were exposed to once-a-month injectable contraceptives for two years and were followed for 120 days after the last injection. The urinary concentration of oestrone glucuronide and pregnanediol glucuronide was determined daily in all subjects beginning one month after the last injection. The results disclosed that ovulatory cycles were documented after 120 days of the last injection in six women of each studied group. Similar endometrial bleeding patterns were observed in both groups, indicating that the two drugs have alike pharmacokinetic and pharmacodynamic effects.

PIP: At the family planning clinic of the medical school in Coahuila, Mexico, providers recruited 11 volunteers requesting an injectable contraceptive into Group I (Mesigyna: 50 mg norethisterone enanthate + 5 mg estradiol valerate) and 10 similar volunteers into Group II (Cyclofem: 25 mg medroxyprogesterone acetate + 25 mg estradiol cypionate). After they used the injectables continuously for two years, researchers followed them for 120 days after the last injection. Early morning urine samples were taken every day between day 30 and day 120 after the last injection to measure estrone glucuronide and pregnanediol glucuronide. Researchers also measured the urinary luteinizing hormone level. Normal ovulatory cycles returned within the first to third month after injection in six users from each group. In fact, all but one woman in the Group I had a normal ovulatory cycle during the first month. The other woman had a normal cycle during the second month. During months 1, 2, and 3, the numbers of women in group II who had a normal ovulatory cycle were 3, 2, and 1, respectively. The two groups did not have significant differences in the first bleeding-free interval (51 for Group I vs. 43 for Group II) and in the total number of bleeding/spotting days (11 vs. 14). These findings suggest that long-term use of these injectable contraceptives did not cause chronic inhibition of the hypothalamus-pituitary-ovarian axis and that the ovarian function and the endometrial bleeding patterns returned to normal similarly in both groups. Thus, national family planning programs in developing and developed countries may want to consider offering them as part of the contraceptive mix.

Assessment of a new low-dose once-a-month injectable contraceptive.

Norethisterone (NET) in combination with mestranol (ME), in a macrocrystalline aqueous suspension that provides sustained release of steroids, was assessed as a once-a-month injectable contraceptive in ten healthy women of reproductive age. The ovarian function was studied before and after the intramuscular administration of 12mg NET plus 1.2mg ME, delivered as crystals of 150 micron average size. Serial blood samples were taken throughout the injection intervals in all women to measure serum progesterone (P), estradiol (E2), and NET. The NET/ME preparation effectively inhibited ovulation in 23 out of the 25 injection intervals studied. The administration of this formulation induced in some women a small degree of follicular maturation not followed by luteal activity. The endometrial bleeding patterns after each injection showed a bleeding-free period of two to three weeks. The overall data demonstrate that the parenteral administration of a macrocrystalline steroid preparation of NET/ME can bring about a sustained release contraceptive system at a substantially lower dose than those currently employed in once-a-month injectable contraception.

Pharmacokinetics of different doses of norethisterone oenanthate.

Doses of norethisterone oenanthate of 300, 150, 100 and 50 mg were administered to four groups of subjects. Due to wide intersubject variations there were no statistically significant differences in the pharmacokinetic parameters for the different groups but there were significant correlations between the dose and the mean values for these parameters. There was little difference between the groups in the duration for which ovarian function was suppressed due to the inter-subject variation being greater than the inter-dose effect. The duration of the antifertility action of norethisterone oenanthate cannot be increased by increasing the dose above the standard 200 mg; however, with an injection interval of 60 to 70 days, it seems likely that the dose could be reduced to 150 mg.

PIP: Doses of norethisterone enathate of 300, 150, 100, and 50 mg were administered to 4 groups of subjects. Due to wide intersubject variations, there were no statistically significant differences in the pharmacokinetic paraetmers for the different groups but there were significant correlations between the dose and the mean values for these parameters. There was little difference between the groups in duration for which ovarian function was suppressed due to the intersubject variation being greater than the interdose effect. The duration of the antifertility action of norethisterone enanthate cannot be increased by increasing the dose above the standard 200 mg; however, with an injection interval of 60-70 days, it seems likely that the dose could be reduced to 150 mg.

Plasma levels and pharmacokinetics of norethindrone and ethinylestradiol administered in solution and as tablets to women.

Twenty-four normal adult female volunteers were dosed orally with a solution and tablet formulation containing the contraceptive combination of norethindrone (NET, 1.0 mg) and ethinylestradiol (EE2, 0.12 mg) in a crossover bioequivalence study. Blood was sampled sequentially following single oral doses and the plasma separated for analysis of NET and EE2 by specific radioimmunoassays. Comparisons of both drugs following a dose in solution and tablets were made with respect to the following parameters: (a) plasma concentrations at each sample time; (b) maximum plasma concentration (Cpmax); (c) time to maximum plasma concentration (Tmax); (d) total area under the plasma concentration vs. time curve (AUC), and (e) plasma half-life (t1/2). It was found that the tablet and solution doses were bioequivalent with respect to EE2 absorption. However, absorption of NET from solution and tablet doses exhibited significant differences with respect to plasma levels at certain time points as well as AUC (which were higher following the tablet dose), but Cpmax, Tmax and t1/2 were not significantly different. Pharmacokinetic analysis of both drugs following the tablet dose was carried out using a two-compartment open model. The absorption rate constant (ka) and peripheral to central compartment transfer rate constant (k21) were similar for NET and EE2, but statistically significant differences were observed with respect to the distribution rate constant (alpha), the central to peripheral transfer rate constant (k12), the overall elimination rate constant (ke1), and volume of distribution (V1/F). The elimination rate constant (beta) for both drugs showed a difference of borderline statistical significance.

Effects of different doses of norethisterone on ovarian function, serum sex hormone binding globulin and high density lipoprotein-cholesterol.

The ovarian effects of different doses of norethisterone (NET) were compared in 45 normally menstruating women in order to find the lowest effective dose of the Chinese NET "visiting pill". Subjects were randomly divided into 3 groups. Each subject in each group was taking 0.5, 1.5 or 3.0 mg per day from days 5 to day 18 of the cycle. Blood samples were taken on days 5, 8, 11, 14, 17, 20, 23, 26 and 29 of the cycle. Serum oestradiol (E2), progesterone (P), sex hormone binding globulin (SHBG), high density-lipoprotein cholesterol (HDL-C), and NET concentrations were measured. Ovulation, delayed ovulation, ovulation inhibition and follicular activity were classified by the analysis of the peripheral serum levels of sex hormones. Ovulation occurred in 7 women in the 0.5 mg group, in 2 women in the 1.5 mg group and in none of the 3.0 mg group. Mean serum SHBG levels were reduced progressively by 6.6% (Group 0.5), 15.5% (Group 1.5) and 23.4% (Group 3.0). There were no significant changes in HDL-C levels in any group. There was a significant correlation of mean serum NET concentrations with dose. The lack of complete inhibition of ovulation in most women in the 1.5 mg and 0.5 mg groups might suggest that the dose of NET required when used as a visiting pill could not be reduced below 3.0 mg.

PIP: In Shanghai, China, 45 25-35 year old women took a daily norethisterone (NET) "visiting pill" (vacation pills) on menstrual cycle days 5-18 as part of a clinical study comparing various doses of NET on ovarian function, sex hormone binding globulin (SHBG), and high density lipoprotein-cholesterol (HDL-C). The aim of the study was to determine the lowest effective dose of the NET visiting pill. Even though some ovarian activity occurred at all 3 doses (0.5, 1.5, and 3 mg), no woman experienced ovulation at 3 mg NET/day during days 5-18 of the cycle. It suppressed ovulation in 11 (73.3%) of the 15 women. Follicular activity occurred in the remaining 4 women. Ovulation occurred in 33% of women taking the 1.5 mg dose and in 66% of those taking the 0.5 mg dose. The higher the NET dose, the greater was the fall in mean serum SHBG levels from control levels (3 mg, 23.4%; 1.5 mg, 15.5%; and 0.5 mg, 6.6%). Both the regression equation and log dose regression equation showed a significant correlation between mean serum NET levels and dose (p .001). HDL-C levels remained basically the same as control levels. Since, at the 1.5 mg dose, ovulation occurred in 5 women and only 5 women experienced complete inhibition, a dose no lower than 3 mg should be used for the NET visiting pill.

Glucose and insulin levels after six months of treatment with a triphasic oral contraceptive containing ethinyl estradiol and norethindrone.

A prospective study of carbohydrate metabolism was done on 33 women who used a triphasic oral contraceptive (OC) containing ethinyl estradiol and norethindrone for six months. A three-hour oral glucose tolerance test was administered before and after the OC usage, and both the blood glucose and insulin levels were determined. A significant decrease in the fasting glucose level was found with treatment. All other glucose values and insulin levels were unchanged.

PIP: To evaluate the effects of a triphasic oral contraceptive (OC) containing ethinyl estradiol and norethindrone on carbohydrate metabolism, both blood glucose and insulin levels were measured over the 6-month study period in 33 new acceptors. An identical oral glucose tolerance test was administered to each study subject immediately before commencing OC use and again during the 6th cycle of treatment; thus, each subject served as her own control. All glucose tolerance test results were normal and all fasting values were under 100 mg%. The only change accompanying triphasic OC use was a significant decrease in fasting glucose values. Mean control levels of plasma glucose (mg%) were 74.1 after a 10-hour fast and 113.4, 94.9, 89.7, and 86.2 0.5, 1, 2, and 3 hours, respectively, after consumption of 100 grams of glucose. 6-month levels averaged 70.2 at fasting, 115.3 at 0.5 hours, 102.3 at 1 hour, 92.8 at 2 hours, and 87.5 at 3 hours. The mean total insulin value was 213.7 + or - 27.4 mcgU pretreatment and 218.5 + or - 17.3 after 6 months of OC use--a nonsignificant difference. Earlier studies have demonstrated alterations in carbohydrate metabolism in users of high-dose OCs, presumably attributable to the progestogen component. Triphasic formulations achieve maximum reduction of the progestogen content of OCs by using 3 different doses throughout the month. Future longterm studies of users of low-dose and triphasic OCs are expected to show minimal clinical sequelae in the vascular systems of users.