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PubMed1979

Norethindrone acetate inhibition of splanchnic triglyceride secretion in conscious glucose-fed siwne.

The effects of conventional doses of two synthetic contraceptive steroids on the concentration and rate of secretion of plasma triglycerides from the splanchnic region were investigated. Studies were undertaken in miniature swine under steady state conditions produced by prolonged constant hypercaloric intravenous infusions of glucose. The steroids, alone or in combination, were administered with the high carbohydrate diet for at least 2 weeks prior to study of splanchnic metabolism and were also infused intravenously during the studies. Splanchnic triglyceride secretion was determined from measurements of plasma flow and transsplanchnic radiochemical gradients of plasma triglycerides. Compared with studies in the untreated animal, norethindrone acetate significantly reduced the arterial concentration (1.1 +/- 0.1 vs. 0.7 +/- 0.1 mM) and rate of splanchnic secretion of plasma triglyceride fatty acids (2.0 +/- 0.4 vs. 0.8 +/- 0.1 micro mol/min.kg body wt(0.75)) and decreased the percent of free fatty acids entering the splanchnic region that was converted to plasma triglycerides (22 +/- 5 vs. 13 +/- 3%, P < 0.05). Ethynylestradiol, in the dose employed, had no significant effect on these variables; however, ethynylestradiol and norethindrone acetate together gave responses similar to norethindrone acetate alone. When the glucose was given intraduodenally vs. intravenously, values for splanchnic metabolism of triglycerides were unchanged. The hypolipemic effect of norethindrone acetate in glucose-fed swine was attributable to inhibition of hepatic triglyceride secretion.-Wolfe, B. M., and D. M. Grace. Norethindrone acetate inhibition of splanchnic triglyceride secretion in conscious glucose-fed swine.

Animals↗
PubMed1976

Metabolism of oral contraceptive drugs. The formation and disappearance of metabolites of norethindrone and mestranol after intravenous and oral administration.

Previous studies from this laboratory reported that 3H-labeled metabolites with half-lives of more than 24 hours may remain in the plasmaa of women receiving an intravenous injection of 3H norethindrone or 3H mestranol. To confirm the presence of these metabolites, blood samples were collected for five days after injection of 3H norethindrone or 3H mestranol; 3H representing metabolites of norethindrone disappeared with half-life values of 42 to 84 hours (mean 67 hours), while 3H representing metabolites of mestranol declined with an average half-life of 45 hours (range 37 to 65 hours). When the 3H-labeled drugs were administered orally, metabolites of similar half-life were formed. Because these compounds exist for several days after a single administration and since oral contraceptive drugs are normally taken daily, the possiblity of the accumulation of 3H in the plasm of women receiving several consecutive doses of 3H norethindrone was investigated. The results of this study show a stepwise accumulation of the 3H metabolites when 3H norethindrone was administered in six daily oral doses. However, the 3H levels declined from the peak on the sixth and last day of the treatment at a rate equivalent to those previously measured after intravenous or oral administration.

Administration, Oral↗
PubMed1977

Influence of norethindrone on drug-metabolizing enzymes of female rat liver in various B-vitamin deficiency states.

Ingestion of high levels of thiamin significantly decreased the activity of cytochrome P-450, NADPH cytochrome c reductase, and the metabolism of aniline and ethylmorphine. Apparent VmaxS for ethylmorphine N-demethylase and aniline hydroxylase were decreased by high levels of riboflavin even though NADPH cytochrome c reductase was elevated. High levels of dietary pyridoxine significantly decreased only the Vmax for aniline hydroxylase. Generally, norethindrone produces either no change or slight depression of cytochrome P-450 regardless or diet, whereas the administration of norethindrone produced no change or an increase in activity of c reductase and ethylmorphine N-demethylase. Norethindrone induces aniline hydroxylase in animals fed all diets except those deficient in thiamin and riboflavin. The activities of the four parameters of the drug metabolizing system measured in these studies as well as the effects of norethindrone are clearly affected by the dietary status of the animal.

Aniline Hydroxylase↗
PubMed2001

Bleeding patterns in postmenopausal women using continuous combination hormone replacement therapy with conjugated estrogen and medroxyprogesterone acetate or with 17beta-estradiol and norethindrone acetate.

OBJECTIVE: We studied bleeding patterns in postmenopausal women who were using 2 types of continuous combination regimens. STUDY DESIGN: A prospective, double-blind, randomized study of 208 postmenopausal women treated with conjugated estrogen, 0.625 mg, and medroxyprogesterone acetate, 5 mg, or with 17beta-estradiol, 2 mg, and norethindrone acetate, 1 mg. RESULTS: The mean number of bleeding days decreased during the first 4 months of treatment (P <.002) but not thereafter. The number of bleeding days was fewer (P <.002) and the time until amenorrhea was shorter (P <.02) in patients receiving conjugated estrogen and medroxyprogesterone acetate than in patients receiving 17beta-estradiol and norethindrone acetate. The odds ratio for progression to amenorrhea with the use of conjugated estrogen and medroxyprogesterone acetate was 1.58, in comparison with the use of 17beta-estradiol and norethindrone acetate. A thick endometrium at the start of treatment resulted in more bleeding days than were found for a thin endometrium (P <.03). Body mass index, age, and blood pressure had no predictive value for bleeding problems. CONCLUSIONS: Treatment with continuous combined conjugated estrogen and medroxyprogesterone acetate resulted in fewer bleeding problems than did treatment with 17beta-estradiol and norethindrone acetate. Endometrial thickness may help to predict the chance of achieving amenorrhea during early hormone replacement therapy.

Aging↗
PubMedDate not supplied

The effect of varying low-dose combinations of norethindrone acetate and ethinyl estradiol (femhrt) on the frequency and intensity of vasomotor symptoms.

OBJECTIVE: To determine whether there is a significant reduction in frequency and severity of hot flashes in symptomatic postmenopausal women who are administered continuously different dose combinations of norethindrone acetate and ethinyl estradiol. DESIGN: Two randomized clinical trials (Study 1 and Study 2) were conducted in which study participants recorded in daily diaries the frequency of their hot flashes. Study 2 participants also recorded the number of mild, moderate, or severe hot flashes they experienced. In Study 1, a total of 219 postmenopausal women reporting vasomotor symptoms were placed randomly into groups to receive either a placebo or 1 of 4 treatments (0.2 mg/1 microg; 0.5 mg/2.5 microg; 1 mg/5 microg; or 1 mg/10 microg norethindrone acetate/ethinyl estradiol). In Study 2, a total of 266 highly symptomatic postmenopausal women were placed randomly to receive either a placebo or 1 of 3 treatment groups [0.5 mg/2.5 microg; 1 mg/5 microg; or 1 mg/10 microg norethindrone acetate (NA)/ethinyl estradiol (EE)]. Total duration of treatment was 16 weeks in Study 1 and 12 weeks in Study 2. Study 1 subjects had to have at least 10 hot flashes during the week before randomization. Study 2 subjects had to have at least 56 moderate to severe hot flashes during the week before randomization. RESULTS: In both studies, there was a dose-related decrease in hot flash frequency with the highest dose (1 mg NA/10 microg EE) group that had the greatest response. Significant differences from placebo (p < 0.05, Dunnett's test) occurred within 4 weeks in Study 1 for hot flash frequency with a percent reduction in frequency ranging from 33% for placebo to 84% for both the 1 mg NA/10 microg EE and 1 mg NA/5 microg EE dose groups. Likewise, Study 2 significant reductions in hot flash frequency occurred by Week 2 for 1 mg NA/10 microg EE, Week 3 for 1 mg NA/5 microg EE, and Week 5 for 0.5 mg NA/2.5 microg EE (p < 0.05, Dunnett's test). This dose effect was also apparent with regard to severity. In addition, more subjects had clinically meaningful reductions in hot flash frequency or elimination as the dose combinations increased. CONCLUSION: There were significant reductions in hot flash frequency and severity with continuous treatment with norethindrone acetate and ethinyl estradiol combinations. The time at which significant reductions were observed, as well as the magnitude of the response, were dose dependent. The opportunity for lower-dose options of a new continuous-combined hormone replacement therapy provides therapeutic flexibility for women who are recently menopausal.

Adult↗
PubMed1979

Inhibition of hepatic drug metabolism by norethindrone.

In order to assess the effect of norethindrone on hepatic drug metabolism in man, hepatic N-demethylation of aminopyrine was studied by means of the aminopyrine breath test (ABT) in 7 healthy women during two menstrual cycles. Aminopyrine metabolic clearance rates were also studied in 3 women. The women were examined at the ends of the first, second, and third weeks before starting progestogen therapy and at the same times during a second menstrual cycle during which they took norethindrone, 350 microgram/day. The ABT was 5.1 +/- 1.9% (mean +/- SD) during the three control weeks and lower (p less than 0.001) during the three weeks on norethindrone, 3.9 +/- 0.9%. Aminopyrine metabolic clearance rate also fell during norethindrone therapy. The data suggest that progestogens inhibit hepatic microsomal function.

Adult↗
PubMed1983

In vivo release of norethindrone coupled to a biodegradable poly(alpha-amino acid) drug delivery system.

The in vivo release of norethindrone from a biodegradable steroid-polymer conjugate was studied in rats. The drug-polymer conjugate, consisting of [3H]norethindrone coupled via a 17-carbonate bond to poly-N5-(3-hydroxypropyl)-L-glutamine was administered to female rats by subcutaneous injection. The in vivo release of steroid, determined by measuring the daily radioactivity output in urine and feces, was fairly constant though it showed a gradual decrease during the 9-month study period. The data indicate that this biodegradable norethindrone-polymer conjugate is a potential candidate for the controlled delivery of norethindrone to effect long-term contraception.

Animals↗
PubMed1990

Determination of norethindrone stability on red delicious apples.

A stability-indicating assay procedure for the determination of norethindrone on the surface of Red Delicious apple slices was developed. The apple slice is homogenized in pH 10 borate buffer solution and norethindrone is then partitioned into chloroform using a diffusion chamber that has a membrane that is permeable to hydrophobic compounds separating the buffer and chloroform. An aliquot of the chloroform extract is then evaporated to dryness and reconstituted in tetrahydrofuran. The reconstituted sample is then chromatographed on a C18 reversed-phase column using a mobile phase consisting of water:tetrahydrofuran:methanol (63:26:11, v/v/v). Detection is in the UV range at 254 nm. The chromatographic system is specific for norethindrone in the presence of its autoxidation products. Stability data indicate that norethindrone is stable for up to 6 h on the surface of Red Delicious apples.

Chromatography, High Pressure Liquid↗
PubMed2005

Simultaneous determination of norethindrone and ethinyl estradiol in human plasma by high performance liquid chromatography with tandem mass spectrometry--experiences on developing a highly selective method using derivatization reagent for enhancing sensitivity.

In the present work, for the first time, a liquid chromatographic method with tandem mass spectrometric detection (LC-MS/MS) for the simultaneous analysis of norethindrone, and ethinyl estradiol, was developed and validated over the concentration range of 50-10000pg/ml and 2.5-500pg/ml, respectively, using 0.5 ml of plasma sample. Norethindrone, ethinyl estradiol, and their internal standards norethindrone-(13)C2, and ethinyl estradiol-d4, were extracted from human plasma matrix with n-butyl chloride. After evaporation of the organic solvent, the extract was derivatized with dansyl chloride and the mixture was injected onto the LC-MS/MS system. The gradient chromatographic elution was achieved on a Genesis RP-18 (50 mm x 4.6 mm, 3 microm) column with mobile phase consisted of acetonitrile, water and formic acid. The flow rate was 1.0 ml/min and the total run time was 5.0 min. Important parameters such as sensitivity, linearity, matrix effect, reproducibility, stability, carry-over and recovery were investigated during the validation. The inter-day precision and accuracy of the quality control samples at low, medium and high concentration levels were <6.8% relative standard deviation (RSD) and 4.4% relative error (RE) for norethindrone, and 4.2% RSD and 5.9% RE for ethinyl estradiol, respectively. Chromatographic conditions were optimized to separate analytes of interest from the potential interference peaks, arising from the derivatization. This method could be used for pharmacokinetic and drug-drug interaction studies in human subjects.

Chromatography, High Pressure Liquid↗
PubMed1986

Factors responsible for the formation of different N-alkylated porphyrins in rat liver microsomal systems exposed to norethindrone. The role of 3 alpha-hydroxysteroid dehydrogenase.

Incubation of rat liver microsomes with norethindrone and a NADPH-generating system leads to the formation of one N-alkylated porphyrin (green pigment, GP1). Administration of this steroid to male rats in vivo results in the formation of three more-polar green pigments (GP2, 3 and 4). A cytosolic protein (green-pigment converting protein) has been purified from rat liver that, when added to liver microsomal mixtures containing norethindrone (0.03 mM) and a NADPH-generating system, results in the formation of all four green pigments (GP1, 2, 3 and 4). Field-desorption mass spectrometry of the purified green pigments gave protonated molecules, [M + H]+, at m/z 905 for GP1, m/z 909 for GP2, m/z 925 for GP3 and 4. The Mr of the purified cytosolic protein on SDS/polyacrylamide-gel electrophoresis or gel filtration was 37000. Polyacrylamide-gel isoelectric focusing gave a pI value of 5.9. Antibodies raised in rabbits against this protein, after preincubation with rat liver cytosol, subsequently prevented the formation of the more-polar norethindrone-induced green pigments (GP2, 3 and 4). The purified protein in the presence of either NADH or NADPH catalysed the reduction of delta 4-ring-reduced norethindrone, 5 alpha-oestran-17 alpha-ethynyl-17 beta-ol-3-one and, with the appropriate cofactor, the oxidation and reduction of steroids lacking the ethynyl function, e.g. androsterone or dihydrotestosterone. Indomethacin inhibited the reduction of dihydrotestosterone by this protein with an I50 (concn. causing 50% inhibition) value of 4.9 microM. From its physical and enzymic properties it is concluded that green-pigment converting protein is the same as 3 alpha-hydroxysteroid dehydrogenase (EC 1.1.1.50).

3-Hydroxysteroid Dehydrogenases↗
PubMed1983

Effects of chronic mestranol and (or)norethindrone treatment on ethanol-associated decreases in hepatic benzo[a]pyrene hydroxylase activity and increases in central vein fat accumulation in the female Wistar rat.

Female Wistar rats were fed a liquid diet, Sustacal, which contained ethanol (40% of calories) or isocaloric sucrose. Mestranol and norethindrone in pharmacological doses were also administered via this diet. Hepatic microsomal benzo[a]pyrene (BP) hydroxylase, epoxide hydrase, aniline hydroxylase, and aminopyrine-N-demethylase activities were measured after 3 and 6 months treatment. In addition, hepatic histology and electron microscopic studies were carried out in an attempt to monitor ethanol-associated fat accumulation in the central vein region. Mestranol or norethindrone alone for 3 months produced an elevation of BP hydroxylase activity which was no longer present after 6 months treatment. When compared with the 3-month time period, BP hydroxylase activity was significantly decreased in livers of animals which had ingested ethanol (group 10 vs. group 2), ethanol plus mestranol (group 12 vs. group 4), and ethanol plus norethindrone (group 14 vs. group 6) for 6 months. However, in the steroid-treated groups, the ethanol associated decreases were not as large as that seen without ethanol over the 3-month time period (group 11 vs. group 3; group 13 vs. group 5). No decrease was observed in the combined steroid plus ethanol-treated groups. Ethanol treatment for 6 months increased hepatic epoxide hydrase activity in both the nonsteroid and mestranol-treated group. Aniline hydroxylase was increased by ethanol in the combined steroid-treated animals. Otherwise there were no significant changes in the enzyme activities measured. Hepatic histology studies carried out on the 6-month ethanol-treated animals provided evidence of fat accumulation in the central vein region of the liver lobule, as expected. However, the steroid- plus ethanol-treated groups exhibited less apparent fat accumulation in the central vein region. These data do not support the hypothesis that mestranol and (or) norethindrone will accentuate the inhibition of liver BP hydroxylase or the central vein fat accumulation produced by chronic ethanol ingestion in the female rat.

Animals↗
PubMed1998

Effects of rifabutin and rifampicin on the pharmacokinetics of ethinylestradiol and norethindrone.

This open-label, randomized, three-way crossover study of 28 healthy premenopausal women was conducted to compare the impact of concomitant rifabutin and rifampicin on the safety, pharmacokinetics, and pharmacodynamics of the oral contraceptives ethinylestradiol and norethindrone (Ortho-Novum 1/35; Ortho Pharmaceutical, Raritan, NJ). Each participant received oral contraceptives daily for 21 days for the first control cycle, then was randomized to one of two sequences to receive oral contraceptives with concomitant rifampicin and rifabutin at equal doses of 300 mg/day for 10 days. Ethinylestradiol, norethindrone, follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone, rifampicin, and rifabutin (and metabolite) were measured in plasma over the same time frames in all three cycles. Safety was assessed from before the beginning to the end of each cycle. Twenty-two subjects completed all three cycles. Compared with the control cycle, rifabutin and rifampicin significantly altered the disposition of the oral contraceptive. Area under the concentration-time curve from 0 to 24 hours (AUC0-24) and maximum plasma concentration (Cmax) of ethinylestradiol decreased by 64% and 42%, respectively, after coadministration with rifampicin and by 35% and 20%, respectively, after coadministration with rifabutin. The AUC0-24 of norethindrone decreased by 60% and 20% after coadministration with rifampicin and rifabutin, respectively. Unlike progesterone levels, FSH and LH levels increased during coadministration with rifampicin and rifabutin. The incidence of spotting was significantly higher after coadministration with rifampicin (36.4%) and rifabutin (21.7%) than during the control cycle (3.7%). Although both rifampicin and rifabutin affected the pharmacokinetics of ethinylestradiol and norethindrone, the magnitude of this effect was more pronounced with rifampicin. Likewise, the fact that the highest incidence of spotting occurred with rifampicin was consistent with higher metabolic induction by rifampicin. Despite the fact that there was no change in progesterone levels, it is recommended that patients be advised to use additional contraceptive methods while receiving rifabutin or rifampicin with oral contraceptives to prevent inadvertent pregnancy.

Adolescent↗
PubMed1992

Reduction of vasomotor symptoms and bone mineral density loss with combined norethindrone and long-acting gonadotropin-releasing hormone agonist therapy of symptomatic endometriosis: a prospective randomized trial.

The hypoestrogenic state induced by gonadotropin-releasing hormone agonists (GnRHa) has been shown to suppress symptomatic endometriosis effectively but to elicit vasomotor symptoms and loss of bone mineral density. The role of norethindrone as a supplement to GnRHa in eliminating such side effects was assessed by enrolling 20 patients with symptomatic endometriosis diagnosed laparoscopically in a randomized, prospective, double-blinded trial. All patients received the long-acting GnRHa leuprolide acetate 3.75 mg im every 4 weeks for 24 weeks. Ten patients self-administered norethindrone 5 then 10 mg by mouth daily, whereas the remainder self-administered placebo tablets. Results of this study showed that combination therapy was as effective as GnRHa alone in significantly reducing circulating gonadotropin and estrogen levels (P less than 0.01), extent of visible endometriotic implants (P less than 0.01), and painful symptoms (P less than 0.01). Marked vasomotor and vaginal symptoms experienced by patients given GnRHa alone were minimized in those receiving GnRHa with norethindrone. Lumbar spine bone mineral density loss, measured by dual energy x-ray absorptiometry, was significantly reduced and more completely reversed in patients receiving combination therapy (P less than 0.05). A reversible decrease in high density lipoprotein-cholesterol and increase in low density lipoprotein:high density lipoprotein ratio was noted only in the patients receiving combination therapy, but not in those receiving GnRHa only. The addition of norethindrone to GnRHa is an effective means of treating symptomatic endometriosis while ameliorating side effects induced by GnRHa alone.

Bone Density↗
PubMedDate not supplied

Reference period analysis of vaginal bleeding with triphasic oral contraceptive agents containing norethindrone or levonorgestrel: a comparison study.

The World Health Organization recommends the use of fixed reference periods for quantification of the incidence and severity of vaginal bleeding when patients use various forms of contraception. Ninety- and 110-day reference periods were used in the analysis of data from daily menstrual diaries kept by 72 healthy women in a one-year study of oral contraceptive agents containing ethinyl estradiol and either norethindrone or levonorgestrel. Analysis of bleeding patterns reported during both 90-day and 110-day periods revealed fewer days of bleeding and/or spotting overall with norethindrone than with levonorgestrel (e.g., a mean of 16.06 vs. 19.55 days, respectively, over the first 90-day period; P = .013) and significantly shorter bleeding and/or spotting episodes with the norethindrone preparation. This trend persisted when data were adjusted for a day-1 pill start. Using either method of analysis, duration of bleeding episodes was shorter among subjects taking norethindrone than levonorgestrel. Pills were missed in both study groups, but more women in the LNG/EE group missed from 1 to 3 pills in at least one cycle (31 vs. 21 in the NET/EE group). The between-group difference in bleeding events may be due to intrinsic hormonal differences in regimens or to the greater number of pills missed among levonorgestrel users.

Adult↗
PubMed1991

Norethindrone scatters silver-stained nucleolar organizer regions of Ishikawa cells.

We investigated the effects of sex steroids on silver-stained nucleolar organizer regions (Ag-NORs) and DNA/RNA kinetics in Ishikawa cells. Norethindrone and its isomer norethynodrel exclusively caused Ag-NORs to scatter in the nuclear matrix, from the nucleolus. No such effect occurred with the other sex steroids tested, including progestational, androgenic, and estrogenic compounds. Nuclear argyrophilic substances induced by norethindrone, as well as nucleolar ones, were neither DNA nor RNA but protein. Electron microscopy showed that norethindrone caused nucleolar segregation, in which the fibrillar components disappeared, and it produced islets, consisting of dense fibrillar materials, in the nucleoplasm. Ag-NORs observed on the fibrillar components in control nucleoli were translocated onto the dense fibrillar materials in the nucleoplasm. Although scattering was preferentially found in the cells synthesizing DNA, the scintillation assay of DNA/RNA kinetics suggested that scattering was related to the inhibition of RNA synthesis. These results imply that norethindrone preferentially interacts with intranucleolar DNA when its duplication is occurring and then interferes with rRNA synthesis. Scattering of Ag-NORs might not be caused by the hormonal activity of these agents but by a pharmacological effect derived from their molecular structures.

Cell Line↗
PubMed1987

Treatment of postmenopausal hyperparathyroidism with norethindrone. Effects on biochemistry and forearm mineral density.

The effects of norethindrone (5 mg daily) on biochemical variables and forearm mineral density were assessed in 20 postmenopausal women with mild primary hyperparathyroidism. Norethindrone produced a significant fall in plasma calcium levels and the fasting urinary calcium-creatinine and hydroxyproline-creatinine ratios after three months of treatment. There was no change in the plasma parathyroid hormone concentrations. The forearm mineral density before treatment was low in 16 of the 20 patients and there was a significant increase in forearm mineral density after norethindrone treatment. No side effects were reported. We conclude that norethindrone is an effective treatment for mild hyperparathyroidism in postmenopausal women.

Aged↗
PubMed1979

The effect of lynestrenol and norethindrone on the carbohydrate and lipid metabolism in subjects with gestational diabetes.

The aim of this study was to investigate the effect of two different low-dose progestogens--norethindrone 0.3 mg per day and lynestrenol 0.5 mg per day--on carbohydrate and lipid metabolism in women who have had gestational diabetes. Fifteen patients were treated with norethindrone and 17 with lynestrenol, over a period of one year. The control group consisted of 13 women using an IUD. In both treatment groups all the women had normal OGTT curves during the use of norethindrone or lynestrenol. A very slight deterioration in the glucose tolerance was observed in the norethindrone group. There was no deterioration in the glucose tolerance in the lynestrenol and the IUD groups. We could not find any significant changes in mean fasting plasma cholesterol and triglyceride values.

Adult↗
PubMed1978

First-pass effect of norethindrone in rabbits and rats.

The influence of the route of administration on the pharmacokinetics of the synthetic progestogen norethindrone was studied in the rabbit and rat. In the rabbit, the area under the curve (AUC) after oral administration was 54% of that after i.v. administration. In the rat, the AUC after administration into the hepatic portal vein was 32% of AUCi.v.; after oral administration the AUCoral was 13.7% of AUCi.v. and 57.6% of AUCportal. Therefore, in both the rabbit and rat norethindrone is subject to a first-pass effect. Using the technique of constant withdrawal of blood from the hepatic portal vein after drug administration into the gastrointestinal tract, it was shown the norethindrone is metabolized in the gut wall. Hence, in the rat at least, there are both intestinal and hepatic components of the overall first-pass effect. In addition, increasing the time of intraportal injection from 15 sec to 2 min (thereby reducing the rate of drug delivery to the liver) resulted in the AUC being reduced by 40%. Dose-dependent kinetics were observed with doses of norethindrone greater than 500 microgram/kg.

Administration, Oral↗