(14)C-Norgestrel was administered to seven human subjects and 43% of dose was excreted in the urine within 5 days ... Enzymic hydrolysis released only 32% of the urinary radioactivity and a further 25% was excreted as sulphate conjugates. The metabolites excreted in the urine were much less polar than those following the administration of the related compounds, norethisterone or lynestrenol. The 3alphaOH,5beta and 3betaOH,5beta isomers of the tetrahydronorgestrel (13beta-ethyl-17alpha-ethynyl-5 beta-gonane-3alpha,17beta-diol) were isolated from urine and identified by mass spectrometry and thin-layer and gas-liquid chromatography. Plasma radioactivity decreased more rapidly than after the administration of norethisterone and lynestrenol. About 2% of the administered dose was converted to acidic compounds. There was no apparent difference in the rate of excretion of radioactivity or in the metabolites after either oral or intravenous administration of norgestrel.
The comparative metabolism of dl-, d-, and l-norgestrel was investigated in African Green Monkeys (Cercopithecus aethiops). Total (14)C excretion in urine after a single oral dose of (14)C-dl-norgestrel (1 mg/kg) was significantly higher (51.4 +/- 5.0%) than that observed after administration of the d-enantiomer (37.5 +/- 5.4%) but not the l-enantiomer (44.2 +/- 8.9%). In all cases, the major part of the urinary radioactivity was present in a free fraction (48-62%), while an additional 13-27% was released by beta-glucuronidase preparations. No sulfate conjugates were detected. At least one major (16beta-hydroxylation) and one minor (16alpha-hydroxylation) metabolic pathway were stereoselective, i.e., they are operative with the I-but not the d-enantiomer. Three metabolites, 16beta-hydroxynorgestrel, 16alpha-hydroxynorgestrel, and 16-hydroxytetrahydronorgestrel (believed to be 16beta) were only detected in urine samples obtained from (14)C-dland -l-norgestrel-dosed animals. Following (14)C-d-norgestrel administration, 3alpha, 5beta-tetrahydronorgestrel was found to be the major urinary metabolite. These observations are compared with those reported earlier on the urinary metabolites of dl-norgestrel in women.
The in vitro metabolism of stereo-isomers (d, l and the racemic mixture dl) of norgestrel by a microsomal fraction from rabbit liver was investigated. The metabolism of the biologically active l-norgestrel was more rapid than that of d-norgestrel (sic.) which is biologically inactive. This was mainly due to the more ready conversion of l-norgestrel to ring-A reduced metabolites. There was no difference between the two isomers in respect of the amount undergoing hydroxylation; about 40% of each isomer was converted to hydroxylated metabolites after 30 min incubation. However, there were differences between the isomers, l-norgestrel being converted mainly to the 16beta-hydroxysteroid and d-norgestrel to the 16alpha-hydroxysteroid. Similar amounts of both isomers were hydroxylated at C-6. The metabolism of the racemic mixture was intermediate between that of the d and l isomers.
The rates of metabolism of synthetic gestagens derived from 19-nortestosterone by rabbit liver tissue in vitro were compared. Over a period of 1 hr norethisterone was metabolized as rapidly as 19-nortestosterone whereas d-norgestrel and lynestrenol were metabolized at a slightly lower rate. Less than 5% of l-norgestrel was metabolized. In all cases the reaction product was the tetrahydrosteroid. Lynestrenol was metabolised through norethisterone. Skeletal muscle, lung and small intestine also metabolized norethisterone and d-norgestrel but at a slower rate than liver tissue. Small amounts of norethisterone were metabolized by adipose tissue but heart and spleen were inactive. Lynestrenol and l-norgestrel were not metabolized by any of the extra-hepatic tissues studied.
In vitro studies were conducted on the metabolism of 3 steroids used in OCs (oral contraceptives) by small pieces of human jejunal mucosa. This was done because the gastrointestinal mucosa of humans is known to metabolize a number of drugs. Almost 40% of the ethinyl estradiol, 9.8% of the levonorgestrel, and 7% of the mestranol were metabolized after incubation. All these metabolic responses were significantly different from those in the control groups. Results of the study show that the metabolism of the ethinyl estradiol was related to the weight of the tissue used. These results are consistent with the known marked 1st pass effect of ethinyl estradiol. Norgestrel, known to have little or no 1st pass effect, did not show a high rate of gut metabolism. Under the experimental conditions employed, no Phase 1 metabolism of either ethinyl estradiol or levonorgestrel was apparent.
The metabolism of estrogens and progestagens may be increased by concomitant use of substances known to induce drug-metabolising enzymes, specifically cytochrome P450 enzymes, such as anticonvulsants (eg phenobarbital, phenytoin, carbamazepine), and anti-infectives (eg rifampicin, rifabutin, nevirapine, efavirenz).
Phenytoin and rifampin increase the serum concentrations of sex hormone-binding globulin (SHBG); this significantly decreases the serum concentration of free drug for some progestins, which is a special concern in patients using progestins for contraception. /Progestins/
Drug interaction data are not available for rifabutin, but because its structure is similar to that of rifampin, similar precautions with its use with progestins may be warranted. ... /Progestins/
来源:Hazardous Substances Data Bank (HSDB)
吸收、分配和排泄
左炔诺孕酮从胃肠道吸收，由肝脏代谢，并以葡萄糖醛酸和硫酸盐结合物的形式通过尿液和粪便排出体外。
Norgestrel is absorbed from the gastrointestinal tract, metabolised by the liver and excreted in the urine and faeces as glucuronide and sulphate conjugates.
(14)C-Norgestrel was administered to seven human subjects and 43% of dose was excreted in the urine within 5 days; the biological half-life of the radioactivity was 24 hr. Enzymic hydrolysis released only 32% of the urinary radioactivity and a further 25% was excreted as sulphate conjugates. The metabolites excreted in the urine were much less polar than those following the administration of the related compounds, norethisterone or lynestrenol. The 3alphaOH,5beta and 3betaOH,5beta isomers of the tetrahydronorgestrel (13beta-ethyl-17alpha-ethynyl-5 beta-gonane-3alpha,17beta-diol) were isolated from urine and identified by mass spectrometry and thin-layer and gas-liquid chromatography. Plasma radioactivity decreased more rapidly than after the administration of norethisterone and lynestrenol. About 2% of the administered dose was converted to acidic compounds. There was no apparent difference in the rate of excretion of radioactivity or in the metabolites after either oral or intravenous administration of norgestrel.
The binding of different synthetic steroids, used in hormonal contraception, to Sex Hormone Binding Globulin (SHBG) was studied by measuring their ability to displace tritiated testosterone from SHBG in a competitive protein binding system. Only 19-nortestosterone derivates had any significant ability to displace testosterone from SHBG, d-norgestrel (d-Ng) being the strongest displacer. Increasing the SHBG levels in women with previous constant plasma d-Ng levels increased these levels two- to sixfold. It is concluded that SHBG is the main carrier protein for d-Ng. The strong testosterone displacing activity of d-Ng might also explain androgenic side effects observed with d-Ng containig oral contraceptives.
