Metabolism of a new synthetic progestagen, Org 2969, in female volunteers. Pharmacokinetics after an oral dose

Randomized, Crossover and Single-Dose Bioquivalence Study of Two Oral Desogestrel Formulations (Film-Coated Tablets of 75 μg) in Healthy Female Volunteers

Despite the increase in the substitution of branded medicinal product with generic drugs, this is a controversial issue for some pharmacological groups (such as contraceptives).

The aim of the present clinical trial was to assess the bioequivalence and tolerability of two oral formulations of desogestrel.

Thirty-three healthy female volunteers participated in this randomized and two-way crossover study. During two separate experimental periods, with at least four weeks of washout period, women received a single oral dose of 75 μg of desogestrel from each of the formulations (test formulation and reference formulation). Desogestrel bioavailability was determined by the measurement of 3-ketodesogestrel plasma concentration.

Pharmacokinetic parameters were comparable and the 90% CI for the ratio of C_max (96.14–114.53%) and AUC_0–t (105.73–123.83%) values for the test and reference formulations fell within the established regulatory interval (80–125%). Both formulations were also comparable in terms of tolerability.

From the results of this study it can be concluded that test formulation (desogestrel 75 μg, Cyndea PHARMA S.L.) is bioequivalent to the reference formulation (Cerazet® 75 μg, Organon Española S.A.).

Contraception today

Modern contraceptive methods represent more than a technical advance: they are the instrument of a true social revolution-the "first reproductive revolution" in the history of humanity, an achievement of the second part of the 20th century, when modern, effective methods became available. Today a great diversity of techniques have been made available and-thanks to them, fertility rates have decreased from 5.1 in 1950 to 3.7 in 1990. As a consequence, the growth of human population that had more than tripled, from 1.8 to more than 6 billion in just one century, is today being brought under control. At the turn of the millennium, all over the world, more than 600 million married women are using contraception, with nearly 500 million in developing countries. Among married women, contraceptive use rose in all but two developing countries surveyed more than once since 1990. Among unmarried, sexually active women, it grew in 21 of 25 countries recently surveyed. Hormonal contraception, the best known method, first made available as a daily pill, can today be administered through seven different routes: intramuscularly, intranasally, intrauterus, intravaginally, orally, subcutaneously, and transdermally. In the field of oral contraception, new strategies include further dose reduction, the synthesis of new active molecules, and new administration schedules. A new minipill (progestin-only preparation) containing desogestrel has been recently marketed in a number of countries and is capable of consistently inhibiting ovulation in most women. New contraceptive rings to be inserted in the vagina offer a novel approach by providing a sustained release of steroids and low failure rates. The transdermal route for delivering contraceptive steroids is now established via a contraceptive patch, a spray, or a gel. The intramuscular route has also seen new products with the marketing of improved monthly injectable preparations containing an estrogen and a progestin. After the first device capable of delivering progesterone directly into the uterus was withdrawn, a new system releasing locally 20 microg evonorgestrel is today marketed in a majority of countries with excellent contraceptive and therapeutic performance. Finally, several subcutaneously implanted systems have been developed: contraceptive "rods," where the polymeric matrix is mixed with the steroid and "capsules" made of a hollow polymer tube filled with free steroid crystals. New advances have also been made in nonhormonal intrauterine contraception with the development of "frameless" devices. The HIV/AIDS pandemic forced policy makers to look for ways to protect young people from sexually transmitted diseases as well as from untimely pregnancies. This led to the development of the so-called dual protection method, involving the use of a physical barrier (condom) as well as that of a second, highly effective contraceptive method. More complex is the situation with antifertility vaccines, still at a preliminary stage of development and unlikely to be in widespread use for years to come. Last, but not least, work is in progress to provide effective emergency contraception after an unprotected intercourse. Very promising in this area is the use of selective progesterone receptor modulators (antiprogestins).

The role of CYP2C and CYP3A in the disposition of 3-keto-desogestrel after administration of desogestrel

AIMS

Our objective was to study in vivo the role of CYP2C and CYP3A4 in the disposition of 3-keto-desogestrel after administration of desogestrel, by using the selective inhibitors fluconazole (CYP2C) and itraconazole (CYP3A4).

METHODS

This study had a three-way crossover design and included 12 healthy females, the data from 11 of whom were analyzed. In the first (control) phase all subjects received a single 150 microg oral dose of desogestrel alone. In the second and third phases subjects received a 4 day pretreatment with either 200 mg fluconazole or 200 mg itraconazole once daily in a randomized balanced order. Desogestrel was given 1 h after the last dose of the CYP inhibitor. Plasma 3-keto-desogestrel concentrations were determined for up to 72 h post dose.

RESULTS

Pretreatment with itraconazole for 4 days significantly increased the area under the plasma concentration-time curve (AUC) of 3-keto-desogestrel by 72.4% (95% confidence interval on the difference 12%, 133%; P = 0.024) compared with the control phase, whereas fluconazole pretreatment had no significant effect (95% CI on the difference -42%, 34%). Neither enzyme inhibitor affected significantly the maximum concentration (95% CI on the difference 14%, 124% for itraconazole and -23%, 40% for fluconazole) or elimination half-life (95% CI on the difference -42%, 120% for itraconazole and -24%, 61% for fluconazole) of 3-keto-desogestrel.

CONCLUSIONS

According to the present study, the biotransformation of desogestrel to 3-keto-desogestrel did not appear to be mediated by CYP2C9 and CYP2C19 as suggested earlier. However, the further metabolism of 3-keto-desogestrel seems to be catalyzed by CYP3A4.

Reduction of aromatic steroidal A rings by lithium in ethyl amine

The reduction of 3-methoxy-estra-1,3,5(10)-trien-17beta-ol (6) and 13-ethyl-3-ethoxy-gona-1,3,5(10)-triene-11alpha,17beta-diol (2) by lithium in ethyl amine in the absence of a proton source is described. Both reductions, contrary to the reports of previous investigators, which indicated the 4-ene to be the main reaction product, gave a complex mixture of products. In the case of the reduction of 2, which is an intermediate in the synthesis of the progestagen desogestrel (1), we obtained the expected known 13-ethyl-gona-4-ene-11alpha,17beta-diol (4) in small amounts and three new steroidal monoenes, 13-ethyl-gona-5(10)-ene-11alpha,17beta-diol (11), 13-ethyl-gona-5(6)-ene-11alpha,17beta-diol (12), and 13-ethyl-gona-1(10)-ene-11alpha,17beta-diol (13). These compounds were characterized as the 11,17-diacetates with the 5(10)-ene 11 being the major compound.

Excretion and metabolism of desogestrel in healthy postmenopausal women

The metabolism of desogestrel (13-ethyl-11-methylene-18,19-dinor-17alpha-pregn-4-en-20-yn-17-ol), a progestagen used in oral contraceptives and hormone replacement therapy, was studied in vivo after a single oral administration of 150 microg [14C]-labeled desogestrel and 30 microg ethinylestradiol under steady state conditions to healthy postmenopausal women. After this oral administration, desogestrel was extensively metabolized. The dosed radioactivity was predominantly ( approximately 60%) excreted via urine, while about 35% was excreted via the feces. Desogestrel was metabolized mainly at the C3-, C5-, C6- and C13-CH(2)CH(3) positions. At the C3-position, the 3-keto moiety was found and in addition, 3beta-hydroxy and 3alpha-hydroxy groups were observed in combination with a reduced Delta(4)-double bond (5alpha-H). Hydroxy groups were introduced at the C6- (6beta-OH), the C13-ethyl (C13-CH(2)CH(2)OH) and possibly the C15- (15alpha-OH) position of desogestrel. Conjugation of the 3alpha-hydroxy moiety with sulfonic acid and conjugation with glucuronic acid were also major metabolic routes found for desogestrel in postmenopausal women. The 3-keto metabolite of desogestrel (the biologically active metabolite) was the major compound present in plasma at least up to 24 h after administration of the radioactive dose. Species comparison of the metabolic routes of desogestrel after oral administration indicates that in rats and dogs desogestrel is also mainly metabolized at the C3-position, similar to what is now found for postmenopausal women. Most other metabolic routes of desogestrel were found to differ between species. Finally, major metabolic routes found in the present study in postmenopausal women are in line with outcome of previous in vitro metabolism studies with human liver tissue (microsomes and postmitochondrial liver fractions) and intestinal mucosa.

Bioavailability and bioequivalence of etonogestrel from two oral formulations of desogestrel: Cerazette and Liseta

In a three-period cross-over study with 24 healthy young females (study part 1), the bioavailability of etonogestrel (3-ketodesogestrel) was determined after a single oral dose of two Cerazette tablets (each containing 75 microg desogestrel), one Liseta tablet (containing 150 microg desogestrel and 1.5 mg 17beta-estradiol), and an intravenous dose of 150 microg etonogestrel. Etonogestrel serum levels from 23 subjects could be analysed by radio-immunoassay. The geometric mean bioavailability of etonogestrel from Cerazette and Liseta tablets was 0.79 and 0.82, with 95% confidence intervals of 0.73-0.86 and 0.76-0.88, respectively. Also, the oral formulations were found to be bioequivalent. Subsequently, the single-dose pharmacokinetic parameters of etonogestrel from Cerazette tablets were compared with those after multiple dosing of one Cerazette tablet once daily for 7 days, in a subgroup of 12 subjects (study part 2). A steady state was observed from the fourth day of daily dosing onwards, with time-invariant parameters except for a 14% lower dose-normalised AUC. The least-squares geometric means of the elimination half-life of etonogestrel were approximately 30 h for the three single-dose treatments in study part 1, as well as for the single- and multiple-dose treatments of Cerazette in study part 2, without differences between groups.

Metabolism of gestodene in human liver cytosol and microsomes in vitro

The metabolism of the progestogen gestodene has been studied in human liver cytosol and microsomal incubations. Extraction with diethyl ether was followed by radiometric HPLC analysis. Metabolites were identified by co-chromatography with authentic standards and mass spectrometry (electron impact and chemical ionization). All the cytosolic incubations (n = 4 livers) produced dihydrogestodene as the major metabolite, with lesser amounts of a tetrahydro derivative. It was not possible to separate the 5 alpha- and 5 beta-isomers of dihydrogestodene on the chromatographic system used. Values of Km and V(max) for the delta 4 reductase were determined. Androstenedione (Ki = 2.85 +/- 1.5 microM; n = 4) and cortisol (ki = 24.1 +/- 8.9 microM; n = 4) both inhibited the delta 4-reductase. In contrast desogestrel showed virtually no inhibition at concentrations up to 200 microM. The major microsomal metabolite of gestodene was a hydroxylated derivative although mass spectral analysis was unable to determine the position of insertion of the hydroxyl moiety. The hydroxylation of gestodene (1 microM) was markedly inhibited by ketoconazole (IC50 < 0.1 microM), and also by cyclosporin. This suggests that the cytochrome P450 isozyme CYP3A4 is important in gestodene metabolism. Theophylline and tolbutamide (substrates of CYPIA and CYP2C, respectively) did not affect gestodene metabolism at concentrations up to 100 microM. In conclusion, the major biotransformation of gestodene (A-ring reduction) occurs in the cytosolic fraction of human liver. Microsomal hydroxylation appears to be catalysed by CYP3A4.

Metabolism of the oral contraceptive steroids ethynylestradiol, norgestimate and 3-ketodesogestrel by a human endometrial cancer cell line (HEC-1A) and endometrial tissue in vitro

Human endometrial cancer cells and human endometrial tissue have been extensively used to study steroid hormone action and metabolism. The natural estrogens estradial (E2) and estrone (E1) are known to be metabolized by both cells and tissue with the interconversion of the two steroids and the formation of sulphate conjugates. The aim of the present work was to see if the commonly used oral contraceptive steroids ethynylestradiol (EE2), norgestimate (Ngmate) and 3-ketodesogestrel (3-KDG) were metabolized by a human endometrial cancer cell line (HEC-1A) and human endometrial tissue in vitro. Metabolites were analysed by on-line radiometric HPLC. Endometrial tissue was obtained from women undergoing dilation and curettage or hysterectomy operations. In preliminary studies with endogenous estrogens, HEC-1A cells were able to interconvert E1 and E2; the equilibrium favouring the formation of E2. Normal endometrial tissue extensively converted E2 to E1, tumour tissue appeared to catalyse this reaction much less avidly. In addition sulphate conjugates were formed by normal tissue from some patients. Cell line and endometrial tissue was able to hydrolyse estrone 3-sulphate. With EE2 as substrate there was no evidence of phase I metabolism by cell line or tissue. However, conversion to the presumed 3-sulphate conjugate was observed following incubation with normal tissue from some women. Deacetylation of the progestogen Ngmate to norgestrel oxime (NgOx) was complete within 24 h. There was also some loss of the oxime moiety to give norgestrel (Ng) following incubation with HEC-1A cells. Metabolism of Ngmate was also complete within 24 h following incubation with endometrial tissue. There were both qualitative and quantitative differences in metabolite formation between tissue obtained from different women. In contrast, 3-KDG was relatively resistant to metabolism by cell line and tissue. The major metabolite formed by HEC-1A cells accounted for only 3.3 +/- 0.4% of total added radiolabelled steroid and co-chromatographed with 3 alpha-hydroxydesogestrel. Smaller amounts of other radiometabolites were formed. No phase I metabolites of 3-KDG were formed by normal endometrial tissue, however small amounts of radiometabolites appeared to be formed by malignant tissue. These studies have provided evidence to suggest that the oral contraceptives EE2, Ngmate and 3-KDG are metabolized in the human endometrium. Knowledge of the metabolism of these in target tissues such as the endometrium may be pertinent considering the possibility that metabolites may exert specific effects.

Receptor binding of norgestimate--a new orally active synthetic progestational compound

Binding of the new progestagen, norgestimate (D-(-)-13 beta-ethyl-17 beta-acetoxy-17-ethinyl-4-gonen-3-one-oxime), and its metabolites (levonorgestrel-3-oxime, levonorgestrel-17-acetate and levonorgestrel) to the progesterone receptor was investigated by competition experiments using cytosol from human myometrial tissue. Compared to R5020, a highly potent synthetic ligand for progesterone receptor analysis, the L-isomer of norgestimate shows only a weak specific behaviour with regard to binding to the progesterone receptor from uterine cytosol with an RBA value of 0.8%, whereas the D-isomer of this compound is characterized by a lack of binding activity to the progesterone receptor. Levonorgestrel-3-oxime, one of the possible metabolites of norgestimate, binds to the progesterone receptor with an RBA value of 8%, whereas levonorgestrel-17-acetate, the other possible metabolite of norgestimate, binds with a binding affinity of 110% which is in the same order of magnitude as levonorgestrel itself. The competition experiments suggest that norgestimate is a prodrug and that the metabolites, levonorgestrel and levonorgestrel-17-acetate, which actively bind to the progesterone receptor, must first be formed from the parent drug via metabolic processes in vivo. These are the actual biologically active compounds which are responsible for the gestagenic potency.

Binding of oral contraceptive progestogens to serum proteins and cytoplasmic receptor

Some progesterones widely used in oral contraceptives are characterized at the level of high-affinity receptor binding as well as binding to sex hormone-binding globulin and corticosteroid-binding globulin. With regard to binding to sex hormone-binding globulin, gestodene, levonorgestrel, and to a lesser extent 3-ketodesogestrel (which is only formed from the prodrug desogestrel in the body), show a behavior that is manifested in the relatively high affinity to sex hormone-binding globulin, whereas desogestrel and norgestimate do not display any measurable affinity for this specific steroid-binding serum protein. Furthermore, levonorgestrel and gestodene dissociate very much more slowly from the binding sites of sex hormone-binding globulin than 3-ketodesogestrel. A natural affinity of all these synthetic progestogens tested for corticosteroid-binding globulin could not be established. Gestodene, levonorgestrel, and 3-ketodesogestrel bind to the progesterone, glucocorticoid, and androgen receptor with high affinity, apart from slight differences, whereas estrogen receptor affinity could not be demonstrated in any of the progestogens investigated. In relation to aldosterone, the relative binding affinity values of gestodene, levonorgestrel, and the natural progestogen progesterone are relatively high, whereas 3-ketodesogestrel does not display any measurable affinity for this receptor species.

Serum pharmacokinetics of orally administered desogestrel and binding of contraceptive progestogens to sex hormone-binding globulin

Serum levels of 3-ketodesogestrel and ethinyl estradiol were analyzed by radioimmunoassay in a balanced crossover study with two tablet formulations containing desogestrel (0.150 mg) and ethinyl estradiol (0.030 mg) in 25 women under steady-state conditions after 21 days of treatment. The pharmacokinetic properties of desogestrel were characterized by the following parameters: (1) maximum serum concentration, (2) time to maximum serum concentration, (3) total area under the serum concentration versus time curve, and (4) serum half-life of elimination. The interindividual variation in these parameters was comparable with that observed with other contraceptive combinations containing ethinyl estradiol and norethisterone, levonorgestrel, or gestodene. The serum distribution of contraceptive progestogens is known to be determined by their affinity to sex hormone-binding globulin and the concentration of sex hormone-binding globulin. We analyzed the structural features that determine binding to sex hormone-binding globulin. The 18-methyl group increased and the 11-methylene group weakened the binding to sex hormone-binding globulin. The double bond at C-15 reinforced the binding only when combined with an 18-methyl group. Therefore, the binding of levonorgestrel (the 18-methyl derivative of norethisterone) and gestodene (the delta-15,18 methyl derivative of norethisterone) to sex hormone-binding globulin was much stronger than that of 3-keto-desogestrel and norethisterone.

Metabolism of levonorgestrel, norethindrone, and structurally related contraceptive steroids

There is limited information on the metabolism of levonorgestrel, norethindrone and structurally related contraceptive steroids. Both levonorgestrel and norethindrone undergo extensive reduction of the alpha, beta-unsaturated ketone in ring A. Levonorgestrel also undergoes hydroxylation at carbons 2 and 16. The metabolites of both compounds circulate predominantly as sulfates. In urine, levonorgestrel metabolites are found primarily in the glucuronide form, whereas norethindrone metabolites are present in approximately equal amounts as sulfates and glucuronides. Of the progestogens structurally related to norethindrone, norethindrone acetate, ethynodiol diacetate, norethindrone enanthate, and perhaps lynestrenol, undergo rapid hydrolysis and are converted to the parent compound and its metabolites. There is no convincing evidence that norethynodrel is converted to norethindrone. Of the progestogens structurally related to levonorgestrel, it appears that neither desogestrel nor gestodene are transformed to the parent compound. However, there is evidence that norgestimate can be, at least partly, converted to levonorgestrel. Further studies on the metabolism of these progestogens are required before we can understand their mechanism of action.

Single dose pharmacokinetics of gestodene in women after intravenous and oral administration

Six healthy female volunteers (age 25 - 39 years) received 75 micrograms gestodene intravenously followed by 3 oral administrations of 25, 75 and 125 micrograms gestodene together with 30 micrograms ethinylestradiol (EE2) in a cross-over design. Gestodene plasma levels were determined using a specific RIA. After intravenous administration, plasma gestodene concentrations decayed triphasically with mean half-lives of 0.16 h, 1.5 h and 10 hours. The area under the plasma level curve, the total plasma clearance and the volume of distribution (VZ) were as follows: AUC = 35 +/- 15 ng.h/ml, CL = 0.80 +/- 0.53 ml/min/kg, and VZ = 0.66 +/- 0.43 1/kg, respectively. After oral administration of all doses, maximum plasma levels of 1.0 (25 micrograms), 3.8 (75 micrograms) and 7.0 ng/ml (125 micrograms) were achieved between 1.4 and 1.9 hours after the intake. Post-maximum levels showed 2 disposition phases with half-lives of 1 and 12 - 14 hours. Absolute bioavailabilities were calculated as 87.5 +/- 17.5% (25 micrograms), 99.3 +/- 10.9% (75 micrograms) and 110.8 +/- 17.7% (125 micrograms) indicating that gestodene is completely absorbed and systemically available at all doses investigated.

Metabolism of the contraceptive steroid desogestrel by the intestinal mucosa

1. The intestinal mucosal metabolism of the progestogen oral contraceptive desogestrel (Dg) has been studied in vitro using the Ussing chamber technique. Histologically normal ileum or colon was obtained from eight patients undergoing various resections. The mucosal sheets were mounted between two perspex chambers. 2. Two hours after addition of [3H]-Dg (0.2 microCi; 100 ng) to the mucosal chamber, more than 90% of the steroid was present in that chamber. In studies with colon, metabolite analysis showed that 55.4 +/- 11.7% (mean +/- s.d.; n = 6) of drug present was Dg, 28.9 +/- 11.4% as unconjugated Phase I metabolites, 13.3 +/- 2.6% as sulphate conjugates and 2.5 +/- 1.5% as glucuronide conjugates. 3. By co-chromatography with authentic metabolites and mass spectrometry, it was shown that 3-keto desogestrel is formed in the mucosa. This is the active metabolite of desogestrel. A large peak of radioactivity did not co-chromatograph with any known metabolites and has been tentatively identified as ring hydroxylated products of 3-keto desogestrel. 4. The effect of the synthetic oestrogen ethinyloestradiol (EE2) on the metabolite profile of Dg was studied. In the presence of increasing concentrations of EE2 (100 ng, 1 and 10 micrograms), there was competition for sulphation such that the sulphate fraction decreased by 32, 49 and 48% respectively. 5. The results of this study indicate substantial first pass metabolism of desogestrel by the gut mucosa with evidence for the formation of the active metabolite. The extent of phase I metabolism is unusual.

Serum levels of 3-keto-desogestrel and SHBG during 12 cycles of treatment with 30 micrograms ethinylestradiol and 150 micrograms desogestrel

The serum concentrations of 3-keto-desogestrel (KDG) have been determined radioimmunologically in 11 female volunteers on Day 1, 10, and 21 of the 1st, 3rd, 6th, and 12th cycle of treatment with 30 micrograms ethinylestradiol and 150 micrograms desogestrel during the first 4 hours and 24 hours after intake. On the first day of each cycle the KDG levels were low, but increased thereafter until Day 21. Highest serum concentrations were measured on Day 21 of the 3rd and 6th cycle with peak levels between 1.5 and 6.2 ng/ml. Contrary to this, the KDG levels were significantly reduced during the 12th treatment cycle. The serum concentrations of SHBG rose significantly between Day 1 and Day 21 of each cycle reaching values which were 3-fold of those at the beginning of treatment. During the pill-free intervals, SHBG levels decreased but remained elevated as compared to controls. There was a significant correlation between the SHBG levels and the area under the KDG-concentration-versus-time curves (AUC) indicating a pronounced influence of the serum steroid-binding protein upon the pharmacokinetics of KDG. There were great interindividual differences in the KDG levels. The serum levels of the individual woman remain, however, in a relatively constant range throughout the treatment period of 12 months, possibly due to genetic factors.

Effect of a combination of ethinylestradiol and desogestrel in adolescents with oligomenorrhea and ovarian hyperandrogenism

Nine oligomenorrheic adolescent girls with a clinical and hormonal picture of ovarian hyperandrogenism were treated with a monophasic oral contraceptive (OC) containing 0.03 mg ethinylestradiol (EE) plus 0.150 mg desogestrel (DOG) for six months. The same treatment was administered in eight eumenorrheic adolescents. In both groups the treatment induced a decrease in LH, FSH, androstenedione (delta 4-A), testosterone (T) and dehydroepiandrosterone sulphate (DHEA-S) levels associated with a significant sex-hormone-binding globulin (SHBG) increase. In oligomenorrheic adolescents a marked decrease in both the total ovarian volume and the number of cystic follicles was observed. All parameters, except SHBG and ovarian volume in hyperandrogenic girls, returned to pre-treatment values 3 months after treatment. Subjective improvement of skin problems occurred in six of the nine oligomenorrheic girls. Although temporary, the EE + DOG formulation pill is effective in the treatment of ovarian hyperandrogenism in adolescents. It may also be useful for the prevention of the progressive transformation in the 'classical' and 'irreversible' micropolycystic ovary of adult age.

Plasma concentrations of 3-keto-desogestrel after oral administration of desogestrel and intravenous administration of 3-keto-desogestrel

The plasma concentrations of 3-keto-desogestrel have been measured by radioimmunoassay in a crossover study in nine healthy female volunteers given oral desogestrel (150 micrograms) and ethinyloestradiol (30 micrograms) and intravenous (i.v.) 3-keto-desogestrel (150 micrograms) and ethinyloestradiol (30 micrograms). Bioavailability ranged between 40.0 and 113% with a mean value ( +/- SD) of 76.1 +/- 22.5%. Only 3 subjects had a bioavailability of less than 70%. There was no significant difference in the elimination half life of 3-keto-desogestrel which was 12.6 +/- 4.1h following i.v. administration and 11.9 +/- 4.1h after oral administration of desogestrel.

Serum levels of 3-keto-desogestrel after oral administration of desogestrel and 3-keto-desogestrel

In a cross-over study with orally administered desogestrel (0.150 mg) plus ethinyloestradiol (0.030 mg) and 3-keto-desogestrel (0.150 mg) plus ethinyloestradiol (0.030 mg) in ten women under steady-state conditions, the serum levels of 3-keto-desogestrel were monitored by radioimmunoassay. No statistically significant differences between treatment groups were found with respect to the areas under the curve of the serum levels versus time (AUC), peak heights and peak times. The individual AUCs for 3-keto-desogestrel after dosing with desogestrel (plus EE) or 3-keto-desogestrel (plus EE) show a similar degree of variation. The biotransformation of desogestrel into 3-keto-desogestrel is rapid and appears not to be limited by the metabolic capacity of the normal liver.

A non-chromatographic radioimmunoassay for 3-oxo desogestrel

A non-chromatographic radioimmunoassay for 3-oxo desogestrel (13 beta-ethyl-17-hydroxy-11-methylene-18,19-dinor-pregn-4-en-20-yn-3- one), the biologically-active metabolite of desogestrel (13 beta-ethyl-11-methylene-18,19-dinor-pregn-4-en-20-yn-17-ol), has been developed to facilitate studies of the pharmacokinetics of this steroid. The method uses an antiserum raised against levonorgestrel (13 beta-ethyl-17-hydroxy-18,19-dinor-pregn-4-en-20-yn-3-one). None of the steroids tested which showed significant cross-reactions are believed to be present in plasma after ingestion of desogestrel; furthermore, dilutions of standards and unknowns gave parallel responses in the assay. Intra- and inter-assay coefficients of variation were 12.9 and 11.8% respectively. The sensitivity of the assay was approx 0.02 ng/ml. The peak concentrations of 3-oxo desogestrel after a 150 micrograms dose of desogestrel in three subjects were between 0.48-0.71 ng/ml, and in two subjects 3-oxo desogestrel was still detectable 24 h after dosing.