Influence of repeated oral doses of ethinyloestradiol on the metabolic disposition of [13C2]-ethinyloestradiol in young women.

OBJECTIVE: To examine the influence of daily oral administration of ethinyloestradiol on the total clearance of 13C-labeled ethinyloestradiol in women. METHODS: 19, healthy, young women received a single IV dose of 0.06 mg 13C-ethinyloestradiol. Subsequently, they were treated with daily oral doses of 0.06 mg ethinyloestradiol for 8 days. On the last day of oral treatment, they received a further IV dose of 0.06 mg 13C-ethinyloestradiol. The pharmacokinetic parameters clearance, area under the serum level-time curve, terminal half-life, steady-state volume of distribution and mean residence time of 13C-ethinyloestradiol in each volunteer were evaluated after both IV doses, and the corresponding pairs of parameters were examined statistically for the significance of intraindividual differences. RESULTS: Following the first (second) intravenous administration, the mean area under the curve was 2.54 (2.67) ng.h.ml-1. The terminal half-life and mean residence time were 9.7 (9.6) h and 10.5 (10.1) h, respectively. The steady-state volume of distribution was 4.3 (3.9) 1.kg-1 and the clearance was 7.0 (6.6) ml.min-1.kg-1. No significant difference was observed in any of these parameters between the first and the second IV doses of 13C-EE2. CONCLUSIONS: Since the clearance in particular remained unchanged after repeated oral administration of ethinyloetradiol, the hypothesis that ethinyloestradiol can inhibit its own metabolism in vivo can be rejected.

Synthesis of a deuterated analogue and development of antibody/GC/MS for the determination of nocloprost in plasma.

An analytical method for the determination of the PGE derivative nocloprost in plasma was developed combining the features of both radioimmunoassay and GC/MS. The antibody usually employed in nocloprost radioimmunoassay was coupled to Sepharose 4B and used as a stationary phase for the extraction of the drug. After appropriate derivatisation, nocloprost was determined by GC/MS in the negative ion-chemical ionisation mode. As an internal standard deuterated nocloprost was synthesized and added to the plasma samples before extraction. The extraction recovery was 94% and the limit of detection was 5 pg/ml. Intra- and interassay precision at 100 pg/ml was calculated as 3.3 and 4.0%, respectively.

Identification of 3 alpha-hydroxy-cyproterone acetate as a metabolite of cyproterone acetate in the bile of female rats and the potential of this and other already known or putative metabolites to form DNA adducts in vitro.

Cyproterone acetate (CPA) is a synthetic steroid hormone used in the therapy of prostate cancer in men and different forms of acne and hirsutism in women. CPA has been shown by 32P-postlabeling analysis to bind covalently to hepatic DNA of rats in vivo and in vitro. A prerequisite for DNA adduct formation of CPA is metabolic activation of the drug to a reactive intermediate. In the present study bile was collected from [3H]CPA-treated female rats and, following chromatographic separation of bile extracts, fractions of the eluate were examined for the presence of reactive metabolites which were able to form adducts with calf thymus DNA in vitro. The formation of adducts was detected by 32P-postlabeling analysis. One major metabolite of CPA present in the bile extracts was isolated and, following a thorough structural elucidation by mass spectrometry and 1H-NMR, this metabolite was identified as 3 alpha-hydroxy-cyproterone acetate (3 alpha-OH-CPA). This metabolite was able to form the same major adduct in vitro which has been observed before in CPA-treated rats in vivo and in rat hepatocytes in vitro. A number of already known or putative metabolites of CPA were available as authentic standards and these were also examined for their propensity to form adducts in vitro. A positive result was obtained for 3-O-acetyl-cyproterone acetate, which formed the same major adduct as 3 alpha-OH-CPA. However, the presence of this putative metabolite in rat bile could not be demonstrated. Besides 3 alpha-OH-CPA, additional reactive metabolites of CPA were present in the bile extracts, however, since these were only minor components, their chemical structures could not be elucidated.

Development, validation and practical use of a sensitive and specific radioimmunoassay for the determination of iloprost.

Iloprost is a potent, clinically effective PGI2-mimetic. Therapeutic plasma levels are in the low pg-range and currently analyses of biological samples are performed by GC/MS after antiserum-column extraction. Although this method exhibits high sensitivity and specificity it permits only limited numbers of samples to be analyzed owing to time-consuming work-up. The present report describes the development of a novel highly selective antiserum and its use for the RIA determination of iloprost in biological samples. An antiserum was raised against "iloprost-9-pentynyl"-BSA in rabbits. Iloprost-[3H]-methylester with a specific activity of 66.9 Ci/mmol was used as a tracer. RIA-analyses were carried out with 0.05-0.5 ml plasma adjusted to pH2 with 1 N HCl and extracted with 2.5 ml diethylether. Separation of antiserum bound and unbound iloprost was achieved by the charcoal method. Extraction recovery of iloprost was approximately 90% at pH less than or equal to 4. The detection limit of the novel assay was 1-2 pg/tube corresponding to 5-10 pg/ml plasma (if 0.1-0.2 ml plasma was used). Coefficients of variations were 8% and 2% (within-day, n = 3) and 17% and 12% (day-to-day, n = 5) at 50 and 100 pg/ml. RIA- and GC/MS-levels of iloprost measured in human samples were similar (p less than 0.001). Cross-reactivity HPLC-chromatograms of plasma extracts did not reveal any peak apart from iloprost. The RIA-method exhibits both a similar specificity and detection limit to GC/MS and will be used for further analyses.