Bob Nieuweboer

Investigations of pharmacokinetics of ethinyloestradiol to specific consideration of a possible first-pass effect in women

Ethinyloestradiol-3H was given intravenously and orally to four and three women, respectively, in a dose of 60 micrograms and 3 mg. To another three female volunteers, 100 micrograms of ethinyloestradiol was administered by both routes in succession. Drug concentration in plasma and total radioactivity in plasma, urine and faeces were measured for different periods of time. Intraindividual comparison of the area under the drug level vs. time curve after intravenous and oral administration of 100 micrograms showed that ethinyloestradiol is subject to an about 60% first-pass effect in women. The time course of ethinyloestradiol concentration in plasma can be described by a 3-compartment model after intravenous injection and by a 2-compartment model after oral administration, because an early disposition phase with a half-life of about 15 minutes only becomes visible after i.v. injection. On an average, the terminal half-life of unchanged ethinyloestradiol level and total radioactivity was calculated to be about 1 day. However, a high variability was found with this parameter as well as with the rate and degree of elimination in urine.

Kinetics and biotransformation of lormetazepam

A specific and sensitive radioimmunoassay has been developed for a new benzodiazepine, lormetazepam. After intravenous injection, lormetazepam levels in plasma fell in three (α, β, γ) dispositional phases, two of them (α, β) mainly reflecting different distribution processes. The terminal (γ) phase correlated well with the rate of renal elimination of glucuronides. Oral doses were completely absorbed with widely varying absorption half‐lifes (t½s) amounting to an average of 0.67 ± 0.53 hr. Dose‐dependent maximum plasma levels were reached in about 2 hr. Lormetazepam undergoes first‐pass metabolism of about 20% of an oral dose. Total clearance was in the range of 200 ml/min. There was a trend toward slower terminal disposition phase in elderly subjects. In younger subjects, the terminal phase t½ was about 10 hr. Lormetazepam glucuronide peak plasma levels were reached by about 6 hr. Thereafter, the level fell in one (elimination) phase, with a t½ of 12 hr in young subjects and with a significantly (p < 0.05) different t½ of about 20 hr in the elderly. Renal clearance was calculated as about 30 to 40 ml and did not show an age‐dependent difference. Recovery of lormetazepam glucuronide with urine amounted to 70% to 80% of the dose during 72 hr after intravenous injection in both age groups.

Development of antibody — mediated extraction followed by GC/MS (antibody/GC/MS) and its application to iloprost determination in plasma☆

A new analytical principle has been developed combining the features of both radioimmunoassay and GC/MS. Its application in eicosanoid analysis was tested with the prostacyclin analogue, iloprost. The iloprost antibody, generally employed in RIA measurements, was coupled to Sepharose 4B and used as stationary phase for extraction of the drug. Variations in recovery were corrected by using deuterated iloprost as an internal standard. The samples were derivatized and quantitated by negative-ion chemical ionization-mass spectrometry. Reproducibility was 2.3 % at the 50 pg/ml level and the limit of detection was 5 pg for 1 ml samples. With plasma volumes of up to 20 ml, 0.25 pg/ml could be determined. Antibody/GC/MS proved superior to radioimmunoassay due to its higher specificity and sensitivity and superior to GC/MS with conventional clean-up procedures because of a higher sample capacity.

DEVELOPMENT AND APPLICATION OF A RADIOIMMUNOASSAY OF THE NEW PROGESTAGEN GESTODENE

A radioimmunoassay for the determination of gestodene (17-ethinyl-13-ethyl-17 beta-hydroxy-4,15-gonadien-3-one) in human plasma is described with regard to procedure, specificity, accuracy and reproducibility. Antiserum was raised against gestodene-3-O-(carboxymethyl)oxime-BSA in rabbits and [9,11-3H]-gestodene tracer was used with a specific radioactivity of 2.16 TBq/mmol. The final antiserum dilution was 1: 200,000. RIA was performed according to routine methods using diethylether plasma extracts and the charcoal separation technique. Cross-reactivity of antiserum with cortisol, 17 beta-estradiol, progesterone, testosterone and ethinylestradiol was less than 0.03%; levonorgestrel exhibited a 5% cross-reactivity. No cross-reactivity with metabolites of gestodene or ethinylestradiol was found. Accuracy and precision of the assay were tested using human plasma samples spiked with 1, 5 and 10 ng/ml gestodene. Accuracy was within 94 to 104% of the nominal values. Within-assay and between-assay coefficients of variation were in the range of 4.7-6.5% and 10.3-13.1%, resp. This RIA was used to follow plasma gestodene levels after single oral administration of 75 micrograms of gestodene combined with 30 micrograms ethinylestradiol as tablet and coated tablet in a cross-over design in 6 female test subjects. Plasma gestodene levels were equivalent after both treatments.