Use of microdosing to predict pharmacokinetics at the therapeutic dose: experience with 5 drugs.

Objectives: A volunteer trial was performed to compare the pharmacokinetics of 5 drugs--warfarin, ZK253 (Schering), diazepam, midazolam, and erythromycin--when administered at a microdose or pharmacologic dose. Each compound was chosen to represent a situation in which prediction of pharmacokinetics from either animal or in vitro studies (or both) was or is likely to be problematic.

Methods: In a crossover design volunteers received (1) 1 of the 5 compounds as a microdose labeled with radioactive carbon (carbon 14) (100 microg), (2) the corresponding (14)C-labeled therapeutic dose on a separate occasion, and (3) simultaneous administration of an intravenous (14)C-labeled microdose and an oral therapeutic dose for ZK253, midazolam, and erythromycin.

Ursodeoxycholic acid does not affect ethinylestradiol bioavailability in women taking oral contraceptives.

Objective: Contraception is recommended for female patients during ursodeoxycholic acid (UDCA) treatment for the potential teratogenic effect of this bile acid, and the aim of our study was to determine whether this treatment affects the bioavailability of ethinylestradiol (EE2).

Methods: In this double-blind, randomised study, we measured EE2 pharmacokinetics in eight healthy volunteers randomly allocated to receive oral contraceptive (30 microg EE2 and 75 microg gestodene) plus either UDCA (8-10 mg/kg per day) or placebo for 21 days during the first of three consecutive menstrual cycles. After a washout period during the second cycle, the subjects received the alternative treatment during the third menstrual cycle.

A pharmacokinetic study with a low-dose oral contraceptive containing 20 microg ethinylestradiol plus 100 microg levonorgestrel.

This study investigated the pharmacokinetics of a dose-reduced oral contraceptive containing 20 microg ethinylestradiol (EE) + 100 microg levonorgestrel (LNG) in 18 young, healthy females. Serum levels of EE and LNG were determined after single and repeated daily oral administration over three treatment cycles, each consisting of 21 treatment days followed by a 7-day treatment-free period. Additionally, the time courses of sex hormone-binding globulin (SHBG), corticoid-binding globulin (CBG) and total and free testosterone serum levels were analyzed.

Use of precision cut human liver slices for studying the metabolism and genotoxic potential of xenobiotics by means of the (32)P-postlabelling technique: steps towards method validation using testosterone and 2-aminofluorene.

In the present study, a new in vitro model combining the short-term incubation of precision-cut human liver slices with DNA-adduct analysis by the (32)P-postlabelling technique is proposed for investigation of the genotoxic potential of xenobiotics. For method validation, the metabolic turnover of testosterone (TES) and the DNA-adduct inducing potential of 2-aminofluorene (2-AF) were used. Precision-cut human liver slices were prepared from a total of 12 human liver samples which were freshly obtained as parts of resectates from liver surgery.

Predicting the oral bioavailability of 19-nortestosterone progestins in vivo from their metabolic stability in human liver microsomal preparations in vitro.

It was the aim of this study to investigate whether assessment of the metabolic stability of selected progestins of the 19-nortestosterone type in human microsomal liver preparations was a suitable approach to predict the oral bioavailability of these drugs in humans. The Michaelis-Menten parameters Vmax and KM,app for norethisterone, levonorgestrel, gestodene, desogestrel, 3-keto-desogestrel, norgestimate, and dienogest were determined in in vitro incubations with human liver microsomes. Using these data, both the in vitro intrinsic clearance (CLint) and, after application of a suitable scaling factor, the scaled in vivo CLint were calculated.