Biliary secretion of rosuvastatin and bile acids in humans during the absorption phase.

AIM: The aim of this study was to investigate the biliary secretion of rosuvastatin in healthy volunteers using an intestinal perfusion method after administration of 10mg rosuvastatin dispersion in the intestine. METHODS: The Loc-I-Gut tube was positioned in the distal duodenum/proximal jejunum and a semi-open segment was created by inflating the proximal balloon in ten volunteers. A dispersion of 10mg rosuvastatin was administered below the inflated balloon and bile was collected proximally of the inflated balloon. Bile and plasma samples were withdrawn every 20 min during a 4h period (absorption phase) and additional plasma samples were collected 24 and 48 h post-dose. RESULTS: The study showed that there is a substantial and immediate transport of rosuvastatin into the human bile, with the maximum concentration appearing 42 min after dosing, 39,000+/-31,000 ng/ml. Approximately 11% of the administered intestinal dose was recovered in the bile after 240 min. At all time points the biliary concentration exceeded the plasma concentration, and the average bile to plasma ratio was 5200+/-9200 (range 89-33,900, median 2000). We were unable to identify any bile-specific metabolites of rosuvastatin in the present study. CONCLUSION: Rosuvastatin is excreted via the biliary route in humans, and the transport and accumulation of rosuvastatin in bile compared to that in plasma is rapid and extensive. This intestinal perfusion technique offers a successful way to estimate the biliary secretion for drugs, metabolites and endogenous substances during the absorption phase in healthy volunteers.

Flutamide metabolism in four different species in vitro and identification of flutamide metabolites in human patient urine by high performance liquid chromatography/tandem mass spectrometry.

A new metabolic scheme of flutamide is proposed in this article. Some patients treated with flutamide, a nonsteroidal antiandrogen, have developed severe hepatic dysfunction. Toxic metabolites have been proposed to be responsible for these negative effects. In this study, the qualitative aspects of the in vitro metabolism of flutamide in liver microsomes from human, dog, pig, and rat were evaluated. A direct comparison of the flutamide metabolism in liver and prostate microsomes from pig was made, and the in vivo metabolism of flutamide was investigated in urine from orally treated prostate cancer patients. Liquid chromatography/tandem mass spectrometry was used for analysis. The mass spectrometer was equipped with an electrospray interface and operated in the negative ion mode. In liver microsomes from pig, dog, and rat, extensive hydroxylation of flutamide occurred. One, two, or three hydroxy groups were attached, and isomeric forms were detected for both monohydroxylated and trihydroxylated drug. In pig liver microsomes, isomers of a third metabolite, hydroxylated 4-nitro-3-(trifluoromethyl)-aniline, were also found after incubation with either flutamide or 2-hydroxyflutamide. In human liver microsomes, the pharmacologically active 2-hydroxyflutamide was the only metabolite detected. Several phase I metabolites as well as four intact phase II metabolites could be recovered from the urine samples. For the first time in humans, glucuronic acid conjugates of hydroxylated 4-nitro-3-(trifluoromethyl)-aniline, and mono- and dihydroxylated flutamide were identified, together with hydroxylated 4-nitro-3-(trifluoromethyl)-aniline conjugated with sulfate. In addition, one mercapturic acid conjugate of hydroxylated flutamide, probably formed from flutamide via a reactive intermediate, was detected.

Identification of some new clemastine metabolites in dog, horse, and human urine with liquid chromatography/tandem mass spectrometry.

The metabolism of clemastine was studied in dogs, horses, and humans after a single dose of Tavegyl. The urine collected was extracted by solid-phase extraction or hydrolyzed with beta-glucuronidase and then extracted by liquid-liquid extraction, prior to analysis for unchanged drug and phase I and II metabolites by liquid chromatography/tandem mass spectrometry. The metabolites were identified by their molecular mass and interpretation of the product ion spectra, since no standard substances were available. Unchanged drug was recovered in urine samples from dogs and humans, but not from horses. In dogs and humans, the phase I metabolite, norclemastine, was identified, and clemastine metabolites with one and two additional oxygens were found in all three species. In horses and dogs monohydroxylation on one of the aromatic rings or the adjacent methyl group was favored while, in humans, the additional oxygen was positioned on either the aromatic or the aliphatic part of the structure, and the aliphatic reaction seemed to result in at least three isomers. In the metabolites with two additional oxygens, both the oxygens were found on the aliphatic fragment in humans and dogs, whereas they were situated on the aromatic part of the structure in horses. In human patients, glucuronidated monohydroxyclemastine was recovered, and in urine from horses both mono- and dihydroxyclemastine glucuronides were identified, while phase II metabolites could not be recovered from the dog urine. Clemastine metabolism in dogs and horses has, to our knowledge, not been studied before, and new metabolites from humans are presented in this article. Thus, the metabolites described in the present work have not been previously reported in the literature.