Mikael Hedeland

St John's Wort Decreases the Bioavailability of R- and S-verapamil Through Induction of the First-pass Metabolism

Our objective was to investigate the inducing effect of repeated oral administration of St Johns wort on the jejunal transport and presystemic extraction of R‐ and S‐verapamil in humans.

Multiple transport mechanisms involved in the intestinal absorption and first-pass extraction of fexofenadine.

Our objective was to investigate the main in vivo transport mechanisms of fexofenadine involved in the intestinal absorption and bioavailability of the drug in humans.

Oxaliplatin Degradation in the Presence of Chloride-Identification and Cytotoxicity of the Monochloro Monooxalato Complex

AbstractPurpose. To study the degradation of oxaliplatin in chloride media and evaluate the cytotoxicity of oxaliplatin in normal and chloride-deficient medium. Methods. The products of the reaction of oxaliplatin with chloride were separated on a Hypercarb S column with a mobile phase containing 40% methanol in 0.05 M ammonia and subjected to electrospray ionization mass spectrometry. The cytotoxicity of oxaliplatin in normal and chloride-deficient medium was evaluated by 30-min incubations on human colon adenocarcinoma cells (HT-29). Results. We identified a new intermediate degradation product, the monochloro monooxalato complex ([Pt(dach)oxCl]−) and the final product, the dichloro complex (Pt(dach)Cl2), by liquid chromatography-mass spectrometry. [Pt(dach)oxCl]− was found as the negative ion, M−, at m/z 431, and the positive ion, [M+2H]+, m/z 433. Pt(dach)Cl2 was found as the negative ion, [M-H]−, m/z 377, and the positive ion, [M+NH4]+, m/z 396. The fast initial degradation of oxaliplatin can be coupled to the fast formation of [Pt(dach)oxCl]−. In the cytotoxic assay, the cell survival was not affected by the chloride levels. Conclusions. [Pt(dach)oxCl]−, a new transformation product of oxaliplatin, has been identified. Its in vitro cytotoxic effect does not appear to exceed that of oxaliplatin.

FIRST-PASS EFFECTS OF VERAPAMIL ON THE INTESTINAL ABSORPTION AND LIVER DISPOSITION OF FEXOFENADINE IN THE PORCINE MODEL

The aim of this study in pigs was to investigate the local pharmacokinetics of fexofenadine in the intestine and liver by using the pig as a model for drug transport in the entero-hepatobiliary system. A parallel group design included seven pigs (10–12 weeks, 22.2–29.5 kg) in three groups (G1, G2, G3), and a jejunal single-pass perfusion combined with sampling from the bile duct and the portal, hepatic, and superior caval veins was performed. Fexofenadine was perfused through the jejunal segment alone (G1: 120 mg/l, total dose 24 mg) or with two different verapamil doses (G2: 175 mg/l, total dose 35 mg; and G3: 1000 mg/l, total dose 200 mg). The animals were fully anesthetized and monitored throughout the experiment. Fexofenadine had a low liver extraction (EH; mean ± S.E.M.), and the given doses of verapamil did not affect the EH (0.13 ± 0.04, 0.16 ± 0.03, and 0.12 ± 0.02 for G1, G2, and G3, respectively) or biliary clearance. The EH for verapamil and antipyrine agreed well with human in vivo data. Verapamil did not increase the intestinal absorption of fexofenadine, even though the jejunal permeability of fexofenadine, verapamil, and antipyrine showed a tendency to increase in G2. This combined perfusion and hepatobiliary sampling method showed that verapamil did not affect the transport of fexofenadine in the intestine or liver. In this model the EH values for both verapamil and antipyrine were similar to the corresponding values in vivo in humans.

Development of a chiral non-aqueous capillary electrophoretic system using the partial filling technique with UV and mass spectrometric detection.

A chiral non-aqueous CE system with UV and mass spectrometric detection has been developed. The enantioseparation was promoted by diastereomeric complex (ion-pair) formation between the amines (e.g. salbutamol, atenolol) and the chiral selector, (-)-2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid [(-)-DIKGA]. Different solvent mixtures were studied, as well as different concentrations of (-)-DIKGA and ammonium acetate in the background electrolyte. A partial filling technique was developed with a selector plug composed of (-)-DIKGA and ammonium acetate in a solvent mixture of methanol and 2-propanol. The separated enantiomers of pronethalol were detected by a Q-TOF MS system equipped with a sheath-flow electrospray ionization interface.

Non-aqueous capillary electrophoretic separation of enantiomeric amines with (−)-2,3:4,6-di-O-isopropylidene-2-keto-l-gulonic acid as chiral counter ion

(-)-2,3:4,6-Di-O-isopropylidene-2-keto-L-gulonic acid [(-)-DIKGA] has been introduced as a chiral counter ion in non-aqueous capillary electrophoresis. High enantioresolutions (R(s)> or =3) were obtained for amines, e.g., pronethalol, labetalol and bambuterol. Methanol containing NaOH and (-)-DIKGA was used as the background electrolyte. The counter ion concentration and the nature of the injection medium were found to affect the chiral separation. Covalent coating of the fused-silica capillary reduced the electro-osmotic flow resulting in improved enantioresolutions.

Cellobiohydrolase I as a chiral additive in capillary electrophoresis and liquid chromatography

Cellobiohydrolase I (CBH I) was used as a chiral selector in free solution in capillary electrophoresis, applying the partial filling technique. The enantiomers of the amino alcohols oxprenolol and propranolol could be completely resolved with selector plugs of only 1.0 cm in plain acetate buffer at pH 5.0. Although warfarin migrates in the same direction as CBH I at this pH, its enantiomers were separated and detected at the anodic end of the capillary, well resolved from the protein plug. Furthermore, propranolol was enantioseparated at pH 3.0, where the protein has a positive net charge and migrates in the same direction as this amino alcohol. Addition of 2-propanol significantly improved the peak shape of overloaded peaks. CBH I was also used as a complexing agent in the mobile phase in HPLC for chiral separation of rac-propranolol.

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.

Enterohepatic Disposition of Rosuvastatin in Pigs and the Impact of Concomitant Dosing with Cyclosporine and Gemfibrozil

The hepatobiliary transport and local disposition of rosuvastatin in pig were investigated, along with the impact of concomitant dosing with two known multiple transport inhibitors; cyclosporine and gemfibrozil. Rosuvastatin (80 mg) was administered as an intrajejunal bolus dose in treatments I, II, and III (TI, TII, and TIII, respectively; n = 6 per treatment). Cyclosporine (300 mg) and gemfibrozil (600 mg) were administered in addition to the rosuvastatin dose in TII and TIII, respectively. Cyclosporine was administered as a 2-h intravenous infusion and gemfibrozil as an intrajejunal bolus dose. In treatment IV (TIV, n = 4) 5.9 mg of rosuvastatin was administered as an intravenous bolus dose. The study was conducted using a pig model, which enabled plasma sampling from the portal (VP), hepatic (VH), and femoral veins and bile from the common hepatic duct. The biliary recoveries of the administered rosuvastatin dose were 9.0 ± 3.5 and 35.7 ± 15.6% in TI and TIV, respectively. Rosuvastatin was highly transported into bile as shown by the median AUCbile/AUCVH ratio in TI of 1770 (1640–11,300). Gemfibrozil did not have an effect on the plasma pharmacokinetics of rosuvastatin, most likely because the unbound inhibitor concentrations did not exceed the reported IC50 values. However, cyclosporine significantly reduced the hepatic extraction of rosuvastatin (TI, 0.89 ± 0.06; TII, 0.46 ± 0.13) and increased the AUCVP and AUCVH by 1.6- and 9.1-fold, respectively. In addition, the biliary exposure and fe, bile were reduced by ≈50%. The strong effect of cyclosporine was in accordance with inhibition of sinusoidal uptake transporters, such as members of the organic anion-transporting polypeptide family, rather than canalicular transporters.

The effect of St. John's wort on the pharmacokinetics, metabolism and biliary excretion of finasteride and its metabolites in healthy men

The aim of this study was to investigate what the consequences of induced drug metabolism, caused by St. Johns wort (SJW, Hypericum perforatum) treatment, would have on the plasma, biliary and urinary pharmacokinetics of finasteride and its two previously identified phase I metabolites (hydroxy-finasteride and carboxy-finasteride). Twelve healthy men were administered 5mg finasteride directly to the intestine via a catheter with a multi-channel tubing system, Loc-I-Gut, before and after 14 days SJW (300mg b.i.d, hyperforin 4%) treatment. Bile samples were withdrawn via the Loc-I-Gut device from the proximal jejunum. LC-ESI-MS/MS was used to analyze finasteride and its metabolites in plasma, bile and urine. HPLC-UV was used to analyze hyperforin in plasma. The herbal treatment significantly reduced the peak plasma concentration (C(max)), the area under the plasma concentration-time curve (AUC(0-24h)) and the elimination half-life (t(1/2)) of finasteride. The geometric mean ratios (90% CI) were 0.42 (0.36-0.49), 0.66 (0.56-0.79) and 0.54 (0.48-0.61), respectively. Finasteride was excreted unchanged to a minor extent into bile and urine. Hydroxy-finasteride was not detected in plasma, bile or urine. Carboxy-finasteride was quantified in all three compartments and its plasma pharmacokinetics was significantly affected by SJW treatment. Hyperforin concentration in plasma was 21+/-7ng/ml approximately 12h after the last dose of the 14 days SJW treatment. In conclusion, SJW treatment for 2 weeks induced the metabolism of finasteride and caused a reduced plasma exposure of the drug. New knowledge was gained about the biliary and urinary excretion or the drug and its metabolites.