dextromethorphan and fexofenadine

Cytochrome P450 (CYP) activity can be assessed using a 'cocktail' phenotyping approach. Recently, we have developed a cocktail (Geneva cocktail) which combines the use of low-dose probes with a low-invasiveness dried blood spots (DBS) sampling technique and a single analytical method for the phenotyping of six major CYP isoforms. We have previously demonstrated that modulation of CYP activity after pre-treatment with CYP inhibitors/inducer could be reliably predicted using Geneva cocktail. To further validate this cocktail, in this study, we have verified whether probe drugs contained in the latter cause mutual drug-drug interactions. In a randomized, four-way, Latin-square crossover study, 30 healthy volunteers received low-dose caffeine, flurbiprofen, omeprazole, dextromethorphan and midazolam (a previously validated combination with no mutual drug-drug interactions); fexofenadine alone; bupropion alone; or all seven drugs simultaneously (Geneva cocktail). Pharmacokinetic profiles of the probe drugs and their metabolites were determined in DBS samples using both conventional micropipette sampling and new microfluidic device allowing for self-sampling. The 90% confidence intervals for the geometric mean ratios of AUC metabolite/AUC probe for CYP probes administered alone or within Geneva cocktail fell within the 0.8-1.25 bioequivalence range indicating the absence of pharmacokinetic interaction. The same result was observed for the chosen phenotyping indices, that is metabolic ratios at 2 hr (CYP1A2, CYP3A) or 3 hr (CYP2B6, CYP2C9, CYP2C19, CYP2D6) post-cocktail administration. DBS sampling could successfully be performed using a new microfluidic device. In conclusion, Geneva cocktail combined with an innovative DBS sampling device can be used routinely as a test for simultaneous CYP phenotyping.

Topics: Adolescent; Adult; Bupropion; Caffeine; Cross-Over Studies; Cytochrome P-450 CYP1A2; Cytochrome P-450 CYP2B6; Cytochrome P-450 CYP2C19; Cytochrome P-450 CYP2C9; Cytochrome P-450 CYP2D6; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Dextromethorphan; Dose-Response Relationship, Drug; Dried Blood Spot Testing; Drug Interactions; Female; Flurbiprofen; Genotyping Techniques; Humans; Male; Midazolam; Omeprazole; Phenotype; Terfenadine; Young Adult

An LC-MS/MS method has been developed for the simultaneous quantification of P-glycoprotein (P-gp) and cytochrome P450 (CYP) probe substrates and their Phase I metabolites in DBS and plasma. P-gp (fexofenadine) and CYP-specific substrates (caffeine for CYP1A2, bupropion for CYP2B6, flurbiprofen for CYP2C9, omeprazole for CYP2C19, dextromethorphan for CYP2D6 and midazolam for CYP3A4) and their metabolites were extracted from DBS (10 µl) using methanol. Analytes were separated on a reversed-phase LC column followed by SRM detection within a 6 min run time.. The method was fully validated over the expected clinical concentration range for all substances tested, in both DBS and plasma. The method has been successfully applied to a PK study where healthy male volunteers received a low dose cocktail of the here described P-gp and CYP probes. Good correlation was observed between capillary DBS and venous plasma drug concentrations.. Due to its low-invasiveness, simple sample collection and minimal sample preparation, DBS represents a suitable method to simultaneously monitor in vivo activities of P-gp and CYP.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Bupropion; Caffeine; Calibration; Chromatography, High Pressure Liquid; Cytochrome P-450 Enzyme System; Dextromethorphan; Dried Blood Spot Testing; Flurbiprofen; Half-Life; Male; Midazolam; Omeprazole; Pharmaceutical Preparations; Substrate Specificity; Tandem Mass Spectrometry; Terfenadine

The suitability of the capillary dried blood spot (DBS) sampling method was assessed for simultaneous phenotyping of cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp) using a cocktail approach. Ten volunteers received an oral cocktail capsule containing low doses of the probes bupropion (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), midazolam (CYP3A), and fexofenadine (P-gp) with coffee/Coke (CYP1A2) on four occasions. They received the cocktail alone (session 1), and with the CYP inhibitors fluvoxamine and voriconazole (session 2) and quinidine (session 3). In session 4, subjects received the cocktail after a 7-day pretreatment with the inducer rifampicin. The concentrations of probes/metabolites were determined in DBS and plasma using a single liquid chromatography-tandem mass spectrometry method. The pharmacokinetic profiles of the drugs were comparable in DBS and plasma. Important modulation of CYP and P-gp activities was observed in the presence of inhibitors and the inducer. Minimally invasive one- and three-point (at 2, 3, and 6 h) DBS-sampling methods were found to reliably reflect CYP and P-gp activities at each session.

Topics: Administration, Oral; Adult; ATP Binding Cassette Transporter, Subfamily B, Member 1; Bupropion; Caffeine; Capsules; Carbonated Beverages; Chromatography, High Pressure Liquid; Chromatography, Reverse-Phase; Coffee; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Dextromethorphan; Dried Blood Spot Testing; Enzyme Inhibitors; Feasibility Studies; Flurbiprofen; Humans; Isoenzymes; Male; Midazolam; Omeprazole; Pharmaceutical Preparations; Phenotype; Pilot Projects; Predictive Value of Tests; Spectrometry, Mass, Electrospray Ionization; Substrate Specificity; Tandem Mass Spectrometry; Terfenadine; Young Adult