As a plausible explanation for the large interindividual variability in the pharmacokinetics of the neuroleptic agent haloperidol, the contributions of CYP3A isozymes (CYP3A4 and the polymorphic CYP3A5) predominantly involved in haloperidol bioactivation to the neurotoxic pyridinium species 4-(4-Chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-pyridinium (HPP ) were assessed in human liver micro...

As a plausible explanation for the large interindividual variability in the pharmacokinetics of the neuroleptic agent haloperidol, the contributions of CYP3A isozymes (CYP3A4 and the polymorphic CYP3A5) predominantly involved in haloperidol bioactivation to the neurotoxic pyridinium species 4-(4-Chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-pyridinium (HPP ) were assessed in human liver micro...

In vitro studies were performed to identify the human cytochrome P450 enzyme(s) involved in the hydroxylation (isopropyl moiety) of a previously reported endothelin ETA receptor antagonist, compound A [( )-(5S,6R,7R)-2-isopropylamino-7-{4-methoxy-2-[(2R)3-methoxy-2-methylpropyl]}-5-(3,4-methylenedioxyphenyl)cyclopenteno(1,2-b) pyridine 6-carboxylic acid]. Several lines of evidence indicated tha...

Capravirine, a new non-nucleoside reverse transcriptase inhibitor, undergoes extensive oxygenation reactions, including N-oxidation, sulfoxidation, sulfonation, and hydroxylation in humans. Numerous primary (mono-oxygenated) and sequential (di-, tri-, and tetraoxygenated) metabolites of capravirine are formed via the individual or combined oxygenation pathways. In this study, cytochrome P450 en...

Linezolid (Zyvox), the first of a new class of antibiotics, the oxazolidinones, is approved for treatment of Gram-positive bacterial infections, including resistant strains. The disposition of linezolid in human volunteers was determined, after a 500-mg (100-mCi) oral dose of [C]linezolid. Radioactive linezolid was administered as a single dose, or at steady-state on day 4 of a 10-day, 500-mg b...

The clinical pharmacokinetic behavior of paclitaxel (Taxol) is distinctly nonlinear, with disproportional increases in systemic exposure with an increase in dose. We have recently shown that Cremophor EL, the formulation vehicle used for i.v. administration of paclitaxel, alters drug distribution as a result of micellar entrapment of paclitaxel, and we speculated that the free drug fraction (fu...

The clinical pharmacokinetic behavior of paclitaxel (Taxol) is distinctly nonlinear, with disproportional increases in systemic exposure with an increase in dose. We have recently shown that Cremophor EL, the formulation vehicle used for i.v. administration of paclitaxel, alters drug distribution as a result of micellar entrapment of paclitaxel, and we speculated that the free drug fraction (fu...

Previously we described a transgenic mouse model [FVB/NTg(CYP3A4-luc)Xen] using a reporter construct consisting of 13 kilobases of the human CYP3A4 promoter driving the firefly luciferase gene in the inbred FVB/N mouse strain. Here we report regulation of the same CYP3A4-luc reporter gene in a transgenic outbred mouse strain (CD-1) and in a transgenic rat (SpragueDawley). Basal reporter express...

Gemfibrozil more potently inhibits CYP2C9 than CYP2C8 in vitro, and yet the opposite inhibitory potency is observed in the clinic. To investigate this apparent paradox, we evaluated both gemfibrozil and its major metabolite, an acyl-glucuronide (gemfibrozil 1-Oglucuronide) as direct-acting and metabolism-dependent inhibitors of the major drug-metabolizing cytochrome P450 enzymes (CYP1A2, 2B6, 2...

The N-demethylation of dacarbazine in liver microsomes was significantly increased by treatment of rats with b-naphthoflavone, dexamethasone, or phenobarbital. However, the extent of increase in the N-demethylation observed in b-naphthoflavone-treated rats was much greater than that observed in dexamethasone-treated rats. A good correlation between N-demethylation of dacarbazine and O-deethylat...