Comparison of predicted intrinsic hepatic clearance of 30 pharmaceuticals in canine and feline liver microsomes.

1. Known cytochrome P450 (CYP) substrates in humans are used in veterinary medicine, with limited knowledge of the similarity or variation in CYP metabolism. Comparison of canine and feline CYP metabolism via liver microsomes report that human CYP probes and inhibitors demonstrate differing rates of intrinsic clearance (CL).

Development of an in vitro screen for compound bioaccumulation in Haemonchus contortus.

The objective of the current study was to establish an in vitro screen and a highly sensitive analytical assay to delineate key physicochemical properties that favor compound bioaccumulation in the L3 life stage of a Haemonchus contortus isolate. Time-dependent studies revealed that absorption and elimination kinetics during the first 6 hr of exposure were sufficient to achieve maximum bioaccumulation for the majority of compounds tested. In subsequent studies, the larvae were incubated for 6 hr in a medium containing 146 compounds (5 μM initial concentration), including both human and veterinary medicines, characterized by a broad range of physicochemical properties.

A non-acidic sulfaphenazole analog demonstrating high intrinsic clearance and selectivity by canine CYP2C21.

In contrast to human CYP2C9, non-human CYP2C enzymes do not appear to preferentially bind and metabolize anionic drugs. Using analogs of sulfaphenazole, the effect of an acidic sulfonamide group on apparent affinity and turnover rates was characterized with canine CYP2C21. Blocking the sulfonamide with a methyl group increased the intrinsic clearance by CYP2C21 > 100-fold and decreased K(m).

Current cytochrome P450 phenotyping methods applied to metabolic drug-drug interaction prediction in dogs.

Recombinant cytochrome P450 (P450) phenotyping, different approaches for estimating fraction metabolized (f(m)), and multiple measures of in vivo inhibitor exposure were tested for their ability to predict drug interaction magnitude in dogs. In previous reports, midazolam-ketoconazole interaction studies in dogs have been attributed to inhibition of CYP3A pathways. However, in vitro phenotyping studies demonstrated higher apparent intrinsic clearances (CL(int,app)) of midazolam with canine CYP2B11 and CYP2C21.

Developmental changes in human liver CYP2D6 expression.

Within the human cytochrome P450 family, specific forms show developmental expression patterns that can affect drug clearance, efficacy, and safety. The objective of this study was to use dextromethorphan O-demethylase activity and quantitative Western blotting to identify CYP2D6 developmental expression patterns in a large (n = 222) and developmentally diverse set of pediatric liver samples. Immunodetectable levels of CYP2D6 protein determined for selected samples across all age categories showed a significant correlation with the corresponding dextromethorphan O-demethylase activity.

In vitro drug-drug interaction screens for canine veterinary medicines: evaluation of cytochrome P450 reversible inhibition.

Little information regarding the metabolic pathways of pharmaceutical agents administered to dogs, or the inhibition of those metabolic pathways, is available. Without this information, it is difficult to assess how combinations of drugs, whether new or old or approved or nonapproved, may increase the risk for metabolic drug-drug interactions in dogs. Because mammalian xenobiotic metabolism pathways often involve the hepatic cytochrome P450 (P450) monooxgenases, canine liver microsome P450 inhibition screens were tested to evaluate the potential metabolic drug interaction risk of commonly used veterinary medicines.

Epirubicin glucuronidation and UGT2B7 developmental expression.

The usefulness of epirubicin in the treatment of adult and childhood malignant diseases is related in part to the potential reduction in cardiac toxicity compared with that of other anthracyclines given at equivalent doses. An important pathway for epirubicin detoxification is UGT2B7-dependent glucuronidation. This study was implemented to provide a preclinical evaluation of the metabolism of epirubicin with respect to age-related changes in epirubicin glucuronidation in pediatric liver microsomes.

Developmental expression of the major human hepatic CYP3A enzymes.

The human cytochrome P4503A forms show expression patterns subject to developmental influence. CYP3A7 and CYP3A4 are generally classified as the major fetal and adult liver forms, respectively. However, characterization of CYP3A4, -3A5, and -3A7 developmental expression has historically been confounded by the lack of CYP3A isoform-specific antibodies or marker enzyme activities.

Expression and characterization of functional dog flavin-containing monooxygenase 1.

A full-length dog (beagle) flavin-containing monooxygenase 1 (FMO1) cDNA (dFMO1) was obtained from liver by reverse transcription-polymerase chain reaction. The amino acid sequence of dFMO1 was 89% homologous to human FMO1. Using a baculovirus expression system in Sf-9 insect cells, dFMO1 was expressed to protein levels of 0.

Identification of phenylisoxazolines as novel and viable antibacterial agents active against Gram-positive pathogens.

A new and promising group of antibacterial agents, collectively known as the oxazolidinones and exemplified by linezolid (PNU-100766, marketed as Zyvox), have recently emerged as important new therapeutic agents for the treatment of infections caused by Gram-positive bacteria. Because of their significance, extensive synthetic investigations into the structure-activity relationships of the oxazolidinones have been conducted at Pharmacia. One facet of this research effort has focused on the identification of bioisosteric replacements for the usual oxazolidinone A-ring.