Pharmacokinetic comparison of six anthelmintics in sheep, goats, and cattle.

This study was initiated to determine whether a comparative pharmacokinetic (PK) approach could be used to expand the pool of approved anthelmintics for minor ruminant species. Accordingly, the PK profiles of six anthelmintics (levamisole, albendazole, fenbendazole, moxidectin, doramectin, and ivermectin) in sheep, goats, and cattle were determined. The PK values determined for each anthelmintic included Tmax , Tlast , Cmax , AUC, AUC/dose, and Cmax /dose. The results of this study demonstrate that a comparative PK approach does not show commonality in the way these six anthelmintics are individually processed by these three ruminants. While some drugs demonstrated identical PK profiles between sheep and goats, none of these drugs demonstrated PK profiles in sheep and goats comparable to the PK profiles found in cattle. The results from this study suggest drug approval across these three ruminants is not a viable concept. However, the resulting PK profiles for each combination of drug and ruminant species represents a new dataset that can be used to support the US FDA Center for Veterinary Medicine's Minor Use/Minor Species indexing process for drug approvals in minor species such as sheep and goats.

Influence of P-glycoprotein on the disposition of fexofenadine and its enantiomers.

OBJECTIVES: P-glycoprotein (P-gp) is responsible for the efflux of a broad variety of human and veterinary drugs. Canine P-gp polymorphisms alter drug disposition and toxicity, but their impact on the disposition of enantiomeric drugs is unknown. Using fexofenadine as a model compound, we developed and validated HPLC-fluorescence methods to determine the effect of P-gp on the disposition of fexofenadine and its enantiomers. METHODS: A chiral CD-Ph column was used for the separation of (R) and (S)-fexofenadine. Determination of racemic fexofenadine was achieved on an XDB-CN column. Fexofenadine and its enantiomers were detected by fluorescence at the excitation wavelength of 220 nm and emission wavelength of 300 nm. These methods were used to measure concentrations of fexofenadine and its enantiomers in Collie plasma after oral administration. KEY FINDINGS: This study demonstrates that P-gp prefers to transport (S)-fexofenadine, and P-gp deficiency causes the increase in both (R)-fexofenadine and (S)-fexofenadine in plasma. Racemic fexofenadine, (R)-fexofenadine and (S)-fexofenadine were increased in ABCB1-1Δ Collies (118.7, 72.0 and 48.3 ng/ml) compared to wild-type Collies (25.0, 16.5 and 7.7 ng/ml) at 1 h postadministration. The results demonstrate that the stereoselectivity of P-gp plays a key role in the disposition of fexofenadine enantiomers. CONCLUSIONS: The information derived from this drug model will be used to determine whether additional safety or efficacy requirements are necessary for enantiomeric drugs that would be used in dogs or humans.

Development of an ion chromatography-inductively coupled plasma-mass spectrometry method to determine inorganic arsenic in liver from chickens treated with roxarsone.

Roxarsone, (4-hydroxy-3-nitrophenyl)arsonic acid, is an arsenic-containing compound that has been approved as a feed additive for poultry and swine since the 1940s; however, little information is available regarding residual arsenic species present in edible tissues. We developed a novel method for the extraction and quantification of arsenic species in chicken liver. A strongly basic solution solubilized the liver, and ultrafiltration removed macromolecules and particulate material. Ion chromatography separated the species [arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, (4-hydroxy-3-aminophenyl)arsonic acid, (4-hydroxy-3-acetaminophenyl)arsonic acid, and roxarsone] in the extracts, which were then detected by inductively coupled plasma-mass spectrometry. The extraction oxidized most arsenite to arsenate. For fortification concentrations at 2 µg kg(-1) and above, recoveries ranged from 70 to 120%, with relative standard deviations from 7 to 34%. We detected roxarsone, its 3-amino and 3-acetamido metabolites, inorganic arsenic, and additional unknown arsenic species in livers from roxarsone-treated chickens. Both the originating laboratory and a second laboratory validated the method.

Effects of intravenous administration of lipopolysaccharide on cytochrome P450 isoforms and hepatic drug metabolizing enzymes in swine.

OBJECTIVE: To investigate effects of bacteria-mediated inflammation on hepatic drug metabolizing enzymes (DMEs) in swine via a lipopolysaccharide (LPS) challenge technique. ANIMALS: 22 Poland China-Landrace crossbred barrows. PROCEDURES: In experiment 1, 10 market-weight swine were treated with LPS (20 microg/kg, IV [n = 5 swine]) or sham-injected (5) 24 hours before slaughter. In experiment 2, 12 growing and finishing swine were treated with LPS at 2 or 20 microg/kg, IV (n = 3 swine/age group/treatment) 24 hours before slaughter. Hepatic DMEs, cytochrome P450 (CYP) isoforms, and CYP-mediated reactions were measured. RESULTS: In experiment 1, LPS administered at 20 microg/kg decreased most hepatic DME components and inhibited enzymatic activities. In experiment 2, both doses reduced protein content in subcellular fractions and inhibited some DME- and CYP-mediated activities. In growing and finishing swine, CYP2A and CYP2B isoforms were not detected after treatment with LPS; the CYP1A2 isoform was eliminated in growing but not in finishing swine. Lipopolysaccharide also reduced CYP2D6 content in growing and finishing swine but increased CYP2E content. Lipopolysaccharide had no effect on swine CYP2C11, CYP2C13, or CYP3A content. The CYP2B-mediated 7-pentoxyresorufin O-dealkylase activity in growing and finishing swine was totally eliminated, and 7-ethoxyresorufin (indicating CYP1A activity) and aniline (mediated by CYP2E) metabolism was decreased. CONCLUSIONS AND CLINICAL RELEVANCE: Effect of LPS treatment on swine CYPs appeared to be isoform specific; age-related metabolic status of the swine and the LPS dose modified this effect. Lipopolysaccharide-induced inflammation may affect metabolism of drugs and xenobiotics in swine.

Effect of oral administration of low doses of pentobarbital on the induction of cytochrome P450 isoforms and cytochrome P450-mediated reactions in immature Beagles.

OBJECTIVE: To determine the effect of oral administration of low doses of pentobarbital on cytochrome P450 (CYP) isoforms and CYP-mediated reactions in immature Beagles. ANIMALS: 42 immature (12-week-old) Beagles. PROCEDURE: Dogs were grouped and treated orally as follows for 8 weeks: low-dose pentobarbital (50 microg/d; 4 males, 4 females), mid-dose pentobarbital (150 microg/d; 4 males, 4 females), high-dose pentobarbital (500 microg/d; 4 males, 4 females), positive-pentobarbital control (10 mg/kg/d; 2 males, 2 females), positive-phenobarbital control (10 mg/kg/d; 2 males, 2 females), and negative control (saline 10.9% NaCl] solution; 5 males, 5 females). Serum biochemical and hematologic values were monitored. On necropsy examination, organ weights were determined, and histologic evaluation of tissue sections of liver, kidney, small intestine, testes, epididymis, and ovaries was performed. Hepatic and intestinal drug-metabolizing enzyme activities were measured, and relative amounts of CYP isoforms were determined by western blot analysis. RESULTS: The amount of a hepatic CYP2A-related isoform in dogs from the high-dose pentobarbital treatment group was twice that of dogs from the negative control group. CYP2C was not detectable in small intestinal mucosa of dogs from the negative control group; measurable amounts of CYP2C were found in dogs from the various (low-, mid-, and high-dose) pentobarbital treatment groups and from positive-pentobarbital and positive phenobarbital control groups. Several CYP-mediated reactions increased in a dose-dependent manner. The lowest calculated effective dose of pentobarbital ranged from 200 to 450 microg/d. CONCLUSIONS AND CLINICAL RELEVANCE: Several CYP isoforms and their associated reactions were induced in dogs by oral administration of low amounts of pentobarbital.