Polarization-independent plasmonic subtractive color filtering in ultrathin Ag nanodisks with high transmission.

We demonstrate a TE/TM polarization-independent plasmonic subtractive color filtering scheme employing ultrathin two-dimensional Ag nanodisks. These TE/TM polarization-independent subtractive color filters exhibit small feature sizes (below 200 nm) and high transmission up to 70% in the visible spectral region, superior to previously reported plasmonic color filters. Simulated optical transmission spectra and colors are in good agreement with experimental results. The color-filtering behaviors strongly depend on thickness and period of nanodisks. Underlying mechanisms are also discussed in detail.

Stereoselective binding of propranolol to human plasma, alpha 1-acid glycoprotein, and albumin.

Our aim was to determine possible stereoselectivity in the plasma binding of propranolol. Equilibrium dialysis with plasma from seven healthy subjects and a deuterium-labeled pseudoracemate of propranolol was used. Plasma binding of the propranolol enantiomers differed with the unbound fraction of (-)-propranolol (22 +/- 2%; mean +/- SE) being smaller than that of (+)-propranolol (25.3 +/- 1.9%). The (-)/(+)-propranolol ratio for the unbound fraction, a measure of the stereoselectivity, was 0.86 +/- 0.02. There was an inverse correlation between the unbound (-)/(+)-propranolol ratio in individual subjects and overall binding of (+/-)-propranolol, indicating greater stereoselectivity at higher total binding. To assess the site of the stereoselective binding to plasma proteins, the binding of (+)- and (-)-propranolol to human alpha 1-acid glycoprotein (AGP) and human serum albumin (HSA) was examined. The binding to AGP was stereoselective for (-)-propranolol with a (-)/(+)-propranolol ratio for the unbound fraction of 0.79 +/- 0.01, whereas (+)-propranolol was bound to a greater extent to HSA with a (-)/(+)-propranolol ratio for the unbound fraction of 1.07 +/- 0.01. Although these results demonstrate opposite stereoselectivity in the binding of (+)- and (-)-propranolol to AGP and HSA, the stereoselective binding of (-)-propranolol to AGP predominates in plasma. This stereoselective plasma binding of the (-)-enantiomer of propranolol could limit the access of this more active enantiomer to beta-receptors or other active sites. The uptake of propranolol by red blood cells was not stereoselective.

Increased clearance of propranolol and theophylline by high-protein compared with high-carbohydrate diet.

The objective of this study was to determine whether changes in dietary protein and carbohydrate influence the oral clearance of propranolol, a high-clearance drug, and theophylline, a low-clearance drug. Six normal subjects studied in a clinical research center each received a single oral dose of propranolol, 80 mg, and theophylline, 5 mg/kg, after having been on each of two well-defined diets for a period of 10 days. When the diet was altered from high carbohydrate/low protein to low carbohydrate/high protein, the oral clearance of propranolol increased by 74% +/- 20% (mean +/- SE; range 9% to 156%; P less than 0.01) with no change in plasma half-life or plasma binding. This dietary change resulted in an increase in theophylline clearance of 32% +/- 6% (range 18% to 50%; P less than 0.02) and a corresponding decrease in plasma half-life of 26% +/- 6% (range 6% to 42%; P less than 0.05) with no alteration in the apparent volume of distribution. These observations reemphasize the importance of diet in drug disposition and suggest that the clearance of high-clearance drugs like propranolol is more susceptible than the clearance of low-clearance drugs to dietary manipulations, effects that may have to be considered in drug therapy.

Pharmacokinetics of potential anti-AIDS agents thiofoscarnet and foscarnet in the cat.

The pharmacokinetics of thiophosphonoformate (TPFA) and phosphonoformate (foscarnet, PFA) were studied in normal adult cats, a species susceptible to feline immunodeficiency virus (FIV) infection. Parent drugs and metabolites were quantitated by high-performance liquid chromatography (HPLC). TPFA had a mean terminal plasma half-life of 42 min, a total clearance of 4.58 ml/min/kg, and a renal clearance of 1.24 ml/min/kg (N = 4). TPFA underwent in vivo metabolism to PFA and thiophosphonic acid (TPA); the latter was inactive against HIV reverse transcriptase. The 6-h cumulative urinary excretion was 42.3% of the intravenous administered dose of TPFA, consisting of 23.5% unchanged TPFA, 13.8% PFA, and 5.0% TPA. In comparison, PFA had a mean (N = 5) terminal half-life of 172 min and a total clearance of 1.88 ml/min/kg, approximating its renal clearance. There was no evidence of PFA metabolism. Oral doses of TPFA were administered either in enteric-coated capsules or in solution by gavage. The mean oral bioavailability of encapsulated TPFA and PFA was 22 and 8%, respectively. When given by gavage, TPFA had a higher mean bioavailability (33%), but with a greater variability. Based on the 6-h cumulative urinary excretion of TPFA, the mean oral bioavailability of TPFA was 44%, similar to that based on plasma data. The TPFA appears to be superior to PFA because of its greater oral bioavailability and its ability to deliver an active metabolite, PFA, to the systemic circulation after oral dosing.

Pharmacokinetic and pharmacodynamic properties of conventional and CD-formulated diltiazem in cats.

The i.v. and apparent steady-state kinetics of diltiazem HCI (DLT) and slow-absorption long-acting diltiazem (CD) given p.o. were investigated in cats. The effects of p.o. diltiazem on heart rate and PR interval were also studied. Plasma diltiazem concentrations were determined by ultraviolet high-performance liquid chromatography (UV-HPLC), using verapamil as the internal standard. Heart rate and PR interval determinations were evaluated over a 24-hour period for the PO formulations and compared with values under diltiazemfree conditions. The mean systemic clearance and apparent volume of distribution of i.v. diltiazem were 15.0 mL/min/kg and 2.70 L/kg, respectively. The elimination half-life of diltiazem after i.v. and p.o. DLT administration were approximately 120 minutes. In contrast, the terminal half-life of CD was 460 minutes. The mean apparent bioavailability of DLT p.o. was 71%, which was significantly higher than that observed with CD (36%). Heart rate and PR intervals in cats receiving the 2 formulations at steady-state were not different from those measured in the drug-free state. We conclude that DLT at 1 mg/kg p.o. tid and CD at 10 mg/kg p.o. sid provide plasma concentrations that are known to have pharmacodynamic effects in other species.

Determination of concentration of albendazole sulfoxide in plasma and uterine fluid of heifers.

OBJECTIVES: To determine time and concentration of peak plasma and uterine fluid concentrations of albendazole (ABZ) sulfoxide (ABZSO) in heifers after oral administration of ABZ. SAMPLE POPULATION: 25 young Angus and Simmental heifers maintained on pasture with ad libitum access to hay and water. PROCEDURE: Heifers were assigned at random to ABZ or control (water) groups, and were drenched with ABZ suspension at a dosage of 15, 30, 60, or 120 mg/kg of body weight, or with water. Plasma was collected hourly, from 14 to 25 hours after administration of ABZ or water. After a drug-withdrawal period, heifers were synchronized for estrus and drenched with 60 mg of ABZ/kg, or water (50 ml). Each uterine horn was flushed. All samples were extracted and subjected to high-performance liquid chromatography analysis. RESULTS: For all groups, highest mean +/- SEM plasma concentration of ABZSO was observed between 15 and 16 hours after ABZ administration, at 2.0 +/- 0.4 micrograms/ml (15 mg/kg), 5.3 +/- 1.0 micrograms/ml (30 mg/kg), 7.4 +/- 1.5 micrograms/ml (60 mg/kg), and 11.1 +/- 2.7 micrograms/ml (120 mg/kg). Mean concentration for all uterine horn fluid samples was 265 +/- 25 ng/ml/horn; range was 79 to 546 ng/ml/horn. The only significant (P = 0.0006) source of variation was the technician performing the flush. Mean concentration for each technician was 184 +/- 24 ng/ml/horn and 345 +/- 35 ng/ml/horn. CLINICAL RELEVANCE: Teratogenic and embryotoxic effects of ABZSO differ for ewes and heifers. Albendazole sulfoxide is detectable in the uterus of heifers; however, ABZSO peaks in heifer plasma earlier and at a lower concentration than that reported for ewes, perhaps contribution to differences in susceptibility at similar dosages.

Pharmacokinetics of digoxin in sheep: limitations of the use of biological half-life for interspecies extrapolation.

After of single IV digoxin injection of 50 micrograms/kg of body weight, the serum digoxin concentrations of 4 sheep were fitted to a 2-compartment open model. The mean value for the elimination half-life was 7.15 hours; for area volume of distribution, 13.8 L/kg; and for total body clearance, 1.36 L/kg/hr. A comparison of this study with previous studies in sheep and cattle revealed that serious misconceptions could arise if one chose to rely upon elimination half-life as the sole descriptor of drug disposition. A more informative characterization was determined to be total body clearance and area volume of distribution.

Glucuronidation in the chimpanzee (Pan troglodytes): studies with acetaminophen, oestradiol and morphine.

The chimpanzee has recently been characterized as a surrogate for oxidative drug metabolism in humans and as a pharmacokinetic model for the selection of drug candidates. In the current study, the glucuronidation of acetaminophen, morphine and oestradiol was evaluated in the chimpanzee to extend the characterization of this important animal model. Following oral administration of acetaminophen (600 mg) to chimpanzees (n=2), pharmacokinetics were comparable with previously reported human values, namely mean oral clearance 0.91 vs. 0.62+/-0.05 l h-1 kg-1, apparent volume of distribution 2.29 vs. 1.65+/-0.25 l kg-1, and half-life 1.86 vs. 1.89+/-7h, for chimpanzee vs. human, respectively. Urinary excretions (percentage of dose) of acetaminophen, acetaminophen glucuronide and acetaminophen sulfate were also similar between chimpanzees and humans, namely 2.3 vs. 5.0, 63.1 vs. 54.7, and 25.0 vs. 32.3%, respectively. Acetaminophen, oestradiol and morphine glucuronide formation kinetics were investigated using chimpanzee (n=2) and pooled human liver microsomes (n=10). V(max) (app) and K(m)(app) (or S(50)(app)) for acetaminophen glucuronide, morphine 3- and 6-glucuronide, and oestradiol 3- and 17-glucuronide formation were comparable in both species. Eadie-Hofstee plots of oestradiol 3-glucuronide formation in chimpanzee microsomes were characteristic of autoactivation kinetics. Western immunoblot analysis of chimpanzee liver microsomes revealed a single immunoreactive band when probed with anti-human UGT1A1, anti-human UGT1A6, and anti-human UGT2B7. Taken collectively, these data demonstrate similar glucuronidation characteristics in chimpanzees and humans.

Effects of chlorpromazine on the disposition and beta-adrenergic blocking activity of propranolol in the dog.

The effects of chlorpromazine (100 mg p.o., 2 hr before propranolol) on the disposition and beta-adrenergic blocking actions of both intravenous (6 mg) and oral (40 mg) propranolol were studied in the dog. Chlorpromazine pretreatment significantly reduced (69%) the oral clearance of propranolol, resulting in significant increases in propranolol bioavailability (159%), and in the total beta-adrenergic blocking activity (111%) after the oral dose. The increase in the total beta-adrenergic blocking activity of oral propranolol after chlorpromazine pretreatment was mostly due to an increased contribution from the parent compound; the apparent activity from active propranolol metabolites was not affected by chlorpromazine. Chlorpromazine pretreatment had no significant influence on the systemic clearance, elimination half-life, apparent volume of distribution, and plasma binding of propranolol, or on the apparent hepatic blood flow. After intravenous propranolol, chlorpromazine pretreatment had no effect on either the total amount of beta-adrenergic blocking activity or the amount of activity attributable to active metabolites. The decreased oral propranolol clearance by chlorpromazine was seen as a shift to the left in the propranolol dose vs. AUC relationship, eliminating the apparent nonlinear kinetic behavior of oral propranolol, and reducing the apparent oral threshold dose. Chlorpromazine's major, if not only, effect on propranolol disposition was to reduce the presystemic elimination of propranolol, possibly through inhibition of its metabolism via a pathway other than ring oxidation.

Determination of the stereochemical composition of the major metabolites of verapamil in dog urine with enantioselective liquid chromatographic techniques.

The stereochemical composition of verapamil and seven of its basic-extractable metabolites, isolated from the urine of dogs administered oral racemic verapamil, was determined by HPLC, using an Ultron OVM (ovomucoid) column. One dog was given oral (R)-verapamil alone in order to discriminate the (R)- and (S)-enantiomers of the metabolites. Structure identification of the isolated verapamil metabolites was accomplished using a combination of HPLC-MS and FAB-MS-MS techniques. Six of the urinary verapamil metabolites, including verapamil, were predominantly of the (R)-configuration, whereas one of the metabolites was predominantly in the (S)-form. The remaining isolated metabolite was comprised of approximately equal amounts of the two forms.

Interactions of phenobarbital with propranolol in the dog. 1. Plasma protein binding.

A new drug interaction is described in which the plasma binding of propranolol is markedly stimulated by chronic phenobarbital administration in dogs. After 3 weeks of phenobarbital therapy, the percentages of unbound propranolol fell from 15.2 +/- 1.2 (mean +/- S.E.) to 2.4 +/- 0.3 (P less than .001). The time course of the induction and recovery of the binding of propranolol was also investigated. A half-maximal stimulation of binding was seen by day 3 of phenobarbital therapy and a plateau was reached after 2 weeks. After discontinuing phenobarbital, the recovery was delayed with the midpoint of the return to a normal binding value occurring on day 17. A new model of the time course for induction which includes the pharmacokinetics of the inducing agent has been developed. The stimulation of protein production by phenobarbital is assumed to follow Michaelis-Menten kinetics, but with a lag phase for the expression of the induction. Using this model, the Km for phenobarbital-stimulated production of the binding protein was 1200 ng/ml, the turnover T1/2 of the protein was 3.4 days and the T1/2 for the lag phase was also 3.4 days. The increased plasma protein binding was highly correlated (r = 0.97) with the elevated concentration of nonprecipitable glycoproteins. This most likely represents induction of alpha-1 acid glycoprotein which is the principal binding protein of propranolol in man. The plasma binding of propranolol was also stimulated with chronic phenytoin in these dogs and with a single dose of Arochlor 1254 in rats.

Interaction of phenobarbital with propranolol in the dog. 3. Beta blockade.

The chronic administration of phenobarbital (180 mg/day p.o.) alters the binding, bioavailability, metabolism and pharmacokinetics of propranolol. Consequently, phenobarbital affects the pharmacological activity of propranolol as measured by inhibition of isoproterenol tachycardia in dogs. Altered binding affects beta blockade in two ways; a reduction in the free fraction and the volume of distribution. To separate the effects of active metabolites from the parent drug, we have used an integrated form of the equation (DR -- 1) = K.(p), where DR is the dose ratio and p is the concentration of the free (unbound) propranolol in plasma. The activity due to propranolol itself is subtracted from the total observed amount of beta blockade. In this way, phenobarbital was shown to increase the amount of beta blockade which was due to active metabolites. Phenobarbital treatment shortened the time course of beta blockade. The beta blocking half-life for propranolol followed its pharmacokinetic half-life closely for a variety of experimental conditions. This suggests that pharmacological activity data could be used to describe pharmacokinetics without measuring blood concentrations.

Isolation, purification, and structure identification of glucuronic acid conjugates of propranolol and alprenolol and their ring-hydroxylated metabolites.

The purpose of this study was to develop a procedure for the isolation, purification, and structure identification of glucuronic acid conjugates of propranolol and alprenolol and their active metabolites, 4-hydroxypropranolol and 4-hydroxyalprenolol. As both aliphatic and aromatic glucuronides may be formed from 4-hydroxypropranolol and 4-hydroxyalprenolol, the structure identification of these conjugates has to be based on the intact conjugates. Using DEAE-Sephadex anion-exchange chromatography, milligram quantities of these glucuronides were isolated from urine of dogs pretreated with propranolol and alprenolol, respectively. A high degree of purification was achieved by reversed-phase HPLC. Structure identification of the methyl ester-trimethylsilyl derivatives was accomplished by electron impact GC/MS. Only one 4-hydroxypropranolol glucuronide was found, having the glucuronic acid linked to the aromatic hydroxyl group. For 4-hydroxyalprenolol glucuronide, however, two structures were identified, one with the glucuronic acid linked to the aromatic hydroxyl group, and the other with the glucuronic acid linked to the aliphatic hydroxyl group of the side chain. Using this analytical approach, 4-hydroxypropranolol glucuronide was identified in the urine of patients on propranolol therapy. In man, as in the dog, only the aromatic glucuronide was found, i.e. containing an unsubstituted beta-blocking side chain.

The effects of chronic oral diltiazem and cimetidine dosing on the pharmacokinetics and negative dromotropic action of intravenous and oral diltiazem in the dog.

The kinetics and negative dromotropic action of intravenous (1 mg kg-1) and oral (5 mg kg-1) diltiazem were studied in dogs after acute doses, after treatment for 3 days with oral diltiazem (5 mg kg-1, t.i.d.), and after 3 days' treatment with oral diltiazem (5 mg kg-1 t.i.d.) and cimetidine (200 mg t.i.d.). Plasma concentrations of diltiazem and two of its metabolites, desacetyldiltiazem and desmethyldiltiazem were measured by HPLC. Chronic oral dosing significantly lowered both the systemic and oral clearance of diltiazem, with no changes in either the volume of distribution or blood binding of diltiazem. Cimetidine treatment resulted in a significant reduction in diltiazem oral clearance from chronic control with no effect on its systemic clearance. The AUCs of both metabolites increased by greater than threefold from acute to chronic oral dosing; however, the ratio of each metabolite's AUC to that of diltiazem AUC was not significantly altered. Cimetidine treatment significantly lowered these ratios. The negative dromotropic potency of diltiazem after the acute oral dose was three times greater than that after intravenous or chronic control dosing. Cimetidine treatment resulted in further lowering chronic oral diltiazem potency. These data indicate that the disposition and negative dromotropic action of diltiazem is dependent both on the route of administration and the duration of treatment, and can be altered by co-administration with cimetidine.

Pharmacokinetics of sulfadimethoxine and ormetoprim in a 5:1 ratio following intraperitoneal and oral administration, in the hybrid striped bass (Morone chrysops x Morone saxitalis).

Selected pharmacokinetic parameters for sulfadimethoxine and ormetoprim, administered in a 5:1 ratio, via the oral and intraperitoneal (i.p.) routes were determined in the hybrid striped bass (Morone chrysops x Morone saxitalis). Plasma concentrations of both drugs were determined by high-performance liquid chromatography. A first-order one-compartment model adequately described plasma drug disposition. The elimination half-lives for sulfadimethoxine following i.p. and oral administration were 26 and 10.5 h, respectively. The half-lives for ormetoprim administered via i.p. and oral routes were 7.5 and 3.9 h, respectively. Cmax for sulfadimethoxine via the i.p. and oral routes were calculated to be 27.7 (+/-9.0) microg/mL at 3.6 h and 3.2 (+/-1.2) microg/mL at 1.2 h, respectively. Cmax for ormetoprim via the i.p. route was calculated to be 1.2 (+/-0.5) microg/mL at 9.1 h and 1.58 (+/-0.7) microg/mL at 5.7 h for the oral route. The oral availability of sulfadimethoxine relative to the i.p. route was 4.6%, while the oral availability of ormetoprim relative to the i.p. route was 78.5%. Due to the nonconstant ratio of these drugs in the plasma of the animal, the actual drug ratio to use for determining minimum inhibitory concentration (MIC) is unclear. Using the ratio of the total amount of each drug that is absorbed as a surrogate for the mean actual ratio may be the best alternative to current methods. Using this ratio as determined in these studies, (2.14:1 sulfadimethoxine:ormetoprim) to determine the MICs the single 50 mg/kg oral dose of the 5:1 combination of sulfadimethoxine and ormetoprim appears to provide plasma concentrations high enough to inhibit the growth of Yersinia ruckeri, Edwardsiella tarda, and Escherichia coli.

Interactions of phenobarbital with propranolol in the dog. 2. Bioavailability, metabolism and pharmacokinetics.

This article describes the effects of chronically administered phenobarbital (180 mg/day p.o.) in dogs on the bioavailability of single 40-mg oral doses of propranolol and on the pharmacokinetics and the patterns of propranolol metabolism in urine after both oral (40 mg) and i.v. (6 mg) doses. Phenobarbital decreased the bioavailability of propranolol from 7.7 to 3.5%. By using a gas chromatography/mass spectrometry technique, the quantitative metabolic pattern of i.v. propranolol was unaltered by phenobarbital, but increases in hydroxylation and induction of new metabolites were observed for oral propranolol after phenobarbital treatment. Chronic phenobarbital treatment led to significant decreases in the half-lives of propranolol after both i.v. and oral doses. Little change was observed in the hepatic blood flow, systemic clearance or intrinsic oral clearance. These data demonstrate the completely nonrestrictive elimination of propranolol. With phenobarbital, both the extent of plasma protein binding and the distribution into erythrocytes change significantly, yet the overall clearance remains unaltered. The half-lives fell in responses to the binding-induced reduction in the apparent volume of distribution.

Influence of food on the intravenous and oral dose kinetics of propranolol in the dog.

The intravenous and oral dose kinetics of propranolol were studied in the dog both in a fasted state and immediately after a meal consisting of 100 g of cooked beef liver. Fifty microCi of 3H-propranolol was administered intravenously simultaneously with a 40-mg oral dose of unlabeled propranolol. Plasma 3H-propranolol was measured by specific extraction and liquid scintillation spectrometry, and unlabeled plasma propranolol was determined by gas chromatography-mass spectrometry. Feeding significantly reduced (25%) the elimination half-life and increased (52%) the systemic clearance of intravenous propranolol. The increase in the systemic clearance of propranolol after feeding was mostly due to an increase (60%) in apparent hepatic blood flow, which appeared to remain elevated for 5-7 hr. The meal had no influence on the apparent volume of distribution or plasma binding. Feeding did not affect the area under the concentration-time curve of oral propranolol, but significantly delayed the rate of oral propranolol absorption, shifting the time to reach peak plasma levels from 60 to 158 min. The results of this study suggest that feeding alters the disposition of propranolol in the dog by producing a sustained increase in hepatic blood flow.

The influence of cimetidine on the pharmacokinetics of the enantiomers of verapamil in the dog during multiple oral dosing.

The disposition of intravenously (0.5 mg/kg) and orally (5 mg/kg) administered verapamil was studied in six dogs after 3 days' pre-treatment with verapamil alone (5 mg/kg, every 8 h) and during concomitant oral administration of cimetidine (16 mg/kg, every 8 h). Racemic verapamil and norverapamil, an active metabolite of verapamil, were measured by fluorescence high performance liquid chromatography using an achiral phenyl column. The isolated racemic verapamil was rechromatographed on an Ultron-OVM chiral column, which separated the two verapamil enantiomers. Cimetidine co-administration significantly reduced the systemic clearance of racemic verapamil as well as that of its enantiomers by 25-29%. The clearance of racemic verapamil administered orally as well as that of its enantiomers was also reduced by 28% during cimetidine coadministration. The decrease in verapamil metabolism by cimetidine appeared to be non-stereoselective. On the other hand, cimetidine co-administration had no significant effect on the apparent volume of distribution of racemic verapamil and its enantiomers or the plasma protein binding or the blood to plasma concentration ratio of racemic verapamil. In addition, the ratio of the area under the plasma concentration-time curve for norverapamil to that of verapamil was unaffected by cimetidine co-administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning of canine cytochrome P450 2E1 cDNA: identification and characterization of two variant alleles.

Cytochrome P450 (CYP) 2E1 is a toxicologically important enzyme that inactivates a number of drugs and xenobiotics and also bioactivates many xenobiotic substrates to their hepatotoxic or carcinogenic forms. Although cDNAs for the human, rodent, and rabbit forms of CYP2E1 have been isolated and studied extensively, there is an absence of information about canine CYP2E1, despite the fact that the dog is routinely used in drug safety studies. In this study, we isolated and sequenced a full-length CYP2E1 cDNA from a beagle liver cDNA library. The deduced canine CYP2E1 amino acid sequence exhibited 75 to 76% identity with rat, mouse, and rabbit CYP2E1 sequences, and 77% identity with human CYP2E1. Two populations of clones, differing at a single nucleotide, were isolated from the unamplified library. The T1453C base change results in a Tyr485His amino acid substitution, which is well beyond the heme binding region but is possibly part of a beta-sheet structure. An allele-specific polymerase chain reaction-based restriction enzyme test was developed for genotyping individual dogs from genomic DNA samples. One hundred mixed breed dogs were genotyped, and the frequencies of the Tyr485 and His485 alleles were found to be 0. 85 and 0.15, respectively. The canine Tyr485 and His485 alleles and human CYP2E1 were expressed in Escherichia coli cells, and catalytic activities of the proteins were assessed using the substrate chlorzoxazone. Although the two canine enzymes had similar catalytic activity; significant kinetic differences were seen between canine and human CYP2E1s.