The toxicity and biotransformation of single doses of acetaminophen in dogs and cats

Pharmacokinetic profile of oral and subcutaneous administration of paracetamol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy

The pharmacokinetic profile of paracetamol in koalas is described when administered orally at 15 mg/kg; followed by the same dose, administered every 12 hours (hrs), repeated five times. After the initial oral administration, the median (range) maximal plasma concentration (Cmax), the time Cmax was reached (Tmax) and elimination half-life (t1/2) were 16.93 μg/mL (13.66 to 20.25 μg/mL); 4 hrs (4 to 8 hrs) and 5.54 hrs (4.66 to 7.67 hrs), respectively. When paracetamol was administered orally at 15 mg/mL every 12 hrs, the trough total plasma concentration range remained comparable to the therapeutic range in humans i.e. 4 to 20 μg/mL that is known to provide some analgesia. However, there is a smaller proportion of free drug (i.e. not bound to plasma proteins; and the active form) available in koala plasma (approximately 40% unbound) compared to human plasma (approximately 80% unbound). Consequently, even when there are similar total drug plasma concentrations in both koala and human plasma, the therapeutic efficacy may be reduced in koalas compared to humans. The initial oral dose and subsequent twice daily doses resulted in no obvious adverse effects in any koala. Haematology, plasma electrolyte and biochemical analyte values remained within their reference ranges eight hrs after the last dose but there was a significant change in alanine transaminase (ALT) levels (an increase), and in total protein (a decrease) (both p = 0.03). A dose of 15 mg/kg was also administered as a subcutaneous injection, diluted 50:50 with saline, to two koalas. As the oral formulation and the subcutaneous administration resulted in comparable absorption, the study focused on the oral profile. Based on these results there is an argument to recommend a slight increase in the oral paracetamol dose for the koala, however further investigation is required to confirm whether repeated administration of a slightly higher dose may be associated with more severe or additional significant changes in haematology, electrolytes or biochemical analytes. However, a preferable recommendation would be to administer this dosage of paracetamol in combination with another analgesic such as tramadol, as a subcutaneous injection, to improve efficacy.

The Dangers of Acetaminophen for Neurodevelopment Outweigh Scant Evidence for Long-Term Benefits

Based on available data that include approximately 20 lines of evidence from studies in laboratory animal models, observations in humans, correlations in time, and pharmacological/toxicological considerations, it has been concluded without reasonable doubt and with no evidence to the contrary that exposure of susceptible babies and children to acetaminophen (paracetamol) induces many, if not most, cases of autism spectrum disorder (ASD). However, the relative number of cases of ASD that might be induced by acetaminophen has not yet been estimated. Here, we examine a variety of evidence, including the acetaminophen-induced reduction of social awareness in adults, the prevalence of ASD through time, and crude estimates of the relative number of ASD cases induced by acetaminophen during various periods of neurodevelopment. We conclude that the very early postpartum period poses the greatest risk for acetaminophen-induced ASD, and that nearly ubiquitous use of acetaminophen during early development could conceivably be responsible for the induction in the vast majority, perhaps 90% or more, of all cases of ASD. Despite over a decade of accumulating evidence that acetaminophen is harmful for neurodevelopment, numerous studies demonstrate that acetaminophen is frequently administered to children in excess of currently approved amounts and under conditions in which it provides no benefit. Further, studies have failed to demonstrate long-term benefits of acetaminophen for the pediatric population, leaving no valid rationale for continued use of the drug in that population given its risks to neurodevelopment.

Effects of coenzyme Q10 and N-acetylcysteine on experimental poisoning by paracetamol in Wistar rats

Paracetamol (PAR) is a drug widely used in human and veterinary medicine as an analgesic and antipyretic, often involved in cases of intoxication. The most common clinical signs result from damage to red blood cells and hepatocytes, and this intoxication is considered a model for the induction of acute liver failure. In the present study, the hepatoprotective effects of coenzyme Q10 (CoQ10) and N-acetylcysteine (NAC) against experimental paracetamol (PAR) poisoning were analysed. Thirty-five adult Wistar rats (Rattus novergicus albinus) were randomly assigned to five groups, and thirty-one of these survived the treatments. Negative control group (CON-) received 1mL of 0.9% NaCl orally (PO). Other groups received 1.2g/kg of PAR (PO). Positive control group (CON+) received only PAR. NAC group received 800 mg/kg intraperitoneally (IP) of NAC 1h after the administration of PAR and at 12 h received 1mL of 0.9% NaCl, IP. The fourth group (CoQ10) received 1h and 12 h after intoxication, CoQ10 (10mg/kg IP). And the fifth group (NAC+CoQ10) received NAC (800mg/kg, IP) and CoQ10 (10mg/kg, IP). After 12 hours, the rats were euthanized and necropsied to collect liver and kidney tissues for histopathological evaluation and electronic microscopy. A single dose of PAR caused severe acute hepatitis. NAC couldn't reverse the liver and kidney damages. The group that received CoQ10 and NAC had moderate liver damage, while the group that received only CoQ10 had lower values of liver enzymes and mild liver and kidney damage. Animals that received treatment with CoQ10 or NAC+CoQ10 presented normal hepatocyte mitochondria and nuclei. Although CoQ10 couldn't reverse PAR organ damage, results indicate promising hepatoprotection in Wistar rats.

Emerging organic contaminants in springs of the highly karstified Dinaric region

Emerging organic contaminants (EOCs) have become of increasing interest due to concerns about their impact on humans and the wider environment. Karst aquifers are globally widespread, providing critical water supplies and sustaining rivers and ecosystems, and are particularly susceptible to pollution. However, EOC distributions in karst remain quite poorly understood. This study looks at the occurrence of EOCs in the Croatian karst, which is an example of the "classical" karst, a highly developed type of karst that occurs throughout the Dinaric region of Europe. Samples were collected from 17 karst springs and one karst lake used for water supply in Croatia during two sampling campaigns. From a screen of 740 compounds, a total of 65 compounds were detected. EOC compounds from the pharmaceutical (n = 26) and agrochemical groups (n = 26) were the most frequently detected, while industrials and artificial sweeteners had the highest concentrations (range 8-440 ng/L). The number of detected compounds and the frequency of detection demonstrate the vulnerability of karst to EOC pollution. Concentrations of 5 compounds (acesulfame, sucralose, perfluorobutane sulfonate, emamectin B1b, and triphenyl phosphate) exceeded EU standards and occurred at concentrations that are likely to be harmful to ecosystems. Overall, most detections were at low concentrations (50 % <1 ng/L). This may be due to high dilution within the exceptionally large springs of the Classical karst, or due to relatively few pollution sources within the catchments. Nevertheless, EOC fluxes are considerable (10 to 106 ng/s) due to the high discharge of the springs. Temporal differences were observed, but without a clear pattern, reflecting the highly variable nature of karst springs that occurs over both seasonal and short-term timescales. This research is one of a handful of regional EOC investigations in karst groundwater, and the first regional study in the Dinaric karst. It demonstrates the need for more frequent and extensive sampling of EOCs in karst to protect human health and the environment.

The Clinical Pharmacology and Therapeutic Evaluation of Non-Steroidal Anti-Inflammatory Drugs in Adult Horses

This review firstly examines the underlying pathophysiology of pain and inflammation associated with orthopedic disease and endotoxemia. Then, it reviews the clinical pharmacology (pharmacokinetics and pharmacodynamics) of both conventional and non-conventional NSAIDs in the adult horse, and finally provides an overview of different modalities to evaluate the therapeutic efficacy of NSAIDs in research.

Metabolism and disposition of JNJ-10450232 (NTM-006) in rats, dogs, nonhuman primates and humans

JNJ-10450232 (NTM-006), a novel non-opioid, non-nonsteroidal anti-inflammatory drug with structural similarities to acetaminophen, demonstrated anti-pyretic and/or analgesic activities in preclinical models and humans and reduced potential to cause hepatotoxicity in preclinical species. Metabolism and disposition of JNJ-10450232 (NTM-006) following oral administration to rats, dogs, monkeys and humans are reported. Urinary excretion was the major route of elimination based on recovery of 88.6% (rats) and 73.7% (dogs) of oral dose. The compound was extensively metabolized based on low recovery of unchanged drug in excreta from rats (11.3%) and dogs (18.4%). Clearance is driven by O-glucuronidation, amide hydrolysis, O-sulfation and methyl oxidation pathways. The combination of metabolic pathways driving clearance in human is covered in at least one preclinical species despite a few species-dependent pathways. O-Glucuronidation was the major primary metabolic pathway of JNJ-10450232 (NTM-006) in dogs, monkeys and humans, although amide hydrolysis was another major primary metabolic pathway in rats and dogs. A minor bioactivation pathway to quinone-imine is observed only in monkeys and humans. Unchanged drug was the major circulatory component in all species investigated. Except for metabolic pathways unique to the 5-methyl-1H-pyrazole-3-carboxamide moiety, metabolism and disposition of JNJ-10450232 (NTM-006) are similar to acetaminophen across species.

Effects of housing environment on oral absorption of acetaminophen in healthy Beagles

OBJECTIVE

To evaluate the effects of housing environment on oral absorption of acetaminophen in dogs.

ANIMALS

6 healthy Beagles.

PROCEDURES

Acetaminophen (325 mg, PO; mean dose, 31.1 mg/kg) was administered in a crossover study design with dogs housed in their normal environment or in a cage in an unfamiliar environment. There was a 7-day washout period between phases. Blood samples were collected for 24 hours following acetaminophen administration, and plasma acetaminophen concentrations were determined with high-pressure liquid chromatography.

RESULTS

A 2-compartment model with lag time was the best fit for both phases of the study. None of the primary or secondary pharmacokinetic parameters were significantly different between the 2 housing environments.

CLINICAL RELEVANCE

Findings suggested that in dogs, housing environment (normal environment vs a cage in an unfamiliar environment) did not significantly affect oral absorption and, by extension, gastric emptying of acetaminophen.

Association of Veterinary Hematology and Transfusion Medicine (AVHTM) transfusion reaction small animal consensus statement (TRACS). Part 3: Diagnosis and treatment

OBJECTIVE

To systematically review available evidence to develop guidelines for diagnosis and treatment of transfusion-associated reactions in dogs and cats.

DESIGN

Standardized and systemic evaluation of the literature (identified through Medline via PubMed and Google Scholar searches) was carried out for identified transfusion reaction types in dogs and cats. The available evidence was evaluated using PICO (Population, Intervention, Comparison, Outcome) questions generated for each reaction type. The evidence was categorized by level of evidence (LOE) and quality (Good, Fair, or Poor). Guidelines, diagnostic, and treatment algorithms were generated based on the evaluation of the evidence. Consensus on the final guidelines was achieved through Delphi-style surveys. Draft recommendations were disseminated through veterinary specialty listservs for review and comments, which were evaluated and integrated prior to final publication.

RESULTS

Medline via PubMed and Google Scholar databases were searched. There were 14 Population Intervention Comparison Outcome questions identified and corresponding worksheets were developed focusing on the diagnosis and treatment of transfusion-associated reactions in dogs and cats. Fourteen guidelines and four algorithms were developed with a high degree of consensus.

CONCLUSIONS

This systematic evidence evaluation process yielded recommended diagnostic and treatment algorithms for use in practice. However, significant knowledge gaps were identified, demonstrating the need for additional research in veterinary transfusion medicine.

Clinical evaluation of postoperative analgesia, cardiorespiratory parameters and changes in liver and renal function tests of paracetamol compared to meloxicam and carprofen in dogs undergoing ovariohysterectomy

Background

In veterinary medicine, the administration of nonsteroidal anti-inflammatory analgesics (NSAIDs) for the control of postsurgical pain in dogs and cats is common given the anti-inflammatory, analgesic, and antipyretic effects of these drugs. This study compared the serum biochemical changes and postoperative analgesic effects of paracetamol, meloxicam, and carprofen in bitches submitted to an ovariohysterectomy using the Dynamic Interactive Visual Analog Scale (DIVAS) and Pain Scale of the University of Melbourne (UMPS) scoring systems.

Methods

Thirty bitches of different breeds underwent elective ovariohysterectomies and were randomly assigned to one of three treatment groups: a paracetamol group [15 mg kg^-1 intravenous (IV)], a carprofen group (4 mg kg^-1 IV), and a meloxicam group (0.2 mg kg^-1 IV). All treatments were administered 30 minutes prior to surgery. Paracetamol was administered every 8 hours postoperatively for 48 hours total, while carprofen and meloxicam were intravenously administered every 24 hours. An evaluation of post-surgical pain was done with the DIVAS and the UMPS. The first post-surgical pain measurement was performed 1 hour after surgery and then 2, 4, 6, 8, 12, 16, 20, 24, 36, and 48 hours after surgery.

Results

All groups exhibited a gradual reduction in pain throughout the postoperative period in both scales; however, neither scale significantly differed between the three treatment groups (P > 0.05) during the 48 postoperative hours.

Conclusions

Paracetamol was as effective as meloxicam and carprofen for post-surgical analgesia in bitches subjected to elective ovariohysterectomy. The present study demonstrates that paracetamol may be considered a tool for the effective treatment of acute perioperative pain in dogs. Furthermore, this drug led to no adverse reactions or changes in the parameters assessed in the present study, indicating its safety.

Disposition of cyadox in domesticated cats following oral, intramuscular, and intravenous administration

Cyadox (CYX) is a synthetic antibacterial agent of quinoxaline with much lower toxic effects. A safety criterion of CYX for clinical use was established by studying the pharmacokinetics and metabolism of CYX after oral (PO), intramuscular (IM), and intravenous (IV) administration. CYX was administered in six domesticated cats (three males and three females) by PO (40 mg/kg.b.w.), IM (10 mg/kg.b.w.), and IV (10 mg/kg.b.w.) routes in a crossover pattern. Highly sensitive liquid chromatography with ultraviolet detection (HPLC-UV) method was developed for detection of CYX and its metabolites present in plasma, urine, and feces. The bioavailability of CYX after PO and IM routes was 4.37% and 84.4%. The area under curves (AUC), mean resident time (MRT), and clearance (CL) of CYX and its metabolites revealed that CYX quickly metabolized into its metabolites. The total recovery of CYX and its main metabolites was >60% after each route. PO delivery suggesting first pass effect in cats that might make this route suitable for intestinal infection and IM injection could be better choice for systemic infections. Less ability of glucuronidation did not show any impact on CYX metabolism. The findings of present study provide detailed information for evaluation of CYX.

A review of recent developments in the pharmacological prevention and treatment of endocrinopathic laminitis

Despite the prevalence of endocrinopathic laminitis, the pharmacologic options for preventing and treating the disease are severely limited. The present review aims to discuss the spectrum of potential therapeutic agents for the condition, ranging from early experimental compounds to agents nearing registration. There are different pharmacologic targets for, and approaches to, managing laminitis. Reducing hyperinsulinaemia is central to diminishing endocrinopathic laminitis risk, and a detailed understanding of the pathophysiology of insulin dysregulation is necessary to identify pathways that can be targeted to minimise post-prandial insulin secretion and action. This area of research is advancing rapidly, with several exciting prospects, such as sodium-dependent glucose co-transporter-2 inhibitors, on the horizon for the treatment of equine metabolic dysfunction. Drugs that directly target the lamellae and aim to reduce the damage inflicted on the lamellae as part of this condition, are not yet available. Although progress in this area of laminitis therapy is slower, improved understanding of the events that lead to lamellar failure has enabled the investigation of novel drugs that aim to prevent laminitis at the site of the lesion. Finally, a brief review is included of the directions being taken in the management of the chronic and acute pain that accompanies laminitis. Medications for relieving the pain associated with laminitis are currently the most-prescribed drugs for the disease, and range from simple, affordable and thoroughly tested options, such as phenylbutazone, to newer, less-understood applications such as paracetamol and gabapentin. In the future, endocrinopathic laminitis management plans will likely take a multi-faceted approach that still hinge on effective dietary management and exercise, but also include drugs that address foot pathology, pain and underlying endocrine disturbances.

Characterization of function and genetic feature of UDP-glucuronosyltransferase in avian species

Birds are exposed to many xenobiotics during their lifetime. For accurate prediction of xenobiotic-induced toxic effects on avian species, it is necessary to understand metabolic capacities in a comprehensive range of bird species. However, there is a lack of information about avian xenobiotic metabolizing enzymes (XMEs), particularly in wild birds. Uridine diphosphate glucuronosyltransferase (UGT) is an XME that plays an important role in phase II metabolism in the livers of mammals and birds. This study was performed to determine the characteristics of UGT1E isoform in avian species, those are related to mammals UGT 1A. To understand the characteristics of avian UGT1E isoforms, in vitro metabolic activity and genetic characteristics were investigated. Furthermore, mRNA expression levels of all chicken UGT1E isoforms were measured. On in vitro enzymatic analysis, the white-tailed eagle, great horned owl, and Humboldt penguin showed lower UGT-dependent activity than domestic birds. In synteny analysis, carnivorous birds were shown to have fewer UGT1E isoforms than herbivorous and omnivorous birds, which may explain why they have lower in vitro UGT activity. These observations suggested that raptors and seabirds, in which UGT activity is low, may be at high risk if exposed to elevated levels of xenobiotics in the environment. Phylogenetic analysis suggested that avian UGT1Es have evolved independently from mammalian UGT1As. We identified the important UGT isoforms, such as UGT1E13, and suspected their substrate specificities in avian xenobiotic metabolism by phylogenetic and quantitative real-time PCR analysis. This is the first report regarding the genetic characteristics and interspecies differences of UGT1Es in avian species.

Phylogenetic origins for severe acetaminophen toxicity in snake species compared to other vertebrate taxa

While it has been known for a while that some snake species are extremely sensitive to acetaminophen, the underlying mechanism for this toxicity has not been reported. To investigate if essential detoxification enzymes are missing in snake species that are responsible for biotransformation of acetaminophen in other vertebrate species, livers were collected from a variety of snake species, together with samples from alligator, snapping turtle, cat, rat, and cattle. Subcellular fractions were analyzed for enzymatic activities of phenol-type sulfotransferase and UDP‑glucuronosyltransferase, total glutathione S‑transferase, and N‑acetyltransferase. The results showed that none of the snake species, together with the cat samples, had any phenol-type glucuronidation activity, and that this activity was much lower in alligator and turtle samples than in the mammalian species. Combined with the lack of N‑acetyltransferase activity in snakes and cats, this would explain the accumulation of the aminophenol metabolite, which induces methemoglobinemia and subsequent suffocation of snakes and cats after acetaminophen exposure. While previous investigations have concluded that in cats the gene for the phenol-type glucuronosyltransferase isoform has turned into a pseudogene because of several point mutations, evaluation of genomic information for snake species revealed that they have only 2 genes that may code for glucuronosyltransferase isoforms. Similarity of these genes with mammalian genes is <50%, and suggests that the expressed enzymes may act on other types of substrates than aromatic amines. This indicates that the extreme sensitivity for acetaminophen in snakes is based on a different phylogenetic origin than the sensitivity observed in cats.

Uridine Diphosphate-Glucuronosyltransferase (UGT) 2B Subfamily Interspecies Differences in Carnivores

UDP-glucuronosyltransferases (UGTs) are among the most important xenobiotic metabolizing enzymes that conjugate a wide range of chemicals. Previous studies showed that Felidae and Pinnipedia species have very low UGT activities toward some phenolic compounds because of the UGT1A6 pseudogene and small numbers of UGT1A isozymes. In addition to the UGT1As, UGT2Bs isozymes also conjugate various endogenous (eg, estrogens, androgens, and bile acids) and exogenous compounds (opioids, non-steroidal anti-inflammatory drugs, and environmental pollutants). However UGT2B activity and genetic background are unknown in carnivore species. Therefore, this study was performed to elucidate the species differences of UGT2Bs. Using typical substrates for UGT2Bs, UGT activity was measured in vitro. In addition, UGT2B genetic features are analyzed in silico. Results of UGT activity measurement indicate marked species differences between dogs and other carnivores (cats, Northern fur seals, Steller sea lions, Harbor seals, and Caspian seals). Dogs have very high Vmax/Km toward estradiol (17-glucuronide), estrone, lorazepam, oxazepam, and temazepam. Conversely, cats and pinniped species (especially Caspian seals and Harbor seals) have very low activities toward these substrates. The results of genetic synteny analysis indicate that Felidae and pinniped species have very small numbers of UGT2B isozymes (one or none) compared with dogs, rodents, and humans. Furthermore, Felidae species have the same nonsense mutation in UGT2B, which suggests that Felidae UGT2B31-like is also a pseudogene in addition to UGT1A6. These findings of lower activity of UGT2B suggest that Felidae and some pinniped species have very low UGT activity toward a wide range of chemicals. These results are important for Felidae and Pinnipedia species that are frequently exposed to drugs and environmental pollutants.

Anthropogenic and Naturally Produced Brominated Phenols in Pet Blood and Pet Food in Japan

Present study determined concentrations and residue patterns of bromophenols (BPhs) in whole blood samples of pet cats and pet dogs collected from veterinary hospitals in Japan. BPhs concentrations were higher in cat blood than in dog blood, with statistically insignificant differences (p = 0.07). Among the congeners, 2,4,6-tribromophenol (TBPh) constituted the majority of BPhs (>90%) detected in both species. Analysis of commercial pet food to estimate exposure routes showed that the most abundant congener in all pet food samples was 2,4,6-TBPh, accounting for >99% of total BPhs. This profile is quite similar to the blood samples of the pets, suggesting that diet might be an important exposure route for BPhs in pets. After incubation in polybrominated diphenyl ether (PBDE) mixtures (BDE-47, BDE-99 and BDE-209), 2,4,5-TBPh was found in dog liver microsomes but not in cat liver microsomes, implying species-specific metabolic capacities for PBDEs. Formation of 2,4,5-TBPh occurred by hydroxylation at the 1' carbon atom of the ether bond of BDE-99 is similar to human study reported previously. Hydroxylated PBDEs were not detected in cats or dogs; therefore, diphenyl ether bond cleavage of PBDEs can also be an important metabolic pathway for BPhs formation in cats and dogs.

Poisoning of dogs and cats by drugs intended for human use

One of the main causes of poisoning of small animals is exposure to drugs intended for human use. Poisoning may result from misuse by pet owners, off-label use of medicines or, more frequently, accidental ingestion of drugs that are improperly stored. This review focuses on classes of drugs intended for human use that are most commonly involved in the poisoning of small animals and provides an overview of poisoning episodes reported in the literature. To perform this review a comprehensive search of public databases (PubMed, Web of Science, Scopus, Google Scholar) using key search terms was conducted. Additionally, relevant textbooks and reference lists of articles pertaining to the topic were reviewed to locate additional related articles. Most published information on small animal poisoning by drugs intended for human use was from animal and human poison control centres or from single case reports. The dog was the species most frequently poisoned. The major drugs involved included analgesics (nonsteroidal anti-inflammatory drugs), antihistamines (H1-antihistamines), cardiovascular drugs (calcium channel blockers), central nervous system drugs (selective serotonin reuptake inhibitors, baclofen, benzodiazepines and zolpidem), gastrointestinal drugs (loperamide), nutritional supplements (vitamin D and iron salts) and respiratory drugs (β2-adrenergic receptor agonists).

Identification of interspecific differences in phase II reactions: determination of metabolites in the urine of 16 mammalian species exposed to environmental pyrene

Interspecific differences in xenobiotic metabolism are a key to determining relative sensitivities of animals to xenobiotics. However, information on domesticated livestock, companion animals, and captive and free-ranging wildlife is incomplete. The present study evaluated interspecific differences in phase II conjugation using pyrene as a nondestructive biomarker of polycyclic aromatic hydrocarbon (PAH) exposure. Polycyclic aromatic hydrocarbons and their metabolites have carcinogenic and endocrine-disrupting effects in humans and wildlife and can have serious consequences. The authors collected urine from 16 mammalian species and analyzed pyrene metabolites. Interspecific differences in urinary pyrene metabolites, especially in the concentration and composition of phase II conjugated metabolites, were apparent. Glucuronide conjugates are dominant metabolites in the urine of many species, including deer, cattle, pigs, horses, and humans. However, they could not be detected in ferret urine even though the gene for ferret Uridine 5'-diphospho-glucuronosyltransferase (UDP-glucuronosyltransferase, UGT) 1A6 is not a pseudogene. Sulfate conjugates were detected mainly in the urine of cats, ferrets, and rabbits. Interestingly, sulfate conjugates were detected in pig urine. Although pigs are known to have limited aryl sulfotransferase activity, the present study demonstrated that pig liver was active in 1-hydroxypyrene sulfation. The findings have some application for biomonitoring environmental pollution.

Feline drug metabolism and disposition: pharmacokinetic evidence for species differences and molecular mechanisms

Although it is widely appreciated that cats respond differently to certain drugs compared with other companion animal species, the causes of these differences are poorly understood. This article evaluates published evidence for altered drug effects in cats, focusing on pharmacokinetic differences between cats, dogs, and humans, and the molecular mechanisms underlying these differences. More work is needed to better understand drug metabolism and disposition differences in cats, thereby enabling more rational prescribing of existing medications, and the development of safer drugs for this species.

The flat cat: 1. a logical and practical approach to management of this challenging presentation

AIM

Detailed information regarding the causes and treatment of acute collapse in the cat can be difficult to locate in a single published source. This two-part review aims to provide a logical approach to the clinical assessment and stabilisation of the critically ill collapsed cat.

PRACTICAL RELEVANCE

Cats are particularly challenging when presented as emergency patients, often in the later stages of an illness or with a vague history and non-specific signs. The nuances of the critically ill cat are considered, especially for shock and its management.

CLINICAL CHALLENGES

Shocked cats do not present in the classic stages typically seen in dogs, and the signs are more subtle. Therefore, the clinician must consider whether physical parameters are appropriate for the state and environment of the patient; for example, a normal heart rate in a shocked cat would be considered inappropriate.

AUDIENCE

This review is directed at any veterinarian working with feline patients, and particularly those dealing with emergencies on a regular basis.

EVIDENCE BASE

There is an extensive body of published literature, both original studies and textbook chapters, pertaining to the causes and treatment of collapse in the cat. In this article the authors draw on information from original publications, reviews and their clinical experience to provide practical guidance to assist in the emergency setting.

Evolution of a major drug metabolizing enzyme defect in the domestic cat and other felidae: phylogenetic timing and the role of hypercarnivory

The domestic cat (Felis catus) shows remarkable sensitivity to the adverse effects of phenolic drugs, including acetaminophen and aspirin, as well as structurally-related toxicants found in the diet and environment. This idiosyncrasy results from pseudogenization of the gene encoding UDP-glucuronosyltransferase (UGT) 1A6, the major species-conserved phenol detoxification enzyme. Here, we established the phylogenetic timing of disruptive UGT1A6 mutations and explored the hypothesis that gene inactivation in cats was enabled by minimal exposure to plant-derived toxicants. Fixation of the UGT1A6 pseudogene was estimated to have occurred between 35 and 11 million years ago with all extant Felidae having dysfunctional UGT1A6. Out of 22 additional taxa sampled, representative of most Carnivora families, only brown hyena (Parahyaena brunnea) and northern elephant seal (Mirounga angustirostris) showed inactivating UGT1A6 mutations. A comprehensive literature review of the natural diet of the sampled taxa indicated that all species with defective UGT1A6 were hypercarnivores (>70% dietary animal matter). Furthermore those species with UGT1A6 defects showed evidence for reduced amino acid constraint (increased dN/dS ratios approaching the neutral selection value of 1.0) as compared with species with intact UGT1A6. In contrast, there was no evidence for reduced amino acid constraint for these same species within UGT1A1, the gene encoding the enzyme responsible for detoxification of endogenously generated bilirubin. Our results provide the first evidence suggesting that diet may have played a permissive role in the devolution of a mammalian drug metabolizing enzyme. Further work is needed to establish whether these preliminary findings can be generalized to all Carnivora.

Clinical interpretation of pharmacokinetic and pharmacodynamic data in zoologic companion animal species

The treatment and prevention of pain in zoologic companion animals is difficult because of the lack of data available on the safety and efficacy of analgesics. Pharmacokinetic (PK)-pharmacodynamic (PD) studies integrate changes in drug concentrations and changes in the drug's effect. All experimental studies assessing the PDs of analgesics have limitations in animals, but the data provided by experimental studies are valuable in designing dosages. Placebo-controlled, randomized, and blinded clinical trials provide the best PK and PD data, but are rarely performed in major veterinary species because of the number of animals required for the study, lack of preliminary PK and PD data in a given species, species-specific differences in PK and PD, and ethical and toxicologic concerns. The usefulness and limitations as well as considerations for interpreting PK, PD, and controlled clinical studies are discussed. An example of allometric analysis of buprenorphine in mammals is also included.

Pharmacokinetics of acetaminophen, codeine, and the codeine metabolites morphine and codeine-6-glucuronide in healthy Greyhound dogs

The purpose of this study was to determine the pharmacokinetics of codeine and the active metabolites morphine and codeine-6-glucuronide after i.v. codeine administration and the pharmacokinetics of acetaminophen (APAP), codeine, morphine, and codeine-6-glucuronide after oral administration of combination product containing acetaminophen and codeine to dogs. Six healthy Greyhound dogs were administered 0.734 mg/kg codeine i.v. and acetaminophen (10.46 mg/kg mean dose) with codeine (1.43 mg/kg mean dose) orally. Blood samples were collected at predetermined time points for the determination of codeine, morphine, and codeine-6-glucuronide plasma concentrations by LC/MS and acetaminophen by HPLC with UV detection. Codeine was rapidly eliminated after i.v. administration (T(1/2) = 1.22 h; clearance = 29.94 mL/min/kg; volume of distribution = 3.17 L/kg) with negligible amounts of morphine present, but large amounts of codeine-6-glucuronide (C(max) = 735.75 ng/mL) were detected. The oral bioavailability of codeine was 4%, morphine concentrations were negligible, but large amounts of codeine-6-glucuronide (C(max) = 1952.86 ng/mL) were detected suggesting substantial first pass metabolism. Acetaminophen was rapidly absorbed (C(max) = 6.74 microg/mL; T(max) = 0.85 h) and eliminated (T(1/2) = 0.96 h). In conclusion, the pharmacokinetics of codeine was similar to other opioids in dogs with a short half-life, rapid clearance, large volume of distribution, and poor oral bioavailability. High concentrations of codeine-6-glucuronide were detected after i.v. and oral administration.

Development of an invasively monitored porcine model of acetaminophen-induced acute liver failure

BACKGROUND

The development of effective therapies for acute liver failure (ALF) is limited by our knowledge of the pathophysiology of this condition, and the lack of suitable large animal models of acetaminophen toxicity. Our aim was to develop a reproducible invasively-monitored porcine model of acetaminophen-induced ALF.

METHOD

35kg pigs were maintained under general anaesthesia and invasively monitored. Control pigs received a saline infusion, whereas ALF pigs received acetaminophen intravenously for 12 hours to maintain blood concentrations between 200-300 mg/l. Animals surviving 28 hours were euthanased.

RESULTS

Cytochrome p450 levels in phenobarbital pre-treated animals were significantly higher than non pre-treated animals (300 vs 100 pmol/mg protein). Control pigs (n = 4) survived 28-hour anaesthesia without incident. Of nine pigs that received acetaminophen, four survived 20 hours and two survived 28 hours. Injured animals developed hypotension (mean arterial pressure; 40.8 +/- 5.9 vs 59 +/- 2.0 mmHg), increased cardiac output (7.26 +/- 1.86 vs 3.30 +/- 0.40 l/min) and decreased systemic vascular resistance (8.48 +/- 2.75 vs 16.2 +/- 1.76 mPa/s/m3). Dyspnoea developed as liver injury progressed and the increased pulmonary vascular resistance (636 +/- 95 vs 301 +/- 26.9 mPa/s/m3) observed may reflect the development of respiratory distress syndrome.Liver damage was confirmed by deterioration in pH (7.23 +/- 0.05 vs 7.45 +/- 0.02) and prothrombin time (36 +/- 2 vs 8.9 +/- 0.3 seconds) compared with controls. Factor V and VII levels were reduced to 9.3 and 15.5% of starting values in injured animals. A marked increase in serum AST (471.5 +/- 210 vs 42 +/- 8.14) coincided with a marked reduction in serum albumin (11.5 +/- 1.71 vs 25 +/- 1 g/dL) in injured animals. Animals displayed evidence of renal impairment; mean creatinine levels 280.2 +/- 36.5 vs 131.6 +/- 9.33 mumol/l. Liver histology revealed evidence of severe centrilobular necrosis with coagulative necrosis. Marked renal tubular necrosis was also seen. Methaemoglobin levels did not rise >5%. Intracranial hypertension was not seen (ICP monitoring), but there was biochemical evidence of encephalopathy by the reduction of Fischer's ratio from 5.6 +/- 1.1 to 0.45 +/- 0.06.

CONCLUSION

We have developed a reproducible large animal model of acetaminophen-induced liver failure, which allows in-depth investigation of the pathophysiological basis of this condition. Furthermore, this represents an important large animal model for testing artificial liver support systems.

Interpretation of liver enzymes

Abnormalities in liver enzymes are commonly encountered in clinical practice. Knowledgeable assessment requires a full understanding of their pathophysiology and provides an important means of detecting the earliest stage of many serious hepatobiliary disorders. The best interpretations are achieved using an integrated approach, combining historical and physical findings with routine and specialized diagnostic procedures and imaging studies. Information in this article provides the foundation, by example, for understanding the reliability of single time point enzyme measurements, the value of sequential measurements, the importance of interpreting the activity of enzymes in light of their half life and tissue of origin, and the influence of the induction phenomenon.

Nonsteroidal anti-inflammatory drugs in cats: a review

OBJECTIVE

To review the evidence regarding the use of nonsteroidal anti-inflammatory drugs (NSAIDs) in cats.

DATABASES USED

PubMed, CAB abstracts.

CONCLUSIONS

Nonsteroidal anti-inflammatory drugs should be used with caution in cats because of their low capacity for hepatic glucuronidation, which is the major mechanism of metabolism and excretion for this category of drugs. However, the evidence presented supports the short-term use of carprofen, flunixin, ketoprofen, meloxicam and tolfenamic acid as analgesics in cats. There were no data to support the safe chronic use of NSAIDs in cats.

The molecular toxicology of acetaminophen

The history of the development of the analgestic drug acetaminophen is reviewed with an emphasis on the characteristics of its overdose toxicity. The P450-catalyzed oxidation of acetaminophen generates a reactive electrophile that binds covalently to proteins. Involvement of specific P450 enzymes in acetaminophen toxicity can be probed by experiments with knock-out mice. The identification of specific target proteins may help to clarify the mechanism of acetaminophen hepatoxocity.

The use of cholecystokinin as an adjunctive treatment for toxin ingestion

STUDY OBJECTIVE

To determine if pharmacologic trapping of ingested toxins in the stomach using cholecystokinin (CCK) in addition to activated charcoal (AC) decreases the absorption of ingested toxins.

METHODS

We performed a two-phase study that was prospective, randomized, blinded, and placebo-controlled, using a subtoxic acetaminophen (APAP) animal model. Eight adult beagle dogs were studied to detect a 20% decrease in 4h APAP levels with a power of 80%. A control arm using APAP at 100 mg/kg without AC or CCK was first performed. APAP levels were drawn at 0.5, 1, 1.5, 2, 4, 8, and 24 h. This was repeated in a CCK dose finding phase using a 60-min CCK infusion (4 vs. 8 pmol/kg/min) starting at 30 min post-APAP ingestion. Once the optimal CCK dose was established, animals in the treatment phase received AC and a 1 h infusion of CCK (vs. placebo). The efficacy of CCK when started at 30 and 60 min post-APAP ingestion was tested.

RESULTS

In the dose finding arm 8 pmol/kg/min was well tolerated and also reduced maximum APAP levels by a mean of 49% from control. This dose was then used for the treatment phase. Four-hour APAP levels, maximum APAP levels, and area under the curve (AUC) were measured. No significant differences were found between placebo and CCK arms at either the 30 or 60 min postingestion interventions.

CONCLUSIONS

In this model, CCK infusion did not decrease the absorption of APAP. Adding charcoal to the model overcame the suggested beneficial effect of CCK alone in the dosing arm.

S-adenosylmethionine (SAMe) in a feline acetaminophen model of oxidative injury

S-adenosylmethionine (SAMe) is reported to have hepatoprotective and antioxidant functions. Acetaminophen (paracetamol) was used to induce oxidative damage in cats, and to then determine the effect of SAMe treatment on erythrocyte morphology, PCV, liver histopathology, thiobarbituate reacting substances (TBARS), reduced glutathione (GSH), and oxidised glutathione (GSSG). Cats receiving acetaminophen had a significant increase in methemoglobin and Heinz body production. A significant effect for the interaction of time and treatment was found for Heinz body production and changes in PCV. No significant changes were found in blood or hepatic TBARS. Blood GSH increased significantly in all cats, while the blood GSH:GSSG ratio tended to increase the most in cats given acetaminophen only. The hepatic GSH:GSSG ratio tended to increase in cats given SAMe and decrease in cats given acetaminophen, but this effect was not significant. SAMe protected erythrocytes from oxidative damage by limiting Heinz body formation and erythrocyte destruction and maybe useful in treating acetaminophen toxicity.

Urine sulfated and nonsulfated bile acids as a diagnostic test for liver disease in cats

Urine bile acid (UBA) tests reflecting "average" serum bile acid (SBA) concentrations may have greater practical utility than paired SBA samples in cats. This study evaluated whether urine sulfated bile acids (USBAs), urine nousulfated bile acids (UNSBAs), or a combined approach had a clinical utility equivalent to SBAs. Routine serum biochemistry tests, SBA concentrations, and urine samples were collected from 54 cats with hepatobiliary disease, 17 cats with nonhepatic disorders, and 8 healthy cats. UBAs were measured by a quantitative enzymatic colorimetric method, and results were normalized with urine creatinine (UCr) concentrations. Significantly higher values occurred in cats with liver disease than in cats without liver disease for USBA : UCr, UNSBA:UCr, and (USBA and UNSBA) : UCr, P < .05 each. UBA tests with diagnostic performance (sensitivity [SS], specificity [SP], and positive and negative predictive values [PV+ and PV-]) equivalent to SBAs were the UNSBA : UCr and the combined test (SS: 87, 87 versus 85; SP: 88, 88 versus 88; PV+: 96, 96 versus 96; PV-: 68, 65 versus 68; UNSBA : UCr, [USBA, and UNSBA]: UCr versus SBA, respectively). Clinical applications of the UNSBA : UCr or the combined (USBA and UNSBA) : UCr test should be useful as convenient diagnostic tests for identifying cats with liver disease and high SEA concentrations.

Acetaminophen toxicosis in a Dalmatian

An 11-year-old, spayed female Dalmatian was presented with suspected acetaminophen toxicosis. The dog was severely depressed. Methemoglobinemia, facial edema, and hemoglobinuria responded to treatment with intravenous fluids, N-acetylcysteine, ascorbic acid, and sodium bicarbonate. There was no clinical evidence of hepatic damage typical of acetaminophen toxicity in the dog.

S-adenosyl-L-methionine (SAMe) for the treatment of acetaminophen toxicity in a dog

An 8-month-old, spayed female Shetland sheepdog presented 48 hours after ingesting acetaminophen (1 gm/kg body weight). On presentation, the dog was laterally recumbent and hypovolemic. The dog had brown mucous membranes, severe Heinz-body hemolytic anemia, bleeding tendencies, and a red blood cell (RBC) glutathione (GSH) concentration that was 10% of reference values, despite a regenerative erythroid response. Treatment with s-adenosyl-l-methionine (SAMe) as a GSH donor successfully rescued this dog, despite the animal's late presentation after drug ingestion. A loading dose (40 mg/kg body weight) of a stable SAMe salt per os was followed by a maintenance dose (20 mg/kg body weight) sid for 7 days. Additional therapeutic interventions included an intravenous (i.v.) infusion of one unit of packed RBCs (on admission), i.v. fluid support (3 days), and famotidine (7 days) to reduce gastric acidity. Sequential assessment of RBC GSH concentrations and RBC morphology documented response to antidote administration within 72 hours. This case suggests that SAMe may provide a therapeutic option for treatment of acetaminophen toxicosis in dogs capable of retaining an orally administered antidote and maintaining adequate hepatic function for metabolism of SAMe to its thiol substrates.

Role of CCR2 in macrophage migration into the liver during acetaminophen-induced hepatotoxicity in the mouse

The biological effects of monocyte chemoattractant protein (MCP) 1 are mediated by binding to C-C chemokine receptor (CCR) 2. In the present studies, we used CCR2 knockout (CCR2-/-) mice to examine the role of MCP-1 in acetaminophen-induced macrophage accumulation in the liver, expression of inflammatory cytokines, and hepatotoxicity. We found that hepatic expression of CCR2 and MCP-1 was increased 10-fold and 20-fold, respectively, 12 to 72 hours after administration of acetaminophen to wild-type mice. Expression of these proteins was localized in centrilobular regions of the liver. Whereas MCP-1 was expressed by both hepatocytes and macrophages, CCR2 was identified in inflammatory macrophages. F4/80 is a marker of mature macrophages expressed in large quantities by Kupffer cells. In wild-type mice, a 75% decrease in F4/80-positive macrophages was observed 24 to 48 hours after administration of acetaminophen. In contrast, expression of macrosialin (CD68), a marker of activated macrophages, increased 2-fold 24 to 72 hours after administration of acetaminophen and was associated with inflammatory cells. Although there was a decrease in the overall severity of inflammation and in the number of macrosialin-positive macrophages 72 hours after administration of acetaminophen in CCR2-/- mice, the number of F4/80-positive cells did not change. Loss of CCR2 was also found to alter acetaminophen-induced expression of tumor necrosis factor alpha, monocyte chemoattractant protein 3, and KC/gro. However, the overall outcome of acetaminophen-induced hepatic injury was not affected. In conclusion, these data indicate that MCP-1 and CCR2 contribute to the recruitment of a subset of activated macrophages into the liver during acetaminophen-induced hepatotoxicity that may be important in resolution of tissue injury.

Uncertainty factors for chemical risk assessment: interspecies differences in glucuronidation

For the risk assessment of effects other than cancer, a safe daily intake in humans is generally derived from a surrogate threshold dose (e.g. NOAEL) in an animal species to which an uncertainty factor of 100 is usually applied. This 100-fold is to allow for possible interspecies (10-fold) and interindividual (10-fold) differences in response to a toxicant, and incorporates toxicodynamic and toxicokinetic aspects of variability. The current study determined the magnitude of the interspecies differences in the internal dose of compounds for which glucuronidation is the major pathway of metabolism in either humans or in the test species. The results showed that there are major interspecies differences in the nature of the biological processes which influence the internal dose, including the route of metabolism, the extent of presystemic metabolism and enterohepatic recirculation. The work presented does not support the refinement of the interspecies toxicokinetic default to species- and pathway-specific values, but demonstrates the necessity for risk assessments to be carried out using quantitative chemical-specific data which define the fundamental processes which will influence the internal dose of a chemical (toxicokinetics), or the interaction of toxicant with its target site (toxicodynamics).

Acetaminophen UDP-glucuronosyltransferase in ferrets: species and gender differences, and sequence analysis of ferret UGT1A6

The principal objective of this study was to determine whether ferrets glucuronidate acetaminophen more slowly compared with other species, and if so investigate the molecular basis for the difference. Acetaminophen-UDP-glucuronosyltransferase (UGT) activities were measured using hepatic microsomes from eight ferrets, four humans, four cats, four dogs, rat, mouse, cow, horse, monkey, pig and rabbit. Gender differences between male and female ferret livers were explored using enzyme kinetic analysis. Immunoblotting of microsomal proteins was also performed using UGT-specific antibodies. Finally, the exon 1 region of UGT1A6, a major acetaminophen-UGT, was sequenced. Glucuronidation of acetaminophen was relatively slow in ferret livers compared with livers from all other species except cat. Gender differences were also apparent, with intrinsic clearance (Vmax/Km) values significantly higher in male compared with female ferret livers. Furthermore, Vmax values correlated with densitometric measurements of two protein bands identified with a UGT1A subfamily-specific antibody. No deleterious mutations were identified in the exon 1 or flanking regions of the ferret UGT1A6 gene. In conclusion, like cats, ferret livers glucuronidate acetaminophen relatively slowly. However, unlike cats, in which UGT1A6 is encoded by a pseudogene and dysfunctional, there are no defects in the ferret UGT1A6 gene which could account for the low activity.

Animal models of fulminant hepatic failure: need to test liver support devices

Fulminant hepatic failure is one of the most dramatic entities in clinical medicine, but experimental studies of its pathogenesis, evolution and treatment have, so far been limited by the lack of satisfactory animal models for testing new supportive treatment options. The variable aetiology, complex pathogenetic mechanisms and inconstant clinical evolution of human fulminant hepatic failure make it particularly difficult to establish an "ideal fulminant hepatic failure animal model" suitable for all studies: it is no longer mandatory to develop one single model serving all possible scientific needs, but the use of a specific model for a specific issue is more advisable. The currently available animal models of fulminant hepatic failure are the hepatotoxic, surgical and combined hepatotoxic and surgical models. From a general point of view, surgical models may be particularly appropriate for studying the consequences of hepatic necrosis on cerebral oedema. The anhepatic model is very useful for validating new supportive measures to bridge the period between the onset of fulminant hepatic failure and the time at which a suitable organ becomes available and, despite the many difficulties involved in their development, hepatotoxic models may still be useful for mimicking an acetaminophen overdose. The efficacy and reproducibility of a liver support system can be demonstrated by means of preclinical experimental models that mimic the specific application required in humans as closely as possible.

Biotransformation Enzymes as Determinants of Xenobiotic Toxicity in Domestic Animals

After coming in contact with living organisms, the majority of foreign compounds undergo a number of chemical reactions known as biotransformations. These are performed by hepatic and extra-hepatic enzyme systems and usually yield more polar derivatives, referred to as 'metabolites', which may leave the body via the urinary and biliary routes or be excreted in animal products such as milk and eggs. Biotransformation does not always imply detoxification because in certain instances metabolites will be produced that are capable of reacting with tissue macromolecules or acquiring toxic properties different to or greater than those of the parent molecule. In this review, which is focused on domestic animals, the role played by oxidative, reductive, hydrolytic and conjugative biotransformation enzymes in the activation/detoxification of xenobiotics is examined. The relationship between extra-hepatic metabolism and target organ toxicity as well as the action of rumen microflora on feed additives, phytotoxins, and pesticides are then discussed. Some of the most important metabolic-based species-related susceptibilities to different poisons, and the influence of enzyme inducers or inhibitors on xenobiotic toxicity and drug safety are also reviewed.

Effect of a bioflavonoid dietary supplement on acetaminophen-induced oxidative injury to feline erythrocytes

OBJECTIVE

To determine the effect of a commercial bioflavonoid antioxidant on acetaminophen-induced oxidative injury to feline erythrocytes.

DESIGN

Randomized controlled study.

ANIMALS

45 healthy age-matched cats.

PROCEDURE

Cats were assigned to 3 experimental groups. Groups 1 and 3 received a bioflavonoid antioxidant (10 mg/d) orally for 2 weeks. Groups 2 and 3 received an oxidative challenge with acetaminophen (90 mg/kg [41 mg/lb] of body weight, PO) on day 7. Packed cell volume, percentage of erythrocytes with Heinz bodies, blood methemoglobin concentration, and blood reduced and oxidized glutathione concentrations were determined at various times during the 2-week study period.

RESULTS

Adverse effects were not associated with bioflavonoid antioxidant administration alone. Acetaminophen administration resulted in a significant increase in methemoglobin concentration in groups 2 and 3; differences were not detected between these groups. Heinz body concentrations in groups 2 and 3 increased after acetaminophen administration; however, the increase in cats that received the antioxidant was significantly less than in group-2 cats. Total blood glutathione concentrations did not change significantly in groups 2 and 3 after acetaminophen administration; however, ratio of reduced to oxidized glutathione concentration increased significantly after administration in group-2 cats, compared with group-3 cats.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of bioflavonoid antioxidants to cats at risk for oxidative stress may have a beneficial effect on their ability to resist oxidative injury to erythrocytes.

Molecular genetic basis for deficient acetaminophen glucuronidation by cats: UGT1A6 is a pseudogene, and evidence for reduced diversity of expressed hepatic UGT1A isoforms

The domestic cat has a significantly lower capacity to glucuronidate planar phenolic xenobiotics compared with most other mammalian species. The aim of this study was to determine the mechanistic basis for this anomaly. Current knowledge of the substrate specificity of UDP-glucuronosyltransferase (UGT) isoforms indicates that the cat may either lack or poorly express UGT1A6. Initially, a novel cloning technique was used to identify UGT1A genes expressed in cat liver. Only two unique UGT1A isoforms could be discriminated. The first (28%, of clones) was most homologous to UGT1A1 (the bilirubin-UGT), while the second (72% of clones) showed homology to several isoforms, but could not be unambiguously identified, and was designated cat UGT1A02. Southern blot analysis confirmed the presence of a single UGT1A6-homologous region in the cat genome. Subsequent cloning and sequencing of the entire UGT1A6 exon 1 coding region revealed five deleterious genetic mutations. Identical mutations were found by sequencing of UGT1A6 exon 1 from five other unrelated cats. Four of these five genetic lesions were also identified in the UGT1A6 exon 1 region of a margay (Leopardus wiedii). Finally, RT-PCR of liver mRNA from four different cats confirmed the presence of UGT1A1 and UGT1A02, but not UGT1A6. In conclusion, UGT1A6 is a pseudogene in the domestic cat and in at least one other phylogenetically related species. Furthermore, cats appear to have a less diverse pattern of UGT1A isoform expression compared with other species. Such differences most likely reflect the highly carnivorous diet of Feliform species and resultant minimal exposure to phytoalexins.