Anticoagulant rodenticide poisoning in farmed Patagonian mara (Dolichotis patagonum).

BACKGROUND: Anticoagulant rodenticide (AR) poisoning was diagnosed in 3 Patagonian maras (Dolichotis patagonum) raised in the mara farm in Thailand. To date, there have been no reports of maras with diagnosed AR poisoning. CASE PRESENTATION: The first clinical sign of the sickening maras was anorexia. Fifteen from 50 maras were dead over a 3-5 day period after the clinical signs had occurred. Positive results to AR were detected in all of the maras' liver specimens by screening test using thin layer chromatography and spectrophotometry methods. Supportive therapy was selected for the treatment of the 35 surviving maras. During the follow - up observation period of 12 months, all of the surviving maras were healthy and no reproductive loss. CONCLUSIONS: This is the first report on suspected AR poisoning in maras in Thailand based on history taking, clinical signs, gross pathology lesions and chemical analysis. AR poisoning in the present report is possibly from contaminated animal food. Therefore, quality control of food should be fastidious when feeding maras.

Bromadiolone may cause severe acute kidney injury through severe disorder of coagulation: a case report.

BACKGROUND: Bromadiolone is a wide-use long-acting anticoagulant rodenticide known to cause severe coagulation dysfunction. At present, there have been no detailed reports of acute kidney injury (AKI) resulting from bromadiolone poisoning. CASE PRESENTATION: A 27-year-old woman was admitted to the hospital due to severe coagulopathy and severe AKI. Coagulation test revealed a prothrombin time exceeding 120 s and an international normalized ratio (INR) greater than 10. Further examination for coagulation factors showed significantly reduced level of factors II, VII, IX and X, indicating a vitamin K deficiency. The AKI was non-oliguric and characterized by gross dysmorphic hematuria. Following the onset of the disease, the patient's serum creatinine rose from 0.86 to 6.96 mg/dL. Suspecting anticoagulant rodenticide poisoning, plasma bromadiolone was identified at a concentration of 117 ng/mL via gas chromatography/mass spectrometry. All other potential causes of AKI were excluded, except for the presence of a horseshoe kidney. The patient's kidney function fully recovered after the coagulopathy was corrected with high doses of vitamin K and plasma transfusion. At a follow-up 160 days post-discharge, the coagulation function had normalized, and the serum creatinine had returned to 0.51 mg/dL. CONCLUSION: Bromadiolone can induce AKI through a severe and prolonged coagulation disorder. Kidney function can be restored within days following treatment with high-dose vitamin K1.

Assessing the clinical efficacy of low-volume therapeutic plasma exchange in achieving recovery from acute liver failure induced by yellow phosphorous poisoning.

BACKGROUND: Acute liver failure (ALF) following yellow phosphorous (YP) ingestion is similar to acetaminophen-induced ALF and it has become a public concern in our region. This study assessed low volume therapeutic plasma exchange (LV-TPE) efficacy in improving the transplant free survival in YP poisoning. METHODS: Adult patients with toxicology reports of YP and ALF requiring critical care were included in the study. LV-TPE was planned for three consecutive days and three more if required. Performed 1.3 to 1.5 plasma volume replacing with 0.9% normal saline, 5% human albumin solution, and fresh frozen plasma based on ASFA 2019 criteria. MELD score, laboratory parameters, LV-TPE details were captured. The study end point was clinical outcome of the patients. RESULTS: Among 36 patients, 19 underwent LV-TPE and 17 opted out of LV-TPE and they were included as a control arm. The MELD score was 32.64 ± 8.05 and 37.83 ± 9.37 in both groups. There were 13 survivors in LV-TPE group leading to a 68.42% reduction in mortality. The coagulation and biochemical parameters showed a significant percentage change after LV-TPE. Refractory shock, delay in initiating procedure and acidosis were independent predictors of mortality. CONCLUSION: A well-timed LV-TPE improves the survival of patients with ALF due to YP poisoning.

Second-Generation Anticoagulant Rodenticide Toxicosis in a Wild Carnaby's Cockatoo (Zanda latirostris).

A wild male Carnaby's cockatoo (Zanda latirostris) was presented to a veterinary hospital after falling from a tree. The bird showed few clinical signs during the first days of hospitalization. On Day 4, the cockatoo showed excessive hemorrhage at a venipuncture site, epistaxis, and significant anemia (packed cell volume, 15%). The cockatoo was euthanized due to ongoing blood loss, weakness, and inappetence. Liver concentrations of brodifacoum (0.439 mg/kg wet weight) and difenacoum (0.033 mg/kg wet weight) had a total anticoagulant rodenticide concentration of 0.472 mg/kg wet weight and were above the threshold for toxicity for many avian species. To the authors' knowledge, this is the first time that anticoagulant rodenticide intoxication has been identified in a wild Australian psittacine species.

High prevalence of anticoagulant rodenticide exposure in New England Fishers (Pekania pennanti).

Anticoagulant rodenticides (ARs) are increasingly recognized as a threat to non-target species including native wildlife. Fishers (Pekania pennanti) are generally considered deep forest inhabitants that are not expected to have high exposure to ARs. To evaluate the distribution and levels of ARs in fishers, we analyzed liver samples from fisher carcasses (N = 45) opportunistically trapped across Vermont and New Hampshire between 2018 and 2019. Liquid chromatography-mass spectrometry was used to detect and quantify 11 different ARs in the liver tissue of each fisher at the time of trapping. All but one sample analyzed were positive for exposure to ARs, and 84% were positive for more than one type of AR. The most prevalent ARs detected were diphacinone (96%) and brodifacoum (80%). No samples had detectable levels of coumachlor, coumafuryl, difenacoum, pindone, or warfarin. These results are mostly consistent with findings for fishers in California as well as with a variety of rodent specializing avifauna throughout the Northeast USA but, show a higher prevalence of exposure and a different distribution of AR types than other studies. These results help establish current baseline exposure to ARs in fishers in the Northeast USA and suggest that ARs could pose a threat to wild mesocarnivore species in this region.

Nitrobenzoxadiazole derivatives of the rat selective toxicant norbormide as fluorescent probes for live cell imaging.

Norbormide [5-(α-hydroxy-α-2-pyridylbenzyl)-7-(α-2-pyridylbenzylidene)-5-norbornene-2,3-dicarboximide] (NRB, 1), an existing but infrequently used rodenticide, is known to be uniquely toxic to rats, but relatively harmless to other rodents and mammals. As a vasoactive agent, NRB induces a species-specific vasocontractile effect that is restricted to the peripheral arteries of the rat. Despite the precise mechanisms behind this phenomenon having yet to be fully clarified, it is postulated that the molecular target of NRB could be located within the plasma membrane of rat peripheral artery myocytes (e.g. rat caudal artery myocytes). As such, the primary objective of this study was to develop a fluorescently labelled derivative of NRB to investigate its subcellular distribution/localization in both NRB-sensitive (freshly isolated rat caudal artery myocytes, FIRCAMs) and NRB-insensitive (human hepatic stellate, LX2) cells. Of the examples prepared, lead structure endo-NRB-NBD-bPA subsequently demonstrated retention of the parent toxicant's pharmacological profile (in terms of its ability to induce both a vasocontractile response in rat caudal artery rings in vitro, and a lethal end-point in rats in vivo). Endo-NRB-NBD-bPA was also shown to be significantly less permeable (an integral feature in the design of fluorescent probes targeting cell-surface receptors) to both LX2 cells and FIRCAMs. Disappointingly, no fluorescence could be observed on the plasma membrane of FIRCAMs stained with endo-NRB-NBD-bPA.

Comparative pharmacokinetics of difethialone stereoisomers in male and female rats and mice: development of an intra- and inter-species model to predict the suitable formulation mix.

The ecotoxicity of anticoagulants used for rodent pests' management is a major concern, particularly with second generation anticoagulants, which are more persistent in the body of rodents and therefore more likely to cause secondary exposure in their predators. One of the solutions envisaged to mitigate this risk is to use stereoisomers of these anticoagulants, each of which has particular pharmacokinetics. However, the few studies published to date have considered only one species and one sex. Here, we study the pharmacokinetics of the 4 stereoisomers of 3.4 mg/kg of difethialone in rats (Rattus norvegicus) and 3 mg/kg in mice (Mus musculus) in both sexes and propose a model to choose the optimal stereoisomer efficacy/ecotoxicity mixture for the management of all these animals. Our results show that while the most persistent stereoisomer (E3-cis) is common to both species and sexes, the pharmacokinetics of the other stereoisomers show marked differences between sexes and species. Thus, the area under curve (AUC) of E4-trans in male rats is four times lower than in females or mice, making it a priori unusable in male rats. Conversely, our modeling seems to show that the E1-trans stereoisomer seems to offer the best compromise AUC persistence. In conclusion, we highlight that studies on anticoagulants must necessarily integrate research on the effect of gender and species both on efficacy and with regard to the ecotoxicity of these molecules.

Anticoagulant rodenticide use in oil palm plantations in Southeast Asia and hazard assessment to non-target animals.

Anticoagulant rodenticides (ARs) are used worldwide for the control of rodent pests and are the main method of control of rat pest populations in agricultural areas. The main aim of this review is to discuss the risk of ARs to non-target wildlife in oil palm areas in Southeast Asia, mainly Indonesia and Malaysia. We discussed AR use in oil palm areas and toxicities of ARs on target and non-target animals. We also reviewed published literature on wildlife species reported in oil palm areas in Southeast Asia and utilizing this information, we assessed the hazard risk of ARs to non-target wildlife in oil palm plantations. ARs are a secondary exposure hazard to rodent-consuming mammalian carnivores, such as leopard cats and civets, and rodent-consuming raptors, such as barn owls. Consumption of dead poisoned prey puts scavengers, such as water monitors, at high risk for AR exposure. Domestic livestock and granivorous birds are at high risk for AR exposure via primary exposure to toxic bait, while omnivores such as macaques and wild pigs are at moderate risk for both primary and secondary exposure to ARs. The effects of ARs on barn owls have been well studied in the field and in laboratory secondary toxicity studies. Thus, the nest-box occupancy and reproductive parameters of local barn owl populations can be monitored as an indicator of the AR exposure level in the area. CLINICAL TRIALS REGISTRATION: No clinical trials were involved in this study.

Distribution of non-synonymous Vkorc1 mutations in roof rats (Rattus rattus) in France and in Spain - consequences for management.

Rodent control is mainly done using anticoagulant rodenticides leading to the death of rodents through internal bleeding by targeting the VKORC1 protein. However, mutations in VKORC1 can lead to resistance to anticoagulant rodenticides that can cause treatment failure in the field. This study provides the first insight into the distribution, frequency and characterization of Vkorc1 mutations in roof rats (Rattus rattus) in France and in three administrative areas of Spain. The roof rat is present in France while it was thought to have almost disappeared with the expansion of the brown rat. Nevertheless, it has been found mainly in maritime areas. 151 roof rats out of 219 tested presented at least one missense mutation in the coding sequences of Vkorc1 gene (i.e. 69.0% of the rat). Nine Vkorc1 genotypes were detected (Y25F, A26P, R40G, S57F, W59C, W59R, H68N, Y25F/K152T and Y25F/W59R. Biochemical characterization of the consequences of these different genotypes proved that these various genotypes did not induce severe resistance to anticoagulant rodenticides. Even if many mutations of the Vkorc1 gene are present in roof rat populations in France, their management may be based in a first approach, considering the low levels of resistance induced, on the use of first-generation anticoagulants less dangerous for wildlife. The use of second-generation may be considered when treatment failure is observed or when bait consumption is limited.

Changing trends in the profile of rodenticide poisoning.

Background: Deliberate self-poisoning (DSP) is one of the leading causes of mortality and morbidity, with rodenticides being common compounds used by many victims. However, comprehensive data regarding the spectrum and outcome of rodenticide poisoning is scant. Method: This retrospective study was conducted in the Emergency Department (ED) of a large tertiary care hospital in South India between January 2017 and December 2018. All patients with deliberate consumption of rodenticides were included in the analysis. Results: During the study period, 1802 patients presented with DSP, among which 145 (8%) consumed rodenticide compounds. The mean (SD) age was 27.9 (10.7) years. Young adults (16-30 years) comprised 73% (106/145) of the study population. The majority (87%) were triaged as priority 2, while 10% were triaged as priority 1. Common rodenticide compounds consumed were yellow phosphorous (57%: 82/145), coumarins (12%: 17/145), zinc phosphide (19%: 27/145), and aluminum phosphide (1%: 1/145). A significant proportion of patients (18.6%) were under the influence of alcohol. Among the 73 males, 25 (34.2%) gave a history of co-consumption of alcohol. There was a history of previous DSP attempts in 6%. The majority (68%) of the patients were discharged alive from the hospital, and the in-hospital mortality rate was 9%. Age >30 years (adjusted OR: 2.2; 95% CI: 1.00-5.05; p value: 0.04) was an independent predictor of poor outcome. Conclusion: Rodenticide compound consumption for DSP is prevalent in young adults and is associated with significant mortality, especially with yellow phosphorous poisoning. The current trend in our country of the increasing use of highly fatal phosphorous compounds over the innocuous coumarin derivatives is a cause of grave concern.

Urban rat exposure to anticoagulant rodenticides and zoonotic infection risk.

Anticoagulant rodenticides (ARs) deployed to control rodent pest populations can increase the risk of pathogen infection for some wildlife. However, it is unknown whether ARs also increase infection risk for target rodents, which are common hosts for zoonotic (animal-to-human transmitted) pathogens. In this study, we tested whether rats exposed to ARs were more likely to be infected with zoonotic pathogens, specifically Leptospira spp. or Escherichia coli, after controlling for known predictors of infection (i.e. sex, age, body condition). We collected biological samples from 99 rats trapped in Chicago alleys and tested these for Leptospira infection, E. coli shedding and AR exposure. We found that rats that had been exposed to ARs and survived until the time of trapping, as well as older rats, were significantly more likely to be infected with Leptospira spp. than other rats. We found no significant association between E. coli shedding and any predictors. Our results show that human actions to manage rats can affect rat disease ecology and public health risks in unintended ways, and more broadly, contribute to a growing awareness of bidirectional relationships between humans and natural systems in cities.

Lethal coagulopathy resulting from the consumption of contaminated synthetic cannabinoids: the story of a public health crisis.

In March 2018, Illinois saw the outbreak of an unprecedented public health crisis, which manifested as the development of a potentially lethal coagulopathy associated with the consumption of synthetic cannabinoids. This outbreak impacted a reported 174 patients, and was responsible for the deaths of five patients. While events unfolded, it was uncovered that the coagulopathy was not caused directly by the consumption of synthetic cannabinoids, but by the contamination of these products with Brodifacuom, bromadiol and difenacoum, potent Vitamin K antagonists that are the active ingredient in most rodenticides. This article chronicles the first reported instance of clinically significant Long Acting Anticoagulant Rodenticide poisoning on such a widespread and uniform scale, and examines the challenges posed to the providers and Public Health authorities tasked with the management of this outbreak. Crisis preparedness determines mitigation, response and recovery during trying times. It is prudent that healthcare agencies engage in collective measures to establish preparedness plans and build up their capacity to respond to health-related crises such as the one faced by Illinois in early 2018. By examining the solutions developed to tackle each unique challenge, the objective of this article is to lay a framework for action and response to similar public health crises.

The VKORC1 ER-luminal loop mutation (Leu76Pro) leads to a significant resistance to warfarin in black rats (Rattus rattus).

Well-known 4-hydroxycoumarin derivatives, such as warfarin, act as inhibitors of the vitamin K epoxide reductase (VKOR) and are used as anticoagulants. Mutations of the VKOR enzyme can lead to resistance to those compounds. This has been a problem in using them as medicine or rodenticide. Most of these mutations lie in the vicinity of potential warfarin-binding sites within the ER-luminal loop structure (Lys30, Phe55) and the transmembrane helix (Tyr138). However, a VKOR mutation found in Tokyo in warfarin-resistant rats does not follow that pattern (Leu76Pro), and its effect on VKOR function and structure remains unclear. We conducted both in vitro kinetic analyses and in silico docking studies to characterize the VKOR mutant. On the one hand, resistant rats (R-rats) showed a 37.5-fold increased IC50 value to warfarin when compared to susceptible rats (S-rats); on the other hand, R-rats showed a 16.5-fold lower basal VKOR activity (Vmax/Km). Docking calculations exhibited that the mutated VKOR of R-rats has a decreased affinity for warfarin. Molecular dynamics simulations further revealed that VKOR-associated warfarin was more exposed to solvents in R-rats and key interactions between Lys30, Phe55, and warfarin were less favored. This study concludes that a single mutation of VKOR at position 76 leads to a significant resistance to warfarin by modifying the types and numbers of intermolecular interactions between the two.

Rodenticide Poisoning: Critical Appraisal of Patients at a Tertiary Care Center.

IMPORTANCE: Rodenticide poisoning is a common occurrence in India. Of the different classes of rodenticides available, yellow phosphorus is considered highly toxic. There are scarce epidemiological data regarding the ingestion of yellow phosphorus in the subcontinent. OBJECTIVES: This study aimed to identify the clinical profile of rodenticide-poisoned patients and delineate mortality predictors. DESIGN: Prospective observational study. SETTING AND PARTICIPANTS: Study was conducted at the Department of Internal Medicine, Government Villupuram Medical College and Hospital. All adult inpatients with a history of rodenticide poison exposure were eligible participants. A total of 99 patients completed the study protocol. MAIN OUTCOME: Survival with or without morbidity and death. RESULTS: In all, 90.91% of patients consumed the paste formulation of rodenticide [yellow phosphorus (67.2%) and yellow phosphorus + zinc phosphide (24%)].The time to resuscitation showed significance to mortality. Survival rate among patients instituted gastric decontamination within 2 hours of exposure (97.87%) was significantly higher than those who were not (84.62%) (p = 0.033). The clinical picture revealed conspicuous absence of signs and symptoms during the first 24 hours. In all, 72.73% (n = 72) manifested with toxidrome after a lag period of 24-36 hours (range 18-72 hours). The dominant clinical manifestations included abdominal pain (52.53%), jaundice (22.21%), coagulopathy (15.15%), encephalopathy (10.10%), shock (10.10%), acute kidney injury (AKI; 7.08%), and multi-organ failure (17.17%). Laboratory data showed elevated aspartate transaminase (AST; 48.47%), alanine aminotransferase (ALT; 49.50%), bilirubin levels (22.21%), metabolic acidosis (10.12%), serum creatinine (7.08%), prothrombin time prolongation (PT/INR; 15.15%), and activated partial thromboplastin time (aPTT) (3.30%). The mortality was 9.1% (n = 9) of which 77.78% (n = 7) died of fulminant hepatic failure. The mean time for death was 4.22 days since exposure (range 2-8 days). CONCLUSION: Rodenticide poisoning in Southern India is dominated by yellow phosphorus. In this study, we identified delayed resuscitation, jaundice, hepatic encephalopathy, elevation of AST and ALT to >1000 IU/L, metabolic acidosis, and refractory shock as reliable predictors of bad outcome in this patient population. The common mode of death was fulminant hepatic failure. RELEVANCE: Rodenticide poisoning ranks second in mortality hierarchy at our institute, and systematic analysis of this patient population is an urgent need. HOW TO CITE THIS ARTICLE: Gopalakrishnan S, Kandasamy S, Iyyadurai R. Rodenticide Poisoning: Critical Appraisal of Patients at a Tertiary Care Center. Indian J Crit Care Med 2020;24(5):295-298.

Adherence to Long-Term Follow-Up of Patients with Life-Threatening, Inhaled Synthetic Cannabinoids-Associated Coagulopathy in Chicago.

A large-scale outbreak of life-threatening, inhaled synthetic cannabinoids (Spice/K2)-associated coagulopathy with bleeding complications was recently reported in Illinois. The causative agents were brodifacoum, difenacoum, and bromadiolone, potent, long-acting, 4-hydroxycoumarin anticoagulant rodenticides (LAAR) that were mixed with Spice/K2 products procured and then inhaled by the victims. We report on 3 poisoned patients who reside in underserved, socioeconomically disadvantaged neighborhoods of Chicago that were admitted and treated successfully at two inner-city, tertiary care hospitals in Chicago. The patients were discharged from the hospitals on daily long-term high-dose oral vitamin K1 (VK1), provided free of charge. However, 2 patients were lost to follow-up prior to safe discontinuation of oral VK1 therapy. The third patient was treated and followed successfully for 7 months when VK1 was discontinued. We conclude that prolonged oral VK1 therapy and follow-up of acute, life-threatening LAAR poisoning are variable and present challenges to healthcare providers. Appropriate practice guidelines to improve patient access and adherence to daily high-dose oral VK1 therapy and follow-up should be developed and implemented.

Bromadiolone poisoning leading to subarachnoid haemorrhage: A case report and review of the literature.

WHAT IS KNOWN AND OBJECTIVE: Many cases of rodenticide poisoning have been reported. Bromadiolone, often called a super-warfarin, is a second-generation dicoumarin rodenticide with long half-life. The main clinical manifestations of bromadiolone poisoning are excessive or inappropriate bleeding of skin mucosa, digestive tract and urinary tract. However, the phenomenon of central nervous system (CNS) toxicity is an uncommon medical emergency. We present a case of SAH and intracerebral haematoma mediated by bromadiolone intoxication, revealing that bromadiolone poisoning might cause intracerebral haematoma. CASE DESCRIPTION: A 44-year-old woman presented with skin mucosa haemorrhage and haematuresis initially. The patient developed lethargy, headache, nausea and vomiting. The toxicology test result revealed that the presence of bromadiolone in her blood. Coagulation test results showed a longer prothrombin time (PT), activated partial thromboplastin time (APTT) and a high international normalized ratio (INR). SAH, frontal lobe haematoma, midline shift and brain oedema were discovered by skull CT examination. The coagulation disorders were addressed after the treatment of vitamin K and fresh frozen plasma. The intracranial symptoms were relieved after surgery and the treatment with mannitol. WHAT IS NEW AND CONCLUSION: This case suggests that bromadiolone poisoning should be diagnosed and treated as early as possible. Bromadiolone poisoning might cause SAH and intracerebral haematoma, which is rare but potentially lethal. It is important to strengthen the diagnosis and post-treatment monitoring.

Rodenticide Poisoning.

How to cite this article: D'Silva C, Krishna B. Rodenticide Poisoning. Indian J Crit Care Med 2019;23(Suppl 4):S272-S277.

Urbanization and anticoagulant poisons promote immune dysfunction in bobcats.

Understanding how human activities influence immune response to environmental stressors can support biodiversity conservation across increasingly urbanizing landscapes. We studied a bobcat (Lynx rufus) population in urban southern California that experienced a rapid population decline from 2002-2005 due to notoedric mange. Because anticoagulant rodenticide (AR) exposure was an underlying complication in mange deaths, we aimed to understand sublethal contributions of urbanization and ARs on 65 biochemical markers of immune and organ function. Variance in immunological variables was primarily associated with AR exposure and secondarily with urbanization. Use of urban habitat and AR exposure has pervasive, complex and predictable effects on biochemical markers of immune and organ function in free-ranging bobcats that include impacts on neutrophil, lymphocyte and cytokine populations, total bilirubin and phosphorus. We find evidence of both inflammatory response and immune suppression associated with urban land use and rat poison exposure that could influence susceptibility to opportunistic infections. Consequently, AR exposure may influence mortality and has population-level effects, as previous work in the focal population has revealed substantial mortality caused by mange infection. The secondary effects of anticoagulant exposure may be a worldwide, largely unrecognized problem affecting a variety of vertebrate species in human-dominated environments.

"Got rats?" Global environmental costs of thirst for milk include acute biodiversity impacts linked to dairy feed production.

Rodents damaging alfalfa crops typically destined for export to booming Eastern markets often cause economical losses to farmers, but management interventions attempting to control rodents (i.e., use of rodenticides) are themselves damaging to biodiversity. These damages resonate beyond dairy feed producing regions through animal migration and are an overlooked part of the transferred environmental burden caused by a growing thirst for milk in China and elsewhere.

Investigation of hepatic warfarin metabolism activity in rodenticide-resistant black rats (Rattus rattus) in Tokyo by in situ liver perfusion.

Anti-blood coagulation rodenticides, such as warfarin, have been used all over the world. They inhibit vitamin K epoxide reductase (VKOR), which is necessary for producing several blood clotting factors. This inhibition by rodenticides results in lethal hemorrhage in rodents. However, heavy usage of these agents has led to the appearance of rodenticide-resistant rats. There are two major mechanisms underlying this resistance, i.e., mutation of the target enzyme of warfarin, VKOR, and enhanced metabolism of warfarin. However, there have been few studies regarding the hepatic metabolism of warfarin, which should be related to resistance. To investigate warfarin metabolism in resistant rats, in situ liver perfusion of warfarin was performed with resistant black rats (Rattus rattus) from Tokyo, Japan. Liver perfusion is an in situ methodology that can reveal hepatic function specifically with natural composition of the liver. The results indicated enhanced hepatic warfarin hydroxylation activity compared with sensitive black rats. On the other hand, in an in vitro microsomal warfarin metabolism assay to investigate kinetic parameters of cytochrome P450, which plays a major role in warfarin hydroxylation, the Vmax of resistant rats was slightly but significantly higher compared to the results obtained in the in situ study. These results indicated that another factor like electron donators may also contribute to the enhanced metabolism in addition to high expression of cytochrome P450.