Time to Peak International Normalized Ratio Rise in Acute and Acute-on-Chronic Warfarin Overdoses.

ABSTRACT: Guidelines exist on the management of supratherapeutic/subtherapeutic international normalized ratio (INR) values for patients on warfarin. However, there is a paucity of the literature relating to an acute overdose of warfarin. This is a retrospective cohort study for all acute and acute-on-chronic (AOC) warfarin overdoses reported to the Maryland Poison Center in patients ≥12 years between January 1st, 2000, until October 31st, 2019, managed in a health care facility. The primary outcome was to determine the time after presentation to peak INR. Secondary outcomes included risk factors associated with INR >10 and describing patient characteristics. A total of 163 overdoses were included, 68 acute and 95 AOC. In patients who did not receive reversal therapies, INR peaked at a median value of 3.8 (interquartile range 2.6-5.5) between 24 and 36 hours. The median time to phytonadione was 22.0 hours. Most patients received phytonadione (62.0%), with fewer receiving blood products (16.6%). The median warfarin dose ingested was 75 mg. The AOC group had a greater mean age (56 vs. 43 years), median INR value (2.4 vs. 1.4), and men (62.1% vs. 41.2%). Factors associated with an INR > 10 included initial INR and reported quantity ingested. Peak INR was greater in the AOC than the acute overdose group (6.1 vs. 3.4), although the bleeding rate was similar. Peak INR values after warfarin overdose occur between 24 and 36 hours after presentation. Initial INRs and reported quantity ingested may be useful to predict those needing treatment.

Avian interspecific differences in VKOR activity and inhibition: Insights from amino acid sequence and mRNA expression ratio of VKORC1 and VKORC1L1.

Worldwide use of anticoagulant rodenticides (ARs) for rodents control has frequently led to secondary poisoning of non-target animals, especially raptors. In order to suggest some factors that may help considering the mechanism of the incidents, this study focused on the avian vitamin K 2, 3-epoxide reductase (VKOR) that is the target protein of ARs. We addressed the interspecific differences in VKOR activity and inhibition related to amino acid sequence and mRNA expression of VKORC1 and VKORC1-like1 (VKORC1L1). Poultry have been considered to be more tolerant to ARs than mammals. However, VKOR activity of owls, hawks, falcon and surprisingly, canaries, was lower and inhibited by warfarin more easily than that of chickens and turkeys. The amino acid sequence of VKORC1 and VKORC1L1 implied that the value of Ki for VKOR activity to ARs could depend on the amino acid at position 140 in the TYX warfarin-binding motif in VKORC1, and other amino acid mutations in VKORC1L1. The mRNA expression ratio of VKORC1:VKORC1L1 differed between turkey (8:1) and chicken (2:3) liver. VKORC1L1 has been reported to be resistant to warfarin compared to VKORC1. Hence, both the Ki of specific VKORC1 and VKORC1L1, and the mRNA expression ratio would cause avian interspecific difference of the VKOR inhibition. Our study also suggested the high inhibition of VKOR activities in raptors and surprisingly that in canaries as well. These factors are the most likely to contribute to the high sensitivity to ARs found in raptors.

An analytical strategy for the identification of carbamates, toxic alkaloids, phenobarbital and warfarin in stomach contents from suspected poisoned animals by thin-layer chromatography/ultraviolet detection.

In this study, an analytical strategy to identify brucine, strychnine, methomyl, carbofuran (alkaline compounds), phenobarbital, and warfarin (acid compounds) using thin-layer chromatography (TLC) screening with ultraviolet (UV) detection at 254 nm in stomach content is shown. The optimum mobile phase was found to be a chloroform: ethyl acetate: diethylamine (0.5:8.5:1) mixture for alkaline substances while a mixture of chloroform: acetone (9:1) has given better results for acidic substances. As for extraction, an equal proportion between distillated water and crude material (1:1) is required. For alkaline compounds, a filtration system was created in order to avoid any interferences from the biological matrix while for acidic compounds only centrifugation (4000 rpm/10 minutes) was required to obtain an appropriate sample. After the respective pretreatments, a one-step liquid-liquid extraction (LLE) has been employed for alkaline substances using a 3 mL of chloroform: ethyl ether (2:1) mixture for 2 min while acidic analytes used 3 mL of chloroform only during 5 min. For both methodologies described, the respective organic layers were dried down and re-suspended with 50 µL of methanol for further TLC plate application. The methodologies have been developed, successfully validated and applied to gastric contents from real case samples of suspected animal poisoning. Positive results from TLC/UV screening were confronted with HPLC-UV and confirmed by GC-MS.

Retrospective Study of the Characteristics of Anticoagulant-Type Rodenticide Poisoning in Hong Kong.

INTRODUCTION: Warfarin- and superwarfarin-type anticoagulants are commonly used as rodenticides. Exposure to these agents, especially superwarfarins with long-acting anticoagulant effect, can cause life-threatening coagulopathy in humans. Most superwarfarin poisoning cases had an obvious history of exposure, though occult cases without exposure history have also been reported. The current study aims to examine anticoagulant-type rodenticide poisoning in Hong Kong and to identify the similarities and differences between patients with known exposure history and those whose exposure is recognized only through laboratory testing. METHODS: The present study was conducted in a tertiary referral clinical toxicology laboratory in Hong Kong. This was a retrospective cohort study of all patients with biochemically confirmed anticoagulant-type rodenticide exposure, from 2010 to 2014. RESULTS: Superwarfarin was the most common group of anticoagulant-type rodenticides identified (87.8%), in which bromadiolone and brodifacoum were the most frequently encountered. Among the 41 cases identified, 31 had an obvious exposure history, and 10 were occult poisoning in which the context of exposure remained unidentified. All occult poisoning patients without exposure history presented with bleeding events. These occult poisoning cases often went unrecognized by frontline clinicians, leading to delayed investigation and initiation of treatment. This group of patients was associated with a longer time to diagnose coagulopathy (p < 0.001) and confirm rodenticide poisoning (p < 0.05), a higher rate of international normalized ratio (INR) rebound after initiation of antidote (p < 0.001), and a longer time needed for normalizing INR (p < 0.05). CONCLUSION: Occult superwarfarin poisoning is an important yet under-recognized differential cause of unexplained coagulopathy. A high index of clinical suspicion and availability of specialized toxicological test for superwarfarins play a vital role in diagnosis and early initiation of appropriate management. The underlying cause of such poisoning remains obscure and warrants further study.

Evaluation of Fixed-Dose Four-Factor Prothrombin Complex Concentrate for Emergent Warfarin Reversal in Patients with Intracranial Hemorrhage.

BACKGROUND: Different strategies exist for dosing four-factor prothrombin complex concentrate (PCC4) for international normalized ratio (INR) reversal in the setting of life-threatening bleeding. Fixed doses ranging from 1000 IU to 1750 IU have demonstrated efficacy similar to weight-based dosing, however, few studies look exclusively at intracranial hemorrhage (ICH). OBJECTIVE: Our aim was to evaluate whether a fixed dose of 1000 IU of PCC4 achieves INR reversal similar to weight-based dosing in patients with ICH who were anticoagulated with warfarin. METHODS: We compared a weight-based dose vs. 1000 IU PCC4 between January 2014 and January 2017. The primary end point was achieving an INR < 1.5. Secondary end points included in-hospital mortality, patient disposition, and reversal defined by INR < 1.6. RESULTS: A total of 31 patients were included in the weight-based group and 30 were included in the fixed-dose group, with baseline INRs of 2.98 and 2.84, respectively (p = 0.39). Twenty-two patients (71%) achieved an INR < 1.5 in the weight-based group vs. 16 (53%) in the fixed-dose group (p = 0.15), while 25 (81%) achieved an INR < 1.6 in the weight-based group vs. 22 (73%) in the fixed-dose group (p = 0.49). There was no difference in the number of patients discharged to home (19% vs. 20%; p = 0.95) or in-hospital mortality (26% vs. 27%; p = 0.93). CONCLUSIONS: We found a non-statistically significant difference in warfarin reversal to an INR goal of < 1.5 when comparing a fixed dose of 1000 IU PCC4 and a weight-based dose for ICH. Further studies correlating clinical outcomes with INR reversal are needed.

Deliberate self-poisoning with long-acting anticoagulant rodenticides.

Long-acting anticoagulant rodenticides, also called superwarfarins, are known for their greater potency, longer half-life and delayed onset of symptoms. Cases of superwarfarin poisoning can pose a diagnostic and clinical challenge due to a wide array of presentations and prolonged severe coagulopathy requiring months of high-dose oral vitamin K therapy. The most common presentation of long-acting anticoagulant rodenticide poisoning is mucocutaneous bleeding, with other common presentations including haematuria, gingival bleeding, epistaxis and gastrointestinal bleeding. We discuss a case of deliberate self-poisoning with long-acting anticoagulant rodenticides presenting with haematuria and coagulation values above measurable limits. This case is important as it required immediate and maintenance therapy in order to prevent profound bleeding, as well as the evaluation of the patient's psychosocial factors to ensure medical compliance and to prevent refractory complications or repeated self-harm.

Warfarin Poisoning with Delayed Rebound Toxicity.

BACKGROUND: Intentional poisoning with warfarin is not the same as over-anticoagulation, for which guidelines exist. The coagulopathy resulting from a warfarin overdose is reversed with vitamin K1, the dose and timing of which is often guided by experience with the management of over-anticoagulation with warfarin therapy, rather than acute overdose. CASE REPORT: We report a case of a 50-year-old man who ingested an unknown amount of his warfarin, venlafaxine, and paracetamol. He presented with an international normalized ratio (INR) of 2.5, which steadily increased over 24 h to 7, despite receiving an initial 1 mg of vitamin K1. He was then treated with 5 mg vitamin K1, and once the INR returned to 4.5, 40 h post ingestion, he was discharged home. He was also treated with a full course of acetylcysteine for the paracetamol overdose. The following day his INR rebounded to 8.5 and he suffered a spontaneous epistaxis requiring readmission; he was treated with low titrated doses of vitamin K1. The warfarin concentration was 74.6 µg/mL 26 h post ingestion and decreased to 3.7 µg/mL over 72 h. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Our case highlights the risk of a rebound elevated INR even 3 days after acute warfarin overdose despite treatment with vitamin K1. Understanding the pharmacokinetics of vitamin K1 in comparison with warfarin, repeat INR testing, and continued treatment with oral vitamin K1 may help avoid complications of rebound coagulopathy in warfarin overdose.

The emerging threat of superwarfarins: history, detection, mechanisms, and countermeasures.

Superwarfarins were developed following the emergence of warfarin resistance in rodents. Compared to warfarin, superwarfarins have much longer half-lives and stronger affinity to vitamin K epoxide reductase and therefore can cause death in warfarin-resistant rodents. By the mid-1970s, the superwarfarins brodifacoum and difenacoum were the most widely used rodenticides throughout the world. Unfortunately, increased use was accompanied by a rise in accidental poisonings, reaching >16,000 per year in the United States. Risk of exposure has become a concern since large quantities, up to hundreds of kilograms of rodent bait, are applied by aerial dispersion over regions with rodent infestations. Reports of intentional use of superwarfarins in civilian and military scenarios raise the specter of larger incidents or mass casualties. Unlike warfarin overdose, for which 1-2 days of treatment with vitamin K is effective, treatment of superwarfarin poisoning with vitamin K is limited by extremely high cost and can require daily treatment for a year or longer. Furthermore, superwarfarins have actions that are independent of their anticoagulant effects, including both vitamin K-dependent and -independent effects, which are not mitigated by vitamin K therapy. In this review, we summarize superwarfarin development, biology and pathophysiology, their threat as weapons, and possible therapeutic approaches.

Superwarfarin ingestion treated successfully with prothrombin complex concentrate.

Superwarfarin, a common component of rat poison, can cause long-lasting, severe coagulopathy and life-threatening hemorrhage when ingested. We report a case of intentional rat poison consumption with subsequent hemorrhage and hypotension requiring rapid coagulopathy reversal and resuscitation in the emergency department. In addition to traditional blood products, prothrombin complex concentrate was administered. Although prothrombin complex concentrate is increasingly used for severe hemorrhage in anticoagulated patients, it may be particularly useful in superwarfarin ingestions given the extreme, persistent coagulapathies that can occur.

[Vitamin K antagonists overdose]. / Przedawkowanie antagonistów witaminy K.

Nowadays, anticoagulant therapy belongs to the most commonly used forms of pharmacotherapy in modern medicine. The most important representatives of anticoagulants are heparins (unfractionated heparin and low-molecular-weight heparin) and coumarin derivatives (vitamin K antagonists--VKA). Next to the many advantages of traditional oral anticoagulants may also have disadvantages. In Poland most often used two VKA: acenocoumarol and warfarin. The aim of the work is the analysis of the causes of the occurrence of bleeding disorders and symptoms of overdose VKA in patients to be hospitalized. In the years 2012 to 2014 were hospitalized 62 patients with overdose VKA (40 women and 22 men). The average age of patients was 75.3 years) and clotting disturbances and/or bleeding. At the time of the admission in all patients a significant increase in the value of the INR was stated, in 22 patients INR result was " no clot detected", on the remaining value of the INR were in the range of 7 to 13.1. On 51 patients observed different severe symptoms of bleeding (hematuria, bleeding from mucous membranes of the nose or gums ecchymoses on the extremities, bleeding from the gastrointestinal tract--as in 5 patients has led to significant anemia and transfusion of concentrated red blood cells. Up on 33 patients kidney function disorder were found--exacerbated chronic renal failure and urinary tract infection. 8 diagnosed inflammatory changes in the airways. On 13 patients, it was found a significant degree of neuropsychiatric disorders (dementia, cognitive impairment), which made impossible the understanding the sense of treatment and cooperation with the patient. In 6 patients the symptoms of overdose were probably dependent on the interaction with the congestants at the same time (change the preparation of anticoagulant, NSAIDs, antibiotics). In 2 cases, the overdose was a suicide attempt in nature. In addition to the above mentioned disorders, on two of those patients diagnosed with a malignant disease. Two patients died, the other has been improving and anticoagulant therapy with VKA was continued, in 4 VKA were changed to low-molecular-weight heparin, and on 4 commissioned new generation anticoagulant (rivaroxaban).

Warfarin overdose: a 25-year experience.

Warfarin, a vitamin K antagonist, is widely used for the prophylaxis and treatment of thromboembolic disease. While guidelines exist for management of a supratherapeutic international normalized ratio following therapeutic warfarin use, these guidelines are not designed for management of the acute warfarin overdose. There is a paucity of literature describing the latter. The primary objective of this manuscript is to characterize the coagulopathy and describe the bleeding events that occur after a warfarin overdose. A secondary goal is to describe the amount of vitamin K administered to patients presenting with warfarin overdoses. A retrospective chart review of patients admitted with an acute warfarin overdose at two tertiary care medical centers in the USA was conducted. Clinical characteristics were abstracted, and bleeding categories (major, minor, trivial) were defined a priori. Twenty-three patients were admitted during the time period; males accounted for 15/23 (62.5 %) subjects. The median (interquartile range (IQR)) age was 43 (32-48.5) years. Seventeen subjects received vitamin K, with a median (IQR) dose of 15 (10-50) mg. The maximal total amount of vitamin K administered to a single patient during the index hospitalization was 110 mg. Three bleeding events occurred; one classified as major, and two as minor. All patients made a full recovery. In this case series of acute warfarin overdose, nearly all patients developed a coagulopathy, and nearly three-quarters of patients received vitamin K. Bleeding events occurred in a minority of patients.

Assessment of the contribution of NAD(P)H-dependent quinone oxidoreductase 1 (NQO1) to the reduction of vitamin K in wild-type and NQO1-deficient mice.

NQO1 [NAD(P)H quinone oxidoreductase 1; also known as DT-diaphorase] is a cytosolic enzyme that catalyses the two-electron reduction of various quinones including vitamin K. The enzyme may play a role in vitamin K metabolism by reducing vitamin K to vitamin K hydroquinone for utilization in the post-translational γ-glutamyl carboxylation reactions required by several proteins involved in blood coagulation. The aim of the present study was to assess the contribution of NQO1 to vitamin K reduction and haemostasis in an in vivo model. We examined the contribution of NQO1 to haemostasis by examining survival rates in mice poisoned with the anticoagulant warfarin. Supraphysiological amounts of vitamin K sufficiently reversed the effects of warfarin in both wild-type and NQO1-deficient mice. Additionally, vitamin K reductase activities distinct from VKOR (vitamin K epoxide reductase) and NQO1 were measured in vitro from both wild-type and NQO1-defecient mice. The results of the present study suggest that NQO1 does not play a major role in the production of vitamin K hydroquinone and supports the existence of multiple vitamin K reduction pathways. The properties of a NAD(P)H-dependent vitamin K reductase different from NQO1 are described.

Intoxicación por rodenticidas superwarfarínicos en adultos: bromadiolona, brodifacoum y difetialona / Superwarfarin rodenticide intoxication in adults: an update on bromadiolone, brodifacoum, and difethialone

Se presentan tres casos clínicos de tentativas suicidas por ingesta de rodenticidas superwarfarínicos (bromadiolona, brodifacoum y difetialona) en tres pacientes adultos. Ningúnpaciente presentó alteraciones en la coagulación ni problemas clínicos relevantes, por lo que fueron dados de alta desde urgencias (2 casos a domicilio y 1 caso con ingreso en psiquiatría). Se realiza una puesta al día del plan de actuación a seguir, en base a los casos clínicos publicados en los últimos diez años (AU)

We report 3 cases in which adults used a superwarfarin rodenticide (bromadiolone, brodifacoum, or difethialone) to attempt suicide. No patient developed coagulation abnormalities or significant clinical problems, and all were dischanged alive from the emergency department (2 to home, 1 to a psychiatric facility). An updated action plan based on case reports published in the last 10 years is also provided (AU)

Toxicological evaluation of two children diagnosed as Munchausen syndrome by proxy.

Munchausen syndrome by proxy is a kind of child abuse in which affected children are often hospitalized for long periods and endure repetitive, painful and expensive diagnostic attempts. We present herein two toxicologically confirmed cases of Munchausen syndrome by proxy. Case 1 is a 16-month-old male who had fever, peripheral cyanosis, tremor, and reported cardiac arrest. Symptoms recurred in the hospital when the mother administered fluids. Toxicology detected 3.5 ng/ml mercury (Hg) in the fluid and 9.4 microg Hg/g creatinine in the urine. Case 2 is a 14-year-old female who had irregular blood findings and multiple hospitalizations. Serum analysis detected warfarin. Both mothers were transferred to psychiatric care. Munchausen syndrome by proxy should be suspected when clinical/laboratory findings are negative, illness descriptions are inconsistent, and frequent hospitalization yields no diagnosis. Psychiatric evaluation and toxicological analysis are recommended.

Performance of a point-of-care device in determining prothrombin time in an anticoagulation clinic.

New portable devices for the measurement of the prothrombin time and the international normalized ratio (INR) from capillary blood samples have demonstrated to have good correlation with classic laboratory methods in multiple clinical settings. In this study, we evaluated the performance of the point-of-care device CoaguChek XS (CoaguChek XS; Roche Diagnostics, Basel, Switzerland), comparing the INR results with the standard laboratory method (automatic coagulometer) in an outpatient anticoagulation clinic. Results were compared by linear regression and Bland-Altman plot. Two hundred paired results were collected from 170 patients in a period of 90 days. The main indications for anticoagulation were prophylaxis of venous thromboembolic events, atrial fibrillation and prosthetic heart valves. Mean INR results obtained with the portable device and with the standard laboratory method were 2.22 ±â€Š0.70 and 2.30 ±â€Š0.77, respectively. The proportion of patients with supratherapeutic INRs was 13.5%. The CoaguChek XS monitor tended to underestimate the INR on average by 0.08 U. The correlation coefficient (R) between the two methods was 0.91 (P < 0.0001). The CoaguChek XS device is suitable for INR monitoring in patients in outpatient oral anticoagulation clinics.

Rapid warfarin reversal: a 3-factor prothrombin complex concentrate and recombinant factor VIIa cocktail for intracerebral hemorrhage.

OBJECT: Intracerebral hemorrhage (ICH) is the most serious bleeding complication of vitamin K antagonist (VKA) therapy, carrying a high mortality. Rapid reversal of VKA in ICH is critical. Plasma therapy, the standard of care in the US, is not optimal. The ideal prothrombin complex concentrate (PCC) containing all vitamin K-dependent factors (VKDFs) is not available in the US. Therefore, the authors developed a Trauma Coumadin Protocol (TCP) consisting of a 3-factor PCC available in the US (which contains insufficient factor VII [FVII]) with a low-dose recombinant FVIIa to rapidly reverse VKA. METHODS: Forty-six patients treated with the TCP were retrospectively analyzed. Fourteen patients had pre- and post-TCP plasma samples collected to assess their VKDF increment. Eleven patients had measurable intraparenchymal hematomas, which were evaluated for expansion. RESULTS: The mean pre- and post-TCP international normalized ratios (INRs) were 3.4 (median 2.9) and 1.0 (median 0.9), respectively. Once corrected, INR was maintained at < 1.3 during a patient's hospital stay. The pre-TCP median values of FII, FVII, FIX, and FX were 28%, 21%, 45%, and 20%, respectively; post-TCP median values increased to 144%, 417%, 102%, and 143%, respectively. Four of the 11 patients with measurable intraparenchymal hemorrhage had expansion at 24 hours after TCP. One patient probably (8 hours post-TCP) and 1 patient possibly (3 days post-TCP) had thrombotic complications. CONCLUSIONS: The TCP was very effective in rapidly reversing VKA-associated coagulopathy; however, this protocol should be used cautiously in patients at high risk for thrombosis.

Acquired coagulopathy caused by intoxication with the superwarfarin-type anticoagulant rodenticide flocoumafen.

A 28 year-old heretofore healthy woman was transferred to our hospital with a two-month history of recurring episodes of bleeding. Administration of vitamin K and prothrombin complex concentrates in the transferring hospital had only temporarily corrected both the markedly elevated international normalized ratio (INR) and the prolonged activated partial thromboplastin time (aPTT). The patient's medical and family history revealed no reason for these abnormalities. Our laboratory analyses revealed a sustained deficiency of vitamin K-dependent clotting factors. Presence of an acquired inhibitor of clotting factors was excluded. Thus we suspected, intoxication with an anticoagulant rodenticide. Liquid chromatography-mass spectrometry (LC-MS/MS) revealed pharmacologically active concentrations of flocoumafen, a rodenticide belonging to the superwarfarin family, in the patient's serum. While the long elimination half-life of superwarfarins is well described in rodents, information on pharmacokinetics in humans is not yet available. Therefore, patient management was not limited to prolonged administration of vitamin K, but also included repeated measurements of flocoumafen serum levels. During follow-up visits, clotting tests remained normal and flocoumafen levels gradually decreased, reaching the limit of quantification after 48 days. Based on the repeated measurements of flocoumafen serum levels, a half-life of 6.7 days was estimated in our patient, which is in clear contrast to the 220 days reported in rodents. Thus, monitoring flocoumafen serum concentrations in affected patients may provide a rational basis for the duration of vitamin K substitution and adequate follow-up intervals.

Suboptimal effect of a three-factor prothrombin complex concentrate (Profilnine-SD) in correcting supratherapeutic international normalized ratio due to warfarin overdose.

BACKGROUND: Plasma transfusion is standard therapy for urgent warfarin reversal in the United States. "Four-factor" prothrombin complex concentrate (PCC), available in Europe, has advantages over plasma therapy for warfarin reversal; however, only "three-factor" PCCs (containing relatively low Factor [F]VII) are available in the United States. STUDY DESIGN AND METHODS: The efficacy of a three-factor PCC for urgent warfarin reversal was evaluated in 40 patients presenting with supratherapeutic international normalized ratio (ST-INR > 5.0) with bleeding (n = 29) or at high risk for bleeding (n = 11). In 13 patients, pre- and posttherapy vitamin K-dependent factors were assayed. Historical controls (n = 42) treated with plasma alone were used for rate of ST-INR correction comparison. RESULTS: Treatment with plasma alone (mean, 3.6 units) lowered the INR to less than 3.0 in 63 percent of historical controls. Low-dose (25 U/kg) and high-dose (50 U/kg) PCC alone lowered INR to less than 3.0 in 50 and 43 percent of patients, respectively. Additional transfusion of a small amount of plasma (mean, 2.1 units) increased the rate of achieving an INR of less than 3.0 to 89 and 88 percent for low- and high-dose PCC therapy, respectively. FII, F IX, and FX increments were similar for PCC-treated patients with or without supplemental plasma; FVII was significantly higher in the PCC plus plasma group compared to the PCC-only group (p = 0.001). CONCLUSION: Three-factor PCC does not satisfactorily lower ST-INR due to low FVII content. Infusion of a small amount of plasma increases the likelihood of satisfactory INR lowering.