Warfarin overdose: a 25-year experience

Carbon Monoxide as a Potential Therapeutic Agent: A Molecular Analysis of Its Safety Profiles

Carbon monoxide (CO) is endogenously produced in mammals, with blood concentrations in the high micromolar range in the hemoglobin-bound form. Further, CO has shown therapeutic effects in various animal models. Despite its reputation as a poisonous gas at high concentrations, we show that CO should have a wide enough safety margin for therapeutic applications. The analysis considers a large number of factors including levels of endogenous CO, its safety margin in comparison to commonly encountered biomolecules or drugs, anticipated enhanced safety profiles when delivered via a noninhalation mode, and the large amount of safety data from human clinical trials. It should be emphasized that having a wide enough safety margin for therapeutic use does not mean that it is benign or safe to the general public, even at low doses. We defer the latter to public health experts. Importantly, this Perspective is written for drug discovery professionals and not the general public.

Warfarin Overdose in an Adolescent Not Dependent on Anticoagulation: Reversal Strategy and Kinetics

INTRODUCTION

Warfarin induces coagulopathy. Guidelines protocolize reversal of supratherapeutic international normalized ratio (INR) in patients dependent on anticoagulation, but practices vary for reversing warfarin-induced coagulopathy after overdose in non-warfarin-dependent patients.

CASE REPORT

This is the report of a 15-year-old female who ingested her father's warfarin (100-200 mg) in a self-harm attempt. At hour 24 post-ingestion, her INR was 2.00 and she was admitted for monitoring. Reversal of coagulopathy was initially deferred pending the INR trend. The INR was 5.10 at hour 60 and 2.5 mg oral vitamin K1 (VK1) was given. At hour 85, the INR peaked at 6.67 and she received a second oral dose of 2.5 mg VK1. On day 8, she was medically cleared with an INR of 1.31. On day 11, she developed lower abdominal pain and diarrhea. Imaging revealed a duodenal hematoma, and symptoms improved spontaneously. She was again medically cleared 13 days post-ingestion. Her serum warfarin concentration peaked at 19 mcg/mL at hour 46. Serial warfarin concentrations were obtained, demonstrating first-order elimination kinetics and a 30-hour half-life.

CONCLUSION

A restrictive approach to coagulopathy reversal in non-warfarin-dependent patients with intentional warfarin overdose may result in worsening coagulopathy, bleeding, and lengthy hospital stay. Given the risk for significant, prolonged coagulopathy, these patients should be treated early with VK1, with subsequent serial INR monitoring and probable additional VK1 dosing. Delayed peak warfarin concentrations support consideration of gastrointestinal decontamination in late presenters.

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.

Antithrombotic and Antiplatelet Drug Toxicity

Anticoagulant and antiplatelet drugs target a specific portion of the coagulation cascade or the platelet activation and aggregation pathway. The primary toxicity associated with these agents is hemorrhage. Understanding the pharmacology of these drugs allows the treating clinician to choose the correct antidotal therapy. Reversal agents exist for some of these drugs; however, not all have proven patient-centered outcomes. The anticoagulants covered in this review are vitamin K antagonists, heparins, fondaparinux, hirudin derivatives, argatroban, oral factor Xa antagonists, and dabigatran. The antiplatelet agents reviewed are aspirin, adenosine diphosphate antagonists, dipyridamole, and glycoprotein IIb/IIIa antagonists. Additional notable toxicities are also reviewed.

An Adapted Neural-Fuzzy Inference System Model Using Preprocessed Balance Data to Improve the Predictive Accuracy of Warfarin Maintenance Dosing in Patients After Heart Valve Replacement

BACKGROUND

Tailoring warfarin use poses a challenge for physicians and pharmacists due to its narrow therapeutic window and substantial inter-individual variability. This study aimed to create an adapted neural-fuzzy inference system (ANFIS) model using preprocessed balance data to improve the predictive accuracy of warfarin maintenance dosing in Chinese patients undergoing heart valve replacement (HVR).

METHODS

This retrospective study enrolled patients who underwent HVR between June 1, 2012, and June 1, 2016, from 35 centers in China. The primary outcomes were the mean difference between predicted warfarin dose by ANFIS models and actual dose and the models' predictive accuracy, including the ideal predicted percentage, the mean absolute error (MAE), and the mean squared error (MSE). The eligible cases were divided into training, internal validation, and external validation groups. We explored input variables by univariate analysis of a general linear model and created two ANFIS models using imbalanced and balanced training sets. We finally compared the primary outcomes between the imbalanced and balanced ANFIS models in both internal and external validation sets. Stratified analyses were conducted across warfarin doses (low, medium, and high doses).

RESULTS

A total of 15,108 patients were included and grouped as follows: 12,086 in the imbalanced training set; 2820 in the balanced training set; 1511 in the internal validation set; and 1511 in the external validation set. Eight variables were explored as predictors related to warfarin maintenance doses, and imbalanced and balanced ANFIS models with multi-fuzzy rules were developed. The results showed a low mean difference between predicted and actual doses (< 0.3 mg/d for each model) and an accurate prediction property in both the imbalanced model (ideal prediction percentage, 74.39-78.16%; MAE, 0.37 mg/daily; MSE, 0.39 mg/daily) and the balanced model (ideal prediction percentage, 73.46-75.31%; MAE, 0.42 mg/daily; MSE, 0.43 mg/daily). Compared to the imbalanced model, the balanced model had a significantly higher prediction accuracy in the low-dose (14.46% vs. 3.01%; P < 0.001) and the high-dose warfarin groups (34.71% vs. 23.14%; P = 0.047). The results from the external validation cohort confirmed this finding.

CONCLUSIONS

The ANFIS model can accurately predict the warfarin maintenance dose in patients after HVR. Through data preprocessing, the balanced model contributed to improved prediction ability in the low- and high-dose warfarin groups.

Unintentional ingestion of a high dose of acenocoumarol in a young child

Acute intoxication with a vitamin K antagonist may cause serious coagulopathy. We report the accidental ingestion of a high dose of acenocoumarol in a young child. Two intravenous administrations of 5 mg of vitamin K, in combination with fast and repeated administration of activated charcoal and sodium sulfate, were sufficient to prevent coagulopathy and related symptoms, despite a confirmed elevated blood acenocoumarol concentration (260 µg/L).

Risk factors associated with warfarin overdose and complications related to warfarin overdose in the emergency department

The aim of this study was to investigate risk factors of bleeding and mortality in patients with warfarin overdose (WOD). Totally, 783 patients were included, of which, 272 patients (34.7%) with an INR below 5,364 patients (46.5%) with an INR between 5-10, and 147 patients (18.8%) with an INR of 10 or above. Demographic, clinical, and laboratory findings of the patients were obtained from the Real Life Data Provision Center and Hospital Information Management System. Admittance in autumn (OR = 1.75; p = 0.012), INR = 5-10 (OR = 2.65; p < 0.001), INR ≥ 10 (OR = 9.06; p < 0.001), and antiplatelet use alongside warfarin (OR = 1.93; p < 0.001) were found to be independent risk factors for bleeding in this study. The age (OR= 1.03; p = 0.005), bleeding (OR = 1.69; p = 0.020), primary hypertension (OR = 1.72; p = 0.031), and INR ≥ 10 (OR = 2.02; p = 0.025) were found to be independent risk factors for mortality. The cutoff value for INR in predicting bleeding was found to be >6.35 with 74.2% sensitivity and 72.7% specificity. The significant risk factors were determined in WOD development. INR level, autumn, and antiplatelet use were independently associated with bleeding due to WOD. In addition, bleeding, hypertension and INR levels were independently related to in-hospital-mortality due to WOD.

A cell-based high-throughput screen identifies drugs that cause bleeding disorders by off-targeting the vitamin K cycle

Drug-induced bleeding disorders contribute to substantial morbidity and mortality. Antithrombotic agents that cause unintended bleeding of obvious cause are relatively easy to control. However, the mechanisms of most drug-induced bleeding disorders are poorly understood, which makes intervention more difficult. As most bleeding disorders are associated with the dysfunction of coagulation factors, we adapted our recently established cell-based assay to identify drugs that affect the biosynthesis of active vitamin K-dependent (VKD) coagulation factors with possible adverse off-target results. The National Institutes of Health (NIH) Clinical Collection (NCC) library containing 727 drugs was screened, and 9 drugs were identified, including the most commonly prescribed anticoagulant warfarin. Bleeding complications associated with most of these drugs have been clinically reported, but the pathogenic mechanisms remain unclear. Further characterization of the 9 top-hit drugs on the inhibition of VKD carboxylation suggests that warfarin, lansoprazole, and nitazoxanide mainly target vitamin K epoxide reductase (VKOR), whereas idebenone, clofazimine, and AM404 mainly target vitamin K reductase (VKR) in vitamin K redox cycling. The other 3 drugs mainly affect vitamin K availability within the cells. The molecular mechanisms underlying the inactivation of VKOR and VKR by these drugs are clarified. Results from both cell-based and animal model studies suggest that the anticoagulation effect of drugs that target VKOR, but not VKR, can be rescued by the administration of vitamin K. These findings provide insights into the prevention and management of drug-induced bleeding disorders. The established cell-based, high-throughput screening approach provides a powerful tool for identifying new vitamin K antagonists that function as anticoagulants.

Spontaneous bladder rupture secondary to warfarin overdose: a case report

BACKGROUND

Warfarin, a vitamin K antagonist, is a widely used medication for the treatment and prophylaxis of thromboembolic events. Patients with various clinical conditions due to warfarin overdose present to emergency departments. Although there may be serious bleeding due to a warfarin overdose, no bleeding may also be seen in some clinical conditions. Some of these bleedings may be life-threatening and result in death. Warfarin overdose and related cases of spontaneous bladder rupture are not frequently observed in the literature. We present a case of spontaneous bladder rupture due to warfarin overdose that was unexpectedly seen in a patient using warfarin for coronary artery disease and arrhythmia.

CASE PRESENTATION

A 77-year-old Caucasian male patient was admitted to the emergency department with abdominal pain, haematuria, and a reduced volume of urine lasting for three days. The patient's amount of urine was reduced, and he came to the hospital for the first time with this complaint. The patient had local bruises on his arms and legs. From the ultrasound, retrograde cystography and computed tomography images, it was thought that there was blood accumulation due to bladder rupture to the intraperitoneal region. Spontaneous bladder rupture secondary to warfarin overdose was considered for this patient who also had an international normalized ratio (INR) level of 13.4. After the INR level was normalized with vitamin K and a prothrombin complex concentrate, the patient underwent surgery. During the operation, a catheter was placed in the bladder, and the bladder mucosa and muscle were closed separately with a primary repair performed by a urologist. The patient was discharged on the 8th postoperative day without any complications.

CONCLUSION

In addition to the known findings of warfarin overdose in these patients presenting to the emergency department, we think that the emergency department staff should suspect bladder rupture, which is a fatal complication in the presence of signs such as oliguria, haematuria, anuria, abdominal pain, and syncope.

Higher Incidence of Ischemic Stroke in Patients Taking Novel Oral Anticoagulants

Background and Purpose—

The increased use of novel oral anticoagulants (NOACs) to control atrial fibrillation is largely driven by the assumption that they are equally effective as warfarin at preventing ischemic stroke while putting patients at lower risk of hemorrhages. To test this hypothesis, a retrospective study of the relative incidence of strokes among patients taking NOACs versus those taking warfarin is performed.

Methods—

Relative stroke incidence in the 2 groups of patients was compared using odds ratios and Fisher exact tests for significance using a data set of 71 365 on NOACs and 59 546 patients on warfarin. In addition, the 7033 patients with a record of both warfarin and NOAC use were analyzed as a separate cohort.

Results—

There is a significantly higher (odds ratio=1.29, <0.001) frequency of ischemic strokes among patients prescribed NOACs compared with those on warfarin. The relative frequency of ischemic strokes was also higher for every individual NOAC compared with warfarin (these higher frequencies are statistically significant for dabigatran and apixaban, though not for edoxaban and rivaroxaban). There is a lower incidence of intracranial hemorrhages and nontraumatic hemorrhages in general among patients taking NOACs, consistent with the published literature. Comparisons of the demographic and clinical profiles of the patients taking NOACs to those on warfarin do not show significantly higher background stroke risk in NOAC patients; in fact, patients on NOACs tend to be at lower background risk overall for ischemic strokes.

Conclusions—

Because NOAC use is associated with higher ischemic stroke risk together with a lower risk of hemorrhages than warfarin use, it can be concluded that patients on warfarin are more strongly anticoagulated. The observed effect could be a secondary consequence of dosage control or alternatively a result of different anticoagulant effects among the different medications.

Evaluation of oral anticoagulants with vitamin K epoxide reductase in its native milieu

Warfarin, acenocoumarol, phenprocoumon, and fluindione are commonly prescribed oral anticoagulants for the prevention and treatment of thromboembolic disorders. These anticoagulants function by impairing the biosynthesis of active vitamin K-dependent coagulation factors through the inhibition of vitamin K epoxide reductase (VKOR). Genetic variations in VKOR have been closely associated with the resistant phenotype of oral anticoagulation therapy. However, the relative efficacy of these anticoagulants, their mechanisms of action, and their resistance variations among naturally occurring VKOR mutations remain elusive. Here, we explored these questions using our recently established cell-based VKOR activity assay with the endogenous VKOR function ablated. Our results show that the efficacy of these anticoagulants on VKOR inactivation, from most to least, is: acenocoumarol > phenprocoumon > warfarin > fluindione. This is consistent with their effective clinical dosages for stable anticoagulation control. Cell-based functional studies of how each of the 27 naturally occurring VKOR mutations responds to these 4 oral anticoagulants indicate that phenprocoumon has the largest resistance variation (up to 199-fold), whereas the resistance of acenocoumarol varies the least (<14-fold). Cell-based kinetics studies show that fluindione appears to be a competitive inhibitor of VKOR, whereas warfarin is likely to be a mixed-type inhibitor of VKOR. The anticoagulation effect of these oral anticoagulants can be reversed by the administration of a high dose of vitamin K, apparently due to the existence of a different enzyme that can directly reduce vitamin K. These findings provide new insights into the selection of oral anticoagulants, their effective dosage management, and their mechanisms of anticoagulation.

Warfarin maintenance dose Prediction for Patients undergoing heart valve replacement- a hybrid model with genetic algorithm and Back-Propagation neural network

Warfarin is the most recommended anticoagulant drug for patients undergoing heart valve replacement. However, due to the narrow therapeutic window and individual dose, the use of warfarin needs more advanced technology. We used the data collected from a multi-central registered clinical system all over China about the patients who have undergone heart valve replacement, subsequently divided into three groups (training group: 10673 cases; internal validation group: 3558 cases; external validation group: 1463 cases) in order to construct a hybrid model with genetic algorithm and Back-Propagation neural network (BP-GA), For testing the model's prediction accuracy, we used Mean absolute error (MAE), Root mean squared error (RMSE) and the ideal predicted percentage of total and dose subgroups. In results, whether in internal or in external validation group, the total ideal predicted percentage was over 58% while the intermediate dose subgroup manifested the best. Moreover, it showed higher prediction accuracy, lower MAE value and lower RMSE value in the external validation group than that in the internal validation group (p < 0.05). In conclusion, BP-GA model is promising to predict warfarin maintenance dose.

Assessing Bleeding Risk in Patients With Intentional Overdoses of Novel Antiplatelet and Anticoagulant Medications

STUDY OBJECTIVE

In recent years, the use of novel anticoagulants and antiplatelet agents has become widespread. Little is known about the toxicity and bleeding risk of these agents after acute overdose. The primary objective of this study is to evaluate the relative risk of all bleeding and major bleeding in patients with acute overdose of novel antiplatelet and anticoagulant medications.

METHODS

This study is a retrospective study of acute ingestion of apixaban, clopidogrel, ticlopidine, dabigatran, edoxaban, prasugrel, rivaroxaban, and ticagrelor reported to 7 poison control centers in 4 states during a 10-year span. The prevalence of bleeding for each agent was calculated, and hemorrhage was classified as trivial, minor, or major.

RESULTS

A total of 322 acute overdoses were identified, with the majority of cases involving clopidogrel (260; 80.7%). Hemorrhage occurred in 16 cases (4.9%), including 7 cases of clopidogrel, 6 cases of rivaroxaban, 2 cases of dabigatran, and 1 case of apixaban. Most cases of hemorrhage were classified as major (n=9). Comparing the novel anticoagulants with the P2Y12 receptor inhibitors, the relative risk for any bleeding with novel anticoagulant was 6.68 (95% confidence interval 2.63 to 17.1); the relative risk of major bleeding was 18.1 (95% confidence interval 3.85 to 85.0).

CONCLUSION

Acute overdose of novel anticoagulants or antiplatelet agents is associated with a small risk of significant hemorrhage. The risk is greater with the factor Xa inhibitors and direct thrombin inhibitors than with the P2Y12 receptor antagonists.

Detection of the anticoagulant drug warfarin by palladium complexes

This work illustrates the application of palladium complexes in the significant sensing of warfarin, a commercial anticoagulant drug, not only in organic solvents but also in aqueous medium.

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.

Massive intoxication with rivaroxaban, phenprocoumon, and diclofenac: A case report

RATIONALE

Oral anticoagulants and painkillers, some with an additional effect on the coagulation system, are widely used and are therefore prone to abuse and (intentional) overdose. We report the case of a patient with a massive mixed anticoagulant intoxication.

PATIENT CONCERNS

The patient had ingested 1960 mg rivaroxaban, 31.5 mg phenprocoumon, 1425 mg diclofenac, and 21,000 mg metamizole in suicidal intention.

DIAGNOSES

Massive mixed anticoagulant overdose.

INTERVENTIONS

The patient was closely monitored. The phenprocoumon overdose was treated by the administration of vitamin K and PCC.

OUTCOMES

Despite the massive inhibition of the coagulation system, the patient did not experience bleeding apart from a slight gross hematuria.

LESSONS

Despite the ingestion of a massive amount of rivaroxaban, the plasma levels were not as high as feared, due to the ceiling effect of rivaroxaban absorption. Elimination occurred according to the half-life of rivaroxaban and was not unduly prolonged by the ingested quantity.

Steps to diagnosis of a case of surreptitious intake of one of the newer direct oral anticoagulants: a case report and literature review

Little is known about the effects of newer oral anticoagulants on various coagulation factors. When presented with a case of intentional or suspected overdose with an abnormal coagulation profile, it is imperative to have a working diagnostic algorithm to narrow the cause to a specific drug or drug class. This may become more crucial and time sensitive when dealing with a case of acute hemorrhage. Here we discuss the first reported case of what appears to be a surreptitious intake of newer oral anticoagulants and the steps leading to the diagnosis.

Antidotes to coumarins, isoniazid, methotrexate and thyroxine, toxins that work via metabolic processes

Some toxins cause their effects by affecting physiological processes that are fundamental to cell function or cause systemic effects as a result of cellular interaction. This review focuses on four examples, coumarin anticoagulants, isoniazid, methotrexate and thyroxine from the context of management of overdose as seen in acute general hospitals. The current basic clinical pharmacology of the toxin, the clinical features in overdose and evidence base for specific antidotes are discussed. The treatment for this group is based on an understanding of the toxic mechanism, but studies to determine the optimum dose of antidote are still required in all these toxins except thyroxine, where treatment dose is based on symptoms resulting from the overdose.

Anticoagulation drug therapy: a review

Historically, most patients who required parenteral anticoagulation received heparin, whereas those patients requiring oral anticoagulation received warfarin. Due to the narrow therapeutic index and need for frequent laboratory monitoring associated with warfarin, there has been a desire to develop newer, more effective anticoagulants. Consequently, in recent years many novel anticoagulants have been developed.

The emergency physician may institute anticoagulation therapy in the short term (e.g. heparin) for a patient being admitted, or may start a novel anticoagulation for a patient being discharged. Similarly, a patient on a novel anticoagulant may present to the emergency department due to a hemorrhagic complication. Consequently, the emergency physician should be familiar with the newer and older anticoagulants. This review emphasizes the indication, mechanism of action, adverse effects, and potential reversal strategies for various anticoagulants that the emergency physician will likely encounter.