Deficiency of coagulation factors is associated with the bleeding diathesis of severe yellow fever.

Yellow fever (YF) is an acute tropical infectious disease caused by an arbovirus and can manifest as a classic hemorrhagic fever. The mechanism of the bleeding diathesis in YF is not well understood. We assessed clinical and laboratory data (including a panel of coagulation tests) from 46 patients with moderate (M) and severe (S) YF admitted to a local hospital between January 2018 and April 2018. Among 46 patients, 34 had SYF of whom 12 (35%) patients died. A total of 21 (45%) patients developed some type of bleeding manifestation and 15 (32%) presented severe bleeding. Patients with SYF had more severe thrombocytopenia (p = 0.001); prolonged activated partial thromboplastin time (aPTT) and thrombin time (TT) (p = 0.03 and p = 0.005, respectively); reduced plasma levels of coagulation factor (F) II (p < 0.01), FIX (p = 0.01), and FX (p = 0.04); and D-dimer levels almost 10 times higher (p < 0.01) when compared with patients with MYF. Patients who died had more bleeding (p = 0.03), more major bleeding (p = 0.03), prolonged international normalized ratio (INR) and aPTT (p = 0.003 and p = 0.002, respectively), as well as lower activity of FII (p = 0.02), FV (p = 0.001), FVII (p = 0.005), FIX (p = 0.01), and protein C (p = 0.01) than the ones who survived. FVIII levels were either normal or increased in all patients studied. Our results suggest that the bleeding diathesis of SYF is associated with the deficiency of coagulation factors produced by the liver. Prolonged INR and aPTT and reduced FII, FV, FVII, FIX, and protein C were associated with death.

Infection of hematopoietic stem cells by Leishmania infantum increases erythropoiesis and alters the phenotypic and functional profiles of progeny.

Immunosuppression is a well-established risk factor for Visceral Leishmaniasis. Post-immunosuppression leishmaniasis is characterized by an increase of parasite burden, hematopoietic disorders and unusual clinical manifestations. Although there are many reports on bone marrow findings in VL, less is known about the relationship between parasite dynamics in this organ and the function of either hematopoietic stem cells and progenitor cells themselves. In the present study, we tackle these issues using a new approach of infecting human stem cells derived from bone marrow with L. infantum. Using this strategy, we show that human hematopoietic stem cells (hHSC) are able to phagocytize L. infantum promastigotes and release modulatory and pro-inflammatory cytokines, mainly TNF-α. Our results demonstrated that L. infantum infection in vitro enhances hematopoiesis, favoring the development of erythrocitic lineage through a mechanism yet unknown. Moreover, we found that L. infantum infection alters the phenotypic profile of the hematopoietic progeny; modifying the surface markers expression of differentiated cells. Thus, our study represents a rare opportunity to monitor the in vitro differentiation of human stem cells experimentally infected by L. infantum to better understand the consequences of the infection on phenotypic and functional profile of the cell progeny.

ABO blood group polymorphisms and risk for ischemic stroke and peripheral arterial disease.

Recent studies have demonstrated association between ABO blood system and thrombosis, indicating that individuals belonging to non-O blood groups (A, B or AB) present an increased risk of venous thrombosis, heart disease, and ischemic stroke (IS) as compared to O blood group carriers. In this study, we investigated the frequency of ABO blood group polymorphisms and its association with IS and peripheral arterial disease. Significant differences were observed for O1 (OR 0.57, 95% CI 0.35-0.95, p < 0.05) and O2 (OR 3.47, 95% CI 1.15-10.28, p < 0.05) alleles among IS patients while significant differences were observed for B phenotype (26.3 vs 9.5%, OR 3.42, 95% CI 1.32-8.76, p = 0.01, patients vs controls, respectively) and alleles A1 (OR 0.31, 95% CI 0.11-0.84, p < 0.05), O2 (OR 4.61, 95% CI 1.59-13.23, p < 0.01) and B (OR 3.42, 95% CI 1.62-7.13, p < 0.001) alleles for PAD patients. O1 allele was an independent variable (OR 0.27, 95% CI 0.12-0.57, p < 0.001) for IS patients. These data suggest the relationship of non-O blood groups in pathogenesis of thrombosis events and a possible protective effect of O blood group.

Heavy menstrual bleeding in women with inherited bleeding disorders in use of LNG-IUS: A systematic review and single-arm meta-analysis.

OBJECTIVES: Inherited bleeding disorders may cause heavy menstrual bleeding in women, impacting quality of life and impairing daily and social activities. The levonorgestrel-releasing intrauterine system is a potential treatment for these women, which might reduce menstrual blood loss. STUDY DESIGN: We performed a systematic review and single-arm meta-analysis to examine the levonorgestrel-releasing intrauterine system in women with inherited bleeding disorders and heavy menstrual bleeding. RESULTS: A systematic search on PubMed, Embase and Cochrane yielded 583 results, of which six observational studies (n = 156) met inclusion criteria. Levonorgestrel-releasing intrauterine system use in patients with inherited bleeding disorders and heavy menstrual bleeding was associated with amenorrhea in 60% of patients and a significant increase of 1.40 g/dL in hemoglobin and of 19.75 ng/mL in ferritin levels when comparing post- and pre-treatment levels. The post-treatment mean hemoglobin was 13.32 g/dL and the mean ferritin was 43.22 ng/dL. The rate of intrauterine device expulsion or removal due to mal position was low (13%), as was the need for intrauterine device removal due to lack of efficacy (14%). CONCLUSION: The levonorgestrel-releasing intrauterine system may improve bleeding patterns and quality of life in patients with inherited bleeding disorders and heavy menstrual bleeding. IMPLICATIONS: Women with inherited bleeding disorders could benefit from levonorgestrel-releasing intrauterine system, so its use should be an option for this women.

Hypocoagulability in severe yellow fever infection is associated with bleeding: results from a cohort study.

Background: Severe yellow fever infection (YFI) may be complicated by a hemorrhagic diathesis. However, the hemostasis profile of YFI has rarely been reported. Objectives: The aim of this study was to characterize the hemostatic features of YFI by using a rotational thromboelastometry (ROTEM). Methods: We evaluated clinical, laboratory, and ROTEM parameters in adults with severe YFI and their correlation with hemostatic variables according to bleeding and death. Results: A total of 35 patients were included (median age, 49 years). ROTEM was performed in 22 patients, of whom 21 (96%) presented bleeding and 4 (18%) died. All patients who died had major bleeding. Patients who died presented prolonged clotting time (CT; median, 2326 seconds; IQR, 1898-2986 seconds) and reduced alpha angle (median, 12°; IQR, 12°-15°) in comparison with patients who had minor (median CT, 644 seconds; IQR, 552-845 seconds and alpha angle, 47°; IQR, 28°-65°) and major (median CT, 719 seconds; IQR, 368-1114 seconds and alpha angle, 43°; IQR, 32°-64°) bleeding who survived. In patients who had bleeding, CT showed a strong negative correlation with factor (F)V (r = -.68), FIX (r = -.84), and FX (r = -.63) as well as alpha angle showed a strong negative correlation with FIX (r = -.92). In patients who died, the correlations were even stronger. A total of 19/21 (90%) patients presented hypocoagulability assessed by ROTEM. Conclusion: Hypocoagulabitity is the hallmark of the bleeding diathesis of severe YFI. Abnormal CT and alpha angle associated with death and could be used as potential predictors of adverse outcome in severe YFI.

Influence of polymorphisms in CYP2C9, VKORC1, MDR1 and APOE genes on the warfarin maintenance dose in Brazilian patients.

Background: Polymorphisms in the CYP2C9, VKORC1, MDR1 and APOE genes may impact warfarin dose. Aim: To investigate the influence of sociodemographic, clinical factors and polymorphisms *1, *2 and *3 for CYP2C9, -1639G>A for VKORC1, 3435C>T for MDR1, and ϵ2, ϵ3 and ϵ4 for APOE genes on the mean weekly warfarin maintenance dose in adults. Methods: This cross-sectional study recruited a calculated sample of 315 patients in three anticoagulation clinics in Brazil. A model containing the variables significantly associated with warfarin dose was estimated. Results: The mean age of patients was 64.1 ± 13.1 years, with 173 (54.9%) women. Age, use of amiodarone, genotype VKORC1 GA, genotype VKORC1 AA, genotypes CYP2C9*1/*2 or *1/*3 and genotypes CYP2C9*2/*2 or *2/*3 or *3/*3 were associated with a reduced warfarin dose. Conclusion: This study pointed out factors that could impact the management of oral anticoagulation.

Association of Fibrinolytic Potential and Risk of Mortality in Cancer Patients.

Cancer is a leading cause of death, and the fibrinolytic system shows cooperative effects that facilitate the growth of tumors and the appearance of metastases. This prospective study aimed to evaluate the fibrinolytic potential in cancer patients and its association with mortality outcomes using the fluorometric method of simultaneous thrombin and plasmin generation. The study included 323 cancer patients and 148 healthy individuals. During the 12-month follow-up, 68 patients died. Compared to the control group, cancer patients showed alterations in thrombin production consistent with a hypercoagulability profile, and an increase in plasmin generation. Mortality risk was associated with two parameters of thrombin in both univariate and multivariable analysis: maximum amplitude (Wald 11.78, p < 0.001) and area under the curve (Wald 8.0, p < 0.005), while such associations were not observed for plasmin. In conclusion, this was the first study able to demonstrate the simultaneous evaluation of thrombin and plasmin generation in newly diagnosed untreated cancer patients. Patients with cancer have been observed to exhibit a hypercoagulable profile. During the study, two parameters linked to thrombin generation, MA and AUC, were identified and found to have a potential association with mortality risk. However, no associations were found with parameters related to plasmin generation.

Plasminogen activator inhibitor-1 4G/5G promoter polymorphism and PAI-1 plasma levels in young patients with ischemic stroke.

The 4G/5G polymorphism in the plasminogen activator inhibitor-1 (PAI-1) gene, has been associated with arterial disease. In this study, we investigated the association of IS in young patients with CRP and PAI-1 levels and frequency of insertion-deletion polymorphism of PAI-1 gene. The plasma levels of PAI-1 and CRP and the frequency of 4G/5G polymorphism were analyzed in 127 Brazilian young patients that presented IS and in 201 healthy and unrelated control subjects. The levels of CRP (P < 0.001) and PAI-1 (P < 0.001) were significantly higher in patients when compared with control group. Only PAI-1 plasma levels were independently associated with risk of IS (OR 3.40; 95% CI 1.49-7.74; P = 0.001) after adjustments for lifestyles covariates. The 4G/4G genotype was significantly more frequent among control subjects as compared to patients (OR 0.41; 95% CI 0.24-0.68; P < 0.001). Although increased PAI-1 plasma levels are associated with development of IS in Brazilian young patients, they are not influenced by the 4G/5G PAI-1 polymorphism.

JAK2V617F mutation in patients with splanchnic vein thrombosis.

BACKGROUND: Splanchnic vein thrombosis can be the presenting manifestation of myeloproliferative neoplasms. However, the diagnosis of a myeloproliferative neoplasm in these patients is often problematic, and more objective criteria are needed. AIM: To determine the frequency of the mutation JAK2V617F in patients with splanchnic vein thromboses. METHODS: A consecutive series of 108 adult patients with portal vein thrombosis (n = 77) and Budd-Chiari syndrome (n = 31) referred for hemostasis evaluation was retrospectively studied, with a median follow-up of 51 months (1-104). RESULTS: One or more prothrombotic risk factors were present in 63% of the patients. Twenty-four (22%) out of the 108 patients presented the JAK2V617F, including 2 cirrhotic patients. Most had a low mutated allele burden (median 16.5%). JAK2V617F was present in all four patients with a previous diagnosis of a myeloproliferative neoplasm. In nine JAK2V617F-positive patients, the diagnosis of a myeloproliferative neoplasm was made at the thrombosis work-up, during follow-up or after JAK2V617F detection. Among the other 11 patients carrying the mutation, 2 patients have died, 4 had no evidence suggesting a myeloproliferative neoplasm, 1 had a normal bone marrow biopsy, and the other 4 could not be persuaded to undergo a biopsy. Among the patients without an overt myeloproliferative neoplasm, 15 out of 99 (15%) presented the JAK2V617F mutation. None of the JAK2V617F-negative patients have developed signs of a myeloproliferative neoplasm during follow-up. CONCLUSIONS: Our findings suggest that JAK2V617F occurs in a high proportion of patients with splanchnic vein thrombosis, and reinforces the diagnostic utility of JAK2V617F testing in this setting.

Inhibitory effects of dabigatran etexilate, a direct thrombin inhibitor, on osteoclasts and osteoblasts.

INTRODUCTION: Anticoagulants are widely used in orthopedic surgery to decrease the risk of deep vein thrombosis. While significant bone impairment is induced by long-term heparin therapy, little is known about the effects of direct oral anticoagulants (DOACs). Herein, we investigated the effects of dabigatran etexilate (Pradaxa®), a DOAC inhibitor of thrombin, on bone cells using in vitro and ex vivo cell culture models. MATERIALS AND METHODS: Osteoblasts and osteoclasts exposed to different concentrations of dabigatran etexilate and untreated cells were assayed for cell differentiation and activity. Favorable osteogenic conditions for osteoblasts were tested using titanium with nanotopography (Ti-Nano). In addition, mice treated with a dabigatran etexilate solution had bone marrow cells analyzed for the ability to generate osteoclasts. RESULTS: Dabigatran etexilate at concentrations of 1 µg/mL and 2 µg/mL did not impact osteoclast or osteoblast viability. The drug inhibited osteoclast differentiation and activity as observed by the reduction of TRAP+ cells, resorption pits and gene and protein expression of cathepsin K. Consistently, osteoclasts from mice treated with dabigatran showed decreased area, resorptive activity, as well as gene and protein expression of cathepsin K. In osteoblast cultures, grown both on polystyrene and Ti-Nano, dabigatran etexilate reduced alkaline phosphatase (ALP) activity, matrix mineralization, gene expression of ALP and osteocalcin. CONCLUSIONS: Dabigatran etexilate inhibited osteoclast differentiation in ex vivo and in vitro models in a dose-dependent manner. Moreover, the drug reduced osteoblast activity even under optimal osteogenic conditions. This study provides new evidence regarding the negative overall impact of DOACs on bone cells.

Bleeding assessment in oral surgery: A cohort study comparing individuals on anticoagulant therapy and a non-anticoagulated group.

Some prospective studies have been designed specifically to investigate perioperative bleeding in dental surgery. The quantitative assessment of intraoperative blood loss can be useful for indicating the real risk of bleeding complications, especially in medically compromised individuals. The aim of this study was to evaluate the pattern of bleeding in individuals under vitamin K antagonist (VKA) therapy and non-anticoagulated individuals submitted to dental extractions. Perioperative bleeding was evaluated by using a total collected bleeding corrected by absorbance reading (dental bleeding score). 138 procedures were performed. When the perioperative dental bleeding score was correlated with the number of extracted teeth, the quantity of bleeding was found to be directly proportional to the procedure. Extractions of two or more teeth presented higher scores than single extractions (p = 0.003). In a comparative analysis between the VKA and non-anticoagulated groups, no significant difference in the scores was found. The previous history of complications in dental procedures (p = 0.001) and the use of additional hemostatic measures were higher in the VKA group (p = 0.017). VKA therapy did not impact significantly the volume of blood lost during dental extractions. Perioperative bleeding assessment might be a useful parameter for evaluating patients under antithrombotic treatment.

Protocol of a clinical trial study involving educational intervention in patients treated with warfarin.

BACKGROUND: Atrial fibrillation (AF) is the most common sustained arrhythmia worldwide. Oral anticoagulation is an effective strategy for primary and secondary prevention of stroke in patients with AF. Warfarin is an oral anticoagulant widely prescribed and, despite its benefits, the achievement of the goals of drug therapy depends on patient involvement, among other factors. Educational interventions can contribute for effectiveness and safety of oral anticoagulation therapy. We sought to describe the protocol of a clinical trial designed to evaluate the effect of a patient-centered educational strategy focused on low-income patients with AF and poor anticoagulation control. METHODS: Patients ≥18 years with AF, on warfarin for at least 6 months and time in therapeutic range (TTR) <60% will be recruited at 2 anticoagulation clinics (ACs) in Brazil. Patients from 1 AC will be allocated to the intervention group and patients from the other AC will be allocated to the control group. Intervention group will attend educational sessions based on a patient-centered care approach, and the control group will receive usual care. The intervention will be based on Paulo Freire's theory and tailored according to practices involving health empowerment and techniques applied to individuals with limited socioeconomic status. The intervention is estimated to last 5 months. We will consider TTR as the primary outcome and knowledge and self-reported non-adherence to warfarin therapy as secondary outcomes. TTR values and non-adherence will be measured before intervention (T0) and at times immediately after (T1), and 3 (T2), 6 (T3), 9 (T4), and 12 (T5) months after intervention. Knowledge will be measured at times T0, T1 e T5. The calculated sample size indicated 85 patients in each group. DISCUSSION: The proposed study aims to investigate whether an innovative educational approach to deliver care to a low-income population on warfarin improves anticoagulation control. Once our hypothesis is confirmed, our findings are expected to help improving anticoagulation control, knowledge on warfarin therapy and adherence to drug therapy. Thus, we believe our results may contribute to improve oral anticoagulation effectiveness in a low-income population. TRIAL REGISTRATION: Registro Brasileiro de Ensaios Clínicos (ReBEC) RBR- 9cy6py and UTN: U1111-1217-0151 (March, 2019).

Predictive ability of scores for bleeding risk in heart disease outpatients on warfarin in Brazil.

INTRODUCTION: Bleeding is a common complication in patients taking warfarin. We sought to compare the performance of nine prediction models for bleeding risk in warfarin-treated Brazilian outpatients. METHODS: The dataset was derived from a clinical trial conducted to evaluate the efficacy of an anticoagulation clinic at a public hospital in Brazil. Overall, 280 heart disease outpatients taking warfarin were enrolled. The prediction models OBRI, Kuijer et al., Kearon et al., HEMORR2HAGES, Shireman et al., RIETE, HAS-BLED, ATRIA and ORBIT were compared to evaluate the overall model performance by Nagelkerke's R2 estimation, discriminative ability based on the concordance (c) statistic and calibration based on the Hosmer-Lemeshow goodness-of-fit statistic. The primary outcomes were the first episodes of major bleeding, clinically relevant non-major bleeding and non-major bleeding events within 12 months of follow-up. RESULTS: Major bleeding occurred in 14 participants (5.0%), clinically relevant non-major bleeding in 29 (10.4%), non-major bleeding in 154 (55.0%) and no bleeding at all in 115 (41.1%). Most participants with major bleeding had their risk misclassified. All the models showed low overall performance (R2 0.6-9.3%) and poor discriminative ability for predicting major bleeding (c <0.7), except Shireman et al. and ORBIT models (c 0.725 and 0.719, respectively). Results were not better for predicting other bleedings. All models showed good calibration for major bleeding. CONCLUSIONS: Only two models (Shireman et al. and ORBIT) showed at least acceptable performance in the prediction of major bleeding in warfarin-treated Brazilian patients. Accurate models warrant further investigation to be used in similar populations.

Langerhans cell histiocytosis: a 16-year experience.

OBJECTIVES: To describe the clinical course of Langerhans cell histiocytosis and to compare its outcome according to age, staging of the disease and treatment response. METHODS: Retrospective analysis of data on 33 children with Langerhans cell histiocytosis followed at Hospital das Clínicas, Universidade Federal de Minas Gerais, Brazil, between 1988 and 2004. RESULTS: Age at diagnosis ranged from 2 months to 16 years (median: 2.5 years). Seventeen children were male. The follow-up period varied from 21 days to 16.2 years (median: 3.4 years). The most common clinical manifestations at diagnosis were osteolytic lesions, enlarged lymph nodes and skin lesions. The overall survival rate for the whole group was 86.1% at 16 years (95%CI 66.6-94.6%). Deaths occurred in patients with multisystem disease and organ dysfunction at diagnosis. Those patients who had a "better" response to treatment in the sixth week were likely to have a significantly higher overall survival rate than those who showed disease progression. Overall survival rate was significantly higher for patients with single-system disease. The disease-free survival rate for the whole group was 30.9% at 16 years (95%CI 15.6-47.5%), and was significantly higher for those with single-system disease. Age groups were not associated with different disease-free survival rates. Diabetes insipidus was the most common sequela. No cases of secondary neoplasms were observed. CONCLUSION: The clinical manifestations of Langerhans cell histiocytosis vary widely, with a high relapse rate and low mortality rate.

Cross-cultural Adaptation of the Oral Anticoagulation Knowledge Test to the Brazilian Portuguese. / Adaptação Transcultural do Oral Anticoagulation Knowledge Test para o Português do Brasil.

Patients' knowledge about oral anticoagulant therapy may favor the achievement of therapeutic results and the prevention of adverse pharmacotherapy-related events. Brazil lacks validated instruments for assessing the patient's knowledge about treatment with warfarin. This study aimed to perform the cross-cultural adaptation of the Oral Anticoagulation Knowledge (OAK) Test instrument from English into Portuguese. This is a methodological study developed in an anticoagulation clinic of a public university hospital. The study included initial translation, synthesis of translations, back-translation, review by the experts committee and pre-testing with 30 individuals. We obtained semantic equivalence through the analysis of the referential and general meaning of each item. The conceptual equivalence of the items sought to demonstrate the relevance and acceptability of the instrument. The process of cross-cultural adaptation produced the final version of the OAK Test in Brazilian Portuguese entitled "Teste de Conhecimento sobre Anticoagulação Oral". There was a suitable semantic and conceptual equivalence between the adapted version and the original version, as well as an excellent acceptability of this instrument.

Factor V Leiden and increased risk for arterial thrombotic disease in young Brazilian patients.

The contribution of mutations in the prothrombin (FII G20210A), methylenetetrahydrofolate reductase (C677T) genes and factor V Leiden (FVL) to the pathogenesis of arterial thrombosis remains controversial. In this study, these polymorphisms were investigated by polymerase chain reaction-restriction fragment length polymorphism in a group of 53 patients that presented arterial thrombosis other than myocardial infarction as a first thrombotic event and 275 control subjects living in the state of Minas Gerais, Brazil. Odds ratio (OR) and chi tests were applied for statistical comparisons. Similar frequencies were detected among patients and control subjects for the C677T mutation. The 20210A mutation was present in 3.6% of the control subjects but was not detected among ischemic stroke patients. Significant differences were detected only for factor V Leiden (odds ratio 7.11; 95% confidence interval 1.55-32.73). Our data indicate that, among these genetic factors, factor V Leiden was identified as an important risk factor for arterial thrombosis in this group of patients. In addition, our results indicate regional differences in the incidence of these genetic factors in Brazil, as compared to the incidences reported in other studies.

Clotting factor XIII and desmopressin improve hemostasis in uncontrolled bleeding.

PURPOSE: To investigate hemostatic effects of supplementary factor XIII and desmopressin (DDAVP) in resuscitation of uncontrolled bleeding. METHODS: Fifty-four rabbits were randomized in nine groups: G1: Sham; G2: FXIII and normotensive resuscitation (NBP); G3: FXIII and permissive hypotension (PH) (MAP 60% baseline); G4: FXIII/DDAVP/NBP; G5: FXIII/DDAVP/PH; G6: NBP only; G7: FXIII no hemorrhage; G8: FXIII/DDAVP no hemorrhage; G9: PH only. Thromboelastometry and intra-abdominal blood loss were assessed. Scanning electron microscopy (EM) of the clots was performed. RESULTS: Compared to Sham, only G8 (FXIII/DDAVP w/o hemorrhage) showed clotting time (CT) significantly lower (p<0.05). NBP alone (G6) resulted in significantly prolonged CT compared to G2, G3 and G5 (p<0.05). Similarly, median alpha angle was significantly larger in G3,4,5, and 9 compared to G6 (p<0.05). Area under the curve was significantly greater in G5 than G2. Intra-abdominal blood loss was lower in G5 and G9 compared to G2 and G6. FXIII/DDAVP and PH resulted in more robust fibrin mesh by EM. CONCLUSIONS: Normotensive resuscitation provokes more bleeding and worsens coagulation compared to pH, that is partially reversed by factor XIII and desmopressin. FXIII and DDAVP can synergistically improve coagulation. Permissive hypotension reduces bleeding regardless of those agents.

Polymorphisms of CYP2C9, VKORC1, MDR1, APOE and UGT1A1 genes and the therapeutic warfarin dose in Brazilian patients with thrombosis: a prospective cohort study.

BACKGROUND: There are several pharmacogenetic algorithms to determine the warfarin doses required in patients treated for thromboembolism, but they only explain 60% of dose variation, suggesting that other genes may influence the dose required. OBJECTIVES: This study aimed to evaluate the impact of clinical factors and CYP2C9*2, CYP2C9*3, VKORC1-1639G>A, MDR1 3435C>T, APOE* ε4, and UGT1A1(TA)n polymorphisms on the warfarin dose required, especially in those individuals requiring a high warfarin dose. METHODS: We studied 116 Brazilian patients who received warfarin therapy for thromboembolism. Associations between dose variability and age, body mass index (BMI), gender, use of warfarin antagonists, and genetic polymorphisms were examined. RESULTS: CYP2C9*2, CYP2C9*3, VKORC1-1639G>A, and APOE *ε4 were associated with lower warfarin doses. Of these subjects, 21% required a warfarin dose higher than 70 mg/week, which was associated with a BMI greater than 25 kg/m(2), use of warfarin antagonists, and the presence of the MDR1 3435T allele and UGT1A1(TA) 7 polymorphism. These individuals were considered to exhibit warfarin resistance. The individuals with the MDR1 3435TT genotype required a dose 21% higher than that required by 3435CT and 3435CC individuals. The UGT1A1(TA) 7 allele was positively correlated with the warfarin dose. CONCLUSION: CYP2C9*2, CYP2C9*3, VKORC1-1639G>A, and APOE *ε4 were associated with lower warfarin doses, while MDR1 3435C>T and UGT1A1(TA) n polymorphisms were associated with a requirement for higher doses. This is the first study to evaluate warfarin resistance, APOE *ε4 and UGT1A1(TA) n genotypes in the Brazilian population, and the association of these two genotypes with warfarin dose required.