warfarin and Metabolism--Inborn-Errors

Anticoagulant and antiplatelet drugs effectively prevent thrombotic events in patients with cardiovascular diseases, ischemic stroke, peripheral vascular diseases, and other thromboembolic diseases. However, genetic and non-genetic factors affect the response to antithrombotic therapy and can increase the risk of adverse events. This narrative review discusses pharmacogenomic studies on antithrombotic drugs commonly prescribed in Brazil. Multiple Brazilian studies assessed the impact of pharmacokinetic (PK) and pharmacodynamic (PD) gene variants on warfarin response. The reduced function alleles CYP2C9*2 and CYP2C9*3, and VKORC1 rs9923231 (c.-1639G>A) are associated with increased sensitivity to warfarin and a low dose requirement to prevent bleeding episodes, whereas CYP4F2 rs2108622 (p.Val433Met) carriers have higher dose requirements (warfarin resistance). These deleterious variants and non-genetic factors (age, gender, body weight, co-administered drugs, food interactions, and others) account for up to 63% of the warfarin dose variability. Few pharmacogenomics studies have explored antiplatelet drugs in Brazilian cohorts, finding associations between CYP2C19*2, PON1 rs662 and ABCC3 rs757421 genotypes and platelet responsiveness or clopidogrel PK in subjects with coronary artery disease (CAD) or acute coronary syndrome (ACS), whereas ITGB3 contributes to aspirin PK but not platelet responsiveness in diabetic patients. Brazilian guidelines on anticoagulants and antiplatelets recommend the use of a platelet aggregation test or genotyping only in selected cases of ACS subjects without ST-segment elevation taking clopidogrel, and also suggest CYP2C9 and VKORC1 genotyping before starting warfarin therapy to assess the risk of bleeding episodes or warfarin resistance.

Topics: Anticoagulants; Aryldialkylphosphatase; Brazil; Clopidogrel; Cytochrome P-450 CYP2C9; Fibrinolytic Agents; Genotype; Humans; Metabolism, Inborn Errors; Pharmacogenetics; Platelet Aggregation Inhibitors; Vitamin K Epoxide Reductases; Warfarin

Warfarin and other 4-hydroxycoumarin-based oral anticoagulants targeting vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) are administered to humans, mice and rats with different purposes in mind - to act as pesticides in high-dosage baits for killing rodents, but also to save lives when administered in low dosages as antithrombotic drugs in humans. However, high-dosage warfarin used to control rodent populations has resulted in numerous mutations causing warfarin resistance. Currently, six single missense mutations in mice, 12 distinct missense mutations in rats, as well as compound heterozygous or homozygous mutations with up to six distinct missense mutations per Vkorc1 allele have been described. Warfarin resistance missense mutations for human VKORC1 have also been found world-wide, but differ characteristically from those in rodents. In humans, 26 distinct mutations have been characterized, but occur only rarely either in heterozygous or, even rarer, in homozygous form. In this review, we summarize the known VKORC1 missense mutations causing warfarin and other 4-hydroxycoumarin drug resistance, identify genomics databases as new sources of data, explore possible underlying genetic mechanisms, and summarize similarities and differences between warfarin resistant VKORC1 variants in humans and rodents.

Topics: Anticoagulants; Genetic Predisposition to Disease; Humans; Metabolism, Inborn Errors; Mutation, Missense; Thrombosis; Vitamin K Epoxide Reductases; Warfarin

Topics: Antipyrine; Binding Sites; Humans; Metabolic Clearance Rate; Metabolism, Inborn Errors; Orosomucoid; Pharmaceutical Preparations; Phenotype; Polymorphism, Genetic; Propranolol; Protein Binding; Serum Albumin; Warfarin

Topics: Adult; Aged; Alcohol Oxidoreductases; Antipyrine; Asian People; Child, Preschool; Cholinesterases; Cyanides; Dicumarol; Diseases in Twins; Drug Hypersensitivity; Erythrocytes; Favism; Female; Glucosephosphate Dehydrogenase Deficiency; Hemoglobins; Humans; Isoniazid; Liver; Male; Metabolism, Inborn Errors; Middle Aged; Pharmacogenetics; Phenylbutazone; Phenylthiourea; Phenytoin; Pregnancy; Primaquine; Twins; Warfarin

The increased warfarin sensitivity observed after mechanical mitral valve replacement (MVR) operations dictates clinical discretion in warfarin dose initiation. Evidence is still lacking with regard to anticoagulation management of MVR patients.. This study aimed to compare initiating warfarin at the recommended dosing regimen versus empirically lowered doses intended to account for the variation in warfarin sensitivity.. A prospective, single-blind, randomized, comparative study was conducted in postoperative MVR patients. Patients were randomly assigned to either the 5 mg group (n = 25) or the 3 mg group (n = 25) and were initiated on a 5 or 3 mg warfarin dose, respectively. Time to target international normalized ratio (INR), time in therapeutic range, occurrence of bleeding/thromboembolic events, and cost of bridging with enoxaparin were assessed for both groups.. Target INR was achieved earlier in the 5 mg group than in the 3 mg group (p = 0.033), with a mean ± SD of 5.3 ± 2.0 and 6.6 ± 2.0, respectively (95% confidence interval of the mean difference 1.022-1.890). Bleeding events did not differ significantly between the two groups. The cost of enoxaparin consumption per patient was significantly higher in the 3 mg group versus the 5 mg group (p = 0.002).. The initiation of warfarin at a 5 mg dose in MVR patients was more efficacious than the 3 mg dose in terms of time to reach the target INR. Moreover, the cost of enoxaparin bridging was significantly reduced with a 5 mg warfarin initiation dose. Bleeding events were comparable.. NCT04235569, 22 January 2020.

Topics: Anticoagulants; Drug Resistance; Enoxaparin; Hemorrhage; Humans; International Normalized Ratio; Metabolism, Inborn Errors; Mitral Valve; Prospective Studies; Single-Blind Method; Warfarin

Missense vitamin K epoxide reductase (VKOR) mutations in patients cause resistance to warfarin treatment but not abnormal bleeding due to defective VKOR activity. The underlying mechanism of these phenotypes remains unknown. Here we show that the redox state of these mutants is essential to their activity and warfarin resistance. Using a mass spectrometry-based footprinting method, we found that severe warfarin-resistant mutations change the VKOR active site to an aberrantly reduced state in cells. Molecular dynamics simulation based on our recent crystal structures of VKOR reveals that these mutations induce an artificial opening of the protein conformation that increases access of small molecules, enabling them to reduce the active site and generating constitutive activity uninhibited by warfarin. Increased activity also compensates for the weakened substrate binding caused by these mutations, thereby maintaining normal VKOR function. The uninhibited nature of severe resistance mutations suggests that patients showing signs of such mutations should be treated by alternative anticoagulation strategies.

Topics: Anticoagulants; Humans; Metabolism, Inborn Errors; Vitamin K Epoxide Reductases; Warfarin

Warfarin is a widely used anticoagulant with a narrow therapeutic index and large interpatient variability in the therapeutic dose. Warfarin sensitivity has been reported to be associated with increased incidence of international normalized ratio (INR) > 5. However, whether warfarin sensitivity is a risk factor for adverse outcomes in critically ill patients remains unknown. In the present study, we aimed to evaluate the utility of different machine learning algorithms for the prediction of warfarin sensitivity and to determine the impact of warfarin sensitivity on outcomes in critically ill patients.. Nine different machine learning algorithms for the prediction of warfarin sensitivity were tested in the International Warfarin Pharmacogenetic Consortium cohort and Easton cohort. Furthermore, a total of 7,647 critically ill patients was analyzed for warfarin sensitivity on in-hospital mortality by multivariable regression. Covariates that potentially confound the association were further adjusted using propensity score matching or inverse probability of treatment weighting.. We found that logistic regression (AUC = 0.879, 95% CI: 0.834-0.924) was indistinguishable from support vector machine with a linear kernel, neural network, AdaBoost and light gradient boosting trees, and significantly outperformed all the other machine learning algorithms. Furthermore, we found that warfarin sensitivity predicted by the logistic regression model was significantly associated with worse in-hospital mortality in critically ill patients with an odds ratio (OR) of 1.33 (95% CI, 1.01-1.77).. Our data suggest that the logistic regression model is the best model for the prediction of warfarin sensitivity clinically and that warfarin sensitivity is likely to be a risk factor for adverse outcomes in critically ill patients.

Topics: Algorithms; Anticoagulants; Critical Illness; Drug Resistance; Hospital Mortality; Humans; International Normalized Ratio; Metabolism, Inborn Errors; Warfarin

Effective prevention of thromboembolism is essential for patients with mechanical prosthetic heart valves. For this group of patients, vitamin K antagonists (VKAs) remain the drug group of choice despite the widespread use of new anticoagulants in other diseases. As a consequence, warfarin resistance remains a serious challenge for physicians. The current report describes a 65-year-old male patient that had a mechanical prosthetic aortic valve implanted due to severe aortic insufficiency after infective endocarditis. Despite consistent increases in his warfarin dose, the level of international normalized ratio (INR) remained very low. The patient was considered to have warfarin resistance. Warfarin was successfully replaced by another VKA, acenocoumarol, which resulted in a stable INR observed over 1 year of follow-up. Achieving the target INR in patients with mechanical prosthetic heart valves using VKAs is the main goal of thromboprophylaxis. Although the genetic changes that cause warfarin resistance are understood, the options to overcome these pharmacogenetic issues remain limited. Based on the success with this current patient, physicians with similar patients with warfarin resistance might wish to consider replacing warfarin with acenocoumarol.

Topics: Acenocoumarol; Aged; Anticoagulants; Fibrinolytic Agents; Heart Valve Prosthesis; Humans; International Normalized Ratio; Male; Metabolism, Inborn Errors; Venous Thromboembolism; Warfarin

To describe the impact of hospitalization with COVID-19 infection on warfarin dose requirements in adult inpatients.. A retrospective chart review of 8 adults on warfarin admitted to Michigan Medicine with COVID-19 infection was conducted and reported as a case series. Outcomes of interest were difference in average daily dose of warfarin prior to admission (PTA) and while inpatient (IP), warfarin sensitivity, time in therapeutic range (TTR), confirmed or suspected thromboembolic event, any major or clinically significant bleeding episodes, and in-hospital mortality. IP average daily warfarin doses were lower when compared to PTA average daily doses [1.3 mg (1.3) vs. 6.2 mg (4.1)]. The mean percentage decrease in dose was 68.8% (23) and the mean absolute dose difference was 4.8 mg (4.3). Mean IP percentage tests in range was 30.8% (24.6) and mean IP warfarin sensitivity was 4.2 (3.8), both of which differed from PTA TTR and warfarin sensitivity for those with data available (n = 3, n = 6, respectively). One patient was treated for suspected acute pulmonary embolism while on warfarin and one patient experienced clinically relevant bleeding. In-hospital mortality was zero, mean length of stay (LOS) was 17 days (14.4), and mean intensive care unit (ICU) LOS for the 3 patients requiring ICU level care was 14.3 days (4.5).. Decreased warfarin dose requirements were evident in this group of adults hospitalized with COVID-19 infection. These findings suggest lower doses of warfarin may be needed to achieve therapeutic anticoagulation while inpatient.

Topics: Adult; Anticoagulants; COVID-19 Drug Treatment; Drug Resistance; Hospitalization; Humans; International Normalized Ratio; Metabolism, Inborn Errors; Retrospective Studies; Warfarin

Vitamin K epoxide reductase (VKOR) drives the vitamin K cycle, activating vitamin K-dependent blood clotting factors. VKOR is also the target of the widely used anticoagulant drug, warfarin. Despite VKOR's pivotal role in coagulation, its structure and active site remain poorly understood. In addition, VKOR variants can cause vitamin K-dependent clotting factor deficiency or alter warfarin response. Here, we used multiplexed, sequencing-based assays to measure the effects of 2,695 VKOR missense variants on abundance and 697 variants on activity in cultured human cells. The large-scale functional data, along with an evolutionary coupling analysis, supports a four transmembrane domain topology, with variants in transmembrane domains exhibiting strongly deleterious effects on abundance and activity. Functionally constrained regions of the protein define the active site, and we find that, of four conserved cysteines putatively critical for function, only three are absolutely required. Finally, 25% of human VKOR missense variants show reduced abundance or activity, possibly conferring warfarin sensitivity or causing disease.

Topics: Catalytic Domain; Cysteine; Drug Resistance; Genetic Variation; HEK293 Cells; Humans; Metabolism, Inborn Errors; Models, Molecular; Mutation, Missense; Sequence Analysis, DNA; Vitamin K Epoxide Reductases; Warfarin

To investigate the frequency and degree of azole antifungal agents that influence the anticoagulant activity of warfarin to reduce the potential bleeding risk and provide a reference for rational administration of warfarin in clinics.Patients with an abnormal international normalized ratio (INR; INR ≥ 4.5) and treated with warfarin plus azole antifungal agents were screened from February 2011 to July 2016, and their data were extracted.Thirty-two patients treated with warfarin plus azole antifungal agents were included. The INR of all the included patients increased by more than 20% of the INR of warfarin alone, and the warfarin sensitivity index showed an upward trend. The INRs of 21 patients treated with fluconazole (FLCZ) and warfarin was closely monitored for 1 week after the combination treatment, and the interaction between warfarin and the azole antifungal agents peaked on the seventh day. The INRs when warfarin was coadministered with azoles (Y) correlated significantly with those in the absence of azoles (X): FLCZ: Y = 1.2515X + 2.1538, R = 0.8128; and voriconazole Y = 2.4144 X + 2.6216, R2 = 0.7828.The combination of FLCZ and voriconazole will enhance the anticoagulant effect of warfarin. Therefore, it is recommended to detect the genotype of CYP2C9 in patients and evaluate the interaction between the 2 drugs to adjust the warfarin dose. It is also recommended to closely monitor INR within 1 week of the addition of azole antifungal agents.

Topics: Adult; Aged; Anticoagulants; Antifungal Agents; Azoles; Cardiovascular Diseases; Cytochrome P-450 CYP2C9; Drug Resistance; Drug Therapy, Combination; Female; Genotype; Humans; International Normalized Ratio; Male; Metabolism, Inborn Errors; Middle Aged; Retrospective Studies; Treatment Outcome; Warfarin

Warfarin is a widely used anticoagulant with a narrow therapeutic index and large interpatient variability in the therapeutic dose. Complications from inappropriate warfarin dosing are one of the most common reasons for emergency room visits. Approximately one third of warfarin dose variability results from common genetic variants. Therefore, it is very necessary to recognize warfarin sensitivity in individuals caused by genetic variants. Based on combined polymorphisms in CYP2C9 and VKORC1, we established a clinical classification for warfarin sensitivity. In the International Warfarin Pharmacogenetic Consortium (IWPC) with 5542 patients, we found that 95.1% of the Black in the IWPC cohort were normal warfarin responders, while 74.8% of the Asian were warfarin sensitive (P < 0.001). Moreover, we created a clinical algorithm to predict warfarin sensitivity in individual patients using logistic regression. Compared to a fixed-dose approach, the clinical algorithm provided significantly better performance. In addition, we validated the derived clinical algorithm using the external Easton cohort with 106 chronic warfarin users. The AUC was 0.836 vs. 0.867 for the Easton cohort and the IWPC cohort, respectively. With the use of this algorithm, it is very likely to facilitate patient care regarding warfarin therapy, thereby improving clinical outcomes.

Topics: Aged; Aged, 80 and over; Algorithms; Anticoagulants; Cohort Studies; Cytochrome P-450 CYP2C9; Drug Resistance; Female; Genotype; Humans; Logistic Models; Male; Metabolism, Inborn Errors; Middle Aged; Pharmacogenomic Variants; Polymorphism, Single Nucleotide; Prognosis; Vitamin K Epoxide Reductases; Warfarin

Warfarin shows large inter- and intra-individual variabilities in its pharmacokinetics and pharmacodynamics. Sufficient understanding of factors affecting the response to warfarin is necessary to achieve improved outcomes for warfarin therapy. In this study, we evaluated effects of fasting on the anticoagulant properties of warfarin.. We conducted a retrospective observational study involving a total of 58 patients, who received cardiovascular surgeries and subsequent warfarin therapy. The effect of dietary intake on the anticoagulant properties with warfarin was assessed by measurement of the international normalized ratio of prothrombin time (PT-INR): the anticoagulant activities of warfarin were expressed as the warfarin sensitivity index (WSI). Additionally, fluctuations in WSI during the study period were obtained as differences between the maximum and minimum WSI.. The maximum PT-INR and WSI values were significantly higher for patients who were fasting for different reasons during the postoperative period than those in the group without reduced dietary intake. The differences between maximum and minimum WSI in the fasting group significantly increased compared with those in the groups with moderate or no reduced dietary intake. Meanwhile, effects of other markers of clinical conditions including the baseline Child-Pugh score and Charlson Comorbidity Index on WSI were not significant.. Our results indicate that postoperative fasting was significantly associated with the anticoagulation activity of warfarin. In patients fasting for different reasons during the postoperative period, closer control of PT-INR values and warfarin adjustments may be required to avoid adverse effects such as bleeding in warfarin treatment.

Topics: Aged; Aged, 80 and over; Anticoagulants; Blood Coagulation; Blood Coagulation Tests; Drug Resistance; Fasting; Hemorrhage; Humans; International Normalized Ratio; Metabolism, Inborn Errors; Middle Aged; Prothrombin Time; Retrospective Studies; Warfarin

Warfarin is the most commonly prescribed anticoagulant drug; however, a narrow therapeutic range and a high risk of bleeding or stroke complicate its clinical use. Warfarin resistance was defined as prolonged warfarin requirements of more than 15 mg/day to achieve therapeutic anticoagulation or failure to achieve therapeutic anticoagulation with more than 20 mg/day. The resistance is associated with polymorphisms of the vitamin K epoxide reductase-oxidase complex (VKORC1) and cytochrome P450-2C9 (CYP2C9) genes, which affect warfarin pharmacodynamics and pharmacokinetics, respectively. Identification of the VKORC1 -1639 (A/G) and CYP2C9 (*1/*2/*3) allelic variants was performed using the PGX-Thrombo Strip in 41 patients with warfarin resistance compared with 30 patients with normal warfarin response out of 352 diagnosed cases of deep vein thrombosis. In warfarin-resistant patients, the VKORC1-1639 genotype frequencies were GG 0.756, GA 0.244 and AA 0.0, whereas in warfarin responder patients, they were: GG 0.333, GA 0.400 and AA 0.276 with P ≤ 0.001. The CYP2C9 genotype frequencies showed nonsignificant difference in both group of patients (P = 0.31). Our results suggest that the VKORC1-1639 GG and the wild type CYP2C9*1*1genotypes are associated with the high-dose requirement for warfarin therapy, and that VKORC1-1639 GG is responsible for warfarin resistance and failure in Egyptian patients.

Topics: Adult; Alleles; Anticoagulants; Arabs; Cytochrome P-450 CYP2C9; Drug Administration Schedule; Egypt; Female; Gene Expression; Gene Frequency; Genotype; Humans; Male; Metabolism, Inborn Errors; Middle Aged; Polymorphism, Genetic; Prospective Studies; Venous Thrombosis; Vitamin K Epoxide Reductases; Warfarin

Coumarin-derivative anticoagulant rodenticides used for rodent control are posing a serious risk to wild bird populations. For warfarin, a classic coumarin derivative, chickens have a high median lethal dose (LD50), whereas mammalian species generally have much lower LD50. Large interspecies differences in sensitivity to warfarin are to be expected. The authors previously reported substantial differences in warfarin metabolism among avian species; however, the actual in vivo pharmacokinetics have yet to be elucidated, even in the chicken. In the present study, the authors sought to provide an in-depth characterization of warfarin metabolism in birds using in vivo and in vitro approaches. A kinetic analysis of warfarin metabolism was performed using liver microsomes of 4 avian species, and the metabolic abilities of the chicken and crow were much higher in comparison with those of the mallard and ostrich. Analysis of in vivo metabolites from chickens showed that excretions predominantly consisted of 4'-hydroxywarfarin, which was consistent with the in vitro results. Pharmacokinetic analysis suggested that chickens have an unexpectedly long half-life despite showing high metabolic ability in vitro. The results suggest that the half-life of warfarin in other bird species could be longer than that in the chicken and that warfarin metabolism may not be a critical determinant of species differences with respect to warfarin sensitivity.

Topics: Administration, Oral; Animals; Biological Assay; Birds; Chickens; Cytochrome P-450 Enzyme System; Drug Resistance; Feces; Female; Half-Life; Kinetics; Male; Metabolism, Inborn Errors; Metabolome; Microsomes, Liver; Rats, Wistar; Warfarin

Warfarin, a racemic mixture of S- and R-enantiomers, is the cornerstone of therapy in patients following cardiac valve replacement. S-warfarin is metabolized to 7-S-hydroxywarfarin by the cytochrome P450 isoform 2C9 encoded by CYP2C9 gene. R-warfarin is metabolized by multiple cytochromes P450. We sought to assess the impact of clinical and genetic factors on circulating warfarin metabolites following valve implantation.. Venous blood was collected from 120 patients after 3 months since elective mitral and/or aortic valve replacement. Plasma S-warfarin, R-warfarin, S-7-hydroxywarfarin, and R-7-hydroxywarfarin were determined using high-performance liquid chromatography. The S-7-hydroxywarfarin/S-warfarin and S-warfarin/R-warfarin (S/R) ratios, along with warfarin sensitivity index (WSI), defined as INR/S-warfarin ratio, were calculated. Vitamin K epoxide reductase complex subunit 1 (VKORC1) c.-1639A, CYP2C9*3 and CYP2C9*2 alleles were determined using real-time polymerase chain reaction.. The S-warfarin was higher in former smokers (p = 0.047) and the VKORC1 c.-1639A allele carriers (p < 0.0001). The S-7-hydroxywarfarin was lower in carriers of the VKORC1 c.-1639A allele (p = 0.0005) and CYP2C9*3 (p = 0.047). The S-7-hydroxywarfarin/S-warfarin ratio was lower in the carriers of CYP2C9*3 (p = 0.008), but not in those with VKORC1 -c.1639A allele. The S/R ratio was higher in patients with hypertension (p = 0.01). The independent predictors of elevated S/R ratio defined as the upper quartile were diabetes (p = 0.045), CYP2C9*3 (p < 0.0001) and CYP2C9*2 (p = 0.0002). The independent predictors of elevated WSI were current smoking (p = 0.049), implantation of mechanical valve (p = 0.006) and VKORC1c.-1639A allele (p = 0.007).. We conclude that not only genetic, but also several clinical factors affect warfarin metabolites in patients following cardiac valve implantation.

Topics: Alleles; Aortic Valve; Cytochrome P-450 CYP2C9; Drug Resistance; Female; Humans; Male; Metabolism, Inborn Errors; Middle Aged; Mitral Valve; Vitamin K Epoxide Reductases; Warfarin

Warfarin is the most frequently prescribed anticoagulant for the long-term treatment in the clinic. Recent studies have shown that polymorphic alleles within the CYP2C9, VKORC1, and CYP4F2 genes are related to the warfarin dosage requirement. In this study, a novel non-synonymous mutation (1009C>A) in CYP2C9 was detected in a warfarin-hypersensitive patient, while the other two candidate genes were both found to be homozygous for the wild-type alleles. The newly identified point mutation results in an amino acid substitution at position 337 of the CYP2C9 protein (P337T) and has been designated as the novel allele CYP2C9*58. When expressed in insect cell microsomes, the relative intrinsic clearance values of the CYP2C9.58 variant for tolbutamide and losartan were quite similar to those of the typical defective variant CYP2C9.3, whereas the clearance value of CYP2C9.58 for diclofenac was slightly higher than that of another typical defective variant CYP2C9.2. These data suggested that when compared with wild-type CYP2C9.1, the enzymatic activity of the novel allelic variant has been greatly reduced by the 1009C>A mutation. If patients carrying this allele take drugs metabolized by CYP2C9, their metabolic rate might be slower than that of wild-type allele carriers and thus much more attention should be paid to their clinical care.

Topics: Aged; Alleles; Amino Acid Substitution; Anticoagulants; Cytochrome P-450 CYP2C9; Drug Resistance; Female; Genetic Association Studies; Genetic Variation; Humans; Metabolism, Inborn Errors; Microsomes; Point Mutation; Warfarin

The package insert of the antithrombotic agent warfarin warns users of its interaction with azole antifungals. However, information on the frequency or degree of these interactions is limited. In particular, the time to onset of azole-mediated prothrombin time prolongation, expressed as the international normalized ratio (INR), is poorly characterized. Therefore, we retrospectively examined the INR in 29 patients administered warfarin with fluconazole (FLCZ), voriconazole (VRCZ), or itraconazole (ITCZ). INRs in 18 patients taking FLCZ and in 5 patients taking VRCZ significantly increased from 1.40 to 2.94 and from 1.95 to 2.89, respectively. The warfarin sensitivity index (WSI), calculated as INR/daily warfarin dose, also significantly increased from 1.06 to 1.89 with FLCZ and showed an upward trend from 1.13 to 2.23 with VRCZ. ITCZ had no influence on the INR or WSI in 6 patients. The INRs observed when warfarin was coadministered with azoles (Y) correlated significantly with those observed in the absence of azoles (X): FLCZ, Y=4.94X-3.96, r(2)=0.80; VRCZ, Y=2.13X-1.27, r(2)=0.93. Moreover, in all 8 patients with closely monitored INRs, the WSI increased within 1 week of FLCZ or VRCZ coadministration. In conclusion, FLCZ and VRCZ augmented the anticoagulant activity of warfarin. The INR should be closely monitored within 1 week of initiating FLCZ or VRCZ coadministration with warfarin, especially in patients with high INRs.

Topics: Adult; Aged; Aged, 80 and over; Anticoagulants; Antifungal Agents; Drug Interactions; Drug Resistance; Female; Fluconazole; Humans; International Normalized Ratio; Itraconazole; Male; Metabolism, Inborn Errors; Middle Aged; Retrospective Studies; Voriconazole; Warfarin

Warfarin directly inhibits the vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) enzyme to effect anticoagulation. VKORC1 function has historically been assessed in vitro using a dithiothreitol (DTT)-driven vitamin K 2,3-epoxide reductase (VKOR) assay. Warfarin inhibits wild-type VKORC1 function by the DTT-VKOR assay. However, VKORC1 variants with warfarin resistance-associated missense mutations often show low VKOR activities and warfarin sensitivity instead of resistance.. A cell culture-based, indirect VKOR assay was developed and characterized that accurately reports warfarin sensitivity or resistance for wild-type and variant VKORC1 proteins.. Human coagulation factor (F)IX and VKORC1 variants were coexpressed in HEK 293T cells under standardized conditions at various warfarin concentrations. Secreted FIX activity served as surrogate marker to report wild-type and variant VKORC1 inhibition by warfarin.. Warfarin dose-response curves fit to the secreted FIX activity data for coexpressed hVKORC1 wild-type, Val29Leu, Val45Ala and Leu128Arg variants. The corresponding calculated IC50 values were 24.7, 136.4, 152.0 and 1226.4 nm, respectively. Basal activities in the absence of warfarin for all VKORC1 variants were similar to that of wild-type VKORC1. Ranked IC50 values from the cell culture-based assay accurately reflect elevated warfarin dosages for patients with VKORC1 missense mutation-associated warfarin resistance.

Topics: Anticoagulants; Dithiothreitol; HEK293 Cells; Humans; Inhibitory Concentration 50; Metabolism, Inborn Errors; Mutation, Missense; Phenotype; Vitamin K Epoxide Reductases; Warfarin

The aim of the present study was to investigate the genetic variability of VKORC1, CYP2C9 and CYP4F2 genes in patients who required a very low and high warfarin dose, in order to identify novel variants that could help to explain the particular extreme dose requirements.. Among patients followed and treated with warfarin at the Center of Haemostasis and Thrombosis of the PTV, we selected twelve patients showing a high divergence from warfarin standard doses required to achieve the therapeutic effect. All VKORC1, CYP2C9 and CYP4F2 coding regions, 3' and 5' UTR and exon/intron boundaries were analyzed by direct sequencing.. The 1173T and -1639A allele variants in VKORC1 gene, associated with warfarin sensitivity, were present, as expected, mostly in low dose patients while 3730A allele, linked to warfarin resistance, has been found only in high dose patients. Interestingly, we found that three out of six low dose subjects presented CYP2C9*3/*3 homozygous genotype, very rare in Caucasians. Besides these common polymorphisms, we identified 5 SNPs in CYP2C9 gene and 19 SNPs in CYP4F2 gene. Among these, all polymorphisms identified in CYP2C9 gene were present only in low dose patients and three of them resulted in linkage with CYP2C9*2 and CYP2C9*3. Regarding CYP4F2 SNPs, we did not observe differences between the high and low dose patients. At the end, the whole sequencing did not reveal any novel polymorphism/mutation.. Further studies are required to identify other genetic factors contributing to extreme warfarin requirement.

Topics: Anticoagulants; Aryl Hydrocarbon Hydroxylases; Cytochrome P-450 CYP2C9; Cytochrome P-450 Enzyme System; Cytochrome P450 Family 4; Dose-Response Relationship, Drug; Drug Resistance; Humans; Italy; Metabolism, Inborn Errors; Pharmacogenetics; Polymorphism, Single Nucleotide; Vitamin K Epoxide Reductases; Warfarin; White People

Some patients show warfarin resistance needing more than 70 mg of warfarin per week. In this study, we examined if C3435T polymorphism of MDR1 gene could be a factor of warfarin resistance.. We examined 196 blood specimens from the patients who took warfarin more than 42 mg/week for at least 1 year. The subjects consisted of 74 European Americans, 59 African Americans, 42 Hispanic Americans and 21 Asian Americans. Genotype of C3435T polymorphism was determined by using real-time polymerase chain reaction (PCR).. Ninety (45.9%) of the 196 patients had C3435T genotype and the remaining patients had C3435C genotype (35.7%) and T3435T genotype (18.4%). Mean dose of warfarin of patients with C3435C, C3435T and T3435T genotypes were 59.5mg/week, 56.9 mg/week and 55.6 mg/week, respectively. There was no statistical difference in the dose of warfarin between the 3 genotypes within each race.. Our results suggest that C3435T polymorphism of MDR1 gene is not associated with warfarin resistance.

Topics: Adult; Aged; Anticoagulants; ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Atrial Fibrillation; Drug Administration Schedule; Female; Gene Frequency; Genotype; Humans; Male; Metabolism, Inborn Errors; Middle Aged; Polymorphism, Single Nucleotide; Pulmonary Embolism; Racial Groups; Venous Thrombosis; Warfarin

We present a case report of a young man with spontaneous deep venous thrombosis. He tested positive for heterozygote factor V Leiden mutation and was treated with warfarin. However, he turned out to be resistant to warfarin, and another venous thrombosis occurred during the insufficient treatment. The antithrombotic treatment was then successfully replaced by phenprocoumon. This case report emphasizes the importance of critically evaluating the efficacy of a treatment and substitute if proven insufficient.

Topics: Activated Protein C Resistance; Adult; Anticoagulants; Humans; Male; Metabolism, Inborn Errors; Thrombophilia; Venous Thrombosis; Warfarin

The aim of this study was to reveal the contribution of CYP4F2, CYP2C9, and VKORC1 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of warfarin in Japanese pediatric patients. Genetic analyses of CYP4F2 (rs2108622), CYP2C9 (*2 and *3), and VKORC1 (-1639G>A) were performed, and plasma unbound warfarin, vitamin K1 (VK1), and menaquinone-4 (MK-4) concentrations were determined in 37 Japanese pediatric patients. The patients with CYP4F2 variant alleles C/T and T/T scored significantly lower values for the warfarin sensitivity index (INR/Cpss) and had significantly higher plasma concentrations of MK-4 than patients with the CYP4F2 allele C/C. Moreover, the plasma MK-4 concentration was negatively correlated with the warfarin sensitivity index. In contrast, the VKORC1 genetic polymorphism did not influence the warfarin sensitivity index. In patients with the CYP2C9 *3 allele, the unbound oral clearance values (normalized to body surface area) for S-warfarin were found to be significantly lower than in patients with the wild-type allele. In conclusion, CYP4F2 genetic polymorphism and plasma MK-4 concentration influence the pharmacodynamics of warfarin, suggesting a mechanism though which CYP4F2 genotype affects warfarin dose.

Topics: Adolescent; Alleles; Anticoagulants; Aryl Hydrocarbon Hydroxylases; Asian People; Child; Child, Preschool; Cytochrome P-450 CYP2C9; Cytochrome P-450 Enzyme System; Cytochrome P450 Family 4; Drug Resistance; Female; Humans; Infant; Male; Metabolism, Inborn Errors; Polymorphism, Genetic; Vitamin K 1; Vitamin K 2; Vitamin K Epoxide Reductases; Warfarin

Warfarin is a rodenticide commonly used worldwide. It inhibits coagulation of blood by inhibiting vitamin K 2,3-epoxide reductase (VKOR) activity. An inadequate supply of vitamin K blocks the production of prothrombin and causes hemorrhage. Recently, warfarin-resistant brown rats (Rattus norvegicus) were found around the Aomori area of Japan. There is no significant difference in the metabolic activity of warfarin in sensitive and resistant brown rats. To clarify the mechanism underlying warfarin resistance, we cloned the VKORC1 gene from rats and identified a novel substitution of arginine to proline at position 33 of the VKORC1 amino acid sequence. Then, we determined the differences in kinetics of VKOR activity between warfarin-resistant and sensitive rats. Hepatic microsomal VKOR-dependent activity was measured over a range of vitamin K epoxide concentrations from 6.25 to 150 µM. The Vmax values of resistant rats (0.0029 ± 0.020 nmol/min/mg) were about one tenth of those of sensitive rats (0.29 ± 0.12 nmol/min/mg). The Km values of resistant rats (47 ± 32 µM) were similar to those of sensitive rats (59 ± 18 µM). Warfarin-sensitive rats exhibited enzyme efficiencies (Vmax/Km) which were ten-fold greater than those observed in resistant rats. It may mean that VKOR activity of warfarin-resistant Aomori rats is almost lost, because their enzymatic efficiencies are very low even without warfarin. Further studies are needed to clarify how these rats can survive with a markedly reduced VKOR activity and how they simultaneously exhibit warfarin resistance.

Topics: Animals; Female; Gene Expression Regulation, Enzymologic; Japan; Male; Metabolism, Inborn Errors; Mixed Function Oxygenases; Mutation; Rats; Rats, Sprague-Dawley; RNA, Messenger; Rodenticides; Vitamin K; Vitamin K 1; Vitamin K Epoxide Reductases; Warfarin

Topics: Antithrombin III Deficiency; Female; Heparin; Humans; Metabolism, Inborn Errors; Pregnancy; Pregnancy Complications, Hematologic; Thromboembolism; Warfarin

The members of this family with ATIII deficiency have been followed for at least 12 years (1976-1989). All those with previous venous thrombo-embolism have been free from recurrence when on warfarin. During the half century 1931-1981, all 11 full term pregnancies in four affected patients were associated with venous thromboembolism; one patient was enigmatic having one full term pregnancy, without thrombotic event; between 1982 and 1989 three pregnancies have been actively managed with no clinical thrombosis. Management involved use of monitored, self administered, subcutaneous heparin before or very soon after conception and throughout pregnancy (warfarin having been stopped), planned delivery under cover of intravenous antithrombin III, reduction of heparin dosage at delivery and reintroduction of warfarin in the puerperium. The recognised hazards of heparin therapy in pregnancy did not occur. The involvement of the arterial system is reviewed. Clinical evidence provides tentative suggestions on (a) possible additional risk of cigarette smoking (b) avoidance of venography (c) avoidance of varicose vein surgery. A probe is now available for the defective antithrombin III gene in this family, but there has been no occasion yet to apply this in antenatal diagnosis.

Topics: Abortion, Spontaneous; Adult; Antithrombin III; Antithrombin III Deficiency; Cause of Death; Contraindications; Drug Administration Schedule; Female; Follow-Up Studies; Genetic Counseling; Heparin; Humans; Incidence; Infant, Newborn; Male; Metabolism, Inborn Errors; Pedigree; Phlebography; Pregnancy; Pregnancy Complications, Hematologic; Thromboembolism; Warfarin

Topics: Bone and Bones; Cartilage; Child; Chondrodysplasia Punctata; Female; Humans; Metabolism, Inborn Errors; Mixed Function Oxygenases; Nose; Pregnancy; Teratogens; Vitamin K; Vitamin K Epoxide Reductases; Warfarin

A 48 year old man with normal hepatic function presented with abnormally prolonged bleeding following orally administered warfarin. Warfarin and diphenylhydantoin are known to be hydroxylated in the liver. To investigate the possibility of the patient having a metabolic (hydroxylating) defect, his ability to metabolize diphenylhydantoin was studied, as it would have been unethical to administer warfarin again. Parallel studies were carried out on two healthy subjects as a basis for comparison. On three separate occasions the elimination half-life for diphenylhydantoin in the patient (158, 87, 72 hours) was significantly longer than those obtained in the normal subjects (31 and 32 hours). This difference was most probably due to decreased hydroxylation of diphenylhydantoin to 5-(p-hydroxy-phenyl)-5-phenylhydantoin since his urinary elimination of this substance was demonstrated to be significantly less than that of the normal subjects. The results suggest that this patient had a reduced capacity to hydroxylate diphenylhydantoin, and this defect in liver hydroxylation may explain his increased sensitivity to warfarin.

Topics: Half-Life; Humans; Male; Metabolism, Inborn Errors; Middle Aged; Phenobarbital; Phenytoin; Warfarin