The association of vitamin K status with warfarin sensitivity at the onset of treatment

A Rare Case of Acquired Bleeding Disorder in a 24-Year-Old Hispanic Female

Vitamin K is a fat-soluble vitamin that has a major role in coagulation pathways thus its deficiency can lead to major bleeding disorders. Vitamin K deficiency in an otherwise healthy adult is rare. Inadequate oral intake of vitamin K remains the most common cause of vitamin K deficiency. Here, we report a young female who presented for evaluation of heavy menstrual bleeding and was found to be deficient in vitamin K-dependent coagulation factors, with correction upon mixing study. She was diagnosed with vitamin K deficiency due to poor oral intake. With this case, we report a rare and avertible cause of major bleeding to raise awareness among clinicians about patients’ daily nutritional requirements.

Vitamin K and cardiovascular complications in CKD patients

Vitamin K, well known for its role in coagulation, encompasses two major subgroups: Vitamin K1 is exclusively synthesized by plants, whereas vitamin K2 mostly originates from bacterial synthesis. Vitamin K serves as a cofactor for the enzyme γ-glutamyl carboxylase, which carboxylates and thereby activates various vitamin K dependent proteins. Several vitamin K-dependent proteins are synthesized in bone but the role of vitamin K for bone health in CKD patients, in particular the prevention of osteoporosis is still not firmly established. Here we focus on another prominent action of vitamin K, in particular vitamin K2, namely the activation of matrix Gla protein (MGP), the most potent inhibitor of cardiovascular calcifications. Multiple observational studies link relative vitamin K deficiency or low intake to cardiovascular calcification progress, morbidity and mortality. Patients with advanced chronic kidney disease (CKD) are particularly vitamin K deficient, in part because of dietary restrictions but possibly also due to impaired endogenous recycling of vitamin K. At the same time this population is characterized by markedly accelerated cardiovascular calcifications and mortality. High dose dietary supplementation with vitamin K2, in particular the most potent form menaquinone-7 (MK7), can potently reduce circulating levels of dephosphorylated uncarboxylated, i.e. inactive MGP in patients with end stage kidney disease. However, despite this compelling data basis, several randomized controlled trials with high dose MK7 supplements in patients with advanced CKD have failed to confirm cardiovascular benefits. Here we discuss potential reasons and solutions for this.

Trends of INR and Fecal Excretion of Vitamin K During Cholestasis Reversal: Implications in the Treatment of Neonates With Intestinal Failure-Associated Liver Disease

BACKGROUND

Vitamin K is a fat-soluble compound that plays important roles in coagulation. In children with intestinal failure-associated liver disease (IFALD), the disrupted enterohepatic circulation can lead to intestinal loss of vitamin K. Fish oil-based lipid emulsion (FOLE) has proven effective in treating IFALD. As biliary excretion is restored during cholestasis reversal, the accelerated vitamin K loss can pose a risk for deficiency.

METHODS

Ten neonates with IFALD and receiving FOLE monotherapy were prospectively enrolled in the study from 2016 to 2018. In addition to weekly measurements of international normalized ratio (INR) and direct bilirubin (DB), ostomy output was collected for determination of fecal concentrations of phylloquinone (PK). Trends of DB, INR, and fecal PK concentrations were summarized with locally estimated scatterplot smoothing.

RESULTS

The median time (interquartile range) from FOLE initiation to cholestasis reversal was 59 (19-78) days. During cholestasis reversal, INR remained relatively unchanged, whereas the mean (95% confidence interval) daily fecal excretion of PK increased from 25.1 (5.0-158.5) ng at the time of FOLE initiation to 158.5 (31.6-1000.0) ng at complete reversal. Examination of individual trends in fecal PK excretion and INR revealed little correlation between the 2 measurements (r = -0.10; P = 0.50).

CONCLUSION

Children with IFALD are at risk for vitamin K deficiency during cholestasis reversal. Close monitoring and quantified supplementation of vitamin K may be warranted during this period. However, this should not be guided by INR alone, as it is a poor indicator of vitamin K status.

Predictors of warfarin dose requirements in South African patients attending an anticoagulation clinic

INTRODUCTION

Warfarin is the most common oral anticoagulant for the treatment and prevention of thromboembolic disease. However, it has a wide interpatient variability in dose requirements due to various genetic and clinical factors.

MATERIALS AND METHODS

This study investigated the effect of clinical and genetic factors on the variability of warfarin dose requirements in 147 South African patients (81 white and 66 black). The study was performed at a University Hospital Anticoagulation Clinic managed by nursing sisters at the Charlotte Maxeke Johannesburg Academic Hospital.

RESULTS

The most common indication for anticoagulation was atrial fibrillation (n = 55, 37.4%). The mean warfarin dose was significantly higher in black patients as compared to white patients (5.4 ± 2.9 mg/day and 3.8 ± 2.1 mg/day, respectively; P < 0.001). Older age was significantly associated with a lower maintenance warfarin dose (P < 0.001). Drugs which decreased the international normalized ratio (INR) were significantly associated with a higher maintenance warfarin dose of 6.4 ± 3.4 mg/day (P < 0.034). In contrast, there was no significant difference in warfarin dosage requirements in the presence of CYP2C9 and VKORC1 variant alleles (P > 0.05). Patients, however, homozygous for CYP2C9 *1,*3, and VKORC1 required less than 5 mg/day of warfarin to maintain the INR within the therapeutic range.

CONCLUSION

In conclusion, this study indicates that clinical characteristics including; age, ethnic group, and drugs which decrease the INR might help to predict better dose requirements in this population group and thereby reduce the risk of bleeding and thrombotic complications.

Observations on Possible Effects of Daily Vitamin K Replacement, Especially Upon Warfarin Therapy

Daily parenteral vitamin K supplement is now recommended by the U.S. Food and Drug Administration (FDA) for patients receiving IV hyperalimentation. This is considered as preferable to the previous recommendations of weekly parenteral or oral supplement, or as in some cases no supplement at all. Supplemental vitamin K1 will ensure adequate supplies for hepatic saturation and thus the production of clotting factors II, VII, IX, and X, plus the anticoagulants protein C, protein S, and protein Z. But this is not the entire story. This recommended supplement will affect other physiologic systems that also use vitamin K-dependent gamma-carboxylation. Vitamin K is not 1 molecule but rather 2 natural substances, vitamin K1 and K2, and the synthetic K3's. It is not understood, what, if any, effect may occur because of the saturation or competition from the vitamin K1 upon the functioning of vitamins K2 and the derivatives of K3 in vivo upon bone mineralization, cell growth, and blood vessel health, all known to be influenced by the vitamins K. There are probably other physiologic systems yet to be studied relative to vitamins K and gamma-carboxylation. This review also considers the available research upon warfarin when given to patients receiving hyperalimentation and what effects the vitamin K supplements may have. Because studies to date have not controlled for vitamin K intake, consideration is given to whether one should expect any change in previously reported outcomes when using low-dose warfarin for prophylaxis against central vein thrombosis. Also considered are possible positive or negative effects that chronic warfarin therapy may have upon the other vitamin K-dependent systems under discussion. This review offers a platform for further discussion and derived clinical research provoked by this new FDA recommendation.

Establishing a rat model for the study of vitamin K deficiency

The main vitamin K-deficient model, minidose warfarin, is different from the pathological mechanism of vitamin K deficiency, which is a shortage of vitamin K. The objective of this study was to establish a new method of vitamin K-deficient model combining a vitamin K-deficient diet with the intragastrical administration of gentamicin in rats. The clotting was assayed by an automated coagulation analyser. The plasma PIVKA-II was assayed by ELISA. The vitamin K status was detected by an HPLC-fluorescence system. In the diet- and gentamicin-induced vitamin K-deficient 14-day group, the rats had undetected vitamin K1 and vitamin K2 in the liver and a prolonged APTT. In the 21-day group, there was also a prolonged PT and a decrease of the FIX activities. In the 28-day group, the undetected vitamin K1 and vitamin K2, the prolonged PT and APTT, and the decrease of the FII, FVII, FIX, and FX activities prompted the suggestion that there were serious deficiencies of vitamin K and vitamin K-dependent coagulation in rats. It is suggested that the diet- and gentamicin-induced vitamin K-deficient 14-day or 21-day model can be used for studies related to the status of vitamin K. The vitamin K-deficient 28-day model can be applied to research involving both the status of vitamin K and of vitamin K-dependent coagulation. In conclusion, the combination of a vitamin K-deficient diet with the administration of gentamicin results in a useful model of vitamin K-deficieny.

Interaction Between Dietary Vitamin K Intake and Anticoagulation by Vitamin K Antagonists: Is It Really True?: A Systematic Review

Educational advice is often given to patients starting treatment with vitamin K Antagonists (VKAs). A great emphasis is made on nutritional information. Common belief is that dietary vitamin K intake could counteract the anticoagulant effect by VKAs and for many years, patients have been discouraged to consume vitamin-K-rich foods, such as green leafy vegetables.The objective of this study is to summarize the current evidence supporting the putative interaction between dietary vitamin K intake and changes in INR with the VKAs.Data sources are MEDLINE via PubMed and Cochrane database.All clinical studies investigating the relationship between dietary vitamin K and measures of anticoagulation were included. We excluded all studies of supplementation of vitamin K alone.We performed a systematic review of the literature up to October 2015, searching for a combination of "food," "diet," "vitamin K," "phylloquinone," "warfarin," "INR," "coagulation," and "anticoagulant."Two dietary interventional trials and 9 observational studies were included. We found conflicting evidence on the effect of dietary intake of vitamin K on coagulation response. Some studies found a negative correlation between vitamin K intake and INR changes, while others suggested that a minimum amount of vitamin K is required to maintain an adequate anticoagulation. Median dietary intake of vitamin K1 ranged from 76 to 217 μg/day among studies, and an effect on coagulation may be detected only for high amount of vitamin intake (>150 μg/day).Most studies included patients with various indications for VKAs therapy, such as atrial fibrillation, prosthetic heart valves, and venous thromboembolism. Thus, INR target was dishomogeneous and no subanalyses for specific populations or different anticoagulants were conducted. Measures used to evaluate anticoagulation stability were variable.The available evidence does not support current advice to modify dietary habits when starting therapy with VKAs. Restriction of dietary vitamin K intake does not seem to be a valid strategy to improve anticoagulation quality with VKAs. It would be, perhaps, more relevant to maintain stable dietary habit, avoiding wide changes in the intake of vitamin K.

Disadvantages of VKA and requirements for novel anticoagulants

Vitamin K antagonists have been in wide use for over 70 years. Warfarin, the most commonly used vitamin K antagonist, has been shown to be highly effective in treating and preventing thrombosis. Despite this, warfarin has many disadvantages, which has led to the development of a new class of oral anticoagulants targeted to specific coagulation factors designated as target-specific oral anticoagulants (TSOAs). TSOAs include the thrombin inhibitors (dabigatran) and factor Xa inhibitors (rivaroxaban, apixaban). This chapter reviews the disadvantages of warfarin and evaluates both the advantages and disadvantages of the new oral anticoagulants.

Pharmacokinetics and Pharmacodynamics of Warfarin When Coadministered With Pentosan Polysulfate Sodium

The effect of pentosan polysulfate sodium on warfarin pharmacokinetics and pharmacodynamics was investigated in healthy subjects. Warfarin was titrated to an international normalized ratio between 1.4 and 1.8. Subjects continued their titrated dose of warfarin and received pentosan polysulfate sodium 100 mg or placebo every 8 hours for 7 days. The Cmax of R- and S-warfarin was approximately 840 to 890 ng/mL and 680 to 730 ng/mL, respectively, and was similar in the absence and presence of pentosan polysulfate sodium. The half-life for R- and S-warfarin was 52 to 56 hours and 36 to 40 hours, respectively. Prothrombin time, partial thromboplastin time, and the international normalized ratio for warfarin + placebo and warfarin + pentosan polysulfate sodium were comparable. The AUC(INR) indicated no treatment effect (P = .772); however, there was a period effect. Analysis of variance for the treatments by period indicated no treatment effect (P > .1). Adverse events were mild and included headache, epistaxis, and rash. Most adverse events were unrelated to treatment and were seen during warfarin titration. Pentosan polysulfate sodium did not affect warfarin pharmacokinetics or pharmacodynamics.

Influence of CYP4F2 polymorphisms and plasma vitamin K levels on warfarin sensitivity in Japanese pediatric patients

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.

Effect of the VKORC1 D36Y variant on warfarin dose requirement and pharmacogenetic dose prediction

Pharmacogenetic dosing algorithms help predict warfarin maintenance doses, but their predictive performance differs in different populations, possibly due to unsuspected population-specific genetic variants. The objectives of this study were to quantify the effect of the VKORC1 D36Y variant (a marker of warfarin resistance previously described in 4% of Ashkenazi Jews) on warfarin maintenance doses and to examine how this variant affects the performance of the International Warfarin Pharmacogenetic Consortium (IWPC) dose prediction model. In 210 Israeli patients on chronic warfarin therapy recruited at a tertiary care centre, we applied the IWPC model and then added D36Y genotype as covariate to the model (IWPC+D36Y) and compared predicted with actual doses. Median weekly warfarin dose was 35 mg (interquartile range [IQR], 24.5 to 52.5 mg). Among 16 heterozygous D36Y carriers (minor allele frequency = 3.8%), warfarin weekly dose was increased by a median of 43.7 mg (IQR, 40.5 to 47.2 mg) compared to non-carriers after adjustment for all IWPC parameters, a greater than two-fold dose increase. The IWPC model performed suboptimally (coefficient of determination R²=27.0%; mean absolute error (MAE), 14.4 ± 16.2 mg/week). Accounting for D36Y genotype using the IWPC+D36Y model resulted in a significantly better model performance (R²=47.2%, MAE=12.6 ± 12.4 mg/week). In conclusion, even at low frequencies, variants with a strong impact on warfarin dose may greatly decrease the performance of a commonly used dose prediction model. Unexpected discrepancies of the performance of universal prediction models in subpopulations should prompt searching for unsuspected confounders, including rare genetic variants.

Effects of CYP4F2 polymorphism on response to warfarin during induction phase: a prospective, open-label, observational cohort study

BACKGROUND

The cytochrome P450 (CYP) 4F2 isozyme has been reported to metabolize vitamin K(1) in vitro, and the V433M polymorphism in the CYP4F2 gene has been associated with reduced vitamin K(1) metabolism and the need for a higher maintenance dosage in patients receiving warfarin.

OBJECTIVE

The purpose of the present study was to evaluate the effects of V433M polymorphism on warfarin response during the induction phase.

METHODS

Warfarin-naive white patients in whom warfarin was scheduled to be initiated with a target INR of 2 to 3 were enrolled into the study. On enrollment, a single blood sample for the genotyping of CYP4F2, CYP2C9, and VKORC1 was drawn. The international normalized ratio (INR) was followed daily during induction and twice weekly until stable anticoagulation was reached. The relationships between several markers of warfarin response during induction and CYP4F2 polymorphism were determined.

RESULTS

The cohort consisted of 241 patients (115 men; mean [SD] age, 55.2 [19.4] years; weight, 79.5 [18.3] kg). Most of the patients were carriers of the CYP4F2 CC genotype (112 patients) or the CT genotype (104 patients). In carriers of the TT genotype (25 patients), INR >3 was >4-fold lower compared with that in carriers of the CC or CT genotype, suggesting that patients with the TT genotype were less sensitive to warfarin during induction. Also in TT carriers, the extent of excessive anticoagulation was >10-fold lower than in the other carriers. Both of these findings had a nominal P value of <0.05. After adjustment for false discovery rate, none of the findings remained significant at a threshold q value of <0.05. Among CC carriers, the concurrent use of a statin was associated with a 1-mg/d reduction in warfarin maintenance dosage. No similar effect was noted in the CT or TT carriers, suggesting a possible genetic influence on warfarin-statin interaction.

CONCLUSIONS

These preliminary findings suggest that among white patients treated with warfarin, CYP4F2 polymorphism had a measurable effect on warfarin responsiveness during induction; however, the observed differences failed to reach the level of statistical significance. The possibility that the effect of statins on warfarin anticoagulation varies among carriers of different CYP4F2 genotypes could not be excluded and should be evaluated further in a larger patient sample.

Clinical and genetic determinants of warfarin pharmacokinetics and pharmacodynamics during treatment initiation

Variable warfarin response during treatment initiation poses a significant challenge to providing optimal anticoagulation therapy. We investigated the determinants of initial warfarin response in a cohort of 167 patients. During the first nine days of treatment with pharmacogenetics-guided dosing, S-warfarin plasma levels and international normalized ratio were obtained to serve as inputs to a pharmacokinetic-pharmacodynamic (PK-PD) model. Individual PK (S-warfarin clearance) and PD (I_max) parameter values were estimated. Regression analysis demonstrated that CYP2C9 genotype, kidney function, and gender were independent determinants of S-warfarin clearance. The values for I_max were dependent on VKORC1 and CYP4F2 genotypes, vitamin K status (as measured by plasma concentrations of proteins induced by vitamin K absence, PIVKA-II) and weight. Importantly, indication for warfarin was a major independent determinant of I_max during initiation, where PD sensitivity was greater in atrial fibrillation than venous thromboembolism. To demonstrate the utility of the global PK-PD model, we compared the predicted initial anticoagulation responses with previously established warfarin dosing algorithms. These insights and modeling approaches have application to personalized warfarin therapy.

The role of dietary vitamin K in the management of oral vitamin K antagonists

Vitamin K antagonists (VKA) have been the mainstay of oral anticoagulant therapy for over 60years. In this review we critically assess the evidence for the importance of vitamin K nutrition during VKA therapy; the methodologies for measuring dietary intakes; the vitamin K intake data in patients on VKA and healthy people; and the experimental evidence for the influence of vitamin K intakes and biochemical measures of vitamin K status on VKA response. Several studies show that dietary intakes of phylloquinone (vitamin K1) are associated to the sensitivity and stability of anticoagulation during initiation and maintenance dosing with low habitual intakes associated with greater instability of the INR and risk of sub-therapeutic anticoagulation. Preliminary evidence suggests that the stability of anticoagulation therapy may be improved by daily vitamin K supplementation, but further studies are needed to find out whether this, or other dietary interventions, can improve anticoagulant control in routine clinical practice.

The missing association: sequencing-based discovery of novel SNPs in VKORC1 and CYP2C9 that affect warfarin dose in African Americans

It is well recognized that the genetic variants VKORC1-1639, CYP2C9*2, and CYP2C9*3 contribute to warfarin dose response. This has led to warfarin dosing algorithms that include these polymorphisms and explains between 47% and 56% of variability in dose in Caucasians. However, these polymorphisms explain significantly less of the variance in dose among African Americans. In order to identify novel variations that affect warfarin dose in African Americans, we used a targeted resequencing strategy that examined evolutionarily conserved sequences and regions of putative transcriptional binding. Through ethnicity-specific warfarin dose model building in 330 African Americans, we identified two novel genetic associations with higher warfarin dose, namely, VKORC1-8191 (rs61162043, P = 0.0041) and 18786 in CYP2C9 (rs7089580, P = 0.035). These novel finds are independent of the previous associations with these genes. Our regression model, encompassing both genetic and clinical variables, explained 40% of the variability in warfarin dose in African-American subjects, significantly more than any model thus far.

Warfarin and vitamin K intake in the era of pharmacogenetics

The considerable variability in the warfarin dose-response relationship between individuals, is explained mainly by genetic variation in its major metabolic (CYP2C9) and target (VKORC1) enzymes. Despite the predominance of pharmacogenetics, environmental factors also affect the pharmacokinetics and pharmacodynamics of warfarin, and are often overlooked. Among these factors, dietary and supplemental vitamin K consumption is a controllable contributor to within-, and between-patient variability of warfarin sensitivity. In this commentary we review the current role of vitamin K in warfarin anticoagulation therapy, with emphasis on the following: 1 The effect of dietary and supplemental vitamin K on warfarin anticoagulation, beyond the impact of genetic variability in CYP2C9 and VKORC1. We deal separately with the effects of vitamin K on warfarin dose requirements during the induction of therapy, as opposed to its effect on stability of anticoagulation control during maintenance therapy. 2 The role of vitamin K supplementation in warfarin treated patients with vitamin K deficiency as well as in patients with unstable warfarin anticoagulation, and 3 The role of therapeutic vitamin K in cases of warfarin over-anticoagulation.

Vitamin K1 supplementation to improve the stability of anticoagulation therapy with vitamin K antagonists: a dose-finding study

BACKGROUND

Poor anticoagulant stability in patients using vitamin K antagonists is a risk factor for both bleeding and thrombosis. In previous studies supplementation with low dose vitamin K(1) was shown to improve the stability of anticoagulant control. We set up a study to confirm earlier reports and to determine the optimal daily dose of vitamin K(1) in preparation of a large study with clinical endpoints.

DESIGN AND METHODS

Four hundred patients from two anticoagulation clinics starting with vitamin K antagonists, independently of a possible history of instable anticoagulation, were randomized to receive either placebo or 100, 150 or 200 μg of vitamin K(1) together with their treatment with vitamin K antagonists. The treatment was administered for 6 to 12 months. Anticoagulation stability, expressed as the percentage of time that the International Normalized Ratio was within the therapeutic range, was compared between the groups.

RESULTS

After adjustment for age, sex, vitamin K antagonist used, anticoagulation clinic and interacting drugs as confounding factors the difference in percentage of time with the International Normalized Ratio within the therapeutic range between the placebo group and the vitamin K(1) groups was 2.1% (95% CI: -3.2% - 7.4%) for the group taking 100 μg, 2.7% (95% CI: -2.3% -7.6%) for the group taking 150 μg and 0.9% (95% CI: -4.5% - 6.3%) for the group taking 200 μg vitamin K(1) group, in favor of the vitamin K(1) groups. The patients from both the 100 μg group and the 150 μg group had a 2-fold higher chance of reaching at least 85% of time with the International Normalized Ratio within the therapeutic range. There were no differences in thromboembolic or hemorrhagic complications between the groups.

CONCLUSIONS

In patients starting vitamin K antagonists, supplementation with low dose vitamin K(1) resulted in an improvement of time that anticoagulation was within the therapeutic range. Differences between doses were, however, small and the improvement is unlikely to be of clinical relevance. For future studies we recommend selecting only patients with instable anticoagulant control. (This study was registered at www.isrctn.org as ISRCTN37109430).

Patient Factors That Influence Warfarin Dose Response

Warfarin has long been the mainstay of oral anticoagulation therapy for the treatment and prevention of venous and arterial thrombosis. The narrow therapeutic index of warfarin, and the complex number of factors that influence international normalized ratio (INR) response, makes optimization of warfarin therapy challenging. Determination of the appropriate warfarin dose during initiation and maintenance therapy requires an understanding of patient factors that influence dose response: age, body weight, nutritional status, acute and chronic disease states, and changes in concomitant drug therapy and diet. This review will examine specific clinical factors that can affect the pharmacokinetics and pharmacodynamics of warfarin, as well as the role of pharmacogenetics in optimizing warfarin therapy.

Relationship between aging and dosage of warfarin: the current status of warfarin anticoagulant therapy for Japanese outpatients in a department of cardiovascular medicine

BACKGROUND

Oral anticoagulant therapy with warfarin is essential for the optimal prophylaxis of thrombosis and embolism in many vascular disorders whose prevalence is high among elderly patients. Elderly Caucasians show increased sensitivity to oral anticoagulants. Although the Japanese are more sensitive to warfarin therapy than Caucasians, the relationship between age and warfarin dosage in the Japanese has not been investigated in detail. Here, we investigated this relationship in Japanese patients.

METHODS

The subjects comprised 102 outpatients (28-87 years) who showed a stable anticoagulant effect (prothrombin time expressed in terms of the international normalized ratio [PT-INR] between 1.6 and 2.6) following long-term warfarin therapy at the Department of Cardiovascular Medicine, National Hospital Organization Hakodate Hospital. The relationship between age, PT-INR, and daily warfarin dose was retrospectively investigated.

RESULTS

The mean values of the characteristics of all the patients were as follows: age, 70.7 (+/-10.5) years; daily dose of warfarin, 2.68 (+/-0.95)mg; PT-INR, 1.99 (+/-0.24). The PT-INR was not correlated with increasing age. The daily dosage of warfarin and the dosage adjusted according to the PT-INR (dose/PT-INR), wherein the lower values indicate a higher sensitivity to warfarin therapy, were significantly inversely correlated with age. In the high PT-INR (PT-INR>2.1) group, no significant difference was observed between the older and younger patients with regard to any characteristics. Conversely, in the low PT-INR (1.6 ≤ PT-INR ≤ 2.1) group, the dose/PT-INR was significantly reduced in the older patients (≥ 65 years); however, no significant difference was observed in the PT-INR value.

CONCLUSIONS

Both age and the controlled PT-INR value are factors responsible for the increasing sensitivity to warfarin in Japanese patients under optimal anticoagulant therapy. Since elderly Japanese patients with low PT-INR values are especially sensitive to warfarin, greater caution should be exercised while determining the dosage schedule in such patients.

Dietary Vitamin K in Oral Anticoagulation Patients: Clinician Practices and Knowledge in Outpatient Settings

Background:

Dietary vitamin K is a recognized variable associated with oral anticoagulant therapy. However, current practices of dietary education and instruction regarding vitamin K, as well as factors influencing related decision-making, are unknown. Research has examined healthcare providers' ability to identify a meal containing vitamin K, but the ability to classify portions of specific vegetables according to vitamin K content has not been evaluated.

Objective:

To characterize dietary evaluation and instructional methods provided to patients receiving warfarin therapy, assess factors influencing instructional methods, and evaluate clinician knowledge of vitamin K content for specific vegetable portions.

Methods:

A cross-sectional online survey of US healthcare providers involved with management of outpatient oral anticoagulation therapy was conducted.

Results:

One hundred twenty-two responses were received. Seventy-four percent of respondents collected initial dietary history from all patients and 52% asked all patients for dietary history at follow-up visits. Taking a verbal dietary history from all patients was significantly associated with larger clinic size and managing patients in person. Eighty-two percent of respondents reported providing dietary vitamin K education to all patients. Low patient literacy was a common factor influencing instruction to avoid foods high in vitamin K. Overall mean score reflecting the ability to classify vegetable portions by vitamin K content was 64.6 ± 10.9%.

Conclusions:

Acquisition of dietary history by anticoagulation providers is not always completed at initial and follow-up patient visits. Provision of patient education at initial visits is relatively high. Patient factors such as low literacy may influence a clinician's decision to provide a specific method of dietary instruction, including avoidance of foods high in vitamin K. Clinicians are least likely to correctly identify vegetable portions containing vitamin K in the range of 10–99 μg and should consider portion size when assessing dietary history.

Relationship between diet and anticoagulant response to warfarin: a factor analysis

BACKGROUND

Diet composition is one of the factors that may contribute to intraindividual variability in the anticoagulant response to warfarin.

AIM OF THE STUDY

To determine the associations between food pattern and anticoagulant response to warfarin in a group of Brazilian patients with vascular disease.

METHODS

Recent and usual food intakes were assessed in 115 patients receiving warfarin; and corresponding plasma phylloquinone (vitamin K(1)), serum triglyceride concentrations, prothrombin time (PT), and International Normalized Ratio (INR) were determined. A factor analysis was used to examine the association of specific foods and biochemical variables with anticoagulant data.

RESULTS

Mean age was 59 +/- 15 years. Inadequate anticoagulation, defined as values of INR 2 or 3, was found in 48% of the patients. Soybean oil and kidney beans were the primary food sources of phylloquinone intake. Factor analysis yielded four separate factors, explaining 56.4% of the total variance in the data set. The factor analysis revealed that intakes of kidney beans and soybean oil, 24-h recall of phylloquinone intake, PT and INR loaded significantly on factor 1. Triglycerides, PT, INR, plasma phylloquinone, and duration of anticoagulation therapy loaded on factor 3.

CONCLUSIONS

Fluctuations in phylloquinone intake, particularly from kidney beans, and plasma phylloquinone concentrations were associated with variation in measures of anticoagulation (PT and INR) in a Brazilian group of patients with vascular disease.

Dietary vitamin K intake and anticoagulation in elderly patients

PURPOSE OF REVIEW

Vitamin K is an essential co-factor for the synthesis of several coagulation factors. Oral anticoagulants competitively inhibit enzymes that participate in vitamin K metabolism. The purpose of this review is to evaluate the potential interaction of dietary vitamin K and coagulation stability, particularly in the elderly patient.

RECENT FINDINGS

Recent prospective evidences suggest that dietary vitamin K plays an essential role in anticoagulation stability. Vitamin K intake of more than 250 microg/day was shown to decrease warfarin sensitivity in anticoagulated patients consuming regular diets. In a randomized crossover study, brief periods of changes on vitamin K intake also had significant effects on coagulation parameters. Patients that were allocated to an 80% decrease of intake increased International Normalized Ratio (INR) by almost 30% 7 days after the intervention. Similarly, it was estimated by dietary records that for each increase in 100 microg of vitamin K intake, the INR would be reduced by 0.2. A recent study also demonstrated that over-the-counter multivitamin supplements contain enough vitamin K1 to significantly alter coagulation parameters.

SUMMARY

Contemporary data strengthen the concept that the interaction between dietary vitamin K and coumarin derivatives is clinically relevant and plays a major role in INR fluctuations in chronic anticoagulated patients.

Pharmacogenetics of oral anticoagulants

The use of oral anticoagulants (OA) is problematic due to its association with hemorrhagic complications. OA metabolism relies on the CYP2C9 complex. Genetic variations compromising metabolic competence of this complex may explain the risk of excessive and hazardous anticoagulation. A pharmacogenetics-based approach to this issue could be beneficial for choosing adequate dose and duration of treatment, in addition to having a better understanding of pharmacological interactions to which OA are susceptible. However, evidence from several basic and clinical studies indicates that both a complicated system of regulation of expression of multiple genes and the influence of a wide variety of epigenetic factors could be responsible for adverse drug reactions associated with the use of OA. Emphasis on understanding the gene-environment interactions could attain new paths to facilitate the use of these important drugs in the quotidian clinical practice.

Interaction of warfarin with drugs, natural substances, and foods

Variability in the anticoagulant response to warfarin is an ongoing clinical dilemma. Fluctuations in dietary vitamin K are an important source of variance, and the need for constancy in vitamin K intake is routinely emphasized for warfarin-treated patients. Anticoagulant response is also influenced by a number of drugs that induce or inhibit warfarin metabolism, as well as by genetic polymorphisms that may modulate expression or activity of CYP2C9, the isoform mediating clearance of S-warfarin. The possible role of dietary factors other than vitamin K, as well as of herbal medicines or supplements as contributors to the instability of anticoagulation in warfarin-treated patients, has received recent attention. St. John's wort and possibly some ginseng formulations may have the potential to diminish warfarin anticoagulation, apparently by inducing CYP2C9 activity. Otherwise, there is no reliable evidence to indicate that any dietary component (other than vitamin K) or any herbal product has an effect on the anticoagulant response to warfarin. Scientific conclusions on this important therapeutic issue should be based on valid scientific data rather than unvalidated case reports.

Vitamin supplementation: what the gastroenterologist needs to know

BACKGROUND

The vitamin business is a multimillion dollar industry. Aggressive marketing strategies are used to make claims for the health benefits of these products. Observational studies suggest that people who consume vitamin supplements decrease their risks for cancer, cardiovascular disease, and gastrointestinal disease. What is the evidence for these claims, and as a prescribing gastroenterologist, is there a scientific basis for vitamin supplementation?

METHODS

A narrative review focusing on randomized controlled trials, where available, plus observational studies obtained from personal files, "on-line" searches, and references in reviewed articles.

RESULTS

From the perspective of a gastroenterologist, there is strong evidence to recommend B12 supplementation in gastric and intestinal disease, as well as pernicious anemia. There exists moderate evidence to support B12 supplements in pancreatic disease. Vitamin D and calcium supplementation are recommended for persons with disorders of malabsorption, cholestasis, and illnesses requiring chronic steroids. Only observational studies suggest a correlation between vitamin D/calcium and decreased colorectal adenoma recurrence. Although folic acid supplementation is beneficial in persons on medications such as methotrexate and sulfasalazine, studies are contradictory with regard to folic acid and colon cancer prevention. Overall, antioxidants have not been proven to decrease the risk for colorectal adenoma, gastric cancer, or esophageal cancer.

CONCLUSIONS

Observational studies do not correlate with randomized clinical trials; therefore, few definitive recommendations can be made. Vitamin supplements are appropriate for recognized deficiencies; however, there is a lack of evidence to support their effects in the prevention of chronic disease.

Role of dietary vitamin K intake in chronic oral anticoagulation: prospective evidence from observational and randomized protocols

PURPOSE

The potential association between vitamin K intake and coagulation instability has been explored primarily in case reports and small, retrospective, uncontrolled studies. We prospectively evaluated the effects of dietary vitamin K intake on anticoagulation parameters.

METHODS

In an observational protocol, clinical characteristics and vitamin K intake, assessed semiquantitatively, were evaluated in 39 outpatients who made 230 visits to our anticoagulation clinic. In a randomized crossover protocol, 12 patients with stable anticoagulation underwent 4-day in-hospital dietary interventions, 1 to 2 weeks apart, providing a 500% increase and an 80% decrease in vitamin K intake relative to the baseline level.

RESULTS

Univariate analysis of the observational data demonstrated a progressive, statistically significant inverse association between the vitamin K intake score and different levels of anticoagulation. Multivariate logistic regression analysis showed that vitamin K intake was independently associated with both overcoagulation and undercoagulation. In the randomized protocol, the international normalized ratio increased from 2.6 +/- 0.5 at baseline to 3.3 +/- 0.9 at day 7 (P = 0.005) in subjects on the vitamin K-depleted diet and decreased from 3.1 +/- 0.8 at baseline to 2.8 +/- 0.6 at day 4 (P = 0.04) in those on the vitamin K-enriched diet.

CONCLUSION

Our prospective data strengthen the concept that the interaction between vitamin K and coumarin is a clinically relevant, major independent factor that interferes with anticoagulation stability.

Multivitamin supplements may affect warfarin anticoagulation in susceptible patients

OBJECTIVE

To report an interaction of a multivitamin preparation containing small amounts of vitamin K(1) (25 microg) with warfarin in a case series and to assess the prevalence of vitamin K(1) deficiency in ambulatory anticoagulated patients.

CASE SUMMARIES

We describe 3 patients whose anticoagulation was stabilized with warfarin in whom initiation or cessation of a self-prescribed multivitamin supplement delivering 25 microg of vitamin K(1) daily was associated with an otherwise unexplained significant fall or rise in international normalized ratio (INR), respectively, with major thrombosis or hemorrhage in 2. This interaction was rated probable on the Naranjo probability scale. Suspecting vitamin K(1) deficiency as an explanation for this oversensitivity, we assessed the prevalence of vitamin K(1) deficiency in our clinic by determining plasma vitamin K(1) levels in 179 stable consecutive patients, finding very low levels (<0.1 ng/mL) in 22 of 179 (12%).

DISCUSSION

Vitamin K(1) supplements of 25 microg daily are far below the dose thought to affect anticoagulant control. We hypothesize that, in our patients, unsuspected vitamin K(1) deficiency caused an oversensitivity to small vitamin K(1) supplements. In patients with low vitamin K(1) status, even such low doses represent a significant increment in daily intake, thus lowering the sensitivity to warfarin. Our analysis suggests that low vitamin K(1) status exists in a small, but important, minority of ambulatory patients undergoing anticoagulation.

CONCLUSIONS

Clinicians should instruct anticoagulated patients to report the use of multivitamin supplements and inquire about it in cases of unexplained INR changes.

Patient-specific factors predictive of warfarin dosage requirements

OBJECTIVE

To identify patient-specific factors predictive of maintenance warfarin dosage requirements >5 mg/d.

METHODS

One hundred forty-six adults taking warfarin were identified from a community hospital and an outpatient anticoagulation clinic. Patient demographics and data on warfarin doses, laboratory results, and medication use were obtained by abstracting patient records. Estimates of vitamin K intake were obtained using a questionnaire and structured interview. Multiple logistic regression was used to identify patient characteristics independently predictive of warfarin maintenance requirements >5 mg/d. An assessment tool for estimating an individual patient's likelihood of requiring warfarin maintenance doses >5 mg/d was derived from the logistic regression model and was assessed in both the study cohort and a separate historical validation cohort of 125 patients.

RESULTS

Five factors were independently associated with warfarin requirements >5 mg/d: age <55 years, male gender, African American ethnicity, vitamin K intake >400 micro g/d, and body weight >or=91 kg. The assessment tool derived from these factors correctly classified semiquantitative warfarin requirements as non-high-dose in 84 of 93 study cohort patients and 71 of 78 validation cohort patients, and correctly classified requirements as high-dose in 10 of 13 study cohort patients and 11 of 15 validation cohort patients.

CONCLUSIONS

African American ethnicity is a newly identified predictor of warfarin requirements >5 mg/d and is independent of dietary vitamin K intake. An assessment tool incorporating this and other predictors can estimate a patient's likelihood of requiring such dosages.