Evaluation of warfarin initiation regimens in elderly inpatients

The Influence of NSAIDs on Coumarin Sensitivity in Patients with CYP2C9 Polymorphism After Total Hip Replacement Surgery

OBJECTIVE

To determine the influence of NSAIDs on the international normalized ratio (INR) in patients with cytochrome P450 (CYP)-2C9 enzyme variants starting acenocoumarol (an oral coumarin) therapy during the first 7 days after total hip replacement surgery.

METHODS

In this prospective study, an age-dependent protocol was used for the initiation of the acenocoumarol dose. Low-molecular-weight heparin was given for 5 days. The study included 100 patients undergoing total hip replacement surgery. After the inclusion of the last patient, polymerase chain reaction CYP2C9 mutation testing was performed for all patients. Drug-use evaluation of NSAIDs and other potential coumarin-drug interactions was also performed.

RESULTS

Eleven patients had an INR on 1 or more days >4.9. There were 52 patients who were using NSAIDs. Patients with a CYP2C9 mutation had a mean INR curve similar to patients without the mutation when NSAIDs were not coadministered. Within the group of patients heterozygous for a CYP2C9 mutation (n=30) only concomitant use of a NSAID resulted in an INR >4.9 (0% vs 38.9%, p<0.05).

CONCLUSION

In the group of patients with a CYP2C9 variant (*2 or *3 alleles), only concomitant use of a NSAID resulted in INRs >4.9. The cost effectiveness of CYP2C9 screening before elective surgery has yet to be determined.

Oral anticoagulant therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

The objective of this article is to summarize the published literature concerning the pharmacokinetics and pharmacodynamics of oral anticoagulant drugs that are currently available for clinical use and other aspects related to their management.

METHODS

We carried out a standard review of published articles focusing on the laboratory and clinical characteristics of the vitamin K antagonists; the direct thrombin inhibitor, dabigatran etexilate; and the direct factor Xa inhibitor, rivaroxaban

RESULTS

The antithrombotic effect of each oral anticoagulant drug, the interactions, and the monitoring of anticoagulation intensity are described in detail and discussed without providing specific recommendations. Moreover, we describe and discuss the clinical applications and optimal dosages of oral anticoagulant therapies, practical issues related to their initiation and monitoring, adverse events such as bleeding and other potential side effects, and available strategies for reversal.

CONCLUSIONS

There is a large amount of evidence on laboratory and clinical characteristics of vitamin K antagonists. A growing body of evidence is becoming available on the first new oral anticoagulant drugs available for clinical use, dabigatran and rivaroxaban.

Optimizing use of current anticoagulants

Although warfarin has been the mainstay of oral anticoagulation therapy for decades, evidence-based methods for improving the quality of warfarin therapy remain underused. The arrival of new anticoagulants that do not require routine laboratory monitoring and lack the significant dietary and drug interaction potential that are seen with warfarin is an important evolutionary step in the management of thromboembolic disease. However, it will be years before the efficacy and long-term safety of these new agents are defined. Newer oral anticoagulants will be more expensive than generic warfarin. This article examines various approaches to optimize the clinical use of warfarin. For patients able to achieve stable anticoagulation control, warfarin remains an important therapeutic option, delivering similar clinical outcomes at a fraction of the cost to the health care system.

Pharmacogenetic testing and therapeutic drug monitoring are complementary tools for optimal individualization of drug therapy

Genetic factors contribute to the phenotype of drug response, but the translation of pharmacogenetic outcomes into drug discovery, drug development or clinical practice has proved to be surprisingly disappointing. Despite significant progress in pharmacogenetic research, only a few drugs, such as cetuximab, dasatinib, maraviroc and trastuzumab, require a pharmacogenetic test before being prescribed. There are several gaps that limit the application of pharmacogenetics based upon the complex nature of the drug response itself. First, pharmacogenetic tests could be more clinically applicable if they included a comprehensive survey of variation in the human genome and took into account the multigenic nature of many phenotypes of drug disposition and response. Unfortunately, much of the existing research in this area has been hampered by limitations in study designs and the nonoptimal selection of gene variants. Secondly, although responses to drugs can be influenced by the environment, only fragmentary information is currently available on how the interplay between genetics and environment affects drug response. Third, the use of a pharmacogenetic test as a standard of care for drug therapy has to overcome significant scientific, economic, commercial, political and educational barriers, among others, in order for clinically useful information to be effectively communicated to practitioners and patients. Meanwhile, the lack of efficacy is in this process is quite as costly as drug toxicity, especially for very expensive drugs, and there is a widespread need for clinically and commercially robust pharmacogenetic testing to be applied. In this complex scenario, therapeutic drug monitoring of parent drugs and/or metabolites, alone or combined with available pharmacogenetic tests, may be an alternative or complementary approach when attempts are made to individualize dosing regimen, maximize drug efficacy and enhance drug safety with certain drugs and populations (e.g. antidepressants in older people).

Vitamin K antagonist use in the elderly: special considerations

As the population ages, the number of patients aged 75 years and over treated with vitamin K antagonists (VKAs) is steadily increasing. In this age group, the two main indications for oral anticoagulant therapy are the treatment of venous thromboembolic disease and the prevention of systemic embolism in patients with nonvalvular atrial fibrillation. In both indications, a target international normalized ratio of 2.5 (range: 2.0-3.0) is recommended. Although VKAs are beneficial in thromboembolic disorders, they are still underused. In this review, we will focus on two crucial topics in elderly patients, the specific management of VKAs in these patients and the hemorrhagic risk. Current recommendations concerning the management at the start of treatment, education and adequate monitoring may help to minimize the hemorrhagic risk in these frail patients.

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.

A 10 mg warfarin initiation nomogram is safe and effective in outpatients starting oral anticoagulant therapy for venous thromboembolism

The optimal means of initiating warfarin therapy for acute venous thromboembolism in the outpatient setting remains controversial. We have previously demonstrated the efficacy of a 10 mg initiation nomogram in a randomized controlled trial; however, some clinicians remain reluctant to use this nomogram due to a fear of potential increased bleeding. To review the safety and efficacy of a 10 mg warfarin nomogram we conducted a retrospective cohort study of patients prospectively treated for venous thromboembolism according to a 10 mg nomogram in an outpatient thrombosis clinic. All patients received standard treatment with low molecular weight heparin for 5 to 7 days and warfarin for at least 3 months. Four-hundred and fourteen patients were included in the analysis, of whom 295 (71%) fully adhered to the nomogram. In the whole cohort, 8 patients (1.9%) experienced recurrent thrombosis, 4 (0.97%) suffered a major bleeding event, and 3 (0.72%) suffered a minor bleeding event. There were no deaths related to thrombosis or bleeding. Four patients (0.97%) died from unrelated causes. Twenty-two (5.3%) patients experienced an INR > or =5.0 in the first 8 days of therapy, and none of these patients experienced a bleeding event. Eighty-four percent of patients achieved a therapeutic INR by day 5. In outpatients, a 10 mg nomogram results in timely achievement of a therapeutic INR with an acceptable incidence of bleeding and recurrent thromboembolism.

Pharmacology and management of the vitamin K antagonists: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This article concerning the pharmacokinetics and pharmacodynamics of vitamin K antagonists (VKAs) is part of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). It describes the antithrombotic effect of the VKAs, the monitoring of anticoagulation intensity, and the clinical applications of VKA therapy and provides specific management recommendations. Grade 1 recommendations are strong and indicate that the benefits do or do not outweigh the risks, burdens, and costs. Grade 2 recommendations suggest that the individual patient's values may lead to different choices. (For a full understanding of the grading, see the "Grades of Recommendation" chapter by Guyatt et al, CHEST 2008; 133:123S-131S.) Among the key recommendations in this article are the following: for dosing of VKAs, we recommend the initiation of oral anticoagulation therapy, with doses between 5 mg and 10 mg for the first 1 or 2 days for most individuals, with subsequent dosing based on the international normalized ratio (INR) response (Grade 1B); we suggest against pharmacogenetic-based dosing until randomized data indicate that it is beneficial (Grade 2C); and in elderly and other patient subgroups who are debilitated or malnourished, we recommend a starting dose of < or = 5 mg (Grade 1C). The article also includes several specific recommendations for the management of patients with nontherapeutic INRs, with INRs above the therapeutic range, and with bleeding whether the INR is therapeutic or elevated. For the use of vitamin K to reverse a mildly elevated INR, we recommend oral rather than subcutaneous administration (Grade 1A). For patients with life-threatening bleeding or intracranial hemorrhage, we recommend the use of prothrombin complex concentrates or recombinant factor VIIa to immediately reverse the INR (Grade 1C). For most patients who have a lupus inhibitor, we recommend a therapeutic target INR of 2.5 (range, 2.0 to 3.0) [Grade 1A]. We recommend that physicians who manage oral anticoagulation therapy do so in a systematic and coordinated fashion, incorporating patient education, systematic INR testing, tracking, follow-up, and good patient communication of results and dose adjustments [Grade 1B]. In patients who are suitably selected and trained, patient self-testing or patient self-management of dosing are effective alternative treatment models that result in improved quality of anticoagulation management, with greater time in the therapeutic range and fewer adverse events. Patient self-monitoring or self-management, however, is a choice made by patients and physicians that depends on many factors. We suggest that such therapeutic management be implemented where suitable (Grade 2B).

Delivery of Optimized Anticoagulant Therapy: Consensus Statement from the Anticoagulation Forum

Objective:

To provide recommendations, policies, and procedures pertaining to the provision of optimized anticoagulation therapy designed to achieve desired clinical endpoints while minimizing the risk of anticoagulant-related adverse outcomes (principally bleeding and thrombosis).

Study Selection and Data Extraction:

Due to this document's scope, the medical literature was searched using a variety of strategies. When possible, recommendations are supported by available evidence; however, because this paper deals with processes and systems of care, high-quality evidence (eg, controlled trials) is unavailable. In these cases, recommendations represent the consensus opinion of all authors who constitute the Board of Directors of The Anticoagulation Forum, an organization dedicated to optimizing anticoagulation care. The Board is composed of physicians, pharmacists, and nurses with demonstrated expertise and significant collective experience in the management of patients receiving anticoagulation therapy.

Data Synthesis:

Recommendations for delivering optimized anticoagulation therapy were developed collaboratively by the authors and are summarized in 9 key areas: (I) Qualifications of Personnel, (II) Supervision, (III) Care Management and Coordination, (IV) Documentation. (V) Patient Education, (VI) Patient Selection and Assessment, (VII) Laboratory Monitoring, (VIII) Initiation and Stabilization of Warfarin Therapy, and (IX) Maintenance of Therapy. Recommendations are intended to inform the development of care systems containing elements with demonstrated benefit in improvement of anticoagulation therapy outcomes. Recommendations for delivering optimized anticoagulation therapy are intended to apply to all clinicians involved in the care of outpatients receiving anticoagulation therapy, regardless of the structure and setting in which that care is delivered.

Conclusions:

Anticoagulation therapy, although potentially life-saving, has inherent risks. Whether a patient is managed in a solo practice or a specialized anticoagulation management service, a systematic approach to the key elements outlined herein will reduce the likelihood of adverse events. The need for continued research to validate optimal practices for managing anticoagulation therapy is acknowledged.

Pharmacogenetics of warfarin: regulatory, scientific, and clinical issues

Using pharmacogenetics-based therapy, clinicians can estimate the therapeutic warfarin dose by genotyping patients for single nucleotide polymorphisms (SNPs) that affect warfarin metabolism or sensitivity. SNPs in the cytochrome P450 complex (CYP2C9) affect warfarin metabolism: patients who have the CYP2C9*2 and/or CYP2C9*3 variants metabolize warfarin slowly and are more likely to have an elevated International Normalized Ratio INR or to hemorrhage during warfarin initiation than patients without these variants. SNPs in vitamin K epoxide reductase (VKORC1) correlate with warfarin sensitivity. Patients who are homozygous for a common VKORC1 promoter polymorphism, -1639 G>A (also designated as VKOR 3673, haplotype A, or haplotype*2), are warfarin sensitive and typically require lower warfarin doses. By providing an estimate of the therapeutic warfarin dose, pharmacogenetics-based therapy may improve the safety of anticoagulant therapy. To improve drug safety, the FDA updates labels of previously approved drugs as new clinical and genetic evidence accrues. The labels of medical products serve to inform prescribers and patients about potential ways to improve the benefit/risk ratio and/or optimize doses of medical products. On August 16, 2007, the FDA updated the label of warfarin to include information on pharmacogenetic testing and to encourage, but not require, the use of this information in dosing individual patients initiating warfarin therapy. The FDA completed the label update in August 2007.

Anticoagulant Treatment of Deep Vein Thrombosis and Pulmonary Embolism

Venous thrombosis is a common disease. As the mean age of the population increases, so does the incidence of venous thromboembolism. Anticoagulant therapy is equally effective in young and older patients, and can reduce substantially the associated morbidity and mortality. When considering long-term oral anticoagulant therapy in older patients, however, careful ongoing evaluation is imperative to ensure that the risk of bleeding does not outweigh the antithrombotic benefits.

Pharmacogenetics-Based Coumarin Therapy

To reduce the risk of hemorrhage, experts advocate prescribing the anticipated therapeutic dose to patients who are beginning coumarin therapy, but until now there was no accurate way to estimate that dose. Using pharmacogenetics-based coumarin therapy, clinicians can now estimate the therapeutic dose by genotyping their patients for single nucleotide polymorphisms (SNPs) that affect coumarin metabolism or sensitivity.

SNPs in the cytochrome P450 complex (CYP2C9) affect coumarin metabolism. Patients with either of two common variants, CYP2C9*2 or CYP2C9*3, metabolize coumarins slowly and are twice as likely to have a laboratory or clinical adverse event, unless their initial coumarin doses are reduced. SNPs in vitamin K epoxide reductase (VKORC1) correlate with coumarin sensitivity. Patients known to be homozygous for a common VKORC1 promoter polymorphism, −1639 G>A (also designated as VKOR 3673, haplotype A, or haplotype*2), should be started on lower coumarin doses than genotype GG patients. By providing an estimate of the therapeutic coumarin dose, pharmacogenetics-based therapy may improve the safety and effectiveness of coumarin therapy.

Haemorrhagic Complications of Vitamin K Antagonists in the Elderly

In patients >75 years of age, the two main indications for oral anticoagulant therapy with vitamin K antagonists (VKAs) are treatment of venous thromboembolic disease and prevention of systemic embolism in patients with nonvalvular atrial fibrillation. In both indications, a target International Normalized Ratio of 2.5 (range 2.0-3.0) is recommended. Bleeding is the adverse effect feared by physicians that most limits the use of VKAs in older frail patients. In this paper, we discuss (i) the risk of VKA-related bleeding with advancing age; (ii) the severity of bleeding complications and particularly the risk of intracranial haemorrhage in older patients; (iii) the risk factors for bleeding related to patient characteristics; and (iv) the risk factors or determinants for bleeding related to treatment variables (warfarin induction and maintenance administration, instability of anticoagulation, poor compliance and patient's education level, and concomitant use of drugs). Avoiding over-anticoagulation and/or reducing periods of overdosing in the course of oral anticoagulant treatment with tailored monitoring may help to minimise the risk of bleeding in older patients.

The pharmacology and management of the vitamin K antagonists: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This article concerning the pharmacokinetics and pharmacodynamics of vitamin K antagonists (VKAs) is part of the Seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. The article describes the antithrombotic effect of VKAs, the monitoring of anticoagulation intensity, the clinical applications of VKA therapy, and the optimal therapeutic range of VKAs, and provides specific management recommendations. Grade 1 recommendations are strong, and indicate that the benefits do, or do not, outweigh the risks, burdens, and costs. Grade 2 suggests that individual patient's values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this article are the following: for dosing of VKAs, we suggest the initiation of oral anticoagulation therapy with doses between 5 and 10 mg for the first 1 or 2 days for most individuals, with subsequent dosing based on the international normalized ratio (INR) response (Grade 2B). In the elderly and in other patient subgroups with an elevated bleeding risk, we suggest a starting dose at < or = 5 mg (Grade 2C). We recommend basing subsequent doses after the initial two or three doses on the results of INR monitoring (Grade 1C). The article also includes several specific recommendations for the management of patients with INRs above the therapeutic range and for patients requiring invasive procedures. For example, in patients with mild to moderately elevated INRs without major bleeding, we suggest that when vitamin K is to be given it be administered orally rather than subcutaneously (Grade 1A). For the management of patients with a low risk of thromboembolism, we suggest stopping warfarin therapy approximately 4 days before they undergo surgery (Grade 2C). For patients with a high risk of thromboembolism, we suggest stopping warfarin therapy approximately 4 days before surgery, to allow the INR to return to normal, and beginning therapy with full-dose unfractionated heparin or full-dose low-molecular-weight heparin as the INR falls (Grade 2C). In patients undergoing dental procedures, we suggest the use of tranexamic acid mouthwash (Grade 2B) or epsilon amino caproic acid mouthwash without interrupting anticoagulant therapy (Grade 2B) if there is a concern for local bleeding. For most patients who have a lupus inhibitor, we suggest a therapeutic target INR of 2.5 (range, 2.0 to 3.0) [Grade 2B]. In patients with recurrent thromboembolic events with a therapeutic INR or other additional risk factors, we suggest a target INR of 3.0 (range, 2.5 to 3.5) [Grade 2C]. As models of anticoagulation monitoring and management, we recommend that clinicians incorporate patient education, systematic INR testing, tracking, and follow-up, and good communication with patients concerning results and dosing decisions (Grade 1C+).

Evaluation of a warfarin initiation protocol for older people

A protocol for initiation of warfarin therapy, targeted specifically for older people and based on individual responses to initial warfarin doses, was evaluated in a case-control study. People within the protocol group: (i) received higher initial doses of warfarin, (ii) reached an international normalized ratio (INR) of 2 more quickly, (iii) spent more time with INR of 2-3 in the first week and (iv) were less likely to be over-anticoagulated. However, the proportion of people who reached an INR of 2 too quickly (in <4 days) was no greater. The protocol correctly predicted the maintenance dose range of warfarin in over 70% of cases.

Correlation of the change in the International Normalized Ratio and decreasing the Coumadin dosage following total joint arthroplasty

This retrospective pilot study determined whether a change in the daily International Normalized Ratio (INR) correlates with a decrease in Coumadin (DuPont Pharma, Wilmington, Del) dosage. Four hundred seventeen patients yielded 1167 pairs of INR values and Coumadin doses. An increase in INR > 0.4 units correlated 81% with a decrease in the Coumadin dose (P < .05). In patients aged > or = 70 years, the correlation fell to 70% compared to an 89% correlation in patients aged < 70 years (P < .05). The correlation fell to 78% in women, while men exhibited an increase to 87% (P < .05). Although this is a pilot study, when managing postoperative Coumadin anticoagulation for orthopedic patients, an increase in INR > 0.4 units correlates highly with the need to decrease the Coumadin dose. A prospective study is needed to test the usefulness of this parameter.

Anticoagulation therapy

Despite refinements and standardization in the use of anticoagulants, many problems remain for clinicians. Dr. Crowther describes appropriate starting and maintenance doses of warfarin, factors accounting for inter- and intra-observer variability and importantly, the management of the over-anticoagulated patients and bleeding patients. Dr. White compares unfractionated heparin (UFH) and low molecular weight heparin (LMWH) and addresses whether there truly are differences in the efficacy and safety of different LMWH's for both arterial and venous indications. Dr. Ortel discusses the management of the problem patient who requires anticoagulants, the management of heparin-induced thrombocytopenia, the pregnant patient, the obese patient, patients who have renal insufficiency and/or liver disease, patients with malignant disease, and other challenging patient populations.