Management and dosing of warfarin therapy

Anticoagulants in coronary artery disease

Anticoagulant therapy for acute coronary syndromes is becoming more complex as newer agents are added to unfractionated heparin and warfarin. The anticoagulants used in current clinical practice are low molecular weight heparins, direct thrombin inhibitors, and heparinoids. Properties of and recent clinical trial data regarding these newer anticoagulants are reviewed in reference to current American College of Cardiology/American Heart Association guidelines.

Conventional oral anticoagulation may not replace prior transesophageal echocardiography for the patients with planned catheter ablation for atrial fibrillation

INSTRUCTION

Preablation transesophageal echocardiography (TEE) is dispensable for the patients with planned catheter ablation for atrial fibrillation (AF) and having received at least a 3-week oral anticoagulation therapy according to the recommendations of the Venice Consensus. But the role of prior TEE and the effect of preablation short-term oral anticoagulation drugs (OACs) under the circumstance are still unclear.

METHODS AND RESULTS

A total of 188 patients with planned catheter ablation for AF and without previous long-term oral anticoagulation, whose duration of AF exceeded 48 h, were randomly divided into receiving 3-week OACs (OACs group) before heparin bridging or receiving no prior OACs (N-OACs group). Follow-up was performed until a TEE had been performed on all the cases before ablation. Consequently, the prevalence of atrial thrombi is 6.3% and 11.7%, respectively (P < 0.05), and the prevalence of minor bleeding is 5.3% and 0%, respectively (P < 0.05), in OACs and N-OACs group. There was no thrombotic event, major hemorrhage, in both groups.

CONCLUSION

After a 3-week effective oral anticoagulation, atrial thrombi could be resolved partly but not completely in the patients with AF who had not received long-term oral anticoagulation previously. To ensure safety, prior TEE may be necessary for the patients with planned catheter ablation for AF.

Laboratory and clinical outcomes of pharmacogenetic vs. clinical protocols for warfarin initiation in orthopedic patients

BACKGROUND

Warfarin is commonly prescribed for prophylaxis and treatment of thromboembolism after orthopedic surgery. During warfarin initiation, out-of-range International Normalized Ratio (INR) values and adverse events are common.

METHODS

In orthopedic patients beginning warfarin therapy, we developed and prospectively validated pharmacogenetic and clinical dose refinement algorithms to revise the estimated therapeutic dose after 4 days of therapy.

RESULTS

The pharmacogenetic algorithm used the cytochrome P450 (CYP) 2C9 genotype, smoking status, peri-operative blood loss, liver disease, INR values and dose history to predict the therapeutic dose. The R(2) was 82% in a derivation cohort (n = 86) and 70% when used prospectively (n = 146). The R(2) of the clinical algorithm that used INR values and dose history to predict the therapeutic dose was 57% in a derivation cohort (n = 178) and 48% in a prospective validation cohort (n = 146). In 1 month of prospective follow-up, the percent time spent in the therapeutic range was 7% higher (95% CI: 2.7-11.7) in the pharmacogenetic cohort. The risk of a laboratory or clinical adverse event was also significantly reduced in the pharmacogenetic cohort (Hazard Ratio 0.54; 95% CI: 0.30-0.97).

CONCLUSIONS

Warfarin dose adjustments that incorporate genotype and clinical variables available after four warfarin doses are accurate. In this non-randomized, prospective study, pharmacogenetic dose refinements were associated with more time spent in the therapeutic range and fewer laboratory or clinical adverse events. To facilitate gene-guided warfarin dosing we created a non-profit website, http://www.WarfarinDosing.org.

Inappropriate prescribing in older people

Optimal prescribing is critical to the goals of geriatric medicine of curing disease, eliminating or reducing symptoms, and improving functioning. However, prescribing decisions in older people are often complex. There is marked heterogeneity in health status and functional capacity amongst older people, who range from fit, active, independent individuals to those who are physically and mentally frail, with limited physiological reserve. Age-related changes in physiology affect drug pharmacokinetics and pharmacodynamics, and together with various pathological processes, increase the risk of adverse drug events (ADEs). This risk is heightened by prescription of multiple medications to treat multiple co-morbidities. Consequently, balancing safety and quality of prescribing for older people with appropriate treatment of all co-morbidities can be challenging.

CYP2C9 Genotype-guided Warfarin Prescribing Enhances the Efficacy and Safety of Anticoagulation: A Prospective Randomized Controlled Study

Warfarin anticoagulation effect is characterized by marked variability, some of which has been attributed to CYP2C9 polymorphisms. This study prospectively examines whether a priori knowledge of CYP2C9 genotype may improve warfarin therapy. Patients were randomly assigned to receive warfarin by a validated algorithm ("control", 96 patients) or CYP2C9 genotype-adjusted algorithms ("study", 95 patients). The first therapeutic international normalized ratio and stable anticoagulation were reached 2.73 and 18.1 days earlier in the study group, respectively (P<0.001). The faster rate of initial anticoagulation was driven by a 28% higher daily dose in the study group (P<0.001). Study group patients spent more time within the therapeutic range (80.4 vs 63.4%, respectively, P<0.001) and experienced less minor bleeding (3.2 vs 12.5%, P<0.02, respectively). In conclusion, CYP2C9 genotype-guided warfarin therapy is more efficient and safer than the "average-dose" protocol. Future research should focus on construction of algorithms that incorporate other polymorphisms (VKORC1), host factors, and environmental influences.

Design, synthesis, and biological evaluation of pyrazinones containing novel P1 needles as inhibitors of TF/VIIa

Herein is described the design, synthesis, and enzymatic activity of a series of substituted pyrazinones as inhibitors of the TF/VIIa complex. These inhibitors were designed to explore replacement and variation of the P1 amidine described previously [J. Med. Chem.2003, 46, 4050]. The P1 needle replacements were selected based upon their reduced basicity compared to the parent phenyl amidine (pKa approximately 12). A contributing factor towards the oral bioavailability of a compound is the ionization state of the compound in the intestinal tract. The desired outcome of the study was to identify an orally bioavailable TF-VIIa inhibitor.

A rapid method for the quantification of the enantiomers of Warfarin, Phenprocoumon and Acenocoumarol by two-dimensional-enantioselective liquid chromatography/electrospray tandem mass spectrometry

We describe a new fully validated enantioselective LC-MS/MS method for stereospecific quantification of both the racemic forms of Warfarin (WF), Phenprocoumon and Acenocoumarol in human plasma. Measurement specificity was assessed by using different blank donor plasma samples, where no interfering reagent peak appeared at the retention time (RT) of the targeted analytes. Response was linear for all analytes. Typical linear regression coefficients have >0.99. The recoveries ranged from 98% to 118%. Determinations in 10 normal healthy individuals revealed a high reproducibility of RTs. These findings confer to the method suitability for large population studies.

Inappropriate prescribing in the elderly

BACKGROUND AND OBJECTIVE

Drug therapy is necessary to treat acute illness, maintain current health and prevent further decline. However, optimizing drug therapy for older patients is challenging and sometimes, drug therapy can do more harm than good. Drug utilization review tools can highlight instances of potentially inappropriate prescribing to those involved in elderly pharmacotherapy, i.e. doctors, nurses and pharmacists. We aim to provide a review of the literature on potentially inappropriate prescribing in the elderly and also to review the explicit criteria that have been designed to detect potentially inappropriate prescribing in the elderly.

METHODS

We performed an electronic search of the PUBMED database for articles published between 1991 and 2006 and a manual search through major journals for articles referenced in those located through PUBMED. Search terms were elderly, inappropriate prescribing, prescriptions, prevalence, Beers criteria, health outcomes and Europe.

RESULTS AND DISCUSSION

Prescription of potentially inappropriate medications to older people is highly prevalent in the United States and Europe, ranging from 12% in community-dwelling elderly to 40% in nursing home residents. Inappropriate prescribing is associated with adverse drug events. Limited data exists on health outcomes from use of inappropriate medications. There are no prospective randomized controlled studies that test the tangible clinical benefit to patients of using drug utilization review tools. Existing drug utilization review tools have been designed on the basis of North American and Canadian drug formularies and may not be appropriate for use in European countries because of the differences in national drug formularies and prescribing attitudes.

CONCLUSION

Given the high prevalence of inappropriate prescribing despite the widespread use of drug-utilization review tools, prospective randomized controlled trials are necessary to identify useful interventions. Drug utilization review tools should be designed on the basis of a country's national drug formulary and should be evidence based.

Anticoagulation in Ambulatory Care

PURPOSE OF THE MANUSCRIPT: Anticoagulation is warranted for the treatment of various disorders including cardiac, vascular, and postsurgical causes. Many centers have nurse case managers to coordinate care for patients on anticoagulation. This increases the demand for specific guidelines to assist nurse case managers to ensure quality of care. This review will address guidelines for nurse case managers and providers regarding initiating anticoagulation treatment and monitoring prothrombin time and international normalized ratio. Information will also be provided regarding when the nurse case manager should notify the providers to establish target international normalized ratio. This review will also provide educational tools to serve as standards for patient teaching, including drug and food interactions.

PRIMARY PRACTICE SETTING(S)

This article applies to adult ambulatory practice that includes primary care, cardiology, and vascular and surgical settings.

IMPLICATIONS FOR CASE MANAGEMENT PRACTICE

The complexity of managing anticoagulation in ambulatory practice warrants case management. The nurse case manager will establish a rapport with patients to improve compliance, providing patient education about diet, dosages, and drug interactions to reduce medication errors and bleeding complications. This review on anticoagulation management will assist nurse case managers and providers to provide better quality of care.

Potent and selective TF/FVIIa inhibitors containing a neutral P1 ligand

Inhibition of tissue factor/factor VIIa complex (TF/FVIIa) is an attractive strategy for antithrombotic therapies. We began with an investigation of a non-amidine TF/FVIIa inhibitor based on a modification of amidine compound 1. Optimization of the substituents on the P1 phenyl portion of the compound 1 led to a neutral or less basic alternative for the 4-amidinophenyl moiety. By further optimization of the substituents on the central phenyl ring, a highly potent and selective TF/FVIIa inhibitor 17d was discovered.

Warfarin maintenance dose adjustment with indirect pharmacodynamic model in rats

The purpose of the study was to adjust the individual maintenance dose of warfarin with a simple approach based on indirect pharmacodynamic model (IDR). Based on the distinct pharmacokinetic and pharmacodynamic features of warfarin, the relationship between the maintenance dose and the steady-state anticoagulation effect was simplified and an approach for the maintenance dose adjustment was proposed. According to the steady-state anticoagulation effect before and after multiple doses (0.1 mg kg(-1)day(-1)), the optimal maintenance doses were predicted for the target anticoagulation effect (INR(target)=2.5), then the actual anticoagulation effect (prothrombin times, PT) on the 6th (8 pm)\8th (8 am)\10th (2 pm) day after dose adjustment according the present method was compared with the target effects with a view of determination the feasibility and accuracy of the proposed approach. The proposed method was also used to adjust warfarin maintenance doses in the presence of metabolism inhibitor metronidazole. The results suggested that the proposed approach could appropriately achieve the target international normalized ratio (INR(target)) when warfarin used alone or in combination with metronidazole, the actual INR values of three days were 2.69+/-0.18 and 2.52+/-0.22 (mean+/-S.D.), respectively. The method provided a relatively simple and accurate strategy for warfarin maintenance dose adjustment.

Study on warfarin plasma concentration and its correlation with international normalized ratio

A sensitive high-performance liquid chromatographic (HPLC) method was developed for warfarin determination in plasma of patients who undertook cardiac valve replacement and were on anticoagulation with warfarin. The method described proved to be accurate, sensitive, easy to perform, reproducible and specific for plasma warfarin measurement with relative standard deviation (R.S.D.) of <5.27% for inter-day and <6.89% for intra-day. The assay was linear in warfarin concentration ranges of 0.12-3 microg/ml (r=0.9995) with mean recovery of 94.6%. The mean warfarin plasma concentration of 58 patients with heart valve replacement within 1 month of post operation was 567.6+/-122.3 ng/ml. The anticoagulant effect of the drug was monitored by international normalized ratio (INR). The correlation of warfarin dosage and concentration with INR was analysed, and the coefficients were 0.21, 0.1<p<0.2 and 0.30, 0.02<p<0.1, respectively. The correlation of warfarin dosage or concentration with INR is very poor, and hence in order to adjust the dosage more objectively and accurately, concentration monitoring is necessary and helpful for the patient management. It is needed especially when the ideal INR is difficult to target.

The influence of co-treatment with carbamazepine, amiodarone and statins on warfarin metabolism and maintenance dose

AIMS

Warfarin is a frequently used anticoagulant drug with narrow therapeutic index and high interindividual variability in the dose requirement. We have previously shown that warfarin dose is influenced by cytochrome P450 (CYP) 2C9 genotype, age, body weight and co-treatment with drugs that interfere with warfarin metabolism. As, in many patients, drug co-treatment cannot be avoided, we investigated the effect of co-treatment with carbamazepine, amiodarone and statins on warfarin metabolism and maintenance dose.

METHODS

Caucasian patients on stable maintenance warfarin therapy with CYP2C9*1/*1 genotype (n=82) were included in the study. Plasma concentrations of (S)- and (R)-warfarin as well as warfarin hydroxylated metabolites were determined using HPLC assay and corresponding clearances of (S)- and (R)-warfarin were calculated.

RESULTS

Patients co-treated with carbamazepine (n=5) had significantly higher plasma 10-hydroxywarfarin concentrations than patients not taking any interacting drugs (n=54) (median: 0.327 microg/ml vs 0.030 microg/ml, p=0.003). (S)- and (R)-warfarin clearances were also higher in the carbamazepine co-treated group (p=0.003), as were warfarin dose requirements (median: 9.00 mg/day vs 3.86 mg/day, p=0.003). Under the conditions of this study, patients co-treated with amiodarone (n=6) did not differ significantly regarding any measured characteristic from patients with no interacting drug treatment, while patients co-treated with simvastatin or lovastatin (n=17) had lower 10-hydroxywarfarin concentration (p=0.02).

CONCLUSIONS

We confirmed important interaction between carbamazepine and warfarin metabolism which can be of major clinical importance. If treatment with carbamazepine cannot be avoided, patients taking warfarin should be frequently monitored, especially when initiating or stopping carbamazepine therapy.

The Risk of Hemorrhage Among Patients With Warfarin-Associated Coagulopathy

OBJECTIVES

Among warfarin-treated patients with international normalized ratio (INR) >5, we sought to determine the risk of major bleeding within 30 days.

BACKGROUND

For warfarin-treated patients, the risk of bleeding increases as the INR rises, particularly if the INR exceeds 4. The 30-day risk of hemorrhage among outpatients with excessively prolonged INR values is unknown.

METHODS

To assess anticoagulation care in the U.S., a cohort of 6,761 patients taking warfarin was prospectively assembled from 101 participating sites (43% were community-based cardiology practices). From this cohort, 1,104 patients were identified with a first episode of INR >5.

RESULTS

A total of 979 met eligibility criteria; complete follow-up information was available for 976 (99.7%). Ninety-six percent (n = 937) of patients had an INR value between 5 and 9; 80% of INR values were <7. Thirteen patients (1.3%) experienced major hemorrhage during the 30-day follow-up period; among patients whose INR was >5 and <9, 0.96% experienced major hemorrhage. None of the bleeding events was fatal. Intervention with vitamin K was uncommon (8.7%). Warfarin doses were withheld for the majority of patients. Fifty percent of patients who were managed conservatively and retested on day 4 or 5 had an INR of 2.0 or less.

CONCLUSIONS

For warfarin-treated outpatients presenting with an INR >5 and <9, the 30-day risk of major bleeding is low (0.96%). Intervention with vitamin K among asymptomatic patients presenting with an INR <9 is not routine practice in the U.S.

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.

[Use of anticoagulant treatments in the elderly]

PURPOSE

The frequency of pathologies requiring anticoagulant treatment (thromboembolic disease, atrial fibrillation) is particularly high in people above 75. The risk of haemorrhagic complications is also highest in this population of patients.Therefore, the assessment of the risk/benefit ratio of an anticoagulant treatment may overestimate the haemorrhagic risk and lead to the under-using of anticoagulant treatment in such pathologies as atrial fibrillation. CURRENT KNOWLEDGE AND KEY-POINTS: However, the use of "classical" anticoagulant treatments such as non-fractionated heparin, low-molecular-weight heparin, and above all, antivitamin K requires special precautions. Several hemorrhagic risk factors are well known and should be spotted out. Finally, the risk/benefit ratio of an anticoagulant treatment in the elderly patients must rely on a comprehensive geriatric assessment.

PROSPECTS AND PROJECTS

In the era of "new anticoagulant treatments", and particularly of per-os antithrombin, it may seem anachronous to issue a statement over the use of "classical anticoagulant treatments", but in the present state of knowledge, the evaluation of these new molecules is not sufficient in the elderly population of patients.

Concomitant drug, dietary, and lifestyle issues in patients with atrial fibrillation receiving anticoagulation therapy for stroke prophylaxis

Atrial fibrillation is a common cardiac arrhythmia and the leading risk factor for stroke. In those at moderate to high risk of stroke, oral anticoagulation therapy with warfarin (a vitamin K antagonist) significantly reduces not only the frequency of such events but also their severity and the associated risk of death. However, achieving optimal anticoagulation with this agent is clinically challenging in view of its complex pharmacokinetic and pharmacodynamic profile. In this regard, concomitant drug therapy (both prescription and over-the-counter medications, including herbal products, vitamins, and various nutritional supplements), along with alcohol intake, dietary factors, and changes in lifestyle, can significantly affect anticoagulation control and thereby expose patients to the risk of bleeding or thromboembolic complications (due to over- and underanticoagulation, respectively). Therefore, it is recommended that intensified monitoring of anticoagulation be performed at initiation and discontinuation of concomitant drug therapy, and in the case of significant dietary and lifestyle changes. Moreover, many patients receive inadequate education and are unaware of such risks and their implications, highlighting the need for better awareness and education on this important aspect of anticoagulation therapy.

Structure-based design and synthesis of pyrazinones containing novel P1 ‘side pocket’ moieties as inhibitors of TF/VIIa

We describe the structure-based design, synthesis, and enzymatic activity of a series of substituted pyrazinones as inhibitors of the TF/VIIa complex. These inhibitors contain substituents meta to the P(1) amidine designed to explore additional interactions with the VIIa residues in the so-called 'S(1) side pocket'. A crystal structure of the designed inhibitors demonstrates the ability of the P(1) side pocket moiety to engage Lys192 and main chain of Gly216 via hydrogen bond interactions, thus, providing additional possibility for chemical modification to improve selectivity and/or physical properties of inhibitors.

Determination of warfarin enantiomers and hydroxylated metabolites in human blood plasma by liquid chromatography with achiral and chiral separation

An assay comprising two simple, selective and isocratic HPLC methods with UV detection was developed and validated for measuring warfarin enantiomers and all five warfarin monohydroxylated metabolites in patient blood plasma. Following liquid/liquid extraction from 1 ml of blood plasma a baseline separation of analytes was achieved on chiral (alpha(1) acid glycoprotein - AGP) and achiral (C(18)) column. Both methods were consistent (R.S.D.<6.9% for warfarin enantiomers and<8.9% for monohydroxylated metabolites) and linear (r>0.998). The limits of detection were 25 ng/ml for warfarin enantiomers, 25 ng/ml for 4'-, 10-, 6- and 7-hydroxywarfarin, 35 ng/ml for 8-hydroxywarfarin and 50 ng/ml for racemic warfarin. In a clinical study in 204 patients, it was confirmed that the assay is appropriate for evaluation of influences of genetic polymorphisms, demographic factors and concomitant drug treatment on warfarin metabolism.

Poor agreement among prothrombin time international normalized ratio methods: comparison of seven commercial reagents

BACKGROUND

Prothrombin time (PT) has long been the most popular test for monitoring oral anticoagulation therapy. The International Normalized Ratio (INR) was introduced to overcome the problem of marked variation in PT results among laboratories and the various recommendations for patient care. According to this principle, all reagents should be calibrated to give identical results and the same patient care globally. This is necessary for monitoring of single patients and for application of the results of anticoagulation trials and guidelines to clinical practice.

METHODS

We took blood samples from 150 patients for whom oral anticoagulation had been prescribed. Plasmas were separated and PTs determined by use of seven commercial reagents and four calibrator sets. The differences in results were assessed by plotting, for each possible pair of methods, the differences in INR values for each sample against the mean INR value (Bland-Altman difference plots).

RESULTS

Mean results differed significantly (P <0.001) for 17 of 21 possible paired comparisons of methods. Only two pairs of methods produced very similar results when assessed for problems of substantial differences in INR values; a significant, systematic increase in the difference with INR; and a significant systematic increase in the variation in difference with increasing INR values.

CONCLUSIONS

The agreement among several (and perhaps most) commercial INR methods is poor. The failure of current calibration strategies may severely compromise both the monitoring of individual patients and the application of oral anticoagulation guidelines and trial results to clinical practice.

Preventing Warfarin-related Bleeding

Warfarin is one of the most common anticoagulants in current use. It maintains a narrow therapeutic index resulting in a significant amount of bleeding. Changes in concomitant medication use and acute illnesses are common causes of overanticoagulation. Monitoring regimens based on patient characteristics and the intensity and duration of anticoagulant therapy, along with simple prediction rules, can reduce the risk of warfarin-related bleeding. Supratherapeutic international normalized ratios are usually best treated by holding a dose and/or reducing the weekly dose of warfarin. Patients with acute bleeding require more urgent warfarin reversal.

Patient preferences for capillary vs. venous INR determination in an anticoagulation clinic: a randomized controlled trial

BACKGROUND

Patients who are receiving warfarin therapy require frequent blood testing to monitor the intensity of anticoagulation. Although previous studies suggest that capillary blood monitoring of the international normalize ratio (INR) is rapid and reliable, patient preferences for the method of blood drawing have not been investigated.

METHODS

We performed a randomized controlled trial of patients attending an anticoagulation clinic in which patients were randomly allocated to undergo capillary or venous INR monitoring. Patient satisfaction with the outpatient visit, pain associated with blood drawing, and time spent in the clinic were assessed for each patient.

RESULTS

Sixty patients were studied. Using a 10-point visual analogue scale to quantify patient satisfaction (0-very satisfied; 10-very dissatisfied), patients expressed a strong preference for capillary INR monitoring over venous INR monitoring (1.64 vs. 4.45; P < 0.001). Using a 10-point visual analogue scale to quantify pain with blood sampling (0-no pain; 10-very painful), patients who underwent capillary INR testing had less pain than venous INR testing (0.83 vs. 2.23; P < or = 0.004). Patients spent, on average, 33 fewer minutes in the clinic with capillary INR testing than venous INR testing (P < 0.001).

DISCUSSION

Our findings support the routine use of capillary blood testing, using a portable monitor, for the management of patients in outpatient anticoagulation clinics.

Physician compliance with outpatient oral anticoagulant guidelines in Auvergne, France

OBJECTIVE

Oral anticoagulants (OA) are commonly used, but they can lead to severe bleeding. We studied the indications and monitoring of OA in patients treated by general practitioners.

DESIGN

Retrospective cross-sectional study.

SETTING

Primary care.

PATIENTS

Four hundred thirty-eight randomly selected patients of a population of 2,452 patients treated with OA were studied.

INTERVENTIONS

We compared the indications for OA as reported by general practitioners with indications as defined according to recent guidelines.

MAIN RESULTS

Twenty-five percent of patients should not have been treated with OA. Inappropriate indications (13% of patients) were atrial fibrillation without risk factor (3.9%), prior uncomplicated myocardial infarction (2.7%), peripheral arterial disease (2.7%), superficial thrombophlebitis (2.3%), and atherothrombotic ischemic stroke (1.6%). For 12% of patients, the duration of OA was too long (venous thromboembolism without permanent risk factor in 10%). Frequency of International Normalized Ratio (INR) measurement was insufficient for 14% of patients and target INR was not achieved in 31%.

CONCLUSIONS

Our study demonstrated that clinicians' adherence to recommendations regarding indications for OA and management of this treatment should be improved. Implementation of anticoagulation clinics is probably needed.

Venous stasis syndrome: the long-term burden of deep vein thrombosis

Currently there is no cure for venous stasis syndrome, a common complication of deep vein thrombosis. Prophylaxis with anticoagulant agents, including new drugs presently under investigation, may decrease the incidence and costs associated with this condition.

Cost-savings analysis of using a portable coagulometer for monitoring homebound elderly patients taking warfarin

The authors present a prospective cost-savings analysis to determine how the use of portable coagulometers in the home health setting affects medical expenditure. Thirty-five elderly patients (mean age 67 years) receiving cardiac home health care and long-term oral anticoagulation were evaluated with paired measurements of the international normalized ratio by both a traditional, laboratory-based prothrombin time and a point-of-care coagulometer (CoaguChek, Roche Diagnostics, Basel, Switzerland). Costs for materials, procedures, transportation, and labor were summed for both methods, and it was found that cost of international normalized ratio determination by the portable coagulometer was significantly less than the traditional method ($6.85 vs. $17.30; p<0.001). The authors conclude that by saving on the costs of transporting and processing traditional international normalized ratio specimens, use of point-of-care coagulometers by home health nurses could reduce medical expenditure. The cost savings and potential improvement in quality of care argue for equipping home health nurses with portable coagulometers.

Structure-based drug design of pyrazinone antithrombotics as selective inhibitors of the tissue factor VIIa complex

Structure-based drug design coupled with polymer-assisted solution-phase library synthesis was utilized to develop a series of pyrazinone inhibitors of the tissue factor/Factor VIIa complex. The crystal structure of a tri-peptide ketothiazole complexed with TF/VIIa was utilized in a docking experiment that identified a benzyl-substituted pyrazinone as a P(2) surrogate for the tri-peptide. A 5-step PASP library synthesis of these aryl-substituted pyrazinones was developed. The sequence allows for attachment of a variety of P(1) and P(3) moieties, which led to synthesis pyrazinone 23. Compound 23 exhibited 16 nM IC(50) against TF/VIIa with >6250x selectivity versus Factor Xa and thrombin. This potent and highly selective inhibitor of TF/VIIa was chosen for pre-clinical intravenous proof-of-concept studies to demonstrate the separation between antithrombotic efficacy and bleeding side effects in a primate model of thrombosis.

Outpatient treatment of acute venous thromboembolic disease

Once- or twice-daily subcutaneous dosing of LMWHs without laboratory monitoring has facilitated outpatient VTE therapy. Clinical trials have demonstrated at least equivalent efficacy and safety and potential cost savings of outpatient therapy for uncomplicated proximal DVT with LMWH when compared with inpatient therapy. Explicit criteria exist for outpatient DVT therapy. Home therapy for PE requires further evaluation before it can be recommended outside of a trial or other supervised setting.

Warfarin dose reduction vs watchful waiting for mild elevations in the international normalized ratio

BACKGROUND

Whether clinicians should decrease the warfarin dose in response to a mild, asymptomatic elevation in the international normalized ratio (INR) is unknown.

OBJECTIVES

The study objectives were as follows: (1) to evaluate the safety of an anticoagulation service (ACS) policy advocating that the warfarin dose not be changed for isolated, asymptomatic INRs of < or = 3.4; (2) to compare the dosing strategies of an ACS and primary care providers (PCPs); and (3) to quantify the relationship between reduction of the warfarin dose and the subsequent fall in the INR.

DESIGN AND SETTING

Randomized controlled study of health maintenance organization outpatients who were receiving warfarin.

PATIENTS

We identified 231 patients with a target INR of 2.5 and an isolated, asymptomatic INR between 3.2 and 3.4. Our ACS monitored 103 of the patients; PCPs monitored the remaining 128 patients.

MEASUREMENTS

From all 231 patients, we obtained INRs and warfarin dosing history. From the 103 ACS enrollees, we also recorded adverse events.

RESULTS

One ACS patient had epistaxis in the 30 days after the elevated INR. Twenty-three percent of ACS enrollees and 47% of PCP patients reduced their warfarin dose (p < 0.001). The median follow-up INRs were similar in both cohorts: 2.7 in the ACS enrollees and 2.6 in the PCP patients. However, in a subgroup analysis of 190 patients who presented with an INR of 3.2 or 3.3, ACS enrollees were more likely to have a follow-up INR in the range of 2 to 3 (p = 0.03). The median follow-up INR was 2.7 in 148 patients who maintained their warfarin dose, 2.5 in 77 patients who decreased their dose by 1 to 20%, and 1.7 in 6 patients who decreased their dose by 21 to 43% (p < 0.001).

CONCLUSIONS

These findings support maintaining the same warfarin dose in asymptomatic patients with an INR of < or = 3.3, and reducing the dose for patients who have a greater INR or an increased risk of hemorrhage. Warfarin dose reductions > 20% should be avoided for mildly elevated INRs.

Coumarin therapy in thrombosis

Oral anticoagulants are the most commonly used agents in the long-term prophylaxis and treatment of arterial and venous thrombotic disorders. As new and expanded indications for their use, such as the prevention of recurrent myocardial infarction or the treatment of systemic embolism in atrial fibrillation, are developed, the use of oral anticoagulants is rising. Also, in North America, oral anticoagulants are used commonly for preventing venous thromboembolism following orthopedic surgery. This article reviews the pharmacology of warfarin sodium, the most commonly used oral anticoagulant in North America, and discusses practical aspects of the use of this agent in thrombotic disorder management.

DVT prophylaxis and anticoagulation in the surgical patient

One of the most common postoperative complications is venous thromboembolism, a term encompassing deep vein thrombosis and pulmonary embolism. This article reviews the epidemiology, natural history, difficulties in diagnosis, and strategies for the prevention of postoperative venous thromboembolism. We thoroughly review the currently available methods for thromboprophylaxis including: early ambulation, elastic compression stockings, pneumatic compression devices, inferior vena cava filters, and a variety of pharmacologic agents such as unfractionated heparin, warfarin, aspirin, low molecular weight heparin, and pentasaccharides. Finally, we review the perioperative management of patients on long-term oral anticoagulation.

Use of cardiovascular medications in the elderly

Cardiovascular disease is the leading cause of death in patients aged 65 and above. Although elderly persons represent only 12.4% of the US population, they account for about a third of drug expenditures. However the appropriate use of cardiovascular medications in these patients has been shown to reduce the rate of cardiovascular morbidity and mortality. The normal aging and the disease process in the elderly result in significant changes at the structural and molecular level in the elderly. The changes that take place in the autonomic nervous system, the kidneys, and the liver in the elderly modify the metabolism and clinical effects of most medications. Elderly patients are also susceptible to side effects and adverse drug reactions. Physicians should have a clear understanding of the normal aging processes, the abnormal changes due to disease process and the changes in the pharmacology of drugs in the elderly to deliver proper care to the elderly patient.

Substitution of generic warfarin for Coumadin in an HMO setting

BACKGROUND

Substitution of generic warfarin for Coumadin presents safety concerns due to warfarin's narrow therapeutic index and because a prior generic formulation was removed from the US market after it was associated with adverse events.

OBJECTIVE

To determine whether a health maintenance organization (HMO) can add generic warfarin to its formulary without adversely affecting warfarin management or increasing adverse events.

DESIGN

In a prospective, observational study, an HMO that formerly dispensed only Coumadin added a generic warfarin preparation (Barr Laboratories, Pomona, NY) to its formulary.

SETTING

An anticoagulation service (ACS) affiliated with an HMO that was based in St. Louis, MO.

PARTICIPANTS

The cohort consisted of 182 enrollees in the ACS as of May 1, 1999. At the start of the study, these participants were taking Coumadin; by October 31, 2000, all had switched to Barr warfarin.

MEASUREMENTS AND MAIN RESULTS

We collected data 8 months prior to and 10 months after the introduction of generic warfarin for the following endpoints: international normalized ratio (INR) control, frequency of INR monitoring, number of dose changes, and rate of thrombotic and hemorrhagic events. Statistical process control charts were used to differentiate between random variation in the endpoints and changes due to different warfarin formulations, and we used the Wilcoxon signed-rank test to look for a change in any endpoint after patients changed to generic warfarin. No significant differences were found in any endpoint.

CONCLUSIONS

Substitution of Barr warfarin for Coumadin did not significantly affect INR control, warfarin management, or adverse events. Our findings suggest that HMOs can safely substitute at least 1 generic formulation of warfarin without extra monitoring.

Establishing and running an effective telephone-based anticoagulation service

Observational studies and randomized controlled trials have revealed improvement in international normalized ratio (INR) control and reduced thrombotic and hemorrhagic events in patients taking warfarin who are managed by an anticoagulation service (ACS) compared with traditional physician care. In this article, we describe how to establish a multidisciplinary telephone-based ACS to monitor INRs, dose warfarin, and heparin therapy, and to educate patients by telephone. We address how to improve ACS efficiency by using an electronic medical record, charting by exception, holding group-based education, communicating by telephone, and conducting quality assurance. We also make recommendations for improving the quality of care of patients taking anticoagulants that can be implemented in any setting and we discuss how to apply these guidelines to other remote disease-state management programs (eg, diabetes).

Anticoagulation in the elderly

Oral anticoagulation therapy has demonstrated benefit in the treatment and prevention of a variety of thromboembolic disorders. Most individuals who receive oral anticoagulant therapy are elderly patients with nonvalvular atrial fibrillation and acute or recurrent venous thromboembolism. Anticoagulation in elderly patients poses unique challenges for the practicing clinician because they are simultaneously at higher risk for recurrent thromboembolism and major bleeding, including catastrophic intracranial hemorrhage. The pharmacology of warfarin in the elderly is reviewed, including important drug interactions and current dosing recommendations for elderly patients. Evidence of the benefits and risks of oral anticoagulation therapy are reviewed for patients with atrial fibrillation and venous thromboembolism. This information should enable practitioners to better assess the relative risks and benefit of oral anticoagulation therapy to guide treatment decisions in the elderly.

Patient self-monitoring of oral anticoagulant therapy: potential benefits and implications for clinical practice

Coumarin derivatives are widely used oral anticoagulants for patients with chronic atrial fibrillation, venous thromboembolism, valvular heart disease, myocardial infarction or a mechanical prosthetic heart valve. Because of the narrow therapeutic window associated with coumarins and the potential for drug interactions, frequent monitoring of anticoagulation is required to maintain the International Normalized Ratio (INR) between 2.0 to 3.5 for most clinical indications. Monitoring of oral anticoagulant therapy is placing a considerable burden on healthcare providers because many patients require life-long treatment with coumarins, and because of an increasing number of elderly patients with conditions that are treated with coumarins. A novel approach that might, in part, address this healthcare need is patient self-monitoring of anticoagulation with a portable coagulometer. Several cohort studies and randomized controlled trials have found that anticoagulation self-monitoring is as good as, or better than, conventional monitoring in a specialized anticoagulation clinic or by a general practitioner. The advantages of anticoagulation self-monitoring include reduced patient inconvenience relating to anticoagulation clinic visits and laboratory monitoring of warfarin therapy, and fewer INR levels outside the therapeutic INR range if INR measurements are preformed more frequently with anticoagulation self-monitoring. Thus, anticoagulation self-monitoring has the potential to reduce the incidence of thromboembolic and bleeding episodes in patients who are receiving long term oral anticoagulant therapy. The potential drawbacks of anticoagulation self-monitoring include the costs of the portable coagulometer. Additionally, self-monitoring is limited to patients who have the cognitive and physical capabilities to perform the technique required for the portable coagulometer.