Computer assisted management of warfarin treatment

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.

The cost-effectiveness of computer-assisted anticoagulant dosage: results from the European Action on Anticoagulation (EAA) multicentre study

BACKGROUND

Increased demand for oral anticoagulation has resulted in wider adoption of computer-assisted dosing in anticoagulant clinics. An economic evaluation has been performed to investigate the cost-effectiveness of computer-assisted dosing in comparison with manual dosing in patients on oral anticoagulant therapy.

METHODS

A trial-based cost-effectiveness analysis was conducted as part of the EAA randomized study of computer-assisted dosage vs. manual dosing. The 4.5-year multinational trial was conducted in 32 centres with 13 219 anticoagulation patients randomized to manual or computer-assisted dosage. The main outcome measures were total health care costs, clinical event rates and cost-saving per clinical event prevented by computer dosing compared with manual dosing.

RESULTS

Mean dosing costs per patient were lower (difference: euro47) for computer-assisted dosing, but with little difference in clinical event costs. Total overall costs were euro51 lower in the computer-assisted dosing arm. There were a larger number of clinical events in the manual dosing arm. The overall difference between trial arms was not significant (difference in clinical events, -0.003; 95% CI, -0.010-0.004) but there was a significant reduction in events with DVT/PE, suggesting computer-assisted dosage with the two study programs (dawn ac or parma 5) was at least as effective clinically as manual dosage. The cost-effectiveness analysis indicated that computer-assisted dosing is less costly than manual dosing.

CONCLUSIONS

Results indicate that computer-assisted dosage with the two programs (dawn ac and parma 5) is cheaper than manual dosage and is at least as effective clinically, indicating that investment in this technology represents value for money.

Measuring quality of oral anticoagulation care: extending quality measurement to a new field

BACKGROUND

Oral anticoagulation with warfarin is an increasingly common medical intervention. Despite its efficacy, warfarin is difficult to manage, contributing to potential for patient harm. Efforts to measure the quality of oral anticoagulation care have focused disproportionately on the identification of ideal candidates for warfarin therapy, with comparatively little effort in measuring the quality of oral anticoagulation care once therapy has begun. To address this gap in the literature, a MEDLINE search was conducted for all papers relevant to possible quality measures in oral anticoagulation care, including measures of structure, process, and outcomes of care.

LIMITATIONS, CONCERNS, AND CHALLENGES OF QUALITY MEASUREMENT IN ORAL ANTICOAGULATION

Because they do not have intrinsic significance, measures of structure and process should be strongly related to outcomes that matter to merit our interest. Consensus guidelines may provide useful guidance to practicing clinicians but may not represent valid process measures. Outcome measures must be studied with databases that provide sufficient statistical power to reliably demonstrate real differences between providers or sites of care.

CONCLUSION

Oral anticoagulation care, a common and serious condition, is in need of a program of quality measurement. This article suggests a research agenda to begin such a program. Previous research has established the evidence for anticoagulant therapy across a broad spectrum of indications and has helped to achieve consensus on the optimal target intensity for various indications. The next task will be to use this body of evidence to develop valid measures of the structure, process, and outcomes of oral anticoagulation care. Quality indicators provide a framework for quality improvement, two goals of which are to maximize the effectiveness of therapy and to minimize harm.

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).

A mainframe interfacing computer management system for the control of oral anticoagulant therapy

A unique computerized management system has been used to control the anticoagulation of over 400 patients at a large teaching hospital for the last eighteen months. The system is located on the main pathology computer which can be interfaced with the patient administration system (PAS). This enables files in the anticoagulant program to be linked with files in the PAS and files in the haematology database. This system has many advantages over a stand-alone microcomputer system and will form the basis for the next generation of computerized anticoagulant management systems.

An international multicenter randomized study of computer-assisted oral anticoagulant dosage vs. medical staff dosage

BACKGROUND

Increased demand for oral anticoagulants is overwhelming facilities worldwide, resulting in increasing use of computer assistance. A multicenter clinical endpoint study has been performed to compare the safety and effectiveness of computer-assisted dosage with dosage by experienced medical staff at the same centers.

METHODS

A randomized study of dosage of two commercial computer-assisted dosage programs (PARMA 5 and DAWN AC) vs. manual dosage at 32 centers with an established interest in oral anticoagulation in 13 countries. The aim was to recruit a minimum of 16,000 patient-years randomized to medical staff or computer-assisted dosage. In total, 13,219 patients participated, 6503 patients being randomized to medical staff and 6716 to computer-assisted dosage. The safety and effectiveness of computer-assisted dosage were compared with those of medical staff dosage.

RESULTS

In total, 13,052 patients were recruited (18,617 patient-years). International Normalized Ratio (INR) tests numbered 193 890 with manual dosage and 193,424 with computer-assisted dosage. The number of clinical events with computer-assisted dosage was lower (P = 0.1), but in the 3209 patients with deep vein thrombosis/pulmonary embolism, they were reduced by 37 (24%, P = 0.001). Time in target INR range was significantly improved by computer assistance as compared with medical staff dosage at the majority of centers (P < 0.001).

CONCLUSIONS

The safety and effectiveness of computer-assisted dosage has been demonstrated using two different marketed programs in comparison with experienced medical staff dosage at the centers with established interest in anticoagulation. Significant prevention of clinical events in patients with deep vein thrombosis/pulmonary embolism and the achievement of target INR in all clinical groups has been observed. The reliability and safety of other marketed computer-assisted dosage programs need to be established.

Management of oral anticoagulation in a population of children with cardiac disease using a computerised system to support decision-making

OBJECTIVE

To assess the impact of a computerised system to support decision-making concerning the management of warfarin used in maintenance of anti-coagulation.

DESIGN

Retrospective case series study comparing manual and computerised records of prescribing.

SETTING

A tertiary paediatric cardiology department in a teaching hospital.

PARTICIPANTS

The 26 children receiving warfarin to maintain anticoagulation at the time of introduction of a computerised system to support decision-making.

INTERVENTIONS

A rules-based computerised system to support decisions, based on existing departmental guidelines, for management of anticoagulation using warfarin was introduced to aid prescribing physicians.

MAIN OUTCOMES

We assessed the stability of the International Normalised Ratio, along with the number of checks made of the ratio, and the adjustments of dosage. Dosages, and recheck interval prescriptions, were compared to the guidelines established by our department.

RESULTS

We compared 274 prescriptions made manually, and 608 made using the computerised system to support decision-making, covering periods of 4, and 11, months respectively. The mean proportion of time spent by the patients within their target range for the International ratio was maintained during the period studied, at 76 percent versus 79 percent (p = 0.79). The median number of checks of the ratio made for each patient over a period of 28 days was unchanged, at 1.9 versus 2.1 (p = 0.58). There was a significant change in prescribing practices, which more closely followed the departmental guidelines.

CONCLUSION

The introduction of a computerised system to support decision-making maintained the stability of the International ratio using warfarin, without increasing the number of checks or adjustments of dosages, in a point-of-care service for anticoagulation in children.

Efficacy of computer-aided dosing of warfarin among patients in a rehabilitation hospital

OBJECTIVE

To determine whether computer-aided dosing of warfarin is superior to physician dosing to maintain a patient in a rehabilitation hospital within a target international normalized ratio goal.

DESIGN

Randomized, double-blinded, clinical trial in an inpatient rehabilitation hospital. A total of 30 consecutive patients admitted receiving warfarin were randomized to either clinician dosing or computer-aided warfarin dosing for the duration of their hospitalization. The main outcome measures included the percentage of days in a therapeutic anticoagulation range and the number of blood draws. Exclusion criteria included short length of stay (n=110, 39%) and a physician declared international normalized ratio target range of <2.0 (n=67, 23%). A total of 73 patients were excluded because of heme-positive stools at admission, recent gastrointestinal bleed, early discharge or consent refusal. Dawn AC software was used to determine warfarin dosage and frequency of blood draws to maintain a target international normalized ratio of 2.0-3.0 for the computer-dosed group (n=14). Several physicians recommended warfarin dosages for the second group (n=16). Two were dropped from the computer model secondary to lost data files for these two patients.

RESULTS

Computer-aided dosing of warfarin resulted in 61.7% of days within the therapeutic range (international normalized ratio, 2-3), whereas clinician dosing resulted in only 44.1%. There were no significant differences in the number of blood draws or demographic variables between the two groups.

CONCLUSION

Computers were significantly better at maintaining patients within a therapeutic international normalized ratio range than physicians. There were no significant differences in the number of recommended blood draws.

Audit of correction of high INR in an anticoagulation clinic

Examination of the ways in which staff in the anticoagulation clinic dealt with high International Normalized Ratio (INR) results, not dosed by the computer programme, revealed an unacceptable variation in dosage change. Our aim has been to produce a protocol for either manual use and/or transfer to the computer, which would safely correct INR above the upper limit of the therapeutic range, 4.5 to a maximum of 8.0 within 7 days. We collected a large number of results (4.095) and arranged them in four INR groups (4.6-5.0, 5.1-6.0, 6.1-7.0 and 7.1-8.0) and three dosage classes (<3, 3-8 and >8 mg) in order to analyse the effects of the regimens used. This has enabled us to construct a protocol partly empirically and partly by use of a graph correlating dosage change with reduction in the INR, which will now be tested in the clinic. This protocol will deal with all INR up to a maximum of 7.0 as we have decided to contact patients with higher results. Putting this protocol onto the computer should reduce manual dosing by 15%.

A model-based algorithm for the monitoring of long-term anticoagulation therapy

It has been shown that computerized algorithms for the prescription of coumarin derivates can improve the quality of long-term anticoagulation treatment. These algorithms are usually based on an empiric relationship between dosage and International Normalized Ratio and do not quantify the delaying effect of the drug's pharmacokinetics or the effect of alternating doses that are used to approximate a certain average dosage. Our objective was to develop a mathematical model that takes into account these effects and to develop a new algorithm based on this model that can be used to further optimize the quality of long-term anticoagulation treatment. We simplified a general model structure that was proposed by Holford in 1986 so that the parameters can be estimated using data that are available during long-term anticoagulation treatment. The constant parameters in the model were estimated separately for phenprocoumon and acenocoumarol using data from 1279 treatment courses from three different anticoagulation clinics in the Netherlands. The only variable parameter in the model is the sensitivity of the patient, which is estimated during the course of each treatment. A total of 194 dosage and appointment intervals that were proposed by the new algorithm were scored as 'good', 'acceptable', or 'bad' by two dosing experts. One hundred and seventy-eight (91.8%) proposals were considered good by at least one expert and bad by none. In 39 cases the experts disagreed. We believe that this algorithm will allow further improvement of anticoagulation treatments.

Computer Assisted Anticoagulant Therapy

The constantly workload increase has led to the development of Computerised Decision Support Systems (CDSS) for a better management of patient care. Many clinical situations have been investigated to verify the utility of CDSS: few have demonstrated stable effects. One area where success has been reported is the field of oral anticoagulation management. CDSS system has demonstrated to be able to improve the treatment quality in comparison to manual method. In the future scenario of oral anticoagulant management CDSS will have a pivotal part, the constant increase of patients number and their pressure on thrombosis centres had led to the development of alternative models for delivery OAT: Primary care, General Practitioner, Patient self testing and self management and the use of CDSS has been central to the decentralisation process and may be useful in maintaining the efficacy and quality of anticoagulant control. GP with the aid of CDSS are able to deliver OAT as well as expert physician of Thrombosis Centre in terms of time spent by patient in therapeutic range.

Warfarin for non-rheumatic atrial fibrillation: five year experience in a district general hospital

OBJECTIVES

To assess the long term efficacy of and risks associated with computer aided oral anticoagulation for non-rheumatic atrial fibrillation (NRAF) in a district hospital setting.

DESIGN

Retrospective, age stratified, event driven clinical database analysis.

SETTING

District general hospital.

PARTICIPANTS

739 patients receiving warfarin for NRAF between 1996 and 2001. Patients were selected from an anticoagulation database through appropriate filter settings.

MAIN OUTCOME MEASURES

Anticoagulation control (international normalised ratio (INR)) and hospitalisations for bleeding complications, thromboembolic events, and stroke.

RESULTS

Over 1484 patient-years, computer assisted anticoagulation was uncontrolled in 38.3% of patients (INR < 2.0 or > 3.0). No significant differences in INR control were observed with respect to patient age (< 65, 65-75, and > 75 years), although to achieve adequate control of anticoagulation, the frequency of testing increased significantly with age. Annual risks of bleeding complications, thromboembolism, and stroke were 0.76%, 0.35%, and 0.84%, respectively. No significant differences in these events were observed between the three age groups studied. Patients who had thromboembolic events and haemorrhagic complications were significantly more likely to have been under-anticoagulated (INR < 2.0) and over-anticoagulated (INR > 3.0), respectively, at the time of their clinical event.

CONCLUSIONS

Computerised long term oral anticoagulation for NRAF in a community setting of elderly and diverse patients is safe and effective. Anticoagulation control, bleeding events, thromboembolic episodes, and stroke rates are directly comparable with those reported in major clinical trials. The authors therefore support the strategy of rate control with long term oral anticoagulation for NRAF in general clinical practice.

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+).

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.

Management and dosing of warfarin therapy

When initiating warfarin therapy, clinicians should avoid loading doses that can raise the International Normalized Ratio (INR) excessively; instead, warfarin should be initiated with a 5-mg dose (or 2 to 4 mg in the very elderly). With a 5-mg initial dose, the INR will not rise appreciably in the first 24 hours, except in rare patients who will ultimately require a very small daily dose (0.5 to 2.0 mg). Adjusting a steady-state warfarin dose depends on the measured INR values and clinical factors: the dose does not need to be adjusted for a single INR that is slightly out of range, and most changes should alter the total weekly dose by 5% to 20%. The INR should be monitored frequently (eg, 2 to 4 times per week) immediately after initiation of warfarin; subsequently, the interval between INR tests can be lengthened gradually (up to a maximum of 4 to 6 weeks) in patients with stable INR values. Patients who have an elevated INR will need more frequent testing and may also require vitamin K1. For example, a nonbleeding patient with an INR of 9 can be given low-dose vitamin K1 (eg, 2.5 mg phytonadione, by mouth). Patients who have an excessive INR with clinically important bleeding require clotting factors (eg, fresh-frozen plasma) as well as vitamin K1.

Influence of cytochrome P-450 CYP2C9 polymorphisms on warfarin sensitivity and risk of over-anticoagulation in patients on long-term treatment

Cytochrome P-450 2C9 is the principle enzyme that terminates the anticoagulant effect of warfarin. Genetic polymorphisms inCYP2C9 producing variants with altered catalytic properties have been identified. Patients (n = 561) with a target international normalized ratio (INR) of 2.5 who had been treated with warfarin for more than 2 months were anonymously genotyped for the wild-typeCYP2C9*1 allele and the 2C9*2 and2C9*3 variants. The mean maintenance dose of warfarin in patients who were wild-type for both alleles was 5.01 mg. The maintenance dose of warfarin was significantly related to genotype (Kruskall-Wallis, χ2 = 17.985, P = .001) with mean maintenance doses in patients with variant alleles between 61% and 86% of that in wild-type patients. The odds ratio for the2C9*2 allele in patients with a maintenance dose of 1.5 mg or less was 5.42 (95% CI 1.68-17.4). The odds ratio for one or more variant alleles in patients developing an INR of 8.0 or greater was 1.52 (95% CI 0.64-3.58). The SD of the mean INR, percentage of high INRs, and person-time spent in range were determined as parameters of stability. There was no difference between patients grouped according to genotype for any parameter of stability. This study confirmed an association between CYP2C9 genotype and warfarin sensitivity. However, the possession of a variant allele does not increase the likelihood of severe over-anticoagulation or stability of anticoagulation during long-term therapy.

Influence of cytochrome P-450 CYP2C9 polymorphisms on warfarin sensitivity and risk of over-anticoagulation in patients on long-term treatment

Cytochrome P-450 2C9 is the principle enzyme that terminates the anticoagulant effect of warfarin. Genetic polymorphisms inCYP2C9 producing variants with altered catalytic properties have been identified. Patients (n = 561) with a target international normalized ratio (INR) of 2.5 who had been treated with warfarin for more than 2 months were anonymously genotyped for the wild-typeCYP2C9*1 allele and the 2C9*2 and2C9*3 variants. The mean maintenance dose of warfarin in patients who were wild-type for both alleles was 5.01 mg. The maintenance dose of warfarin was significantly related to genotype (Kruskall-Wallis, χ2 = 17.985, P = .001) with mean maintenance doses in patients with variant alleles between 61% and 86% of that in wild-type patients. The odds ratio for the2C9*2 allele in patients with a maintenance dose of 1.5 mg or less was 5.42 (95% CI 1.68-17.4). The odds ratio for one or more variant alleles in patients developing an INR of 8.0 or greater was 1.52 (95% CI 0.64-3.58). The SD of the mean INR, percentage of high INRs, and person-time spent in range were determined as parameters of stability. There was no difference between patients grouped according to genotype for any parameter of stability. This study confirmed an association between CYP2C9 genotype and warfarin sensitivity. However, the possession of a variant allele does not increase the likelihood of severe over-anticoagulation or stability of anticoagulation during long-term therapy.

Multicentre randomised study of computerised anticoagulant dosage. European Concerted Action on Anticoagulation

BACKGROUND

The demand for anticoagulant treatment is increasing. We compared the benefits of computer-generated anticoagulant dosing with traditional dosing decided by experienced medical staff in achieving target international normalised ratios (INRs).

METHODS

In five European centres we randomly assigned 285 patients in the stabilisation period and stabilised patients to the computer-generated-dose group (n=137) or traditional-dose group (n=148). Centres had a specialist interest in oral anticoagulation but no previous experience with computer-generated dosing. The computer program calculated doses and times to next visit. Our main endpoint was time spent in target INR range (Rosendaal method).

FINDINGS

For all patients combined, computer-generated dosing was significantly beneficial overall in achieving target INR (p=0.004). The mean time within target INR range for all patients and all ranges was 63.3% (SD 28.0) of days in the computer-generated-dose group compared with 53.2% (27.7) in the traditional-dose group. For the stabilisation patients alone, computer-generated doses led to a non-significant benefit in all INR ranges (p=0.06), whereas in the stable patients the benefit was significant (p=0.02).

INTERPRETATION

The computer program gave better INR control than the experienced medical staff and at least similar standards to the specialised centres should be generally available. Clinical outcome and cost effectiveness remain to be assessed.

Analysis of risk factors for over-anticoagulation in patients receiving long-term warfarin

A cohort of patients with an INR >7.0 were identified prospectively and compared with a group of patients with stable anticoagulant control. During the study 15,100 INR measurements were recorded and 31 (0.2%) were >7.0. Odds ratios of patient characteristics were calculated as an estimate of relative risk for the development of a high INR. The highest risk factor was a target INR of 3.5 (OR 7.3, 95% CI 2.6-20.2). The second highest risk factor was antibiotic therapy in the 4 weeks preceding the high INR (OR 6.2, 95% CI 1.4-27.7). Bleeding was reported more frequently in the high INR group (OR 5.4, 95% CI 2.1-13.9). Five major bleeds occurred in this group compared to none in the stable group. This analysis identifies risk factors for over-anticoagulation and hence when to intensify monitoring and when to consider pre-emptive warfarin dose reductions.

Review of computerized decision support systems for oral anticoagulation management

Computerized decision support systems (CDSS) are available to assist clinicians in the therapeutic management of oral anticoagulation. We report the findings relating to CDSS for oral anticoagulation management of a primary-care-based systematic review which largely focused on near-patient testing. Seven papers were reviewed which covered four different systems. The methodology of these papers was generally poor, although one randomized controlled trial showed improved therapeutic control associated with computerized management compared with human performance.

New approaches to the delivery of anticoagulant services

Anticoagulant services are changing in response to the increasing demands on the service. New approaches to the delivery of the service are evolving with more local delivery of services and a shift in the service from secondary to primary care. This change has been assisted by the development of near patient testing devices and the use of computerized anticoagulant decision support systems that are increasingly used in both secondary and primary care. The evolving role of the clinical nurse/pharmacist in the provision of this service is an important development enabling more rapid discharge of patients and the provision of local delivery of service.

Management of warfarin (coumarin) overdose

Treatment with coumarin oral anticoagulants, such as warfarin, is effective antithrombotic therapy, but patients treated with these drugs are at significant risk of bleeding. The risk of haemorrhage increases with increasing intensity of anticoagulation and overanticoagulation is common. Reversal can be achieved by stopping the coumarin drug or administration of vitamin K, fresh frozen plasma or coagulation factor concentrates. However, there are surprisingly few studies defining the optimum dose of these products and there are no randomized studies comparing the relative benefit and risk of coagulation factor concentrates versus fresh frozen plasma. Guidelines for the management of overdose are based on level III and IV evidence and are, therefore, only grade B recommendations at best. Further studies are required to determine the most effective use of products and the dose required for safe reversal of overanticoagulation.

Outcomes research using the electronic patient record: Beth Israel Hospital's experience with anticoagulation

Using data captured as part of the routine care of outpatients taking the oral anticoagulant warfarin, we described variation in recording reasons for anticoagulation, selecting target International Normalized Ratio (INR) ranges, and performing coagulation blood tests. Laboratory results were directly captured by or entered into an Anticoagulation Flowsheet, a computer program which is fully integrated with our Online Medical Record (OMR). We studied the 177 patients with flowsheets between October 1993 and January 1995. 90% had a reason for anticoagulation entered; 29 different target INR ranges were entered. For patients with a target INR of 2.0-3.0, the mean number of weeks between blood tests, after a test which was in range, was three weeks (standard deviation 1.7 weeks, range one to twelve weeks). We conclude that routinely collected data contained in an electronic patient record (EPR) can be a rich resource for describing and evaluating clinical practice. We also address several limitations to using EPR data: validity of EPR information, lack of coded information, and imperfect capture of clinician thought processes.

A computerized intervention to improve timing of outpatient follow-up: a multicenter randomized trial in patients treated with warfarin. National Consortium of Anticoagulation Clinics

OBJECTIVE

To evaluate a computerized scheduling model that employs nonlinear optimization to recommend optimal follow-up intervals for patients taking warfarin.

DESIGN

Randomized trial.

SETTING

5 anticoagulation clinics.

PATIENTS/PARTICIPANTS

620 patients expected to receive warfarin for > or = 6 weeks.

INTERVENTIONS

Computer-generated recommendations for scheduling the next visit were presented to or withheld from practitioners.

MEASUREMENTS AND MAIN RESULTS

The main outcome measures were the follow-up interval scheduled by the provider, the interval at which the patient actually returned to clinic, and the quality of anticoagulation control (computed as the absolute difference between the measured and target prothrombin times [PTRs] or international normalized ratios [INRs]). Follow-up intervals scheduled for the patients whose practitioners received computer-generated recommendations were significantly longer than those for control patients (mean, 4.4 vs 3.5 weeks, p < 0.001), despite the fact that the practitioners modified the suggested return interval by > 1 week on 40% of the visits. The interval at which the intervention group actually returned to clinic was also longer (mean, 4.4 vs 4.1 weeks, p < 0.05), even though the control patients tended to return at longer intervals than were scheduled by their practitioners. Control of anticoagulation was nearly the same among experimental and control patients. Life-threatening complications occurred in the care of three experimental patients and one control patient, while other serious complications occurred in the care of 16 experimental patients and 17 control patients.

CONCLUSIONS

Recommendations based on nonlinear optimization prompted clinicians to schedule less frequent follow-up for patients taking warfarin, with no deterioration in anticoagulation control. This approach to scheduling can potentially reduce utilization while maintaining quality of care for patients who require long-term monitoring.

Prospective comparative study of computer programs used for management of warfarin

AIMS

To compare the effectiveness of three computerised systems that are currently used for assisting warfarin control in outpatients with the customary dosing method used by experienced medical staff.

METHODS

A pilot randomised study of three systems with a follow up independently randomised study of two of these was made on 186 patients receiving long term treatment or who had recently started warfarin treatment and had been discharged from hospital.

RESULTS

All three computerised systems seemed to give satisfactory control compared with the traditional dosing method. For patients receiving more intensive treatment with an assigned target range of 3.0-4.5 computerised dosage programs achieved significantly better control; the medical staff undertreated such patients almost 50% of the time.

CONCLUSION

Computer based programs can assist outpatient anticoagulant control with warfarin during both early and long term treatment. For most patients the control achieved is as good as that obtained by the customary method of dosing, by experienced clinic doctors, although the latter tend to be too conservative when dosing patients within the intense target range of 3.0 to 4.5 International Normalised Ratio (INR). The computers were significantly more successful in this higher range.

Factors affecting the precision of warfarin treatment

AIM

To determine what factors influence the precision of anticoagulant control using warfarin by examining the computerised records of 2207 patients.

METHODS

Records from seven district general hospitals were combined and analysed. The precision of anticoagulant control was taken as the absolute deviation of International Normalised Ratio (INR) from target at the most recent determination. This quantity was examined using univariate and multiple regression analyses.

RESULTS

Deviation of INR from target was continuously distributed, almost symmetrically about a mean of zero. The patients' age and sex had little bearing on control. Patients with a high target INR were more likely to be undertreated, and patients taking higher doses of warfarin were more likely to be overtreated. Previous over- or undertreatment were strongly related to poorer current control. The control of treatment varied substantially among the seven hospitals. One possible cause of this variation was the dose adjustment coefficient: the greater the dose adjustment for a given deviation from target INR, the better was the control achieved.

CONCLUSION

Several groups of patients were identified whose control was less satisfactory and in whom anticoagulant treatment needs particular scrutiny: these include patients with a record of previous over- or undertreatment, but not elderly patients in general. The variation in control among hospitals is a source of concern that merits further attention to achieve better uniformity of anticoagulant treatment.

Factors affecting the maintenance dose of warfarin

AIM

To identify the possible factors determining the dose of warfarin prescribed in patients receiving anticoagulant treatment.

METHODS

The computerised records of 2305 patients maintained on the drug in seven hospitals were amalgamated and classified into one of seven diagnostic groups. The associations with the dose of warfarin prescribed were investigated by univariate and multiple regression analysis. Differences between hospitals were studied with regard to the coagulometric method and the thromboplastin preparation used.

RESULTS

The geometric mean dose of warfarin was 4.57 mg and 5% of patients were prescribed 10 mg or greater. There was a noticeable decrease in dose with increasing age, which averaged about 6 mg for patients aged 30 but 3.5 mg for those aged 80. Men required slightly more warfarin than women. Patients with heart disease or atrial fibrillation required lower doses of warfarin, while higher doses were required by patients with deep vein thrombosis. Significant differences in mean warfarin dose among the seven hospitals were evident. These differences could not be explained entirely by the use of different coagulometric methods or thromboplastins.

CONCLUSIONS

Clinicians should be aware that older patients need reduced doses of warfarin. The considerable differences in doses of warfarin among hospitals indicates that further efforts to improve uniformity are required.

A model for planning optimal follow-up for outpatients on warfarin anticoagulation. Warfarin Optimal Outpatient Follow-up Study Group

Patients taking warfarin for long-term anticoagulation require frequent clinic visits to monitor the prothrombin time ratio (PTR), a measure of blood clotting. A dynamic stochastic model using nonlinear optimization was developed to select follow-up visit intervals that minimize the overall costs of patient care. Assuming that fluctuations in a patient's PTR behave as a random diffusion process, future PTR fluctuations are unknown, except as revealed by past PTRs. To determine the incidence and costs of complications in relation to PTR, the authors reviewed the charts of 216 patients who had 719 patient-years of follow-up with 695 trivial, significant, life-threatening, or fatal complications. They modeled the relationship between costs of complications and deviation of the PTR from the therapeutic target as a fourth-order convex polynomial. The model is used to compute the interval to the next follow-up visit to minimize accumulated potential costs. Variables in the optimization are the cost of a monitoring visit and the expected costs of complications. The latter are derived from the current PTR, the variability of the patient's past PTR values, the number of past PTRs available, and the target PTR for the patient. No attempt is made to predict the level of the next PTR or suggest adjustments in the warfarin dose. Shorter follow-up is recommended for patients who have histories of large fluctuations in past PTRs and for patients with few prior PTR determinations. As visits accumulate, the patient's degree of variability can be estimated more accurately and visit intervals adjusted accordingly. The scheduling method balances costs to the health care system of monitoring each patient against the expected costs of complications. This approach has the potential to reduce the number of monitoring visits necessary for safe management of anticoagulated patients with stable PTRs and to improve control among unstable patients.

Experience with a computer-assisted anticoagulant clinic

A microcomputer has been used for 6 years to assist in the running of the anticoagulant clinic for over 300 patients in a district general hospital. The dose adjustments and the time intervals to the next visit are decided automatically. The system has proved very satisfactory in practice, as shown by data presented. There is considerable saving of medical and secretarial time. There has been no equipment failure necessitating reversion to manual methods. The system produces letters (or labels), lists and continuous statistics, and allows the selection of various options, which makes it adaptable to the requirements of other hospitals.

Computer control of anticoagulant dose for therapeutic management

OBJECTIVE

To improve the standard of managing anticoagulant treatment and provide a basis for therapeutic quality control.

DESIGN

Implementation of a comprehensive computerised system for decision support.

SETTING

Three anticoagulation clinics in South Warwickshire.

SUBJECTS

Patients in South Warwickshire receiving anticoagulant treatment from September 1988 to March 1989.

MAIN OUTCOME MEASURE

International normalised ratio was measured and recorded at each visit.

RESULTS

688 Patients' visits were analysed statistically, and a 38% improvement was achieved in the results of international normalised ratios falling within the recommended therapeutic ranges of the British Society for Haematology.

CONCLUSIONS

The implementation of a computerised anticoagulation support system resulted in better management of patients. The system provides a basis for uniform management of treatment and a common platform for national or international trials.