Outpatient anticoagulation issues for the primary care physician

Prospective alpha allocation in the Clarification of Optimal Anticoagulation through Genetics (COAG) trial

BACKGROUND

The Clarification of Optimal Anticoagulation through Genetics (COAG) trial is a large, multicenter, double-blinded, randomized trial to determine whether use of a genotype-guided dosing algorithm (using clinical and genetic information) to initiate warfarin treatment will improve anticoagulation status when compared to a dosing algorithm using only clinical information.

PURPOSE

This article describes prospective alpha allocation and balanced alpha allocation for the design of the COAG trial.

METHODS

The trial involves two possibly heterogeneous populations, which can be distinguished by the difference in warfarin dose as predicted by the two algorithms. A statistical approach is detailed, which allows an overall comparison as well as a comparison of the primary endpoint in the subgroup for which sufficiently different doses are predicted by the two algorithms. Methods of allocating alpha for these analyses are given - a prospective alpha allocation and allocating alpha so that the two analyses have equal power, which we call a 'balanced alpha allocation.'

RESULTS

We show how to include an analysis of the primary endpoint in a subgroup as a co-primary analysis. Power can be improved by incorporating the correlation between the overall and subgroup analyses in a prospective alpha allocation approach. Balanced alpha allocation for the full cohort and subgroup tests to achieve the same desired power for both of the primary analyses is discussed in detail.

LIMITATIONS

In the COAG trial, it is impractical to stratify the randomization on subgroup membership because genetic information may not be available at the time of randomization. If imbalances in the treatment arms in the subgroup are found, they will need to be addressed.

CONCLUSIONS

The design of the COAG trial assures that the subgroup in which the largest treatment difference is expected is elevated to a co-primary analysis. Incorporating the correlation between the full cohort and the subgroup analyses provides an improvement in power for the subgroup comparison, and further improvement may be achieved via a balanced alpha allocation approach when the parameters involved in the sample size calculation are reasonably well estimated.

Warfarin therapy: in need of improvement after all these years

BACKGROUND

Warfarin therapy has been used clinically for over 60 years, yet continues to be problematic because of its narrow therapeutic index and large inter-individual variability in patient response. As a result, warfarin is a leading cause of serious medication-related adverse events, and its efficacy is also suboptimal.

OBJECTIVE

To review factors that are responsible for variable response to warfarin, including clinical, environmental, and genetic factors, and to explore some possible approaches to improving warfarin therapy.

RESULTS

Recent efforts have focused on developing dosing algorithms that included genetic information to try to improve warfarin dosing. These dosing algorithms hold promise, but have not been fully validated or tested in rigorous clinical trials. Perhaps equally importantly, adherence to warfarin is a major problem that should be addressed with innovative and cost-effective interventions.

CONCLUSION

Additional research is needed to further test whether interventions can be used to improve warfarin dosing and outcomes.

Anticoagulation management: a new approach

Anticoagulation therapy has been identified as an area in which new approaches to treatment and monitoring may allow for significant improvements in healthcare quality and costs. We evaluated the potential benefits of a new approach to anticoagulation therapy, utilizing decision support software, point-of-service testing, and workflow redesign. We performed an intervention study in the setting of a university-affiliated primary care clinic, involving 40 patients receiving chronic anticoagulation therapy. Study measurement included anticoagulation control, complications of therapy and related costs, as well as clinic revenue and overhead costs. After implementation of the new approach, the frequency of international normalized ratio (INR) results within therapeutic range increased from 34% to 67%. During a 1-year follow-up period, complications related to anticoagulation therapy were reduced by 91% (p < 0.01). Labor-related overhead costs decreased from approximately 12,600 to 3,100 US dollars. During the same period, the clinic generated approximately 35,000 US dollars in new revenue. For every dollar spent on clinic implementation and maintenance, over 25 US dollars was returned from cost containment and new revenue production. This approach allows a clinic to show improved anticoagulation control and complication rates while simultaneously improving financial performance.

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).

Prevalence of ocular hemorrhage in patients receiving warfarin therapy

BACKGROUND

Warfarin, the drug most commonly used for outpatient anticoagulation therapy, has bleeding as its main side effect. The objective of this study was to determine the prevalence of ocular hemorrhage in patients receiving warfarin and to compare it to the prevalence in the general population.

METHODS

Patients receiving warfarin therapy who were attending the anticoagulation clinic at a tertiary care hospital in Montreal between October and December 1996 received a flyer inviting them to have their eyes examined to look for "ocular bleeding." Consenting patients were examined for subconjunctival hemorrhage, gross hyphema, and vitreous and retinal hemorrhages through external ocular examination and funduscopic examination with the pupils dilated using direct and indirect ophthalmoscopy.

RESULTS

Of the 1225 patients seen at the clinic 126 (10%) agreed to participate. Four patients (3%) were found to have intraretinal hemorrhage at the time of examination. All hemorrhages were visually insignificant.

INTERPRETATION

The risk of retinal hemorrhage in patients without preexisting ocular disease, such as retinal neovascularization or choroidal vasculopathy, who are receiving warfarin therapy is so small that it should not deter physicians from prescribing this drug when indicated.

Use of enoxaparin for the chronically anticoagulated patient before and after procedures

Patients who require chronic anticoagulation and a procedure have been traditionally managed either by stopping warfarin and starting intravenous standard heparin or by adjusted dose subcutaneous standard heparin or taken off all anticoagulation for a week before the procedure. Enoxaparin may be useful as an alternative method of anticoagulation, avoiding hospitalization and the need for frequent monitoring.

Initiation of warfarin therapy: recommendations and clinical pearls

Warfarin is a commonly used medication with a narrow therapeutic index. The initiation of warfarin requires consideration of a variety of factors, which include reviewing the indications and contraindications for this agent, performing a thorough clinical assessment along with a risk-benefit analysis for anticoagulation, consideration of warfarin pharmacology, developing strategies to monitor the intensity of anticoagulation and for the detection of adverse events, and education of the patient. The process of warfarin initiation has been studied by many researchers, but much of this literature has not been employed in clinical practice. This article presents a strategy for the clinician to use when initiating patients on warfarin.