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Adherence to warfarin treatment among patients with atrial fibrillation
1Clinical Pharmacology Unit, Department of Medicine/Solna, Karolinska Institute, Stockholm, Sweden, mika.skeppholm@ds.se.
Insights
Assessing warfarin adherence in atrial fibrillation patients using prescription data reveals significant gaps. Many patients lack sufficient medication, indicating a need for improved adherence strategies.
Area of Science:
- Pharmacoeconomics
- Clinical Pharmacy
- Health Services Research
Background:
- Warfarin treatment is crucial for reducing stroke risk in atrial fibrillation patients.
- Effective warfarin therapy hinges on patient adherence, which is challenging to measure accurately.
- Prescription data offers a potential, yet complex, avenue for assessing adherence due to variable dosing.
Purpose of the Study:
- To evaluate two distinct methods for assessing patient adherence to warfarin therapy.
- To determine the reliability of prescription data in estimating warfarin adherence.
- To identify adherence patterns and discontinuation rates in a large cohort of atrial fibrillation patients.
Main Methods:
- A retrospective analysis of Swedish healthcare registers was conducted.
- Age- and sex-specific warfarin dosage requirements were established from extensive blood test and dosing data.
- Prescription data from 163,785 atrial fibrillation patients were analyzed over a mean follow-up of 3.9 years to compare needed versus dispensed warfarin quantities.
Main Results:
- Approximately 45% of patients had insufficient warfarin supplies for 80% of their at-risk periods.
- Initial discontinuation rates ranged from 16-21% within the first year, with subsequent annual rates of 8-9%.
- Patients with high bleeding risk or low embolic risk exhibited poorer medication endurance.
Conclusions:
- Prescription data provides a viable method for estimating group-level warfarin adherence.
- Findings indicate suboptimal adherence in a large atrial fibrillation cohort, necessitating targeted interventions.
- This adherence estimation method can facilitate comparisons between warfarin and newer oral anticoagulants.
Background:
Treatment with warfarin greatly reduces the risk of stroke related to atrial fibrillation, but will not be effective unless patients adhere to treatment. Lack of fixed dosing makes it difficult to objectively estimate adherence to treatment from prescription data.
Objective:
To evaluate two methods that assess adherence to warfarin from prescription data.
Design:
Retrospective study of Swedish health care registers.
Patients And Methods:
Age- and sex-specific dose requirements were determined from approx. 1 million blood tests and dosing instructions. By applying these dosages to 163,785 warfarin-treated patients with atrial fibrillation, we calculated the quantity of warfarin that was needed to keep these patients on effective treatment during a mean follow-up of 3.9 years and compared that with the dispensed quantities. The ratio of available drug/time at risk constitutes a measure of adherence on group level. In addition, time intervals between refills were used to assess discontinuation.
Results:
Both methods showed that 45% of the patients did not have enough warfarin to last 80% of the time at risk. Between 16 and 21% of the patients discontinued within the first year, followed by 8-9% annually during the following years. Patients with high bleeding risk and patients with low embolic risk showed lower endurance.
Conclusions:
Adherence to treatment with warfarin can be estimated on group level from prescription data and may be useful for comparison of adherence with warfarin and new oral anticoagulants. When applied to a large warfarin-treated cohort with atrial fibrillation, we found that adherence is low and that measures aiming for improvements are needed .
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