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Top 10 Variables: Testing Frequency
Thursday, November 1, 2007
PTINR.com Staff
After 50 years of commercial availability, shortening the testing interval presents the drug’s most promising new safety angle
Improved INR control may be as easy as testing more frequently. The longer a patient goes between blood tests; the greater the chance the results of the last blood test will not be where it was the last time it was checked. Bleeding is the most common side effect of warfarin and directly related to warfarin (Coumadin ®) control. Bleeding is a risk for INRs that drift between INR tests. The blood test (measured as an INR number) is the only method of determining the intensity of anticoagulation and determination of protection for the patient.
Traditional means of managing patients includes frequent testing early on for patients new to Coumadin?. As patients establish their maintenance dose and INR test results fall within the target range; testing frequency wanes to monthly for many patients.
A landmark study published early in 2006 analyzed 14 independent studies and found that more frequent testing, i.e. weekly: improved INR control, reduced bleeding by 33%, reduced stroke by 55% and reduced mortality by 33%. 8 months following the meta-analysis, the Food and Drug Administration (FDA) revised the labeling on all warfarin products and included a black box warning – the industry’s strongest position.
Like the diabetic model – more frequent testing yields greater control of the disease and treatment. Monthly testing allows for up to 90 meals and over 100 potential prescription drug interactions (5 prescriptions/day) between testing – plenty long enough for a drug-drug or drug-food interaction to develop. Shortening the testing interval provides greater protection against unwanted and unexpected interactions that place patients at increased risk.