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Published on: September 9, 2012
Changes in plasma warfarin levels and variations in steady-state prothrombin times
Clinical Pharmacology and Therapeutics
|November 1, 1995
Summary
Plasma warfarin levels strongly predict prothrombin time variations in patients on anticoagulation. However, individual sensitivity and other factors significantly influence this relationship, impacting treatment monitoring.
Area of Science:
- Pharmacology
- Clinical Chemistry
- Internal Medicine
Background:
- Warfarin is a widely used oral anticoagulant for long-term therapy.
- Monitoring prothrombin times (PT) is crucial for safe and effective warfarin treatment.
- Variability in PT responses necessitates understanding contributing factors.
Purpose of the Study:
- To quantify the contribution of plasma warfarin levels to serial prothrombin time (PT) variations.
- To investigate individual patient sensitivity to warfarin.
- To identify factors influencing the correlation between warfarin concentration and anticoagulant effect.
Main Methods:
- Prospective observational cohort study at two anticoagulation clinics.
- Serial prothrombin times and plasma total warfarin levels were measured.
- Analysis of covariance was used to assess relationships.
Main Results:
- Plasma warfarin concentration significantly predicted anticoagulant effect (R2 = 0.75, p = 0.0001).
- Warfarin concentration accounted for 15.3% of total variance; individual sensitivity explained 31.1%.
- Correlation between warfarin levels and PT varied widely among subjects.
Conclusions:
- Plasma warfarin levels are a strong predictor of PT changes.
- Individual variability in warfarin sensitivity and other factors significantly impact PT.
- Measurement error or pharmacodynamic changes may play a role in PT variability.
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