Warfarin Dosing in Patients with Renal Failure

Although warfarin labels claim dosing adjustments are not required for renal failure patients, a new study finds that patients with moderate and severe kidney impairment need reduced warfarin doses.

In patients with kidney impairment, warfarin is initiated at similar doses and managed similarly as in the general medical population. Unfortunately, few data exist to guide dose adjustment in patients with decreased kidney function. In a study published in the American Journal of Kidney Disease, Nita A. Limdi, PharmD, PhD, of the University of Alabama at Birmingham and colleagues performed a cross-sectional analysis to determine the degree of warfarin dose reduction associated with kidney impairment and to outline recommendations for warfarin dosing.

Subjects who were long-term warfarin users and had mild (≥60 mL), moderate (30-59 mL), and severe kidney impairment, as measured by estimated glomerular filtration rates, were included in the study. A total of 708 subjects from anticoagulation clinics at University of Alabama (UAB) and University of Chicago (UC) were followed.

Warfarin dose (milligrams per day) was evaluated using linear regression after adjustment for clinical, demographic, and genetic factors, including age, race, sex, body mass, sociodemographic factors, smoking status, alcohol, vitamin K intake, and comorbid conditions such as congestive heart failure.

Limdi and colleagues found that the prevalences of moderate (31.8% and 27.6%) and severe kidney impairment (8.9% and 6.6%) were similar in the UAB and UC cohorts. Warfarin dose requirements were significantly lower in patients with moderate and severe kidney impairment compared with those with no or mild kidney impairment in the UAB and UIC cohorts. Compared with patients with no or mild kidney impairment, patients with moderate kidney impairment required 9.5% lower doses of warfarin, and patients with severe kidney impairment required 19% lower doses of the drug.

They concluded that “moderate and severe kidney impairment were associated with a reduction in warfarin dose requirements,” and that although dosing of the done is done individually, physicians are urged to consider renal function when dosing to make it easier for patients to keep their international normalized ratios in therapeutic range.

For more:

• American Journal of Kidney Disease: Warfarin Dosing in Patients with Impaired Kidney Function
• Journal of the American Society of Nephrology: Kidney Function Influences Warfarin Responsiveness and Hemorrhagic Complications
• HCPLive: Renal Week 2010