Sliding Scales Effective, Safe for Warfarin Dosing in HD Patients
Pharmacists can effectively oversee warfarin dosing in hemodialysis (HD) patients, according to a pilot study.
A team of Ontario pharmacists and nephrologists created two types of warfarin sliding scales (WSSs): one for patients taking warfarin at home and a second for those taking the medication at an HD unit. Pharmacists design the slding scale for each patient based on the international normalized ratio (INR) and warfarin-dosing trends. The scale is then approved by nephrologists, and is administered by nurses.
The team tested the effectiveness and safety of the WSSs in maintaining therapeutic INRs at safe levels in 27 HD patients who were stable on warfarin. The WSSs significantly increased the proportion of patients with an INR of 2-3 from 50.7% to 59.7%. In addition, the proportion of patients with an INR greater than 4 fell significantly from 4.2% to 1.2%.
“The sliding scales provided consistency in warfarin dosing by avoiding drastic changes in warfarin doses as a result of over-reaction to sub- or supra-therapeutic INRs,” concluded lead investigator Grace Leung, PharmD, Nephrology Pharmacist of York Central Hospital in Richmond Hill, Ontario. “And nursing and physician time was saved because nurses no longer needed to call physicians about patients' INRs.”
Dr. Leung and her colleagues reported the findings at the 32nd Annual Dialysis Conference in San Antonio.
“I think this is an interesting quality-improvement study which suggests that clinical algorithms may improve the safety of warfarin administration in hemodialysis patients,” said Kevin Chan, MD, a Senior Director at Fresenius Medical Care North America. “Warfarin can sometimes precipitate unintended bleeding, and clinical tools that help decrease this risk would be of benefit to dialysis patients on this drug.”
Another expert, Mark Segal, MD, PhD, Associate Professor of Nephrology at the University of Florida, Gainesville, was also impressed by the concept.
“Most nephrologists use a semi-protocol for warfarin dosing in their head anyway, so to have it formalized I think is a very good thing,” said Dr. Segal. “It also has the advantages of involving limited nephrologist time and of increasing patient education, which is critical for warfarin.”
Similar to an insulin sliding scale, a warfarin sliding scale is a set of instructions on dosing warfarin based on INR results. The home WSS is for patients taking warfarin at home. The HD-unit WSS is for patients taking warfarin in the HD unit, as they have poor compliance to warfarin. The WSSs are individualized for each patient and no two scales are the same.
The investigators compared subjects' INR levels from the six weeks immediately preceding start of WSS implementation to the six-week period after the scales' use began. The subjects' average age was 76.2 years and the ratio of males to females was 2:1. Three-quarters—74%—were using warfarin for atrial fibrillation and 67% were not taking any other anticoagulants.
The results showed a statistically significant 9% absolute increase (relative increase of 17.8%) in the proportion of patients at a therapeutic INR level and an absolute reduction of 3% (relative reduction of 71.4%) in the number of patients at a supra-therapeutic INR. The proportion of patients with an INR of below 1.5 did not change significantly, with an absolute reduction of 1.6% (relative reduction of 16.5%). There were no bleeding or clotting events associated with use of the WSSs.