Dietary Manipulation to Stabilize INR
Dietary Manipulation to Stabilize INR
Abstract & Commentary
By Michael H. Crawford, MD, Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco. Dr. Crawford serves on the speakers bureau for Pfizer. This article originally appeared in the November issue of Clinical Cardiology Alert. At that time it was peer reviewed by Ethan Weiss, MD, Assistant Professor of Medicine, Division of Cardiology and CVRI, University of California, San Francisco; Dr. Weiss reports no financial relationship to this field of study.
Synopsis: A list of 16 vitamin K-rich foods can be used to develop a safe and feasible dietary management strategy in anticoagulated patients that may enhance achievement of target INR.
Source: de Assis MC, et al. Improved oral anticoagulation after a dietary vitamin K-guided strategy: A randomized controlled trial. Circulation 2009;120:1115-1122.
Erratic intraindividual INR values on chronic warfarin therapy are thought to be due to variability in vitamin K intake in the diet. Thus, de Assis et al from Brazil hypothesized that a dietary vitamin K management strategy would result in improved long-term anticoagulation as compared to traditional systems based upon drug-dose adjustments alone. In a single-center open trial, 132 patients requiring chronic anticoagulation with mechanical valves (58%) or atrial fibrillation (35%) were randomized to vitamin K-rich food intake manipulation based upon INR or conventional INR-guided, drug-dosage adjustments. The primary endpoint was the percentage of patients within target INR range 90 days after randomization. Patients eligible for the study were those on therapy for > 3 months who had an INR value out of range but > 1.5 and < 4.0 and not experiencing bleeding or thrombosis.
One patient died, but not related to anticoagulation. The vitamin K group reached their target INR range more quickly than the conventional group and, at 90 days, 74% in the vitamin K group were at target compared to only 58% of the conventional group (P = 0.04). Minor bleeding was more common in the conventional group vs the vitamin K group (7 vs 1 patient; P = 0.06). de Assis et al concluded that a vitamin K dietary management strategy to achieve target INR in anticoagulated patients is feasible, safe, and may enhance achievement of target INR.
Maintenance of target INRs in patients over time is challenging. I have often told frustrated patients that if they ate the same thing every day we could keep them in perfect balance, but no one ever does that for obvious reasons. However, this study suggests that by paying attention to the intake of 16 foods, INR stability can be achieved. These foods are: arugula, asparagus, broccoli,Brussels sprouts, cabbage, cauliflower, collard greens, cucumbers, green peas, green tea, lettuce, liver, spinach,turnip, vegetable oil, and watercress. They do not recommend avoiding these otherwise healthy foods, but keeping their intake constant. In the trial, they adjusted INR, if it was low, by cutting the intake of the vitamin K-rich foods by half. If the INR was high, they increased their intake by 100%. No restrictions on serving size were given, only directions to change the number of servings per week. Very few patients required parenteral vitamin K administration for over-anticoagulation (2 in the conventional group and 1 in the vitamin K group). Crossover to conventional management occurred in 11 patients in the vitamin K group (16%) because target INR could not be achieved with diet adjustments alone. Most of these patients never achieved target INR during the study period and, in 3, their INR was > 4.0.
The major limitation to this study is the short follow-up. We do not know if dietary adjustments will permit long-term stability without drug-dose changes. I suspect dosage adjustments and dietary control will be necessary long term, but if diet-control techniques minimize dosage changes and prolong the interval between blood samples, this would be a significant advantage. I am sure the nurses who often run anticoagulation clinics can learn how to assess diet and suggest adjustments; algorithms for this already exist. Whether long-term costs will be altered by this approach is not known. As a start, I am going to give my patients on warfarin a list of these 16 foods and tell them to keep the combined total number of servings of these foods the same each week and see if this helps stabilization.It has been known for decades that influenza viruses have a propensity to affect muscle. Muscle aches from mild to severe occur regularly with the acute attack of the virus.
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