Dietary Manipulation to Stabilize INR
Abstract & Commentary
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 their INR, rather than warfarin dose adjustments. The other group had conventional INR-guided, drug-dosage adjustments. The primary endpoint was the percentage of patients within their 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.
Results: One patient died, but not related to anticoagulation. The vitamin K group reached their target INR range more quickly then 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 (seven vs. one 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.
Commentary
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, brussel sprouts, cabbage, cauliflower, collard greens, cucumbers, green peas, green tea, lettuce, liver, spinach, turnip, vegetable oil, and watercress. They do not recommend not eating these otherwise healthy foods, but keeping their intake constant. In the trial, they adjusted INR, if it was high, by cutting the intake of the vitamin K-rich foods by half. If the INR was low, 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; two in the conventional group and one 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 three, their final 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 asses 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 the 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.
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.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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