PURPOSE: To determine the influence of body weight on the international normalized ratio (INR) response to a fixed dose of vitamin K in overanticoagulated patients. METHODS: Retrospective review of records of patients who received 1 mg of vitamin K subcutaneously to correct excessive INR. Dose of vitamin K in milligrams per kilograms plotted against change in INR in 24 hours. RESULTS: Fifteen patients were identified who met all inclusion criteria. Linear regression analysis plotted INR response at 24 hours versus dose of vitamin K adjusted for body weight. Pearson's product moment correlation (R = 0.85) indicated a significant relationship between INR response at 24 hours to an adjusted body weight dose of subcutaneous vitamin K (P = 0.0000523). A strong correlation (r = 0.69) also existed between INR response at 24 hours and the actual body weight dose of subcutaneous vitamin K (P = 0.004). CONCLUSIONS: In overanticoagulated patients, variability in response to vitamin K may be explained by variability in body weight. Dosing vitamin K according to body weight may result in a more predictable INR response.
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