Publications (2)5.36 Total impact
- [Show abstract] [Hide abstract]
ABSTRACT: The case of a patient receiving long-term anticoagulation with warfarin who had supratherapeutic International Normalized Ratios (INRs) after receiving concomitant acetaminophen and moxifloxacin as prophylaxis with bacille Calmette-Guérin (BCG) therapy for bladder cancer is reported. An 89-year-old man receiving long-term anticoagulation with warfarin sodium (total weekly dosage of 19 mg) arrived at the anticoagulation clinic for his monthly visit. On the day before this visit, he had received the third of six serial weekly BCG bladder instillations for the treatment of bladder cancer. He did not report that acetaminophen 1000 mg four times daily and one dose of moxifloxacin 400 mg had been prescribed before these instillations. An INR check revealed a value of 6.7. He was instructed to take 2.5 mg of oral phytonadione and to withhold his warfarin dose that night. On the next day, his INR was 3.2. Each time he arrived at the anticoagulation clinic after his BCG therapy, his INR was supratherapeutic, except after his fourth treatment (INR of 2.5), which can be explained by residual effects from the phytonadione he received a week earlier. After completion of his BCG therapy, he was instructed to resume his usual warfarin sodium dosage of 19 mg weekly, and his INR remained in the desired therapeutic range. According to the Drug Interaction Probability Scale, the development of supratherapeutic INRs was probably associated with concomitant acetaminophen and moxifloxacin use. An 89-year-old man receiving long-term anticoagulation with warfarin had supratherapeutic INRs after receiving acetaminophen and moxifloxacin as prophylaxis during BCG therapy for bladder cancer.
- [Show abstract] [Hide abstract]
ABSTRACT: Warfarin dosing remains challenging because of its narrow therapeutic window and large variability in dose response. We sought to analyze new factors involved in its dosing and to evaluate eight dosing algorithms, including two developed by the International Warfarin Pharmacogenetics Consortium (IWPC). we enrolled 108 patients on chronic warfarin therapy and obtained complete clinical and pharmacy records; we genotyped single nucleotide polymorphisms relevant to the VKORC1, CYP2C9, and CYP4F2 genes using integrated fluidic circuits made by Fluidigm. When applying the IWPC pharmacogenetic algorithm to our cohort of patients, the percentage of patients within 1 mg/d of the therapeutic warfarin dose increases from 54% to 63% using clinical factors only, or from 38% using a fixed-dose approach. CYP4F2 adds 4% to the fraction of the variability in dose (R) explained by the IWPC pharmacogenetic algorithm (P<0.05). Importantly, we show that pooling rare variants substantially increases the R for CYP2C9 (rare variants: P=0.0065, R=6%; common variants: P=0.0034, R=7%; rare and common variants: P=0.00018; R=12%), indicating that relatively rare variants not genotyped in genome-wide association studies may be important. In addition, the IWPC pharmacogenetic algorithm and the Gage (2008) algorithm perform best (IWPC: R=50%; Gage: R=49%), and all pharmacogenetic algorithms outperform the IWPC clinical equation (R=22%). VKORC1 and CYP2C9 genotypes did not affect long-term variability in dose. Finally, the Fluidigm platform, a novel warfarin genotyping method, showed 99.65% concordance between different operators and instruments. CYP4F2 and pooled rare variants of CYP2C9 significantly improve the ability to estimate warfarin dose.
Stanford MedicineStanford, California, United States