Value of VKORC1 (-1639G>A) rs9923231 genotyping in predicting warfarin dose: A replication study in South Indian population

A case of pulmonary embolism with bad warfarin anticoagulant effects caused by E. coli infection

Warfarin is an anticoagulant commonly used as an oral drug in preventing and treating thromboembolic diseases. The international normalized ratio (INR) is a clinical monitoring anticoagulation intensity index that adjusts the dose based on important references. In particular, INR value must be strictly monitored when warfarin is used for anticoagulation therapy in infected patients. Herein, we report a 54-year-old female patient diagnosed with pulmonary embolism and venous thrombosis of the lower limbs. After the warfarin administration, the INR was always substandard. The patient did not take other warfarin-interacting drugs or foods during the hospital stay. Metagenome next-generation sequencing suggested a bloodstream infection caused by Escherichia coli, which was further confirmed by blood culture. After meropenem administration for anti-infective treatment, the INR value rose rapidly to a standard level. Considering the lack of relevant reports, this case is the first report of potential interaction between E. coli and warfarin. Further, in patients with thromboembolic diseases complicated by infection, antibiotics should be chosen reasonably with close monitoring of the INR to avoid the interaction of warfarin and antibiotics and to ensure the effectiveness and safety of warfarin treatment.

Pharmacogenetic variants influence vitamin K anticoagulant dosing in patients with mechanical prosthetic heart valves

Background: Vitamin K antagonists (VKAs) are class I oral anticoagulants that are widely prescribed following surgical heart valve implantation. The objective of this study was to quantify the relative effects of VKORC1, CYP2C9 and CYP4F2 genotypes in predicting VKA dosing. Materials & methods: A total of 506 South Indian patients with mechanical prosthetic heart valves who were prescribed oral VKAs, such as warfarin or acenocoumarol, were genotyped. The discriminatory ability of mutant genotypes to predict dose categories and bleeding events was assessed using regression analysis. Results: The VKORC1 rs9923231, CYP2C9*3 and CYP4F2*3 mutant genotypes significantly influenced VKA-dose requirements and explained 27.47% of the observed dose variation. Conclusion: These results support pharmacogenetic screening for initial VKA dosing among South Indian patients with mechanical prosthetic heart valves.

Warfarin dose requirement in patients having severe thrombosis or thrombophilia

AIMS

Warfarin dose requirement varies significantly. We compared the clinically established doses based on international normalized ratio (INR) among patients with severe thrombosis and/or thrombophilia with estimates from genetic dosing algorithms.

METHODS

Fifty patients with severe thrombosis and/or thrombophilia requiring permanent anticoagulation, referred to the Helsinki University Hospital Coagulation Center, were screened for thrombophilias and genotyped for CYP2C9*2 (c.430C>T, rs1799853), CYP2C9*3 (c.1075A>C, rs1057910) and VKORC1 c.-1639G>A (rs9923231) variants. The warfarin maintenance doses (target INR 2.0-3.0 in 94%, 2.5-3.5 in 6%) were estimated by the Gage and the International Warfarin Pharmacogenetics Consortium (IWPC) algorithms. The individual warfarin maintenance dose was tailored, supplementing estimates with comprehensive clinical evaluation and INR data.

RESULTS

Mean patient age was 47 years (range 20-76), and BMI 27 (SD 6), 68% being women. Forty-six (92%) had previous venous or arterial thrombosis, and 26 (52%) had a thrombophilia, with 22% having concurrent aspirin. A total of 40% carried the CYP2C9*2 or *3 allele and 54% carried the VKORC1-1639A allele. The daily mean maintenance dose of warfarin estimated by the Gage algorithm was 5.4 mg (95% CI 4.9-5.9 mg), and by the IWPC algorithm was 5.2 mg (95% CI 4.7-5.7 mg). The daily warfarin maintenance dose after clinical visits and follow-up was higher than the estimates, mean 6.9 mg (95% CI 5.6-8.2 mg, P < 0.006), with highest dose in patients having multiple thrombophilic factors (P < 0.03).

CONCLUSIONS

In severe thrombosis and/or thrombophilia, variation in thrombin generation and pharmacodynamics influences warfarin response. Pharmacogenetic dosing algorithms seem to underestimate dose requirement.