Quality of Anti-Coagulation, Predictors, and Consequences of Deranged Inr of Patients on Warfarin Therapy

Abstract

Objective: Warfarin therapy is considered challenging because of the narrow therapeutic index and various pharmacokinetic and pharmacodynamic interactions. Inability to maintain the international normalized ratio (INR) in therapeutic range results into adverse events. The study aims to characterize the quality of anti-coagulation with warfarin and its outcome in terms of adverse events along with analysis of various predictors for INR control. Methods: A cross-sectional study was conducted at a tertiary care center involving all adult patients (≥18 years) on warfarin therapy presenting to the cardiology outpatient department for 1 year. Current INR, time in therapeutic range (TTR), and adverse events, if any were documented and managed appropriately. Logistic regression analysis was used to calculate odds ratios and 95% confidence intervals (CI) to model the predictors of deranged INR values. Results: Of all 425 patients, 164 (38.58%) patients had non-target INR values, 111 (26.11%) were subtherapeutic, and 53 (12.47%) were supratherapeutic. Increased incidence of subtherapeutic range INR was found in women (IRR=1.09; p=0.002) and in patients with valvular atrial fibrillation (IRR=1.24; p<0.001). On the other hand, increased incidence of supratherapeutic INR was found in patients having renal failure (IRR=1.12; p<0.001). Four (2.4%) patients with subtherapeutic INR developed stroke and 3 (1.92%) patients with high INR resulted into bleeding. Conclusion: The study found low percentage of TTR in patients on warfarin therapy. Predictors for poor anticoagulation control were women, valvular atrial fibrillation, renal failure along with drug interactions, and non-adherence to therapy.