Study of co-prescription of drugs potentially interacting with warfarin in indonesian ambulatory patients

Background: Despite the growing use of Direct Oral Anticoagulant (DOAC), the most prescribed oral anticoagulant currently in Indonesia is warfarin. Efficacy and safety of warfarin are influenced by various factors including drug-drug interactions. Patients in ambulatory care often receive more than one prescription leading to potential drug-drug interactions. However, there is no data from Indonesia has been published. This study aimed to assess the prevalence of other drugs potentially interacting with warfarin and their interaction risk. Method: It was a descriptive cross-sectional study. We identified warfarin prescriptions issued between January 2015 and December 2019 using electronic prescription and electronic medical records. Analysis of interaction risk was performed using Medscape. Result: During 4 years, there were 50 patients fulfilling inclusion criteria with 715 prescriptions issued. From 50 patients, 94% at least received 1 concomitant drug. The four most commonly interacting drugs prescribed during warfarin therapy were spironolactone (58%), simvastatin (54%), allopurinol (32%) and low dose acetylsalicylic acid (20%). Furthermore, there were 38% of patients received concomitant drugs classified as serious interaction as follows allopurinol, amiodarone, and fenofibrate. As much as 16% of patients had adverse outcomes and some of this may be associated with warfarin-drug interaction. Conclusion: This study indicates that the prevalence of co-prescription with potentially interacting drugs during warfarin therapy in ambulatory patients is high. Strategy to identify and manage warfarin-drugs interaction is warranted to avoid potential adverse events.