Favipiravir is one of the mostly used antiviral agents for the treatment of COVID‐19 infection in many countries, including Thailand. This study aimed to investigate the effect of favipiravir‐warfarin interaction in terms of changing in INR of patients. Medication charts of all inpatients in a hospital in Thailand between April 2021 and March 2022 were reviewed. Patients who received either warfarin with standard care or warfarin with favipiravir were included. The INR levels of patients were monitored at baseline and the earliest date post‐treatment, as well as other laboratory parameters. There were 43 and 53 patients in the warfarin‐favipiravir and the warfarin only groups. Baseline characteristics, such as sex, age, BMI, and warfarin dose, were not significant different between the two groups. The results showed that the mean INR of patients using favipiravir and warfarin was increased from 2.14 to 3.88 (p‐value <0.001), while the patients using warfarin alone had no increase in the mean INR (1.93 vs. 1.91, p‐value 0.906). Other parameters were not significantly changed, including WBC, RBC, hemoglobin, hematocrit, and liver function. However, an increase in platelet count was observed in the favipiravir‐warfarin group, but not in the control group. This real‐world study highlighted a significant increase in the INR levels of patients who used favipiravir together with warfarin, compared to patients who used only warfarin. However, the interaction did not affect other laboratory parameters, except an increase in platelet count.
This article is protected by copyright. All rights reserved