Category: Federal Forum Posters
Purpose: Influenza chemoprophylaxis with oseltamivir is recommended by the Centers for Disease Control for patients 65 years and older or with certain chronic conditions, increasing the likelihood of co-administering oseltamivir and warfarin. Case reports and small studies suggest a potential interaction between oseltamivir and warfarin impacting international normalized ratio (INR), while pharmacology studies are not suggestive of an interaction impacting coagulation. There is limited literature exploring concomitant warfarin and extended oseltamivir use beyond a 5-day treatment course. The purpose of this study is to assess the impact of prophylactic oseltamivir on INR in patients on stable chronic warfarin therapy.
Methods: This is a retrospective cohort study conducted within the Veterans Health Administration and will be submitted to the Institutional Review Board for approval. Evaluable patients are those at least 18 years old on chronic warfarin therapy who received oseltamivir for influenza prophylaxis between August 1, 2008 and May 31, 2018. A computer-generated list of patients who received oseltamivir and warfarin in the inpatient or outpatient setting during the study period will be created and analyzed for the presence of pre-specified inclusion criteria. All available INR values within the specific time frame surrounding the oseltamivir prescription order will be extracted to determine the patient’s inclusion in the study. The corresponding INRs prior to and after the concomitant use of warfarin and oseltamivir will be used to analyze the primary and secondary endpoints. The primary endpoint is change in INR from baseline to post-oseltamivir prescription. Documented diagnosis codes and appropriate demographic and lab information will be collected to assess secondary outcomes. Secondary endpoints include frequency of bleeding and thrombosis events, differences between post-oseltamivir INRs for patients with multiple INRs recorded, change in INR in patients with impaired renal function, and impact on INR based on duration of prophylactic oseltamivir therapy.
Results: not applicable
Conclusion: not applicable
Kristin Smith– PGY1 Pharmacy Resident, Durham VA Health Care Center, Durham, NC