Use of Oseltamivir at an Academic Hospital: Antimicrobial Stewardship Lessons from the H1N1 Influenza Pandemic

Background:   Antimicrobial stewardship programs have traditionally been focused on optimizing the use of antibacterial and antifungal agents.  In light of the H1N1 influenza pandemic, judicious use of antiviral agents with influenza activity has become increasingly important.

Objective:   To describe inpatient oseltamivir utilization during the H1N1 influenza pandemic at an urban, academic medical center and to describe the results of a pharmacy intervention to decrease unnecessary use of this agent

Methods:   We prospectively identified inpatients receiving oseltamivir using a daily pharmacy surveillance report from October 12 – November 3, 2009.   A clinical pharmacist (C.R.P.) reviewed influenza test results for each patient and recommended discontinuation of oseltamivir when a negative PCR result became available or when an appropriate treatment course was completed.

Results:  During the surveillance period, 90 inpatients receiving oseltamivir were identified.  Of these patients, only 23 (26%) tested positive for influenza A by rapid test alone (1) or by PCR (22), while 39 (43%) tested negative for influenza by PCR.  The influenza status of 28 patients (31%) was unknown because either no sample was obtained for testing (25, 28%) or the sample obtained was of insufficient quantity (3, 3%).  The median duration of inpatient oseltamivir therapy for the positive, negative, and unknown influenza-status cases was 3.5 days (interquartile range 2.3 – 5.0), 3.0 days (2.0 – 4.5), and 3.5 days (2.0 – 4.1), respectively.  Positive, negative, and unknown status cases accounted for 30%, 39%, and 30% of all inpatient oseltamivir days of therapy, respectively.  Of 39 patients who tested negative for influenza, 8 (21%) completed 5 days of inpatient therapy before PCR results were reported, 13 (33%) were discharged to complete a 5-day course before PCR results were reported, and treatment was discontinued in 17 (44%) due to a negative PCR.  Pharmacy recommendations to discontinue oseltamivir were made in 13 (21%) of 61 cases with either a positive or negative PCR result: 11 of the recommendations were made on the basis of a negative PCR result, and 2 based on completion of a 10-day treatment course in critically ill patients. 

Conclusions:   Despite a pharmacy intervention to promote appropriate discontinuation of oseltamivir, cases with an eventual negative influenza PCR and those where an appropriate diagnostic test was not obtained accounted for 70% of all inpatient oseltamivir utilization.  These data highlight the importance of a sensitive test with a rapid turnaround time and a procedure to consistently obtain appropriate specimens in suspected cases to minimize unnecessary oseltamivir use in patients without influenza.