BACKGROUND: Clinical event rates may differ among patients treated in the real 
world (RW) compared to randomized controlled trials (RCTs). When translating the 
efficacy of new treatments to RW, the relative risk reductions (RRRs) from RCTs 
may produce different absolute risk reductions in RW.
OBJECTIVE: To estimate the absolute effect of apixaban on stroke and major 
bleeding (MB) rates in a RW non-valvular atrial fibrillation (NVAF) population.
METHODS: NVAF patients were selected during 2007-2010 from a population of U.S. 
commercial and Medicare health plans using the Medco claims database. Pharmacy 
claims were used to define warfarin exposure periods. Stroke and MB were 
identified using diagnosis codes. RW event rates were calculated during periods 
of warfarin exposure. The numbers of stroke and MB events estimated to be 
avoided in RW with apixaban versus warfarin were calculated by applying RRRs 
from the ARISTOTLE trial to RW rates from the Medco database. The Medco data did 
not contain information for patients receiving apixaban as it was not on the 
market at the time of analysis.
RESULTS: Stroke and MB rates among RW NVAF patients during warfarin exposure 
were higher compared with event rates in patients treated with warfarin in 
ARISTOTLE (stroke: 5.29 vs. 1.51 per 100 person years (PYs); MB: 10.78 vs. 3.09 
per 100 PYs). If RRRs from trials persist in RW, apixaban vs. warfarin would 
result in greater absolute risk reductions (ARRs) and a lower number needed to 
treat (NNT) in RW vs. ARISTOTLE (stroke: 91 vs. 313; MB: 30 vs. 105).
CONCLUSION: The impact of apixaban, as an alternative to warfarin in RW may be 
greater than in RCTs. The NNT with apixaban versus warfarin in RW may be lower 
versus ARISTOTLE if RRRs from the trial persists in RW and if baseline stroke 
and MB rates among RW patients are higher compared to trial participants.