Effect of naproxen on protein binding of warfarin in human serum

The effect of the non-steroidal anti-inflammatory agent naproxen on the protein binding of racemic warfarin in pooled human serum was determined by equilibrium dialysis. The free fraction of warfarin in serum increased practically linearly with increasing naproxen concentration. At the highest naproxen concentration tested (400 mcg/ml), the warfarin free fraction was 74% larger than the control free fraction value.