Influence of renal dysfunction on warfarin plasma protein binding.

The in vitro plasma protein binding of warfarin was evaluated by ultrafiltration in plasma from seven normal subjects and seven patients with varying degrees of renal dysfunction. The unbound, or free, warfarin fraction was twice as high in the plasma samples withdrawn from patients with renal impairment than in the samples obtained from normal volunteers. Furthermore, there was a positive correlation between the extent of renal dysfunction and the magnitude of the free warfarin fraction when either creatinine clearance, plasma creatinine, or BUN was used to estimate renal function.