1979 Volume 27 Issue 2 Pages 463-467
The binding of carbutamide to rabbit plasma protein in vivo and in vitro was studied by using a new ultrafiltration technique. The binding of carbutamide to rabbit plasma protein in vivo markedly decreased with increasing plasma concentration of carbutamide. On the other hand, the binding of carbutamide to rabbit plasma protein in vitro hardly changed. Over one half of carbutamide in rabbit blood was observed to be as N4-acetyl-carbutamide. N4-Acetylcarbutamide was highly bound to rabbit plasma protein, and caused a marked decrease in the binding of carbutamide to rabbit plasma protein in vitro. These results indicate that the difference of binding of carbutamide to rabbit plasma protein in vivo and in vitro is due to the displacement of carbutamide from plasma protein binding sites by N4-acetylcarbutamide.