Notes: N-Acetyl-L-thyroxine is an acetylated derivative of L-thyroxine (Item No. 14116).{61994} It only weakly binds to thyroxine-binding globulin (TBG) in isolated human serum with a relative binding affinity of 25 compared with L-thyroxine. N-Acetyl-L-thyroxine is also a potential impurity in commercial preparations of L-thyroxine.{61995}