The binding of prednisolone in human serum and to recrystallized human albumin in vitro.

1 Prednisolone binding in human serum and to recrystallized human serum albumin was measured by continuous ultrafiltration. 2 At serum concentrations of prednisolone up to 0.6 micron, 95.0% was bound but at higher concentrations the binding became non-linear falling to 80.5% at 1.8 microns. At even higher concentrations binding in serum became linear again and paralleled the binding to albumin which was linear throughout the entire range of prednisolone concentrations. 3 A binding model was proposed which included a saturable component attributable to binding to transcortin and a non-saturable binding to albumin. 4 Computer simulations using the experimentally determined binding parameters of the model indicated that binding in serum was critically dependent on transcortin concentration and almost independent of albumin concentration.