The separation of unbound prednisolone in plasma by centrifugal ultrafiltration.

To study variable plasma protein binding of prednisolone in children with nephrotic syndrome we have devised a simple rapid method for measuring unbound prednisolone. The plasma was initially ultrafiltered at 37 degrees C fixed angle head at 1500 g for 30 min then the filtrate was analysed by high pressure liquid chromatography. The effects of variable ultrafiltration conditions were studied. The method was used to compare the AUC unbound prednisolone in a nephrotic child (plasma albumin concentration 18 g L-1) with a control (plasma albumin concentration 43 g L-1); their respective AUC unbound prednisolone values were 4.02 mg h L-1 and 1.07 mg h L-1.