Plasma protein binding interaction of prednisone and prednisolone

The plasma protein binding interaction of prednisone and prednisolone were characterized by equilibrium dialysis. Prednisone and prednisolone are bound equally but weakly to human albumin (affinity constant, K ≈ 1 × 10³M^-1). Transcortin affinity for prednisolone is 10-fold greater (51.3 × 10⁶ M^-1) than that for prednisone (4.3 × 10⁶ M^-1). In competition under pharmacologie conditions, prednisolone inhibits prednisone bining to transcortin producing linear binding averaging 55%. Prednisone does not affect prednisolone binding and does not complicate pharmacokinetic studies of the latter.