BIOAVAILABILITY AND REVERSIBLE METABOLISM OF PREDNISONE AND PREDNISOLONE IN MAN

The pharmacokinetics of prednisone and prednisolone was examined in 12 healthy male subjects to assess the bioavailability and the parameter s of reversible metabolism between the two steroids. After an oral pre dnisone dose of 0.8 mg kg(-1) and an intravenous prednisolone dose of 0.66 mg kg-(1), the bioavailability was found to be about 62%. The fra ction of the dose recovered in the urine as the hydroxylated metabolit es of prednisone and prednisolone was lower after the oral prednisone dose, suggesting that poor absorption of prednisone was the main cause of the low bioavailability. There was a high degree of interconversio n between prednisone and prednisolone with 76% of the dose being recyc led. The formation clearance of prednisolone from prednisone is much g reater than the formation clearance of prednisone from prednisolone or the irreversible elimination clearances of the two steroids. The poss ible dose dependences of bioavailability and interconversion may be im portant factors in prednisolone therapy.