Kinetics and interconversion of prednisolone and prednisone studied with new radioimmunogassays

To determine the kinetics of metabolism and interconversion of prednisolone and prednisone, the plasma levels of these synthetic glucocorticoids were measured by new radioimmunoassays (RIA) after intravenous (iv) or oral administration to normal humans. Following the iv injection of prednisolone phosphate in 8 normal subjects, the mean half-time of prednisolone was 240+/-20 min (mean+/-SE) and the metabolic clearance rate was 82+/-7.2 1/24 h/m2. Of 10 mg of prednisone given orally to 5 normal subjects, 69+/-5% was absorbed and converted to peripheral plasma prednisolone within 8 h. The data indicate that prednisone is extensively metabolized to prednisolone before it clears the splanchnic circulation and the formation prednisone by oxidation of the 11-hydorxyl group of prednisolone appears to occur mainly in peripheral tissues.