Absorption and excretion of 17, 21-dihydroxy-20-ketosteroids in dogs.

tions of hydrocortisone and cortisone to man have established the plasma half-life of hydrocortisone to be 2 hours and that of cortisone 1 hour (1, 2). From isotopic determinations in urine, the half-life of hydrocortisone in the body has been found to be 6 hours and that of cortisone 3.6 hours (3, 4). Thus, cortisone is not only cleared from the plasma more rapidly than hydrocortisone but it is also metabolized and excreted at a faster rate. In rats (5), hydrocortisone acetate has been shown to be very slowly absorbed from injection sites, whereas hydrocortisone is more rapidly absorbed than cortisone, cortisone acetate, or hydrocortisone acetate. In these studies it was shown that biologic activity was dependent upon the rate of absorption of the steroids from the injection sites. It therefore seemed desirable to compare the absorption, excretion, and half-life in plasma of several steroids including the newer forms, 9a-fluorohydrocortisone, prednisone, and prednisolone. Information regarding the mechanism responsible for the greater biologic activity of these steroids might be obtained in such studies.