Comparison of absorption, disposal, and activity of soluble and repository corticosteroid esters

Plasma concentrations of H 3 dexamethasone and C 14 dexamethasone were maximal at one and 8 hours, respectively, following the intramuscular iniection of 1,2,4‐H 3 ‐ dexamethasone phosphate or 16‐methyl‐C 14 ‐dexamethasone acetate. Urinary 17‐hydroxy‐corticosteroid levels return to normal 3 to 4 and 7 to 8 days following iniection of the phosphate ester and acetate ester, respectively. The minimal plasma concentration of dexamethasone for maximal suppression of the pituitary‐adrenal axis appears to be between 0.5 and 1.0 µg per cent. The slower rate of appearance in blood and the more delayed excretion of C 14 compared with H 3 probably reflect the slower rate of absorption of the acetate ester.