Antinociceptive activity of propionyl esters of morphine: a reevaluation.

The antinociceptive activity of the propionyl homologues of 3-O- and 6-O-acetyl- and 3,6-O-diacetylmorphine was re-investigated using materials of unequivocally established structure. Testing was in male Wistar rats at 60 min following subcutaneous administration by the rat tail-flick method. Results indicate that the antinociceptive activity of 3-O-propionylmorphine was similar to that of 3-O-acetylmorphine. 6-O-Propionylmorphine and 3,6-O-dipropionylmorphine had similar antinociceptive activity and, like 6-O-acetylmorphine, 6-O-propionylmorphine may be the pharmacologically active principle responsible for the antinociceptive activity of its disubstituted homologue.