A total of 175 mg of naltrexone monohydrate, suspended in small particles of a polylactide plastic (500 mg), was injected intramuscularly in dogs whose spinal cords had been transected at the T5-10 levels.
This produced a level of blockade against the effects of morphine (1 mg/kg) on the flexor and skin twitch reflex and pupillary diameter for a duration of 21 to 29 days. In some instances levels of blockade could still be detected 33 days after administration.
This preparation demonstrates the feasibility of a slow release form of a narcotic antagonist that may have value in the treatment of narcotic addicts.
Martin WR, Sandquist VL. A Sustained Release Depot for Narcotic Antagonists. Arch Gen Psychiatry. 1974;30(1):31-33. doi:10.1001/archpsyc.1974.01760070019003