Effectiveness of lofexidine in blocking morphine-withdrawal signs in the rat.

Discontinuation of chronic morphine infusion in rats resulted in the reliable occurrence of withdrawal body shakes. This sign of narcotic withdrawal was dose-dependently reduced by lofexidine (0.04-0.64 mg/kg) and clonidine (0.01-0.16 mg/kg). As with clonidine, the activity of lofexidine was not prevented by naloxone (5 mg/kg). In addition, diarrhea induced by naloxone (5 mg/kg) in morphine dependent rats was also prevented by lofexidine or clonidine pretreatment. These data suggest that lofexidine, like clonidine, may reduce the narcotic withdrawal syndrome in humans.