Antihistaminic-opioid combination: effect on locomotor activity in mice.

Various laboratory studies have been recently prompted by reports indicating abuse by heroin addicts of the narcotic agonist-antagonist pentazocine combined with the antihistaminic tripelennamine. For what concerns the effects on locomotor activity, it was demonstrated that three histamine H1 receptor antagonists, chlorpheniramine, diphenhydramine and tripelennamine enhance morphine-, but not amphetamine and scopolamine-induced hyperactivity in mice. These results suggested that antihistaminics may specifically interfere with locomotor effects of opioids. Such hypothesis was strengthened by further findings indicating enhancement by tripelennamine of the locomotor stimulation induced by buprenorphine, a drug possessing morphine-like properties.