Effects of quinidine and cimetidine on methamphetamine stereotypy in rats

The effects of quinidine and cimetidine on methamphetamine-induced stereotyped behavior were studied in rats. Quinidine (10, 30 and 50 mg/kg) and cimetidine (100, 250 and 500 mg/kg) were administered orally 60 min prior to subcutaneous injection of a fixed dose of methamphetamine (5 mg/kg). It was found that quinidine and cimetidine very markedly potentiated the intensity of methamphetamine stereotypy. The duration of the stereotypy in the group pretreated with either drug was 2.3-4.0 times longer than that in the control group. Furthermore, the urinary pH levels of rats were measured after administrations of methamphetamine alone and of methamphetamine following the drugs in question. Urinary pH was not changed by pretreatments with those drugs, suggesting that the enhancing effects of quinidine and cimetidine on methamphetamine-induced stereotyped behavior are not derived from a change in urinary pH level. The enhancement of methamphetamine-induced stereotyped behavior may be explained by inhibitory effects of quinidine and cimetidine on the metabolism of methamphetamine.