Toxicity of phencyclidine and ethanol in combination.

The role of ethanol in phencyclidine-related death and loss of motor co-ordination was studied in male ICR albino mice. LD50s, and ED50s for loss of righting reflex, and for the "rotarod" test were determined for each drug in the presence of various doses of the other. Isobolograms (plots of equieffective dose combinations) of these LD50s and ED50s showed that low doses of ethanol reduced the LD50 of phencyclidine (PCP) by about 20%, while higher doses (1-3 g/kg) of ethanol were without further effect. In contrast to effects on lethality, there was synergism (potentiation) of loss of motor co-ordination. Doses of ethanol above 1 g/kg reduced the ED50 of PCP for loss of righting from about 60 mg/kg to 1-3 mg/kg. Similarly, low doses of PCP (less than 40 mg/kg) reduced the ED50 of ethanol from 3 g/kg to 1 g/kg. There was a slight but consistent synergism between the drugs in the rotarod test over the range of effective doses (0.25-2.0mg/kg PCP and 0.1-1.2 g/kg ethanol). It is concluded that consumption of ethanol does not greatly increase the risk of death from PCP overdose; however the severe adverse effects on motor co-ordination of moderate doses of PCP together with moderate doses of ethanol are greatly potentiated by doses of the other drug. It is estimated that commonly used doses could result in total loss of motor ability, which could explain the prevalence of accidental deaths (especially drowning) when PCP and ethanol have been consumed together.