[Interactions between nitrous oxide and central depressants]

The combined effects on mice of N2O and various central depressants were investigated. A loss of the righting reflex was taken as the criterion for the drug effects. Essential differences could be demonstrated in the type of interaction: diazepam, flunitrazepam, and medazepam have a supra-additive effect in combination with N2O; the solvent of diazepam and an experimental product, Ro 21-3981 (8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo [1,5-a] [1,4]-benzodiazepine maleate) a simply additive one. However, the interactions between N2O and barbiturates (pentobarbitone and phenobarbitone), and N2O and ethanol were found to be infra-additive. The results of this and previous investigations indicate that additive or supra-additive interactions can only be expected in those cases in which at most one of the two active ingredients in addition to its depressive effect also exhibits an excitatory component.