Comparative evaluation of the effects of some common premedications on the safety index of volatile anaesthetics in mice.

The safety index of ether, chloroform and halothane in mice has been determined after administration of each of seven combinations of drugs commonly used in pre-anaesthetic medication. Following hyoscine-morphine and pentobarbitone-atropine the index for ether was significantly higher than that of the control series, whilst following atropine-pethidine it was significantly lower. The index for chloroform was not significantly altered following any of the drug combinations. Following hyoscine-morphinej promethazine-atropine and pentobarbitone-atropine the safety index for halothane was significantly higher than that of the control series. The results are discussed in the light of previous investigation in mice on the effects of premedication when each drug was used alone.