The synergistic toxicity of local and general anesthetics.

Abstract

The author has had occasion to determine the lethal dosages of cocain and alypin for cats by intravenous injection. Solutions of the drugs, generally 1 to 1000, were injected into the femoral vein at regular intervals and the lethal dose of each drug per kilo weight of cat was determined. It was found that the toxicity of both cocain and alypin was very much increased or potentiated when the animals were kept under complete general anesthesia. Thus it was found that whereas the lethal dose of cocain per kilo weight of cat when injected intravenously under very light anesthesia was from 30 to 40 mg., the fatal dose for cats under complete general anesthesia was about 25 mg. per kilo weight and under deep ether anesthesia it was as low as 15 mg. per kilo weight. In the case of alypin it was found that when injected in cats practically under no ether anesthesia, the lethal dose varied from 30 to 24 mg. per kilo weight; under complete but light ether anesthesia the lethal dose was from 18 to 24 mg. per kilo weight, while under deep anesthesia the fatal dose was as low as 6 to 7 mg. Similar toxic synergism in cocain and alypin on the one hand and general chlorbutanol anesthesia was also noted. The above experiments were performed several years ago but have been repeated recently with the same results and are deemed to be worthy of mention in connection with the present renewal of interest in the toxicity of local anesthetics. In the experience of the author a combination of local and general anesthetics is dangerous and this fact should be borne in mind by surgeons who may desire to switch from a local anesthetic to a general one.