The relative efficacy of antidotes.

For many physicians an antidote is an antidote. According to the International Programme on Chemical Safety definition, an antidote is a therapeutic substance used to counteract the toxic action(s) of a specified xenobiotic. Given this wide definition, the efficacy of an antidote may vary considerably depending on which toxic action(s) being counteracted and the level of counteracting power. An almost 100% efficacy is seen using specific antagonists, such as naloxone in opiate poisoning or flumazenil in benzodiazepine poisoning, e.g. resulting in complete reversal of opiate toxicity unless complications, such as anoxic brain damage, have developed. At the other end of the efficacy scale, we may place chelating agents for heavy metal poisoning and diazepam for organophosphorus insecticide poisoning which are considered only to be an adjuncts to supportive care. When teaching clinical toxicology or recommending the use of antidotes in poisoned patients, the expected efficacy level of the antidote in question should be stressed. This may be particularly important in severe poisoning when the antidote may only be considered as an important adjunct to supportive care, e.g. deferoxamine in acute iron poisoning. Unless this is stressed, the unexperienced physician may rely too much on the antidote and pay insufficient attention to the supportive care. The varying efficacy levels will be discussed based on the presently ongoing International Programme on Chemical Safety/Commission of the European Communities evaluation program on antidotes.