Survey of animal drugs with carcinogenic properties

Residues of animal drugs with carcinogenic potential cannot always be avoided in food. The risk/benefit evaluation of carcinogenic drugs used in food-producing animals is a scientifically unresolved problem. Nonetheless, a pragmatic solution taking into account such drugs' putative mechanisms of action, their relative potency, and their significance in the prevention and therapy of disease must and can be achieved. While it is unlikely that a new animal drug possessing overt carcinogenic properties would pass the approval process practiced in most countries today, a number of carcinogenic drugs for use in food-producing animals are currently on the market. Their re-evaluation from the viewpoint of human food safety is necessary, particularly if they are genotoxic (for example nitrofurans, nitroimidazoles, quinoxaline-di-N-oxides). The carcinogenicity of hormonally active animal drugs, none of which has genotoxic potential, is believed to be related to their hormonal action. Thus, the establishment of a threshold level for these drugs and their residues appears possible. It is difficult to evaluate certain other nongenotoxic animal drugs which are carcinogenic at very high dose levels and in one species only. No carcinogenic substance, regardless of its hypothetical mechanism of action, should be used in food-producing animals for which a very significant therapeutic benefit has not been demonstrated.