Induction of leukaemia in chloramphenicol-treated toads

Chloramphenicol has been associated with the development of aplastic anaemia. As it is still widely used in Egypt, we studied its effect on 100 Egyptian toads [Bufo regularis] given a dose of chloramphenicol of 5 mg/40 g body weight for 12 weeks. We found it induced numerous, severe ultrastructural changes in almost all types of leukocytes. These changes were similar to those induced by the chemical carcinogen 7, 12-dimethylbenz[a]anthracene in 100 toads used as the carcinogen control group, and similar to those in leukocytes reported in humans with leukaemia. We recommend regulations be applied on the use of this antibiotic in countries where it is still widely used.

Regulation of Carcinogens in Terms of Life Shortening

Because of the difficulty in using the results of conventional quan titative risk assessment in the regulation of carcinogens, an approach to setting carcinogen standards is presented based on the reduction of cancer-induced life span shortening to statistically nonsignificant levels. An argument is made that the time of cancer occurrence is more important than the risk of cancer. The rationale is that the objective of carcinogen control is to delay the single-risk time of cancer occurrence. Whether this benefit is associated with a decrease, increase or no change in the risk of dying of cancer depends on concomitant changes in the temporal pattern of other causes of death. For indispensable carcinogens the permissible exposure is the level which shortens the time to background cancer by an amount equal to the uncertainty in the time of background cancer occurrence. This approach is illustrated by the use of the ED01 2-FAA bioassay on mice.