Suppressive effects of josamycin on the development of altered liver cell loci and chronic nephropathy in a carcinogenicity study

The carcinogenicity of josamycin was examined in Fischer 344 (F344) rats. G roups of 50 males and 50 females were given the compound in their diet at c oncentrations of 0 (control), 1.25 or 2.5% for 104-weeks; these dose levels were selected on the basis of the results of a subchronic study, in which animals rather rejected 5% josamycin. All surviving rats were killed at wk 106. A variety of rumours developed in all groups, including the control gr oup, but all the neoplastic lesions were histologically similar to those kn own to occur spontaneously in this strain of rats, and no statistically sig nificant increase in the incidence of any tumour was found in the treated g roups of either sex. Interestingly, the josamycin treatment significantly r educed the development of altered liver cell foci and chronic nephropathy i n a dose-dependent manner. Thus, it was concluded that, under the present e xperimental conditions, josamycin is not carcinogenic in F344 rats. (C) 199 8 Elsevier Science Ltd. All rights reserved.