Investigations on the carcinogenicity of dipyrone in rats

A carcinogenicity study with dipyrone (metamizol methanesulfonate) was conducted in male and female Wistar rats. The compound was administered with the feed for a period of 24 months in doses of 0, 1000, or 3000 ppm, followed by a 6-month recovery period (without compound administration). The rats in the high-dose group, especially the females, showed a statistically significant body weight gain retardation which was not correlated with reduced feed consumption. The chronic administration of dipyrone did not influence the survival of the rats. No treatment-related changes in clinical signs and hematological parameters occurred. The absolute and relative weights of thyroids and pituitaries in the high-dose males were increased statistically significantly but were still within the normal range of the rat strain used. Histological examination of the animals which died intercurrently or were killed in extremis or at the end of the recovery period did not reveal any nonneoplastic or neoplastic changes which were compound related under the test conditions used. All of the tumors in all groups of animals were considered spontaneous in nature. Dipyrone did not show carcinogenic potential in rats in this study.