Methods for the estimation of the excretion of proxicromil and its metabolites in the milk of nursing rat mothers.

1. The excretion of proxicromil and its metabolites into the milk of nursing rat mothers and its ingestion by rat pups have been investigated. 2. The methodology employed, hand-milking of the mothers and analysis of suckling rat pups or their stomach contents, has been developed from a review of the scientific literature. The most dependable of the methods used was the analysis of the stomachs of suckling rat pups. This method provided a useful index of radioactivity excreted into milk and allowed calculation of neonate exposure. 3. At a maternal dose level of 20 mg/kg a significant proportion of the dose (1-2%) was excreted into the milk. Analysis of milk taken from rat pup stomachs indicated that both proxicromil (63%) and its hydroxylated metabolites (37%) were present in the milk.