Distribution of radioactively labelled eltoprazine in rat and dog

Eltoprazine labelled with 14C either in the phenyl or the piperazine ring was administered orally to rats and dogs. While distribution of radioactivity was not affected by the position of label during the first hours after dosing, from six hours onward concentrations of radioactivity in the organs of rats were higher after [14C]piperazine-labelled eltoprazine. In most organs, radioactivity originating from the [14C]phenyl-labelled compound was detectable up to 72 hours, while [14C]piperazine-labelled material could still be detected 384 hours after dosing. These results suggest that the piperazine ring may be broken down to aliphatic amines which are retained in the body. Quantitatively, however, this is of minor importance, representing about 1% of the dose. With either label, the highest concentrations of the radiolabel were found in liver and kidney. Excretion of radioactivity in rat and dog urine and faeces was not influenced by the position of the radiolabel.