Niclosamide residues in milk and tissues of lactating goats

Radiocarbon labeled niclosamide was orally administered to two groups of lactating goats at levels equivalent to about 2 ppm in drinking water for five consecutive days, and at levels equivalent to about 10 ppm in drinking water (1-day basis) as a single dose. Residues of the molluscicide in milk did not exceed 0.001 ppm at any time. About 50% of the administered radioactivity was eliminated in faeces, while about 30% was excreted through urine in treated animals within 6 days after final dosing. TLC analysis revealed the presence of two unidentified niclosamide metabolites. The unchanged molluscicide was present only in trace amounts. Highest radiocarbon residues in tissues of the treated goats occurred in the liver (0.01-0.04 ppm niclosamide equivalent). From these data, it was concluded that absorbed niclosamide is almost completely metabolized and rapidly eliminated through urine of goats. Little or no residues were detected in lean muscles and milk which are consumed by humans. There was no significant deposition of the molluscicide or its metabolites in fat. (author)