The Major Metabolites of Niclosamide: Identification by Mass Spectrometry

Abstract

Despite the widely held view that the extensively used intestinal taeniacide, niclosamide (2′,5-dichloro-4′-nitro salicylanilide) is poorly absorbed from the mammalian gastrointestinal tract (1–3) the only experimental support for such a view is provided by an early study by(4),who employing a colorimetric method of limited specificity assessed the levels of niclosamide remaining in the gastrointestinal tract at selected intervals of time following oral administration. Synthesis of a [14C]niclosamide and its employment in metabolic studies has now shown that this drug is not only absorbed in considerable amounts but is extensively metabolized in the rat. The major metabolites have been characterized by chromatography and mass spectrometry.