Species differences in the metabolism of pamatolol, a cardioselective beta--adrenoceptor antagonist

The metabolism of pamatolol was studied in man, dogs, rats and mice after oral administration of a single dose. The drug was well absorbed in the gastro-intestinal tract and excreted in the urine, mainly in unchanged form, within 24 hrs. Four urinary metabolites were identified by gas chromatographic-mass spectrometric techniques. The metabolic data, in man, dog and mouse was found to be similar, both qualitatively and quantitatively. One metabolism route, involving aliphatic hydroxylation and subsequent oxidation, was found, to a significant extent only in the rat. The species variation between the mouse and the rat with regard to long-term toxicity of pamatolol is discussed. Artefact formation during trace analysis was observed.