The metabolism of [2-14C]methimazole in the rat

1 The metabolism of [2-¹⁴C]methimazole was studied in Sprague-Dawley rats after a daily intraperitoneal dose of 17±6?mg/kg for three days.

2. 78±4% of the administered ¹⁴C was excreted in the urine; only 6±7% dose as methimazole. After extraction of the urine with chloroform and n-butanol, 47±5% of administered ¹⁴C remained in the urine.

3. Six solvent-extractable metabolites were isolated and characterized by t.l.c. and high-resolution mass spectrometry, as N-methylimidazole, S-methylmethimazole, 3-methyl-2-thiohydantoin, 1-methyl-2-thiohydantoic acid, N-methylthiourea and a methylhydantoin.