Impurities in drugs I: Imipramine, desipramine, and their formulations.

Nineteen lots of imipramine tablets and four lots of desipramine tablets were examined for impurities by TLC. Iminodibenzyl, desipramine, and 10,11-dihydro-5-[3-(methylamino-3'-dimethylaminopropyl)propyl]-5H-dibenz[b,f]azepine dihydrobromide (I) were found in some imipramine tablets, and iminodibenzyl and imipramine were found in some desipramine tablets, all at levels of less than 0.3% of label claim of the drug. Except for I, the identity of the impurities was established by comparison with known standards; I was synthesized and its composition was established by elemental analysis. All impurities, including I, were characterized by TLC, GLC, and mass spectrometry.