Cuprous complexes formed with isonicotinic hydrazide.

Chelate formation by Cu(II) and isonicotinic acid hydrazide has been postulated as an important step in the antitubercular activity of isonicotinic hydrazide (Isoniazid). Reevaluation of the copper-isonicotinic hydrazide system gives evidence for the formation of a Cu(I) species rather than a Cu(II) species. The reduction of Cu(II) to Cu(I) and the subsequent formation of an isonicotinic hydrazide complex with the latter ion, therefore, may be the critical reaction responsible for the efficacy of isonicotinic hydrazide against Mycobacterium tuberculosis.