Isocarboxazid is an inhibitor of monoamine oxidase (MAO; IC50 = 4.8 μM for rat brain MAO).1 It induces a 4-fold increase in tryptamine action in isolated rat fundal strips at a concentration of 50 nM. In vivo, isocarboxazid potentiates tryptamine toxicity (LD50 = 8 mg/kg following subcutaneous administration of 250 mg/kg tryptamine). It inhibits 90% of MAO activity in isolated rat hearts and reduces cardiomegaly induced by isoproterenol in rats at a dose of 20 mg/kg.2 Oral administration of isocarboxazid (10 mg/kg) increases levels of dopamine and norepinephrine and reduces levels of the monoamine metabolites DOPAC, homovanillic acid , and 5-hydroxy indole-3-acetic acid by 43, 32, and 28%, respectively, in mouse brain.3 Formulations containing isocarboxazid have been used for the treatment of minor depression.4
1.Maxwell, D.R., Gray, W.R., and Taylor, E.M.Relative activity of some inhibitors of mono-amine oxidase in potentiating the action of tryptamine in vitro and in vivoBr. J. Pharmacol. Chemother.17(3)310-320(1961) 2.Stanton, H.C., Bowman, Z., and Cooper, C.M.Effects of monoamine oxidase inhibitors on isoproterenol-induced cardiomegaly in ratsToxicol. Appl. Pharmacol.16(1)256-263(1970) 3.Yokoyama, T., Kamioka, T., Iwata, N., et al.Effects of RS-2232, a potential antidepressant, on the levels of monoamines, precursor amino acids and their related metabolites in mouse brainJpn. J. Pharmacol.44(4)413-420(1987) 4.Barbui, C., Cipriani, A., Patel, V., et al.Efficacy of antidepressants and benzodiazepines in minor depression: Systematic review and meta-analysisBr. J. Psychiatry198(1)11-16(2011)