An inhibitor of δ-aminolevulinic acid dehydratase (Ki = 300 nM); inhibits heme biosynthesis at 0.1 and 1 mM; an abnormal metabolite of tyrosine that accumulates in, and is used as a biomarker for, hereditary tyrosinemia type I; increases levels of δ-aminolevulinic acid in urine, decreases heme levels in liver, kidney, spleen, and vascular tissues, and reduces sensitivity of isolated rat aortic rings to endothelium-dependent and -independent vasodilation at 40 mg/kg twice daily