A sterile, lyophilized powder of hemin, the Fe3+ oxidation product of heme (Fe2+), derived from processed red blood cells. Therapeutic hemin appears to inhibit delta-aminolevulinic acid (ALA) synthetase, a rate-limiting enzyme in the porphyrin/heme biosynthetic pathway, resulting in inhibition of the hepatic and/or marrow synthesis of porphyrin precursors. The mechanism by which therapeutic hematin produces symptomatic improvement in patients with acute episodes of the hepatic porphyrias has not been determined.