Preclinical study of the safety of arhem (heme arginate), a new drug intended for the treatment of porphyrin metabolism disorders, has been performed. Arhem proved to be a nontoxic preparation with a large therapeutic margin (high ratio of the toxic dose to effective dose). Even during long-term administration at high doses, arhem does not affect most systems and organs, except for the liver and red blood, where the changes caused by high doses of the drug are a consequence of its medical efficacy.