Abstract:Haem arginate is a new haem compound recently introduced for treatment of porphyrias. Previously haematin has been reported to increase certain hydroxylase activities in extrahepatic tissues, but even in therapeutic doses it impairs the microsomal foreign substance metabolism in the liver. Haem arginate at a dose equivalent to haem 10 mg/kg (threefold therapeutic dose) did not prolong the hexobarbital sleeping time of mice, 20 mg/kg did prolong the hexobarbital and possibly also the ethanol sleeping time. Haem arginate administered in high doses prior to oral propranolol did not alter the bioavailability of the latter. With regard to drug interactions haem arginate may be safer than haematin.