HEME OXYGENASE-INHIBITING METALLOPORPHYRI NS - AN ORIGINAL APPROACH TO THE PHARMACOLOGICAL TREATMENT OF NEONATAL JAUNDICE

Metalloporphyrins (MPs) inhibit the enzyme heme oxygenase, which oxidi zes heme to bilirubin. It has been suggested that MPs may be useful in neonatal hyperbilirubinemia to decrease conversion of heme to bilirub in. Studies in experimental animals have investigated many MPs, includ ing protoporphyrins and mesoporphyrins bound to tin, zinc, and chromiu m. Research has focused mainly on SnPP/SnMP, which is responsible for a significant reduction in plasma and tissue bilirubin. Heme does not accumulate but is excreted via the bile. SnPP/SnMP can induce mild pho tosensitization, requiring that caution be exercised when phototherapy is used. The results of animal studies have been confirmed by two cli nical studies in infants with ABO incompatibility jaundice and in prem ature infants, as well as by several studies in patients with Crigler- Najjar disease. Zinc and chromium, which have been the focus of more r ecent studies, may be even more effective and devoid of phototoxicity in animals. Although use of heme oxygenase inhibitors to treat neonata l hyperbilirubinemia is promising, data comparing this approach with c onventional pharmacotherapy, phototherapy, and exchange transfusion ar e needed.