Human hemin (Normosang) has been licensed for the treatment of acute attacks of hepatic porphyria (see p194). Porphyria results in a block on the biosynthesis of haem. This leads to a lack of haem, which is necessary for the synthesis of haemoproteins. The block in haem synthesis also causes accumulation of haem precursors, which are either directly or indirectly toxic. By administering Normosang, normal levels of haem are achieved, the haem deficit is reduced and, by a negative feedback mechanism, production of the toxic haem precursors (porphyrins) is reduced.
Orphan Europe, the manufacturer of Normosang in the UK, says that, although haem has been known to be effective in acute attacks for over 20 years, previous formulations have been unstable and were associated with thrombophlebitis and coagulopathy. They say that Normosang is more stable and less irritant. About one in 10,000 people in the UK have the genetic abnormality that causes porphyria, although many never experience symptoms of the disease. Acute attacks may be mild and self-limiting or be severe enough to warrant hospitalisation. Patients may suffer such symptoms as severe abdominal pain, muscle weakness, tachycardia and mental disturbances, such as hallucinations and schizophrenic-like behaviour. According to the summary of product characteristics (SPC), Normosang is most effective at reducing gastrointestinal symptoms but has less effect on neurological complications.
Normosang has been available on a named-patient basis for four years, according to the manufacturer.