Fewer than 100 children in the United States are affected by HT-1.
Nitisinone is an orphan drug. Orphan products are developed to treat rare diseases, or conditions that affect fewer than 200,000 people in the US.
The Orphan Drug Act provides a 7-year period of exclusive marketing to the first sponsor who obtains marketing approval for a designated orphan drug.
Due to liver failure or liver cancer, children with hereditary tyrosinemia type I rarely survive into their twenties without a liver transplant.
However, for children treated early enough with nitisinone, liver failure and liver cancer occur at much-reduced rates.
|Four-year survival rate:|
Nitisinone and restricted diet: 88%
Restricted diet alone: 29%
Nitisinone was studied in more than 180 patients with a median age of 9 months when therapy started.
When the drug was combined with a restricted diet, the 4-year survival rate of children under 2 months of age at the time of diagnosis was 88%.
Historical data for children treated with dietary restrictions alone shows a survival rate of 29% for the same time period.
Nitisinone must be used in conjunction with a diet restricted in the amino acids tyrosine and phenylalanine. High tyrosine levels may be toxic to eyes, skin, and the nervous system.
The most common side-effects of the drug were related to high tyrosine levels, due to patients not eating the appropriate foods, as well as rare cases of mild reductions in platelet and white blood cell counts.
The FDA note that nitisinone should be prescribed by physicians experienced in treating hereditary tyrosinemia type I, as the correct dose must be adjusted for each patient according to specific biochemical tests.
Access to a nutritionist skilled in managing children with inborn errors of metabolism requiring a low protein diet is an important part of therapy, they add.
Blood tests should be monitored regularly, to maintain the correct dose for that patient, and to monitor for potential adverse events, they conclude.
The drug will be marketed under the name, Orfadin.