The FDA has approved nitisinone capsules (Orfadin, Swedish Orphan International AB, Stockholm, Sweden) for use as an adjunct to dietary restriction of tyrosine and phenylalanine in the treatment of hereditary tyrosinemia type 1 (HT-1).
Nitisinone was studied in more than 200 patients whose median age was 9 months when therapy started. The drug's effectiveness was inferred by its effect on reduction of concentration of succinylacetone in plasma and urine to a level below the reference limit, and by normalization of erythrocyte porphobilinogen synthase activity. Resulting improvements in these indices were statistically significant (P<.001).
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