Orfadin (nitisinone)

The only drug treatment for HT-1, available as Orfadin capsules and liquid, Nityr tablets and generic capsules. Before nitisinone, most children with early HT-1 needed a liver transplant or did not survive.

In HT-1, the last enzyme in the tyrosine breakdown pathway does not work, so toxic chemicals such as succinylacetone build up and damage the liver and kidneys. Nitisinone blocks an earlier step in the same pathway, so those toxic chemicals are not made. The trade-off is that tyrosine itself builds up, which is why a diet low in tyrosine and phenylalanine is part of treatment.

Nitisinone has no boxed warning and no contraindications. The main risk is tyrosine climbing too high, above 500 micromol/L, which can cause eye problems, painful thick skin on the palms and soles, and learning or developmental problems. That risk is managed with diet, not by changing the dose. Low white blood cell or platelet counts happened in about 3% of people. Orfadin liquid contains glycerol, so large single doses can upset the stomach.

Taken by mouth starting at 0.5mg/kg twice a day, raised to 0.75mg/kg twice a day if succinylacetone is still found after 4 weeks, up to 2mg/kg a day. Children 5 and older who are well controlled can switch to once a day. Orfadin capsules are taken at least 1 hour before or 2 hours after a meal, while Orfadin liquid and Nityr tablets can be taken with or without food.

Capsules can be opened into water, formula or applesauce, and Nityr tablets can be dissolved or crushed. A diet low in tyrosine and phenylalanine is always part of treatment.

With private insurance, the drugmaker's copay card can lower what you pay for Orfadin. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE. Pick your insurance below to see which offers fit you.

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Approved for hereditary tyrosinemia type 1 in babies, children and adults, always with a diet low in tyrosine and phenylalanine. Once-daily dosing is only for people 5 and older who are well controlled. Harliku, a separate nitisinone tablet, is approved only for adults with alkaptonuria.

Source: Orfadin4U (Sobi) and Cycle Vita (Nityr)

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Approval rested on a study of 207 people with HT-1, mostly babies, treated with nitisinone and diet and compared with past children treated by diet alone. Among babies whose symptoms began before 2 months of age, 88% were alive at 4 years on nitisinone against 29% with diet alone. Among those whose symptoms began at 2-6 months, 94% were alive at 4 years against 60%. Painful nerve crises fell to about 0.3% of patients a year, against the 5-20% a year expected without it.

Swedish Orphan (now Sobi) won FDA approval for Orfadin capsules on January 18, 2002. An Orfadin liquid followed on April 22, 2016, and Cycle Pharmaceuticals' Nityr tablets were approved on July 26, 2017. The first generic nitisinone capsules were approved on August 26, 2019. In 2025 the FDA also approved a separate low-dose nitisinone tablet, Harliku, for adults with alkaptonuria.