The FDA-approved drug nitisinone treats hereditary tyrosinemia type 1 (HT-1), a rare genetic condition that alters how the amino acid tyrosine is broken down in the body. If untreated, HT-1 leads to the buildup of toxic metabolites, including succinylacetone, which can seriously harm the liver and kidneys. The tyrosine metabolic pathway requires the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), which the reversible synthetic compound nitisinone inhibits. Nitisinone helps reduce the production of hazardous metabolites by blocking this enzyme, which lowers the risk of liver and kidney damage in HT-1 patients.
Nitisinone’s starting oral dosage is 0.5 mg/kg twice daily, with adjustments made dependent on how each patient responds. Nitisinone 2 mg dosage needs to be gradually increased while being checked with regular testing for succinylacetone, liver health, and alpha-fetoprotein levels. Suppose succinylacetone is still detectable after a month. In that case, the dosage can be increased to 0.75 mg/kg twice a day, and depending on the results of biochemical analysis, it could even be increased to 1 mg/kg. Additional biochemical measures such as plasma succinylacetone, urine 5-aminolevulinate, and erythrocyte porphobilinogen should be regularly examined during the start of therapy or if the patient’s condition worsens.
Warnings and Precautions
- Elevated Plasma Tyrosine Levels: Inadequate tyrosine and phenylalanine intake may lead to high plasma tyrosine levels, resulting in symptoms, developmental delay, or painful hyperkeratotic plaques.
- Leukopenia and Severe Thrombocytopenia: Regularly monitor platelet and white blood cell counts.
- Adverse Reactions from Glycerol Content: Nitisinone oral suspension may cause headaches, upset stomach, and diarrhea due to glycerol content. Consider switching patients to Nitisinone capsules.
Storage and Handling
Nitisinone is available in capsule forms. The Nitisinone capsules are available in doses of 2 mg, 5 mg, 10 mg, or 20 mg in the market.
- One should store Nitisinone capsules between 2°C-8°C (36°F-46°F).
- Alternatively, they can be stored at room temperature for up to 45 days at a maximum of 25°C (77°F).