Nitisinone Drug Information

Nitisinone capsules are indicated for the treatment of adult and pediatric patients with hereditary tyrosinemia type 1 (HT-1) in combination with dietary restriction of tyrosine and phenylalanine. Nitisinone is a hydroxy-phenylpyruvate dioxygenase inhibitor indicated for the treatment of adult and pediatric patients with hereditary tyrosinemia type 1 (HT-1) in combination with dietary restriction of tyrosine and phenylalanine.

Dosage Starting Dosage

The recommended starting dosage of nitisinone capsules is 0.5 mg/kg administered orally twice daily. Maintenance Regimen In patients 5 years of age and older who have undetectable serum and urine succinylacetone concentrations after a minimum of 4 weeks on a stable dosage of nitisinone, the total daily dose of nitisinone may be given once daily (e.g., 1 to 2 mg/kg once daily) . Dosage Titration Titrate the dosage in each individual patient based on biochemical and/or clinical response. Monitor plasma and/or urine succinylacetone concentrations, liver function parameters and alpha-fetoprotein levels.

If succinylacetone is still detectable in blood or urine 4 weeks after the start of nitisinone treatment, increase the nitisinone dosage to 0.75 mg/kg twice daily. A maximum total daily dosage of 2 mg/kg may be needed based on the evaluation of all biochemical parameters. If the biochemical response is satisfactory (undetectable blood and/or urine succinylacetone), the dosage should be adjusted only according to body weight gain and not according to plasma tyrosine levels.

During initiation of therapy, when switching from twice daily to once daily dosing, or if there is a deterioration in the patient’s condition, it may be necessary to follow all available biochemical parameters more closely (i.e. plasma and/or urine succinylacetone, urine 5-aminolevulinate (ALA) and erythrocyte porphobilinogen (PBG)-synthase activity). Maintain plasma tyrosine levels below 500 micromol/L by dietary restriction of tyrosine and phenylalanine intake. In patients who develop plasma tyrosine levels above 500 micromol/L, assess dietary tyrosine and phenylalanine intake. Do not adjust the nitisinone dosage in order to lower the plasma tyrosine concentration.

Administration

Administration of nitisinone capsules: Maintain dietary restriction of tyrosine and phenylalanine when taking nitisinone. Capsules: Take at least one hour before, or two hours after a meal . For patients who have difficulty swallowing the capsules, the capsules may be opened and the contents suspended in a small amount of water, formula or apple sauce immediately before use.

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. Nitisinone was studied in one open-label, uncontrolled study of 207 patients with HT-1, ages 0 to 22 years at enrollment (median age 9 months), who were diagnosed with HT-1 by the presence of succinylacetone in the urine or plasma. The starting dose of nitisinone was 0.3 to 0.5 mg/kg twice daily, and the dose was increased in some patients to 1 mg/kg twice daily based on weight, biochemical, and enzyme markers.

The recommended starting dosage of nitisinone is 0.5 mg/kg twice daily. Median duration of treatment was 22 months (range 0.1 to 80 months). The most serious adverse reactions reported during nitisinone treatment were thrombocytopenia, leukopenia, porphyria, and ocular/visual complaints associated with elevated tyrosine levels . Fourteen patients experienced ocular/visual events. The duration of the symptoms varied from 5 days to 2 years.

Six patients had thrombocytopenia, three of which had platelet counts 30,000/microL or lower. In 4 patients with thrombocytopenia, platelet counts gradually returned to normal (duration up to 47 days) without change in nitisinone dose. No patients developed infections or bleeding as a result of the episodes of leukopenia and thrombocytopenia.

Patients with HT-1 are at increased risk of developing porphyric crises, hepatic neoplasms, and liver failure requiring liver transplantation. These complications of HT-1 were observed in patients treated with nitisinone for a median of 22 months during the clinical trial (liver transplantation 13%, liver failure 7%, malignant hepatic neoplasms 5%, benign hepatic neoplasms 3%, porphyria 1%). The most common adverse reactions reported in the clinical trial are summarized in Table 1. TABLE 1 Most Common Adverse Reactions in Patients with HT-1 Treated with Nitisinone* Elevated tyrosine levels Leukopenia Thrombocytopenia Conjunctivitis Corneal opacity Keratitis Photophobia Eye pain Blepharitis Cataracts Granulocytopenia Epistaxis Pruritus Exfoliative dermatitis Dry skin Maculopapular rash Alopecia >10% 3% 3% 2% 2% 2% 2% 1% 1% 1% 1% 1% 1% 1% 1% 1% 1% *reported in at least 1% of patients Adverse reactions reported in less than 1% of the patients, included death, seizure, brain tumor, encephalopathy, hyperkinesia, cyanosis, abdominal pain, diarrhea, enanthema, gastrointestinal hemorrhage, melena, elevated hepatic enzymes, liver enlargement, hypoglycemia, septicemia, and bronchitis.

Nitisinone is a moderate CYP2C9 inhibitor, a weak CYP2E1 inducer and an inhibitor of OAT1/OAT3. Table 2 includes drugs with clinically important drug interactions when administered concomitantly with nitisinone and instructions for preventing or managing them. Table 2: Clinically Relevant Interactions Affecting Co-Administered Drugs Sensitive CYP2C9 Substrates (e.g., celecoxib, tolbutamide) or CYP2C9 Substrates with a Narrow Therapeutic Index (e.g., phenytoin, warfarin) Clinical Impact Increased exposure of the co-administered drugs metabolized by CYP2C9. Intervention Reduce the dosage of the co-administered drugs metabolized by CYP2C9 drug by half. Additional dosage adjustments may be needed to maintain therapeutic drug concentrations for narrow therapeutic index drugs.

See prescribing information for those drugs. OAT1/OAT3 Substrates (e.g., adefovir, ganciclovir, methotrexate) Clinical Impact Increased exposure of the interacting drug Intervention Monitor for potential adverse reactions related to the co-administered drug. CYP2C9 Substrates : Increased systemic exposure of these co-administered drugs; reduce the dosage.

Additional dosage adjustments may be needed to maintain therapeutic drug concentrations for narrow therapeutic index drugs. OAT1/OAT3 Substrates : Increased systemic exposure of these co-administered drugs; monitor for potential adverse reactions.

Pregnancy Risk Summary Limited available data with nitisinone use in pregnant women are not sufficient to determine a drug-associated risk of adverse developmental outcomes. Animal reproduction studies have been conducted for nitisinone. In these studies, nitisinone was administered to mice and rabbits during organogenesis with oral doses of nitisinone up to 20 and 8 times respectively, the recommended initial dose of 1 mg/kg/day.

In mice, nitisinone caused incomplete skeletal ossification of fetal bones and decreased pup survival at doses 0.4 times the recommended initial dose, and increased gestational length at doses 4 times the recommended initial dose. In rabbits, nitisinone caused maternal toxicity and incomplete skeletal ossification of fetal bones at doses 1.6 times the recommended initial dose. The background risk of major birth defects and miscarriage for the indicated population are unknown.

In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively. Data Animal Data Reproduction studies have been performed in mice at oral doses of about 0.4, 4 and 20 times the recommended initial dose (1 mg/kg/day) and in rabbits at oral doses of about 1.6, 4 and 8 times the recommended initial dose based on the body surface area. In mice, nitisinone has been shown to cause incomplete skeletal ossification of fetal bones at 0.4, 4 and 20 times the recommended initial dose, increased gestational length at 4 and 20 times the recommended initial dose, and decreased pup survival at 0.4 times the recommended initial dose based on the body surface area.

In rabbits, nitisinone caused incomplete skeletal ossification of fetal bones at 1.6, 4 and 8 times the recommended initial dose based on the body surface area.

Pediatric Use The safety and effectiveness of nitisinone have been established in pediatric patients for the treatment of HT-1 in combination with dietary restriction of tyrosine and phenylalanine. Use of nitisinone in pediatric patients is supported by evidence from one open-label, uncontrolled clinical study conducted in 207 patients with HT-1 ages 0 to 22 years (median age 9 months).

Accidental ingestion of nitisinone by individuals eating normal diets not restricted in tyrosine and phenylalanine will result in elevated tyrosine levels. In healthy subjects given a single 1 mg/kg dose of nitisinone, the plasma tyrosine level reached a maximum of 1200 micromol/L at 48 to 120 hours after dosing. After a washout period of 14 days, the mean value of plasma tyrosine was still 808 micromol/L. Fasted follow-up samples obtained from volunteers several weeks later showed tyrosine values back to normal.

There were no reports of changes in vital signs or laboratory data of any clinical significance. One patient reported sensitivity to sunlight. Hyper-tyrosinemia has been reported with nitisinone treatment .