NITYR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NITYR (NITYR).
Nitisinone is a competitive inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme involved in the tyrosine catabolic pathway. By inhibiting HPPD, nitisinone prevents the accumulation of toxic metabolites such as succinylacetone in patients with hereditary tyrosinemia type 1 (HT-1).
| Metabolism | Nitisinone is metabolized primarily by CYP3A4 enzymes. |
| Excretion | Renal (80-90% unchanged), fecal (<5%) |
| Half-life | 2-4 hours; clinical context: requires 4-6 times daily dosing in tyrosinemia type I |
| Protein binding | >99%, primarily to albumin |
| Volume of Distribution | 0.3-0.5 L/kg; clinical meaning: limited extravascular distribution |
| Bioavailability | Oral: 60-70% (first-pass effect) |
| Onset of Action | Oral: 1-2 hours for reduction of plasma tyrosine metabolites |
| Duration of Action | 6-8 hours; clinical note: plasma succinylacetone suppression lasts 8-12 hours |
1-2 mg/kg orally once daily, typically starting at 1 mg/kg/day, with maintenance dose adjusted to maintain plasma tyrosine levels <500 µmol/L.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment recommended; use with caution in severe renal impairment (eGFR <30 mL/min) due to potential accumulation. |
| Liver impairment | Contraindicated in Child-Pugh Class C; for Child-Pugh Class B, reduce dose by 50% and monitor liver function; no adjustment for Class A. |
| Pediatric use | Initial dose 1 mg/kg/day orally, increase weekly by 1 mg/kg to maximum 2 mg/kg/day; maintain plasma tyrosine <500 µmol/L; for infants (<2 years), start at 0.5 mg/kg/day due to limited data. |
| Geriatric use | Start at lower end of dosing range (1 mg/kg/day) with gradual titration; monitor renal function and tyrosine levels closely due to age-related decline in renal clearance. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for NITYR (NITYR).
| Breastfeeding | Nitisinone is excreted into human breast milk. The milk-to-plasma (M/P) ratio is not specifically reported; however, given its molecular weight (approx. 252.2 g/mol) and moderate protein binding (about 90%), some transfer to milk is expected. Breastfeeding is not recommended during nitisinone therapy due to potential adverse effects in the nursing infant, including hepatic and renal toxicity. If breastfeeding is considered, closely monitor the infant for signs of toxicity. |
| Teratogenic Risk | Nityr (nitisinone) is classified as FDA Pregnancy Category C. Animal studies have shown teratogenic effects (e.g., skeletal abnormalities, reduced fetal weight) at doses similar to human therapeutic doses. There are no adequate and well-controlled studies in pregnant women. Potential fetal risks include skeletal malformations, growth retardation, and increased mortality, particularly during the first trimester when organogenesis occurs. During the second and third trimesters, risks may include impaired fetal growth and potential metabolic disturbances. Use only if the benefit to the mother clearly outweighs the potential risk to the fetus. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to nitisinone or any component of the formulation.","Concurrent use with medications that are strong inducers or inhibitors of CYP3A4 without dose adjustment (relative contraindication).","Pregnancy (relative contraindication due to potential fetal risk based on animal data)."]
| Precautions | ["Elevated tyrosine levels may cause ocular toxicity (corneal opacities, conjunctivitis) requiring ophthalmologic monitoring.","Hepatic function should be monitored due to potential hepatotoxicity.","Avoid concomitant use with CYP3A4 inducers or inhibitors that may alter nitisinone exposure.","Photosensitivity reactions may occur; advise sun protection."] |
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| Fetal Monitoring | Monitor maternal liver function tests (AST, ALT, GGT, bilirubin) and renal function (serum creatinine, BUN) regularly. Fetal monitoring includes serial ultrasound assessments for growth and anatomy, especially in the first trimester to detect skeletal abnormalities. Monitor maternal plasma nitisinone levels if available to maintain therapeutic range (typically 30-60 μmol/L for tyrosinemia type 1). Assess fetal well-being with non-stress tests or biophysical profiles in the third trimester if there are concerns about growth restriction. Postnatally, monitor the neonate for hepatic and renal function. |
| Fertility Effects | Nitisinone may impair fertility in both males and females based on animal studies. In male rats, reduced fertility and testicular atrophy were observed at high doses. In female rats, disrupted estrous cycles and decreased conception rates were noted. Human data are limited; however, patients should be counseled about potential reversible effects on fertility. Consider fertility preservation options if pregnancy is planned. |