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Nitisinone
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Nitisinone is a prescription drug used in the treatment of the genetic disease hereditary tyrosinemia type 1 (HT-1). In this disorder, the body is unable to metabolize the amino acid tyrosine. The accumulation of toxic compounds in individuals with this disorder often causes kidney and liver damage. Nitisinone was originally developed as a pesticide. The Food and Drug Administration approved nitisinone on January 18, 2002. Nitisinone is marketed as Orfadin by Swedish Orphan International.
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Uses
Nitisinone is used to treat HT-1 in addition to dietary restriction of tyrosine and phenylalanine intake.
How Nitisinone is Taken
Nitisinone is available in capsules of 2 mg, 5 mg, and 10 mg. The recommended initial dosing is 1 mg/kg body weight daily, divided equally into one morning dose and one evening dose. The effect of food on the absorption of nitisinone is not known. Taking the doses at least one hour before a meal reduces the risk of food hindering the absorption. A maximum dose of 2 mg/kg/day may be needed, especially in infants. The capsule can be broken open and the liquid applied to food for children who cannot take the capsule.
How Nitisinone Works
HT-1 is caused by a deficiency in fumarylacetoacetase (FAH), the final enzyme in the pathway that breaks down tyrosine. Nitisinone inhibits 4-hydroxyphenyl-pyruvate dioxygenase, an enzyme upstream of FAH in this pathway. This inhibition prevents the accumulation of intermediate compounds in the pathway, which are toxic to the liver and kidneys.
How the Body Affects Nitisinone
Peak circulating levels of nitisinone are reached 3 hours after ingestion of the capsule and within 15 minutes of taking the liquid. The half-life of nitisinone, the time needed for the concentration of the drug in the blood to be reduced by half, is approximately 58 hours. The metabolism and excretion of nitisinone in humans are not known.
Side Effects
The most common side effects of nitisinone, which occurred in more than 1% of patients in clinical trials, were the following:
- liver tumors
- liver failure
- inflammation of the membrane on the cornea and other corneal issues
- hypersensitivity to light
- eyelid inflammation
- eye pain
- cataracts
- low blood platelet counts
- low white blood cell count
- porphyria
- nose bleed
- itching
- skin disorders (redness, scaling, or dry skin)
- hair loss
Risks and Precautions
Dietary restriction of tyrosine and phenylalanine intake is absolutely necessary in patients with HT-1, even those taking nitisinone. Elevated Tyrosine levels increase the risk of eye and skin problems as well as nervous system complications (mental retardation and developmental delay).
Drug Interactions
No drug interaction studies have been conducted to date.
Research
People with HT-1 under six months of age have a four-year survival probability of 60%. The four-year survival probability in these patients treated by dietary restriction and nitisinone is 94%.[1]
References
External Links
FDA: Patient Information Sheet
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