Nitisinone

How it works

It inhibits 4-hydroxyphenylpyruvate dioxygenase, an enzyme upstream in tyrosine catabolism, thereby preventing the formation of toxic downstream metabolites such as succinylacetone.

Prescribing in practice

• It must be combined with strict dietary restriction of tyrosine and phenylalanine, as raised tyrosine levels can cause ocular and skin complications and may affect neurodevelopment.
• Slit-lamp eye examination is required if visual symptoms or eye signs occur, as corneal deposits can develop with elevated tyrosine.
• Transient thrombocytopenia, leucopenia and raised tyrosine levels can occur, requiring blood and amino acid monitoring.

Monitoring

Monitor plasma tyrosine and succinylacetone, full blood count, liver function and perform ophthalmic assessment if eye symptoms arise.

Counselling the patient

• Strict adherence to the tyrosine- and phenylalanine-restricted diet is essential alongside the medicine.
• Report any eye symptoms such as pain, redness or blurred vision promptly.
• Attend all blood tests and dietetic reviews.

Evidence & guidelines

Nitisinone, together with dietary management, has transformed outcomes in hereditary tyrosinaemia type 1 and is also used in alkaptonuria.