[New drugs; nitisinone].

Nitisinone is an inhibitor of 4-hydroxyphenyl-pyruvate dioxygenase (4HPPD). Its rare area of use is hereditary tyrosinaemia, a life-threatening disease in which the last step in the catabolism of tyrosine cannot be taken due to the absence of an enzyme. The inhibition of 4HPPD, an enzyme that is active early in the catabolic cascade, prevents the accumulation of toxic metabolites of tyrosine.