Expert: Competitive inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD), the second enzyme in the tyrosine degradation pathway. By blocking HPPD, nitisinone prevents formation of homogentisic acid (HGA) and downstream toxic metabolites (maleylacetoacetate, fumarylacetoacetate) that cause hepatorenal toxicity in HT1 and ochronosis in alkaptonuria.

Everyday: Blocks an enzyme (HPPD) early in the tyrosine breakdown pathway. In hereditary tyrosinemia, a later enzyme is broken, causing toxic waste to build up. This drug blocks an earlier step, redirecting the pathway so the toxic waste never forms. Like diverting a river before it reaches the broken dam — the water goes a different route and the dangerous buildup never happens.

Targets: []

HPPD inhibitor for hereditary tyrosinemia type 1 and alkaptonuria. Orphan drug with stable niche revenue. HT1: transforms a fatal disease into a manageable condition (liver transplant rates dropped dramatically). AKU: first approved therapy. Small patient populations (~1,000 HT1 globally) but high per-patient pricing.