Why was phenacetin banned globally, and what does its regulatory history mean for current API trade and substitution demand?

Why was phenacetin banned globally, and what does its regulatory history mean for current API trade and substitution demand?
Phenacetin, once a leading antipyretic launched by Bayer in 1888, was withdrawn by the FDA in 1983 after decades of widespread use revealed severe chronic toxicity. The core issue was not the predicted imine-quinone pathway but metabolic conversion to N-hydroxy and nitroso compounds, causing analgesic nephropathy and methemoglobinemia. Its structural similarity to paracetamol — differing only by an ethyl group protecting the phenolic hydroxyl — shifted metabolism toward the amino group, creating reactive nitroso metabolites. This regulatory ban eliminated mainstream pharmaceutical demand, but phenacetin persists as a chemical intermediate, especially in China, where sodium sulfide is used in its synthesis. The API now serves niche research and illicit or unregulated analgesic formulations in some regions, keeping a small but steady production base alive.