4-Hydroxyantipyrine is a primary metabolite of the analgesic drug antipyrine (phenazone) and is extensively used in pharmacokinetic and pharmacodynamic studies to evaluate hepatic drug-metabolizing enzyme activity, particularly cytochrome P450 isoforms such as CYP2C9, CYP2C19, and CYP3A4. It functions as a reference standard in analytical methods like HPLC and GC-MS for quantifying drug metabolites in biological samples.

As a synthetic intermediate, it is employed in the preparation of pyrazolone derivatives with potential pharmaceutical applications, including analgesics, anti-inflammatory agents, and antimicrobial compounds.

In research settings, it supports investigations into oxidative metabolism, enzyme induction/inhibition, and toxicological profiling of xenobiotics.