Figure 1
Metabolism of metamizole. The metamizole is non-enzymatically
cleaved to 4-methyl-aminoantipyrine (4-MAA) already in the intestine.
4-MAA is the principal metabolite in plasma and can be converted by
CYP-dependent reactions to 4-aminoantipyrine (4-AA) or
4-formylaminoantipyrine (4-FAA). 4-AA can be acetylated by
N-acetyltransferase 2 (NAT2) to 4-acetyl-aminoantipyrine (4-AAA). The
CYPs involved in the metabolism of 4-MAA have not clearly been
identified.