The unusual occurrence of 4-aminoantipyrine (4-aminophenazone) in human biological fluids

During toxicology screening of human biological fluids, 4-aminoantipyrine (4-AAP) was detected in 19 patients and identified by two-dimensional TLC and UV spectrophotometry with whole blood concentrations of 4-AAP ranging from 0.4 to greater than 4.9 mg/dL. Of the 19 patients, 15 had received prior treatment at a Mexican health-care facility before transfer to this medical center. Since 4-AAP is a known metabolite of aminopyrine, it is likely that the patients had ingested this anti-inflammatory, analgesic agent in Mexico; however, the clinical histories in this respect were vague. Recognition of the presence of 4-AAP in biological fluids is important, since the parent drug may produce fatal agranulocytosis and the compound may complicate the detection of other compounds that simultaneously partition into the weak-base fraction in toxicology screening.