Aminopyrine
Aminophenazone is a pyrazolone with analgesic, anti-inflammatory, and antipyretic properties that carries a risk of agranulocytosis. In biomedical applications, radiolabelled (13C-labeled) aminophenazone has been used in breath tests to measure the cytochrome P-450 metabolic activity in liver function tests. The FDA suspended the use of aminophenazone due to its association with agranulocytosis, a life-threatening side effect.