Nowadays, multiple FDA approved drugs containing pyrazolone nucleus have been explored (Fig. 2) , for instances, edaravone (2) has been used as free radical scavenger for the treatment of amyotrophic lateral sclerosis (ALS) [2] , aminophenazone (3) with antipyretic and anti-inflammatory activities has been used in breath tests to measure the cytochrome P-450 metabolic activity in liver function evaluations [3] , eltrombopag (4) has been used for the treatment of low blood platelet counts in adults with idiopathic chronic immune thrombocytopenia [4] , dichloralphenazone (5) has been used for the relief of tension and vascular headaches [5] , metamizole (6) has been used for perioperative pain, cancer pain, acute injury and other forms of pain and is considered as the strongest antipyretic [6] .