Table 1.

Data on metabolism and potency along with chemical structures of fentanyl and its analogs.11

Compound	Metabolites	Relative Potency (fentanyl)	Structure
Fentanyl	hydroxyfentanyl, hydroxynorfentanyl, despropionylfentanyl	1
Alfentanil	Noralfentanil	0.3
Sufentanil	Norsufentanil, N-phenylpropanamide, demethylsufentanil	10
Acetylfentanyl	Acetylnorfentanyl, 4-ANPP, β- hydroxyacetylfentanyl, 4′-hydroxy-3′-methoxy-acetylfentanyl	0.3
Acryloylfentanyl	Acryloylnorfentanyl, 4-ANPP, β-hydroxyacryloylfentanyl, 4′-hydroxy-3′-methoxy-acryloylfentanyl, and phase II conjugates	0.75
α-Methylfentanyl	Norfentanyl, Despropionyl-α-methylfentanyl, alkyl/aryl hydroxy metabolites	1
Furanylfentanyl	Furano-dihydrodiol formation, 4-ANPP, norfuranylfentanyl, alkyl/aryl hydroxy metabolites, ring opening of the furanyl ring and phase II conjugates	7
Carfentanil	Norcarfentanil, alkyl/aryl hydroxy metabolites, carfentanil acid, keto-carfentanil, N-oxide formation and phase II conjugates	30–100
Isofentanyl	Nor-3-methylfentanyl, alkyl/aryl hydroxy metabolites, carboxypropionyl-isofentanyl, 4′-hydroxy-3′-methoxyisofentanyl, N-oxide formation	NA