Sufentanil (Sufenta) contains the same 4 methoxy methylsubstituent as alfentanil along with an isosteric replacementof the phenyl of the phenethyl group with a thiophene ring. The resulting compound is about 7 times morepotent than fentanyl with an immediate onset of action anda similar recovery time compared with fentanyl. Sufentanilis only available in an injectable formulation and is alsoused as an anesthetic adjunct.