English 4-Fluoroisobutyrfentanyl Cited by user Aethyta on 08 Jan 2018 4-Fluoroisobutyrylfentanyl (also known as 4-FIBF and p-FIBF) is an opioid analgesic that is an analog of butyrfentanyl and structural isomer of 4-Fluorobutyrfentanyl and…