Mirfentanil

Overview
Mirfentanil is a fentanyl derivative with strong selectivity for the μ opioid receptor. At lower doses, it antagonizes the analgesic effects of alfentanil and substitutes for naloxone in morphine-treated monkeys; however, it also reverses naloxone-precipitated withdrawal in pigeons trained to discriminate morphine from naloxone.

At high doses, it exhibits analgesic activity which is not fully reversed by opioid antagonists, suggesting that the drug has both opioid and non-opioid mechanisms of action.