<prompt> Most potent analgesic:COX-2 inhibitorRemifentanilMorphineSufentanil  <response>: Ref: Goodman Gillman 13th ed. P 376 Fentanyl citrate and sufentanil citrate are congeners of fentanyl and are considered as potent analgesics After systemic delivery: Fentanyl is about 100 times more potent than morphine Sufentanil is about 1000 times more potent than morphine Time to peak analgesic effect after IV administration: 5 minutes These drugs are well known to be used as epidural analgesic. 