<prompt> The drug for OPD analgesia is:MorphinePethidineFentanylAlfentanil  <response>: Alfentanil is a potent but sho-acting synthetic opioid analgesic drug, used for anaesthesia in surgery. It is an analogue of fentanyl with around 14 to 110 the potency of fentanyl and around 13 of the duration of action, but with an onset of effects 4x faster than fentanyl. 