<prompt> An analgesic X acts through opioid as well as additional spinal monoaminergic mechanisms. Which of the following can be X?TramadolEtioheptazineDextropropoxypheneAlfentanil  <response>: -Tramadol and tapendadol have additional analgesic mechanisms apa from activation of opioid receptors. -These drugs increase release of serotonin in spinal cord and strengthen the descending inhibitory pathway. 