<prompt> Naltrexone is:-Mu receptor agonistDelta receptor agonistKappa receptor agonistMu receptor antagonist  <response>: Naloxone, naltrexone and nalmefene are potent mu receptor antagonists with significant blocking action at kappa and delta receptors also. Naloxone is given parenterally ineffective orally and is a very sho acting drug. Nalmefene is also given parenterally but has a longer half life. Naltrexone is long acting orally effective opioid antagonist. Naloxegol-Naloxone conjugated to PEG polymer 