Morphine Fentanyl Hydromorphone Onset (min) 5-10 1-2 5-10 Duration (h) 2-4 1-5 2-6 Prolonged in renal yes no no Prolonged in hepatic yes yes yes T 1/2 in hours 1-4 2-5 2-3 Active metabolites yes no no Hypotension yes no yes Flushing yes no yes Bronchospasm yes no no Constipation yes yes yes