Duration of Action of Intravenous Morphine
Intravenous morphine has a duration of action of approximately 4 hours, with peak analgesic effects occurring within 15-30 minutes after administration. 1, 2, 3
Pharmacokinetic Profile
The clinical duration of effect is well-established across multiple guideline sources:
- IV morphine provides analgesia for approximately 4 hours, which is why normal release morphine does not need to be given more often than every 4 hours in clinical practice 1, 2, 4
- Peak effects occur within 15-30 minutes after IV administration, making this route superior for rapid pain control 1, 2, 3
- The elimination half-life is 1.5-2 hours in normal subjects (range 1.5-4.5 hours), with steady state achieved within 24 hours 1, 5
Clinical Dosing Implications
Based on the 4-hour duration of action:
- Rescue doses of IV morphine can be administered as frequently as every 15-30 minutes during acute titration for severe pain, reflecting the rapid onset but allowing time for peak effect assessment 1, 3
- Regular scheduled dosing should be every 4 hours when using IV morphine for maintenance pain control 1, 2
- When converting from continuous IV fentanyl to intermittent IV morphine, the standard interval is every 4 hours 2
Important Clinical Caveats
Large interindividual variation exists in morphine pharmacokinetics and dynamics, particularly in cancer patients, meaning these durations represent averages rather than absolute guarantees 1, 2
The minimum effective concentration varies widely and is influenced by:
- Extent of previous opioid use (tolerance) 5
- Patient age 2, 5
- Renal and hepatic function (morphine is primarily cleared by hepatic glucuronidation with renal excretion) 5
Common adverse effects during IV morphine administration include nausea, vomiting, and respiratory depression, with respiratory effects being slow in onset but prolonged 2, 5