What is the recommended starting rate for a morphine (opioid analgesic) drip?

Morphine Drip Starting Rate

For opioid-naïve patients requiring intravenous morphine infusion, start with 2-5 mg IV bolus doses, then initiate continuous infusion at 0.5-2 mg/hour based on the cumulative bolus dose needed for initial pain control. 1, 2

Initial Bolus Dosing

• Administer 2-5 mg IV morphine boluses every 5-10 minutes until pain relief is achieved in opioid-naïve patients requiring urgent pain control 1, 3
• The FDA-approved starting dose for direct IV injection is 0.1-0.2 mg/kg every 4 hours, which translates to approximately 7-14 mg for a 70 kg adult, though lower initial boluses (2-5 mg) are safer for titration 2
• For more aggressive titration in severe pain, 1.5 mg boluses every 10 minutes can be used until relief is achieved 4
• Track the total cumulative bolus dose required to achieve adequate analgesia, as this guides continuous infusion rate 3

Continuous Infusion Initiation

• Set the hourly infusion rate at 50% of the cumulative bolus dose that provided initial relief 3
• For example, if 8 mg total bolus morphine was needed for pain control, start the infusion at 4 mg/hour 3
• Typical starting infusion rates range from 0.5-2 mg/hour for opioid-naïve patients, though higher rates may be needed based on pain severity 3

Dose Equivalency Context

• IV morphine is approximately 3 times more potent than oral morphine (oral-to-parenteral ratio of 3:1) 1, 5
• The recommended oral starting dose of 5-15 mg for opioid-naïve patients translates to roughly 2-5 mg IV 1
• When converting from IV boluses to continuous infusion, remember that steady-state analgesia requires lower hourly rates than the initial loading dose 3

Monitoring and Titration

• Reassess pain, respiratory rate, sedation level, and vital signs every 15-30 minutes during initial titration 6, 2
• Watch for respiratory depression (rate <10 breaths/minute), excessive sedation, or hypotension as primary safety concerns 2, 7
• If sedation becomes problematic, temporarily stop the infusion until mental status improves, then restart at 50% of the previous rate 3
• Adjust the infusion rate based on ongoing pain assessment and rescue bolus requirements 1

Critical Safety Considerations

• Avoid starting with excessively high infusion rates (>2-3 mg/hour) in opioid-naïve patients, as this dramatically increases risk of respiratory depression without proportional analgesic benefit 6, 2
• Rapid IV administration can cause chest wall rigidity and severe respiratory depression 2
• Use extreme caution in patients with renal insufficiency, as morphine-6-glucuronide accumulation can worsen adverse effects 1, 8
• Do not combine with other CNS depressants without careful monitoring, as this compounds respiratory depression risk 2
• Have naloxone immediately available for reversal of life-threatening respiratory depression 2, 7

Special Populations

• For elderly patients (>70 years), reduce starting doses by 30-50% to account for decreased clearance and increased sensitivity 1, 2
• In patients with fluctuating renal function, consider alternative opioids (fentanyl, hydromorphone) to avoid metabolite accumulation 1
• Pediatric dosing has not been established; avoid use in patients under 18 years without specialist consultation 2

Common Pitfall to Avoid

The most dangerous error is confusing bolus dosing with continuous infusion rates—never use the cumulative bolus dose as the hourly infusion rate (e.g., if 10 mg total bolus was given, do NOT start at 10 mg/hour). Instead, use 50% of that cumulative dose as the hourly rate (5 mg/hour in this example). 3