Recommended IM Morphine Dosage for Opioid-Naive Patients
For opioid-naive patients requiring intramuscular morphine, start with 2-5 mg IM, with the dose adjusted based on patient age, size, and organ function, and repeat every 15 minutes as needed for pain control. 1, 2
Initial Dosing Protocol
The intramuscular route follows similar dosing principles to intravenous administration since both are parenteral routes with comparable bioavailability:
- Start with 2 mg IM morphine as the conservative initial dose for most opioid-naive patients 1
- For patients with moderate-to-severe pain requiring more aggressive initial management, 2-5 mg IM is appropriate 2, 3
- Reduce the starting dose by 30-50% in elderly patients (>70 years) to account for decreased clearance and increased opioid sensitivity 2, 3
Titration Guidelines
- Reassess pain every 15 minutes and administer additional 2 mg boluses as needed 1, 2
- If pain persists after the initial dose, increase subsequent doses by 50-100% of the previous dose, prioritizing rapid dose escalation over conservative dosing 2
- There is no dose ceiling when titrating to symptoms during acute pain management 1, 2
Critical Dose Adjustments
Patient-specific factors requiring dose modification:
- Renal impairment: Start with one-fourth to one-half the usual dose due to morphine-6-glucuronide accumulation risk 2
- Small body size or frail patients: Use the lower end of the dosing range (2 mg) 1
- Elderly patients: Reduce initial dose to approximately 2 mg, accounting for age-related pharmacokinetic changes 2, 4
Documentation and Monitoring
- Document the specific rationale for each dose administered (e.g., "for severe pain rated 8/10" or "for respiratory distress with accessory muscle use") 1, 2
- Monitor respiratory rate, sedation level, and vital signs every 15-30 minutes during initial titration 3
- Watch for signs of respiratory depression, excessive sedation, or other adverse effects that would necessitate dose reduction or naloxone administration 3
Common Pitfalls to Avoid
- Never start with doses ≥20 mg in opioid-naive patients, as this significantly increases adverse effects without proportional analgesic benefit 2
- Avoid using IM morphine as first-line if IV access is available, since IV administration allows for more precise titration with faster onset and easier reversal if needed 5
- Do not assume all patients require the same dose—individualize based on age, renal function, and body habitus 1, 2