Morphine Intramuscular (IM) Dosing Guidelines
For opioid-naïve adults, the standard starting dose of intramuscular (IM) morphine is 5-10 mg, with no specified upper limit during titration to symptoms. 1, 2
Initial Dosing Considerations
- For opioid-naïve patients requiring IM morphine, the recommended starting dose is 5-10 mg 1, 2
- The starting dose should be adjusted based on patient factors including:
- Age (lower doses for elderly patients)
- Size/weight
- Organ dysfunction (particularly renal or hepatic impairment) 1
- Morphine is the initial opioid of choice for pain or dyspnea in opioid-naïve patients 1
Relative Potency
- The relative potency of IM morphine compared to oral morphine is approximately 3:1 (IM is three times more potent than oral) 1
- When converting from oral to IM morphine, divide the oral dose by 3 to find the equivalent IM dose 2
- When converting from IM to oral morphine, multiply the IM dose by 3 (though some authorities suggest only multiplying by 2) 2
Dosing Schedule and Titration
- IM morphine bolus doses can be ordered every 15 minutes as required for breakthrough pain 1
- If a patient requires two bolus doses in an hour, consider doubling the regular dose 1
- For patients receiving continuous opioid infusions who develop pain, a reasonable bolus dose is twice the hourly infusion rate 1
- There is no specified maximum daily dose limit when titrating to symptoms 1
Route Considerations
- The subcutaneous (SC) route is generally preferred over IM for chronic cancer pain due to being less painful 1
- IM administration should be avoided in patients with:
- Coagulation disorders
- Poor peripheral circulation
- Risk of developing erythema, soreness, or sterile abscesses 1
- IV morphine provides faster onset of analgesia (5 minutes) compared to IM morphine (20 minutes) 3
Clinical Efficacy and Safety
- IM morphine is effective for moderate to severe pain management 1
- Common side effects include:
- Constipation (most persistent adverse effect requiring prophylactic laxatives)
- Nausea and vomiting (typically resolve after a few days)
- Sedation, drowsiness, and mental clouding (usually temporary) 1
- Respiratory depression is a potential serious adverse effect, particularly in opioid-naïve patients 1
- Naloxone (0.04-0.4 mg IV or IM) can be used to reverse severe opioid toxicity if needed 1
Special Populations
- For elderly patients (>70 years), consider using lower initial doses 4
- For patients with renal impairment, use with caution as morphine metabolites can accumulate and contribute to toxicity 1
- For patients already on stable doses of opioids, these should be continued at those doses when possible 1
Remember that morphine dosing should be titrated to pain relief with careful monitoring for side effects, particularly in the initial treatment phase.