What are the guidelines for using morphine (opioid analgesic) in pain management?

Guidelines for Using Morphine in Pain Management

Oral morphine is the first-line strong opioid of choice for moderate to severe cancer pain, and should be given without delay to patients whose pain is uncontrolled by step 1 and 2 treatments. 1

Classification and Appropriate Use

Morphine is classified as a strong (WHO level 3) opioid indicated for moderate to severe pain. It is a pure agonist opioid that should not be prescribed concurrently with partial agonist or mixed agonist-antagonist opioids 1.

Pain Severity-Based Approach:

• Mild pain: Start with non-opioid analgesics (paracetamol/NSAIDs) 1
• Moderate pain: Use weak opioids (codeine, tramadol) alone or with non-opioids 1
• Moderate to severe pain: Use strong opioids like morphine 1

Administration Guidelines

Oral Administration (Preferred Route)

• Formulations: Use either immediate-release (IR) or sustained-release (SR) morphine sulfate tablets/capsules, or morphine hydrochloride solution 1
• Titration method:
  1. Start with normal-release morphine every 4 hours plus rescue doses (up to hourly) for breakthrough pain 1
  2. Adjust the regular dose daily based on total rescue morphine required 1
  3. Once stabilized, convert to sustained-release formulation for maintenance 1

Alternative Routes When Oral Route Not Possible

• Subcutaneous: Preferred parenteral route (potency ratio oral:SC = 1:2 to 1:3) 1
• Intravenous: Consider for patients with:
  • Poor peripheral circulation
  • Coagulation disorders
  • Existing IV access
  • Need for rapid pain control 1, 2
• Transdermal: Consider fentanyl patches for stable pain when oral route not possible 1

Dosing Guidelines

Initial Dosing

• IV administration: 0.1-0.2 mg/kg every 4 hours as needed, adjusted based on pain severity, adverse events, and patient factors 3
• Oral administration: Begin at lower end of dosing range with rescue doses available 1

Dose Adjustments

• When switching from another opioid, calculate starting morphine dose using equianalgesic dose ratios 1
• For breakthrough pain, prescribe immediate-release formulation (10-15% of total daily dose) 1
• Never stop morphine treatment abruptly; taper by 30-50% over about a week 1

Managing Side Effects

Common side effects include:

• Constipation: Always anticipate and prescribe prophylactic laxatives 1, 4
• Nausea/vomiting: Prescribe antiemetics (metoclopramide or antidopaminergics) for the first few days 1
• Drowsiness: Usually resolves within days; if persistent, consider dose reduction or opioid rotation 1

Strategies for Persistent Side Effects

1. Evaluate to distinguish between morphine adverse effects, comorbidity, dehydration, or drug interactions 4
2. Consider dose reduction (possibly with addition of co-analgesic) 4
3. If side effects persist:
   • Provide symptomatic management
   • Consider opioid rotation
   • Consider changing route of administration 4

Special Considerations

Renal Impairment

• Use all opioids with caution at reduced doses and frequency 1
• Fentanyl and buprenorphine are safer options in chronic kidney disease stages 4-5 1

Respiratory Concerns

• No contraindication for morphine in patients with asthma or respiratory failure, but monitor closely 1
• Rapid IV administration may cause chest wall rigidity 3

Common Pitfalls to Avoid

• Underdosing: Fear of addiction often leads to inadequate pain control 5
• Abrupt discontinuation: Can cause withdrawal symptoms; always taper gradually 1
• Failure to prevent constipation: Most persistent side effect requiring prophylactic treatment 1, 6
• Dosing errors: Take care to avoid confusion between different concentrations and between mg and mL 3

Monitoring

• Regularly assess pain control and side effects
• Monitor for respiratory depression, sedation, and signs of dependence 7
• For patients requiring high doses, consider specialist pain service consultation 7

Morphine remains the gold standard for moderate to severe cancer pain management, with decades of clinical experience supporting its efficacy and safety when properly prescribed 8.