Summary

Effective pain management is the cornerstone of palliative care. The principles are guided by the WHO Analgesic Ladder, which emphasises a stepwise approach: "By the mouth, by the clock, by the ladder". Morphine remains the gold standard strong opioid for moderate-to-severe cancer pain. Successful management requires not just prescribing opioids, but proactively managing side effects (Constipation/Nausea), utilizing adjuvants (for neuropathic/bone pain), and recognizing opioid toxicity. [1,2]

Key Principles

• By the Mouth: Oral route is preferred as long as possible.
• By the Clock: Regular dosing (e.g., Modified Release BD) prevents pain returning. "PRN" is for breakthrough only.
• By the Ladder: Step up from non-opioids to strong opioids.
• Total Pain: Pain is not just physical. Psychological, spiritual, and social distress lower the pain threshold.

Clinical Pearls

The 1/6th Rule: The breakthrough dose (for "rescue" pain relief) should always be 1/6th of the total 24-hour regular opioid dose.

• Example: Patient on Zomorph 30mg BD (Total 60mg).
• Breakthrough = 60mg / 6 = 10mg Oramorph.

Renal Failure Danger: Morphine is metabolised to Morphine-6-Glucuronide (M6G) which is actively excreted by the kidneys. In renal failure, M6G accumulates and causes neurotoxicity (twitching, agitation, coma). Switch to Alfentanil, Fentanyl, or Buprenorphine (Liver metabolised).

Laxatives: Prescribing a strong opioid without a laxative is negligence. Constipation is predictable and does not develop tolerance. Start Senna + Macrogol immediately.

Step 1: Non-Opioid

• Paracetamol: 1g QDS.
• NSAIDs: Ibuprofen / Naproxen. (Good for bone pain).

Step 2: Weak Opioid

• Codeine: 30-60mg QDS. (Note: pro-drug, metabolised to morphine).
• Tramadol: 50-100mg QDS. (Warning: Lowers seizure threshold, risk of Serotonin Syndrome).
• Dihydrocodeine.

Step 3: Strong Opioid

• Morphine: Gold standard.
• Oxycodone: Second line (if morphine intolerant).
• Fentanyl: Patches (for stable pain).
• Diamorphine: For subcutaneous use (high solubility).
• Methadone: Specialist use (NMDA antagonist properties).

Opioid Naive Patient

1. Immediate Release: Start Oramorph (Morphine Sulfate liquid) 2.5mg - 5mg every 4 hours + PRN.
2. Assess: Review usage after 24-48 hours.
3. Convert: Sum the total daily dose and switch to Modified Release (e.g., MST/Zomorph) given BD.

Patient on Step 2 (Weak Opioid)

1. Stop Codeine/Tramadol.
2. Start Morphine: Calculate equivalent or start low (e.g., Zomorph 10mg BD + Oramorph 2.5mg PRN).

Conversion Ratios (Approximate)

Bone Pain

• NSAIDs: Naproxen / Diclofenac.
• Bisphosphonates: Zoledronic Acid (IV).
• Radiotherapy: Single fraction for metastatic spots.
• Steroids: Dexamethasone.

Neuropathic Pain

Burning, shooting, electric shock.

• Amitriptyline: Start 10mg ON.
• Gabapentin / Pregabalin.
• Dexamethasone: For nerve compression (e.g. spinal cord).

Visceral / Liver Capsule Pain

• Steroids: Dexamethasone reduces capsule swelling.

Signs

• Pinpoint Pupils (Miosis).
• Respiratory Depression (less than 8 breaths/min).
• Myoclonus (Muscle twitching/jerks).
• Hallucinations / Confusion.
• Drowsiness.

Management

1. Mild (Pain controlled, but drowsy): Omit next dose. Reduce dose by 30-50%. Hydrate.
2. Severe (Unrousable, RR less than 8):
   • Naloxone: Use cautiously. Giving a full ampoule (400mcg) will cause acute withdrawal and excruciating pain crisis.
   • Dilution: Mix 400mcg in 10ml saline. Give 0.5ml-1ml (20-40mcg) every 2 mins until RR improves. Goal is reversal of respiratory depression, NOT full alertness.

Indications

• Stable pain.
• Poor compliance / Dysphagia.
• Renal Failure.

Cautions

• Slow Onset/Offset: Takes 12-24 hours to reach steady state. Cover with oral morphine for first 12h.
• Heat: Fever/Hot bath increases absorption -> Toxicity.
• Cachexia: Requires subcutaneous fat. Poor absorption in very thin patients.

Conversion (Rule of Thumb)

• 12 mcg/hr patch ≈ 30-45 mg Oral Morphine / 24h.
• 25 mcg/hr patch ≈ 60-90 mg Oral Morphine / 24h.

           PAIN UNCONTROLLED
                    ↓
           CHECK COMPLIANCE
          (Are they taking it?)
                    ↓
      ┌─────────────┼─────────────┐
   PAIN IS       PAIN IS      TOXICITY
 NOCICEPTIVE   NEUROPATHIC    PRESENT
      ↓             ↓             ↓
 Increase      Add Adjuvant   OPIOID ROTATION
 Opioid Dose   (Pregabalin)   (Switch Morphine
 by 30-50%                    to Oxycodone)

Key Guidelines

Pharmacokinetics

• Morphine: Hydrophilic. Slow onset. Active metabolites.
• Fentanyl: Lipophilic. Fast onset. Inactive metabolites (safer in renal).

Will I become addicted?

No. Using morphine for cancer pain does not make you an addict. Your body gets used to the drug (tolerance), so we might need to increase the dose, but you won't get the psychological craving.

Will the morphine hasten death?

No. There is a myth that morphine stops breathing and ends life. When used correctly for pain, it is very safe. It allows you to rest comfortably.

Why do I need laxatives?

Morphine slows down the bowel. If you don't take laxatives, you will get severe constipation which can be more painful than the cancer itself.

Common Exam Questions

1. Prescribing: "Patient on MST 60mg BD. What is the PRN dose?"
   • Answer: Total = 120mg. 1/6th = 20mg Oramorph.
2. Renal: "Pain relief for patient with eGFR 15?"
   • Answer: Fentanyl / Alfentanil / Buprenorphine. (Avoid Morphine/Codeine).
3. Toxicity: "Patient twitching and confused on Morphine. Action?"
   • Answer: Opioid Toxicity. Check renal function. Hydrate. Rotate opioid.
4. Pharmacology: "Mechanism of Tramadol?"
   • Answer: Weak Mu-agonist + SNRI (Serotonin/Noradrenaline reuptake inhibition).

Viva Points

• Opioid Rotation: Why do it? Incomplete cross-tolerance. Switching to a different opioid allows you to lower the equivalent dose, maintaining analgesia while reducing toxicity.
• Metastatic Bone Pain: Radiotherapy is the most effective specific treatment.

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.