Chronic Pain Management and Palliative Care
Chronic pain and palliative care questions test mechanism-based prescribing and end-of-life decision-making. You must distinguish nociceptive, neuropathic, and nociplastic pain, then choose drugs and interventions that match the mechanism.
Core concepts
- Neuropathic pain: gabapentinoids, tricyclics, duloxetine, topical lidocaine or capsaicin; opioids are second line.
- Nociplastic pain such as fibromyalgia: graded exercise, cognitive behavioural therapy, duloxetine, amitriptyline.
- WHO ladder: non-opioid, then weak opioid, then strong opioid, with adjuvants at every step. Long-term opioids need a functional goal, a written agreement, and scheduled review.
- Opioid rotation requires a 25 to 30% dose reduction for incomplete cross-tolerance.
- Renal failure: avoid morphine (morphine-6-glucuronide accumulates) and codeine; use fentanyl, or hydromorphone with care.
- Methadone prolongs the QT interval; codeine and tramadol are prodrugs with CYP2D6 variability and serotonin toxicity risk.
- Palliative care: treat dyspnoea with low-dose opioids, relieve pain before considering sedation, and use palliative sedation only for refractory symptoms with documented discussion.
Worked example
A patient with cancer pain takes 90 mg of oral morphine daily and can no longer swallow. The oral to parenteral ratio is 2:1, giving 45 mg per 24 hours subcutaneously. Reduce about 25% for incomplete cross-tolerance, giving 30 to 35 mg per 24 hours in a syringe driver, with breakthrough doses of one-sixth of the daily total (about 5 mg) as needed. Reasoning: convert the total daily dose, then reduce, then set breakthrough as a fraction, then review within 24 hours.
Traps that cost marks
- Using the equianalgesic table exactly without reducing for cross-tolerance, causing overdose.
- Prescribing morphine to a dialysis patient.
- Failing to co-prescribe a laxative and an antiemetic with a strong opioid.
- Abruptly withdrawing opioids in a physically dependent patient.
- Judging a nerve block only by pain score, ignoring function and sleep.