A 70-year-old man with chronic kidney disease on oral morphine for cancer pain develops multifocal myoclonus and fluctuating drowsiness with vivid hallucinations over 48 hours. Renal function has worsened recently. The MOST appropriate management is:

• A Add haloperidol and continue the same morphine dose
• B Rotate to fentanyl and reduce the total opioid load ✓
• C Add phenytoin for the myoclonus and continue morphine
• D Increase morphine to cover the worsening pain perception

Explanation

Morphine-6-glucuronide is renally cleared and accumulates in renal failure, producing neurotoxicity: myoclonus, sedation, hallucinations and hyperalgesia. The correct action is dose reduction with rotation to fentanyl, whose metabolites are inactive and safer in renal impairment. Haloperidol may treat hallucinations but leaves the cause untreated. Phenobarbitone or benzodiazepines can suppress myoclonus symptomatically, but continuing morphine allows progression to coma and seizures.

Reference: Oxford Textbook of Palliative Medicine, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.