Fentanyl-induced neurotoxicity and paradoxic pain.

A patient with pain associated with metastatic leiomyosarcoma received escalating doses of opioids. Upon discontinuation of intravenous morphine, transdermal fentanyl was initiated, and after several days, the dose was increased to 200microg/hour for persistent, severe pain. The patient became somnolent, and further dose adjustments and route change were carried out.