Neuropsychiatric side effects due to a transdermal fentanyl patch: hallucinations

Opioid analgesics are used commonly in end-stage cancer patients for pain treatment. Central nervous system adverse effects are rare. A 73-year-old female patient was admitted to the emergency department for auditory and visual hallucinations. The patient had been receiving palliative treatment for liver, cervical, and lumbar bone metastases from an unknown origin. The patient used a transdermal fentanyl patch for palliative pain management and metoclopramide hydrochloride for nausea and vomiting. The patient had suffered weight loss of 10 kg within 5 months, and laboratory findings revealed hypoalbuminemia. The patient was considered to have experienced a fentanyl overdose, and the transdermal fentanyl patch treatment was stopped. The hallucinations improved during follow-up, and the patient was discharged with a dose adjustment. End-stage cancer patients with weight loss and hypoalbuminemia may be more prone to opioid adverse effects, such as hallucinations. The dose of fentanyl must be adjusted for weight loss, and correction of hypoalbuminemia may also lower the incidence of such adverse effects