RESUMEN
Opioid rotation from transdermal fentanyl to an alternate opioid is often necessitated in advanced disease, but is fraught with uncertainty due to variable absorption from the patch in end-stage illness and the lack of a clearly established opioid rotation ratio. The manufacturer of transdermal fentanyl provides opioid rotation recommendations only for rotation from the oral morphine equivalent daily dose (MEDD) of opioid to the patch, not in the opposite direction. This is a case report of a single patient with cancer and cachexia admitted to the palliative care unit of a large academic medical centre in Canada. The patient is a 50-year-old female with widely metastatic breast cancer who developed opioid toxicity when maintenance transdermal fentanyl patch therapy (100 µg patch applied every 72 h) was rotated to subcutaneous hydromorphone infusion to improve pain control. Hydromorphone was initiated at a rate of 1 mg/h by continuous infusion based on an opioid rotation ratio for transdermal fentanyl (µg/h):MEDD (mg/day) of 1:2.4. Opioid toxicity eventually resolved with downward titration of hydromorphone to only 30% of the initially estimated equianalgesic dose. This case highlights the need for close follow-up of all patients undergoing opioid rotation from transdermal fentanyl and reinforces the need to reduce the initial dose of the new opioid by 30%-50% of the calculated MEDD, especially when rotating from a high dose of transdermal fentanyl, or if there are factors potentially impairing absorption from the patch such as age, cachexia and weight loss, or if rotation is performed for reasons other than uncontrolled pain.