Transdermal fentanyl: informed prescribing is essential.

While morphine is historically the gold standard for the management of severe cancer pain, some patients either do not achieve adequate analgesia, or suffer intolerable side-effects. For these patients an alternative opioid is recommended. One such alternative is the potent mu opioid agonist fentanyl, delivered in a transdermal controlled release formulation. Similar to morphine, transdermal fentanyl is effective for the management of moderate to severe cancer pain. However, inappropriate prescribing of transdermal fentanyl, particularly in the clinical setting of unstable pain, can cause significant opioid toxicity, as highlighted in the case reports described.