Unusual case of transdermal fentanyl in cachexia.

Fentanyl has a low molecular weight and is lipophilic making it suitable for transdermal administration. However, multiple factors appear to lead to interindividual variation in absorption via this route. Here we describe an unusual case where a patient was found to have twelve 100 μg/hour fentanyl patches in situ which she was using as background analgesia.