Transdermal fentanyl in cachectic cancer patients.

Fentanyl is an opioid with high lipid solubility, suitable for intravenous, spinal, transmucosal and transdermal administration. The transdermal fentanyl patch has become widely used in the treatment of both malignant and non-malignant chronic pain. The absorption of fentanyl from the patch is governed by the surface area of the patch, by skin permeability and by local blood flow. The aim of this study is to find out whether absorption of fentanyl in cachectic patients with cancer-related pain is different from that of normal weight cancer patients. We recruited ten normal weight (mean body mass index (BMI) 23 kg/m(2)) and ten cachectic (mean BMI 16 kg/m(2)) cancer pain patients. A transdermal fentanyl patch with a dose approximately equianalgesic to the patients' previous opioid dose was administered to the upper arm of the patient for 3 days. Prior to patch application, the height, weight and BMI of the patient, as well as upper arm skin temperature, local sweating, thickness of skin fold and local blood flow were measured. Plasma fentanyl concentrations were analyzed from blood samples taken at baseline, 4, 24, 48 and 72 h. Plasma fentanyl concentrations adjusted to dose were significantly lower at 48 and 72 h in cachectic patients than normal weight patients. The cachectic patients had a significantly thinner upper arm skin fold, but no differences were found in local blood flow, sweating, or skin temperature. Absorption of transdermal fentanyl is impaired in cachectic patients compared with that of normal weight cancer pain patients.