Inter- and intraindividual variabilities in pharmacokinetics of fentanyl after repeated 72-hour transdermal applications in cancer pain patients.

Perception of pain by the patient is frequently one of the early signs preceding a diagnosis of cancer and, later, a sinister sign of disease progression. Among opioid drugs, transdermal fentanyl has been evaluated in the treatment of moderate to severe cancer pain. The objective of this study was to investigate the intra- and interindividual variabilities in pharmacokinetics after fentanyl drug delivery by the transdermal fentanyl patch delivery system in patients with cancer pain. As a first step, a liquid chromatography-mass spectrometry method was developed for the determination of the analgesic fentanyl in human plasma. This method was validated over the concentration range 0.15-100 ng/mL. The study group consisted of 29 inpatients (18 men and 11 women; age range 29-80 years). The initial transdermal fentanyl delivery rate was chosen depending on the patient's analgesic requirements. For 20 patients, the initial TTS fentanyl delivery rate was 25 or 50 microg/h. For 6 patients, the initial delivery rate was 75-150 microg/h. Two patients received up to 300 microg/h fentanyl delivery rate, and 3 patients received up to 350 microg/h fentanyl delivery rate. Fifteen of the 29 patients received rescue doses of subcutaneous or oral morphine, and 26 patients received paracetamol with codeine (30 mg per os). Blood samples were collected at the following intervals: 2-5, 22-26, or 45-47 hours following fentanyl patch application. The severity of pain experienced by the patient was assessed thrice daily using a visual analogue scale. The study period was 46 days. Large patient-to-patient variations in pharmacokinetic parameters occurred, although intraindividual variability was limited. A mean bioavailability of 78% was estimated; the total clearance averaged 41 L/h. From 25 to 100 mug/h fentanyl delivery rate, the pharmacokinetics was linear. At the 2 highest doses, an increase of total clearance was observed (>60 L/h). For the whole group, transdermal fentanyl treatment provided good to excellent pain relief in the majority of patients.