Is Fentanyl Patch End-Of-Dose Failure Associated with Body Mass Index? (FR441A)

•Explain to all patients the nature and possibility of end-of-dose failure to patients when initiating therapy with fentanyl transdermal preparations.•Increase screening of patients on using transdermal fentanyl preparations for end-of-dose failure, with particular attention to patients with cancer cachexia. Transdermal fentanyl is widely used for patients with cancer pain requiring a long-acting opioid analgesic. The delivery of fentanyl in this form relies on a drug reservoir forming in subcutaneous fat. The manufacturer-recommended initial dosing frequency is every 72 hours. However, some patients experience “end-of-dose failure” (EDF) with worsening pain after a shorter interval. No studies have examined whether EDF correlates with body mass index (BMI). To assess whether low BMI is associated with prescription of transdermal fentanyl at q48h dosing frequency. All outpatient fentanyl patch prescriptions dispensed between January 1, 2014 and December 31, 2015 at our academic cancer center were extracted using an institutional database. For each prescription patient age, sex, race, patch dose, dosing frequency, and cancer type, as well as height and weight (used to calculate BMI) were collected. A generalized estimating equations (GEE) model was fit to account for correlation within patient and determine association between BMI and patch frequency. A total of 2,750 patients filled 6,569 fentanyl patch prescriptions over the study period. Patients were a median of 60 years old, 56.1% female, and 73.3% white (11.2% African American, 7.2% Asian). The median number of prescriptions per patient was 1 at a median dose of 37. Among 287 underweight patients (BMI<18.5), 34 (11.8%) received at least one q48h fentanyl patch prescription compared with 62 (10.2%) of obese (BMI>30) patients. Patients who received q48h patch had lower BMI (.58 unit decrease; p<0.01) than patients who received the q72h patch. Lower BMI is associated with q48h fentanyl patch dosing, suggesting that it may also be associated with end-of-dose failure in cancer patients. These patients should be closely monitored and alerted to this possibility.