Pharmacokinetic study between a bilayer matrix fentalyl patch and a monolayer matrix fentanyl patch: single dose administration in healthy volunteers*

AIMS Transdermal fentanyl is a well established treatment for cancer pain. The aim of the present study is to assess the relative bioavailability of fentanyl from two different transdermal systems by evaluating plasma drug concentrations after single administration of Fentalgon® (test), a novel bilayer matrix type patch, and Durogesic SMAT (reference), a monolayer matrix type patch. In the Fentalgon patch the upper 6% fentanyl reservoir layer maintains a stable concentration gradient between the lower 4% donor layer and the skin. The system provides a constant drug delivery over 72 h. METHODS This was an open label, single centre, randomized, single dose, two period crossover clinical trial, that included 36 healthy male volunteers. The patches were applied to non-irritated and non-irradiated skin on the intraclavicular pectoral area. Blood samples were collected at different time points (from baseline to 120 h post-removal of the devices) and fentanyl concentrations were determined using a validated LC/MS/MS method. Bioequivalence was to be claimed if the 90% confidence interval of AUC(0,t) and C(max) ratios (test: reference) were within the acceptance range of 80-125% and 75-133%, respectively. RESULTS The 90% confidence intervals of the AUC(0,t) ratio (116.3% [109.6, 123.4%]) and C(max) ratio (114.4% [105.8, 123.8%] were well included in the acceptance range and the C(max) ratio also met the narrower bounds of 80-125%. There was no relevant difference in overall safety profiles of the two preparations investigated, which were adequately tolerated, as expected for opioid-naïve subjects. CONCLUSIONS The new bilayer matrix type patch, Fentalgon®, is bioequivalent to the monolayer matrix type Durogesic SMAT fentanyl patch with respect to the rate and extent of exposure of fentanyl (Eudra/CT no. 2005-000046-36).