[Evaluation of the 2.5 mg fentanyl patch, applied using the half-side application procedure in patients with cancer pain].

Occasionally, pain control with the fentanyl patch may lead to overdose at an initial dose of 2.5 mg, as well as during dose increase from 2.5 to 5.0 mg. Respiratory depression and other adverse drug reactions associated with fentanyl overdose have been observed in several of our patients. We developed a procedure for applying one-half of the fentanyl patch formulations and evaluated the new mode of application by examining the fentanyl concentration in 32 patients with cancer-related pain who had been using the fentanyl patch for pain control. While some patients were treated with the full-sized 2.5-, 5.0-, or 7.5-mg formulations, others were treated with the half-sized 2.5-mg formulation. The fentanyl patch was equally divided by drawing a line on the side on which the product name and dose were written. Tegaderm was applied to the patient's skin, and after detaching from the protective liner, half of the patch was applied to overlap Tegaderm along the line and the other half applied directly to the skin. Blood samples were collected 48-72 h after patch application. The mean serum concentration of fentanyl given in the half-sized 2.5-mg formulation was 0.286 ng/ml, which was approximately one-half of the concentration of the full-sized 2.5-mg formulation, 0.544 ng/ml. Therefore the 2.5-mg fentanyl patch, applied using the one-half procedure we developed, is clinically useful.