OBJECTIVE The aim of this study was to determine the safety and effectiveness of a transdermal fentanyl delivery system for the relief of pain following abdominal surgery. METHODS In a nonblinded, noncrossover, placebo-controlled study, 40 ASA I and II patients of both sexes, 18-69 years of age, who were scheduled for abdominal surgery under general anesthesia, were randomly divided into two groups of 20 patients each. Patients in group I received a transdermal patch containing 0.16 mg/cm2 of fentanyl, which was applied to the skin over the subclavian area 60 minutes before the induction of anesthesia. For body weight less than 60 kg, a 30 cm2 patch was applied, and for weight greater than 60 kg, a 40 cm2 patch was used. A second group of 20 patients received placebo patches of identical size. Approximately 20 to 30 minutes before the expected end of surgery, 60 mg ketorolac was administered intramuscularly. Patients were observed for 36 hours after placement of the patch. If patients reported their pain at rest as 5 or greater at rest on a 0-10 visual analog scale, they were given 30-mg increments of ketorolac 5 to 7 hours apart. If this regimen did not relieve their pain, they received 1,300 mg acetaminophen between two ketorolac doses. If despite this, they still had pain 30 minutes afterward, intravenous morphine was given, and the patients were excluded from further study. The patch was removed in four patients in the fentanyl group and seven in the placebo group for various reasons, which included, inadequate pain relief requiring additional analgesia postoperatively and more than 1 microgram/kg of sufentanil given intraoperatively or immediately prior to the end of surgery. During the 36-hour observation period, 30 doses of 30 mg ketorolac and 14 doses of 1.3 g acetaminophen were given to 13 patients in the placebo group and 18 doses of ketorolac and 8 doses of acetaminophen were administered to 16 in the fentanyl group. RESULTS The differences in postoperative analgesic requirements were significant. Plasma fentanyl concentrations at 12 and 24 hours after the application of the fentanyl patch were 0.98 +/- 0.14 ng/mL and 1.22 +/- 0.17 ng/mL, respectively. At 8, 16, 24, and 36 hours after application of the patch, the pain relief, assessed by a VAS at rest and with movement, was similar in the two groups. In the fentanyl and control groups, 12 and 5 patients, respectively, experienced nausea, and 2 and 3 patients, respectively, vomited. CONCLUSIONS Similar postoperative analgesia was achieved with less parenteral analgesics in patients who received transdermal fentanyl preoperatively than in control patients. Fentanyl, 50-75 micrograms/h, administered in a transdermal delivery system, did not depress respiratory rate or hemoglobin oxygen saturation. Although the exact role of continuously administered opioids in managing acute postoperative pain has yet to be clearly defined, it is concluded that if properly used, this new transdermal device can be effective in providing a background of analgesia, which may assist in the management of acute postoperative pain as well as some chronic pain states.