Abstract
The authors report two patients with abdominal pain due to carcinomatous peritonitis that did not decrease despite large doses of fentanyl but decreased after addition of low-dose morphine. Case 1 was a 15-year-old girl with abdominal pain due to ovarian cancer with peritoneal dissemination. The abdominal pain was controlled by intravenous fentanyl at a dosage of 300 μg/day for the first 3 months; thereafter, the abdominal pain worsened. Continuous intravenous fentanyl ≤ 2400 μg/day with 16 daily rescues of fentanyl 100 μg plus intravenous ketamine did not control the pain. Addition of morphine at a dosage of 50 mg/day to continuous intravenous fentanyl, however, relieved the abdominal pain. Case 2 was a 33-year-old woman with abdominal pain due to gastric cancer with peritoneal dissemination. The abdominal pain was not controlled by continuous intravenous fentanyl ≤ 9600 μg/day with 25 daily rescues of fentanyl 200 μg plus intravenous ketamine. Addition of morphine at a dosage of 150 mg/day to continuous intravenous fentanyl, however, relieved the abdominal pain. We conclude that tolerance to fentanyl may have occurred in these two patients.
