Direct conversion from oral morphine to transdermal fentanyl: a multicenter study in patients with cancer pain.

Direct conversion from oral morphine to transdermal fentanyl with a ratio of oral morphine/transdermal fentanyl (100:1 mg) daily was examined in patients with cancer pain. Patients with a 'stable and low level of cancer pain' receiving a constant dosage of sustained release morphine during a pre-study phase of 6 days were included in the study. Initial fentanyl dosage was calculated by a conversion table. The transdermal system was changed every 72 h and the dosage was adjusted to the needs of the patients according to the VAS scores and the requirement of liquid morphine, which was allowed to achieve sufficient pain relief. Regression analysis at the end of the study revealed a mean morphine/transdermal fentanyl ratio of 70:1. Pain relief during treatment with transdermal fentanyl was identical to sustained release morphine. However, significantly more patients took supplemental medication with liquid morphine during transdermal fentanyl therapy. The number of patients suffering from pain attacks did not increase with transdermal fentanyl. Constipation and medication with laxatives decreased significantly during fentanyl therapy. Other side effects and vital signs were identical. Three patients suffered from a morphine withdrawal syndrome beginning within the first 24 h of transdermal fentanyl therapy. Cutaneous reactions to the patch were rare, mild and transient. Patients and physicians reported satisfaction with the transdermal therapy. 94.7% of the patients chose to continue the transdermal fentanyl therapy at the end of the study due to better performance in comparison to oral morphine. Due to these results an initial conversion from oral morphine to transdermal fentanyl with the ratio of 100:1 is safe and effective.