Constipation and the use of laxatives: a comparison between transdermal fentanyl and oral morphine

Constipation and the use of laxatives were investigated in patients with ch ronic cancer pain treated with oral morphine and transdermal fentanyl in an open sequential trial. Forty-six patients were treated with slow-release m orphine 30-1000 mg/day for 6 days and 39 of these patients were switched to transdermal fentanyl 0.6-9.6 mg/day with a conversion ratio of 100: 1. Med ian fentanyl doses increased from 1.2 to 3.0 mg/day throughout the 30-day t ransdermal treatment period. Twenty-three patients completed the study. Two patients died from the basic disease while treated with transdermal fentan yl, 12 patients were excluded for various reasons, and not enough data for evaluation were available for two patients. Mean pain intensity decreased s lightly after conversion although the number of patients with breakthrough pain or requiring immediate-release morphine as a rescue medication was hig her with transdermal fentanyl. The number of patients with bowel movements did not change after the opioid switch bur the number of patients taking laxatives was reduced significant ly from 78-87% of the patients per treatment day (morphine) to 22-48% (fent anyl). Lactulose was used mainly and was reduced most drastically but other laxatives were also used less frequently. In this study transdermal fentanyl was associated with a significantly lowe r use of laxatives compared to oral morphine. The difference in the degree of constipation between the two analgesic regimens should be confirmed in a randomized double-blind study that lakes into account both constipation an d use of laxatives.