Opioid type and other clinical predictors of laxative dose in advanced cancer patients: a retrospective study

Constipation is a frequent and underdiagnosed complication in patients with advanced cancer. Constipation in this population is multifactorial, but the use of opioids is one of the main causes. The purpose of this retrospective study was to establish the association between opioid type and laxative dose, as well as the contribution of other clinical factors in advanced cancer patients admitted to a palliative care unit.

The records of consecutive patients admitted to the Acute Palliative Care Unit at the Grey Nuns Hospital between December 1995 and January 1997 were reviewed. Criteria of eligibility were the presence of cancer pain treated by opioids (oral and subcutaneous morphine and hydromorphone, oral methadone), oral laxative treatment capable of achieving at least one bowel movement every 3 days, and the absence of bowel obstruction or colostomy. During period(s) of stable analgesic doses, the charts were reviewed for demographic and clinical characteristics, average number of bowel movements, daily laxative doses, doses and type of opioid, laxative/opioid dose ratio (LOR) (calculated by dividing the total laxative dose by the total opioid dose), functional and cognitive status, food intake, and level of calcium, albumin, and potassium.

Forty-nine evaluable patients were identified. The LOR in patients receiving oral opioids was 0.15 +/- 0.19 vs. 0.18 +/- 0.17 in patients on parenteral opioids (p > 0.2). The LOR in patients receiving methadone was 0.025 +/- 0.027 as compared to 0.24 +/- 0.23 in patients receiving morphine and 0.17 +/- 0.13 in patients on hydromorphone (p < 0.0001). We found a strong association between LOR and abdominal involvement (p < 0.0006), opioid type (p < 0.0001), age (p < 0.0001), and female gender (p < 0.034). There were no significant correlation between LOR and functional status, cognitive status, food intake, and level of calcium or potassium.

We conclude that laxative dose needs to be titrated on an individualized basis. The LOR is lower in patients receiving methadone and in those of male gender, younger age, and absence of abdominal involvement.