Incidence of Delirium during the Initiation Phase of Morphine and Hydromorphone Therapy in Cancer Patients: A Retrospective Comparative Study.

Background: Opioids are known to induce delirium, and the incidence of delirium induced by individual opioids has been investigated. However, only a limited number of studies have examined the incidence of delirium induced by oral hydromorphone.

Objective: To investigate whether differences exist in the incidence of delirium associated with oral morphine and oral hydromorphone during the initiation phase of treatment.

Methods: The participants were opioid-naive inpatients with cancer who started oral morphine or oral hydromorphone at Shizuoka Cancer Center (in Shizuoka, Japan) between June 2017 and November 2020. The incidence of delirium in the first week of opioid use was compared between the 2 groups.

Results: A total of 90 patients met the inclusion criteria, 27 who received oral hydromorphone and 63 who received oral morphine. The incidence rate of delirium in the oral hydromorphone group tended to be higher (19%, 5/27) than in the oral morphine group (8%, 5/63), although the difference was not statistically significant (odds ratio 0.4, 95% confidence interval, 0.1-1.4, p = 0.16 by the Fisher exact test). Propensity score matching was used to control for differences in patient background as confounders in the development of delirium, following which the incidence rate of delirium remained higher, but not significantly so, in the oral hydromorphone group (11%, 2/19) than in the oral morphine group (5%, 1/19) (odds ratio 0.5, 95% confidence interval 0.04-5.7, p > 0.99 by the Fisher exact test).

Conclusions: There was no statistically significant difference in the incidence of delirium between those who received morphine and those who received hydromorphone, which suggests that for opioid-naive inpatients with cancer, oral hydromorphone can be used in a manner similar to that for oral morphine.