The analgesic effect of rescue administration of intravenous acetaminophen in cancer patients may be associated with sex and opioid dose, and the effect would appear to patients administered under 45 mg/day opioid (oral morphine equivalents).

: There have been no investigations examining the analgesic effect of rescue administration of intravenous acetaminophen (IV APAP) for pain in cancer patients. Fifty cancer patients who received IV APAP for pain at Ashiya Municipal Hospital (Hyogo, Japan) between January 2014 and July 2016 were retrospectively evaluated. The degree of pain was evaluated using a 4-point verbal rating scale. Pain intensity differences ≥ 1 defined the IV APAP effective group, and the patient' characteristics were compared by a medical chart review. Variables were extracted from medical records for logistic regression analyses of factors associated with analgesic effect. The cut-off value of opioid dose (oral morphine equivalent) was determined using receiver operator characteristic (ROC) curve analysis. Thirty eight (76%) patients experienced an analgesic effect of rescue administration of IV APAP. Sex (odds ratio [OR] 5.4014; p = 0.0397) and opioid dose used for pain control (OR 0.9901; p = 0.0147) were found to be associated with the efficacy of rescue administration of IV APAP. The cut-off value of opioid dose (oral morphine equivalent), which may be difficult to match the analgesic effect of IV APAP, was calculated to be more than 45 mg/day. This study demonstrated the efficacy of a rescue administration of IV APAP for pain in cancer patients, and revealed that sex and opioid dose may be associated with the analgesic effect. Furthermore, this study also proposes a criterion for the analgesic effect.