Disproportionality analysis of opioid-related urinary retention using the JADER database: Focus on the lack of signal for transdermal fentanyl.

Abstract

Urinary retention is a known adverse effect of opioids, but limited information is available on how this adverse event varies among individual opioids. This study evaluated disproportionality signals between major opioids and urinary retention using the Japanese Adverse Drug Event Report database (JADER). We performed a disproportionality analysis of reports submitted between April 2004 and October 2025. Signals were assessed using reporting odds ratios (RORs), 95% confidence intervals (CIs), and the Information Component (IC). Adverse events were identified using the Medical Dictionary for Regulatory Activities/Japanese version (MedDRA/J) term "urinary retention." A sensitivity analysis was conducted using a broader definition of urinary dysfunction that also included "Dysuria." Time to onset was calculated from the start of opioid administration to event onset, and daily doses were converted to oral morphine equivalents. Significant signals were detected for morphine, oxycodone, tramadol, and codeine. Transdermal fentanyl was the only opioid without a detectable signal, even under the broader definition of urinary dysfunction. Among opioids with detected signals and available dose information, urinary retention was reported even at relatively low morphine-equivalent doses, suggesting the need for careful monitoring at the start of opioid therapy. The absence of a signal for transdermal fentanyl may reflect a lower reporting frequency in JADER, but not a lower clinical risk, of urinary retention. Given the limitations of spontaneous reporting systems, these findings are hypothesis-generating and are insufficient to guide opioid selection or switching.