Objective: To calculate the monthly incidence of opioid-related adverse events in the opioid-naïve patients who contin-ue to use opioids in the post-operative period.
Background data: An estimate of 1-6 percent of surgery patients con-tinues to persistently use the opioids longer than 90 post-operative days. However, the association of the opioid ad-verse events with the persistent post-operative use is not clearly known.
Methods: This is a historical (retrospective) cohort study of the opioid-naïve US Veterans between the ages of 18 and 85. The surgical group (who had major surgery between January 1, 2008 and December 31, 2015) was compared to the control references. The outcome of opioid misuse was either opioid overdose or the development of opioid use disorder. Each case was followed for 13 months. The monthly incidence of opioid misuse was calculated by dividing the number of new opioid misuse divided by the number of patients who are still filling the prescription for opioid medications in that specific month.
Results: A total of 150,088 surgical patients and 1,145,553 controls met the inclusion criteria. The risk of opioid misuse was between 0.3 and 1.8 percent for first 11 post-operative months among both groups. The incidence of opioid misuse increases to 4.6 percent (95 percent CI: 3.2-6.4) at 12 months and to 8.1 percent (95 percent CI: 5.6-11.5) at 13th post-operative month. The incidence also increases to 2.3 percent (95 percent CI: 1.6-3.4) at 12th and 3.9 percent (95 percent CI: 2.5-6.0) at 13th follow-up month among the control references.
Conclusions: After initiation of opioid pre-scription, the opioid misuse occurs, and the incidence increases dramatically after the 11th month regardless of the reason for opioid therapy initiation (surgery vs chronic conditions). The risks/-benefits of opioid use must be evaluated more frequently with the longer opioid use.