Predictors of Long-Term Opioid Use After Opioid Initiation at Discharge From Medical and Surgical Hospitalizations
Opioid analgesics may be initiated following surgical and medical hospitalization or in ambulatory settings; rates of subsequent long-term opioid (LTO) use have not been directly compared. This retrospective cohort study of the Veterans Health Administration (VHA) included all patients receiving a new outpatient opioid prescription from a VHA provider in fiscal year 2011. If a new outpatient prescription was filled within 2 days following hospital discharge, the initiation was considered a discharge prescription. LTO use was defined as an episode of continuous opioid supply lasting a minimum of 90 days and beginning within 30 days of the initial prescription. We performed bivariate and multivariate analyses to identify the factors associated with LTO use following surgical and medical discharges. Following incident prescription, 5.3% of discharged surgical patients, 15.2% of discharged medical patients, and 19.3% of outpatient opioid initiators received opioids long term. Medical and surgical patients differed; surgical patients were more likely to receive shorter prescription durations. Predictors of LTO use were similar in medical and surgical patients; the most robust predictor in both groups was the number of days’ supply of the initial prescription (odds ratio [OR] = 1.24 and 95% confidence interval [CI], 1.12-1.37 for 8-14 days; OR = 1.56 and 95% CI, 1.39-1.76 for 15-29 days; and OR = 2.59 and 95% CI, 2.35-2.86 for >30 days) compared with the reference group receiving ≤7days. Rates of subsequent LTO use are higher among discharged medical patients than among surgical patients. Characteristics of opioid prescribing within the initial 30 days, including initial dose and days prescribed, were strongly associated with LTO use.
While patients may be newly exposed to opioids during medical and surgical hospitalization and the prescription of opioids at discharge is common,1-5 prescribers of opioids at discharge may not intend to initiate long-term opioid (LTO) use. By understanding the frequency of progression to LTO use, hospitalists can better balance postdischarge pain treatment and the risk for unintended LTO initiation.
Estimates of LTO use rates following hospital discharge in selected populations1,2,4-6 have varied depending on the population studied and the method of defining LTO use.7 Rates of LTO use following incident opioid prescription have not been directly compared at medical versus surgical discharge or compared with initiation in the ambulatory setting. We present the rates of LTO use following incident opioid exposure at surgical discharge and medical discharge and identify the factors associated with LTO use following surgical and medical discharge.
METHODS
Data Sources
Veterans Health Administration (VHA) data were obtained through the Austin Information Technology Center for fiscal years (FYs) 2003 through 2012 (Austin, Texas). Decision support system national data extracts were used to identify prescription-dispensing events, and inpatient and outpatient medical SAS data sets were used to identify diagnostic codes. The study was approved by the University of Iowa Institutional Review Board and the Iowa City Veterans Affairs (VA) Health Care System Research and Development Committee.
Patients
We included all patients with an outpatient opioid prescription during FY 2011 that was preceded by a 1-year opioid-free period.7 Patients with broadly accepted indications for LTO use (eg, metastatic cancer, palliative care, or opioid-dependence treatment) were excluded.7
Opioid Exposure
We included all outpatient prescription fills for noninjectable dosage forms of butorphanol, fentanyl, hydrocodone, hydromorphone, levorphanol, meperidine, methadone, morphine, oxycodone, oxymorphone, pentazocine, and tramadol. Consistent with the Centers for Disease Control and Prevention and VA/Department of Defense guidelines, LTO use was defined conceptually as regular use for >90 days. Operationalizing this definition to pharmacy refill data was established by using a cabinet supply methodology,7 which allows for the construction of episodes of continuous medication therapy by estimating the medication supply available to a patient for each day during a defined period based on the pattern of observed refills. LTO use was defined as an episode of continuous opioid supply for >90 days and beginning within 30 days of the initial prescription. While some studies have defined LTO use based on onset within 1 year following surgery,5 the requirement for onset within 30 days of initiation was applied to more strongly tie the association of developing LTO use with the discharge event and minimize various forms of bias that are introduced with extended follow-up periods.
Clinical Characteristics
Patients were classified as being medical discharges, surgical discharges, or outpatient initiators. Patients with an opioid index date within 2 days following discharge were designated based on discharge bed section; additionally, if patients had a surgical bed section during hospitalization, they were assigned as surgical discharges. Demographic, diagnosis, and medication exposure variables that were previously associated with LTO use were selected.8,9 Substance use disorder, chronic pain, anxiety disorder, and depressive disorder were based on International Classification of Diseases, 9th Revision (ICD-9) codes in the preceding year. The use of concurrent benzodiazepines, skeletal muscle relaxants, and antidepressants were determined at opioid initiation.10 Rural or urban residence was assigned by using the Rural-Urban Commuting Area Codes system and mapped with the zip code of a veteran’s residence.11
Analysis
Bivariate and multivariable relationships were determined by using logistic regression. The multivariable model considered all pairwise interaction terms between inpatient service (surgery versus medicine) and each of the variables in the model. Statistically significant interaction terms (P < .05) were retained, and all others were omitted from the final model. The main effects for variables that were involved in a significant interaction term were not reported in the final multivariable model; instead, we created fully specified multivariable models for surgery service and medicine service and reported odds ratios (ORs) for the main effects. All analyses were conducted by using SAS version 9.4 (SAS Institute Inc, Cary, North Carolina).
