Relationship Between Early Prescription Dispensing Patterns and Work Disability in a Cohort of Low Back Pain Workers’ Compensation Claimants: A Historical Cohort Study
SOURCE: Occup Environ Med. 2019 (May 15) [Epub]
Nancy Carnide, Sheilah Hogg-Johnson, Mieke Koehoorn, Andrea D Furlan1, Pierre Côté
Institute for Work and Health,
Toronto, Ontario, Canada.
OBJECTIVES: To examine and compare whether dispensing of prescription opioids, non-steroidal anti-inflammatory drugs (NSAIDs) and skeletal muscle relaxants (SMRs) within 8 weeks after a work-related low back pain (LBP) injury is associated with work disability.
METHODS: A historical cohort study of 55 571 workers’ compensation claimants with LBP claims in British Columbia from 1998 to 2009 was conducted using linked compensation, dispensing and healthcare data. Four exposures were constructed to estimate the effect on receipt of benefits and days on benefits 1 year after injury: drug class(es) dispensed, days’ supply, strength of opioids dispensed and average daily morphine-equivalent dose.
RESULTS: Compared with claimants receiving NSAIDs and/or SMRs, the incidence rate ratio (IRR) of days on benefits was 1.09 (95% CI 1.04 to 1.14) for claimants dispensed opioids only and 1.26 (95% CI 1.22 to 1.30) for claimants dispensed opioids with NSAIDs and/or SMRs. Compared with weak opioids only, the IRR for claimants dispensed strong opioids only or strong and weak opioids combined was 1.21 (95% CI 1.12 to 1.30) and 1.29 (95% CI 1.20 to 1.39), respectively. The incident rate of days on benefits associated with each 7-day increase in days supplied of opioids, NSAIDs and SMRs was 10%, 4% and 3%, respectively. Similar results were seen for receipt of benefits, though effect sizes were larger.
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CONCLUSIONS: Findings suggest provision of early opioids leads to prolonged work disability compared with NSAIDs and SMRs, though longer supplies of all drug classes are also associated with work disability. Residual confounding likely partially explains the findings. Research is needed that accounts for prescriber, system and workplace factors.
KEYWORDS: administrative data; cohort study; low back pain; opioids; prescription dispensing; work disability; workers’ compensation
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From the FULL TEXT Article:
Prescription opioid use among injured workers in North America has been a significant source of concern for more than a decade. From approximately 2000 until 2010, opioid prescriptions provided to injured workers in North America rose steadily. [1, 2] While use among workers’ compensation claimants is on the decline, [1, 3, 4] opioids remain among the most commonly reimbursed prescriptions.  Specifically, early opioid use for work-related low back pain (LBP) has been broadly documented. [6–10]
Our previous systematic review demonstrated an association between early opioids and prolonged work disability for workers with work-related LBP.  However, studies were prone to exposure measurement bias (eg, incomplete prescription data, immortal time bias) and residual confounding, namely related to indication (eg, pain intensity) and preinjury and concomitant healthcare. Two subsequently published studies have been conflicting, with one finding a significant positive association  and the other no association.  Similar limitations, however, persist in these studies.
In our previous analyses, opioids, non-steroidal anti-inflammatory drugs (NSAIDs) and skeletal muscle relaxants (SMRs) were all commonly dispensed early after a work-related LBP injury,  a finding consistent with other LBP studies. [13, 14] These three drug classes have also been included in clinical guidelines on management of acute and subacute episodes of LBP. [15, 16] Research assessing how opioids impact work disability compared with these other clinically relevant medications has yet to be conducted, but can further provide new insights into the management of acute LBP injuries.