Results of a zero-inflated negative binomial regression analysis of the association between early drug class(es) dispensed and strength of opioid received in the first 8 weeks after injury and days on benefits and benefit status after the 8-week exposure window up to 1 year after injury
| Predictor | Days on benefits after 8-week exposure window | On benefits after 8-week exposure window | ||||
| Number of days on benefits after 8-week exposure window, mean (SD), median | IRR (95% CI) | Receiving benefits after 8-week exposure window, n (%) | OR (95% CI) | |||
| Unadjusted | Adjusted | Unadjusted |
Adjusted | |||
| Drug class(es) dispensed in first 8 weeks (n=55 571) | ||||||
| NSAIDs and/or SMRs (n=29 104) | 19.5 (46.9), 0.0 | 1.00 | 1.00* | 10 817 (37.2) | 1.00 | 1.00* |
| Opioids only (n=7730) | 24.9 (56.3), 0.0 | 1.22 (1.17 to 1.28) | 1.09 (1.04 to 1.14) | 3030 (39.2) | 1.08 (1.02 to 1.14) | 0.99 (0.93 to 1.05) |
| Opioids with NSAIDs and/or SMRs (n=18 737) | 38.3 (67.0), 3.0 | 1.40 (1.35 to 1.45) | 1.26 (1.22 to 1.30) | 9889 (52.8) | 1.89 (1.82 to 1.96) | 1.61 (1.54 to 1.69) |
| Strength of opioids dispensed in first 8 weeks (n=26 467) | ||||||
| Weak opioid(s) only (n=23 271) | 31.1 (60.7), 0.0 | 1.00 | 1.00† | 10 903 (46.9) | 1.00 | 1.00† |
| Strong opioid(s) only (n=1711) | 47.0 (75.8), 6.0 | 1.30 (1.20 to 1.40) | 1.21 (1.12 to 1.30) | 941 (55.0) | 1.39 (1.25 to 1.54) | 1.18 (1.05 to 1.32) |
| Weak and strong opioids (n=1485) | 70.5 (87.3), 32.0 | 1.48 (1.37 to 1.59) | 1.29 (1.20 to 1.39) | 1075 (72.4) | 3.13 (2.70 to 3.45) | 2.27 (2.00 to 2.63) |
*Adjusted for sex, age, year of injury, income, diagnosis code, health authority, pain specialist visit within first 8 weeks, cumulative days of opioids in previous year, sedative hypnotic dispense within first 8 weeks, spinal X-ray within first 8 weeks, hospital contact within first 8 weeks, back/neck pain in prior 2 years, cumulative days of NSAIDs in previous year.
†Adjusted for sex, age, year of injury, income, diagnosis code, pain specialist visit within first 8 weeks, sedative hypnotic dispense within first 8 weeks, back/neck pain comorbidity within prior 2 years.
IRR, incidence rate ratio; NSAID, non-steroidal anti-inflammatory drug; SMR, skeletal muscle relaxant.