Long-Term Opioid Therapy in Chronic Non-Cancer Pain: Risks and Benefits

Chronic pain affects nearly 20% of the Swedish population. Pain from the musculoskeletal system together with psychiatric disorders are the chronic conditions that cost the most for the Swedish health care disability insurance and health care systems. Current knowledge suggests that chronic pain is maintained by changes in the nervous system together with psychological and social factors.

Opioids are known to be effective for acute and post-operative pain, and can be indispensable in palliative treatment of cancer pain. Long-term opioid therapy on the other hand is associated witg several risks, e.g., development of opioid dependence and opioid use disorder (OUD), and other opioid related complications including premature death. Clinical experience, qualitative and quantitative research suggest that some individuals with chronic pain do benefit from long-term opioid therapy in terms of clinical significant pain relief with only a low level of negative side-effects. However, evidence of change in functional outcomes and health related quality of life is ambiguous. Therefore, the role of long-term opioid therapy in chronic pain conditions remains debated and sometimes controversial.

In contrast to the well-established opioid epidemic in the U.S., little is known about the use of prescribed opioids in Sweden, and how this has developed during the last decade. The annual prevalence of opioid prescription did not change much during 2006-2017, but there were significant shifts in choice of opioids, with an increase in strong opioids e.g., oxycodone and morphine. Very little is known about what clinical consequences this shift might lead to.

The U-PAIN cohort study aims to examine patterns of prescribed opioid use, risks of adverse effects of long-term opioid therapy, and benefits of long-term opioid therapy, in a prospective clinical cohort.

The study aims to complete a broad bio-psycho-social characterization of the participants relevant to chronic pain. The study participants are followed over 5 years in order to study trajectories for patterns of opioid use, and predictive factors for opioid use disorder, work ability, pain severity and interference, and health-related quality of life.

At baseline, participants will be classified into 4 groups based on their current use of opioids:

1. No use 2. Short-term or intermittent use Criteria: short-term use defined as regular use of opioids for \< 3 months or intermittent use as dosing up to 10 days/months (independent of time frame). 3. Long-term use with low to moderate doses Criteria: use of opioids for more \> 3 months, more the 10 days/month and mean daily dose \< 40 mg (oral morphine milligram equivalent dose (MEE) defined as low dose. Mean daily dose 40-100 mg MEE defined as high dose. 4. Long-term use with high doses Criteria: use of opioids for \> 3 months. More than 100 mg MEE.

Main research questions for the cohort study are:

1. What characterizes patients without opioid use disorder at baseline compared to patients with mild, moderate or severe opioid use disorder respectively at baseline? 2. What variables predict their future:

1. Patterns of opioid use and substance use disorder? 2. Work ability, activity interference, quality of life and pain?

Potential predictors and co-variates include: (1) Individual factor and demographic variables (2) Pain characteristics, (3) Psychiatric co-morbidity and susceptibility for OUD, (3) Cognitive-behavioral variables, and (4) Physical functioning.

The objective is to identify the most salient predictors from each group and combine them into a final model with the best goodness of fit.

The four groups concerning patterns of opioid use will be statistically compared regarding key outcomes at baseline (opioid use disorders, work ability, activity interference, pain and HQoL)) by use of t-tests and chi-square tests. Logistic regression analyses will be applied for the study of predictors of opioid use, OUD, work ability, activity interference and pain. The dependent variables, e.g. OUD/no OUD will be regressed towards hypothetic predictors, grouped as described earlier, to end up with a final model including the most salient predictors from each group of variables. Multivariate regression models will be considered for continuous dependent variables.

In addition this clinical cohort will be open for other studies after ethical vetting, i.e. the cohort is unique and could contribute to further understanding of this population and hence should be open for further research.

• Changes and patterns of opioid use (type of opioid, dose, and duration) [Срок оценки: Baseline, 1 year, 2 years, 3 years, 4 years, 5 years]
• Changes in pain severity and pain interference: The Brief Pain Inventory short-form (BPI-SF) [Срок оценки: Baseline, 1 year, 2 years, 3 years, 4 years, 5 years]
• Changes in health related quality of life: EQ-5D-5L [Срок оценки: Baseline, 1 year, 2 years, 3 years, 4 years, 5 years]
• Depressive symptoms [Срок оценки: Baseline]
• Generalised Anxiety Disorder [Срок оценки: Baseline]
• Sleep [Срок оценки: Baseline]
• Pain self-efficacy [Срок оценки: Baseline]
• Experienced injustice [Срок оценки: Baseline]
• Fear of movement and reinjury [Срок оценки: Baseline]
• Catastrophizing - The Pain Catastrophizing Scale (PCS) - Swedish version. [Срок оценки: Baseline]
• Changes in life habits [Срок оценки: Baseline, 1 year, 2 years, 3 years, 4 years, 5 years]
• Alcohol Use [Срок оценки: Baseline]