Introduction Opioid treatment is associated with a wide range of gastrointestinal adverse effect collectively known as opioid-induced bowel dysfunction (OIBD). The most studied and prevalent symptom is constipation, occurring in up to 81% of patients. These adverse effects complicate effective pain management and furthermore, the current clinical gold standard for objective evaluation of constipation by abdominal x-ray exhibits poor inter-observer reliability and offers no quantifiable measure.

The aims of the present study were 1) to develop a model for OIBD in healthy volunteers and 2) to establish whether a novel semi-automatic segmentation method to assess colon volume using Magnetic Resonance Imaging (MRI) was sensitive to changes in colonic volume brought on by treatment with oxycodone.

Method 25 healthy male subjects (mean age: 28 ± 9 years) were treated for five days with placebo or oxycodone 20 mg/day in a double-blind, cross-over design. Abdominal MRI scans were acquired at baseline and after 5 days of treatment in both treatment arms. Colonic volumes were determined for four separate colon segments (ascending, transverse, descending, and sigmoid+rectum). For each segment, volumes were compared using a two-way repeated measures ANOVA with factors treatment (oxycodone vs. placebo) and day (day 1 vs. day 5).

Results Placebo treatment did not significantly alter volumes for any colon segments. Oxycodone treatment significantly increased the volume of the ascending colon (P < 0.01; day 1: 177 ± 72 mL vs. day 5: 250 ± 95 mL), the transverse colon (P < 0.05; day 1: 192 ± 80 mL vs. day 5: 221 ± 82 mL), and the total colon volume (P < 0.05; day 1: 760 ± 232 mL vs. day 5: 872 ± 220 mL).

Conclusion An experimental model to assess OIBD in healthy volunteers has successfully been developed and may be used in future clinical and pharmacological studies to unravel the underlying pathophysiological mechanisms of OIBD or to assess efficacy of novel treatment strategies such as peripherally acting μ-opioid receptor antagonists (PAMORAs). Additionally, the present MRI-based method for objective assessment of colon volume is sensitive to changes in colon volumes brought on by treatment with oxycodone. Hence, it may be applied in other diseases or syndromes where information on colonic volume, content and morphology is valuable including conditions such as multiple sclerosis and irritable bowel syndrome.

Disclosure of interest None Declared.