Table 1 Overview of measurement tools

Bowel Function Index (Day 0 and day 14)

3 questions about defecation, rated on a scale of 0 (best possible outcome) to 100 (worst possible outcome). Total score ≥ 30 (mean of the three separate scores) indicates clinically significant constipation. A change of the total score of > 12 is regarded as clinically meaningful.

Rome IV criteria for opioid-induced constipation (Day 0 and day 14)

At least two of the following criteria have to be fulfilled in order to diagnose constipation:

- Straining > 25% of defecations

- Lumpy or hard stools in > 25% of defecations

- Sensation of incomplete evacuation in > 25% of defecations

- Sensation of anorectal obstruction/blockage in > 25% of defecations

- Manual manoeuvres to facilitate > 25% of defecations

- < 3 spontaneous defecations per week

EQ-5D-5L questionnaire

(Day 0 and day 14)

5 questions on dimension of health: mobility, self-care, pain/discomfort, usual activities, and anxiety/depression. Each dimension consists of 5 levels: no problems, slight problems, moderate problems, severe problems and extreme problems

Pain (Day 0 and day 14)

Numeric rating scale (0 = no pain, 10 = worst pain imaginable)

Satisfaction with laxatives will be scored on a four-point Likert scale, ranging from unsatisfied to very satisfied

Side effects of laxatives (i.e. bad taste, flatulence and nausea) will be scored on a four-point Likert scale (not at all, a bit, rather, very much)

Patient satisfaction (Day 14)

Side effects (Day 14)

Modified iMCQ (Day 14)

9 questions related to frequent occurring contact with healthcare providers. Each answer is dichotomous (yes/no) with the option to add the number of visits if the answer ‘yes’ is filled in.