Validation of the PAC-SYM questionnaire for opioid-induced constipation in patients with chronic low back pain.

Background: The Patient Assessment of Constipation Symptoms (PAC-SYM) questionnaire is a 12-item self-report instrument divided into abdominal, rectal and stool domains.

Aims: This study aimed to (1) evaluate the psychometric properties of PAC-SYM in assessing the symptoms and severity of opioid-induced constipation; (2) test for differences in opioid-induced constipation between Durogesic fentanyl transdermal reservoir (TDF) and oral sustained-release morphine (SRM) in patients with chronic low back pain (CLBP).

Methods: In a 13-month, open-label, parallel-group study, 680 patients were randomised to receive either TDF (n=338) or SRM (n=342) for CLBP. Assessments were recorded at Visit 1 (baseline), Visit 5 (Day 29) and Visit 17 (Month 13). Concurrent validity, clinical validity and responsiveness of PAC-SYM were determined based on patients' confirmation of constipation (CC) scores. Differences in PAC-SYM scores between treatment groups were also evaluated.

Results: The study included 677 patients, of whom 638 were opioid-naïve. Mean PAC-SYM scores for constipated patients were substantially higher than for non-constipated patients, demonstrating good clinical validity for PAC-SYM. The PAC-SYM could detect changes in bowel function over the treatment period, indicating responsiveness. Homogeneity of each symptom domain exceeded Cronbach's alpha coefficient of 0.70, suggesting good internal consistency and reliability. Changes in mean PAC-SYM scores from baseline to Visit 5 and Visit 17 were significantly lower for the TDF group than for the SRM group, indicating that the TDF group experienced less severe constipation.

Conclusion: PAC-SYM is a reliable, valid and responsive measure of the presence and severity of opioid-induced constipation symptoms.