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

Abstract

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-naı¨ve. 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 α 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.