Patient Assessment of Constipation Quality of Life Questionnaire: Validation in Greek patients under medication for addiction treatment with methadone and buprenorphine

Methadone maintenance treatment (MMT) and buprenorphine maintenance treatment (BMT) are considered effective for opioid use disorders. However, they have been associated with side-effects in the gastrointestinal system, mainly opioid-induced constipation that impairs patient quality of life (QoL). This investigation aimed to validate the patient assessment of constipation quality of life (PAC-QoL) instrument in Greek patients under medication for addiction treatment (MAT) by examining reliability and construct validity. In total, 310 patients under MAT were included in the investigation and completed PAC-QoL questionnaire, Nottingham health profile (NHP) instrument and Bristol stool form scale (BSFS) in Phases 1 (baseline) and 2 (12 days post baseline).The content validity was evaluated by using the item content validity index (I-CVI) along with ceiling and floor effects, internal consistency by measuring Cronbach’s a coefficient, test-retest reliability through intraclass correlation coefficient (ICC), responsiveness with effect size estimation, and convergent validity by correlations with NHP and BSFS. According to the results, a strong positive correlation among PAC-QoL sub-scales was observed. The overall ICC was equal to 0.90, the I-CVI was equal to 1.00, and the Cronbach’s alpha was estimated to the value of 0.96. Furthermore, it appears that the MMT patients experience more severe constipation than their BMT counterparts, and effect size for the total instrument was 0.94. The findings suggest an excellent reliability and validity of PAC-QoL in the Greek language. Moreover, its implementation in research and clinical settings is advocated as a useful tool to identify constipation related to QoL in patients under MAT.