Determinants of medication underuse and medication overuse in patients with chronic non-malignant pain: a multi-center study

BACKGROUND: In chronic non-malignant pain, medication is often used as an important cornerstone of the treatment. Medication non-adherence is a frequent problem in chronic conditions. In patients with chronic non-malignant pain, medication non-adherence ranges between 8% and 53%. Two types of non-adherence can be identified: underuse and overuse of pain medication. OBJECTIVE: To examine determinants of both medication underuse and overuse non-adherence in patients with chronic non-malignant pain, with a focus on factors related to all five categories of determinants of medication non-adherence simultaneously, as proposed by the WHO. DESIGN: A multicenter cross-sectional study. SETTINGS: Three multidisciplinary outpatient pain centers in Flanders, Belgium. PARTICIPANTS: A total of 265 patients with chronic non-malignant pain participated in the study. METHODS: Medication non-adherence was assessed by a self-report interview. Associations of socio-economic, treatment related, condition related, patient related and health care system related factors with medication underuse or overuse were determined by building two separate multivariable binary logistic regression models. RESULTS: Thirty eight percent of the patients were fully adherent. Based on multivariable analyses, underuse was significantly associated with more prescribed analgesics (OR=2.303), self-medication (OR=4.679), lower pain intensity (OR=0.821), active coping strategies (OR=1.132) and lack of information (OR=0.268). Overuse of medication was associated with more prescribed analgesics (OR=1.645) and current smoking (OR=2.744). CONCLUSION: Patients underusing or overusing their medication do have a different risk profile. The set of determinants of non-adherence, proposed by WHO, is suitable to study determinants of underuse, but the framework is less suitable to study determinants of medication overuse.status: publishe