Determinants of medication underuse and medication overuse in patients with chronic non-malignant pain: a multicenter 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.