Drug therapy concerns questionnaire: initial development and refinement.

OBJECTIVE: To develop a scale, designed for self-administration, to assess patient perceptions of drug therapy problems (DTPs).
DESIGN: Cross-sectional survey.
SETTING: California Central Valley. PARTICIPANTS: 200 community-dwelling adults taking at least one prescription medication. MAIN OUTCOME MEASURE: 78 items assessing patient perceptions of DTPs.
INTERVENTIONS: Self-administered questionnaire completed by study participants.
RESULTS: Based on a Medication Evaluation and Response Model proposed in this article, items were developed to assess patient perceptions about potential or actual DTPs. Scales for five of the seven problem domains specified a priori were reliable based on participant responses: Perceived Efficacy, Overmedication Concerns, Adverse Drug Reaction Concerns, Adherence Issues, and Knowledge. Barriers and Intrusiveness were eliminated from, the questionnaire because of weak factor loadings. After making changes in domain assignment and eliminating redundant and weak items, five items remained in each of the five reliable scales, with Cronbach's alpha values ranging from 0.76 to 0.82. Each of the five scales was significantly associated with patient satisfaction with their medications. Individuals who reported fewer DTPs expressed greater overall satisfaction with their medications. In a forward stepwise regression analysis, four of the five scales exhibited independent associations with medication satisfaction, explaining 58.0% of the total variance in satisfaction [F(4,178) = 61.48, P < .0001]. Only the Knowledge scale failed to exhibit an independent association with satisfaction.
CONCLUSION: The findings from this initial stage of scale development are encouraging. The association between the scales and medication satisfaction suggests that the scales may be useful in learning more about those factors that influence how patients evaluate their medications.