Background
Osteoarthritis (OA) is a musculoskeletal disease that causes chronic joint pain and reduced physical functioning. Often affecting knee joints, OA is the most common type of arthritis. By 2020, OA is predicted to become the fourth leading cause of disability globally.
Currently there is no known cure for OA, nor are there effective interventions to slow disease progression. Medication management is symptomatic, mostly with simple analgesics such as acetaminophen and non-steroidal anti-inflammatory drugs (NSAIDs). Increasingly, glucosamine sulfate (GS), is being used as a potential analgesic and disease-modifying agent. In Australia, GS is considered a dietary supplement and is purchased without prescription. Unlike other OA medications, the cost of GS is not subsidised by the Australian government.
As occurs with most chronic conditions, adherence to arthritis medications is low. Factors implicated in adherence to OA and other anti-rheumatic medications include dosing frequency, pain and self-efficacy levels, and physician trust. Intentional non-adherence, that is deliberate decision-making about the use of OA medications, is reported in the literature. In particular, intentional under-dosing and rationing of analgesics occurs. Such decisions appear to be driven by factors including the fear of addiction, previous medication effectiveness, and the burden and illness stigma represented by increased pill loads. For NSAIDs specifically, a high level of trust in the prescribing physician influences decisions.
Primarily, qualitative methods have been used to investigate medication decisions in OA. Although a limited number of studies have used quantitative techniques, the extent to which individuals' trade off one treatment factor for another in decision-making about medication adherence has not been extensively studied. Physicians and policy makers could use such information to tailor adherence support to match the preferences of OA patients.
Discrete choice experiment (DCE) is a survey methodology that can be used to elicit preferences to quantitatively determine the relative influence of factors on decision-making with regard to medication adherence. Developed initially in marketing research, DCEs are used increasingly in health economics and are considered state-of-the-art in this field to elicit preferences for health services. To date, three DCE studies have explored patient preferences for treatment factors associated with knee and/or hip osteoarthritis. In these studies, both efficacy and the gastrointestinal side effects of treatment significantly impacted patient choice. However, other factors potentially relevant to OA medication adherence were not consistently included. In particular, neither the cardiovascular, hepatic or renal side effects nor the chronic or intermittent treatment scheduling of OA therapy were incorporated. Additionally, preferences about acetaminophen were omitted from one study.
In Australia, the LEGS (Long-term Evaluation of Glucosamine Sulfate) study was a two-year, double-blind, placebo-controlled randomised clinical trial aiming to evaluate whether the dietary supplements, GS and/or chondroitin can limit or reduce structural disease progression (cartilage loss), whilst providing pain relief, in people with osteoarthritis of the knee (ClinicalTrials.gov Identifier NCT00513422). Throughout the LEGS study, as is typically the case in clinical trials, a number of trial-related factors could potentially affect treatment decisions and adherence outside of the trial setting. Firstly, as a part of the study protocol, participants were regularly encouraged to persist with the study treatments, even in the absence of knee pain. Furthermore, study treatments were mailed to participants and provided free of charge. The use of DCEs potentially helps understand the effects of such factors, including out-of-pocket costs, beyond the clinical trial setting.
The Medication Decisions in Osteoarthritis Study (MEDOS) aimed to estimate the relative influence of different medication-related factors and respondent characteristics on decisions to continue medications among people with symptomatic OA.