The effects of adherence to non-steroidal anti-inflammatory drugs and factors influencing drug adherence in patients with knee osteoarthritis

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SCIENCE
The effects of adherence to non-steroidal anti-inflammatory drugs and factors influencing drug adherence in patients with knee osteoarthritis
Key Take-Away: 

The study indicates that patients with better adherence to NSAIDs showed better outcomes compared to those with the poor adherence.

The major reasons for morbidity, disability, and loss of function mainly in elderly people is Knee osteoarthritis (OA). It significantly affects the quality of life of the patients with persisting disease. OA is likely to become the 4th prime reason of global disability by 2020.

ABSTRACT: 
Background: 

The major reasons for morbidity, disability, and loss of function mainly in elderly people is Knee osteoarthritis (OA). It significantly affects the quality of life of the patients with persisting disease. OA is likely to become the 4th prime reason of global disability by 2020.

The medications for OA like simple analgesics (acetaminophen and NSAIDs) mainly provides symptomatic relief. Currently there are no effective medications to slow down the progression of OA. However, NSAIDs do not prevent the disease progression, but certainly helps in relieving pain and improves quality of life by blocking nociceptors. The adherence to arthritis medications is known to be low. Dosing frequency, pain and self-efficacy levels, and physician trust are the usual factors in adherence to OA with other rheumatoid diseases. One of other studies had recently found that side effect, out of pocket costs, mode of action, and treatment schedule also poses a considerable effect on the choice to continue medication.

Rationale behind research

  • There is little information about OA patient’s treatment adherence and differences resulting from NSAIDs.

  • Therefore, this study was conducted to investigate the drug adherence and patient reported outcomes.

Objective

 The objectives of this study were:

  • To assess the differences in patient reported outcomes according to the drug adherence.

  • To evaluate the factors affecting them.

Methods: 

 

NOTE: This was a multi-center, prospective and observational study.

  • Study outcomes

  • Patients filled out the questionnaires on the first visit (baseline) and second visit (follow-up) after taking medication (non-selective cyclooxygenase inhibitor or selective cyclooxygenase-2 inhibitor) for 3 weeks. The demographics were collected on the first visit and pain was measured using pain Numeric Rating Scale (NRS) (0 low, 10 high). Joint function was measured by the Korean version of Knee injury and Osteoarthritis Outcome Score (KOOS-K).

  • KOOS-K consists of 5 subscales: Pain, other Symptoms, Activities of Daily Living (ADL), Function in sport and recreation (Sport/Rec), and knee related Quality of life (QOL). Standardized answer choices are given (5 Likert boxes) and each question gets a score from 0 to 4. A normalized score (100 indicating no symptoms and 0 indicating extreme symptoms) is calculated for each subscale. QOL was measured by EQ-5D (Euro Quality of Life-Five Dimensions) and EQ-VAS (Euro Quality of Life-Visual Analogue Scale).

  • After 3 weeks, pain NRS, KOOS-K, EQ-5D, and EQ-VAS were measured like the first visit, and treatment adherence was investigated. Patients responded to questionnaire. In the question about treatment adherence, the patients were designated as ‘Adherent group’, and as ‘Non-adherent group’ based on their answers.

  • Time Points: Baseline and after 3 weeks.

Results: 

 

Baseline: In comparison between the adherent and non-adherent group, there was difference in the distribution of age group whereas, other factors did not show significant differences in their distribution.

Outcomes

  • For the reasons for no strict adherence, 464 patients answered the question (355 patients chose one answer, 93 chose 2 answers, 14 chose 3 answers, and 2 chose 4 answers). The top three reasons were: “My symptom has gone better” (21.5%); “Osteoarthritis medication is thought to be only a pain relief” (16.4%); and “It causes indigestion, discomfort, heart burn, and other GI events” (13.0%).

  • All clinical outcomes including pain NRS, KOOSK and EQ-5D were significantly improved at the follow-up compared to the baseline in total patients group, adherent group, and non-adherent group. Comparison of the clinical outcomes between the adherent group and non-adherent group showed no significant differences in any of the baseline variables except for pain NRS (6.1 ± 1.5 vs. 6.4 ± 1.6, P = 0.027), while, at follow-up, pain NRS (4.3 ± 1.9 vs. 4.9 ± 2.2, P = 0.003), KOOSK symptom (74.3 ± 16.7 vs. 71.6 ± 17.0, P = 0.048), KOOS-K pain (68.6 ± 16.4 vs. 64.9 ± 16.6, P = 0.005), and KOOS-K ADLs score (68.9 ± 16.4 vs. 64.8 ± 17.3, P = 0.003) were significantly higher in the adherent group than non-adherent group.

Figure1: Clinical outcomes of adherent group at baseline and after 3 weeks follow up

Figure2: Clinical outcomes of non-adherent group at baseline and after 3 weeks follow up

  • In logistic regression analysis identifying the factors that affect adherence, elderly patients (70-74 years old and 75-79 years old) and male patients were found to be more adherent, while educational status, frequency of daily NSAIDs administration, duration of knee OA, and other factors did not affect adherence.

Conclusion: 

In this study, both adherent and non-adherent groups showed significantly improved outcomes after 3 weeks of medication treatment, but most of the follow-up outcomes were significantly better in the adherent group as hypothesized. Of those factors affecting the adherence to NSAIDs, older patients and male patients showed better adherence, while educational status, frequency of daily NSAIDs administration did not show difference in adherence.

In this study, there was relatively high drug adherence with the patients group, which is inconsistent with the previous studies (approximately 10% of low adherence rate). The reasons for the relatively higher adherence in the present study may include: 1) Targeting relatively older patients 2) Studying a relatively short period compared to long-term treatment of OA or 3) that it was a self-survey study which could show a relatively higher adherence than monitoring study depending on the patients’ characteristics.

J Korean Med Sci 2016; 31: 795-800
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