Determinants of different types of medication non-adherence in cholesterol lowering and asthma maintenance medications: A theoretical approach

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Abstract

Objective

To quantify and compare the determinants of different types of medication non-adherence in cholesterol lowering and asthma maintenance medications using a theoretical approach.

Methods

Study design was online cross sectional survey. A conceptual framework was developed using Andersen's Behavioral Model and Leventhal's Common Sense Model to understand the determinants of medication non-adherence. Regression analyses were used to test the models for predicting non-adherence.

Results

The models based on Andersen's Behavioral Model and Leventhal's Common Sense Model were significant. While predisposing factors such as treatment convenience and beliefs in medications were significant in cholesterol lowering medications, need factors such as illness perceptions and disease severity were significant in asthma maintenance medications. Among the enabling factors, self efficacy was a significant predictor in both cholesterol lowering and asthma maintenance medications.

Conclusion

Different determinants explained different types of non-adherence and suggest the need to consider different types of non-adherence for different medications as well as different determinants for each type of non-adherence.

Practice implications

Identifying determinants of different types of non-adherence can help health care professionals develop targeted interventions which can be more successful than the current model of single and generalized interventions to reduce non-adherence.

Introduction

Medication non-adherence, the extent to which a person's behavior does not coincide with medical or health advice, is a public health issue estimated to cost $100 billion and contributes to nearly 125,000 deaths each year in the United States [1]. There is a wide variation in non-adherence rate, varying anywhere from 8% in contraception to 71% in arthritis [2]. While the non-adherence rate with medications for acute disease conditions usually ranges from 23 to 40%, that with long term or chronic medications ranges from 6 to 67% [3].

Research on medication non-adherence has developed a variety of intervention strategies to improve adherence. These interventions used either alone or in combination include providing more instructions for patients, increasing communication and counseling between patient and health care provider, increasing the convenience of care provided, involving patients more in their care, providing reminders, and reinforcement or rewards [4]. In 2003, Peterson's meta-analytic review of interventions to improve adherence reported an improvement of only 4–11% [5]. McDonald et al. concluded that though the current intervention programs led to improved adherence and treatment success, the interventions were usually complex, labor-intensive, and not predictably effective [4]. In addition, van Eijken et al.’s systematic literature review of interventions demonstrated that multifaceted and tailored interventions were more effective in improving medication adherence than single and generalized interventions [6].

Interventions may not be as robust as anticipated because the majority of studies examining medication non-adherence have considered it as a single entity without differentiating between the types of non-adherence such as intentional and unintentional non-adherence. As well, the interventions used are not explicitly matched or targeted towards the reasons underlying each type of non-adherence [7], [8], [9], [10]. Studies have often grouped people with varying reasons for non-adherence and used single or combination intervention strategies [11], [12], [13], [14]. However, studies by Donovan, Wore, and Lehane demonstrated the need to separate the different types of non-adherence to understand them better and to develop intervention strategies to improve adherence [15], [16], [17]. Logically, different interventions are needed for non-adherence arising from different reasons. The intervention needed for a patient who is non-adherent thinking that medications are not needed will be different from another patient who is non-adherent due to the complexity of the regimen. In order to provide multifaceted and tailored interventions, it is important to understand the various types of non-adherence and the variables that determine each type of non-adherence.

In addition to understanding the various types of non-adherence, it is also important to know that non-adherence varies by different medications. The majority of studies on medication non-adherence have looked at one medication at a time or all medications combined [18], [19], [20], [21], [22]. In these studies, the patient is often considered the unit of analysis, thus avoiding the possibility that a patient while being adherent with one medication can be non-adherent with another medication. Krigsman and Nilsson examined medication non-adherence across two conditions, COPD and diabetes, concomitantly [23]. Refill adherence patterns were different for both medications, but they failed to provide any reasons for the difference in non-adherence pattern between medications. An earlier study by the authors also confirmed these observations in cholesterol and asthma maintenance medications [24]. Again, acknowledgement of different types of non-adherence within the same individual for different medications suggests interventions must be tailored [6].

In conclusion, there is a wide variance in the non-adherence rates across medications. This variance may arise due to different reasons of medication non-adherence for different medications. However, non-adherence is usually considered as a single entity with little differentiation between the types of non-adherence and using patients as the unit of analysis. Thus, there is a need to understand or define the different types of non-adherence so that appropriate intervention strategies can be developed. The aim of this study was to quantify and compare the determinants of different types of medication non-adherence in cholesterol lowering and asthma maintenance medications using a theoretical approach.

Section snippets

Research design

A cross sectional survey was used for this study. Data were collected using an internet based survey administered by Harris Interactive (HI) who maintains a panel of individuals who have opted to be invited to participate in online surveys. The study population was adult US individuals who were members of the HI panel. The inclusion criteria for participants in the study were (1) 18 years of age or older, (2) members of HI panel, (3) taking either cholesterol lowering medications or asthma

Results

The survey was conducted in December 2007 and the response rate was 31%. A total of 840 completed responses were collected. There were 420 completed responses for cholesterol lowering medications and 399 for asthma maintenance medications. The total completed responses are more than the number of individuals combined on cholesterol lowering and asthma maintenance medications because there were some individuals who were on both medications and answered both surveys.

In the sample with individuals

Discussion

The study demonstrates the complexity of medication non-adherence by quantifying the determinants of different types of medication non-adherence. These results suggest we need to consider different types of non-adherence for different medications as well as different determinants for each type of non-adherence. These results, even with a new self reported non-adherence scale, call into question our consideration of medication non-adherence as a single concept or behavior and reject developing

Role of funding source

None.

Conflict of interest

None.

Acknowledgements

This paper was developed from the primary author's dissertation from the University of Iowa. We would like to acknowledge Harris Interactive® in collecting the data as well as the dissertation committee members for their valuable suggestions.

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