Adherence to treatment in patients with type 2 diabetes

Journal of Diabetes Nursing, Nov-Dec, 2004 by Marie Clark

Introduction

Non-adherence to medication is potentially one of the most serious problems facing diabetes care delivery, particularly in type 2 diabetes. This article, the first of three, looks at the many psychosocial factors that affect how people with diabetes manage their condition, and possible reasons for low adherence, such as rational but mistaken beliefs about the medication. Health psychology models and possible strategies to improve adherence are discussed in relation to diabetes. The need for more research into behavioural aspects of diabetes management in order to tackle adherence is also acknowledged.

Adherence has been defined as the extent to which individuals follow the instructions they are given for prescribed treatments (Haynes et al, 2002). Thus, if a person is prescribed an antibiotic to be taken as one tablet four times a day for a week for an infection, but takes only two tablets a day for five days, their adherence would be (10/28=) 36%. The term adherence is intended to be non-judgmental--a statement of fact rather than of blame of the individual, the prescriber, or the treatment. Compliance and concordance are synonyms for adherence. Adherence to treatment is a complex health behaviour. Problems identified include the individual's failing to initiate therapy, underusing or overusing a treatment, stopping a treatment too soon, and mis-timing or skipping doses (e.g. Ley and Llewelyn, 1995).

Non-adherence to treatment is a formidable problem, leading as it often does to a reduction in or lack of treatment benefits, extra visits to the doctor, unnecessary hospitalisation, decreased satisfaction with medical care and sometimes further medication prescription. This can be extremely costly, not only to the individual involved, but also to the healthcare system as a whole. Non-adherence persists regardless of the medical condition being treated and exists across socioeconomic and geographic boundaries (Myers and Midence, 1998).

Measurement

Since there is no gold-standard method of measuring adherence, one of the main difficulties in managing low adherence is a lack of accurate and affordable measures. Clinicians must frequently rely on their own judgement, but unfortunately demonstrate no better than chance accuracy in predicting the adherence of their patients (Stephenson et al, 1993), even among those for whom they feel confident about their predictions (Gilbert et al, 1980). Based on a systematic review of studies of adherence measures (Stephenson et al, 1993), asking non-responders about their adherence will detect more than 50% of those with low adherence, with a specificity of 87% (Haynes et al, 2002). Even when people indicate that they have not taken all their medications as prescribed, their estimates usually substantially overestimate their actual adherence. The key validated question is 'Have you missed any pills in the past week?' and any indication of having missed one or more pills signals a problem with low adherence.

Overestimation of adherence by patients is difficult to study and is presently poorly documented. Reasons for overestimation could include difficulty recalling the details of medication taking, attempting to please practitioners, to avoid confrontation, or a combination of these factors.

Other practical measures to assess adherence include watching for those who do not respond to increments in treatment intensity and people who fail to attend appointments. More objective measures of adherence can also be of use when available, for example drug levels in the body (blood and urine), but these measures are often subject to wide individual variations in drug absorption, distribution and metabolism. Moreover, this method is intrusive and not necessarily acceptable to everyone, which might distort the sample of people available for assessment. It is also expensive, and not available for all drugs used.

Finally, medication monitors, which are electronic measurement devices used to record for example the opening of a bottle to remove medication, can provide both frequency and patterns of use but these are expensive and cumbersome for routine practice.

Various measures of adherence are listed in Table 1.

Adherence in diabetes

The issue of non-adherence to treatment is particularly pertinent in diabetes care since increasing numbers of large randomised controlled trials (for example the UK Prospective Diabetes Study, 1998) have provided unequivocal evidence of the benefit of glycaemic control through the use of oral hypoglycaemic agents (OHAs) to prevent progression of microvascular complications, and lowering of blood pressure and lipids with further medication to reduce macrovascular disease in people with type 2 diabetes.

Accordingly, considerable effort is now being devoted to ensuring that those with diabetes are prescribed appropriate medication. The National Service Framework for diabetes in England and Wales (Department of Health, 2001) for example, sets as its standard that all individuals with diabetes should have an assessment of glycaemic control, blood pressure and cardiac risk and receive the appropriate medication to reduce them. The consequence of such a policy is that most patients with type 2 diabetes will end up being prescribed at least five, and often more, different types of medication. Indeed, many who also have active ischaemic heart disease are already prescribed over nine different tablets, the rationale being that the cumulative effect of this drug cocktail will be equivalent to the sum of the benefits demonstrated in separate trials.