Which factors predict primary non-adherence to medication?

Which factors predict primary non-adherence to medication?

Poor medication adherence is a real challenge in healthcare. Despite evidence suggesting therapeutic benefit from adherence to a prescribed regimen, it is estimated that approximately 50% of patients worldwide do not take their medications as prescribed—and some simply do not take them at all.

Non-adherence to medication can be primary or secondary. Primary medication non-adherence (PMN) occurs when a patient is prescribed a new medication, but the patient does not receive the medication or an appropriate alternative within an acceptable time after it is prescribed. Secondary nonadherence measures prescription refills among patients who previously filled their first prescriptions. Most medication adherence research to date has focused on secondary nonadherence, PMN has been identified as a major research gap.

The rise of e-prescribing has partly solved this problem, and new arrangements have emerged linking electronic prescription databases with pharmacy dispensing databases. A study conducted in a network of primary care services in Canada sought to identify predictive factors of primary nonadherence and which medications might have the greatest risk of primary nonadherence when prescribed by a primary care physician.

Compliance measures

Measuring medication adherence is challenging, but can be done through a variety of approaches. It includes the following approaches:

  • subjective measures obtained by asking patients, family members, caregivers, and physicians about the patient’s medication use

  • objective measures obtained by counting pills, examining pharmacy refill records, or using electronic medication event tracking systems

  • biochemical measurements obtained by adding a nontoxic marker to a medication and detecting its presence in blood or urine, or by measuring serum drug levels.

Determining factors

A myriad of factors contribute to poor adherence to treatment. Some are patient-related (eg, suboptimal health literacy and lack of involvement in the treatment decision-making process), others are related to physicians (eg, prescribing complex drug regimens, communication barriers, ineffective communication of information about adverse effects, and the provision of care by multiple physicians), and still others are related with healthcare systems (e.g. limited office visit times, limited access to care and lack of healthcare information technology).

Primary nonadherence

The literature reports substantial variation in primary nonadherence, with estimates ranging from as low as 1.9% of cases never completed to as high as 75%.

A study using data from a primary care network in British Columbia, Canada, estimated the rate of primary nonadherence, defined as failure to dispense a new medication or its equivalent within 6 months of the prescription date, based on data from 150,565 newly filled prescriptions. to 34,243 patients.

Degree of non-stickiness

The following patterns of primary non-adherence were observed:

  • Primary nonadherence was lowest for prescriptions issued by prescribers aged 35 years or younger (17.1%) and male prescribers (15.1%).

  • It was similar in patients of both sexes.

  • It was lowest in the oldest subjects and decreased with age (odds ratio). [OR]0.91 for each additional 10 years).

  • It was highest for drugs prescribed mostly as needed, including topical corticosteroids (35.1%) and antihistamines (23.4%).

Predictors of nonadherence

The probability of primary non-adherence showed the following patterns:

  • lower for prescriptions issued by male physicians (OR, 0.66)

  • significantly higher compared with anti-infectives for dermatological agents (OR, 1.36) and lowest for cardiovascular agents (OR, 0.46).

  • lower across therapeutic drug categories (excluding respiratory agents) for those 65 years and older than for those younger than 65 years.

In conclusion, in a general practice setting, the likelihood of primary nonadherence was higher in younger patients, those receiving primary care services from female prescribers, and older patients who were prescribed multiple medications. In all therapeutic categories, the probability of primary nonadherence was lowest for cardiovascular agents and highest for dermatological agents.

Until now, the lack of standardized terminology, operational definitions and methods of measuring primary nonadherence has limited our understanding of the extent to which patients do not use prescribed pharmaceutical treatment. These results reaffirm the need to compare the prevalence of such nonadherence in different healthcare settings.

This article was translated from Univadis Italy, which is part of the Medscape professional network.

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