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Child Psychiatrist /Adult Psychiatrist

Which Factors Predict Primary Nonadherence to Medications?

A medicine box from Monday to Sunday.

Poor adherence to medication is a real challenge in healthcare. Despite evidence indicating therapeutic benefit from adhering to a prescribed regimen, it is estimated that around 50% of patients around the world don't take their medication as it is prescribed — and some simply don't take them at all.

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

Growth in electronic prescribing has partially resolved this issue, and new measures have emerged linking electronic prescribing databases with pharmacy dispensing databases. A study conducted in a network of primary care services in Canada has sought to identify the predictive factors of primary nonadherence and which drugs could be at greatest risk of primary nonadherence when prescribed by a primary care physician.

Adherence Measures Measuring medication adherence is challenging but can be done using various approaches. It comprises the following approaches:

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

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

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

Determining Factors A myriad of factors contributes to poor medication adherence. Some are related to patients (eg, suboptimal health literacy and lack of involvement in the treatment decision-making process), others are related to physicians (eg, prescription of complex drug regimens, communication barriers, ineffective communication of information about adverse effects, and provision of care by multiple physicians), and still others are related to healthcare systems (eg, office visit time limitations, limited access to care, and lack of health information technology). Primary Nonadherence The literature has reported substantial variation in primary nonadherence, with estimates ranging from as little as 1.9% of incident prescriptions never filled to as much as 75%. A study carried out 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, using data from 150,565 new prescriptions issued to 34,243 patients.

Rate of Nonadherence

The following patterns of primary nonadherence 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 among patients of both sexes.

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

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

Predictors of Nonadherence

The odds of primary nonadherence exhibited the following patterns:

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

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

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

In conclusion, in a general medicine setting, the odds of primary nonadherence were higher for younger patients, those who received primary care services from female prescribers, and older patients who were prescribed more medications. Across therapeutic categories, the odds of primary nonadherence were lowest for cardiovascular system agents and highest for dermatological agents.

To date, the lack of a standardized terminology, operational definition, and measurement methods of primary nonadherence has limited our understanding of the extent to which patients do not avail themselves of prescriber-ordered pharmaceutical treatment. These results reaffirm the need to compare the prevalence of such nonadherence in different healthcare settings.


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