Factors Associated with Adherence to Medication Regimens in Older Adults in Northern Portugal

Population aging is accompanied by a rise in the prevalence of chronic pathologies. This, in turn, leads to an increased need for medication and, consequently, challenges in adhering to therapeutic regimens [1]. Polypharmacy, common among older adults, elevates the complexity and risk of drug interactions [2,3], making the control of medication adherence a priority in elderly healthcare. Against this backdrop, the present study aimed to: (i) assess adherence to medication regimens in the elderly population of a municipality in Northern Portugal; (ii) identify the relationship between sociodemographic and clinical variables and adherence; and (iii) analyze the relationship between adherence and the target population’s degree of dependency.

Aging is a universal and complex process, carrying biopsychosocial implications and a significant impact on global demographics [4,5]. In Portugal, the aging index has been on the rise, with projections indicating a continuous growth of the older adult population and an increase in life expectancy [6,7]. The World Health Organization (WHO) defines older adults as individuals aged 65 and above in developed countries [8], emphasizing the importance of promoting healthy aging focused on preserving physical and mental capabilities (WHO, 2015) [9]. Polypharmacy, defined as the use of multiple medications, is a prevalent reality among older adults, especially in contexts of multiple pathologies and prescriptions [1,3]. This situation increases the risk of nonadherence and adverse reactions, negatively impacting the quality of life and independence of older adults [1,2]. Adherence to the therapeutic regimen, defined by the WHO as the extent to which a patient’s behaviour aligns with medical instructions [10], is crucial for treatment effectiveness. Non-adherence is recognized as a global public health problem, linked to increased morbidity and mortality [11].

Several factors influence adherence, including:
i. Socioeconomic and healthcare system factors: Barriers such as inadequate healthcare systems, limited consultation frequency, and lack of follow-up can compromise adherence [2,12].
ii. Individual patient factors: Age, education level, selfperception of health, cognitive and functional difficulties, as well as a lack of understanding about medications, are decisive [1,12,13]. Discontinuing treatment due to symptom improvement or self-medication are common behaviors that compromise adherence [2].
iii. Complexity of the therapeutic regimen: The high number of medications, associated costs, and complex instructions can hinder compliance [2,12].
iv. To improve adherence, it is essential to identify the causes of non-compliance and simplify medication, adjusting therapeutic formulations to the user’s physical difficulties [1]. Clear and objective communication about the regimen, provision of written instructions, and the use of medication organizers, combined with continuous monitoring by healthcare professionals and the involvement of family members or caregivers, are crucial strategies for promoting effective adherence [1].

This study employed an observational, descriptive, and analytical approach, with a cross-sectional cohort design and a quantitative paradigm. The study population comprised individuals aged 65 and older residing in a municipality in Northern Portugal, totalling 8205 people. Non-probability convenience sampling was used, selecting 400 available and voluntary individuals. The sample size was adjusted to 382 individuals based on data from the National Institute of Statistics (INE, 2016) [7]. Inclusion criteria included: Age 65 or older, undergoing pharmacological treatment, oriented in time and space, and providing consent to participate. The exclusion criterion was the presence of aphasia or diction disorders. Data were collected between May 20 and September 20, 2017, using a structured questionnaire with three parts: (i) sociodemographic and clinical characterization; (ii) assessment of medication adherence using the Medication Adherence Scale (MAT); and (iii) assessment of the degree of functionality in basic Activities of Daily Living (ADLs) using the Barthel Index. Statistical analysis was performed using SPSS (Statistical Package for the Social Sciences), version 21.0. Absolute and relative frequencies, mean, standard deviation, and median were used for descriptive analysis. For analytical assessment of adherence, the chi-square test was applied to evaluate the independence of variables, considering test conditions (sample>20, expected frequency>1, and 80% of expected frequencies >5). To compare therapeutic adherence with the mean Barthel score, the non-parametric Mann-Whitney test was used, given the non- normality of distributions confirmed by the Kolmogorov-Smirnov test. A significance level of 5% was adopted. All ethical requirements for conducting scientific studies were adhered to.

The sample of 400 older adults ranged in age from 65 to 98 years (mean 75.33±7.34 years). The majority were female (57.75%), married or in a common-law union (62.75%), resided in a rural area (64.75%), had completed primary education (65.25%), lived with their spouse (61.50%), did not receive home support (73.25%), and had a monthly income between €351 and €550 (37.75%). A total of 1102 pathologies were identified. The most frequent were hypertension (26.13%), affecting 72.00% of respondents; dyslipidemia (18.06%), in 49.75%; and cardiovascular diseases (11.16%), in 30.75%. The average number of diseases per respondent was 2.94±1.52. Regarding medication, 52.75% took up to four medications, and 40.50% took between five and nine. The average daily intake was 4.7±2.73 medications.

Concerning medication management, 58.25% stated they never needed guidance in preparing their medication, but 20.00% always did. When in doubt, 49.3% turned to family members and 40.25% to healthcare professionals. The majority (81.00%) did not substitute their medication, but among those who did (n=76), 61.82% used homemade teas. Most respondents rarely (37.75%) or never (29.75%) forgot to take their medication and did not stop medication because they felt better (58.50%) or worse (59.00%). It was found that 82.75% (n=331) of respondents adhered to their therapeutic regimen, while 17.25% (n=69) were non-adherent. In terms of functionality in ADLs (Barthel Index), 87.00% (n=348) were independent.

Variable cross-tabulation revealed:
i. Adherence to therapy was not significantly associated with sex, age group, marital status, place of residence, cohabitation with a spouse, or monthly income. Although the percentage of adherents decreased with increasing age, this association was not statistically significant.
ii. Adherence to therapy was significantly associated with educational qualifications (p<0.05), with illiterate individuals showing the lowest percentage of adherence (68.42%) and those with higher education showing the highest (91.30%).
iii. Adherence to therapy was significantly associated with whether the individual received support (p<0.05), with those receiving support showing poorer adherence outcomes (73.83% adherent vs. 86.01% of those not receiving support).
iv. Adherence to therapy was not significantly associated with the number of diseases or the number of daily medications.
v. Adherence to the therapeutic regimen was significantly associated with the need for guidance in preparing medication (p<0.05). Those who never needed guidance showed higher adherence (90.13%), while those who “sometimes” or “always” needed guidance showed 70.11% and 75.00% adherence, respectively.
vi. Adherence to the therapeutic regimen was significantly associated with medication alteration (p<0.05), with 88.89% of those who did not substitute medication being adherent, compared to 56.58% of those who did.
vii. Adherent respondents showed a significantly higher mean Barthel Index (95.03±15.17 points) compared to non-adherent users (88.70±24.46 points), with a p-value of 0.003 (Mann- Whitney test), indicating a statistically significant association between adherence and functionality.

This study evaluated medication regimen adherence in 400 older adults in Northern Portugal, revealing a sociodemographic and health profile similar to that found in other regional studies, such as Marcos [2] in Macedo de Cavaleiros, which also identified a predominance of women and similar average ages, consistent with INE data (2016). Although both studies indicated a majority of older adults in rural areas, the present study identified a significantly lower level of illiteracy (14.25% vs. 44.70% in Marcos, 2014), suggesting greater access to basic education in our study population. One of the most notable findings of this study was the high rate of therapeutic regimen adherence (82.75%), sharply contrasting with Marcos [2] study, where only 19.10% of older adults were considered adherent. This striking discrepancy might be attributable to methodological variations in adherence assessment [14] criteria in the current study) or to differences in the characteristics of the populations and healthcare contexts of the respective municipalities..

When analyzing the relationship between adherence and sociodemographic variables, it was found that sex, age group, marital status, place of residence, cohabitation, and monthly income were not statistically significantly associated with adherence. While a trend of decreasing adherence with increasing age was observed in this study, aligning with others [1,12,14], this association was not statistically significant. However, educational level demonstrated a significant association, with lower adherence among illiterate individuals, a finding corroborated by Marcos [2], who highlights difficulty in understanding prescriptions as a limiting factor. Furthermore, the absence of home support was significantly associated with higher adherence, which diverges from Marcos’s [2] study where adherence was higher with support.

In terms of clinical variables, adherence was not significantly associated with the number of diseases or daily medications, though a tendency for decreased adherence with an increased number of pathologies and drugs was observed. This is consistent with literature suggesting that polypharmacy can hinder adherence [3]. Crucially, the need for guidance in preparing medication showed a statistically significant association with adherence: older adults who never needed help exhibited higher adherence (90.13%). This finding aligns with [2,13], underscoring that functional autonomy in medication management is an important predictor of adherence. The substitution of medication also proved to be a significantly associated factor with lower adherence, with individuals who altered their prescribed regimen showing poorer outcomes, emphasizing the importance of education on the risks of self-medication and adherence to the original regimen. Finally, the analysis of functionality demonstrated a statistically significant association between adherence to the therapeutic regimen and the Barthel Index, with non-adherent individuals having, on average, a lower level of functionality. This result corroborates Marcos [2], suggesting that functional dependency can be a barrier to adherence, and conversely, non-adherence can worsen health status and functionality.

This study contributed to the understanding of medication regimen adherence in older adults in Northern Portugal, identifying sociodemographic and clinical factors associated with varying levels of adherence. The results indicated that the majority of participants (82.75%) demonstrated adherence. The findings suggest that higher education is associated with better adherence, and that independence in medication preparation and not substituting prescribed drugs are significant predictors of adherence. Furthermore, non-adherent older adults exhibited lower functionality, as evidenced by a lower Barthel Index. While trends were observed, sex, age, marital status, place of residence, cohabitation, monthly income, number of diseases, and number of medications were not statistically associated with adherence in this study.

Non-adherence to therapeutic regimens is a global public health problem that contributes to disease exacerbation and increased healthcare costs [15]. Understanding the factors influencing adherence in older adults is fundamental for developing effective strategies. The discoveries from this study provide crucial support for healthcare professionals to adapt their interventions more precisely and personally. Such strategies could range from individualized prescription adjustments to involving family members and caregivers, aiming to mitigate factors contributing to non-adherence and promoting treatment continuity and an improved quality of life for older adults [1]. This study’s limitation was the use of a convenience sample. Further investigation through a longitudinal study is recommended to assess the long-term impact of health interventions and deepen the understanding of the complex relationship among aging, functionality, and therapeutic regimen adherence.