Hypertension is one of the most pressing health problems in Korea. The prevalence of hypertension is as high as 24.6% of the Korean adult population, making it the most common chronic disease (Park et al., 2010). Hypertension is a major risk factor for cardiovascular and cerebrovascular diseases, which are the second and third leading causes of mortality in Korea (Statistics Korea, 2011). People with 10 mmHg higher systolic blood pressure (BP) or 20 mmHg higher diastolic BP have approximately a 100% higher risk of stroke or coronary artery than those with normal BP (Park et al., 2010). Therefore, one of the most effective ways to prevent cardiovascular and cerebrovascular diseases could be hypertension control.
There are many ways to control BP, such as exercise, dietary, and medication therapy (Yang et al., 2010). Among them, adhering to a therapeutic regimen of medication is considered to be the most effective way to control blood pressure (Baune et al., 2005; Krousel-Wood et al., 2005; Burnier, 2006). Some evidence in Korea suggests that properly adhering to a medication regimen can prevent adverse outcomes related to hypertension. A poor adherence group showed a 2.2 times higher risk of morbidity, including instances of nephropathy, cerebrovascular disease, and cardiovascular disease (Park et al., 2010). This group was also 2.4 times more likely to be hospitalized in a year (Jang et al., 2008) compared to a group showing better adherence.
To control BP is the most widespread program implemented by nurses at community health centers in Korea. Nurses are responsible for assessing medication-taking behavior (Ben-Natan & Noselozich, 2011) and play a main role in educating hypertensive patients to take medicine appropriately. This means that nurses are required to recognize factors associated with medication adherence to help patients with hypertension.
Several studies have been conducted on the topic of antihypertensive medication adherence in Korea (Jang et al., 2008; Park et al., 2008a,b; 2010). Although there are a variety of factors related to medication adherence, numerous factors were omitted in most studies. Only one study (Park et al., 2008b) explored multiple factors through using health insurance claims data, but it did not consider socioeconomic aspects such as education and per capita income. Studies in Korea also did not identify whether patients in fact took their medicine or not due to limitations related to health insurance claims data. Therefore, this study was designed to identify factors, including demographic, socioeconomic, and health-status variables associated with self-reported nonadherence to antihypertensive regimen.
Medication adherence refers to the extent to which a patient acts in accordance with the prescribed interval and dose of a dosing regimen. In this context, nonadherence means missing medication doses in the context of ongoing use (Cramer et al., 2008).
Adherence is determined by factors related to socioeconomic status, healthcare system, health condition, therapy, and patient-related factors (World Health Organization, 2003). Many studies consider demographic factors as distinct from socioeconomic factors (Lowry et al., 2005; Vawter et al., 2008; Braverman & Dedier, 2009; Friedman et al., 2010).
Gender, age, ethnicity, and residential area were included as demographic factors related to medication adherence in several studies. A few studies reported that it was more probable for males than females to show adherence (Degli Esposti et al., 2002; Park et al., 2008b), while females showed greater adherence to antihypertensive medication regimens in other studies (Jokisalo et al., 2002; Hyre et al., 2007; Friedman et al., 2010). Old age is associated with better adherence in studies conducted in Pakistan (Hashmi et al., 2007), Korea (Park et al., 2008b), the USA (Hyre et al., 2007) and Finland (Jokisalo et al., 2002). Persistence and adherence were both lower in urban residents compared with rural residents in Canada (Friedman et al., 2010), whereas metropolitan residents had higher adherence levels than rural residents in Korea (Park et al., 2008b).
Income, job type, insurance type, and education level as socioeconomic factors affect medication adherence as well. Adherence is increased in patients with higher incomes in Canada (Friedman et al., 2010), and groups composed of those in lower economic classes showed lower adherence rates in Portugal (Santa-Helena et al., 2010) and in the USA (Vawter et al., 2008). Persons working in the unskilled labor market were less likely to adhere to an antihypertensive medication regimen (Santa-Helena et al., 2010). Individuals with low education attainment levels tend to report unintentional nonadherence (Lowry et al., 2005; Uzun et al., 2009).
A good relationship between patient and provider as a factor of the healthcare system improves medication adherence because healthcare professionals empower patients to become involved in their treatment (Fincham, 2007). As for factors of health condition, persons with disabilities, especially mobility and communication disabilities (Park et al., 2008a), depressive symptoms (Morris et al., 2006; Krousel-Wood et al., 2011), and mental function impairments (Vawter et al., 2008) showed inappropriate medication adherence behavior compared to those without such disabilities. In contrast, several studies found that medication adherence was better in patients with comorbidity as compared to those not showing comorbidity (Lagi et al., 2006; Shaya et al., 2009; Friedman et al., 2010).
With regard to factors of therapy, patients prescribed with angiotensin-converting enzyme inhibitors showed better adherence than those taking beta-blockers or diuretics (Fitz-Simon et al., 2005; Friedman et al., 2010), and an increase in the number of pills and the required frequency were related to nonadherence (Bangalore et al., 2007). Regarding patient-related factors, beliefs about medication were related to medication adherence (Gregoire et al., 2006; Lewis et al., 2010) and behavioral attitudes, perceived behavioral control, and subjective norms were positively related to intentions to self-administer medication in the elderly (Ben-Natan and Noselozich, 2011).