Lewis, Lisa M. PhD, RN
Hypertension (HTN) is a huge public health problem and a major contributor to health disparities between blacks and whites in the United States.1 Hypertension has been diagnosed in approximately 41% of blacks.2 Blacks commonly develop HTN at a younger age, are less likely to have their blood pressure (BP) under control, and bear a disproportionate burden of cardiovascular morbidity and mortality outcomes associated with HTN when compared with their white counterparts.3 Consequences of these disparate outcomes include a 30% greater rate of nonfatal stroke, 80% greater rate of fatal stroke, and 420% greater rate of end-stage kidney disease for blacks.3 Given that these racial disparities in the consequences of HTN control account for nearly 8000 preventable and excess deaths annually among blacks, a compelling goal is to increase BP control in blacks.4
Increasing BP control requires a comprehensive approach that includes patient adherence to antihypertensives.5 To achieve better BP control in blacks, optimal medication adherence must be achieved.6,7 Unfortunately, medication nonadherence rates are high among blacks, and there is indication that nonadherence rates for blacks are worse when compared with whites.8–15 If we are going to increase medication adherence among blacks with a diagnosis of HTN, then we must first understand the factors that are associated with adherence. As such, the purpose of this article was to critically review the literature on factors associated with medication adherence in hypertensive blacks. No such systematic review appears to have been previously conducted.
Medication Nonadherence Rates Are Lower Among Hypertensive Blacks
Medication adherence rates among hypertensive patients are difficult to document because of the different operational definitions used by researchers. However, it is estimated that only 51% of patients with HTN adhere to their antihypertensive medications.16 Furthermore, several research studies have confirmed that adherence rates are lower for blacks. Using self-report measures, Krousel-Wood and colleagues17 found that a significantly higher percentage of blacks had low antihypertensive medication adherence when compared with blacks in a cohort study of 2180 older adults 65 years or older (18.4% vs 12.3%; P < .001). Also using self-report measures, Ndumele and colleagues13 found that blacks were 452% less likely to adhere to their antihypertensive medications in a study examining disparities in adherence to hypertensive care among 141 adults followed up in an urban care setting (P = .006). These findings have been confirmed among patients followed up in the Veterans Affairs (VA) healthcare system.18
More objective measures of adherence, such as pharmacy refill records, have also confirmed lower adherence rates for hypertensive blacks. In a study examining predictors of antihypertensive therapy in 568 Medicaid patients, researchers found that blacks had a lower adherence rate when compared with whites (19.69% vs 36.11%; P = .001) using pharmacy refill data.14 In a longitudinal cohort study examining racial differences in antihypertensive medication adherence, Dickson and Plauschinat9 reported that blacks were less adherent than were whites (55% vs 61%; P < .05). Also using pharmacy refill data, Charles and colleagues8 reported a lower adherence rate for blacks (59.9% vs 74.1%; P < .001) in a study examining racial differences in adherence to cardiac medications among 5269 male veterans followed up in a VA healthcare system. These findings have been confirmed by other researchers.19,20
In summary, rates of medication adherence are worse for hypertensive blacks despite the method used to measure adherence. Furthermore, these lower rates of adherence exist even in the VA healthcare system where access to care is generally equal regardless of income or race. What is still not clear, however, are the factors associated with adherence for blacks. A reason that these factors remain unknown could be that researchers have not systematically examined factors affecting adherence in hypertensive blacks. This critical review of the literature on factors affecting medication adherence in hypertensive blacks will address this gap in the literature.
The current review is guided by the research question: What are the factors associated with antihypertensive medication adherence in blacks? Because no model of medication adherence for HTN has been published, the 5 interacting dimensions adherence model from the World Health Organization’s (WHO’s) report on adherence were used to guide this literature review16: (1) social/economic factors, (2) health team and system-related factors, (3) therapy-related factors, (4) condition-related factors, and (5) patient-related factors (Figure).
FIGURE. World Health...Image Tools
The MEDLINE, CINAHL (Cumulative Index to Nursing and Allied Health), and PsycINFO databases were searched using the terms “medication adherence,” “medication compliance,” “hypertension,” and “blacks.” Additional articles were retrieved by reviewing the references of the selected literature. Qualitative or quantitative studies that identified barriers and facilitators of antihypertensive medication adherence in blacks were the major focus of this literature review. Studies that examined racial disparities in medication adherence and reported on factors associated with adherence in blacks were included in this systematic literature review. For quantitative studies, antihypertensive medication adherence needed to be included as a primary or secondary outcome. Dissertations and articles not in English were excluded. The majority of articles screened and excluded were quantitative studies that did not measure medication adherence as a study outcome (Table).
A total of 67 citations from the databases were identified. After screening the abstracts for their relevance and eliminating duplicate records, 15 articles were reviewed. Another 3 articles were added after reviewing the references of the selected literature. The final number of articles included in this review was 18.
The systematic review identified 11 studies in which social/economic factors from the WHO adherence model16 were examined for their association with medication adherence among blacks.
Nine studies examined the association between age and medication adherence among blacks with a diagnosis of HTN. Study findings were inconsistent. Four cross-sectional studies found an association between age and antihypertensive medication adherence.21,31,33,34 Interestingly, the results of these studies reported that younger hypertensive individuals tended to have worse adherence rates when compared with older hypertensive individuals. Five studies did not find an association between age and medication adherence.15,17,23,29,35 Most of these studies were cross-sectional examinations (n = 8), and medication adherence was assessed with self-report measures (n = 7). Schoenthaler and colleagues29 were the only researchers who investigated this relationship longitudinally and did not find an association.
Few studies (n = 5) assessed the relationship between income and medication adherence. Most (n = 4) did not find an association.23,29,34,35 Only 1 study found that income was related to medication adherence.21 In their study, Shea and colleagues21 found that unemployed hypertensive individuals were more likely to be nonadherent than were their employed counterparts. Medication adherence was measured using self-report in all of these studies.
Only 1 study found that education level was associated with medication adherence in hypertensive blacks.29 In their longitudinal study, Schoenthaler and colleagues29 reported that lower educational attainment significantly predicted poorer adherence among primary care hypertensive blacks. In most studies, however, educational level was not associated with medication adherence in hypertensive blacks (n = 6).17,21,23,31,34,35 Adherence was assessed with self-report (n = 6) and electronic monitoring technology (n = 1).
Only 1 study found an association between gender and medication adherence in hypertensive blacks.21 In their cross-sectional study, Shea and colleagues21 found that men were more likely to be nonadherent to their antihypertensive medications than were women. However, most studies (n = 7) found no association,15,17,29,31,33–35 and 2 studies collected data only on male participants.23,25 In these studies, medication adherence was measured with self-report (n = 8), electronic monitoring technology (n = 1), and pharmacy refill data (n = 1).
Four qualitative studies have described hypertensive blacks’ beliefs about social support and medication adherence.24,27,32,36 Generally from family members, social support was identified as a source of influence and encouragement in these studies. Two of the studies reported that having a relationship with God was considered a form of social support.32,36 In quantitative studies (n = 3), however, social support did not predict medication adherence.15,23,35 Researchers assessed medication adherence using self-report (n = 3) and electronic monitoring technology (n = 1). Three of the qualitative studies did not measure adherence.24,26,36
HealthCare Team and System-Related Factors
Healthcare team and system-related factors included studies (n = 7) examining and/or identifying patient-provider communication and logistical barriers to healthcare.15,24,26,27,32,34,35 Most of the research related to healthcare team and system-related factors have been qualitative (n = 4), with patients describing their beliefs that the quality of communication with their healthcare providers is an important influence on their medication adherence.24,26,27,32 In these qualitative studies, researchers did not measure adherence. Quantitative studies (n = 3) supported qualitative findings and have reported that patients with healthcare providers who are empathetic, nonjudgmental, and collaborative are significantly more likely to adhere to their medications.15,34,35 In addition, patients who experience fewer logistic barriers (ie, difficulty obtaining clinic appointments and health insurance) have better medication adherence rates.15
Condition-related factors are those illness-related demands faced by the patient, such as severity of BP, absence or presence of symptoms, and level of disability and/or comorbidities.16 Several studies examined and/or identified condition-related factors.17,22,25–27,29,33,34 Findings from the qualitative studies (n = 3) reported themes that described patients who believed that the absence of HTN symptoms influenced them to become nonadherent.22,26,27 In a cross-sectional study examining comorbidities and medication adherence in blacks, Lagu and colleagues33 found that those patients having stage 2 HTN (either systolic BP >159 mm Hg or diastolic BP >99 mm Hg) were more likely to have better adherence. Two studies found that comorbidities were not associated with adherence,29,34 whereas 1 study found that patients having 5 or more noncardiovascular comorbidities had an increased tendency to adhere to their antihypertensive medication.33 Depression was significantly related to poor medication adherence in hypertensive blacks in 4 quantitative studies, one of which examined the relationship longitudinally.17,25,29,34 Studies examining condition-related factors generally assessed adherence with self-report measures (n = 4). Two qualitative studies, however, did not measure medication adherence.22,26
Therapy-related factors include the complexity of the medical regimen, duration of treatment, frequent changes in treatment, and adverse effects.16 Studies examining therapy-related factors to medication adherence among hypertensive blacks have been primarily qualitative (n = 5). In these qualitative studies, patients have described their adverse effects as causing them to adjust antihypertensive medication dosages as well as to discontinue its use.26–28,32,36 Only 1 study has examined these factors quantitatively, and this study did not find an association between antihypertensive medication adverse effects and medication adherence in black hypertensive patients.15 Most of these qualitative studies did not measure medication adherence (n = 4).
According to the WHO, patient-related factors represent the knowledge, attitudes, beliefs, and perceptions of hypertensive patients.16 The qualitative literature (n = 6) has reported several patient-related factors of medication adherence among hypertensive blacks. Common themes include attitudes and personal health beliefs,22,24,26 control beliefs,27,36 and forgetfulness.27,28
A total of 7 quantitative studies examined patient-related factors. Only 2 quantitative studies examined attitudes and illness beliefs and suggested that they are not associated with medication adherence in hypertensive blacks.23,31 Studies on self-efficacy (n = 2) reported that it is associated with medication adherence.29,35 One study found that decreased knowledge of diseases other than HTN predicted poor medication adherence.15 Patients’ health literacy was not found to be associated with adherence, according to 1 cross-sectional study,34 and 1 study examining patients’ home remedy use found that it was associated with better adherence.30 Most studies examining patient-related factors assessed medication adherence with self-report measures (n = 7).
The purpose of this systematic review was to determine the factors associated with medication adherence in hypertensive blacks. Factors that were consistently associated with adherence were self-efficacy, depression, patient-provider communication, and system-related factors. However, these findings should be interpreted with caution. One reason is that the number of studies conducted exploring reasons for nonadherence in hypertensive blacks is insufficient. In addition to the limited number of studies available, they are also cross-sectional, and this makes it difficult to determine whether these factors cause medication adherence, if they simply covary, or if the relationships are sustained over time.
Despite these limitations to the current literature, the factors identified are important for healthcare providers to consider as they provide care to hypertensive blacks. Given that self-efficacy, healthcare team communication, and system-related factors are modifiable and depression can be treated, they can be the focus of interventions to increase medication adherence.
Factors that were not associated with adherence in this population were social support, attitudes, and illness beliefs. These findings, too, must be interpreted with caution because of the small number of studies and the fact that most were cross-sectional. However, researchers highlighted the importance of these factors in qualitative studies. As such, healthcare providers may still need to address these issues or inquire about them with their hypertensive patients. Indeed, interventions that have included social support and illness beliefs have been associated with moderate improvements in antihypertensive medication adherence.37–39
Demographic factors such as income, educational level, and gender were not associated with medication adherence in this systematic review. However, most studies were conducted with low-income and less-than-high-school–educated patient populations. There was also a trend toward younger hypertensive blacks having worse adherence rates. If this trend in the research continues, the information would be important in identifying patients who might be more at risk for low medication adherence.
This review revealed that much more research is needed to determine which factors influence antihypertensive medication adherence in blacks. Several concerns were identified after this systematic review was completed. The first concern regarding these studies is that most of the studies were based on homogeneous samples of hypertensive blacks. Specifically, most of the studies were conducted with low-income blacks, therefore limiting generalizability.
Another concern in interpreting the results of this review is that most of the studies measured medication adherence using self-report. The state of the science has emerged with more objective measures of medication adherence, such as the Medication Event Monitoring System, which is a method of monitoring medication adherence electronically. Medication Event Monitoring System is an objective and valid method of assessing medication adherence as well as the accepted criterion standard for adherence assessment.40 Consistent objective measurements of adherence are lacking and need to be incorporated as an outcome for future studies exploring factors associated with medication adherence in hypertensive blacks.
A third concern is related to research design. Medication adherence is a multidimensional and dynamic process. It cannot be assumed that medication adherence and factors associated with medication adherence are stable. However, most of the studies were qualitative or cross-sectional. There is a need for more longitudinal analyses of factors associated with medication adherence so that we can determine if an important factor, such as social support, remains unassociated with adherence at different time periods across a patient’s HTN diagnosis.
Finally, other factors, such as perceived discrimination and mistrust of healthcare providers, have been identified as important issues to consider when providing care to hypertensive blacks.36,41–45 Yet, they have not been examined for their associations to medication adherence. Further research needs to document whether these associations exist.
Because of the limited number and methodological limitations of existing studies exploring the factors associated with medication adherence in hypertensive blacks, no definitive conclusions could be made about such associations. Nonadherence to antihypertensive medication is a major consideration for care of hypertensive blacks. Continued support of these patients is crucial to achieving better adherence rates and with the eventual goal of increasing BP control and decreasing adverse health outcomes. To accomplish this goal, future research is needed to determine the factors associated with antihypertensive medication adherence so that targeted interventions can be developed for this vulnerable population.
What’s New and Important
* Factors that may be associated with medication adherence in low-income blacks include self-efficacy, depression, and patient-provider communication and can be the focus of interventions to increase adherence in hypertensive blacks.
* Although social support, attitudes, and illness beliefs were not associated with medication adherence in this systematic review, clinicians should still address these issues with hypertensive blacks.
* More longitudinal research studies need to be conducted that include more heterogeneous samples of hypertensive blacks.
1. Wong MD, Shapiro MF, Boscardin WJ, Ettner SL. Contribution of major diseases to disparities in mortality. N Engl J Med. 2002; 347 (20): 1585–1592.
2. Lloyd-Jones D, Adams RJ, Brown TM, et al.. Heart disease and stroke statistics—2010 update: a report from the American Heart Association. Circulation. 2010; 121 (7): e46–e215.
3. Rosamond W, Flegal K, Furie K, et al.. Heart disease and stroke statistics—2008 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation. 2008; 117 (4): e25–e146.
4. Fiscella K, Holt K. Racial disparity in hypertension control: tallying the death toll. Ann Fam Med. 2008; 6 (6): 497–502.
5. IOM. A Population-Based Policy and Systems Change Approach to Prevent and Control Hypertension. Washington, DC: The National Academies Press; 2010.
6. Chobanian AV, Bakris GL, Black HR, et al.. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: the JNC 7 report. JAMA. 2003; 289 (19): 2560–2572.
7. DiMatteo MR, Giordani PJ, Lepper HS, Croghan TW. Patient adherence and medical treatment outcomes: a meta-analysis. Med Care. 2002; 40 (9): 794–811.
8. Charles H, Good CB, Hanusa BH, Chang C-CH, Whittle J. Racial differences in adherence to cardiac medications. J Natl Med Assoc. 2003; 95 (1): 17–27.
9. Dickson M, Plauschinat CA. Racial differences in medication compliance and healthcare utilization among hypertensive Medicaid recipients: fixed-dose vs free-combination treatment. Ethn Dis. 2008; 18 (2): 204–209.
10. Hyre AD, Krousel-Wood MA, Muntner P, Kawasaki L, DeSalvo KB. Prevalence and predictors of poor antihypertensive medication adherence in an urban health clinic setting. J Clin Hypertens (Greenwich). 2007; 9 (3): 179–186.
11. Kressin NR, Wang F, Long J, et al.. Hypertensive patients’ race, health beliefs, process of care, and medication adherence. J Gen Intern Med. 2007; 22 (6): 768–774.
12. Krousel-Wood MA, Muntner P, Islam T, Morisky DE, Webber LS. Barriers to and determinants of medication adherence in hypertension management: perspective of the cohort study of medication adherence among older adults. Med Clin North Am. 2009; 93 (3): 753–769.
13. Ndumele CD, Shaykevich S, Williams D, Hicks LS. Disparities in adherence to hypertensive care in urban ambulatory settings. J Health Care Poor Underserved. 2010; 21 (1): 132–143.
14. Shaya FT, Du D, Gbarayor CM, Frech-Tamas F, Lau H, Weir MR. Predictors of compliance with antihypertensive therapy in a high-risk medicaid population. J Natl Med Assoc. 2009; 101 (1): 34–39.
15. Turner BJ, Hollenbeak C, Weiner MG, Ten Have T, Roberts C. Barriers to adherence and hypertension control in a racially diverse representative sample of elderly primary care patients. Pharmacoepidemiol Drug Saf. 2009; 18 (8): 672–681.
16. Sabate E. Adherence to Long-term Therapies: Evidence for Action. Geneva, Switzerland: World Health Organization; 2003.
17. Krousel-Wood MA, Muntner P, Joyce CJ, et al.. Adverse effects of complementary and alternative medicine on antihypertensive medication adherence: findings from the cohort study of medication adherence among older adults. J Am Geriatr Soc. 2010; 58 (1): 54–61.
18. Bosworth HB, Dudley T, Olsen MK, et al.. Racial differences in blood pressure control: potential explanatory factors. Am J Med. 2006; 119 (1): 70.e9–70.e15.
19. Poon I, Lal LS, Ford ME, Braun UK. Racial/ethnic disparities in medication use among veterans with hypertension and dementia: a national cohort study. Ann Pharmacother. 2009; 43 (2): 185–193.
20. Siegel D, Lopez J, Meier J. Antihypertensive medication adherence in the Department of Veterans Affairs. Am J Med. 2007; 120 (1): 26–32.
21. Shea S, Misera D, Ehrlich MH, Field L, Francis CK. Correlates of nonadherence to hypertension treatment in an inner-city minority population. Am J Public Health. 1992; 82 (12): 1607–1612.
22. Heurtin-Roberts S, Reisin E. The relation of culturally influenced lay models of hypertension to compliance with treatment. Am J Hypertens. 1992; 5 (11): 787–792.
23. Hill MN, Bone LR, Kim MT, Miller DJ, Dennison CR, Levine DM. Barriers to hypertension care and control in young urban black men [see comment]. Am J Hypertens. 1999; 12 (1O pt 1): 951–958.
24. Rose LE, Kim MT, Dennison CR, Hill MN. The contexts of adherence for African Americans with high blood pressure. J Adv Nurs. 2000; 32 (3): 587–594.
25. Kim MT, Han H-R, Hill MN, Rose L, Roary M. Depression, substance use, adherence behaviors, and blood pressure in urban hypertensive black men. Ann Behav Med. 2003; 26 (1): 24–31.
26. Lukoschek P. African Americans’ beliefs and attitudes regarding hypertension and its treatment: a qualitative study. J Health Care Poor Underserved. 2003; 14 (4): 566–587.
27. Ogedegbe G, Harrison M, Robbins L, Mancuso CA, Allegrante JP. Barriers and facilitators of medication adherence in hypertensive African Americans: a qualitative study [see comment]. Ethn Dis. 2004; 14 (1): 3–12.
28. Viswanathan H, Lambert BL. An inquiry into medication meanings, illness, medication use, and the transformative potential of chronic illness among African Americans with hypertension. Res Social Adm Pharm. 2005; 1 (1): 21–39.
29. Schoenthaler A, Ogedegbe G, Allegrante JP. Self-efficacy mediates the relationship between depressive symptoms and medication adherence among hypertensive African Americans. Health Educ Behav. 2007; 36 (1): 127–137.
30. Tilburt JC, Dy SM, Weeks K, Klag M, Young JH. Associations between home remedy use and a validated self-reported adherence measure in an urban African-American population with poorly controlled hypertension. J Natl Med Assoc. 2008; 100 (1): 91–97.
31. Hekler EB, Lambert J, Leventhal E, Leventhal H, Jahn E, Contrada RJ. Commonsense illness beliefs, adherence behaviors, and hypertension control among African Americans. J Behav Med. 2008; 31 (5): 391–400.
32. Fongwa MN, Evangelista LS, Hays RD, et al.. Adherence treatment factors in hypertensive African American women. Vasc Health Risk Manage. 2008; 4 (1): 157–166.
33. Lagu T, Weiner MG, Eachus S, Tang SSK, Schwartz JS, Turner BJ. Effect of patient comorbidities on filling of antihypertensive prescriptions. Am J Manag Care. 2009; 15 (1): 24–30.
34. Schoenthaler A, Chaplin WF, Allegrante JP, et al.. Provider communication effects medication adherence in hypertensive African Americans. Patient Educ Couns. 2009; 75 (2): 185–191.
35. Braverman J, Dedier J. Predictors of medication adherence for African American patients diagnosed with hypertension. Ethn Dis. 2009; 19 (4): 396–400.
36. Lewis LM, Askie P, Randleman S, Shelton-Dunston B. Medication adherence beliefs of community-dwelling hypertensive African Americans. J Cardiovasc Nurs. 2010; 25 (3): 199–206.
37. Krousel-Wood M, Hyre A, Muntner P, Morisky D. Methods to improve medication adherence in patients with hypertension: current status and future directions. Curr Opin Cardiol. 2005; 20 (4): 296–300.
38. Ogedegbe G, Chaplin W, Schoenthaler A, et al.. A practice-based trial of motivational interviewing and adherence in hypertensive African Americans. Am J Hypertens. 2008; 21 (10): 1137–1143.
39. Schroeder K, Fahey T, Ebrahim S. How can we improve adherence to blood pressure–lowering medication in ambulatory care? Systematic review of randomized controlled trials. Arch Intern Med. 2004; 164 (7): 722–732.
40. Cramer JA. Microelectronic systems for monitoring and enhancing patient compliance with medication regimens. Drugs. 1995; 49: 321–327.
41. Lewis T, Barnes LL, Bienias JL, Lackland DT, Evans DA, Mendes de Leon CF. Perceived discrimination and blood pressure in older African American and white adults. J Gerontol A Biol Sci Med Sci. 2009; 64 (9): 1002–1008.
42. Peters RM. Racism and hypertension among African Americans. West J Nurs Res. 2004; 26 (6): 612–631.
43. Roberts CB, Vines AI, Kaufman JS, James SA. Cross-sectional association between perceived discrimination and hypertension in African-American men and women: the Pitt County Study. Am J Epidemiol. 2008; 167 (5): 624–632.
44. Trivedi AN, Ayanian JZ. Perceived discrimination and use of preventive health services. J Gen Intern Med. 2006; 21 (6): 553–558.
45. Brondolo E, Libby DJ, Denton E-G, et al.. Racism and ambulatory blood pressure in a community sample. Psychosom Med. 2008; 70 (1): 49–56.
© 2012 Lippincott Williams & Wilkins, Inc.