|Year : 2021 | Volume
| Issue : 3 | Page : 178-184
Prevalence and predictors of medication adherence among adult cardiovascular diseases patients in al-Madinah
Abdulrahman Samman Al-Asmari1, Khalid Abdullah S Aljohani2, Mohammad Ayed Aloufi3
1 Department of Academic Affairs and Training, Ministry of Health, Madinah Cardiac Center, Madinah, Saudi Arabia
2 Nursing College, Taibah University, Madinah, Saudi Arabia
3 Department of Nursing, Medical Applied College, Bishah University, Bishah, Saudi Arabia
|Date of Submission||09-Sep-2020|
|Date of Acceptance||05-Nov-2021|
|Date of Web Publication||6-Dec-2021|
Mohammad Ayed Aloufi
Department of Nursing, Medical Applied College, Bishah University, Bishah
Source of Support: None, Conflict of Interest: None
Background: Nonadherence to the medication schedule is common in patients with cardiovascular diseases (CVDs) and may have serious consequences including increased costs, hospital admissions, and death. Aim: In this study, we investigated the prevalence and associated factors of nonadherence in cardiovascular patients in Al-Madinah/Saudi Arabia. Settings and Design: This was a descriptive cross-sectional study carried out at tertiary cardiac center in Al-Madinah. Subjects and Methods: Study variables including sociodemographic characteristics and disease factors were collected from a random sample of patients attending the CVDs the clinic using a structured questionnaire. Adherence was assessed using the Culig's medication adherence scale. Statistical Analysis: Chi-square test and logistic regression analysis were used to evaluate factors associated with nonadherence. Results: A total of 200 adult cardiovascular patients completed the study; 100 (50.0%) were males and 186 (93.0%) resided in the city. The result showed that 26.0% (52/200) of the patients were nonadherent to medications, missing between 1 and 4 days of medication per week. Overall, 177 (88.5%) of the patients indicated that a healthcare worker explained the medications to them before dispensing. The most common reasons for nonadherence were: not being at home at the drug-taking time (84.6%), forgetfulness (82.7%), and fear of side effects (46.2%). Independent predictors of nonadherence were being retired (odds ratio [OR] 3.4; 95% confidence interval [C. I.] 1.3–9.4) and being uneducated or having general education (OR 4.7; 95% C. I. 2.0–11.2). Conclusion: Nonadherence rate was high and was found to be dependent upon patient-level factors. The study recommends improved patient education interventions to boost medication adherence in cardiovascular patients. Further studies are recommended.
Keywords: Cardiac center, cardiovascular, medication adherence, nursing
|How to cite this article:|
Al-Asmari AS, Aljohani KA, Aloufi MA. Prevalence and predictors of medication adherence among adult cardiovascular diseases patients in al-Madinah. Saudi J Health Sci 2021;10:178-84
|How to cite this URL:|
Al-Asmari AS, Aljohani KA, Aloufi MA. Prevalence and predictors of medication adherence among adult cardiovascular diseases patients in al-Madinah. Saudi J Health Sci [serial online] 2021 [cited 2022 Sep 28];10:178-84. Available from: https://www.saudijhealthsci.org/text.asp?2021/10/3/178/331774
| Introduction|| |
The World Health Organization (WHO) defines adherence to medication “as the degree to which a person's behavior with respect to the medication corresponds with the agreed recommendations from a health care provider.” However, only about 50% of individuals with chronic conditions have good adherence to their medication. Therefore, medication adherence is a major global health challenge. The WHO identified several dynamic factors influencing medication adherence and forming framework consisting of five dimensions. These are social and economic-related factors, health system-related factors, condition-related factors, therapy-related factors, and patient-related factors. Poor medication adherence lowers its effectiveness leading to poor patient outcomes.,
Generally, cardiovascular diseases (CVDs) are the leading causes of mortality worldwide with estimated 17.9 million yearly deaths accounting for 31% of mortality rate globally. Drugs used for the management of CVDs such as medications for hypertension, coronary artery diseases, and lipid-lowering agents are among the commonest agents used for the prevention of CVD progression and risk modification. Poor adherence to these agents may lead to a substantial population-level worsening of these diseases as well as high mortality. A meta-analysis of adherence to cardiovascular medications involving almost two million participants revealed that only 60% of CVD patients had good adherence to medications. Furthermore, patients with poor adherence to the cardiovascular medications had a 45% higher risk of mortality. Different rates of adherence have been observed for different cardiovascular medications, with adherence rates as low as 21% found for aspirin, beta-blockers, and lipids. Declining adherence rates over a 6–12-month period were also found for hypertensive medications. Reduced medication adherence has been shown to be associated with various medical/psychosocial complications, reduced health-related quality of life and high costs of care.,
In Saudi Arabia, CVDs like hypertension affect a quarter of the adult population and it is a major determinant for mortality., In addition, almost two-thirds of hypertensive patients in the country have poorly-controlled hypertension., However, there is little information on adherence to medications among Saudi patients with CVD., Khayyat et al., (2007) found that over half (54%) of hypertensive patients Makkah were nonadherent to their medications. Also, another study showed that 41.7%, and 33.7% of patients attending cardiology clinics in Riyadh had medium and low adherence to their medications, respectively. To add to this debate, therefore, the aim of this study has two folds that are: to investigate the prevalence of medication adherence in Saudi Arabian patients attending a tertiary cardiac center; and to identify sociodemographic factors affecting the patients' adherence.
| Subjects and Methods|| |
The was a hospital-based descriptive cross-sectional study carried out from 1st to 31st January 2019 at a tertiary cardiac center in Al-Madinah, Kingdom of Saudi Arabia.
Patients attending the outpatient cardiac clinics of the center who met the following eligibility criteria were invited to enroll for the study. The inclusion criteria were a confirmed diagnosis of hypertension or ischemic heart disease; being 18 years old or older; being able to communicate in the written Arabic language and taking at least one of the following group of medications: antihypertensives, anti-platelet, and statins. Patients who had depression, memory loss, or other mental health issues were excluded from the study. The researchers evaluated each patient for eligibility and invited eligible patients for participation in the study.
Assuming that 33.7% of adult patients with cardiac diseases had poor adherence to treatment, and considering an absolute sampling error of 0.05, and power of 90%; the minimum sample size required was calculated to be 146. In order to account for attrition and to allow for advanced statistical analysis, the sample size was increased to 200 participants. A systematic random sampling approach was used to recruit the eligible participants in the clinic.
Instruments and data collection
The data were collected using a standardized self-administered questionnaire addressing the patients' adherence. The questionnaire had two components: sociodemographic characteristics and medication adherence. The Arabic version instrument was pilot-tested among hypertensive patients not included in the study sample. The instrument items were found not to have any issues requiring modification. The sociodemographic characteristics collected include sex (male, female), position (employee or retired), educational status (uneducated, general education, academic education, graduate studies), residence (city, village), and number of years diagnosed with the cardiac disease. Adherence to medications prescribed was assessed using the Culig's medication adherence scale with written permission from the original author. Good adherence to cardiac medications was defined as not missing taking the prescribed medicine by a doctor any day in the past 7 days while nonadherence was defined as not taking the prescribed medications for one or more days in the past week before the survey. Other dimensions of adherence such as timing and dosing were also assessed. The reliability analysis of the adherence scale revealed a Cronbach alpha of 0.52. Each of the participants was given the questionnaire to complete in a private room.
Statistical analysis was carried out using IBM SPSS Statistics for Windows, Version 24.0. (Armonk, NY: IBM Corp.). A descriptive analysis was performed including means (and standard deviation [SD]) for quantitative variables while group variables were reported as count and percentages. Chi-square tests were used to evaluate the association between adherence to cardiac medications and sociodemographic characteristics of the participants. A multivariable logistic regression analysis was carried out to identify independent predictors of nonadherence. Nonadherence (Yes/No) was the outcome variable while the sociodemographic variables (gender, position, residence, education, and duration illness) were the explanatory variables. All the tests performed were two-sided tests and the criterion for significance was set at P < 0.05.
Approval for the study was obtained from the Institutional Research and Ethics Committee. Anonymity and confidentiality of all participants were preserved and no identifiable information were collected. Participants' participation was considered as a consent of participation and all study information were mentioned on the first page of the questionnaire.
| Results|| |
Characteristics of the participants
A total of 200 patients completed the survey. Of these, 100 (50.0%) were male and 100 (50.0%) were female, 169 (84.5%) of them were employed. Furthermore, 22 (11.0%) were uneducated, while others had either general, academic or graduate-level education. Most of the participants 186 (93.0%) resided in the city, and the Mean ± SD duration of diagnosis of their cardiac disease was 6.91 ± 4.34 years (range: 1, 25 years). The sociodemographic characteristics of the participants are as shown in [Table 1].
Nonadherence to cardiac medications and associated factors
Over a quarter of the study participants, 52 (26.0%) were nonadherent to their medications. Of the patients who were nonadherent to their medications, 23 patients (14 males and 9 females) missed their medications for 1 day, 11 patients (8 males and 3 females) missed for 2 days, 6 patients (5 males and 1 female) missed for 3 days, and 12 patients (7 males and 5 females) missed their medications for 4 or more days. [Table 2] summarizes the level of nonadherence to medication and associated factors among cardiac disease patients in Medina. Nonadherence rate was 18.0% among females and 34.0% among male participants. The difference was statistically significant (P = 0.01). In addition, nonadherence rate was 18.9% among employed participants and 64.5% among retired subjects. The difference was statistically significant (P < 0.001). Furthermore, there was a statistically significant difference in the nonadherence rates according to the educational level of the participants (P < 0.001). Among participants residing in the village, the nonadherence rate was 71.4% compared to 22.6% in participants living in the city. The difference was statistically significant (P < 0.001). Participants who had been diagnosed with a cardiac disease for 5 years or less prior to the survey had a lower nonadherence rate compared to those who had the disease for over 5 years (15.1% vs. 34.2%), the difference also reached statistical significance (P = 0.002).
|Table 2: Nonadherence to medication and associated factors among cardiac disease patients in medina|
Click here to view
Independent predictors nonadherence to cardiac medications
A multivariable logistic regression analysis was carried out to identify the independent predictors of nonadherence to medications among the participants [Table 3]. The analysis revealed that participants who were retired were 3.4 times more likely to be nonadherent to medications compared employed participants (odds ratio [OR] 3.4; 95% confidence interval [C. I.] 1.3–9.4). Furthermore, participants who were uneducated or had general education were 4.7 times more likely to be nonadherent compared to participants who had academic-level education or graduate studies (OR 4.7; 95% C. I. 2.0–11.2).
|Table 3: Independent predictors of nonadherence to medication among cardiac disease patients in medina|
Click here to view
Reasons for nonadherence to medications
A total of 198 participants (99.0%) knew their prescribed drugs, and of all participants, 2 (1.0%) patients indicated that their medications were not taken at a specified time. In addition, 148 (74.0%) indicated that they knew the dose and how to take the prescribed medications. Overall, 177 (88.5%) indicated that a medical doctor, pharmacist, or a nurse explained the medications to the participants before dispensing. The participants who were nonadherent to medications were further asked to indicate their reasons for nonadherence. The most common reasons given by the participants include: 44 (84.6%) indicated that they were not at home at the drug-taking time, 43 (82.7%) indicated that the forgot, 25 (48.1%) indicated that they were afraid of the side-effect of the drugs and 24 (46.2) % indicated that the drugs were not dispensed. [Figure 1] shows the reasons for nonadherence to prescribed medications among the participants.
|Figure 1: Reasons given by the participants for non-adherence to prescribed medications|
Click here to view
| Discussion|| |
In this clinic-based descriptive study evaluating nonadherence to medications among adult individuals with CVDs, we found that over a quarter of the study participants were nonadherent to their medications. Second, we found that nonadherence was significantly lower in females compared to males; and nonadherence rates significantly varied according to position, place of residence, educational status, and duration of illness. However, after adjustments were made for confounders, only position and educational status were independent predictors for nonadherence. The most common reasons for the nonadherence to the medications were; not being at home at the appropriate time, forgetfulness, fear of adverse effects, and alteration of their prescriptions by their doctors.
The effectiveness and efficiency of any medication are highly dependent on the adherence rate of the patient. CVDs have been known to have adverse long-term outcomes in patients. In this study, 26% of the patients were nonadherent to their medications. This was lower than the findings of previous studies in Saudi Arabia which showed that medication nonadherence rate ranged from 33 to 54%., The nonadherence rate observed in this study was similar to the findings of previous studies from Czech Republic (31.5%), the United Kingdom (41.6%), and Canada (23%),, but was lower than the nonadherence rates reported from Cameroon, Ghana, Nigeria, and Sudan.,, The variation in the nonadherence rates reported in these studies may be due to differences in the quality of the health system and access to health services. Thus, countries with better access to health services may report a better adherence rate. Furthermore, the high nonadherence rate observed in this study may due to variation in the duration of illness; most of our patients have been diagnosed with their cardiac illness for over 5 years. Previous studies have indicated that adherence rates may improve with increase in the duration of treatment.,
This study also explored the relation between the socio-demographic factors of the participants and medication nonadherence. Our study revealed that gender has a significant association with nonadherence with male patients being significantly more likely to be nonadherent compared to females. However, after adjustments were made for confounders, there was no significant gender difference in nonadherence rate. Several studies have indicated a wide gender variation in nonadherence rates among patients with cardiac diseases.,,,, Our finding was consistent with the results of previous studies from Saudi Arabia, Cameroon, Vietnam, and Sudan which showed no gender difference in adherence.,,, However, our finding differs from those of studies in Saudi Arabia, the United Kingdom, and Czech Republic which showed that women were more likely to be nonadherent compared to men., Furthermore, our finding differs from those of a study in the United Arab Emirates which showed that male patients were significantly more likely to be nonadherent compared to females. A recent systematic review and meta-analysis of 82 studies revealed no significant sex difference in adherence rates to antihypertensive therapy among adult patients. Thus, the differences in nonadherence rates observed in these studies may be due to variations in the social and cultural factors regarding gender in the study settings.
Furthermore, we found that socioeconomic status based on employment status and level of education were predictors for nonadherence. Indeed, we found that compared to those who were employed, participants who were retired were 3.4 times more likely to be nonadherent to medications. In addition, we found that participants who were uneducated or had general education were 4.7 times more likely to be nonadherent compared to participants who had academic-level education or graduate-level studies. Our finding varied with the report of previous studies from Sudan, Jordan, United Arab Emirate, and Iran which showed no significant relationship between employment status and medication adherence.,,, However, another study in the USA indicated that financial strain from low income or unemployment was a risk factor for poor adherence among cardiovascular patients. Our finding that low educational status was associated with medication nonadherence is consistent with the findings of previous studies., It has been argued that patients with a higher educational status tends to have greater better knowledge about their illness and treatment and therefore have a higher tendency to adhere to treatment. However, some few studies have reported no difference in adherence rates according to educational status., Put together, our study suggests the need to identify and address socioeconomic issues that may address medication adherence among cardiovascular patients.
In this study, place of residence was not a significant predictor nonadherence to treatment. This indicates that there were no significant rural and urban differences in nonadherence rates in the study setting. Our finding is in agreement with the findings of previous studies in Ethiopia, Sudan, Jordan, the United Arab Emirates, and Iran.,, Also, a systematic review and meta-analysis have revealed that there was no difference in medication nonadherence between urban and rural cardiovascular patients. Our study further revealed that duration of illness was significantly associated with medication nonadherence. However, after adjustments were made for confounders, duration of illness was not a significant predictor of nonadherence in our setting. Previous studies assessing the relation between duration of illness and medication adherence have revealed inconsistent findings. A previous study in Malaysia revealed no relationship between duration of illness and medication nonadherence among hypertensive patients. In Egypt, Goweda and Shatla, (2020) revealed that duration of hypertension was inversely associated with medication adherence; while in Turkey, Boratas and Kilic, indicated that longer duration of illness was a significant predictor of higher adherence to medications among hypertensives. Also, a longer duration of illness was a predictor of nonadherence to medications among patients with angina in Jordan. The differences observed in these studies may be because adjustments for confounding effects were not performed in majority of the studies.,
Previous studies have explored multiple reasons for medication nonadherence among cardiac patients and some of the reasons were: losing interest along the way, minimal awareness of the diseases, poor communication between patient and physician, illiteracy, and absence of co-morbidities.,, In this study, the most common reasons highlighted were not being at home at the appropriate time, forgetfulness, fear of adverse effects of the medications, and frequent medication changes. Our finding agrees with the report of Alsolami et al. who found that the primary reason cited for nonadherence among hypertensive patients was they believed that taking the antihypertensive medication is harmful as it brings about adverse health effects. The varied reasons given by the participants of the present study for nonadherence suggest the need to improve patient education on the need to maintain adherence to medications during hospital visits. In this study, 88.5% of the patients highlighted that they were giving some information about their medication by their physician, nurse, or a pharmacist. This indicates that an excellent physician and patient communication alone may not enough in improving medication adherence in this setting. Therefore, the study findings suggest the need to explore patient beliefs, perceptions, attitudes, and values as potential determinants of medication adherence.,
limitations of the study
The study has some limitations. This was a cross-sectional study, therefore, the design of the study may not be used to describe a cause and effect relationship. Second, adherence rates in this study were based on self-report; therefore, the accuracy of the information provided by the participants may be influenced by social desirability bias. Third, individuals with cardiac diseases tend to have comorbidities such as diabetes mellitus, obesity, and chronic kidney disease which may influence adherence. We did not explore the role of comorbidities as predictors of nonadherence in this study. Finally, the study data were collected from a single health facility thereby limiting its generalizability.
Future research directions
Future studies should explore the role of co-morbidities, patient beliefs, and attitudes as potential determinants of adherence. Despite these limitations, this study has a unique contribution to literature since it provides important data about the burden and determinants nonadherence in cardiovascular patients attending cardiac clinics in Saudi Arabia.
| Conclusion|| |
The present study showed a high rate of nonadherence to medication among patients with cardiac diseases and shed the light on the crucial need to identify strategies targeted at improving adherence among patients with CVDs in Saudi Arabia. These findings indicate the need for physicians and other health workers to better educate patients with CVDs on adherence to medications and for governmental policies to boost medication adherence through addressing patient-level factors.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Sabaté E, Sabaté E. Adherence to Long-Term Therapies: Evidence for Action. Geneva: WHO; 2003.
Al-Ganmi AH, Alotaibi A, Gholizadeh L, Perry L. Medication adherence and predictive factors in patients with cardiovascular disease: A cross-sectional study. Nurs Health Sci 2020;22:454-63.
Usherwood T. Encouraging adherence to long-term medication. Aust Prescr 2017;40:147-50.
Bansilal S, Castellano JM, Garrido E, Wei HG, Freeman A, Spettell C, et al.
Assessing the impact of medication adherence on long-term cardiovascular outcomes. J Am Coll Cardiol 2016;68:789-801.
Chowdhury R, Khan H, Heydon E, Shroufi A, Fahimi S, Moore C, et al.
Adherence to cardiovascular therapy: A meta-analysis of prevalence and clinical consequences. Eur Heart J 2013;34:2940-8.
Baroletti S, Dell'Orfano H. Medication adherence in cardiovascular disease. Circulation 2010;121:1455-8.
Simon-Tuval T, Triki N, Chodick G, Greenberg D. The association between adherence to cardiovascular medications and healthcare utilization. Eur J Health Econ 2016;17:603-10.
Saeed AA, Al-Hamdan NA, Bahnassy AA, Abdalla AM, Abbas MA, Abuzaid LZ. Prevalence, awareness, treatment, and control of hypertension among Saudi adult population: A national survey. Int J Hypertens 2011;2011:174135.
Al-Nozha MM, Abdullah M, Arafah MR, Khalil MZ, Khan NB, Al-Mazrou YY, et al.
Hypertension in Saudi Arabia. Saudi Med J 2007;28:77-84.
Altuwairqi HB. Barriers to medication adherence among cardiac patients following at King Fahad Medical City, Riyadh, Saudi Arabia. Saudi J Health Sci 2016;5:20. [Full text]
Khayyat SM, Khayyat SM, Hyat Alhazmi RS, Mohamed MM, Abdul Hadi M. Predictors of medication adherence and blood pressure control among Saudi hypertensive patients attending primary care clinics: A cross-sectional study. PLoS One 2017;12:e0171255.
Čulig J. Patients' adherence to prescribed medication. J Appl Health Sci 2018;4:7-14.
Gupta P, Patel P, Štrauch B, Lai FY, Akbarov A, Marešová V, et al.
Risk factors for nonadherence to antihypertensive treatment. Hypertension 2017;69:1113-20.
Natarajan N, Putnam W, Van Aarsen K, Beverley Lawson K, Burge F. Adherence to antihypertensive medications among family practice patients with diabetes mellitus and hypertension. Can Fam Physician 2013;59:e93-100.
Adidja NM, Agbor VN, Aminde JA, Ngwasiri CA, Ngu KB, Aminde LN. Non-adherence to antihypertensive pharmacotherapy in Buea, Cameroon: A cross-sectional community-based study. BMC Cardiovasc Disord 2018;18:150.
Boima V, Ademola AD, Odusola AO, Agyekum F, Nwafor CE, Cole H, et al.
Factors associated with medication nonadherence among hypertensives in Ghana and Nigeria. Int J Hypertens 2015;2015:205716.
Awad A, Osman N, Altayib S. Medication adherence among cardiac patients in Khartoum State, Sudan: A cross-sectional study. Cardiovasc J Afr 2017;28:350-5.
Mekonnen HS, Gebrie MH, Eyasu KH, Gelagay AA. Drug adherence for antihypertensive medications and its determinants among adult hypertensive patients attending in chronic clinics of referral hospitals in Northwest Ethiopia. BMC Pharmacol Toxicol 2017;18:27.
Fitz-Simon N, Bennett K, Feely J. A review of studies of adherence with antihypertensive drugs using prescription databases. Ther Clin Risk Manag 2005;1:93-106.
Bader RJ, Koprulu F, Hassan NA, Ali AA, Elnour AA. Predictors of adherence to antihypertensive medication in northern United Arab Emirates. East Mediterr Health J 2015;21:309-18.
Biffi A, Rea F, Iannaccone T, Filippelli A, Mancia G, Corrao G. Sex differences in the adherence of antihypertensive drugs: A systematic review with meta-analyses. BMJ Open 2020;10:e036418.
Osman FA, Mohamed HH, Alhaj NA. Non-adherence to antihypertensive medication and its associated factors among cardiac patients at al-Shabaab referred clinic. Sudan J Med Sci 2017;14:24-37.
Nguyen TP, Schuiling-Veninga CC, Nguyen TB, Vu TH, Wright EP, Postma MJ. Adherence to hypertension medication: Quantitative and qualitative investigations in a rural Northern Vietnamese community. PLoS One 2017;12:e0171203.
Behnood-Rod A, Rabbanifar O, Pourzargar P, Rai A, Saadat Z, Saadat H, et al.
Adherence to antihypertensive medications in Iranian patients. Int J Hypertens 2016;2016:1508752.
Jarab AS, Rababa'h AM, Almousa A, Mukattash TL, Bsoul R. Non-adherence to pharmacotherapy and its associated factors among patients with angina in Jordan. J Pharm Health Serv Res 2020;11:61-5.
Osborn CY, Kripalani S, Goggins KM, Wallston KA. Financial strain is associated with medication nonadherence and worse self-rated health among cardiovascular patients. J Health Care Poor Underserved 2017;28:499-513.
Sen HT, Linh TT, Trang DT. Factors related to treatment compliance among patients with heart failure. Ramathibodi Med J 2020;43:30-40.
Ni Z, Dardas L, Wu B, Shaw R. Cardioprotective medication adherence among patients with coronary heart disease in China: A systematic review. Heart Asia 2019;11:e011173.
Amininasab S, Lolaty H, Moosazadeh M, Shafipour V. Medication adherence and its predictors among patients with heart failure. Nurs Midwifery Stud 2018;7:81-6. [Full text]
Fuster V. An alarming threat to secondary prevention: Low compliance (lifestyle) and poor adherence (drugs). Rev Esp Cardiol (Engl Ed) 2012;65 Suppl 2:10-6.
Murphy GK, McAlister FA, Weir DL, Tjosvold L, Eurich DT. Cardiovascular medication utilization and adherence among adults living in rural and urban areas: A systematic review and meta-analysis. BMC Public Health 2014;14:544.
Ramli A, Ahmad NS, Paraidathathu T. Medication adherence among hypertensive patients of primary health clinics in Malaysia. Patient Prefer Adherence 2012;6:613-22.
Goweda RA. Adherence to antihypertensive medications: Rate and predictors. Egypt Family Med J 2020;4:95-109.
Boratas S, Kilic HF. Evaluation of medication adherence in hypertensive patients and influential factors. Pak J Med Sci 2018;34:959-63.
Alsolami F, Correa VI, Hou XY. Factors affecting antihypertensive medications adherence among hypertensive patients in Saudi Arabia. Am J Med Med Sci 2015;5:181-9.
Patel MJ, Shetty L, Rasras A. Assessment of medication adherence and medication knowledge among hypertensive patients in Riyadh, Saudi Arabia. Int J Pharma Res Rev 2015;4:15-23.
[Table 1], [Table 2], [Table 3]