Browse Subject Areas

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Determination of factors affecting medication adherence in type 2 diabetes mellitus patients using a nationwide claim-based database in Japan

  • Takeshi Horii ,

    Contributed equally to this work with: Takeshi Horii, Kenji Momo, Takeo Yasu, Yusuke Kabeya

    Roles Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Writing – original draft

    Affiliation Research and Education Center for Clinical Pharmacy, Division of Clinical Pharmacy, Laboratory of Pharmacy Practice and Science 1, Kitasato University School of Pharmacy, Kanagawa, Japan

  • Kenji Momo ,

    Contributed equally to this work with: Takeshi Horii, Kenji Momo, Takeo Yasu, Yusuke Kabeya

    Roles Conceptualization, Data curation, Methodology, Validation, Writing – review & editing

    Affiliations Department of Pharmacy, The Research Hospital, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan, Department of Hospital Pharmaceutics, School of pharmacy, Showa University, Tokyo, Japan

  • Takeo Yasu ,

    Contributed equally to this work with: Takeshi Horii, Kenji Momo, Takeo Yasu, Yusuke Kabeya

    Roles Data curation, Methodology, Validation, Writing – review & editing

    Affiliation Department of Medicinal Therapy Research, Pharmaceutical Education and Research Center, Meiji Pharmaceutical University, Tokyo, Japan

  • Yusuke Kabeya ,

    Contributed equally to this work with: Takeshi Horii, Kenji Momo, Takeo Yasu, Yusuke Kabeya

    Roles Conceptualization, Formal analysis, Methodology, Supervision, Validation, Writing – review & editing

    Affiliation Department of Home Care Medicine, Sowa Hospital, Kanagawa, Japan

  • Koichiro Atsuda

    Roles Supervision, Validation, Writing – review & editing

    Affiliation Research and Education Center for Clinical Pharmacy, Division of Clinical Pharmacy, Laboratory of Pharmacy Practice and Science 1, Kitasato University School of Pharmacy, Kanagawa, Japan

Determination of factors affecting medication adherence in type 2 diabetes mellitus patients using a nationwide claim-based database in Japan

  • Takeshi Horii, 
  • Kenji Momo, 
  • Takeo Yasu, 
  • Yusuke Kabeya, 
  • Koichiro Atsuda



The extent of medication adherence in patients with type 2 diabetes mellitus (T2DM) several years after starting treatment with hypoglycemic agents remains unknown. Most previous work on medication adherence targeting this group of patients has been undertaken across a single year or is questionnaire based. This study aimed to determine medication adherence status and factors affecting adherence 3 years after initiation of hypoglycemic agents, using a nationwide medical claim-based database in Japan.


This retrospective study was conducted on data from 884 subjects with T2DM to better understand medication adherence, the effects of polypharmacy, and other factors. We also investigated the effects of medication nonadherence on hemoglobin A1c levels. Proportion of days covered was defined as the number of days for which a hypoglycemic agent was prescribed and in the patient’s possession to the number of days in the observation period. A proportion of days covered ≥0.8 were considered adherent, and those with a value <0.8 as nonadherence. Polypharmacy was defined as taking ≥5 medications.


Of the 884 patients investigated, 440 were considered adherent during the study period. Significant factors related to adherence included number of medications (3 or 4, or ≥5), male sex, age 50–<60 years, and total number of visits ≥17. Medication adherence was also a factor related to patients with hemoglobin A1c values < 7.0% at the end of the observation period.


We surveyed medication adherence for 3 years with post medication initiation, and found that subjects aged 50–<60 years, those with ≥3 concomitant medications, and those with a total number of visits ≥17 were more likely to be adherent and persistent, and more likely to continue their hypoglycemic agents. A high degree of medication adherence was found to have a positive influence on hemoglobin A1c levels.


Medication adherence refers to the extent to which patients take their medication regimen as prescribed by their health care provider [1]. A previous study suggests that about a quarter of patients are nonadherent, and that rates of adherence are higher among patients with acute conditions than in those with chronic conditions [2]. Even in the resource-intensive setting of clinical trials, the average adherence rates for trial drugs used in chronic diseases are between 43% and 78% [35]. A systematic review of patients with type 2 diabetes mellitus (T2DM) who remained on treatment with oral hypoglycemic agents for 6–12 months reported adherence rates of between 36% and 93% [6].

Medication adherence has been recognized as key for optimally controlled diabetes [7] in patients with T2DM. Several factors, such as disease and treatment characteristics and complexity, age, sex, stress, depression, and multidrug combinations affect treatment adherence amid changing circumstances in the daily lives of patients with diabetes [8]. When selecting an oral hypoglycemic agent, not only medical outcomes but also the patients’ quality of life and attitude toward treatment should be considered. Maintaining good glycemic control is believed to allow patients to maintain insulin production and reduce insulin resistance. Poor medication adherence makes achieving good glycemic control difficult, which is believed to affect the onset of diabetic microangiopathy (retinopathy, nephropathy, and neuropathy) and increase the risk of diabetic complications [9].

Most studies to date on medication adherence in patients with T2DM were conducted for a maximum of 1 year, with the impact of most of the interventions being assessed for only 6 months [10]. However, once treatment with a hypoglycemic drug is initiated, multi-year drug adherence investigations are needed, since most patients continue to take them for several years after diagnosis.

We conducted a 3-year retrospective study, using data on itemized medical claims, to determine the current status of medication adherence among patients with T2DM. The potential effects of polypharmacy and other factors on medication adherence in these patients were also assessed. We also investigated the effects of medication nonadherence on hemoglobin A1c (HbA1c) levels at the end of the 3-year observation.


Study design and data source

We conducted a retrospective study using an itemized medical claim database maintained by the Japan Medical Data Center. This database includes employment medical claims and medical check-up data provided by multiple health insurance societies [11,12]. This itemized medical claim database includes baseline patient attributes, the disease code (according to the Medical Information System Development Center Standard Disease Nomenclature Master and the International Classification of Diseases (ICD)-10), prescription details, and medical procedures.


The subjects in our study were patients who had visited our institute between May 2005 and January 2013, and fulfilled the following selection criteria: (i) a diagnosis of T2DM (ICD-10: E11) or unspecified diabetes (ICD-10: E14); (ii) a history of being prescribed a hypoglycemic agent; and (iii) data available for 3 years of continuous follow-up. Exclusion criteria included: (i) disease name/code for type 1 diabetes; and (ii) age either <18 years or ≥75 years. The index date was defined as the month during which the prescription for the hypoglycemic agent was issued.

Definition of medication adherence

We utilized the proportion of days covered (PDC) as our index of medication adherence, which we calculated for each patient. PDC is defined as the number of days for which the hypoglycemic agent was prescribed and in the possession of the patient, to the number of days in the observation period:

PDC = [no. of days for which the hypoglycemic agent was possessed during the observation period (days)/observation period (days)]

Patients were categorized in the good adherence group if they achieved a PDC threshold of at least 80% [1316]. A PDC value of ≥0.8 was considered adherence, and of <0.8 was considered nonadherence.

Definition of polypharmacy

As described in a previous study on polypharmacy [17], we defined polypharmacy as the use ≥5 drugs, after excluding the following medications: injectable drugs, external use drugs, antibiotics, and any other drugs used in the treatment of non-chronic diseases, such as infections, prescribed for a total continuous use of less than 7 days. The number of drugs that were prescribed at the start of the observation period was used to determine polypharmacy.

Patient characteristics

Age, sex, and body mass index (BMI) were included as baseline characteristics and were identified using the data listed on the claims in the same year as the index date occurred. Data on HbA1c levels were collected from claims listed in the same year as the month of initiation of the observation period, and claims listed in the same year were those received in each of the 3 years observed after that. The total number of visits to our institute for the purpose of diabetes treatment during the 3-year observation period (the total number of visits) was calculated by counting the number of days on which the subject was prescribed the hypoglycemic agent during that period. Target values for blood glucose control and weight control in diabetic patients was set at HbA1c <7.0% for the former and BMI <25 kg/m2 for the latter as recommended by the Japan Diabetes Society guidelines.

Statistical analysis

Patient data were expressed as mean ± standard deviation (SD). Continuous variables were analyzed using unpaired t-test. Categorical variables were analyzed using chi-square test and are expressed as absolute numbers or percentages. Factors related to adherence at the end of the observation period were examined using logistic regression analysis. The number of oral medications (1, 2, 3, 4, ≥5), sex, age at baseline (<40, 40–49, 50–59 and ≥60 years), HbA1c levels (cut-off value 7.0%), BMI (cut-off value 25 kg/m2), use of hypoglycemic agents, and the total number of visits with cut-off values calculated using receiver operating characteristic (ROC) analysis were used as explanatory variables.

At the end of the observation period, factors related to maintaining HbA1c values <7.0% were analysed. These factors included the abovementioned explanatory variables and medication adherence. Univariate analysis was conducted for each explanatory variable and factors for which P <0.2 were included in a multivariate analysis to calculate the odds ratio (OR). Differences were regarded as significant when P <0.05. All statistical analyses were performed using the Stata software program (version 10; StataCorp, College Station, TX, USA).

Ethical considerations

Because the data were retrospective, deidentified, and anonymous, the institutional review board committee of Ktasato University determined that this study did not constitute research with human subjects. It was therefore exempted from institutional review board consideration.


There was a total of 884 subjects, and their background characteristics are shown in Table 1. We compared the patients’ background characteristics after dividing the subjects into adherent and nonadherent groups. Significant differences (adherent vs. nonadherent) were found in the following: number of medications (2.6 ± 2.0 vs. 2.2 ± 1.5, P <0.001), male gender (87.7% vs. 92.6%, P = 0.016), age (48.4 ± 7.8 years vs. 45.7 ± 8.1 years, P <0.001), polypharmacy (12.5% vs. 7.4%, P <0.001), dipeptidyl peptidase-4 inhibitor use (37.5% vs. 30.6%, P = 0.031), and biguanide use (12.5% vs. 16.9%, P = 0.033).

Table 2 depicts the details of the mean PDC and adherence, depending on the patients’ background characteristics, at the 3-year observation period endpoint. The 49.8% of subjects were classified as adherent, and about half nonadherent. The total number of visits by all subjects for the purpose of diabetes treatment during the 3-year observation period was 24.1 ± 16.0 times, and ROC analysis revealed that this number had a cut-off of 17 times (sensitivity 95.9%, specificity 60.6%) and an area under the curve of 0.86.

Table 2. Adherence in relation to percentage of PDC among patients with at least 3 year of follow-up.

The results of logistic regression analysis using adherence as the response variable are shown in Table 3. These results for the following variables were statistically significant: number of medications 3–4 (OR 1.68, 95% confidence interval (CI) 1.07–2.64, P = 0.024) or ≥5 (OR 2.74, 95% CI 1.38–5.46, P = 0.004), male sex (OR 0.45, 95% CI 0.23–0.89, P = 0.022), age ≥50 and <60 years (OR 2.15, 95% CI 1.15–3.99, P = 0.016), and total number of visits ≤17 (OR 29.9, 95% CI 18.4–48.7, P < 0.001).

Table 3. Logistic regression analysis for factors related to adherence.

The average HbA1c value at the observation endpoint was 7.2 ± 1.4% (mean ± SD), and 52.3% of the subjects achieved an HbA1c value of <7.0%. The results of multivariate analysis (Table 4) indicated that the following factors were statistically significant in achieving HbA1c levels <7.0% at the end of the observation period: adherence (OR 1.84, 95% CI 1.28–2.66, P = 0.001), age ≥50 and <60 years (OR 2.34, 95% CI 1.30–4.21, P = 0.005), HbA1c value of <7.0% (OR 5.01, 95% CI 3.36–7.47, P < 0.001), and sulfonylurea use (OR 0.54, 95% CI 0.34–0.86, P = 0.009).

Table 4. Factors related to the achievement of HbA1c value of <7.0% at the end of the 3-year of follow-up observation period.


Our results indicate that PDC for the 3-year observation endpoint was 79.6%. In only 49.8% of the cases we observed a PDC ≥0.8; thus, about half of the patients were nonadherent. The relatively higher medication adherence in our study than that in previous studies [35], may be attributable to the fact that we had an observation period of three years. A short observation period of only one year in previous studies might have resulted in less chances to improve medication adherence due to the loss of some opportunities where interventions could have been made if a longer period of observation was considered.

Hence, we believe that it is necessary to make efforts to improve medication adherence in order to achieve the target blood glucose level and to control the onset of diabetes complications.

Our study has revealed several factors related to adherence. We observed a positive relationship between adherence and number of visits ≥17 during the 3-year period. Frequent visits provide opportunities for physicians and pharmacists to re-evaluate prescriptions according to the patient’s current condition. The present study demonstrated that polypharmacy and older age were associated with adherence, which is consistent with the results of a previous study [18]. Several studies that assessed patients with T2DM with a high number of medications [19] and complications from other chronic diseases [2023] have shown a positive association between polypharmacy and adherence. The condition of polypharmacy reportedly leads to various complications, and is believed that medication adherence is higher in patients with polypharmacy compared to those with a small number of medications. In contrast, if there are any subjective symptoms due to complications, medication adherence may be increased to improve them.

The relationship between gender and medication adherence is controversial [2427]. In Japan, treatment interruptions in men under 40 years of age with T2DM are higher and medication adherence is reportedly low [28]. We also observed a similar trend, which is probably due to the fact that most of the cases included in our study fell in a similar age range. We also observed that medication adherence improved with age until the age of 60 years, as we did not observe any significant difference in the OR values in patients older than 60 years. In a previous adherence study in Japan [29], the mean PDC and the percent of adherent patients with T2DM had reportedly improved with the increase in the number of concomitant medications, with the highest PDC observed among patients on three or more concomitant medications. The lowest PDC was observed in patients who were only taking medication for T2DM [29]. Although it has been shown that the odds ratio for polypharmacy increases with the older age [30], we did not observe any significant improvement in adherence in the ≥60 age group. This result might be due to the smaller number of cases in the ≥60 age group compared to other age groups in our cohort. Finally, we investigated the factors related to achievement of an HbA1c value of <7.0% at the end of the 3-year observation period. The present study indicated that adherence has a positive effect on the achievement of an HbA1c value of <7.0%, and further investigation of its effect on the risk of diabetic complications is warranted. With adherence, hypoglycemic administration can be expected to be more effective, which in turn is likely to lead to satisfactory HbA1c levels being recorded at the observation endpoint. Although we found that being in the age group ≥50 to <60 years had a positive effect on achievement of the HbA1c level <7.0%, despite the general increase in insulin resistance and decrease in insulin production as a person ages, which may lead to a rise in HbA1c levels. We attribute the positive effect we observed in our study to the fact that medication adherence in this age group was generally good. However, we did not further elucidate the details of this particular aspect. Prescribing sulfonylureas has been reportedly related with older age, long-standing disease, and poor glycemic control [31]. The results of the present study indicated that sulfonylurea use was a risk factor for non-achievement of the HbA1c target of <7.0% because it tends to be used positively in cases that are having difficulty in glycemic control.

Our study has several limitations due to its retrospective nature and the use of itemized medical claims, which will lead to some difficulties in eliminating data and selection biases. We used the information available on Japan Medical Data Center database, which includes claims from employer-sponsored healthcare plans. Hence, our cohort only consisted of adults who were employed. The database includes information on a small number of diabetic patients≥75 years, which were excluded from this study. Nonetheless, previous studies have reported that elderly patients have better medication adherence than younger patients [18,28,32]. Therefore, while we might expect that medication adherence and persistence would be higher in older Japanese patients, further research is required to confirm this hypothesis. We did not collect other data that may have affected medication adherence, such as financial difficulties [33], ethnicity [34,35], psychological factors [36], and the quality of the relationship between patient and physician [37]. Finally, most of the subjects in this study were male; therefore, in order to generalize the findings it is necessary to conduct further studies which include a higher percentage of female patients with T2DM. We plan to conduct a detailed study with a large cohort in the near future.


In this study, we found that older age groups, taking several medications, and regular visits are associated with a better adherence. We also elucidated the effect of adherence on achievement of satisfactory HbA1c levels at the observation endpoint. Because maintaining medication adherence and achieving HbA1c targets are important in reducing the likelihood of diabetic complications, targeted interventions for different groups–such as those of younger age and taking fewer medications–need to be developed.


  1. 1. Osterberg L, Blaschke T. Adherence to medication. N Engl J Med. 2005;353: 487–497 pmid:16079372
  2. 2. DiMatteo MR. Variations in patients’ adherence to medical recommendations: a quantitative review of 50 years of research. Med Care. 2004;42: 200–209. pmid:15076819
  3. 3. Cramer J, Rosenheck R, Kirk G, Krol W, Krystal J, VA Naltrexone Study Group 425. Medication compliance feedback and monitoring in a clinical trial: predictors and outcomes. Value Health. 2003;6: 566–573. pmid:14627063
  4. 4. Waeber B, Leonetti G, Kolloch R, McInnes GT. Compliance with aspirin or placebo in the Hypertension Optimal Treatment (HOT) study. J Hypertens. 1999;17: 1041–1045. pmid:10419079
  5. 5. Claxton AJ, Cramer J, Pierce C. A systematic review of the associations between dose regimens and medication compliance. Clin Ther. 2001;23: 1296–1310. pmid:11558866
  6. 6. Cramer JA. A systematic review of adherence with medications for diabetes. Diabetes Care. 2004;27: 1218–1224. pmid:15111553
  7. 7. Bailey CJ, Kodack M. Patient adherence to medication requirements for therapy of type 2 diabetes. Int J Clin Pract. 2011;65: 314–322. pmid:21314869
  8. 8. Krass I, Schieback P, Dhippayom T. Adherence to diabetes medication: a systematic review. Diabet Med. 2015;32: 725–737. pmid:25440507
  9. 9. Fukuda H, Mizobe M. Impact of nonadherence on complication risks and healthcare costs in patients newly-diagnosed with diabetes. Diabetes Res Clin Pract. 2017;123: 55–62. pmid:27940390
  10. 10. Sapkota S, Brien JA, Greenfield JR, Aslani P. A systematic review of interventions addressing adherence to anti-diabetic medications in patients with type 2 diabetes–components of interventions. PLoS One. 2015; 10(2):e0118296. pmid:25710465
  11. 11. Kimura S, Sato T, Ikeda S, Noda M, Nakayama T. Development of a database of health insurance claims: standardization of disease classifications and anonymous record linkage. J Epidemiol. 2010; 20: 413–419. pmid:20699602
  12. 12. Nakaoka S, Ishizaki T, Urushihara H, Satoh T, Ikeda S, Morikawa K, et al. Echocardiography for the detection of valvulopathy associated with the use of ergot-derived dopamine agonists in patients with Parkinson's disease. Intern Med. 2011;50: 687–694. pmid:21467699
  13. 13. Gibson TB, Song X, Alemayehu B, Wang SS, Waddell JL, Bouchard JR, et al. Cost sharing, adherence, and health outcomes in patients with diabetes. Am J Manag Care. 2010;16: 589–600. pmid:20712392
  14. 14. Juarez DT, Tan C, Davis J, Mau M. Factors affecting sustained medication adherence and its impact on health care utilization in patients with diabetes. J Pharm Health Serv Res. 2013;4: 89–94. pmid:23717343
  15. 15. Choudhry NK, Shrank WH, Levin RL, Lee JL, Jan SA, Brookhart MA, et al. Measuring concurrent adherence to multiple related medications. Am J Manag Care. 2009;15: 457–464. pmid:19589013
  16. 16. Ho PM, Rumsfeld JS, Masoudi FA, McClure DL, Plomondon ME, Steiner JF, et al. Effect of medication nonadherence on hospitalization and mortality among patients with diabetes mellitus. Arch Intern Med. 2006;166: 1836–1841. pmid:17000939
  17. 17. Masnoon N, Shakib S, Kalisch-Ellett L, Caughey GE. What is polypharmacy? A systematic review of definitions. BMC Geriatr. 2017;17: 230. pmid:29017448
  18. 18. Tunceli K, Zhao C, Davies MJ, Brodovicz KG, Alexander CM, Iglay K, et al. Factors associated with adherence to oral antihyperglycemic monotherapy in patients with type 2 diabetes. Patient Prefer Adherence. 2015;9: 191–197. pmid:25670888
  19. 19. Raum E, Kramer HU, Ruter G, Rothenbacher D, Rosemann T, Szecsenyi J, et al. Medication non-adherence and poor glycaemic control in patients with type 2 diabetes mellitus. Diabetes Res Clin Pract. 2012;97: 377–384. pmid:22763108
  20. 20. Patel A, MacMahon S, Chalmers J, Neal B, Billot L, Woodward M, et al. Intensive blood glucose control and vascular outcomes in patients with type 2 diabetes. N Engl J Med. 2008;358: 2560–2572. pmid:18539916
  21. 21. Jamous RM, Sweileh WM, Abu‐Taha AS, Sawalha AF, Zyoud SH, Morisky DE. Adherence and satisfaction with oral hypoglycemic medications: a pilot study in Palestine. Int J Clin Pharm. 2011;33: 942–948. pmid:21918840
  22. 22. Kreyenbuhl J, Dixon LB, McCarthy JF, Soliman S, Ignacio RV, Valenstein M. Does adherence to medications for type 2 diabetes differ between individuals with vs without schizophrenia? Schizophr Bull. 2010;36: 428–435. pmid:18718883
  23. 23. Ahmad NS, Ramli A, Islahudin F, Paraidathathu T. Medication adherence in patients with type 2 diabetes mellitus treated at primary health clinics in Malaysia. Patient Prefer Adherence. 2013;7: 525–530. pmid:23814461
  24. 24. Curkendall SM, Thomas N, Bell KF, Juneau PL, Weiss AJ. Predictors of medication adherence in patients with type 2 diabetes mellitus. Curr Med Res Opin. 2013;29: 1275–1286. pmid:23815104
  25. 25. Donnan PT, MacDonald TM, Morris AD. Adherence to prescribed oral hypoglycaemic medication in a population of patients with type 2 diabetes: a retrospective cohort study. Diabet Med. 2002;19: 279–284. pmid:11942998
  26. 26. Hertz RP, Unger AN, Lustik MB. Adherence with pharmacotherapy for type 2 diabetes: a retrospective cohort study of adults with employer sponsored health insurance. Clin Ther. 2005;27: 1064–1073. pmid:16154485
  27. 27. Tiv M, Viel JF, Mauny F, Eschwege E, Weill A, Fournier C, et al. Medication adherence in type 2 diabetes: the ENTRED study 2007, a French population-based study. PLoS One. 2012;7: e32412. pmid:22403654
  28. 28. Hayashino Y, Suzuki H, Yamazaki K, Izumi K, Noda M, Kobayashi M. Depressive symptoms, not completing a depression screening questionnaire, and risk of poor compliance with regular primary care visits in patients with type 2 diabetes: the Japan Diabetes Outcome Intervention Trial 2 (J-DOIT2) study group. Exp Clin Endocrinol Diabetes. 2011;119: 276–280. pmid:21031344
  29. 29. Kurtyka K, Nishikino R, Ito C, Brodovicz K, Chen Y, Tunceli K. Adherence to dipeptidyl peptidase-4 inhibitor therapy among type 2 diabetes patients with employer-sponsored health insurance in Japan. J Diabetes Investig. 2016;7: 737–743. pmid:27182033
  30. 30. Horii T, Iwasawa M, Kabeya Y, Atsuda K. Polypharmacy and oral antidiabetic treatment for type 2 diabetes characterised by drug class and patient characteristics: A Japanese database analysis. Sci Rep. 2019 Sep 10; 9(1):12992. pmid:31506542
  31. 31. Fujihara K, Igarashi R, Matsunaga S, Matsubayashi Y, Yamada T, Yokoyama H, et al. Comparison of baseline characteristics and clinical course in Japanese patients with type 2 diabetes among whom different types of oral hypoglycemic agents were chosen by diabetes specialists as initial monotherapy (JDDM 42). Medicine. 2017;96: e6122. pmid:28207538
  32. 32. Hayashino Y, Suzuki H, Yamazaki K, Goto A, Izumi K, Noda M. A cluster randomized trial on the effect of a multifaceted intervention improved the technical quality of diabetes care by primary care physicians: The Japan Diabetes Outcome Intervention Trial-2 (J-DOIT2). Diabet Med. 2016;33: 599–608. pmid:26331280
  33. 33. World Health Organization. Adherence to long term therapies: Evidence for action. Geneva: World Health Organization; 2003. p. 221
  34. 34. Adams AS, Trinacty CM, Zhang F, Kleinman K, Grant RW, Meigs JB, et al. Medication adherence and racial differences in A1C control. Diabetes Care. 2008;31: 916–921. pmid:18235050
  35. 35. Trinacty CM, Adams AS, Soumerai SB, Zhang F, Meigs JB, Piette JD, et al. Racial differences in long-term adherence to oral antidiabetic drug therapy: a longitudinal cohort study. BMC Health Serv Res. 2009;9: 24. pmid:19200387
  36. 36. Nagasawa M, Smith MC, Barnes JH Jr, Fincham JE. Meta-analysis of correlates of diabetes patients' compliance with prescribed medications. Diabetes Educ. 1990;16: 192–200. pmid:2139601
  37. 37. Lawton J, Peel E, Parry O, Douglas M. Patients' perceptions and experiences of taking oral glucose-lowering agents: a longitudinal qualitative study. Diabet Med. 2008;25:491–495. pmid:18294222