Metformin adherence in patients with type 2 diabetes and its association with glycated haemoglobin levels

Lynne Chepulis; Christopher Mayo; Brittany Morison; Rawiri Keenan; Chunhuan Lao; Ryan Paul; Ross Lawrenson

doi:10.1071/HC20043

RESEARCH ARTICLE (Open Access)

Metformin adherence in patients with type 2 diabetes and its association with glycated haemoglobin levels

Lynne Chepulis ¹ ⁴ , Christopher Mayo ² , Brittany Morison ¹ , Rawiri Keenan ¹ , Chunhuan Lao ¹ , Ryan Paul ² ³ , Ross Lawrenson ¹ ³

+ Author Affiliations

- Author Affiliations

¹ Medical Research Centre, University of Waikato, Hamilton, New Zealand

² Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand

³ Waikato District Health Board, Hamilton, New Zealand

⁴ Corresponding author. Email: lynnec@waikato.ac.nz

Journal of Primary Health Care 12(4) 318-326 https://doi.org/10.1071/HC20043
Published: 5 November 2020

Journal Compilation © Royal New Zealand College of General Practitioners 2020 This is an open access article licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License

Abstract

INTRODUCTION: Metformin is the initial medication of choice for most patients with type 2 diabetes. Non-adherence results in poorer glycaemic control and increased risk of complications.

AIM: The aim of this study was to characterise metformin adherence and association with glycated haemoglobin (HbA1c) levels in a cohort of patients with type 2 diabetes.

METHODS: Prescription and dispensing data were used for this study. Primary care clinical and demographic data were collected from 10 general practices (October 2016–March 2018) and linked to pharmaceutical dispensing information. Metformin adherence was initially measured by calculating the proportion of patients who had optimal medication cover for at least 80% of days (defined as a medication possession ratio (MPR) of ≥0.8), calculated using dispensing data. Prescription adherence was assessed by comparing prescription and dispensing data. The association between non-adherence (MPR <0.8) and HbA1c levels was also assessed.

RESULTS: Of the 1595 patients with ≥2 metformin prescriptions, the mean MPR was 0.87. Fewer Māori had an MPR ≥0.8 than New Zealand European (63.8% vs. 81.2%). Similarly, Māori received fewer metformin prescriptions (P = 0.02), although prescription adherence did not differ by ethnicity. Prescription adherence was lower in younger patients (P = 0.002). Mean HbA1c levels were reduced by 4.8 and 5.0 mmol/mol, respectively, in all and Māori patients with an MPR ≥0.8. Total prescription adherence reduced HbA1c by 3.2 mmol/mol (all P < 0.01).

DISCUSSION: Ethnic disparity exists for metformin prescribing, leading to an overall reduction in metformin coverage for Māori patients. This needs to be explored further, including understanding whether this is a patient preference or health system issue.

Keywords: Type 2 diabetes; medication adherence; general practice; inequality

References

[1] Atlantis E, Joshy G, Williams M, Simmons D. Diabetes among Māori and other ethnic groups in New Zealand. In: Diabetes Mellitus in Developing Countries and Underserved Communities. S. Dagogo-Jack, ed. Cham, Switzerland: Springer; 2017. p. 165–90.

[2] Ministry of Health. Diabetes; Table 28: Indicators by gender, Māori and non-Māori. Wellington, Ministry of Health; 2018. [cited 2018 August 22]. Available from: https://www.health.govt.nz/our-work/populations/maori-health/tatau-kahukura-maori-health-statistics/nga-mana-hauora-tutohu-health-status-indicators/diabetes

[3] Best Practice Advocacy Centre New Zealand. A rising tide of type 2 diabetes in younger people: what can primary care do? Dunedin: BPAC; 2019. [cited 2019 August]. Available from: https://bpac.org.nz/2018/diabetes.aspx

[4] Fowler M. Microvascular and macrovascular complications of diabetes. Clin Diabetes. 2011; 29 116–22.
| Microvascular and macrovascular complications of diabetes.Crossref | GoogleScholarGoogle Scholar |

[5] Thomas MC, Cooper ME, Zimmet P. Changing epidemiology of type 2 diabetes mellitus and associated chronic kidney disease. Nat Rev Nephrol. 2016; 12 73–81.
| 26553517PubMed |

[6] Mulnier HE, Seaman HE, Raleigh VS, et al. Mortality in people with type 2 diabetes in the UK. Diabet Med. 2006; 23 516–21.
| Mortality in people with type 2 diabetes in the UK.Crossref | GoogleScholarGoogle Scholar | 16681560PubMed |

[7] Khalil H. Diabetes microvascular complications—A clinical update. Diabetes Metab Syndr. 2017; 11 S133–39.
| Diabetes microvascular complications—A clinical update.Crossref | GoogleScholarGoogle Scholar | 27993541PubMed |

[8] Mulnier HE, Seaman HE, Raleigh VS, et al. Risk of myocardial infarction in men and women with type 2 diabetes in the UK: a cohort study using the General Practice Research Database. Diabetologia. 2008; 51 1639–45.
| Risk of myocardial infarction in men and women with type 2 diabetes in the UK: a cohort study using the General Practice Research Database.Crossref | GoogleScholarGoogle Scholar | 18581091PubMed |

[9] New Zealand Guidelines Group. Guidance on the management of type 2 diabetes. Wellington: Ministry of Health; 2011. [cited 2019 January]. Available from: https://www.moh.govt.nz/notebook/nbbooks.nsf/0/60306295DECB0BC6CC257A4F000FC0CB/$file/NZGG-management-of-type-2-diabetes-web.pdf

[10] Best Practice Advocacy Centre New Zealand Managing patients with type 2 diabetes: from lifestyle to insulin. Best Pract J. 2015; 72 32–42.

[11] Best Practice Advocacy Centre New Zealand. HbA1c targets in people with type 2 diabetes - do they matter? Dunedin: BPAC; 2010. [cited 2020 Mar]. Available from: https://bpac.org.nz/BPJ/2010/August/docs/BPJ_30_hba1c_pages8-15.pdf

[12] Liu SC, Tu YK, Chien MN, Chien KL. Effect of antidiabetic agents added to metformin on glycaemic control, hypoglycaemia and weight change in patients with type 2 diabetes: a network meta-analysis. Diabetes Obes Metab. 2012; 14 810–20.
| Effect of antidiabetic agents added to metformin on glycaemic control, hypoglycaemia and weight change in patients with type 2 diabetes: a network meta-analysis.Crossref | GoogleScholarGoogle Scholar | 22486990PubMed |

[13] Scheen AJ, Paquot N. Metformin revisited: a critical review of the benefit–risk balance in at-risk patients with type 2 diabetes. Diabetes Metab. 2013; 39 179–90.
| Metformin revisited: a critical review of the benefit–risk balance in at-risk patients with type 2 diabetes.Crossref | GoogleScholarGoogle Scholar | 23528671PubMed |

[14] Maruthur NM, Tseng E, Hutfless S, et al. Diabetes medications as monotherapy or metformin-based combination therapy for type 2 diabetes: a systematic review and meta-analysis. Ann Intern Med. 2016; 164 740–51.
| Diabetes medications as monotherapy or metformin-based combination therapy for type 2 diabetes: a systematic review and meta-analysis.Crossref | GoogleScholarGoogle Scholar | 27088241PubMed |

[15] Aikens JE, Piette JD. Longitudinal association between medication adherence and glycaemic control in type 2 diabetes. Diabet Med. 2013; 30 338–44.
| Longitudinal association between medication adherence and glycaemic control in type 2 diabetes.Crossref | GoogleScholarGoogle Scholar | 23075262PubMed |

[16] Raum E, Krämer HU, Rüter G, et al. Medication non-adherence and poor glycaemic control in patients with type 2 diabetes mellitus. Diabetes Res Clin Pract. 2012; 97 377–84.
| Medication non-adherence and poor glycaemic control in patients with type 2 diabetes mellitus.Crossref | GoogleScholarGoogle Scholar | 22763108PubMed |

[17] Farahani Dastjani F, Shamsi M, Khorsandi M, et al. To study the factors affecting medication adherence in diabetic patients based on health belief model in Arak, 2014. J Arak Univ Med Sci. 2016; 19 49–58.

[18] Petrenchik L, Loh FE. Factors affecting noninsulin antidiabetic drug adherence in patients with type 2 diabetes. Diabetes. 2018; 67
| Factors affecting noninsulin antidiabetic drug adherence in patients with type 2 diabetes.Crossref | GoogleScholarGoogle Scholar |

[19] Florez H, Luo J, Castillo-Florez S, et al. Impact of metformin-induced gastrointestinal symptoms on quality of life and adherence in patients with type 2 diabetes. Postgrad Med. 2010; 122 112–20.
| Impact of metformin-induced gastrointestinal symptoms on quality of life and adherence in patients with type 2 diabetes.Crossref | GoogleScholarGoogle Scholar | 20203462PubMed |

[20] Bonnet F, Scheen A. Understanding and overcoming metformin gastrointestinal intolerance. Diabetes Obes Metab. 2017; 19 473–81.
| Understanding and overcoming metformin gastrointestinal intolerance.Crossref | GoogleScholarGoogle Scholar | 27987248PubMed |

[21] Kharjul MD, Cameron C, Braund R. Using the Pharmaceutical Collection Database to identify patient adherence to oral hypoglycaemic medicines. J Prim Health Care. 2019; 11 265–74.
| Using the Pharmaceutical Collection Database to identify patient adherence to oral hypoglycaemic medicines.Crossref | GoogleScholarGoogle Scholar | 32171380PubMed |

[22] Horsburgh S, Barson D, Zeng J, et al. Adherence to metformin monotherapy in people with type 2 diabetes mellitus in New Zealand. Diabetes Res Clin Pract. 2019; 158 107902
| Adherence to metformin monotherapy in people with type 2 diabetes mellitus in New Zealand.Crossref | GoogleScholarGoogle Scholar | 31672501PubMed |

[23] Horsburgh S, Norris P. Ethnicity and access to prescription medicines. N Z Med J. 2013; 126 7–11.
| 24162626PubMed |

[24] Statistics New Zealand. Urban/Rural Profile Categories: North Island. Wellington: Statistics New Zealand, 2001. [cited 2018 May 16]. Available from: www.stats.govt.nz

[25] New Zealand Pharmaceutical Schedule. Pharmac; 2018. Report No. 1. Wellington: Pharmac; 2018.

[26] Karve S, Cleves MA, Helm M, et al. Good and poor adherence: optimal cut-point for adherence measures using administrative claims data. Curr Med Res Opin. 2009; 25 2303–10.
| Good and poor adherence: optimal cut-point for adherence measures using administrative claims data.Crossref | GoogleScholarGoogle Scholar | 19635045PubMed |

[27] Wong MC, Kong AP, So WY, et al. Adherence to oral hypoglycemic agents in 26 782 Chinese patients: a cohort study. J Clin Pharmacol. 2011; 51 1474–82.
| Adherence to oral hypoglycemic agents in 26 782 Chinese patients: a cohort study.Crossref | GoogleScholarGoogle Scholar | 21098691PubMed |

[28] Reid J, Cormack D, Crowe M. The significance of socially-assigned ethnicity for self-identified Māori accessing and engaging with primary healthcare in New Zealand. Health. 2016; 20 143–60.
| The significance of socially-assigned ethnicity for self-identified Māori accessing and engaging with primary healthcare in New Zealand.Crossref | GoogleScholarGoogle Scholar | 25645659PubMed |

[29] Lee CH, Sibley CG. Demographic and psychological correlates of satisfaction with healthcare access in New Zealand. N Z Med J. 2017; 130 11–24.
| 28727690PubMed |

[30] Jatrana S, Crampton P, Norris P. Ethnic differences in access to prescription medication because of cost in New Zealand. J Epidemiol Community Health. 2011; 65 454–60.
| Ethnic differences in access to prescription medication because of cost in New Zealand.Crossref | GoogleScholarGoogle Scholar | 20466707PubMed |

[31] Ministry of Health. He Korowai Oranga. Wellington: Ministry of Health; 2019. [cited 2020 April]. Available from: https://www.health.govt.nz/our-work/populations/maori-health/he-korowai-oranga

[32] Doggrell SA, Warot S. The association between the measurement of adherence to anti-diabetes medicine and the HbA1c. Int J Clin Pharm. 2014; 36 488–97.
| The association between the measurement of adherence to anti-diabetes medicine and the HbA1c.Crossref | GoogleScholarGoogle Scholar | 24710953PubMed |

[33] Zullig LL, Gellad WF, Moaddeb J, et al. Improving diabetes medication adherence: successful, scalable interventions. Patient Prefer Adher. 2015; 9 139–49.
| Improving diabetes medication adherence: successful, scalable interventions.Crossref | GoogleScholarGoogle Scholar |

[34] Omran D, Guirguis LM, Simpson SH. Systematic review of pharmacist interventions to improve adherence to oral antidiabetic medications in people with type 2 diabetes. Can J Diabetes. 2012; 36 292–9.
| Systematic review of pharmacist interventions to improve adherence to oral antidiabetic medications in people with type 2 diabetes.Crossref | GoogleScholarGoogle Scholar |

[35] Odegard PS, Carpinito G, Christensen DB. Medication adherence program: adherence challenges and interventions in type 2 diabetes. J Am Pharm Assoc. 2013; 53 267–72.
| Medication adherence program: adherence challenges and interventions in type 2 diabetes.Crossref | GoogleScholarGoogle Scholar |

[36] Lawrenson R, Joshy G, Eerens Y, Johnstone W. How do newly diagnosed patients with type 2 diabetes in the Waikato get their diabetes education? J Prim Health Care. 2010; 2 303–10.
| How do newly diagnosed patients with type 2 diabetes in the Waikato get their diabetes education?Crossref | GoogleScholarGoogle Scholar | 21125071PubMed |

[37] Mosnier-Pudar H, Hochberg G, Eschwege E, et al. How do patients with type 2 diabetes perceive their disease? Insights from the French DIABASIS survey. Diabete Metab. 2009; 35 220–7.
| How do patients with type 2 diabetes perceive their disease? Insights from the French DIABASIS survey.Crossref | GoogleScholarGoogle Scholar | 19303338PubMed |

[38] Murray CM, Shah BR. Diabetes self-management education improves medication utilization and retinopathy screening in the elderly. Prim Care Diabetes. 2016; 10 179–85.
| Diabetes self-management education improves medication utilization and retinopathy screening in the elderly.Crossref | GoogleScholarGoogle Scholar | 26620389PubMed |

[39] Beyene KA, Sheridan J, Aspden T. Prescription medication sharing: a systematic review of the literature. Am J Public Health. 2014; 104 e15–26.
| Prescription medication sharing: a systematic review of the literature.Crossref | GoogleScholarGoogle Scholar | 24524496PubMed |

[40] Ellis J, Mullan J. Prescription medication borrowing and sharing: risk factors and management. Aust Fam Physician. 2009; 38 816–19.
| 19893823PubMed |