Refill adherence and polypharmacy among patients with type 2 diabetes in general practice

Pharmacoepidemiol Drug Saf. 2009 Nov;18(11):983-91. doi: 10.1002/pds.1810.


Background and aims: Non-adherence is considered a major barrier to better outcomes of diabetes care. A relationship has been established between polypharmacy and patients' adherence. This study aims to investigate the occurrence of polypharmacy and non-adherence in general practice, their mutual relationship and the association between adherence and the intermediate outcomes of diabetes care.

Materials and methods: We used the baseline and follow-up data of a randomised controlled trial (RCT) that compared usual care with care in accordance with a locally adapted national guideline. This study took place in the Netherlands and involved 30 general practices and 1283 patients. We obtained a complete medication profile of all participants and calculated the number of prescribed drugs and the adherence indices (AI) for oral blood glucose, blood pressure and cholesterol lowering drugs. Patients with an adherence index < 0.8 were considered non-adherent. Clustering at practice level and case-mix were taken into account.

Results: Approximately 80% of the participating patients demonstrated an adherence index >or= 0.8 for oral blood glucose, blood pressure and cholesterol lowering drugs. In the intervention group, increase of drug prescriptions exceeded that of controls (1.1 +/- 2.0 vs. 0.6 +/- 1.5, p < 0.001, adjusted p < 0.05). There was evidence of an inverse relationship between the number of drugs that had been prescribed during the last 6 months of the study and patients' adherence to blood pressure lowering medications (adjusted OR 0.84, 95%CI 0.78-0.91). After one year, HbA1c and total cholesterol levels were significantly lower in adherent patients.

Conclusion: During the intervention the mean number of drug prescriptions increased in both the study groups. This did not result in a lower adherence to blood glucose and cholesterol lowering medications. Given the relationship between the number of medications and patients' adherence to blood pressure lowering drugs, it may be wise to discuss adherence before prescribing multiple drug regimens.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Aged
  • Anticholesteremic Agents / administration & dosage
  • Anticholesteremic Agents / therapeutic use
  • Antihypertensive Agents / administration & dosage
  • Antihypertensive Agents / therapeutic use
  • Blood Glucose / analysis
  • Blood Pressure / drug effects
  • Cholesterol / blood
  • Diabetes Mellitus, Type 2 / blood
  • Diabetes Mellitus, Type 2 / complications
  • Diabetes Mellitus, Type 2 / drug therapy*
  • Diabetes Mellitus, Type 2 / epidemiology
  • Drug Prescriptions / statistics & numerical data*
  • Female
  • Humans
  • Hypoglycemic Agents / administration & dosage
  • Hypoglycemic Agents / therapeutic use
  • Male
  • Medication Adherence / statistics & numerical data*
  • Netherlands / epidemiology
  • Polypharmacy*
  • Practice Guidelines as Topic
  • Surveys and Questionnaires


  • Anticholesteremic Agents
  • Antihypertensive Agents
  • Blood Glucose
  • Hypoglycemic Agents
  • Cholesterol