Multiple medication adherence and its effect on clinical outcomes among patients with comorbid type 2 diabetes and hypertension

Med Care. 2013 Oct;51(10):879-87. doi: 10.1097/MLR.0b013e31829fa8ed.


Objective: To investigate multiple medication adherence (MMA) and its impact on microvascular and macrovascular complications using instrumental variables (IVs).

Research design: A retrospective observational study was conducted using administrative claims and electronic medical records from a large physician group in Southern California (N=2334).

Subjects: We identified individuals between January 2006 and June 2009 newly starting oral diabetes (DM) or hypertension (HTN) medications with preexisting comorbid HTN or DM prescription history.

Measures: MMA was defined as a proportion of days covered where both DM and HTN medications were simultaneously available over a 33-month follow-up period. Microvascular or macrovascular complications included myocardial infarction, stroke, renal failure, and diabetic retinopathy. Multivariable logistic regressions and an IV estimation using physician-related variables were implemented.

Results: MMA was supoptimal as the mean (SD) proportion of days covered was 0.53 (0.32). Patients were more adherent to medications for a preexisting condition in comparison with those for the newer disease. Older age, number of index medications [OR (95% CI)=1.36 (1.22-1.52)], receiving care from a physician who prescribed statin more frequently [OR (95% CI)=2.63 (1.67-4.14)], and receiving care from the same physician for both DM and HTN [OR (95% CI)=1.57 (1.08-2.27)] were significant factors of being adherent. Using physician-related IVs, MMA reduced microvascular and macrovascular complications. The increase in MMA from 50% to 80% reduced the average predicted probability of microvascular or macrovascular complication rate by 29.5%.

Conclusions: Adherence to medications for DM and HTN were differed and higher MMA reduced microvascular or macrovascular complications when controlling for endogeneity bias.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antihypertensive Agents / administration & dosage*
  • Antihypertensive Agents / adverse effects
  • California / epidemiology
  • Causality
  • Comorbidity
  • Diabetes Complications / epidemiology*
  • Diabetes Mellitus, Type 2 / drug therapy*
  • Diabetes Mellitus, Type 2 / epidemiology
  • Diabetic Retinopathy / epidemiology
  • Drug Therapy, Combination
  • Female
  • Humans
  • Hypertension / drug therapy*
  • Hypertension / epidemiology
  • Hypoglycemic Agents / administration & dosage*
  • Hypoglycemic Agents / adverse effects
  • Logistic Models
  • Male
  • Medication Adherence / statistics & numerical data*
  • Middle Aged
  • Multivariate Analysis
  • Myocardial Infarction / epidemiology
  • Renal Insufficiency / epidemiology
  • Retrospective Studies
  • Stroke / epidemiology
  • Treatment Outcome


  • Antihypertensive Agents
  • Hypoglycemic Agents