Prescribing patterns and adherence to medication among South-Asian, Chinese and white people with Type 2 diabetes mellitus: a population-based cohort study

Aim To determine the prescribing of and adherence to oral hypoglycaemic agents, insulin, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers and statin therapy among South-Asian, Chinese and white people with newly diagnosed diabetes. Methods The present study was a population-based cohort study using administrative and pharmacy databases to include all South-Asian, Chinese and white people aged >= 35 years with diabetes living in British Columbia, Canada (1997-2006). Adherence to each class of medication was measured using proportion of days covered over 1 year with optimum adherence defined as >= 80%. Results The study population included 9529 South-Asian, 14 084 Chinese and 143 630 white people with diabetes. The proportion of people who were prescribed angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, statin or oral hypoglycaemic agents was <= 50% for all groups. South-Asian and Chinese people had significantly lower adherence for all medications than white people, with the lowest adherence to angiotensin-converting enzyme inhibitor treatment (South-Asian people: adjusted odds ratio 0.37, 95% CI 0.34-0.39; P<0.0001; Chinese people: adjusted odds ratio 0.50, 95% CI 0.47-0.54; P<0.0001) and statin therapy (South-Asian people: adjusted odds ratio 0.47, 95% CI 0.41 - 0.53, P < 0.0001; Chinese people: adjusted odds ratio 0.72, 95% CI 0.67 - 0.77; P<0.0001) compared with white people. Conclusion Adherence to evidence-based pharmacotherapy was substantially worse among the South-Asian and Chinese populations. Care providers need to be alerted to the high levels of non-adherence in these groups and the underlying causes need to be investigated.