Most adults with new-onset diabetes in Alberta, Canada, are prescribed metformin monotherapy, but nearly half do not use medication as directed 1 year after initiation, according to findings published in Diabetic Medicine.
David J.T. Campbell
“While the expansion of medical options provides prescribers with more options, local guidelines still recommend that metformin monotherapy be chosen for cases of uncomplicated diabetes with an HbA1c less than 8.5%, due largely to the cost-effectiveness of this therapy relative to other more expensive medications,” David J.T. Campbell, MD, PhD, MSc, FRCPC, assistant professor and consultant endocrinologist in the departments of medicine, community health sciences and cardiac sciences at the Cumming School of Medicine, University of Calgary, in Canada, told Healio. “Therefore, the point of our study was to see if prescribers were still using metformin when appropriate, in the face of so many new medications.”
Campbell and colleagues conducted a retrospective cohort study of adults older than 18 years from Alberta with incident diabetes diagnosed from April 2012 to March 2017. Incident cases were identified using an algorithm of two or more physical claims for diabetes in a 2-year period or at least one hospitalization for diabetes. Adults with an HbA1c between 6.5% and 8.5% and those who filled a prescription for diabetes medication within 1 year of diagnosis were included. Pharmacotherapy was categorized as either metformin monotherapy, non-metformin diabetes medication or metformin-containing combination therapy. Participants were defined as having adhered to medication if they had a supply to cover at least 80% of observed treatment days. Data on age, sex, HbA1c, neighborhood income quintile, geographic location, prescriber specialty and medication costs were also collected.
There were 17,932 adults included in the study cohort, of whom 89% received metformin monotherapy as their initial therapy, 7.6% were prescribed a metformin combination agent and 3.3% received a non-metformin medication. Sulfonylureas and DPP-IV inhibitors were the most commonly co-prescribed medications for those receiving metformin combination therapy and the most common agents for those not prescribed metformin.
Nearly half of do not maintain prescribed regimen
Of the study cohort, 48% did not adhere to diabetes therapy in their first year of treatment. Those who were older (RR = 1.01; 95% CI, 1.01-1.01; P < .001) or had comorbidities were more likely to adhere to treatment. Adults living in the highest neighborhood income quintile were more likely to adhere to treatment compared with those living in the lowest income quintile (RR = 1.12; 95% CI, 1.07-1.17; P < .001). Those treated with medications other than metformin (RR = 1.1; 95% CI, 1.02-1.18; P = .016) or metformin combination therapy (RR = 1.27; 95% CI, 1.22-1.33; P < .001) were more likely to adhere to treatment compared with adults taking metformin.
Within the first year of treatment, 54% of those who started on metformin remained on it. The proportion of adults taking metformin who adhered to medication dropped by 10% after 30, 90 and 100 days. Most of those who discontinued metformin did not switch to another medication. Adults with a higher HbA1c were more likely to discontinue metformin monotherapy and more likely to switch to a combination therapy compared with those with a lower HbA1c.
“There are important implications for patients who discontinue therapy that is initially prescribed,” Campbell said. “We know that metformin helps to lower blood glucose, and there is even evidence that it helps to reduce diabetes complications in the long run, yet many patients are forgoing these benefits by discontinuing their treatment shortly after starting.”
Higher costs with non-metformin monotherapy
Adults prescribed metformin combination therapy or a non-metformin agent had about double the total health care costs compared with those prescribed metformin. After 1 year of medication initiation, adults on metformin monotherapy accrued 139 Canadian dollars in medication costs, whereas those on metformin combination therapy accrued CA$932 in medication costs, and those prescribed non-metformin agents CA$817 in costs.
“We would like to better explore the reasons for nonadherence to metformin and other diabetes treatments in order to plan and design programs and supports to help patients remain on effective medical therapies,” Campbell said. “Furthermore, we hope to use our database of patients with diabetes to answer other real-world medication-related questions, including better understanding if other therapies are used in the appropriate clinical settings, as per guidelines.”
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David J.T. Campbell, MD, PhD, MSc, FRCPC, can be reached at [email protected]