Metformin usually prescribed, but not always taken
Dr. Campbell and colleagues analyzed 17,932 individuals with incident type 2 diabetes diagnosed between April 1, 2012, and March 31, 2017. Overall, 89% received metformin monotherapy as their initial diabetes prescription, 7.6% started metformin in combination with another glucose-lowering drug, and 3.3% were prescribed a nonmetformin diabetes medication. (Those prescribed insulin as their first diabetes medication were excluded.)
The most commonly coprescribed drugs with metformin were sulfonylureas (in 47%) and DPP-4 inhibitors (28%). Of those initiated with only nonmetformin medications, sulfonylureas were also the most common (53%) and dipeptidyl peptidase-4 (DPP-4) inhibitors second (21%).
The metformin prescribing rate of 89% reflects current guidelines, Dr. Campbell noted.
“In hypertension, clinicians weren’t really following the guidelines ... they were prescribing more expensive drugs than the guidelines say. ... We showed that in diabetes, contrary to hypertension, clinicians really are generally following the clinical practice guidelines. ... The vast majority who are started on metformin are started on monotherapy. That was reassuring to us. We’re not paying for a bunch of expensive drugs when metformin would do just as well,” he said.
However, the proportion who had been dispensed metformin to cover the prescribed number of days dropped by about 10% after 30 days, by a further 10% after 90 days, and yet again after 100 days, resulting in just 54% remaining on the drug by 1 year.
Factors associated with higher adherence included older age, presence of comorbidities, and highest versus lowest neighborhood income quintile.
Those who had been prescribed nonmetformin monotherapy had about twice the total health care costs of those initially prescribed metformin monotherapy. Higher health care costs were seen among patients who were younger, had lower incomes, had higher baseline A1c, had more comorbidities, and were men.
How will the newer type 2 diabetes drugs change prescribing?
Dr. Campbell noted that “a lot has changed since 2017. ... At least in Canada, the sodium-glucose cotransporter 2 (SGLT2) inhibitors and glucagon-like peptide 1 receptor agonists were supposed to be reserved as second-line agents in patients with cardiovascular disease, but more and more they’re being thought of as first-line agents in high-risk patients.”
“I suspect as those guidelines are transmitted to primary care colleagues who are doing the bulk of the prescribing we’ll see more and more uptake of these agents.”
Indeed, Dr. Flory said, “The metformin data at this point are very dated and the body of trials showing health benefits for it is actually very weak compared to the big trials that have been done for the newer agents, to the point where you can imagine a consensus gradually forming where people start to recommend something other than metformin for nearly everybody with type 2 diabetes. The cost implications are just huge, and I think the safety implications as well.”
According to Dr. Flory, the SGLT2 inhibitors “are fundamentally not as safe as metformin. I think they’re very safe drugs – large good studies have established that – but if you’re going to give drugs to a large number of people who are pretty healthy at baseline the safety standards have to be pretty high.”
Just the elevated risk of euglycemic diabetic ketoacidosis alone is reason for pause, Dr. Flory said. “Even though it’s manageable ... metformin just doesn’t have a safety problem like that. I’m very comfortable prescribing SGLT2 inhibitors, but If I’m going to give a drug to a million people and have nothing go wrong with any of them, that would be metformin, not an SGLT2 [inhibitor].”
Dr. Campbell and colleagues will be conducting a follow-up of prescribing data through 2019, which will of course include the newer agents. They’ll also investigate reasons for drug discontinuation and outcomes of those who discontinue versus continue metformin.
Dr. Campbell has reported no relevant financial relationships. Dr. Flory consults for a legal firm on litigation related to insulin analog pricing issues, not for or pertaining to a specific company.
A version of this article first appeared on Medscape.com.