Debate: Initial Combination Therapy for Type 2 Diabetes?

Miriam E. Tucker

July 13, 2023

Should pharmacologic treatment of type 2 diabetes start with combination therapy or metformin monotherapy, adding other agents over time?

This question was debated at the recent American Diabetes Association 83rd Scientific Sessions by two well-known clinician-researchers in the diabetes world.

Ralph A. DeFronzo, MD, argued for combination therapy at the time of diagnosis, and David M. Nathan, MD, countered that sequential therapy is a better way to go.

"The Ominous Octet": Addressing Multiple Underlying Defects

Of course, DeFronzo said, the right agents must be selected. "The drugs we're going to use as combination at a minimum have to correct the underlying insulin resistance and beta-cell failure, or we are not going to be successful."

In addition, he said, these drugs should also provide protection against cardiovascular, kidney, and fatty liver disease, because "[managing] diabetes is more than just controlling the glucose."

Recent US data suggest that half of people with diabetes have an A1c above 7%, and a quarter remain above 8%. "We're not really doing a very good job in terms of glycemic control," said DeFronzo, chief of the diabetes division at University of Texas Health, San Antonio.

One reason for this failure, he said, is the complex pathophysiology of type 2 diabetes represented by eight major defects, what he called the "ominous octet": decreased pancreatic insulin secretion, gut incretin effects, glucose uptake in the muscle, increased lipolysis, glucose reabsorption in the kidney, hepatic glucose production, increased glucagon secretion, and neurotransmitter dysfunction.

"There are eight problems, so you're going to need multiple drugs in combination...not ones that just lower the A1c."

And, DeFronzo said, these drugs "must be started early in the natural history of type 2 diabetes if progressive beta-cell failure is to be prevented."

He pointed to the United Kingdom Prospective Diabetes Study (UKPDS), in which the sulfonylurea glyburide was used first, followed by metformin. With each drug, the A1c decreased initially but then rose within 3 years. By 15 years, 65% of participants were taking insulin.

More recently, the GRADE study examined the effects of adding four different glucose-lowering agents (glimepiride, sitagliptin, liraglutide, or insulin glargine) in people who hadn't achieved target A1c with metformin.

"So, by definition, drug number one failed," he observed.

During the study, all participants showed an initial A1c drop, followed by progressive failure, "again...showing that stepwise therapy doesn't work."

All patients with type 2 diabetes at his center are treated using the "DeFronzo algorithm" consisting of three drug classes: a glucagon-like peptide-1 (GLP-1) agonist, a sodium-glucose cotransporter-2 (SGLT2) inhibitor, and pioglitazone, as each of them targets more than one of the "ominous octet" defects.

"The drugs that clearly do not work on a long-term basis are metformin and sulfonylureas," he emphasized.

Several studies demonstrate the efficacy of combination therapy, he said. In one, DURATION 8, the combination of exenatide and dapagliflozin was superior to either agent individually in lowering A1c, cardiovascular events, and all-cause mortality over 2 years.

And in the 5-year VERIFY study, early combination therapy with vildagliptin plus metformin proved superior in A1c-lowering to starting patients on metformin and adding vildagliptin later.

DeFronzo's own "knock-out punch" study, EDICT, in people with new-onset type 2 diabetes, compared the initial combination of metformin, pioglitazone, and exenatide with conventional sequential add-on therapy with metformin, glipizide, and insulin glargine.

The primary endpoint — the difference in the proportion of patients with A1c less than 6.5% — was 70% versus 29% with combination compared to sequential therapy, a difference "as robust as you can be going against the stepwise approach" at P < .00001, he said.

The combination therapy virtually normalized both insulin sensitivity and beta-cell function, whereas the conventional therapy did neither.

Also from DeFronzo's group, in the Qatar study, which compared exenatide plus pioglitazone with basal-bolus insulin in people with about 10 years' duration of type 2 diabetes and A1c above 7.5% taking sulfonylurea plus metformin, the combination therapy produced an A1c of 6.2% versus 7.1% with insulin.

DeFronzo pointed to new language added to the ADA Standards of Medical Care in Diabetes in 2022.

While still endorsing stepwise therapy, the document also says that "there are data to support initial combination therapy for more rapid attainment of glycemic targets and longer durability of glycemic effect." The two references cited are EDICT and VERIFY.

"Finally, the American Diabetes Association has gotten the message," he concluded.

Sequential Therapy: Far More Data, Lower Cost

Nathan began by pointing out that the ADA Standards of Care continues to advise use of metformin as first-line therapy for type 2 diabetes "because of its high efficacy in lowering A1c, minimal hypoglycemia risk when used as monotherapy, weight neutrality with the potential for modest weight loss, good safety profile, and low cost."

He emphasized that he was not arguing "against the use of early or even initial combination therapy when there are co-existent morbidities [such as cardiovascular or chronic kidney disease] that merit use of demonstrably effective medications." But Nathan pointed out, those patients are not the majority with type 2 diabetes.

He laid out four main arguments for choosing traditional sequential therapy over initial combination therapy. For one, it "enables determination of efficacy of adding individual medications, while initial combination precludes determining benefits of individual drugs."

Second, traditional sequential therapy allows for assessment of side effects from individual drugs.

"With DeFronzo's algorithm you throw everything at them, and if they get nausea, vomiting, or diarrhea, you won't know which drug it is...If they get an allergic reaction, you won't know which medication it is," observed Nathan, who is director of the Clinical Research Center and the Diabetes Center at Massachusetts General Hospital, Boston.

Moreover, he said, traditional sequential therapy "promotes individualization, with selection of drugs, which is something we're laboring to achieve. Initial combination obviously limits that."

Further, sequential therapy is "parsimonious and cost-effective, whereas initial combination therapy is expensive, with modest advantages at most."

And, there are "lots of data" supporting traditional sequential therapy and relatively little for initial combination therapy.  

Nathan added that when he searched the literature for relevant randomized clinical trials, he found 16 investigating initial combination therapy versus monotherapy, but only three that examined combination versus sequential therapy.

"Very few of them, except for EDICT and VERIFY, actually include the sequential therapy that we would use in practice," he said.  

Moreover, he observed, except for the VERIFY study, most are less than half a year in duration. And in VERIFY, there was an initial 20% difference in the proportions of patients with A1c below 7.0%, but by 12 months, that difference had shrunk to just 5%-6%.

"So, looking over time is very important," Nathan cautioned. "We really have to be careful...Six months is barely enough time to see A1c equilibrate…You really need to study a long-term, chronic, progressive disease like type 2 diabetes over a long enough period of time to be clinically meaningful."

Nathan acknowledged to DeFronzo that the latter's EDICT study was "well conducted" and "long enough," and that the researchers did examine monotherapy versus sequential therapy. However, he pointed out that it was a small study with 249 patients and the dropout rate was high, with 58% of patients remaining in the study with triple therapy versus 68% for conventional treatment. "That's a bit problematic," Nathan noted.

At 2 years, the "trivial" difference in A1c was 6.5% with conventional therapy versus 6.0% with triple therapy. "This is all on the very flat complications curve with regard to A1c," he observed.

Patients treated with sequential therapy with sulfonylurea and insulin had higher rates of hypoglycemia and weight gain, whereas the combination triple therapy group had more gastrointestinal side effects and edema.

However, the most dramatic difference was cost: the average wholesale price for sequential therapy totaled about $85 per month, compared with $1310 for initial combination therapy. For the approximately 1.5 million patients with new-onset type 2 diabetes in the United States that difference comes to an additional cost per year of about $22 billion, Nathan calculated.

"Although current sequential therapy leaves much to be desired...initial combination therapy has generally only been tested for brief, clinically insufficient periods.

"And therefore, I think sequential therapy is still what is called for," he concluded. "Well-powered, acceptable-duration studies need to be performed before we can adopt initial/early combination therapy as the standard of care."

DeFronzo has reported receiving research support from Boehringer Ingelheim, AstraZeneca, and Merck; payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing, or educational events from AstraZeneca; participation on a data safety monitoring board or advisory board for AstraZeneca, Intarcia, Novo Nordisk, and Boehringer Ingelheim. Nathan has reported no relevant financial relationships.

ADA Scientific Sessions. Presented June 23, 2023.

Miriam E. Tucker is a freelance journalist based in the Washington, DC, area. She is a regular contributor to Medscape, with other work appearing in The Washington Post, NPR's Shots blog, and Diabetes Forecast magazine. She is on Twitter: @MiriamETucker.

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