SAN DIEGO –
This question was debated by two well-known clinician-researchers in the diabetes world at the recent annual scientific sessions of the American Diabetes Association.
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, Dr. 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 U.S. data suggest that half of people with diabetes have a hemoglobin A1c above 7%, and a quarter remain above 8%. “We’re not really doing a very good job in terms of glycemic control,” said Dr. DeFronzo, chief of the diabetes division at University of Texas, 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, Dr. 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.
Dr. 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 with 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 Dr. 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.
Dr. 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.