SGLT2 Inhibitors Have a Breakout Year

Mitchel L. Zoler, PhD

August 07, 2020

The benefits from sodium-glucose cotransporter 2 inhibitor drugs proven during the past year for cutting heart failure hospitalization rates substantially in patients with heart failure with reduced ejection fraction and slowing progression of chronic kidney disease, all regardless of diabetes status, have thrust this drug class into the top tier of agents for potentially treating millions of patients with cardiac or renal disease.

The sodium-glucose cotransporter 2 (SGLT2) inhibitors, first licensed for U.S. marketing in 2013 purely for glycemic control, have, during the 5 years since the first cardiovascular outcome trial results for the class came out, shown benefits in a range of patients reminiscent of what's been established for ACE inhibitors and angiotensin receptor blockers (ARBs).

The wide-reaching benefits of SGLT2 inhibitors have recently become even more relevant by showing clinically meaningful effects in patients without type 2 diabetes (T2D). And in an uncanny coincidence, the SGLT2 inhibitors appear to act in complementary harmony with the ACE inhibitors and ARBs for preserving heart and renal function. These properties have made the SGLT2 inhibitors especially attractive as a new weapon for controlling the ascendant disorder of cardiorenal syndrome.

"SGLT2 inhibitors have a relatively greater impact on cardiovascular outcomes, compared with ACE inhibitors and ARBs, but the effects [of the two classes] are synergistic and ideally patients receive both," said Peter McCullough, MD, a specialist in treating cardiorenal syndrome and other cardiovascular and renal disorders at Baylor, Scott, and White Heart and Vascular Hospital in Dallas. The SGLT2 inhibitors are among the drugs best suited to both treating and preventing cardiorenal syndrome by targeting both ends of the disorder, said Dr. McCullough, who chaired an American Heart Association panel that last year issued a scientific statement on cardiorenal syndrome (Circulation. 2019 Apr 16;139[16]:e840-78).

Although data on the SGLT2 inhibitors "are evolving," the drug class is "going in the direction" of being "reasonably compared" with the ACE inhibitors and ARBs, said Javed Butler, MD, professor and chair of medicine at the University of Mississippi Medical Center, Jackson. "There are certainly complementary benefits that we see for both cardiovascular and renal outcomes."

"We'll think more and more about the SGLT2 inhibitors like renin-angiotensin system [RAS] inhibitors," said David Z. Cherney, MD, referring to the drug class that includes ACE inhibitors and ARBs. "We should start to approach SGLT2 inhibitors like RAS inhibitors, with pleiotropic effects that go beyond glucose," said Dr. Cherney, a nephrologist and professor of medicine at the University of Toronto, during the virtual annual scientific sessions of the American Diabetes Association in June 2020.

Working Together in the Nephron

One of the clearest complementary interactions between the SGLT2 inhibitors and the RAS inhibitors is their ability to reduce intraglomerular pressure, a key mechanism that slows nephron loss and progression of chronic kidney disease. SGLT2 inhibitors reduce sodium absorption in the proximal tubule that causes, through tubuloglomerular feedback, afferent arteriole constriction that lowers intraglomerular pressure, while the RAS inhibitors inhibit efferent arteriole constriction mediated by angiotensin II, also cutting intraglomerular pressure. Together, "they almost work in tandem," explained Janani Rangaswami, MD, a nephrologist at Einstein Medical Center in Philadelphia, vice chair of the Kidney Council of the AHA, and first author of the 2019 cardiorenal syndrome AHA statement.

"Many had worried that if we target both the afferent and efferent arterioles simultaneously, it might increase the risk for acute kidney injury. What has been reassuring in both the recent data from the DAPA-HF trial and in recent meta-analysis was no evidence of increased risk for acute kidney injury with use of the SGLT2 inhibitor," Dr. Rangaswami said in an interview. For example, a recent report on more than 39,000 Canadian patients with T2D who were at least 66 years old and newly begun on either an SGLT2 inhibitor or a different oral diabetes drug (a dipeptidyl peptidase–4 inhibitor), found a statistically significant 21% lower rate of acute kidney injury during the first 90 days on treatment with an SGLT2 inhibitor in a propensity score–matched analysis (CMAJ. 2020 Apr 6;192: e351-60).

Much of the concern about possible acute kidney injury stemmed from a property that the SGLT2 inhibitors share with RAS inhibitors: They cause an initial, reversible decline in glomerular filtration rate (GFR), followed by longer-term nephron preservation, a pattern attributable to reduced intraglomerular pressure. The question early on was: "'Does this harm the kidney?' But what we've seen is that patients do better over time, even with this initial hit. Whenever you offload the glomerulus you cut barotrauma and protect renal function," explained Silvio E. Inzucchi, MD, professor of medicine at Yale University, New Haven, Conn., and director of the Yale Medicine Diabetes Center.

Dr. Inzucchi cautioned, however, that a small number of patients starting treatment with an SGLT2 inhibitor may have their GFR drop too sharply, especially if their GFR was low to start with. "You need to be careful, especially at the lower end of the GFR range. I recheck renal function after 1 month" after a patient starts an SGLT2. Patients whose level falls too low may need to discontinue. He added that it's hard to set a uniform threshold for alarm, and instead assess patients on a case-by-case basis, but "you need some threshold in mind, where you will stop" treatment.

A Smarter Diuretic

One of the most intriguing renal effects of SGLT2 inhibitors is their diuretic action. During a talk at the virtual ADA scientific sessions, cardiologist Jeffrey Testani, MD, called them "smart" diuretics, because their effect on diuresis is relatively modest but comes without the neurohormonal price paid when patients take conventional loop diuretics.

"Loop diuretics are particularly bad," causing neurohormonal activation that includes norepinephrine, renin, and vasopressin, said Dr. Testani, director of heart failure research at Yale. They also fail to produce a meaningful drop in blood volume despite causing substantial natriuresis.

In contrast, SGLT2 inhibitors cause "moderate" natriuresis while producing a significant cut in blood volume. "The body seems content with this lower plasma volume without activating catecholamines or renin, and that's how the SGLT2 inhibitors differ from other diuretics," said Dr. Inzucchi.

The class also maintains serum levels of potassium and magnesium, produces significant improvements in serum uric acid levels, and avoids the electrolyte abnormalities, volume depletion, and acute kidney injury that can occur with conventional distal diuretics, Dr. Testani said.

In short, the SGLT2 inhibitors "are safe and easy-to-use diuretics," which allows them to fill a "huge unmet need for patients with heart failure." As evidence accumulates for the benefits of the drug class in patients with heart failure and renal disease, "uptake will be extensive," Dr. Testani predicted, driven in part by how easy it is to add the class to existing cardiorenal drug regimens.

Other standard therapies for patients with heart failure with reduced ejection fraction (HFrEF) risk electrolyte abnormalities, renal dysfunction, significantly lower blood pressure, often make patients feel worse, and involve a slow and laborious titration process, Dr. Testani noted. The SGLT2 inhibitor agents avoid these issues, a property that has played out in quality of life assessments of patients with HFrEF who received a drug from this class.

Outcomes Met in Trial After Trial

In the DAPA-HF trial, with 4,443 patients with HFrEF and divided roughly equally between those with or without T2D, treatment with dapagliflozin (Farxiga) linked with significant improvements in health status and quality of life measured by the Kansas City Cardiomyopathy Questionnaire (Circulation. 2020 Jan 14;141[2]:90-9). "Not all treatments for HFrEF improve symptoms," but in this study the SGTL2 inhibitor dapagliflozin did, boosting the Kansas City Cardiomyopathy Questionnaire score by about the same magnitude as treatment with a cardiac resynchronization device in patients with HFrEF, said Mikhail N. Kosiborod, MD, director of Cardiometabolic Research at Saint Luke's Mid America Heart Institute in Kansas City, Mo., speaking at the virtual ADA scientific sessions.

Two more recent renal observations have further solidified the growing role of these drugs for kidney protection. Results from the CREDENCE trial that looked at canagliflozin (Invokana) treatment in 4,401 patients with T2D and albuminuria and chronic kidney disease showed canagliflozin treatment cut the primary, composite renal endpoint by a statistically significant 30%, compared with placebo (N Engl J Med. 2019 Jun 13;380[24]:2295-306). The study stopped earlier than planned because of how effective canagliflozin appeared.

"Never before has a renal protection clinical trial stopped for overwhelming efficacy," noted nephrologist Katherine R. Tuttle, MD, executive director for research at Providence Health Care in Spokane, Wash. "It's very exciting to have a treatment that works on both the heart and kidney, given their interrelationship," she said during the ADA sessions. Dr. Tuttle called the cardiorenal effects from the SGLT2 inhibitors "amazing."

Just as the DAPA-HF trial's primary outcome showed the ability of at least one drug from the class, dapagliflozin, to improve outcomes in HFrEF patients without T2D, topline results recently reported from the DAPA-CDK trial showed for the first time renal protection by an SGLT2 inhibitor in patients with chronic kidney disease but no T2D, in a study with about 4,300 patients.

Although detailed results from DAPA-CKD are not yet available, so far the outcomes seem consistent with the CREDENCE findings, and the cumulative renal findings for the class show the SGLT2 inhibitors have "potential for a profound impact on the patients we see in every nephrology clinic, and with dual cardiorenal disease," said Dr. Rangaswami. The class is now established as "standard of care for patients with chronic kidney disease. The CREDENCE results made that clear."

The DAPA-CKD findings in patients with chronic kidney disease regardless of their diabetes status "are very important. We really have not had any advances in this space for some time, and chronic kidney disease patients have very poor outcomes, both cardiovascular and renal," commented Dr. Butler. The advantage from using this drug class in these patients "is huge."

The DAPA-CKD findings are a "major advance," agreed Dr. McCullough.

SGLT2 Inhibitor Use Needs to Grow

Experts lament that although the evidence favoring the class has been very bullish, prescribing uptake has been slow, perhaps partly explained by the retail U.S. cost for most of these agents, generally about $17/day.

Cost is, unfortunately, an issue right now for these drugs, said Dr. Butler. Generic formulations are imminent, "but we cannot accept waiting. Providing this therapy when insurance coverage is available," is essential.

The FDA has already granted tentative approval to some generic formulations, although resolution of patent issues can delay generics actually reaching the market. "Generic dapagliflozin will have a major impact; the marketplace for these drugs will shift very quickly," predicted Dr. McCullough.

But price may not be the sole barrier, cautioned Dr. Rangaswami. "I don't think it's just a cost issue. Several factors explain the slow uptake," of the SGLT2 inhibitors. "The biggest barrier is that this is a new drug class, and understanding how to use the class is not yet where it needs to be in the physician community." One of the biggest problems is that the SGLT2 inhibitors are still primarily regarded as drugs to treat hyperglycemia.

Physicians who treat patients with heart or renal disease "need to wrap their head around the idea that a drug with antihyperglycemic effects is now in their practice territory, and something they need to prescribe," she noted. Currently "there is a reluctance to prescribe these drugs given the perception that they are antihyperglycemic agents, and usually get deferred to primary care physicians or endocrinologists. This results in huge missed opportunities by cardiologists and nephrologists in initiating these agents that have major cardiorenal risk reduction effects."

The key role that cardiologists need to play in prescribing the SGLT2 inhibitors was brought home in a recent study of two representative U.S. health systems that showed patients with T2D were far more likely to see a cardiologist than an endocrinologist (Cardiovasc Endocrinol Metab. 2020 Jun;9[2]:56-9).

"The SGLT2 inhibitors are definitely a game-changing drug class," summed up Dr. Rangaswami. "We're going to see a lot of use in patients with heart and kidney disease."

Dr. Cherney has been a consultant to or has received honoraria from AstraZeneca, Boehringer Ingelheim, Janssen, Lilly, Merck, Mitsubishi Tanabe Pharma, and Sanofi. Dr. Butler has had financial relationships with numerous pharmaceutical companies. Dr. McCullough and Dr. Rangaswami had no disclosures. Dr. Inzucchi has been a consultant to or helped run trials for Abbott, AstraZeneca, Boehringer Ingelheim, Merck, Novo Nordisk, Sanofi/Lexicon, and vTv Therapeutics. Dr. Testani has been a consultant to AstraZeneca, Bayer, Boehringer Ingelheim, Bristol-Myers Squibb, cardionomic, FIRE1 Magenta Med, Novartis, Reprieve, Sanofi, and W.L. Gore. Dr. Kosiborod has been a consultant to or led trials for Amarin, Amgen, Applied Therapeutics, AstraZeneca, Bayer, Boehringer Ingelheim, Glytec, Janssen, Eli Lilly, Merck, Novartis, Novo Nordisk, Sanofi, and Vifor. Dr. Tuttle has been a consultant to AstraZeneca, Boehringer Ingelheim, Gilead, Goldfinch Bio, Eli Lilly, and Novo Nordisk.

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