What Are SGLT2 Inhibitors?

Sodium-glucose cotransporter-2 (SGLT2) inhibitors are a class of oral medications designed for the management of type 2 diabetes. The major agents include empagliflozin, canagliflozin, dapagliflozin, and ertugliflozin. These drugs target a specific protein in the proximal convoluted tubule of the kidney that normally reabsorbs the majority of filtered glucose back into the bloodstream. By inhibiting this protein, SGLT2 inhibitors allow excess glucose to be excreted in the urine, thereby lowering blood glucose levels independently of insulin secretion or action.

The prominent advantage of SGLT2 inhibitors lies in their insulin-independent mechanism. Because they do not stimulate insulin release, the risk of hypoglycemia is relatively low when used as monotherapy or in combination with metformin. Furthermore, the glucosuria induced by these drugs results in a mild osmotic diuresis, which contributes to modest reductions in blood pressure and body weight. These additional benefits have made SGLT2 inhibitors a preferred second- or third-line option in many treatment algorithms, particularly for patients with established cardiovascular disease or chronic kidney disease.

Beyond Glucose Control: Cardiovascular and Renal Benefits

Large cardiovascular outcome trials, such as EMPA-REG OUTCOME for empagliflozin and CANVAS for canagliflozin, have demonstrated significant reductions in major adverse cardiovascular events (MACE), hospitalization for heart failure, and progression of kidney disease. These benefits appear to be at least partly independent of glycemic control and are thought to involve improvements in hemodynamics, reductions in inflammation and oxidative stress, and modulation of myocardial energetics. Consequently, SGLT2 inhibitors are now recommended for patients with type 2 diabetes and established cardiovascular or renal disease, regardless of baseline HbA1c levels.

Understanding Ketoacidosis

Ketoacidosis is a metabolic emergency characterized by an accumulation of ketone bodies (beta-hydroxybutyrate, acetoacetate, and acetone) in the blood, leading to metabolic acidosis. In classic diabetic ketoacidosis (DKA), which is most commonly seen in type 1 diabetes, the absence of insulin allows unchecked lipolysis and fatty acid oxidation, producing high levels of ketones. Hyperglycemia usually accompanies this condition because of concurrent insulin deficiency and increased hepatic glucose output.

However, the ketoacidosis associated with SGLT2 inhibitors often presents in an atypical form known as euglycemic diabetic ketoacidosis (euDKA). In euDKA, blood glucose levels may be only mildly elevated—often below 200–250 mg/dL—while the patient has significant metabolic acidosis and ketonemia. This can delay diagnosis because clinicians typically associate ketoacidosis with high blood glucose. The pathophysiology of euDKA in the setting of SGLT2 inhibitor use is complex and involves reduced renal ketone clearance, increased ketone production due to relative insulin deficiency and glucagon excess, and a shift toward fatty acid metabolism.

Why SGLT2 Inhibitors Can Promote Ketoacidosis

The mechanism by which SGLT2 inhibitors increase the risk of ketoacidosis is multifactorial. First, by lowering plasma glucose through urinary excretion, the drug reduces the amount of glucose available for cellular energy. This can trigger a compensatory increase in lipolysis and ketogenesis, particularly if insulin doses are simultaneously reduced. Second, SGLT2 inhibitors directly lower the renal threshold for ketone reabsorption, meaning that ketones are retained in the blood rather than excreted. Third, these medications can increase glucagon secretion from alpha-cells in the pancreas, which further stimulates hepatic ketogenesis.

Thus, any situation that predisposes a patient to insulin deficiency or increased ketone production—such as illness, decreased caloric intake, heavy exercise, excessive alcohol consumption, or major surgery—can precipitate euDKA in an SGLT2 user.

Risk Factors and Incidence

The overall incidence of DKA in patients using SGLT2 inhibitors is low. Postmarketing studies and meta-analyses estimate it at roughly 0.1% to 0.5% per patient-year, which is comparable to the background risk in type 2 diabetes populations not taking these agents. However, the relative risk appears to be elevated 2- to 4-fold compared with other diabetes medications, especially in certain subgroups.

Patient Populations at Increased Risk

  • Type 1 diabetes patients: Although SGLT2 inhibitors are not approved for type 1 diabetes in most regions, off-label use has been associated with a significantly higher incidence of DKA. The medications lower insulin requirements but simultaneously increase ketone production, making this population particularly vulnerable.
  • Insulin-deficient individuals: In type 2 diabetes, patients with advanced beta-cell failure who require large doses of insulin are at higher risk. Abrupt insulin dose reductions when starting an SGLT2 inhibitor can trigger ketosis.
  • Perioperative patients: Preoperative fasting, dehydration, and changes in insulin or oral medications create a perfect storm for ketone buildup. Many professional societies recommend withholding SGLT2 inhibitors 24–48 hours before elective surgery.
  • Acute illness: Gastroenteritis, infections, and other acute illnesses that cause vomiting, diarrhea, or reduced oral intake can rapidly lead to dehydration and ketogenesis.
  • Alcohol binges: Heavy alcohol consumption can suppress gluconeogenesis and enhance lipolysis, increasing the risk of ketoacidosis.
  • Low-carbohydrate or ketogenic diets: Patients following very low-carbohydrate diets are already in a catabolic state with higher baseline ketone levels; adding an SGLT2 inhibitor may push them over the threshold into clinical ketoacidosis.

Clinical Presentation and Diagnosis

The symptoms of euDKA are similar to those of classic DKA but can be more subtle because of the absence of marked hyperglycemia. Typical clinical features include:

  • Nausea and vomiting
  • Abdominal pain
  • Fatigue, weakness, or malaise
  • Altered mental status (confusion, drowsiness)
  • Rapid, deep breathing (Kussmaul respirations)
  • Fruity breath odor (acetone)

Because blood glucose may be only mildly elevated (e.g., 150–250 mg/dL), clinicians must have a high index of suspicion. The diagnostic workup should include measurement of serum ketones (beta-hydroxybutyrate is preferred), arterial or venous blood gas analysis, and serum electrolytes. A venous pH below 7.3 or bicarbonate below 15 mEq/L, combined with elevated serum ketones and a history of SGLT2 inhibitor use, confirms the diagnosis even if glucose is not markedly elevated.

Risk Mitigation Strategies

Given that SGLT2 inhibitors provide substantial cardiovascular and renal benefits, the best approach is not to avoid them altogether but rather to implement careful risk mitigation strategies. The key measures can be divided into three phases: pre-initiation assessment, ongoing monitoring, and sick-day management.

Pre-Initiation Assessment

  • Patient selection: Avoid using SGLT2 inhibitors in patients with type 1 diabetes (off-label) and in those with a history of recurrent DKA or severe insulin deficiency. In type 2 diabetes, assess the patient's endogenous insulin reserve; patients with poor glycemic control on multiple insulin doses and very high glucose variability may not be ideal candidates.
  • Educate patients about symptoms: Before starting the medication, counsel patients about the signs of ketone buildup (nausea, vomiting, abdominal pain, shortness of breath) and instruct them to check blood ketone levels if symptoms occur. Provide a prescription for a home ketone monitor.
  • Discuss dietary considerations: Advise against strict low-carbohydrate or ketogenic diets while on SGLT2 inhibitors, and warn about excessive alcohol consumption.
  • Plan for surgery: Schedule elective procedures with a plan to hold the SGLT2 inhibitor at least 24 hours (some guidelines recommend 48 hours) before surgery and resume only after the patient is eating and drinking normally postoperatively.

Ongoing Monitoring

  • Routine surveillance: At each follow-up visit, ask about any recent illnesses, hospitalizations, or symptoms suggestive of ketoacidosis. Check urine or blood ketones if the patient reports any suspicious symptoms.
  • Electrolyte monitoring: Because SGLT2 inhibitors increase urinary electrolyte loss, especially sodium and potassium, periodic checks of serum electrolytes are prudent, particularly in elderly patients or those taking diuretics.
  • Review other medications: Concomitant use of insulin secretagogues (e.g., sulfonylureas) or insulin itself requires careful dose adjustments when starting an SGLT2 inhibitor to avoid hypoglycemia. Overly aggressive reduction of insulin doses can paradoxically increase ketosis risk, so titrate insulin slowly.

Sick-Day Rules

When a patient on an SGLT2 inhibitor develops an acute medical condition that impairs oral intake (e.g., vomiting, diarrhea, high fever, or infection), immediate action is needed:

  • Temporary discontinuation: Hold the SGLT2 inhibitor until the patient has fully recovered normal fluid and food intake.
  • Hydration and caloric intake: Encourage clear liquids and small, frequent meals containing carbohydrates to suppress ketogenesis.
  • Monitor ketones: Check urine or blood ketones every 4–6 hours during the illness. If ketones rise above 1.0 mmol/L, increase carbohydrate intake and hydrate aggressively.
  • Adjust insulin or other medications: Never completely stop insulin in type 1 diabetes; in type 2 diabetes, maintain basal insulin if the patient uses it, as insulin helps to suppress ketone production.
  • Seek medical care urgently: If the patient cannot tolerate fluids, has persistent vomiting, or develops altered mental status, they should go to the emergency department.

Treatment of Suspected SGLT2-Associated Ketoacidosis

When a patient presents with suspected euDKA, management follows standard DKA protocols with some modifications. The primary steps are:

  1. Discontinue the SGLT2 inhibitor immediately.
  2. Administer intravenous fluids (typically normal saline) to correct dehydration and reduce ketone reabsorption.
  3. Provide intravenous insulin (preferably via continuous infusion) to shut down ketogenesis, even if blood glucose is not extremely high. Because glucose levels may be only moderately elevated, it is essential to avoid inducing hypoglycemia; consider concurrently administering dextrose (e.g., D5W or D10W) once glucose falls below 200 mg/dL.
  4. Correct electrolyte imbalances—especially potassium, which can decline rapidly when insulin is given.
  5. Monitor ketone levels every 2–4 hours until resolution (beta-hydroxybutyrate normalized and anion gap closed).
  6. Do not restart the SGLT2 inhibitor until the underlying precipitating cause has resolved and the patient is confirmed to have no persistent risk factors.

Clinical Controversies and Evidence Gaps

Despite extensive research, several aspects of SGLT2 inhibitor–associated ketoacidosis remain debated. One unresolved question is whether the risk is uniform across all agents in the class. Some post-hoc analyses suggest that the risk may be slightly higher with canagliflozin compared with empagliflozin, but the absolute difference is small and confounding is difficult to exclude.

Another controversial area is the idea that routine ketone monitoring in all asymptomatic patients on SGLT2 inhibitors could prevent DKA. The evidence shows that most episodes are triggered by intercurrent illness or medication changes, and routine screening of ketones in stable outpatients rarely predicts events, leading to unnecessary anxiety and costs. Thus, current guidelines recommend targeted monitoring only during high-risk situations.

Finally, the optimal duration of SGLT2 inhibitor hold before surgery is not uniformly agreed upon. The U.S. Food and Drug Administration (FDA) has issued a warning recommending that SGLT2 inhibitors be stopped at least 3 days before elective surgery. Other societies, such as the American College of Surgeons and the American Diabetes Association, have offered slightly different timelines (24–48 hours). Given the long pharmacodynamic effect of some SGLT2 inhibitors (e.g., canagliflozin once daily), a cautious 3-day hold is reasonable, but more evidence is needed to refine this recommendation. For more details, clinicians can consult the FDA safety announcement on SGLT2 inhibitors and ketoacidosis.

Guideline Recommendations

Major diabetes organizations have integrated risk mitigation into their consensus reports. The American Diabetes Association (ADA) Standards of Care (available online) recommend avoiding SGLT2 inhibitors in patients with a history of DKA, discontinuing them 24–48 hours before scheduled surgery, and instructing patients to discontinue temporarily during acute illness. The European Society of Cardiology (ESC) similarly includes these precautions in their guidelines on cardiovascular disease prevention.

Meanwhile, the ADA/EASD consensus report on pharmacologic management emphasizes patient education as the cornerstone of prevention. Patients should be taught to recognize early symptoms of ketosis and when to hold the medication. Written sick-day plans should be provided to every patient starting an SGLT2 inhibitor.

Conclusion

SGLT2 inhibitors remain a valuable tool in the management of type 2 diabetes, offering significant reductions in cardiovascular events, heart failure hospitalizations, and kidney disease progression. The risk of ketoacidosis, while low, is real and requires attention from both prescribers and patients. By understanding the pathophysiology of euDKA, identifying high-risk individuals, implementing structured sick-day protocols, and ensuring clear patient communication, healthcare providers can maximize the benefits of this drug class while minimizing the likelihood of serious adverse events.

Ongoing research continues to refine our understanding of which patients are most susceptible and how best to prevent and treat this complication. For now, a balanced approach—prescribing SGLT2 inhibitors to appropriate candidates, maintaining vigilance, and acting quickly when red flags arise—enables safe and effective use of these powerful medications.

For additional reading, the comprehensive review by Burke et al. (2020) in Current Diabetes Reports provides an excellent summary of the evidence on SGLT2 inhibitor–associated ketoacidosis.