Sodium-glucose cotransporter-2 inhibitors lower blood glucose by blocking glucose reabsorption in the kidney, causing glucose to be excreted in the urine. This mechanism is entirely insulin-independent — it works regardless of beta cell function or insulin resistance — and produces a unique constellation of metabolic effects beyond glucose lowering that have transformed the management of heart failure and chronic kidney disease.

Under normal physiology, essentially all of the approximately 180 grams of glucose filtered daily by the glomeruli is reabsorbed in the proximal convoluted tubule. Sodium-glucose cotransporter-2 accounts for approximately 90 percent of this reabsorption in the S1 and S2 segments of the proximal tubule, co-transporting one glucose molecule with two sodium ions using the electrochemical gradient established by the basolateral sodium-potassium adenosine triphosphatase. The remaining 10 percent is handled by sodium-glucose cotransporter-1 in the S3 segment. Sodium-glucose cotransporter-2 inhibitors competitively block the cotransporter, reducing glucose reabsorption capacity from approximately 180 g/day to roughly 60 to 80 g/day. This causes osmotic glycosuria — glucose spilling into urine — and produces a caloric deficit of approximately 200 to 300 kcal per day, contributing to modest weight loss of 2 to 3 kg.

The glycosuric mechanism produces several downstream effects beyond glucose lowering. The osmotic diuresis from glycosuria reduces plasma volume, lowering blood pressure by 3 to 5 mmHg systolic. Natriuresis (sodium excretion accompanying glucose excretion) further reduces volume load. In the kidney, reduced proximal tubule sodium reabsorption increases sodium delivery to the macula densa, restoring tubuloglomerular feedback and reducing hyperfiltration — a mechanism thought to underlie the renoprotective effects of the class. Reduced insulin levels from improved glycemia lower uric acid reabsorption, mildly reducing serum uric acid. Mild osmotic diuresis and natriuresis also reduce cardiac preload and afterload, contributing to the heart failure benefits.

The sodium-glucose cotransporter-2 inhibitor cardiovascular outcome trials established this class as the first oral antihyperglycemic agents with robust evidence for reducing heart failure hospitalization across all trials, and for reducing cardiovascular mortality in the highest-risk populations.

EMPA-REG OUTCOME (empagliflozin, 2015) was the landmark trial. In patients with type 2 diabetes mellitus and established cardiovascular disease, empagliflozin reduced major adverse cardiovascular events by 14 percent, cardiovascular mortality by 38 percent, and heart failure hospitalization by 35 percent — the most striking cardiovascular mortality reduction seen in a diabetes drug trial. CANVAS (canagliflozin, 2017) showed a 14 percent major adverse cardiovascular event reduction but also raised concern about lower extremity amputations (canagliflozin carries an FDA boxed warning). DECLARE-TIMI 58 (dapagliflozin, 2019) enrolled a broader population including patients without prior cardiovascular events and showed no significant major adverse cardiovascular event reduction in the overall population but robust heart failure hospitalization reduction. VERTIS-CV (ertugliflozin, 2020) showed cardiovascular safety but no superiority for any endpoint.

The safety profile of sodium-glucose cotransporter-2 inhibitors includes several distinctive adverse effects that reflect their glycosuric mechanism and require patient counseling. The most serious — euglycemic diabetic ketoacidosis — is rare but potentially fatal if not recognized promptly.

Genital mycotic infections (vulvovaginal candidiasis in women, balanitis in men) occur in 5 to 10 percent of patients and are the most common adverse effect, driven by the glucose-rich urine creating a favorable environment for fungal growth. Urinary tract infections are modestly increased. These effects are manageable and rarely cause discontinuation. Patients should be counseled on hygiene and prompt reporting of symptoms.

Euglycemic diabetic ketoacidosis is a rare but serious complication in which ketoacidosis develops at near-normal blood glucose levels, making it harder to recognize. The mechanism involves reduced insulin secretion (glycosuria lowers the glucose stimulus for insulin), increased glucagon, and a shift toward ketogenesis. It occurs more commonly in type 1 diabetes mellitus (where sodium-glucose cotransporter-2 inhibitors are used off-label) and in perioperative settings. Sodium-glucose cotransporter-2 inhibitors should be held 3 to 4 days before elective surgery. Any patient presenting with nausea, vomiting, or abdominal pain while on these agents should have ketones and arterial pH checked regardless of blood glucose.