SGLT2 Inhibitors

Mechanism

The kidney filters a large volume of glucose-containing plasma daily; normally almost all of it is reclaimed in the proximal tubule through sodium-glucose cotransporter 2 (SGLT2). Gliflozins block SGLT2, so filtered glucose is no longer reabsorbed and is instead excreted in urine (glucosuria). This depends only on how much glucose is filtered, not on insulin secretion or sensitivity, so these drugs work regardless of beta-cell function. The excreted glucose drags water with it osmotically, producing mild diuresis; the same transporter also handles sodium reabsorption, so blocking it causes natriuresis. The overall effect resembles a gentle diuretic layered onto glucose lowering: modest weight loss, modest blood pressure reduction, reduced intravascular volume.

Beyond glycemic control

Outcome trials found this class reduces heart failure hospitalization and cardiovascular death even in people without diabetes and with only mildly elevated glucose. Proposed mechanisms include the volume and pressure effects and favorable changes in cardiac loading and renal hemodynamics, though the full picture remains debated. Separately, the class slows chronic kidney disease progression — reducing decline in kidney function and progression toward kidney failure — again regardless of diabetes status. These findings have expanded approvals to heart failure and chronic kidney disease indications in nondiabetic patients, a major shift from the drugs' original glucose-lowering purpose.

Renal function and efficacy

Because glucose lowering depends on the kidney filtering and dumping glucose, glycemic efficacy declines as kidney function worsens — a weaker kidney filters less, so less glucose spills out. The cardiovascular and kidney-protective benefits, however, persist at reduced kidney function, so these drugs may still be used for heart failure or kidney protection there even as glucose-lowering fades.

Adverse effects and safety

The most predictable adverse effects follow from the mechanism: sugar-rich urine promotes genital mycotic (yeast) infections more than urinary tract infections, though both occur. Teaching should cover genital hygiene and prompt reporting of itching, discharge, or dysuria — this risk runs higher than with most other diabetes drugs. A rare but serious complication is Fournier gangrene, a necrotizing perineal infection; patients should seek urgent care for severe genital or perineal pain, swelling, or fever. These drugs can also cause volume depletion and orthostatic hypotension, worsened by concurrent diuretic use, older age, or already-low blood pressure — dizziness on standing deserves reporting.

The single most important exam concept is euglycemic diabetic ketoacidosis: ketoacidosis can develop with only mildly elevated or near-normal blood glucose, because urinary glucose loss masks the hyperglycemia that would normally flag DKA even as ketones rise. Surgery, prolonged fasting, acute illness, dehydration, and very low carbohydrate intake all push the body toward fat metabolism and ketone production while glucosuria keeps blood sugar deceptively normal. These drugs are therefore typically held before planned surgery, and patients should seek care for nausea, vomiting, abdominal pain, or unusual fatigue even when glucose looks fine.

Canagliflozin carried early signals of increased amputation and fracture risk; larger subsequent evidence has shown this signal attenuated and not consistently replicated across the class, so it belongs in teaching as a historical caution, not a settled hazard.

Hypoglycemia and monitoring

Alone, these drugs carry low hypoglycemia risk since they don't stimulate insulin release. That risk rises mainly when combined with insulin or a secretagogue like a sulfonylurea, sometimes requiring dose adjustment of those agents. Nursing teaching centers on hydration, reporting genital or urinary symptoms, dizziness, and any DKA-type symptoms regardless of glucose readings, plus hold instructions before surgery or acute illness with poor intake.