What are sodium‑glucose co‑transporter‑2 (SGLT2) inhibitors?

What are SGLT2 Inhibitors?

SGLT2 inhibitors are oral antidiabetic medications that block sodium-glucose co-transporter-2 proteins in the proximal renal tubules, thereby reducing glucose reabsorption and increasing urinary glucose excretion to lower blood sugar independently of insulin. 1, 2

Mechanism of Action

• SGLT2 inhibitors work by blocking the predominant transporter responsible for reabsorbing filtered glucose from the kidney back into the bloodstream, causing the body to excrete excess glucose in the urine (glucosuria). 2

• These medications lower the renal threshold for glucose to approximately 180 mg/dL, meaning glucose spills into urine when blood levels exceed this point. 1

• The mechanism is completely insulin-independent, making these drugs effective regardless of diabetes duration, beta-cell function, or degree of insulin resistance. 1, 3

• By reducing glucotoxicity, SGLT2 inhibitors gradually improve beta-cell function and enhance peripheral insulin sensitivity over time through an insulin-sparing effect. 4, 3

Available SGLT2 Inhibitors

The four FDA-approved agents include:

• Empagliflozin (10 mg or 25 mg once daily) 1
• Canagliflozin (100 mg or 300 mg once daily) 1
• Dapagliflozin (10 mg once daily) 1
• Ertugliflozin 1

Dapagliflozin, empagliflozin, and ertugliflozin exhibit the highest selectivity for SGLT2 over SGLT1, distinguishing them from canagliflozin which has appreciable SGLT1 inhibition affecting intestinal glucose absorption. 4

Clinical Effects Beyond Glucose Lowering

Glycemic Control

• SGLT2 inhibitors reduce HbA1c by approximately 0.5% to 1.0% (6-8 mmol/mol). 1, 5
• They carry a low risk of hypoglycemia when used as monotherapy because they do not stimulate insulin secretion. 1

Metabolic Benefits

• Weight loss of 1.5 to 3.5 kg through caloric loss via glucosuria (approximately 64-78 grams of glucose excreted daily). 1, 2
• Systolic blood pressure reduction of 3 to 5 mmHg through osmotic diuresis and natriuresis. 1
• Improvement in lipid profile and reduction in hyperuricemia. 5

Cardiovascular Protection

• SGLT2 inhibitors reduce major adverse cardiovascular events (MACE) and heart failure hospitalization, with empagliflozin specifically reducing cardiovascular death by 38% and all-cause mortality by 32%. 1
• These cardiovascular benefits occur through hemodynamic effects (osmotic diuresis and natriuresis) rather than glucose-lowering or anti-atherosclerotic mechanisms. 5

Renal Protection

• SGLT2 inhibitors slow progression of chronic kidney disease and reduce hospitalization rates for heart failure. 1
• They decrease oxygen consumption by proximal tubular cells, thereby alleviating renal cortical hypoxia that characteristically develops in diabetes. 4
• Cardiorenal benefits persist even when glucose-lowering efficacy is lost at lower eGFR levels, down to approximately 20-25 mL/min/1.73 m². 4

Renal Function Considerations

For Glucose Lowering

• Full efficacy when eGFR ≥45 mL/min/1.73 m² 4
• Reduced efficacy when eGFR 30-45 mL/min/1.73 m² 4
• Minimal to no glucose-lowering effect when eGFR <30 mL/min/1.73 m² 4

For Cardiorenal Protection

• Initiation is discouraged when eGFR <25 mL/min/1.73 m², but continuation is permissible if eGFR falls below this threshold while on therapy because cardiovascular and renal benefits persist independent of glucose-lowering effects. 6
• An early, modest decline in eGFR of 3-5 mL/min after starting therapy does not indicate kidney injury and should not trigger discontinuation. 6

Safety Profile and Adverse Effects

Common Adverse Events

• Genital mycotic infections are the most common adverse event (balanitis in men, candida vaginitis in women) due to glucosuria-driven candida growth. 1, 6
• Volume depletion can occur through osmotic diuresis; caution is warranted in patients concurrently using diuretics, ACE inhibitors, or ARBs. 6

Rare but Serious Adverse Events

• Euglycemic diabetic ketoacidosis can present with blood glucose <200 mg/dL and nonspecific symptoms; ketone assessment is essential regardless of glucose level in any patient on SGLT2 inhibitors who develops metabolic acidosis. 6
• Canagliflozin specifically is associated with increased risk of lower-limb amputation (hazard ratio 1.97) and increased fracture risk (hazard ratio 1.26) compared to placebo. 6
• Acute kidney injury and bone fractures are rare adverse events. 1

Clinical Management Recommendations

Initiation

• When initiating an SGLT2 inhibitor, reduce concomitant insulin dose by 10-20% and consider discontinuing sulfonylureas (especially if HbA1c <8.5%) to avoid hypoglycemia. 6

Peri-operative Management

• SGLT2 inhibitors should be withheld for at least 3 days before major surgery or any prolonged fasting to reduce the risk of ketoacidosis. 6

Monitoring

• Baseline serum estradiol and testosterone measurements in male patients when clinically indicated before initiating therapy, with re-checking at 3-6 months if clinical suspicion of hormonal changes develops. 1
• SGLT2 inhibitors should not be withheld on the basis of theoretical hormonal effects, given their proven mortality and morbidity benefits. 1

Emerging Applications

• SGLT2 inhibitors may have neuroprotective properties due to SGLT2 expression in the central nervous system (cerebellum, hippocampus, frontal cortex), though clinical evidence remains limited. 1, 4
• Potential benefits in non-alcoholic fatty liver disease are being investigated, with clinically significant reductions in serum alanine aminotransferase levels observed. 7