19.4 Sodium-Glucose Cotransporter 2 Inhibitors (SGLT2Is)

Mechanism of Action and Nursing Considerations

SGLT2 inhibitors have become a key drug class in heart failure treatment. They work by blocking glucose reabsorption in the kidneys, which increases urine glucose and sodium output. This unique mechanism reduces cardiac workload and improves heart function through several pathways.

For nurses, the priority areas are monitoring renal function, blood pressure, and electrolytes, while educating patients about infection risk and fluid balance.

Mechanism of SGLT2 Inhibitors

SGLT2 inhibitors block the sodium-glucose cotransporter 2 (SGLT2) protein in the proximal renal tubules. Normally, SGLT2 reabsorbs about 90% of filtered glucose (along with sodium) back into the blood. When you block this transporter, glucose and sodium stay in the tubular lumen and get excreted in the urine.

This produces two important effects:

• Natriuresis (sodium excretion): Losing extra sodium in the urine pulls water with it, reducing blood volume. This decreases both preload and afterload on the heart, lowers ventricular filling pressures and wall stress, and improves cardiac output.
• Glycosuria (glucose excretion): Losing glucose shifts the heart's fuel source toward ketone bodies, which are actually more energy-efficient for cardiac muscle. This reduces myocardial oxygen demand.

Additional proposed mechanisms include:

• Reduction in systemic inflammation and oxidative stress
• Improvement in endothelial function and vascular compliance
• Attenuation of cardiac fibrosis and remodeling (scarring and structural changes)

Side Effects of SGLT2 Inhibitors

Common side effects:

• Genital mycotic infections (vulvovaginal candidiasis in women, balanitis in men): Extra glucose in the urine creates a favorable environment for yeast overgrowth. These are the most frequently reported side effects.
• Urinary tract infections (UTIs): Also related to increased urinary glucose.
• Polyuria and nocturia due to the osmotic diuretic effect.
• Volume depletion symptoms: Hypotension, dizziness, and orthostatic intolerance from excess fluid loss.
• Hypoglycemia, particularly when combined with insulin or insulin secretagogues (sulfonylureas, meglitinides). SGLT2 inhibitors alone rarely cause hypoglycemia, but they amplify the effect of these other drugs.

Key drug interactions:

Nursing Considerations for SGLT2 Inhibitors

1. Assess renal function before starting therapy and periodically during treatment. SGLT2 inhibitors require adequate kidney function to work. Generally, avoid initiating in patients with severe renal impairment (eGFR < 20 mL/min/1.73m²), though current guidelines vary by specific drug. Check your facility's protocol.

2. Monitor blood pressure, daily weight, and fluid status. The diuretic effect can cause volume depletion. If the patient is also on loop or thiazide diuretics, doses may need adjustment to prevent hypovolemia.

3. Evaluate electrolytes, especially potassium and magnesium. Correct any abnormalities promptly and monitor more closely in patients already at risk (e.g., those on other diuretics or digoxin).

4. Assess for genital infections and UTIs. Ask patients about symptoms at each visit. Promptly treat infections and reinforce preventive measures: good perineal hygiene, adequate hydration, and wearing breathable undergarments.

5. Monitor blood glucose in patients with diabetes. SGLT2 inhibitors improve glycemic control, so other antidiabetic medications may need dose reduction to avoid hypoglycemia.

6. Watch for euglycemic diabetic ketoacidosis (DKA). This is rare but serious. The blood glucose may be normal or only mildly elevated, which makes it easy to miss. Suspect it if the patient reports nausea, vomiting, abdominal pain, or fatigue. Check serum ketones and arterial blood gas if concerned.

Patient Education for SGLT2 Inhibitors

• Follow-up visits: Stress the importance of regular lab work and appointments to monitor kidney function, electrolytes, and treatment response.
• Infection awareness: Teach patients to recognize symptoms of genital yeast infections (itching, discharge, redness) and UTIs (burning with urination, frequency, urgency). Encourage good hygiene and adequate fluid intake as preventive strategies.
• Volume depletion signs: Advise patients to report dizziness, lightheadedness, or fainting. Encourage consistent fluid intake, especially in hot weather or during illness.
• Hypoglycemia management (for patients with diabetes): Instruct patients to carry glucose tablets or another rapidly absorbable carbohydrate. Make sure they can recognize symptoms: shakiness, sweating, confusion, rapid heartbeat.
• Lifestyle: Reinforce that SGLT2 inhibitors are an addition to, not a replacement for, diet modifications, exercise, and other heart failure self-management strategies like sodium restriction and daily weight monitoring.

Metabolic Effects and Monitoring

SGLT2 inhibitors shift the body's metabolic balance in several ways beyond their primary mechanism:

• By blocking renal glucose reabsorption, they lower blood glucose through an insulin-independent pathway. This is why they're useful in heart failure patients both with and without diabetes.
• The glucose loss can stimulate gluconeogenesis (glucose production by the liver), which in some cases promotes ketone body production.
• Metabolic acidosis can occur in rare cases. Monitor bicarbonate levels if a patient develops unexplained malaise or rapid breathing.
• Euglycemic DKA deserves special attention: because blood glucose stays near-normal, standard DKA screening can miss it. Risk factors include surgery, prolonged fasting, acute illness, or significant carbohydrate restriction. Educate patients to seek care if they develop nausea, vomiting, or unusual fatigue, even if their blood sugar readings look fine.