A 32-year-old woman with systemic lupus erythematosus (SLE) presents with acute lupus nephritis (Class IV) and proteinuria of 3.5 g/day. She is started on intravenous methylprednisolone 1 g daily for 3 days, followed by oral prednisolone 1 mg/kg/day. After 2 weeks of therapy, she develops severe hyperglycemia (fasting glucose 280 mg/dL), hypertension (160/100 mmHg), and insomnia. Her serum potassium is 3.2 mEq/L. Which of the following best explains the mechanism of hypokalemia in this patient?

Explanation

## Mechanism of Corticosteroid-Induced Hypokalemia **Key Point:** Glucocorticoids, particularly at high doses, possess inherent mineralocorticoid activity that leads to sodium retention and potassium wasting in the renal collecting duct. ### Pathophysiology Glucocorticoids bind to mineralocorticoid receptors in the collecting duct principal cells, activating the epithelial sodium channel (ENaC). This results in: 1. **Sodium reabsorption** — increased Na^+^ uptake via ENaC 2. **Potassium secretion** — increased K^+^ loss into urine via ROMK channels 3. **Chloride reabsorption** — follows sodium passively **High-Yield:** The mineralocorticoid potency of different glucocorticoids varies: | Corticosteroid | Glucocorticoid Activity | Mineralocorticoid Activity | Risk of Hypokalemia | | --- | --- | --- | --- | | Dexamethasone | High | Minimal | Low | | Prednisolone | Moderate | Moderate | Moderate | | Hydrocortisone | Low | High | High | | Methylprednisolone | High | Minimal | Low | **Clinical Pearl:** In this patient, despite methylprednisolone having minimal mineralocorticoid activity, the transition to oral prednisolone (which has moderate mineralocorticoid activity) at 1 mg/kg/day (approximately 32 mg/day) is sufficient to cause significant potassium wasting. ### Why This Patient Developed Hypokalemia - **Dose-dependent effect:** High-dose prednisolone (1 mg/kg/day) amplifies mineralocorticoid effects - **Duration:** 2 weeks of continuous exposure allows cumulative potassium depletion - **Associated hypertension:** Sodium retention from mineralocorticoid activity raises blood pressure, a hallmark of hypokalemic hypertension **Warning:** Hypokalemia with corticosteroids is NOT due to intracellular shift (that occurs with insulin or β~2~-agonists) or GI losses alone — it is primarily renal potassium wasting via the mineralocorticoid pathway. ### Management - Switch to dexamethasone or methylprednisolone (minimal mineralocorticoid activity) if possible - Add potassium-sparing diuretic (spironolactone) or potassium supplementation - Monitor serum potassium weekly during high-dose corticosteroid therapy [cite:KD Tripathi 8e Ch 56]