Losartan is a Potassium-Sparing Medication
Yes, losartan is a potassium-sparing medication that can cause hyperkalemia due to its mechanism of action as an angiotensin II receptor blocker (ARB). 1, 2
Mechanism of Potassium Retention
- Losartan blocks the angiotensin II type 1 (AT1) receptor, which reduces aldosterone production, leading to decreased potassium excretion in the kidneys 2
- As an ARB, losartan is specifically classified in guidelines alongside other medications that can increase serum potassium levels 1
- The FDA label for losartan explicitly warns that "coadministration of losartan with other drugs that raise serum potassium levels may result in hyperkalemia" 2
Risk Factors for Hyperkalemia with Losartan
- Patients with chronic kidney disease (CKD) are at higher risk for hyperkalemia when taking losartan 1, 2
- Concomitant use of potassium supplements increases the risk of hyperkalemia 2, 3
- Dual blockade of the renin-angiotensin system (combining losartan with ACE inhibitors or aliskiren) significantly increases hyperkalemia risk 2
- Combination with potassium-sparing diuretics (spironolactone, triamterene, amiloride) further increases hyperkalemia risk 1, 3
Clinical Implications and Monitoring
- Guidelines recommend monitoring serum potassium levels before initiating losartan therapy, within 1-2 weeks after starting treatment, and periodically during long-term treatment 4
- Patients with renal impairment require careful monitoring of potassium levels when taking losartan 2, 3
- The Veterans Affairs Nephropathy in Diabetes (VA NEPHRON-D) trial showed increased incidence of hyperkalemia when losartan was combined with lisinopril 2
Clinical Benefits Related to Potassium Effects
- In heart failure patients, high-dose losartan (150 mg/day) decreased the risk of hypokalemia compared to low-dose (50 mg/day) treatment 5
- Hypokalemia has been associated with worse outcomes in heart failure patients, including higher risk of cardiovascular death and hospitalization 5
- The potassium-retaining effects of losartan may be beneficial when combined with thiazide diuretics, which can cause hypokalemia 6
Comparison to Other Antihypertensives
- In the ACC/AHA guidelines, losartan is categorized alongside other ARBs that carry an increased risk of hyperkalemia 1
- Unlike thiazide and loop diuretics which cause potassium loss, losartan is classified with medications that can increase serum potassium 1
- Guidelines specifically list amiloride, triamterene, eplerenone, and spironolactone as "potassium-sparing diuretics," while ARBs like losartan are noted separately but with similar potassium-retaining effects 1