In a post‑hysterectomy, post‑menopausal woman on progesterone therapy, how much elemental potassium does losartan potassium contain and can it alone cause hyperkalemia?

Elemental Potassium Content in Losartan Potassium

Losartan potassium contains negligible elemental potassium—approximately 4.24 mg (0.108 mEq) per 50 mg tablet and 8.48 mg (0.217 mEq) per 100 mg tablet—which is far too small to cause hyperkalemia on its own. 1

Understanding the Potassium Content

The molecular weight of losartan potassium is 461.0 g/mol, while elemental potassium has an atomic weight of 39.1 g/mol. This means:

• A 50 mg losartan potassium tablet contains only 4.24 mg of elemental potassium (approximately 0.108 mEq)
• A 100 mg losartan potassium tablet contains only 8.48 mg of elemental potassium (approximately 0.217 mEq) 1

For context, a single banana contains approximately 400-450 mg of elemental potassium, which is 50-100 times more than the amount in a standard losartan dose. 1

The Real Mechanism of Hyperkalemia with Losartan

The hyperkalemia risk from losartan comes from its pharmacologic action blocking the renin-angiotensin-aldosterone system (RAAS), not from the potassium salt component. 2, 3

How Losartan Causes Hyperkalemia

• Losartan blocks angiotensin II receptors, which reduces aldosterone secretion
• Reduced aldosterone decreases renal potassium excretion in the distal tubule and collecting duct
• This impaired renal potassium elimination is the primary mechanism causing elevated serum potassium 3
• The European Heart Journal confirms that RAAS inhibitors, including ARBs like losartan, are well-established causes of hyperkalemia through decreased potassium excretion 2

Clinical Evidence on Hyperkalemia Risk

Incidence in Clinical Trials

In studies of patients with sickle cell disease treated with losartan or other RAAS inhibitors, hyperkalemia occurred in 13% of patients (12 of 92), demonstrating that the drug effect—not the salt form—drives potassium elevation. 2

The HEAAL trial, which compared losartan 150 mg daily versus 50 mg daily in heart failure patients, found:

• Episodes of hyperkalemia (>5.0 mmol/L) occurred in approximately 50% of patients at some point during follow-up
• Higher doses of losartan increased serum potassium levels more than lower doses
• This dose-response relationship confirms the pharmacologic mechanism rather than elemental potassium content 4, 5

Risk Factors for Hyperkalemia

Patients at highest risk include those with:

• Chronic kidney disease (especially eGFR <60 mL/min/1.73 m²) 2
• Diabetes mellitus 2, 4
• Concurrent use of other potassium-retaining medications (spironolactone, amiloride, triamterene, NSAIDs, trimethoprim) 2, 6
• Advanced age 4
• Heart failure 2, 4

Special Considerations for Your Patient Population

In a post-hysterectomy, post-menopausal woman on progesterone therapy:

• Progesterone therapy does not significantly interact with losartan's effect on potassium and is not listed among medications that cause hyperkalemia 2
• The hysterectomy status is irrelevant to potassium homeostasis
• Standard monitoring applies: check serum potassium and creatinine within 1-2 weeks after initiating losartan or increasing the dose 7, 8

Monitoring Recommendations

The European Heart Journal recommends the following potassium thresholds for action: 2, 7

• Mild hyperkalemia (5.0-5.5 mEq/L): Continue losartan with dietary potassium restriction and recheck in 1-2 weeks
• Moderate hyperkalemia (5.5-6.0 mEq/L): Reduce losartan dose by 50% and recheck within 1-2 weeks 7
• Severe hyperkalemia (>6.0 mEq/L): Hold losartan immediately and treat hyperkalemia urgently 7

Common Clinical Pitfall

A critical error is discontinuing losartan prematurely for mild hyperkalemia (5.0-5.4 mEq/L) when the patient has compelling indications such as heart failure, diabetic nephropathy, or hypertension with left ventricular hypertrophy. 2, 7

Instead, the American College of Cardiology recommends:

• Implementing dietary potassium restriction
• Discontinuing other potassium-retaining agents if possible
• Adding a potassium binder (patiromer or sodium zirconium cyclosilicate) to maintain RAAS inhibition 7
• Reducing the losartan dose rather than stopping it entirely 7

The HEAAL trial demonstrated that high-dose losartan (150 mg) reduced cardiovascular death or heart failure hospitalization by 10% despite causing more hyperkalemia, indicating that the benefits outweigh the potassium elevation risk when properly monitored. 9, 4, 5