Can chronic losartan therapy cause hypokalemia in a patient with intermittent low potassium who is also taking pantoprazole, atorvastatin, apixaban, levothyroxine, clonazepam, and escitalopram?

No, Losartan Does Not Cause Hypokalemia—It Causes Hyperkalemia

Losartan is an angiotensin receptor blocker (ARB) that reduces renal potassium excretion and increases the risk of hyperkalemia, not hypokalemia. 1 Your intermittent low potassium is not caused by losartan; in fact, losartan may be helping to prevent even lower potassium levels by reducing renal potassium losses. 1

Understanding Losartan's Effect on Potassium

ARBs like losartan block the renin-angiotensin-aldosterone system (RAAS), which decreases aldosterone activity and reduces potassium excretion by the kidneys. 1 This mechanism makes hyperkalemia (high potassium) the primary electrolyte concern with losartan therapy, not hypokalemia. 1

• Losartan has been shown to increase the risk of hyperkalemia, particularly when combined with other potassium-retaining medications like aldosterone antagonists (spironolactone) or ACE inhibitors. 1, 2
• The NEPHRON-D trial demonstrated that combining losartan with an ACE inhibitor (lisinopril) significantly increased the risk of hyperkalemia and acute kidney injury. 1
• A case report documented severe hyperkalemia (8.4 mEq/L) in a patient taking losartan 50 mg with spironolactone 25 mg, requiring hemodialysis. 2

Identifying the True Cause of Your Hypokalemia

Your intermittent low potassium is likely caused by one of your other medications or an underlying condition, not losartan. 3, 4 The most common culprits in your medication list would be:

Pantoprazole (Proton Pump Inhibitor)

• PPIs can cause hypomagnesemia, which in turn makes hypokalemia resistant to correction. 3
• Hypomagnesemia is the most common reason for refractory hypokalemia and must be corrected before potassium levels will normalize. 3
• Check your magnesium level immediately—target >0.6 mmol/L (>1.5 mg/dL). 3

Other Potential Causes to Investigate

• Inadequate dietary intake: Reduced calorie/protein intake can contribute to hypokalemia, particularly in elderly patients. 3
• Gastrointestinal losses: Diarrhea, vomiting, or laxative use can cause significant potassium depletion. 3, 4
• Transcellular shifts: Certain medications or conditions can shift potassium into cells temporarily. 4

Critical Safety Consideration

If you are taking potassium supplements while on losartan, this combination requires careful monitoring because losartan reduces renal potassium excretion. 1, 3 The European Society of Cardiology recommends that patients on ACE inhibitors or ARBs (like losartan) frequently do not require routine potassium supplementation, and such supplementation may be deleterious. 1, 3

• Check potassium and renal function within 2-3 days and again at 7 days after any change in potassium supplementation while on losartan. 3
• Target serum potassium of 4.0-5.0 mEq/L to minimize mortality risk. 3, 5
• If you develop hyperkalemia (K+ >5.5 mEq/L), potassium supplements should be reduced or discontinued. 3, 5

Recommended Diagnostic Workup

To identify the cause of your intermittent hypokalemia, the following tests should be performed: 3

• Serum magnesium level (most important—hypomagnesemia is present in ~40% of hypokalemic patients) 3
• Complete metabolic panel including sodium, calcium, and glucose 3
• Renal function (creatinine, eGFR) 3
• Review of all medications for potassium-wasting effects 3, 4
• Assessment of dietary potassium intake 3
• Evaluation for gastrointestinal losses (diarrhea, vomiting) 3

Common Pitfall to Avoid

Do not discontinue losartan thinking it is causing your low potassium. 1 Losartan provides important cardiovascular and renal protection, particularly if you have hypertension, heart failure, or chronic kidney disease. 1 Stopping losartan would remove a medication that is actually helping to retain potassium and could worsen your long-term cardiovascular outcomes. 1