Major Drug Interaction — Use With Caution

Combining Losartan Potassium and Spironolactone is a major interaction and should generally be avoided without close medical supervision.

Concurrent use of losartan and spironolactone significantly increases the risk of hyperkalemia (elevated serum potassium). Both drugs reduce potassium excretion through complementary mechanisms — losartan blocks aldosterone secretion via AT1 receptor blockade, while spironolactone directly antagonizes aldosterone receptors in the kidney. The combination can cause life-threatening hyperkalemia, particularly in patients with renal impairment, diabetes, or heart failure.

Mechanism: Losartan reduces angiotensin II-mediated aldosterone secretion from the adrenal cortex (via AT1 receptor blockade), decreasing renal potassium excretion. Spironolactone competitively antagonizes aldosterone at the mineralocorticoid receptor in the collecting duct, further reducing potassium excretion. The additive effect on potassium retention can cause serum potassium to rise to dangerous levels (>6 mEq/L).

Drug Comparison

Losartan Potassium vs. Spironolactone

Compare Losartan Potassium and Spironolactone: mechanism of action, indications, side effects, cost, and which may be right for you.

Drug A

Losartan Potassium

Cozaar

ARBs (Angiotensin II Receptor Blockers)

Drug B

Spironolactone

Aldactone

Quick Comparison

Category	Losartan Potassium	Spironolactone
Drug Class	ARBs (Angiotensin II Receptor Blockers)	—
Rx Status	Rx	Rx
Generic Available	No	No
Typical Cost	$4–$15/month	—

Losartan Potassium Overview

Losartan potassium (Cozaar) is an angiotensin II receptor blocker (ARB) used to treat high blood pressure, protect the kidneys in type 2 diabetes, and reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy. Unlike ACE inhibitors, losartan does not cause a dry cough and carries a significantly lower risk of angioedema. It is also the only ARB with a clinically mean...

Full Losartan Potassium guide →

Spironolactone Overview

Spironolactone is a potassium-sparing diuretic and aldosterone antagonist used to treat heart failure, hypertension, edema, and hyperaldosteronism. It blocks aldosterone receptors in the kidney, reducing sodium retention and potassium excretion.

Full Spironolactone guide →

How Each Drug Works

Losartan Potassium

Mechanism of Action — AT1 Receptor Blockade

Losartan is a selective, competitive antagonist of the angiotensin II type 1 (AT1) receptor. Unlike ACE inhibitors, losartan does not prevent the formation of angiotensin II — instead, it blocks angiotensin II from binding to its primary receptor.

Step-by-step mechanism:

Renin-angiotensin-aldosterone system (RAAS) activation: Renin converts angiotensinogen to angiotensin I; ACE converts angiotensin I to angiotensin II via multiple pat…

Approved Uses (Indications)

Losartan Potassium

FDA-Approved Indications:

Hypertension (adults and pediatric patients ≥6 years):

Treatment of hypertension to reduce blood pressure and lower the risk of cardiovascular events
Can be used as monotherapy or in combination with other antihypertensives
Pediatric use: approved for children ≥6 years with eGFR >30 mL/min/1.73m²

Diabetic Nephropathy (type 2 diabetes with proteinuria and hypertension):

Reduces the rate of progression of nephropathy as measured by doubling of serum creatinine or ESRD
RENAAL trial: 25% reduction in doubling of serum creatinine, 28% reduction in E…

Side Effects

Losartan Potassium

Serious Side Effects

Hyperkalemia — can be severe (>6 mEq/L) in patients with renal impairment, diabetes, or concurrent use of potassium-sparing agentsAcute kidney injury — especially in patients with bilateral renal artery stenosis, solitary kidney, or severe heart failureHypotension — particularly in volume-depleted patients (diuretics, low-sodium diet, dialysis); first-dose effectAngioedema — rare (<0.1%), but can occur; 3–4× less common than with ACE inhibitors; may occur in patients with prior ACE inhibitor-induced angioedemaFetal/neonatal toxicity — can cause oligohydramnios, fetal renal dysfunction, skull hypoplasia, and death (Category D in 2nd/3rd trimester)

Common Side Effects

Dizziness (4–7%)Upper respiratory infection (8%)Fatigue (3–4%)Hyperkalemia (potassium >5.5 mEq/L, especially with renal impairment or diabetes)Hypotension (especially in volume-depleted patients)Elevated serum creatinine (reversible, especially with bilateral renal artery stenosis)Back pain (2–3%)Nasal congestion (2%)

Rare Side Effects

Hepatotoxicity (rare case reports)Rhabdomyolysis (rare, especially with concurrent statin use)Anemia (rare, especially in patients with renal impairment)Thrombocytopenia (rare)

Cost Comparison

Losartan Potassium

$4–$15/month

Generic losartan potassium is available at most pharmacies for $4–$15/month, and is included on most $4 generic drug programs at major pharmacy chains (Walmart, Kroger, Costco). Brand-name Cozaar is significantly more expensive (~$200–$300/month) but is rarely prescribed. Hyzaar (losartan/hydrochlorothiazide combination) is also available generically at similar low cost. GoodRx and RxGo coupons can further reduce the price at most pharmacies.

Spironolactone

Cost varies

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Medical Disclaimer

The information on RxGuide is intended for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician, pharmacist, or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.