What are the indications, dosing recommendations, contraindications, and common adverse effects of losartan (angiotensin II receptor blocker)?

Losartan: Clinical Overview

Losartan is an angiotensin II receptor blocker (ARB) indicated for hypertension, left ventricular hypertrophy reduction in hypertensive patients, and type 2 diabetic nephropathy, with standard dosing of 50 mg once daily (up to 100 mg/day), and is contraindicated in pregnancy and in diabetic patients taking aliskiren. 1

Approved Indications

Losartan has three FDA-approved indications 1:

• Hypertension: First-line treatment for blood pressure reduction
• Left ventricular hypertrophy (LVH): Reduces cardiovascular risk in hypertensive patients with LVH
• Type 2 diabetic nephropathy: Protects kidney function in patients with diabetes and proteinuria

Dosing Recommendations

Standard dosing 1, 2:

• Initial dose: 50 mg once daily
• Maximum dose: 100 mg once daily (can be split into two doses if needed)
• Can be taken with or without food
• No adjustment needed for elderly patients or mild hepatic impairment 3
• No adjustment needed for renal insufficiency (not removed by hemodialysis) 3

Combination therapy: The 2024 ESC guidelines recommend ARBs like losartan combined with either a dihydropyridine calcium channel blocker or thiazide diuretic as preferred first-line therapy for most hypertensive patients 4. A fixed-dose combination of losartan 50 mg/hydrochlorothiazide 12.5 mg is available but not for initial therapy 2, 5.

Contraindications

Absolute contraindications 1:

• Pregnancy (all trimesters - causes serious fetal toxicity and death)
• Hypersensitivity to losartan or any component
• Coadministration with aliskiren in diabetic patients

Relative cautions 1:

• History of angioedema with ARBs (though patients with ACE inhibitor-related angioedema can receive losartan after 6 weeks)
• Severe bilateral renal artery stenosis (risk of acute renal failure)
• Volume depletion or salt depletion (increased hypotension risk)

Common Adverse Effects

Most common adverse effects in hypertensive patients 1:

• Upper respiratory infection (8%)
• Dizziness (3%)
• Nasal congestion (2%)
• Back pain (2%)

In diabetic nephropathy patients 1:

• Diarrhea
• Fatigue
• Low blood sugar
• Chest pain
• Hyperkalemia
• Hypotension

Critical safety point: Losartan has a placebo-like tolerability profile with discontinuation rates of only 2.3% versus 3.7% for placebo 1, 6. Notably, cough occurs in only 3.1% of losartan patients versus 2.6% with placebo—dramatically lower than ACE inhibitors (17-29% versus 62-69% with lisinopril) 1.

Serious Adverse Effects to Monitor

1:

• Hyperkalemia (especially with renal impairment, potassium supplements, or potassium-sparing diuretics)
• Hypotension (particularly first-dose in volume-depleted patients)
• Worsening renal function (monitor for edema, unexplained weight gain)
• Angioedema (rare but requires immediate discontinuation)

Clinical Pearls

Pharmacokinetics 3:

• Rapidly absorbed with peak levels at 1-2 hours
• Converted to active metabolite E3174 (10-40 fold more potent, half-life 6-9 hours)
• Metabolism via CYP2C9, CYP3A4 (genetic polymorphisms in CYP2C9 significantly affect response)
• Linear, dose-proportional kinetics

Drug interactions 1, 3:

• Avoid combining with other RAS blockers (ACE inhibitors or aliskiren) 4
• Monitor potassium with concurrent use of potassium supplements, salt substitutes, or potassium-sparing agents
• NSAIDs may reduce antihypertensive effect and worsen renal function
• Lithium levels may increase
• Minimal interactions with warfarin, digoxin, or hydrochlorothiazide 3

Guideline positioning: The 2024 ESC guidelines place ARBs (including losartan) as first-line agents alongside ACE inhibitors, dihydropyridine calcium channel blockers, and thiazides/thiazide-like diuretics for hypertension management 4. The 2017 ACC/AHA guidelines similarly recommend ARBs as primary agents 2.

Common Pitfalls

• Do not combine two RAS blockers (ACE inhibitor + ARB)—this increases adverse events without additional benefit 4
• Screen for pregnancy before initiating and counsel on contraception—losartan causes fetal death in second/third trimester 1
• Monitor potassium and renal function within 2-4 weeks of initiation, especially in patients with baseline renal impairment or diabetes
• Losartan is not effective for acute blood pressure lowering—onset takes hours to days for full effect

4, 2, 1, 3