What are the side effects of Losartan (angiotensin II receptor antagonist)?

Side Effects of Losartan

Losartan is generally well-tolerated with a side effect profile similar to placebo, with dizziness being the only adverse effect reported more frequently than placebo in clinical trials. 1, 2

Common Side Effects

Losartan's FDA-approved drug label identifies the following common side effects (occurring in ≥2% of patients and more commonly than placebo) 1:

• Dizziness (3% vs. 2% with placebo)
• Upper respiratory infection (8% vs. 7%)
• Nasal congestion (2% vs. 1%)
• Back pain (2% vs. 1%)

Cardiovascular Side Effects

• Low blood pressure (hypotension): May cause lightheadedness or fainting, particularly when starting treatment 1
• Palpitations, syncope, and atrial fibrillation (less common) 1

Renal Side Effects

• Worsening renal function: Particularly in patients with pre-existing kidney disease, bilateral renal artery stenosis, or severe heart failure 1, 3
• Monitoring of renal function is essential when starting losartan, similar to ACE inhibitors 4
• Hyperkalemia (elevated potassium levels) 1

Metabolic Side Effects

• Unlike ACE inhibitors, losartan may lower uric acid levels, which could be beneficial when combined with thiazide diuretics 5

Respiratory Side Effects

• Cough: Significantly less common than with ACE inhibitors 4
• In controlled trials comparing losartan to ACE inhibitors in patients who previously experienced ACE inhibitor-induced cough, only 17-29% developed cough on losartan compared to 62-69% on ACE inhibitors 1

Neurological Side Effects

• Headache, somnolence, sleep disorders, paresthesia, and migraine (less common) 1

Gastrointestinal Side Effects

• Abdominal pain, constipation, nausea, vomiting, and diarrhea (less common) 1

Dermatological Side Effects

• Urticaria, pruritus, rash, and photosensitivity (less common) 1
• Angioedema: Though rare, it can occur with losartan, even in patients who previously experienced angioedema with ACE inhibitors 4

Musculoskeletal Side Effects

• Myalgia and arthralgia (less common) 1

Special Populations

Pregnancy

• Contraindicated in pregnancy (Category D): Can cause fetal injury and death when used in the second and third trimesters 1
• Should be discontinued as soon as pregnancy is detected 1

Elderly

• No overall differences in effectiveness or safety were observed in elderly patients, but greater sensitivity in some older individuals cannot be ruled out 1

Renal Impairment

• Generally no dosage adjustment is necessary for patients with mild to moderate renal impairment 6
• However, caution is advised as losartan may cause acute renal failure in patients sensitive to reduced renal plasma flow 3

Drug Interactions

• Potassium supplements or salt substitutes containing potassium may increase serum potassium 1
• Diuretics, lithium, NSAIDs (including COX-2 inhibitors) may interact with losartan 1
• No clinically significant interactions with hydrochlorothiazide, warfarin, or digoxin 6

Monitoring Recommendations

• Check renal function and potassium within 1-2 weeks of initiation 7
• Follow closely after dose changes, particularly in patients with:
  • Systolic blood pressure below 80 mmHg
  • Low serum sodium
  • Diabetes mellitus
  • Impaired renal function 7

Comparison to ACE Inhibitors

The most notable advantage of losartan over ACE inhibitors is the significantly lower incidence of cough and angioedema, making it an excellent alternative for patients who cannot tolerate ACE inhibitors due to these side effects 4, 1.

Common Pitfalls and Precautions

1. First-dose hypotension: Start with lower doses in volume-depleted patients
2. Renal function deterioration: Monitor closely in patients with renal artery stenosis or severe heart failure
3. Hyperkalemia: Use with caution in patients taking potassium supplements or potassium-sparing diuretics
4. Pregnancy: Must be discontinued immediately if pregnancy is detected
5. Dual RAS blockade: Avoid combining with ACE inhibitors or other ARBs as this increases adverse effects without significant clinical benefit 7

Losartan's favorable side effect profile makes it an important option for patients with hypertension, particularly those who cannot tolerate ACE inhibitors due to cough or angioedema.