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

Side Effects of Losartan

Losartan commonly causes dizziness, upper respiratory infections, nasal congestion, and back pain, with more serious but less common side effects including hypotension, hyperkalemia, and renal dysfunction. 1

Common Side Effects

Losartan, an angiotensin II receptor blocker (ARB), has a generally favorable side effect profile compared to other antihypertensive medications. According to FDA labeling, the most common side effects include:

• "Colds" (upper respiratory infection) - 8% of patients 1
• Dizziness - 3% of patients 1
• Nasal congestion - 2% of patients 1
• Back pain - 2% of patients 1

In patients with type 2 diabetes and diabetic kidney disease, additional common side effects include:

• Diarrhea
• Tiredness
• Low blood sugar
• Chest pain
• High blood potassium
• Low blood pressure 1

Serious Side Effects

While losartan is generally well-tolerated, several serious adverse effects require monitoring:

1. Hypotension

Low blood pressure may cause faintness or dizziness, particularly upon standing. Patients should lie down if feeling faint and contact their doctor immediately 1. This effect is usually less pronounced than with ACE inhibitors, as losartan has a slower onset of action 2.

2. Renal Function Deterioration

• Particularly in patients with pre-existing kidney problems 1
• Monitoring of renal function is essential when initiating therapy 3
• Acute kidney failure has been reported in some patients, similar to effects seen with ACE inhibitors 4

3. Hyperkalemia (High Blood Potassium)

• Requires monitoring, especially in patients with renal impairment 1
• May be exacerbated by concurrent use of potassium supplements or potassium-sparing diuretics 1

4. Angioedema

While less common than with ACE inhibitors, angioedema has been reported with losartan use 2. Symptoms include swelling of the face, lips, throat, or tongue, requiring immediate medical attention 1.

Advantages Over ACE Inhibitors

Losartan offers several advantages over ACE inhibitors:

• Lower incidence of cough: Unlike ACE inhibitors which cause persistent dry cough in up to 20% of patients, losartan has a significantly lower incidence of this side effect 5, 1
• Reduced risk of angioedema: Though still possible, angioedema occurs less frequently with ARBs like losartan than with ACE inhibitors 5
• Uric acid reduction: Losartan uniquely lowers serum uric acid levels by increasing uric acid excretion, which may benefit patients with hyperuricemia 2, 6

Special Populations and Precautions

Pregnancy

• Contraindicated in pregnancy (Category D)
• Can cause injury or death to the unborn baby when used during the second or third trimester 1
• Should be discontinued as soon as pregnancy is detected 1

Breastfeeding

• It is not known if losartan passes into breast milk
• Patients should choose either to take losartan or breastfeed, but not both 1

Elderly Patients

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

Race Considerations

• In the LIFE study, Black patients with hypertension and left ventricular hypertrophy had different outcomes compared to non-Black patients 1

Drug Interactions

Losartan may interact with:

• Potassium supplements
• Salt substitutes containing potassium
• Other medications that may increase serum potassium
• Diuretics
• Lithium
• NSAIDs including COX-2 inhibitors
• Other blood pressure medications 1

Monitoring Recommendations

When starting losartan therapy, patients should be monitored for:

• Blood pressure changes, including postural hypotension
• Renal function
• Serum potassium levels 5

Losartan is generally well-tolerated with a favorable side effect profile compared to other antihypertensive medications, making it a valuable option for patients who cannot tolerate ACE inhibitors due to cough or angioedema.