Adverse Effects of Losartan
Losartan is exceptionally well-tolerated with an adverse event profile similar to placebo, with dizziness being the only consistently drug-related side effect occurring more frequently than placebo. 1
Common Adverse Effects
The most frequently reported adverse events in clinical trials involving over 3,300 patients include:
- Dizziness (3% vs. 2% placebo) - the only adverse effect consistently more common than placebo 1, 2
- Upper respiratory infection (8% vs. 7% placebo) 1
- Nasal congestion (2% vs. 1% placebo) 1
- Back pain (2% vs. 1% placebo) 1
- Headache - frequently reported but not more common than placebo 3
Importantly, the overall discontinuation rate due to adverse events with losartan (2.3%) is actually lower than placebo (3.7%), demonstrating superior tolerability. 1, 2
Cough Profile - A Key Advantage
Losartan has a significantly lower incidence of cough compared to ACE inhibitors, with rates similar to placebo or hydrochlorothiazide. 4
- In controlled trials specifically designed to assess cough in patients who previously experienced ACE inhibitor-induced cough, losartan caused cough in only 17-29% of patients compared to 62-69% with lisinopril 1
- Persistent dry cough occurs in only 3.1% of losartan patients versus 2.6% with placebo 3
- This makes losartan an excellent alternative for patients intolerant to ACE inhibitors due to cough 5
Less Common but Documented Adverse Effects
The following adverse reactions have been reported with ≥2% incidence in clinical trials: 1
Cardiovascular
- Palpitations - though losartan has a notably favorable cardiac tolerability profile 6, 1
- Syncope 1
- Atrial fibrillation 1
- Cerebrovascular accident 1
Neurological
Gastrointestinal
Dermatological
Musculoskeletal
Other Systems
Rare but Serious Adverse Effects
Angioedema/anaphylactoid reactions - the only well-documented serious detrimental side effect of losartan, identified through postmarketing surveillance (similar to ACE inhibitors but less common). 5, 7
Tremors and dysarthria - one case report documented severe tremors and dysarthria requiring hospitalization, though symptoms resolved without treatment; clinical significance remains unclear. 7
Metabolic and Laboratory Effects
Losartan does not cause adverse metabolic effects including: 4
Uric acid effects - losartan has uricosuric properties that lower serum uric acid levels, which may be beneficial when combined with thiazide diuretics but could theoretically lead to uric acid stone formation. 8, 5
Special Population Considerations
Pregnancy
Losartan must be avoided in pregnancy - when given in the second and third trimester, it is often associated with serious fetal toxicity. 9
Renal and Hepatic Impairment
- No dosage adjustment necessary in patients with various degrees of renal insufficiency 9
- No dosage adjustment needed for mild hepatic impairment 9
- Losartan is not removed during hemodialysis 9
Diabetic Patients
- Similar adverse event profile in hypertensive patients with diabetes mellitus (n=133 studied) 3
- Losartan may mask symptoms of hypoglycemia 4
Monitoring Requirements
Regular monitoring should include: 4
- Blood pressure 4
- Serum potassium levels (within 1-2 weeks of initiation) 4, 6
- Kidney function (within 1-2 weeks of initiation) 4, 6
- No specific monitoring for muscle enzymes is required 4
Critical Pitfalls to Avoid
First-dose hypotension is uncommon with losartan due to its slower onset of action, unlike some ACE inhibitors. 5
When normalizing thyroid function in patients with hyperthyroidism, blood pressure monitoring is essential as losartan dosage may need adjustment. 4
Metabolic disturbances (electrolyte abnormalities, renal dysfunction) could manifest as palpitations, emphasizing the importance of early monitoring. 6