What are the side effects of losartan?

Side Effects of Losartan

Losartan is very well tolerated, with dizziness being the only drug-related adverse effect reported more frequently than placebo in clinical trials, and the overall withdrawal rate due to adverse effects (2.3%) is actually lower than placebo (3.7%). 1, 2

Common Side Effects

In Hypertensive Patients

• Upper respiratory infections ("colds"), dizziness, stuffy nose, and back pain are the most frequently reported side effects in patients with high blood pressure 1
• Dizziness is the only adverse effect consistently attributed to losartan across multiple studies 3, 2

In Diabetic Nephropathy Patients

• Diarrhea, tiredness, low blood sugar, chest pain, high blood potassium, and low blood pressure are the most common side effects in patients with type 2 diabetes and diabetic kidney disease 1

Serious but Rare Adverse Effects

Allergic Reactions

• Angioedema (swelling of the face, lips, throat, or tongue) can occur, though it is extremely rare (approximately 0.11% incidence, similar to placebo) 4, 1
• If angioedema develops, stop losartan immediately and seek emergency medical help 1
• Postmarketing surveillance has confirmed that angioedema, while rare, does occur with losartan 3

Cardiovascular Effects

• Hypotension (low blood pressure) may cause faintness or dizziness, particularly in volume-depleted patients 1
• First-dose hypotension is uncommon due to the slower onset of action compared to ACE inhibitors 3, 2

Renal Effects

• Worsening kidney function can occur in patients with pre-existing renal problems, bilateral renal artery stenosis, severe heart failure, or volume depletion 1, 5
• A modest 10–20% rise in serum creatinine after starting losartan is expected and hemodynamic in nature, not indicative of kidney injury unless persistent 4
• Losartan-induced renal dysfunction occurs at a rate of approximately 10.5% in elderly heart failure patients, identical to the rate seen with ACE inhibitors 5

Electrolyte Disturbances

• Hyperkalemia (high blood potassium) can develop, especially in patients with chronic kidney disease, diabetes, or those taking potassium-sparing diuretics or potassium supplements 1, 6
• Losartan typically increases serum potassium by approximately 1 mEq/L 4

Hepatic Effects

• Acute hepatitis has been reported in rare cases (3 patients among millions treated), though causality remains unclear 6

Metabolic and Laboratory Effects

• Losartan does not cause adverse metabolic effects such as decreased HDL cholesterol, increased triglycerides, or new-onset diabetes 7
• 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 7, 3

Advantages Over ACE Inhibitors

• Cough is not a significant problem with losartan; the incidence is similar to placebo and markedly lower than with ACE inhibitors 7, 1, 2
• This makes losartan particularly valuable for patients who develop ACE inhibitor-related cough 8, 2

Absolute Contraindications

Pregnancy

• Losartan is absolutely contraindicated throughout pregnancy due to serious fetal toxicity, including renal dysfunction, oligohydramnios, skull hypoplasia, and fetal death 9, 1, 6
• Discontinue immediately upon pregnancy detection 9

Drug Combinations

• Do not combine losartan with ACE inhibitors or aliskiren (direct renin inhibitor), as dual RAAS blockade increases the risk of hyperkalemia, syncope, and acute kidney injury 2–3-fold without added cardiovascular benefit 9, 4, 1

Monitoring Requirements

• Check serum creatinine/eGFR and potassium within 1–2 weeks after starting losartan or increasing the dose, especially in patients with diabetes or chronic kidney disease 9, 4
• Monitor blood pressure regularly, including orthostatic measurements in elderly patients 9
• Continue monitoring renal function and electrolytes at least annually during maintenance therapy 9

Special Populations

Hepatic Impairment

• Patients with hepatic impairment may have approximately five-fold higher plasma concentrations of losartan; start at 25 mg once daily 9

Renal Impairment

• No dosage adjustment is necessary for various degrees of renal insufficiency, though closer monitoring is required 10, 6
• Losartan is not removed during hemodialysis 10

Drug Interactions

• Potassium-sparing diuretics (spironolactone, triamterene) increase hyperkalemia risk 4, 6
• NSAIDs may blunt losartan's antihypertensive effect and worsen renal function 9
• Lithium co-administration can precipitate lithium toxicity; monitor lithium levels 9
• Losartan has no clinically relevant interactions with hydrochlorothiazide, warfarin, digoxin, cimetidine, or phenobarbital 10, 2

Common Pitfalls to Avoid

• Do not discontinue losartan prematurely for mild hyperkalemia; implement potassium-lowering strategies first 4
• Do not assume renal dysfunction with losartan means ACE inhibitors would be better tolerated—the rates are identical 5
• Do not stop losartan for a modest creatinine rise (10–20%) unless there is evidence of acute tubular necrosis on urinalysis 4