Losartan

Losartan is an angiotensin II receptor blocker (ARB) used to treat hypertension, protect the kidneys in type 2 diabetic nephropathy, and reduce cardiovascular mortality in patients with left ventricular hypertrophy.

It was the first ARB to reach the market and remains among the most prescribed.

Angiotensin II is a potent vasoconstrictor that drives up blood pressure and promotes cardiac and renal remodelling.

Losartan selectively blocks the AT1 receptor subtype, preventing these harmful effects while allowing beneficial signalling through the AT2 receptor to continue.

Renal Protection

In patients with type 2 diabetes and proteinuria, losartan slows the progression of nephropathy independently of its blood-pressure-lowering effect.

By reducing intraglomerular pressure and blocking pro-fibrotic pathways, it preserves kidney function over the long term.

Unique Metabolic Feature

Unlike most ARBs, losartan has a mild uricosuric effect — it lowers serum uric acid levels.

This may be a clinical advantage in patients with concurrent hypertension and gout, though it is not licensed specifically for gout management.

How to Take Losartan

Swallow the tablet with water, with or without food, at the same time each day. Most patients take it in the morning, but evening dosing is equally acceptable.

Starting Treatment

The blood-pressure-lowering effect develops over three to six weeks. Do not stop treatment because the effect seems slow initially. Your prescriber will review and adjust the dose as needed.

Monitoring

Serum potassium and kidney function (creatinine and eGFR) are usually checked within one to two weeks of starting or increasing the dose, and at regular intervals thereafter.

Hypertension

• Starting dose: 50 mg once daily
• Usual maintenance: 50-100 mg once daily
• Patients over 75 or with hepatic impairment: start at 25 mg

Diabetic Nephropathy

• Starting dose: 50 mg once daily, titrated to 100 mg based on blood pressure response

Stroke Risk Reduction (with LVH)

• 50 mg once daily, titrated to 100 mg; often combined with hydrochlorothiazide

Renal Impairment

• No dose adjustment needed unless on haemodialysis (start at 25 mg)

Children (6-18 years, over 20 kg)

• Dosed by body weight; prescriber-directed

Common (up to 1 in 10 patients)

• Dizziness, particularly with the first dose or after dose increases
• Hyperkalaemia (raised potassium), especially in patients with renal impairment
• Fatigue

Uncommon (up to 1 in 100 patients)

• Postural hypotension
• Mild elevation of liver transaminases
• Impaired renal function
• Angioedema (swelling of the face, lips, or throat) — far less common than with ACE inhibitors but still possible

Rare (up to 1 in 1,000 patients)

• Hepatitis
• Rhabdomyolysis
• Anaemia

Very Rare (fewer than 1 in 10,000 patients)

• Vasculitis, including Henoch-Schonlein purpura

Dizziness and first-dose hypotension are more likely in volume-depleted patients. Ensure adequate hydration before starting.

Potassium and Renal Function

Monitor serum potassium and creatinine, especially in patients taking other potassium-raising drugs (potassium supplements, potassium-sparing diuretics, ACE inhibitors).

Dual RAAS blockade (combining an ARB with an ACE inhibitor or aliskiren) is generally not recommended.

Volume Depletion

Patients who are dehydrated or on high-dose diuretics may experience pronounced first-dose hypotension. Correct volume status before starting losartan.

Renal Artery Stenosis

In bilateral renal artery stenosis (or stenosis of a single functioning kidney), losartan may precipitate acute kidney injury. Use with extreme caution and close monitoring.

Pregnancy

All ARBs are contraindicated in the second and third trimesters. Discontinue losartan as soon as pregnancy is confirmed and switch to a safe alternative.

Do not take losartan if you have:

• A known allergy to losartan or any component of the tablet
• Pregnancy (second and third trimesters; avoid in first trimester if possible)
• Severe hepatic impairment
• Concurrent use of aliskiren in patients with diabetes or renal impairment (eGFR < 60)
• Breastfeeding (excretion into breast milk is not fully characterised)
• Bilateral renal artery stenosis (relative contraindication requiring specialist input)