Losartan: NHS information and prescribing guide

Losartan is an angiotensin II receptor blocker (ARB) available in tablet form as losartan potassium. It is one of the most commonly prescribed ARBs on the NHS.

Licensed indications include:

• Hypertension (high blood pressure): NICE (NG136) recommends an ARB as first-line treatment for patients under 55 years of age, or as an alternative to an ACE inhibitor at any age
• Chronic heart failure: when ACE inhibitors are not tolerated
• Diabetic nephropathy: to slow the progression of kidney disease in patients with type 2 diabetes and proteinuria
• Stroke prevention: in hypertensive patients with left ventricular hypertrophy

Losartan works by blocking the angiotensin II type 1 (AT1) receptor, which prevents angiotensin II from constricting blood vessels and promoting sodium and water retention.

The result is lower blood pressure, reduced strain on the heart and protection of the kidneys.

Unlike ACE inhibitors, losartan does not inhibit the breakdown of bradykinin, which means it is significantly less likely to cause the persistent dry cough associated with medicines such as ramipril or lisinopril.

Losartan is taken as a tablet, usually once daily. It can be taken with or without food, at any time of day, though consistency is important.

Dosage by indication (BNF recommendations):

• Hypertension: initially 50 mg once daily, increased if necessary to 100 mg once daily. Patients over 75 years or those with hepatic impairment may start at 25 mg daily
• Heart failure: initially 12.5 mg once daily, titrated at weekly intervals to a target dose of 150 mg once daily as tolerated
• Diabetic nephropathy: initially 50 mg once daily, increased to 100 mg once daily based on blood pressure response
• Stroke prevention: 50 mg once daily, usually combined with a low-dose thiazide diuretic, with the dose increased to 100 mg once daily if needed

Important dosing points:

• Renal function and potassium should be checked before starting and monitored regularly
• In hepatic impairment, a lower starting dose (25 mg) is recommended
• Losartan should not be combined with an ACE inhibitor (dual RAAS blockade) as this increases the risk of hyperkalaemia and kidney injury
• If you miss a dose, take it when you remember unless it is almost time for the next dose. Do not double up.

Losartan is generally well tolerated. The most common side effects are mild and often resolve with continued treatment.

Common:

• Dizziness, especially after the first dose or dose increases
• High potassium (hyperkalaemia), detected on blood tests
• Fatigue

Uncommon:

• Headache, sleep disturbances
• Nausea, diarrhoea, abdominal pain
• Muscle cramps or back pain
• Skin rash

Rare but serious:

• Angioedema (swelling of the face, lips or tongue)
• Acute kidney injury
• Severe hypotension
• Liver function abnormalities

For a detailed discussion of each side effect, including management strategies, see our losartan side effects page.

The key advantage of losartan over ACE inhibitors is the very low incidence of dry cough. In clinical trials, the cough rate with losartan was similar to placebo.

This makes it the go-to alternative for the estimated 10 to 15% of patients who develop a cough on ACE inhibitors.

Losartan interacts with several commonly used medicines. Always inform your doctor or pharmacist about all the medicines you are taking.

Important interactions include:

• ACE inhibitors (ramipril, lisinopril): should not be combined with losartan (dual RAAS blockade) due to increased risk of hyperkalaemia and renal impairment
• Potassium-sparing diuretics (spironolactone, amiloride): increased risk of high potassium; close monitoring is needed if this combination is essential
• NSAIDs (ibuprofen, naproxen, diclofenac): can reduce the blood-pressure-lowering effect and increase the risk of kidney damage; use the lowest dose for the shortest time
• Lithium: losartan can increase lithium levels, potentially leading to toxicity; lithium levels should be monitored more frequently
• Potassium supplements and salt substitutes: increased risk of hyperkalaemia
• Trimethoprim: can raise potassium levels when combined with losartan

The BNF provides a full list of interactions. Your pharmacist will check for interactions each time a new medicine is dispensed.

Regular monitoring is an essential part of safe treatment with losartan. NICE and the BNF recommend the following schedule.

Before starting losartan:

• Blood pressure measurement
• Renal function (eGFR) and electrolytes, including potassium
• Assessment of cardiovascular risk factors

After starting or changing the dose:

• Blood pressure check within 2 to 4 weeks
• Renal function and potassium at 1 to 2 weeks
• Further checks at 4 to 6 weeks if stable

Long-term monitoring:

• Blood pressure at least annually (more often if not at target)
• Renal function and potassium at least annually
• More frequent monitoring if you have chronic kidney disease, heart failure, diabetes or are taking other medicines that affect potassium

Warning signs to report:

• A significant rise in creatinine (more than 30% above baseline) may require a dose reduction or stopping the medicine
• Potassium above 5.5 mmol/L requires action
• A sustained blood pressure below 90/60 mmHg with symptoms may indicate the dose is too high

Your GP practice will usually arrange these tests as part of routine chronic disease management. If you have not had blood tests checked recently, ask at your next appointment.

Losartan is widely available as a generic medicine on the NHS and is one of the most cost-effective ARBs.

Key prescribing information:

• Available in 12.5 mg, 25 mg, 50 mg and 100 mg tablets
• Also available as a combination tablet with hydrochlorothiazide (a diuretic)
• Generic losartan potassium costs the NHS approximately 2 to 4 pence per tablet
• It is included on local formularies across England, Scotland, Wales and Northern Ireland
• Available on standard NHS prescription

NICE positioning:

NICE (NG136) recommends an ARB as an alternative to an ACE inhibitor when cough or other intolerance occurs.

In practice, losartan and candesartan are the most commonly prescribed ARBs in UK primary care.

Repeat prescriptions:

Most patients receive losartan as a repeat prescription.

The NHS Electronic Prescription Service (EPS) means your prescription can be sent directly to your chosen pharmacy, making collection straightforward.

If you have any questions about your losartan prescription, your community pharmacist is always available to help.