Losartan

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Losartan on Prescriptsy

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Losartan is an angiotensin II receptor blocker (ARB) widely prescribed in the United Kingdom for the management of hypertension (high blood pressure), the protection of kidney function in patients with type 2 diabetes and nephropathy (diabetic kidney disease), and the reduction of stroke risk in patients with hypertension and evidence of left ventricular hypertrophy.

It belongs to the sartan class of antihypertensive agents and is available as tablets in strengths of 12.5 mg, 25 mg, 50 mg, and 100 mg.

Losartan was the first ARB to be developed and has been in clinical use since the mid-1990s, with an extensive safety and efficacy record.

High blood pressure is the single largest risk factor for cardiovascular disease in the UK, contributing to approximately half of all heart attacks and strokes.

According to the British Heart Foundation, around 14 million adults in the UK have high blood pressure, and many remain undiagnosed or inadequately treated.

Effective and sustained blood pressure control with agents such as losartan significantly reduces the lifetime risk of heart attack, stroke, heart failure, chronic kidney disease, and vascular dementia.

This page provides a comprehensive clinical overview of losartan, including how it works, dosing guidance, side effects, safety warnings, and how to obtain a prescription in the UK.

Important safety information about losartan

Before reading further, note the following key safety points about losartan.

• Losartan must not be taken during pregnancy at any stage. It can cause serious harm to the developing baby. If you become pregnant while taking losartan, stop the medication and contact your doctor immediately.
• Do not take losartan together with an ACE inhibitor (such as ramipril or lisinopril) or aliskiren if you have diabetes or kidney disease, as this combination increases the risk of dangerously low blood pressure, kidney failure, and high potassium levels.
• Blood tests to check kidney function and potassium levels are required before starting treatment and at regular intervals during therapy.
• If you develop swelling of the face, lips, tongue, or throat (angioedema), seek emergency medical attention immediately.

What is hypertension

Hypertension, or high blood pressure, is a chronic condition in which the force of blood against the walls of the arteries is persistently elevated.

Blood pressure is measured in millimetres of mercury (mmHg) and expressed as two figures: systolic pressure (the pressure when the heart contracts and pushes blood out) and diastolic pressure (the pressure when the heart relaxes between beats).

A normal blood pressure reading is generally below 140/90 mmHg in clinic measurements, or below 135/85 mmHg when measured at home using an ambulatory or home blood pressure monitor.

Hypertension is classified as primary (essential) when there is no identifiable cause, which accounts for approximately 90 to 95% of cases, or secondary when it results from an underlying condition such as renal artery stenosis, primary aldosteronism, phaeochromocytoma, or obstructive sleep apnoea.

Risk factors for primary hypertension include age, family history, excess dietary sodium, obesity, physical inactivity, excessive alcohol intake, and chronic stress.

Uncontrolled hypertension damages the blood vessels, heart, brain, kidneys, and eyes over time.

It is the leading modifiable risk factor for stroke, ischaemic heart disease, heart failure, chronic kidney disease, peripheral arterial disease, and vascular dementia.

Because hypertension is usually asymptomatic until target organ damage has occurred, regular blood pressure screening is recommended for all adults, particularly those aged over 40 years.

NICE Guideline NG136 (Hypertension in adults: diagnosis and management) provides the current UK framework for the identification and treatment of hypertension.

How losartan works: mechanism of action

Losartan works by selectively blocking the angiotensin II type 1 (AT1) receptor.

Angiotensin II is a powerful hormone produced as part of the renin-angiotensin-aldosterone system (RAAS), a hormonal cascade that plays a central role in regulating blood pressure, fluid balance, and sodium retention.

When angiotensin II binds to the AT1 receptor on the walls of blood vessels, it causes vasoconstriction (narrowing of the arteries), which raises blood pressure.

It also stimulates the release of aldosterone from the adrenal glands, promoting sodium and water retention and further increasing blood volume and pressure.

By blocking the AT1 receptor, losartan prevents angiotensin II from exerting these effects.

The result is vasodilation (relaxation and widening of the blood vessels), reduced aldosterone secretion, decreased sodium and water retention, and consequently a sustained reduction in blood pressure.

The unblocked angiotensin II type 2 (AT2) receptor continues to mediate potentially beneficial effects including vasodilation, anti-inflammatory actions, and tissue repair.

Losartan is a prodrug that is extensively metabolised in the liver by cytochrome P450 enzymes, primarily CYP2C9 and CYP3A4, to produce the active metabolite E-3174 (also known as EXP-3174).

This metabolite is 10 to 40 times more potent than the parent compound at blocking the AT1 receptor and has a longer half-life (approximately 6 to 9 hours compared with 2 hours for losartan), which contributes to the sustained 24-hour antihypertensive effect with once-daily dosing.

Unlike ACE inhibitors, losartan does not interfere with the breakdown of bradykinin, which is why ARBs are associated with a substantially lower incidence of the persistent dry cough that commonly leads to discontinuation of ACE inhibitor therapy.

Renoprotective effects

In the kidney, angiotensin II preferentially constricts the efferent arteriole of the glomerulus, increasing intraglomerular pressure and accelerating the progression of diabetic nephropathy and other forms of chronic kidney disease.

By blocking the AT1 receptor, losartan reduces intraglomerular pressure, decreases proteinuria (protein leakage in the urine), and slows the decline in glomerular filtration rate (GFR).

The landmark RENAAL (Reduction of Endpoints in Non-insulin-dependent diabetes mellitus with the Angiotensin II Antagonist Losartan) trial demonstrated that losartan 100 mg daily reduced the risk of doubling of serum creatinine by 25% and the risk of end-stage renal disease by 28% compared with placebo in patients with type 2 diabetes and nephropathy, on top of conventional antihypertensive therapy.

Clinical evidence and national guidelines

Losartan has been studied extensively in large randomised controlled trials across multiple indications. The key evidence base includes the following studies.

The LIFE (Losartan Intervention For Endpoint reduction in hypertension) trial compared losartan-based therapy with atenolol-based therapy in 9,193 patients with hypertension and electrocardiographic evidence of left ventricular hypertrophy.

Despite similar blood pressure reductions in both groups, losartan-based therapy reduced the primary composite endpoint of cardiovascular death, stroke, and myocardial infarction by 13%, driven largely by a 25% relative risk reduction in stroke.

This finding led to the licensed indication for stroke prevention in patients with hypertension and left ventricular hypertrophy.

The RENAAL trial, described above, established the renoprotective benefits of losartan in type 2 diabetic nephropathy.

The ELITE II trial compared losartan with captopril in elderly patients with heart failure but did not demonstrate superiority of losartan for mortality reduction, and losartan does not currently hold a primary licence for heart failure in the UK.

However, it may be used as an alternative when ACE inhibitors are not tolerated.

NICE Guideline NG136 recommends ARBs, including losartan, as first-line treatment for hypertension in patients under 55 years of age (Step 1), or as an alternative to ACE inhibitors for those who cannot tolerate them.

For patients aged 55 years and over, or those of Black African or African-Caribbean family origin, a calcium channel blocker (such as amlodipine) is generally preferred as first-line therapy, with an ARB added at Step 2 if needed.

For patients with diabetes, chronic kidney disease with proteinuria, or heart failure, ACE inhibitors or ARBs are recommended as first-line agents regardless of age or ethnicity, due to their additional renoprotective and cardioprotective properties.

Dosage and administration

Losartan is taken orally as a tablet, usually once daily. The dose depends on the clinical indication, the patient's baseline blood pressure, renal function, and concomitant medications.

Hypertension in adults

The usual starting dose is 50 mg once daily.

If blood pressure is not adequately controlled after 3 to 6 weeks, the dose may be increased to 100 mg once daily.

In patients who may be volume-depleted, such as those receiving high-dose diuretic therapy, or in the elderly, a lower starting dose of 25 mg once daily is recommended to reduce the risk of symptomatic hypotension.

Losartan can be combined with other antihypertensive agents such as amlodipine, indapamide, or bendroflumethiazide to achieve target blood pressure.

Renal protection in type 2 diabetes with nephropathy

The usual starting dose is 50 mg once daily, titrated to 100 mg once daily according to blood pressure response.

Treatment should be initiated alongside other measures to optimise glycaemic control, manage cardiovascular risk factors, and reduce proteinuria.

Losartan should be continued long-term in this patient group unless significant adverse effects develop.

Stroke risk reduction in patients with hypertension and left ventricular hypertrophy

The usual starting dose is 50 mg once daily, with the possibility of adding low-dose hydrochlorothiazide (12.5 mg) if additional blood pressure reduction is required.

The dose of losartan may be increased to 100 mg once daily. Treatment should be maintained long-term to sustain the stroke-preventive benefit demonstrated in the LIFE trial.

Children and adolescents aged 6 to 18 years

Losartan is licensed for use in children aged 6 years and over with hypertension.

For children weighing 20 to 50 kg, the recommended starting dose is 0.7 mg per kg once daily, up to a maximum of 25 mg.

For those over 50 kg, the starting dose is 50 mg once daily. Doses may be adjusted based on blood pressure response.

A liquid formulation can be prepared by a pharmacist for children who cannot swallow tablets.

Practical advice

Losartan tablets should be swallowed whole with water and can be taken with or without food.

Choose a time of day that is easy to remember and take the tablet at the same time each day.

If you miss a dose, take it as soon as you remember unless it is almost time for the next dose. Never take two doses together.

Store losartan tablets in the original packaging, away from moisture and direct sunlight, at room temperature below 30 degrees Celsius. Keep out of reach of children.

Side effects of losartan

Common side effects

The most frequently reported side effects of losartan include dizziness and orthostatic hypotension (feeling light-headed when standing), particularly during the first few days of treatment or after a dose increase.

These effects are usually transient and can be minimised by taking the first dose at bedtime and rising slowly from a seated or lying position.

Other common side effects include fatigue, headache, and upper respiratory tract symptoms such as nasal congestion and sore throat.

Hyperkalaemia

ARBs reduce aldosterone secretion, which can lead to raised serum potassium levels (hyperkalaemia).

This risk is increased in patients with chronic kidney disease, diabetes, those taking potassium supplements, potassium-sparing diuretics (such as spironolactone or amiloride), or other drugs that raise potassium.

Symptoms of severe hyperkalaemia include muscle weakness, irregular heartbeat, and tingling or numbness.

Your prescriber will monitor potassium levels through regular blood tests, particularly in the first weeks after starting treatment and after any dose change.

Uncommon and rare side effects

Uncommon side effects include gastrointestinal symptoms (abdominal pain, nausea, diarrhoea, and constipation), rash, muscle cramps, and back pain. Elevated liver enzymes and hepatitis have been reported rarely.

Changes in kidney function (elevated creatinine) may occur, especially in patients with pre-existing renal impairment, heart failure, or renal artery stenosis.

Angioedema, characterised by rapid swelling of the face, lips, tongue, or throat, is rare but potentially life-threatening.

Patients who have previously experienced angioedema with any medication, including ACE inhibitors, should be monitored closely when starting losartan. Seek emergency medical attention (call 999) if angioedema develops.

Reporting side effects

If you experience any side effect, whether listed here or not, report it to your prescriber.

You can also report suspected adverse reactions directly via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

By reporting side effects, you help provide more information on the safety of this medicine.

Warnings and precautions

Pregnancy and breastfeeding

Losartan is absolutely contraindicated during pregnancy. ARBs act on the renin-angiotensin system, which is essential for normal fetal kidney development.

Use during the second and third trimesters can cause fetal renal failure, oligohydramnios (low amniotic fluid), skull ossification defects, and death.

Use during the first trimester is also not recommended, and women should be switched to a pregnancy-safe alternative (such as labetalol, nifedipine, or methyldopa) before conception if possible.

There are insufficient data on the use of losartan during breastfeeding, and it is generally not recommended for nursing mothers.

Discuss alternative treatments with your prescriber if you are breastfeeding or planning to breastfeed.

Renal artery stenosis

Losartan should be used with extreme caution in patients with haemodynamically significant renal artery stenosis.

By blocking angiotensin II, the drug can reduce efferent arteriolar tone and precipitate a fall in glomerular filtration, potentially causing acute kidney injury.

In patients with bilateral renal artery stenosis or stenosis in a solitary functioning kidney, losartan is generally contraindicated. Renal function must be closely monitored during treatment.

Hepatic impairment

Because losartan is extensively metabolised in the liver, patients with significant hepatic impairment have substantially higher plasma concentrations of the drug.

A lower starting dose of 25 mg once daily is recommended in patients with mild to moderate liver disease.

Losartan is contraindicated in patients with severe hepatic impairment or cholestasis.

Dual blockade of the renin-angiotensin system

Combining losartan with an ACE inhibitor (such as ramipril, enalapril, or lisinopril) or a direct renin inhibitor (aliskiren) is not recommended and is specifically contraindicated in patients with diabetes or renal impairment (eGFR below 60 ml/min/1.73 m2).

Dual blockade increases the risk of hypotension, syncope, hyperkalaemia, and acute renal failure compared with monotherapy.

The ONTARGET trial demonstrated that dual RAAS blockade with telmisartan and ramipril increased the risk of renal events without additional cardiovascular benefit.

Surgery and anaesthesia

If you are scheduled for surgery requiring general or regional anaesthesia, inform your surgeon and anaesthetist that you are taking losartan.

ARBs may enhance the hypotensive effects of anaesthetic agents, and your anaesthetist may recommend withholding the dose on the morning of surgery.

Dehydration and intercurrent illness

During episodes of dehydration caused by vomiting, diarrhoea, excessive sweating, or reduced fluid intake, the blood-pressure-lowering effect of losartan may be exaggerated, increasing the risk of symptomatic hypotension and acute kidney injury.

Patients with heart failure or chronic kidney disease are particularly vulnerable. Maintain adequate fluid intake and seek medical advice if you are unable to keep fluids down.

Your prescriber may advise temporarily stopping losartan during severe illness, consistent with "sick day rules" for renal protection.

How to get a losartan prescription in the UK

Losartan is classified as a prescription-only medicine (POM) in the UK and cannot be bought over the counter.

The usual route is through your GP, who will assess your blood pressure, cardiovascular risk factors, and kidney function before prescribing.

Blood pressure is typically measured on at least two separate occasions, and ambulatory or home blood pressure monitoring may be used to confirm the diagnosis of hypertension before starting treatment.

If you are already taking losartan and require a repeat prescription, this can be arranged through your GP surgery, an authorised online prescriber registered with the GPhC (General Pharmaceutical Council), or through the NHS Electronic Prescription Service (EPS).

All UK prescriptions for losartan are dispensed by registered pharmacies.

The standard NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Patients in England who take multiple medications may benefit from a prepayment certificate (PPC), which caps the annual cost of NHS prescriptions.

Living with hypertension: practical management

Taking losartan as prescribed is an essential component of managing hypertension, but lifestyle modifications can further reduce blood pressure and cardiovascular risk. The following measures are recommended by NICE and the British Heart Foundation.

• Reduce dietary sodium to less than 6 g of salt per day. Avoid adding salt at the table and check food labels for hidden sodium in processed foods, bread, cereals, and ready meals.
• Maintain a healthy body weight. Even modest weight loss of 5 to 10% of body weight can produce clinically meaningful blood pressure reductions.
• Take regular physical activity. Aim for at least 150 minutes of moderate-intensity aerobic exercise per week, such as brisk walking, cycling, or swimming.
• Limit alcohol intake to no more than 14 units per week, spread evenly over 3 or more days, with alcohol-free days.
• Eat a balanced diet rich in fruit, vegetables, whole grains, and low-fat dairy products. The DASH (Dietary Approaches to Stop Hypertension) diet has been shown to lower blood pressure significantly.
• Stop smoking. Although smoking does not directly cause sustained hypertension, it greatly amplifies the cardiovascular risk associated with high blood pressure.
• Monitor your blood pressure at home if advised by your GP. Home monitors validated by the British and Irish Hypertension Society are recommended.

When to seek urgent medical advice

Contact your GP or call NHS 111 if you experience persistent dizziness, fainting episodes, a marked reduction in urine output, or new symptoms such as swelling of the ankles or unexplained weight gain, which may indicate fluid retention or declining kidney function.

Seek emergency care (call 999 or attend A&E) if you develop swelling of the face, lips, tongue, or throat (angioedema), chest pain, sudden severe headache with visual disturbance or confusion (possible hypertensive emergency), or an irregular heartbeat with muscle weakness (possible severe hyperkalaemia).

If you are pregnant or suspect you may be pregnant while taking losartan, stop the medication and contact your prescriber urgently.

Report any suspected adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

Sources

• Losartan Potassium 50 mg Film-coated Tablets, Summary of Product Characteristics (EMC)
• Losartan potassium, British National Formulary (BNF)
• NICE NG136: Hypertension in adults: diagnosis and management
• Losartan, NHS
• High blood pressure, British Heart Foundation
• MHRA Yellow Card Scheme