Losartan

Losartan is an angiotensin II receptor blocker (ARB) widely prescribed for the management of high blood pressure (hypertension), heart failure, and the protection of kidneys in people with type 2 diabetes and elevated protein in the urine (diabetic nephropathy). It also reduces the risk of stroke in patients with hypertension and left ventricular hypertrophy. Sold under the brand name Cozaar, losartan belongs to a class of medicines that work by blocking the action of a hormone called angiotensin II, which normally causes blood vessels to narrow and the heart to work harder.

How Losartan Works

Angiotensin II binds to receptors in blood vessel walls, triggering constriction and increasing blood pressure. Losartan selectively blocks the AT1 receptor, preventing this effect and allowing blood vessels to relax and widen. Unlike ACE inhibitors, which work one step earlier in the same pathway, losartan does not increase bradykinin levels, which means it is far less likely to cause the persistent dry cough that leads many patients to discontinue ACE inhibitors. This makes losartan a particularly important alternative for patients who cannot tolerate ACE inhibitors.

Clinical Uses and Benefits

Beyond blood pressure control, losartan has demonstrated significant cardiovascular and renal benefits in large clinical trials. The LIFE trial showed that losartan reduced the risk of stroke more effectively than the beta-blocker atenolol in high-risk hypertensive patients. In the RENAAL study, losartan slowed the progression of diabetic nephropathy and reduced the risk of end-stage renal disease. For heart failure patients who cannot tolerate ACE inhibitors, losartan offers effective symptom management and improved outcomes.

Important Considerations

Losartan is available as tablets in strengths of 25mg, 50mg, and 100mg, taken once daily with or without food. It may be combined with a low-dose diuretic, such as hydrochlorothiazide, for additional blood pressure reduction. The medicine is generally well tolerated, but it is absolutely contraindicated in pregnancy due to serious risks of fetal harm, particularly during the second and third trimesters. Regular monitoring of kidney function, electrolytes, and blood pressure is recommended, especially when starting treatment or adjusting the dose.

Losartan is taken orally, once daily, at approximately the same time each day. It can be taken with or without food, as food does not significantly affect its absorption.

Starting and Adjusting Treatment

The usual starting dose for hypertension is 50mg once daily, though patients with volume depletion (for example, those on diuretics) or severe liver impairment may begin on 25mg. The dose may be increased to 100mg once daily if blood pressure remains inadequately controlled after several weeks. For diabetic nephropathy, treatment typically starts at 50mg once daily, increasing to 100mg if needed. In heart failure, dosing is usually initiated at low levels and titrated cautiously under specialist supervision.

Monitoring and Ongoing Use

Blood pressure should be measured regularly to assess response to treatment. Kidney function tests and serum electrolytes, particularly potassium, should be checked before starting and periodically during treatment, as losartan can raise potassium levels. Patients should be advised not to stop losartan abruptly without speaking to their doctor, as blood pressure may rise quickly. If a dose is missed, it should be taken as soon as remembered unless the next dose is due, in which case the missed dose should be skipped. Losartan works best as part of a broader strategy including a balanced diet, regular exercise, and reducing salt and alcohol intake.

Adults (hypertension): 50mg once daily; may increase to 100mg once daily. Patients with volume depletion or liver impairment: start at 25mg once daily.

Adults (diabetic nephropathy): 50mg once daily; increase to 100mg once daily based on blood pressure response.

Adults (heart failure): Specialist-directed dosing, typically starting at 12.5mg or 25mg and titrating upward.

Elderly patients: No routine dose adjustment required, though starting at 25mg is advisable in some cases.

Hepatic impairment: Lower starting dose of 25mg; use with caution.

Renal impairment: No initial dose adjustment required, but monitor kidney function and potassium closely.

Children (6 years and over, >20kg): 0.7mg/kg once daily, maximum 50mg/day; available as oral suspension. Not for use in children with GFR below 30mL/min/1.73m2.

Swallow tablets whole with water. Do not crush unless advised. Take at the same time each day for consistent blood pressure control.

Common Side Effects

• Dizziness or lightheadedness, especially on standing up quickly
• Fatigue and tiredness
• Hyperkalaemia (raised blood potassium levels)
• Hypotension (low blood pressure), particularly at the start of treatment
• Back pain and musculoskeletal aches
• Upper respiratory tract infections
• Raised creatinine or blood urea nitrogen on blood tests
• Nasal congestion or sinusitis

Serious Side Effects

• Angioedema (rare): sudden swelling of the face, lips, tongue, or throat, seek emergency help immediately
• Severe hyperkalaemia: dangerously high potassium, causing muscle weakness or heart rhythm abnormalities
• Acute kidney injury: worsening renal function, particularly in patients with bilateral renal artery stenosis
• Foetal toxicity: do not use in pregnancy, can cause severe fetal harm or death
• Liver function abnormalities (rare, monitor if symptoms develop)

Losartan must not be used during pregnancy. Exposure during the second and third trimesters is associated with serious fetal harm including renal dysplasia, oligohydramnios, limb contractures, and neonatal death. Women of childbearing potential must use effective contraception while taking losartan and should stop the medicine immediately if they become pregnant.

Renal and Electrolyte Monitoring

Losartan can reduce blood flow to the kidneys and impair renal function, particularly in patients with pre-existing renal artery stenosis, heart failure, or severe dehydration. Kidney function should be monitored at baseline and during treatment. Losartan can raise serum potassium, which is particularly significant in patients taking potassium supplements, potassium-sparing diuretics, or other medicines that affect potassium. Concurrent use of NSAIDs can further increase the risk of kidney injury and should be avoided where possible.

Volume Depletion and First-Dose Hypotension

Patients who are dehydrated or have low sodium levels (for example, those on high-dose diuretics) are at greater risk of a marked fall in blood pressure with the first dose. Volume status should be corrected before initiating treatment, or therapy should start at the lowest available dose under close supervision.

Driving and operating machinery may be affected by dizziness, particularly when starting treatment or after dose increases. Alcohol can enhance the blood pressure-lowering effect and should be used cautiously.

• Pregnancy (second and third trimesters -- absolutely contraindicated; avoid in first trimester)
• Hypersensitivity to losartan or any component of the formulation
• Concurrent use with aliskiren in patients with diabetes or moderate-to-severe renal impairment (eGFR <60mL/min/1.73m2)
• Concurrent use with sacubitril/valsartan (Entresto) -- do not start within 36 hours of each other
• Severe hepatic impairment (use is not recommended)
• Bilateral renal artery stenosis or stenosis of a solitary functioning kidney (relative contraindication -- use with extreme caution)
• Hereditary or idiopathic angioedema (risk of recurrence)
• Breastfeeding (insufficient data; alternative treatment recommended)