Angiotensin Receptor Blocker (ARB) Pregnancy: Not recommended during the first trimester; contraindicated during the 2nd and 3rd trimesters. Stop immediately when pregnancy is diagnosed and start alternative therapy. Exposure from the second trimester induces fetotoxicity (decreased renal function, oligohydramnios, skull ossification retardation) and neonatal toxicity (renal failure, hypotension, hyperkalaemia). Not recommended during breastfeeding.

Losartan

Brand names: Cozaar

Losartan is an angiotensin II receptor blocker used for hypertension, diabetic nephropathy, and heart failure or cardiovascular protection in patients intolerant of ACE inhibitors.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 50 mg

Route: Oral

Frequency: Once daily

Max: 100 mg once daily (hypertension); 150 mg once daily (heart failure)

Hypertension: usual starting and maintenance dose 50 mg once daily for most patients; maximal antihypertensive effect is attained 3-6 weeks after initiation; some patients may benefit from an increase to 100 mg once daily (in the morning). Hypertensive type II diabetic patients with proteinuria >= 0.5 g/day: start 50 mg once daily, may be increased to 100 mg once daily based on blood pressure response from one month onwards. Heart failure: usual initial dose 12.5 mg once daily, titrated at weekly intervals (12.5 mg, 25 mg, 50 mg, 100 mg, up to a maximum of 150 mg once daily) as tolerated. Reduction in risk of stroke in hypertensive patients with left ventricular hypertrophy documented by ECG: start 50 mg once daily, add a low dose of hydrochlorothiazide and/or increase losartan to 100 mg once daily based on blood pressure response. Intravascular volume depletion (e.g. high-dose diuretics): consider a starting dose of 25 mg once daily. Hepatic impairment: consider a lower dose in patients with a history of hepatic impairment; contraindicated in severe hepatic impairment. Elderly: consider initiating with 25 mg in patients over 75 years of age, but dosage adjustment is not usually necessary. Paediatric (UK SPC): 6 months to <6 years - safety and efficacy not established, no posology recommendation can be made; 6 to 18 years - for patients who can swallow tablets the recommended dose is 25 mg once daily in patients 20 to 50 kg (in exceptional cases up to a maximum of 50 mg once daily), and 50 mg once daily in patients over 50 kg (in exceptional cases up to a maximum of 100 mg once daily), adjusted according to blood pressure response; doses above 1.4 mg/kg (or in excess of 100 mg) daily have not been studied. Not recommended in children under 6 years, in children with GFR <30 ml/min/1.73 m2, or in children with hepatic impairment. US labelling instead states a paediatric starting dose of 0.7 mg/kg once daily (up to 50 mg) - the UK weight-band figures above take precedence; verify paediatric dosing against a children's formulary. Tablets available as 25 mg, 50 mg and 100 mg; swallow whole with a glass of water, with or without food. Interactions listed are drawn from the US labelling in the bundle, as eMC section 4.5 was not captured.

Dose adjustments

Renal

No initial dosage adjustment is necessary in patients with renal impairment or in haemodialysis patients. Monitor plasma potassium and creatinine clearance closely, especially in patients with heart failure and creatinine clearance 30-50 ml/min. Not recommended in children with GFR <30 ml/min/1.73 m2.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
2nd and 3rd trimester of pregnancy
Severe hepatic impairment
Concomitant use with aliskiren-containing products in patients with diabetes mellitus or renal impairment (GFR <60 ml/min/1.73 m2)

Side effects

Dizziness (common; the most common adverse event across trials)
Vertigo (common); somnolence, headache, sleep disorders (uncommon)
(Orthostatic) hypotension including dose-related orthostatic effects (uncommon in hypertension; common in heart failure and in hypertension with type 2 diabetes and renal disease)
Anaemia (common in hypertension with type 2 diabetes and renal disease); hyperkalaemia (higher incidence than placebo in type 2 diabetic nephropathy)
Palpitations, angina pectoris, dyspnoea, cough, abdominal pain, diarrhoea, nausea, vomiting, urticaria, pruritus, rash (uncommon)
Rare: hypersensitivity reactions, anaphylactic reactions, angioedema (including intestinal angioedema), vasculitis, syncope, atrial fibrillation, cerebrovascular accident, hepatitis

Interactions

Agents increasing serum potassium (potassium-sparing diuretics, potassium supplements, potassium-containing salt substitutes, trimethoprim-containing products): risk of hyperkalaemia - not recommended concomitantly; monitor serum potassium
Lithium: increases in serum lithium concentrations and lithium toxicity reported - monitor serum lithium levels
NSAIDs including selective COX-2 inhibitors: increased risk of renal impairment (including acute renal failure) in elderly, volume-depleted or renally impaired patients, and reduced diuretic, natriuretic and antihypertensive effects - monitor renal function
Dual inhibition of the renin-angiotensin system (e.g. with aliskiren or ACE inhibitors): increased risk of renal impairment, hypotension, syncope and hyperkalaemia
Other antihypertensive agents (diuretics, calcium channel blockers, alpha- or beta-blockers, centrally acting agents): may be co-administered, with additive blood-pressure lowering

Clinical monograph

How it works

It selectively blocks the angiotensin II type 1 receptor, causing vasodilatation, reduced aldosterone secretion and lower blood pressure without the bradykinin accumulation seen with ACE inhibitors.

Prescribing in practice

It is contraindicated in pregnancy because angiotensin system blockers cause foetal renal and other malformations, so stop and seek alternatives if pregnancy is planned or confirmed.
Risk of hyperkalaemia and renal impairment increases with potassium supplements, potassium-sparing diuretics, other renin-angiotensin drugs and NSAIDs.
Avoid combining with an ACE inhibitor or aliskiren, and use caution in renovascular disease and volume depletion.

Monitoring

Check renal function and serum potassium before starting and after initiation or dose changes, and monitor blood pressure.

Counselling the patient

Tell your clinician straight away if you become pregnant or are planning pregnancy.
Avoid potassium-containing salt substitutes and over-the-counter anti-inflammatory painkillers unless advised.
A small rise in blood test markers of kidney function can be expected when starting.

Evidence & guidelines

The LIFE and RENAAL trials support losartan for cardiovascular protection and diabetic nephropathy, consistent with NICE hypertension guidance.

Reference: NICE NG136; LIFE Trial (Lancet 2002); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways