Angiotensin II Receptor Blocker (ARB) — Hypertension / Raynaud's / Marfan Syndrome Pregnancy: Not recommended during the first trimester; contraindicated during the 2nd and 3rd trimesters. Patients planning pregnancy should be changed to alternative antihypertensives unless continued therapy is essential. Stop immediately when pregnancy is diagnosed. Exposure from the second trimester induces fetotoxicity and neonatal toxicity. Not recommended during breastfeeding.

Losartan

Brand names: Cozaar

Losartan is an oral angiotensin-II receptor blocker used for hypertension, diabetic nephropathy, and heart failure, including 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 and stroke-risk reduction); 150 mg once daily (heart failure)

Vascular / cardiovascular risk-reduction context. Reduction in the risk of stroke in hypertensive patients with left ventricular hypertrophy documented by ECG: the usual starting dose is 50 mg once daily; a low dose of hydrochlorothiazide should be added and/or the dose of losartan increased to 100 mg once daily based on blood pressure response. Hypertension: usual starting and maintenance dose 50 mg once daily; maximal antihypertensive effect attained 3-6 weeks after initiation; may increase to 100 mg once daily (in the morning). Heart failure: 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. Hypertensive type II diabetic patients with proteinuria >= 0.5 g/day: start 50 mg once daily, may increase to 100 mg once daily based on blood pressure response from one month onwards. Intravascular volume depletion (e.g. high-dose diuretics): consider a starting dose of 25 mg once daily and correct volume/sodium depletion before administration, as symptomatic hypotension may occur after the first dose and after dose increases. Elderly: consider initiating with 25 mg in patients over 75 years of age, though dosage adjustment is not usually necessary. Hepatic impairment: consider a lower dose with a history of hepatic impairment; contraindicated in severe hepatic impairment. Paediatric (UK SPC): not recommended under 6 years; 6 to 18 years - 25 mg once daily in patients 20 to 50 kg (exceptionally up to 50 mg once daily) and 50 mg once daily in patients over 50 kg (exceptionally up to 100 mg once daily); doses above 1.4 mg/kg (or in excess of 100 mg) daily have not been studied. Verify paediatric dosing against a children's formulary. 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. Use with caution in bilateral renal artery stenosis or stenosis of the artery to a solitary kidney.

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 (AT1) receptor, causing vasodilatation, reduced aldosterone secretion and lower blood pressure without affecting bradykinin metabolism.

Prescribing in practice

Contraindicated in pregnancy because it can cause foetal harm, and it should be stopped if pregnancy is planned or confirmed.
It can cause hyperkalaemia and acute kidney injury, particularly with renal artery stenosis, volume depletion, or concurrent potassium-raising drugs or NSAIDs.
Do not combine with an ACE inhibitor or aliskiren because dual renin-angiotensin blockade increases the risk of hyperkalaemia, hypotension and renal impairment.

Monitoring

Monitor blood pressure, renal function and serum potassium, especially after initiation or dose changes.

Counselling the patient

Tell your doctor at once if you become or plan to become pregnant.
Dizziness can occur initially, particularly on standing; rise slowly.

Evidence & guidelines

Supported by major outcome trials in hypertension and diabetic nephropathy and recommended in NICE hypertension guidance.

Reference: LIFE Trial; COMPARE Trial (Marfan); NICE NG136 (Hypertension); BSR/BHPR Raynaud's Guidelines; 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