Angiotensin II receptor antagonist (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 potassium

Brand names: Cozaar

Used in: Chronic Kidney Disease Hypertension

Losartan is an angiotensin-II receptor blocker (ARB) used for hypertension, diabetic nephropathy, and heart failure where an ACE inhibitor is not tolerated.

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)

Losartan potassium is the salt form; tablets are available as 25 mg, 50 mg and 100 mg and should be swallowed whole with a glass of water, with or without food. Hypertension: usual starting and maintenance dose 50 mg once daily for most patients; maximal antihypertensive effect 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 increase to 100 mg once daily based on blood pressure response from one month onwards. 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. Reduction in the risk of stroke in hypertensive patients with ECG-documented left ventricular hypertrophy: start 50 mg once daily, add a low dose of hydrochlorothiazide and/or increase 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 with a history of hepatic impairment; contraindicated in severe hepatic impairment. Elderly: consider initiating with 25 mg in patients over 75 years, though dosage adjustment is not usually necessary. Paediatric (UK SPC): 6 months to <6 years - safety and efficacy not established, no posology recommendation; 6 to 18 years - 25 mg once daily in patients 20 to 50 kg (exceptionally up to 50 mg once daily), 50 mg once daily in patients over 50 kg (exceptionally up to 100 mg once daily), adjusted to blood pressure response; doses above 1.4 mg/kg (or in excess of 100 mg) daily have not been studied. Not recommended under 6 years, with GFR <30 ml/min/1.73 m2, or with hepatic impairment. Verify paediatric dosing against a children's formulary. Note the potassium content of the salt when co-prescribing agents that raise serum potassium. 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.

US labelling (FDA)

Reference — US labelling, may differ from UK

Hypertension • Usual adult dose: 50 mg once daily. (2.1) • Usual pediatric starting dose: 0.7 mg per kg once daily (up to 50 mg). (2.1) Hypertensive Patients with Left Ventricular Hypertrophy • Usual starting dose: 50 mg once daily. (2.2) • Add hydrochlorothiazide 12.5 mg and/or increase losartan potassium to 100 mg followed by an increase to hydrochlorothiazide 25 mg if further blood pressure response is needed. (2.2 , 14.2) Nephropathy in Type 2 Diabetic Patients • Usual dose: 50 mg once daily. (2.3) • Increase dose to 100 mg once daily if further blood pressure response is needed. (2.3) 2.1 Hypertension Adult Hypertension The usual starting dose of losartan potassium tablets is 50 mg …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-10-22. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

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, producing vasodilatation and reduced aldosterone effect without the bradykinin-related cough of ACE inhibitors.

Prescribing in practice

Start low and titrate; check renal function and potassium before and after starting or up-titrating.
Avoid in pregnancy and bilateral renal artery stenosis; use caution with potassium-raising drugs and NSAIDs.
Do not routinely combine an ARB with an ACE inhibitor.

Monitoring

Monitor U&E (renal function and potassium) and blood pressure.

Counselling the patient

Report dizziness, especially after the first doses.
Avoid potassium-based salt substitutes; tell your prescriber if you become pregnant or unwell with vomiting or diarrhoea.

Evidence & guidelines

An ARB option for hypertension, diabetic nephropathy and heart failure where ACE inhibitors are unsuitable (NICE NG136/NG106).

Reference: NICE NG136; ESC; 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.

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