Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
ARB + thiazide Pregnancy: Angiotensin II receptor antagonists are not recommended during the first trimester and are contraindicated during the second and third trimesters (foetotoxicity - decreased renal function, oligohydramnios, skull ossification retardation; neonatal renal failure, hypotension, hyperkalaemia). Stop treatment immediately when pregnancy is diagnosed. Hydrochlorothiazide crosses the placenta and should not be used for gestational oedema, gestational hypertension or pre-eclampsia, nor for essential hypertension in pregnancy except in rare situations where no other treatment could be used. Use during breastfeeding is not recommended (eMC 4.6).

Losartan with hydrochlorothiazide

Brand names: Cozaar-Comp

Used in: Chronic Kidney Disease Hypertension

This is a fixed-dose combination of losartan, an angiotensin-II receptor blocker (ARB), with the thiazide diuretic hydrochlorothiazide, used to treat essential hypertension when blood pressure is not adequately controlled by either component alone.

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: Hypertension: one tablet of losartan 50 mg / hydrochlorothiazide 12.5 mg (usual maintenance dose; source SPC product Cozaar Comp 50 mg/12.5 mg)
Route: Oral - tablets should be swallowed whole with a glass of water; may be taken with or without food
Frequency: Once daily
Max: One tablet of losartan 100 mg / hydrochlorothiazide 25 mg once daily
eMC SPC 4.2. Not for use as initial therapy - only for patients whose blood pressure is not adequately controlled by losartan potassium or hydrochlorothiazide alone. Dose titration with the individual components (losartan and hydrochlorothiazide) is recommended; when clinically appropriate a direct change from monotherapy to the fixed combination may be considered. For patients who do not respond adequately to 50 mg/12.5 mg, the dosage may be increased to one tablet of 100 mg/25 mg once daily, which is the maximum dose. A 100 mg/12.5 mg strength is available for patients already titrated to losartan 100 mg who require additional blood pressure control. In general the antihypertensive effect is attained within three to four weeks after initiation of therapy. Volume and/or sodium depletion should be corrected prior to administration. ELDERLY: dosage adjustment is not usually necessary. HEPATIC IMPAIRMENT: contraindicated in severe hepatic impairment. PAEDIATRIC: there is no experience in children and adolescents (under 18 years), therefore losartan/hydrochlorothiazide should not be administered to children and adolescents - no paediatric dose is stated; refer to a children's formulary. IMPORTANT: the openFDA record held in this source bundle is the US label for LOSARTAN POTASSIUM SINGLE-AGENT (including a paediatric per-kg regimen of 0.7 mg/kg once daily) - that is a component-only label and must NOT be applied to this fixed combination. The posology above is taken entirely from the UK SPC for the combination. NOTE: eMC 4.5 was not captured in this bundle.

Dose adjustments

Renal

No initial dosage adjustment is necessary in patients with moderate renal impairment (creatinine clearance 30-50 ml/min). Not recommended for haemodialysis patients. Must not be used in patients with severe renal impairment (creatinine clearance < 30 ml/min) - contraindicated (eMC 4.2, 4.3).

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 losartan, to sulphonamide-derived substances (as hydrochlorothiazide) or to any of the excipients
  • Therapy-resistant hypokalaemia or hypercalcaemia; refractory hyponatraemia
  • Severe hepatic impairment; cholestasis and biliary obstructive disorders
  • Symptomatic hyperuricaemia/gout
  • Second and third trimesters of pregnancy
  • Severe renal impairment (creatinine clearance < 30 ml/min); anuria
  • Concomitant use with aliskiren-containing products in patients with diabetes mellitus or renal impairment (GFR < 60 ml/min/1.73 m2)

Side effects

  • Dizziness - the only adverse reaction reported as substance-related at an incidence greater than placebo in 1% or more of patients treated with the combination in controlled hypertension trials
  • Hepatitis - rare (post-marketing, with the combination)
  • Hyperkalaemia and elevation of ALT - rare (post-marketing, with the combination)
  • Losartan component: abdominal pain, nausea, diarrhoea, dyspepsia - common
  • Losartan component: asthenia, fatigue, chest pain - common; hypotension and orthostatic hypotension - uncommon
  • Losartan component: angioedema including swelling of the larynx and glottis causing airway obstruction, and anaphylactic reactions - rare

Interactions

  • Aliskiren-containing products - contraindicated in patients with diabetes mellitus or renal impairment (GFR < 60 ml/min/1.73 m2); dual inhibition of the renin-angiotensin system increases the risk of renal impairment, hypotension, syncope and hyperkalaemia (eMC 4.3; US label 7.4)
  • Potassium-sparing diuretics, potassium supplements, potassium-containing salt substitutes or other drugs that may increase serum potassium (e.g. trimethoprim-containing products) - concomitant use is not recommended (eMC 4.4)
  • Vigorous diuretic therapy, dietary salt restriction, diarrhoea or vomiting - increased risk of symptomatic hypotension, especially after the first dose; correct volume and/or sodium depletion before administration (eMC 4.4)
  • Lithium - increases in serum lithium concentrations and lithium toxicity have been reported with angiotensin II receptor antagonists; monitor serum lithium levels (US label 7.2)
  • NSAIDs including selective COX-2 inhibitors - in elderly, volume-depleted or renally impaired patients may cause deterioration of renal function including acute renal failure, and may reduce the antihypertensive effect (US label 7.3)
  • NOTE: eMC 4.5 was not captured in this source bundle - the full UK interaction list must be checked against the SPC before publication.

Clinical monograph

How it works

Losartan blocks the angiotensin-II type 1 receptor to cause vasodilatation and reduce aldosterone-mediated sodium retention, while hydrochlorothiazide enhances renal sodium and water excretion, giving additive blood-pressure lowering.

Prescribing in practice

  • The combination is contraindicated in pregnancy because the ARB component can cause serious foetal harm and must be discontinued as soon as pregnancy is detected.
  • Avoid dual blockade of the renin-angiotensin system, and take care with potassium supplements or potassium-sparing diuretics because the combined potassium effect is unpredictable.
  • Hydrochlorothiazide can provoke hyponatraemia, hypokalaemia, gout and photosensitivity, and is associated with a small increased risk of non-melanoma skin cancer.

Monitoring

Monitor blood pressure, renal function and serum electrolytes (sodium and potassium) before and during treatment, especially after dose adjustment or intercurrent illness.

Counselling the patient

  • Do not take this medicine if you are or might become pregnant, and tell your doctor straight away if you conceive.
  • Protect your skin from strong sunlight while on the diuretic component.
  • Report dizziness, muscle cramps or unusual thirst, which can indicate a salt or water imbalance.

Evidence & guidelines

Combining an ARB with a thiazide diuretic for blood pressure uncontrolled on monotherapy aligns with NICE hypertension guidance and established trial evidence for the class.

Reference: NICE NG136; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Drugs
Pathways