ARB + thiazide Pregnancy: Not recommended during the first trimester of pregnancy and CONTRAINDICATED during the 2nd and 3rd trimesters. Exposure to angiotensin II receptor antagonists in the 2nd and 3rd trimesters is known to induce human fetotoxicity (decreased renal function, oligohydramnios, skull ossification retardation) and neonatal toxicity (renal failure, hypotension, hyperkalaemia). Patients planning pregnancy should be changed to alternative antihypertensives with an established safety profile; when pregnancy is diagnosed, treatment should be stopped immediately. Hydrochlorothiazide crosses the placenta and its use in the 2nd and 3rd trimesters may compromise foeto-placental perfusion and cause icterus, electrolyte disturbance and thrombocytopenia; it should not be used for gestational oedema, gestational hypertension or pre-eclampsia. (US labelling: Pregnancy Category D.)

Olmesartan with hydrochlorothiazide

Brand names: Olmetec Plus

This is a fixed-dose oral combination of olmesartan, an angiotensin-II receptor blocker, with hydrochlorothiazide, a thiazide diuretic, used for essential hypertension not controlled by olmesartan 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: Olmesartan medoxomil 20 mg / hydrochlorothiazide 12.5 mg, one tablet once daily, in patients whose blood pressure is not adequately controlled by the optimal monotherapy of olmesartan medoxomil 20 mg alone. The combination is NOT for use as initial therapy

Route: Oral — the tablet should be swallowed with a sufficient amount of fluid (e.g. one glass of water), should not be chewed, and should be taken at the same time each day; with or without food

Frequency: Once daily

Max: 20 mg olmesartan medoxomil / 25 mg hydrochlorothiazide once daily — this may be given to patients whose blood pressure is not adequately controlled by 20 mg/12.5 mg, and is the highest step stated in the retrieved SPC (which covers the 20 mg/12.5 mg strength)

Dose titration of the individual components is recommended. When clinically appropriate, a direct change from monotherapy with olmesartan medoxomil 20 mg to the fixed combination may be considered, taking into account that the antihypertensive effect of olmesartan medoxomil is maximal by about 8 weeks after initiating therapy. ELDERLY (65 years or over): the same dosage of the combination is recommended as for adults. HEPATIC IMPAIRMENT: use with caution in mild to moderate impairment; in patients with moderate hepatic impairment an initial dose of 10 mg olmesartan medoxomil once daily is recommended and the maximum dose should not exceed 20 mg once daily (i.e. titrate the components separately). Close monitoring of blood pressure and renal function is advised in hepatically impaired patients receiving diuretics and/or other antihypertensives. There is no experience in severe hepatic impairment, in which the combination should not be used, nor in cholestasis and biliary obstruction. PAEDIATRIC: safety and efficacy in children and adolescents below 18 years has not been established and no data are available. The SPC's §4.8 notes that higher-strength combinations (40 mg/12.5 mg and 40 mg/25 mg) have been studied for safety, but the posology section of this SPC does not give a titration step above 20 mg/25 mg. US labelling cross-check: recommended starting dose 40/12.5 mg once daily in patients not adequately controlled on olmesartan monotherapy, or 20/12.5 mg once daily in patients not adequately controlled on hydrochlorothiazide monotherapy or with dose-limiting adverse reactions to it; adjust after 2 to 4 weeks as needed to a maximum of 40 mg/25 mg.

Dose adjustments

Renal

Contraindicated in severe renal impairment (creatinine clearance < 30 mL/min). No dosage adjustment is necessary in mild to moderate renal impairment (creatinine clearance 30 to < 60 mL/min), but the combination should be administered with caution and periodic monitoring of renal function, serum potassium, creatinine and uric acid levels is advised. Thiazide-associated azotaemia may occur in patients with impaired renal function; if progressive renal impairment becomes evident, careful reappraisal of therapy is necessary with consideration of discontinuing the diuretic. There is no experience in patients with recent kidney transplantation.

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 substances, to any excipient, or to other sulfonamide-derived substances (hydrochlorothiazide is a sulfonamide derivative)
Severe renal impairment (creatinine clearance < 30 mL/min)
Refractory hypokalaemia, hypercalcaemia, hyponatraemia and symptomatic hyperuricaemia
Severe hepatic impairment, cholestasis and biliary obstructive disorders
2nd and 3rd trimester of pregnancy
Concomitant use with aliskiren-containing products in patients with diabetes mellitus or renal impairment (GFR < 60 mL/min/1.73 m2)

Side effects

Headache (2.9%), dizziness (1.9%) and fatigue (1.0%) — the most commonly reported reactions with the combination
Metabolic and electrolyte disturbances attributable to hydrochlorothiazide — hypokalaemia, hyponatraemia, hypomagnesaemia, hypochloraemia, hypercalcaemia, hyperuricaemia (very common), hyperglycaemia, hypercholesterolaemia and hypertriglyceridaemia; hyperkalaemia (rare) with olmesartan
Blood disorders — thrombocytopenia (uncommon with the combination); aplastic anaemia, bone marrow depression, haemolytic anaemia, leukopenia, neutropenia/agranulocytosis (rare)
Anaphylactic reactions (uncommon); sialadenitis (rare); non-melanoma skin cancer (basal cell and squamous cell carcinoma) — frequency not known
US labelling lists the most common adverse reactions (incidence at least 2%) as nausea, hyperuricaemia, dizziness and upper respiratory infection, and notes sprue-like enteropathy, acute myopia and secondary angle-closure glaucoma

Interactions

Aliskiren-containing products — contraindicated in patients with diabetes mellitus or renal impairment (GFR < 60 mL/min/1.73 m2)
Dual blockade of the renin-angiotensin-aldosterone system with ACE inhibitors, angiotensin II receptor blockers or aliskiren — increases the risk of hypotension, hyperkalaemia and decreased renal function including acute renal failure; not recommended, and ACE inhibitors and ARBs should not be used concomitantly in patients with diabetic nephropathy
Lithium — increases in serum lithium concentrations and lithium toxicity reported with ARBs or hydrochlorothiazide; monitor serum lithium levels (US label §7.2)
NSAIDs including selective COX-2 inhibitors — reduced diuretic, natriuretic and antihypertensive effects and increased risk of renal toxicity, particularly in elderly, volume-depleted or renally impaired patients (US label §7.3)
Other agents that raise serum potassium — risk of hyperkalaemia; monitor serum potassium (US label §7.1)
Colesevelam hydrochloride — consider administering olmesartan at least 4 hours before the colesevelam dose; cholestyramine and colestipol reduce the absorption of thiazides; antidiabetic drugs may require dosage adjustment (US label §7.5, §7.6)

Clinical monograph

How it works

Olmesartan blocks the angiotensin-II type-1 receptor to reduce vasoconstriction and sodium retention, while hydrochlorothiazide enhances renal excretion of sodium and water; the diuretic-driven activation of the renin-angiotensin system is offset by the receptor blocker.

Prescribing in practice

Avoid in pregnancy because the angiotensin-receptor-blocker component is foetotoxic; advise effective contraception and review before conception.
The thiazide can precipitate hyponatraemia, hypokalaemia, hyperuricaemia with gout and dehydration, and may unmask or worsen glucose intolerance.
Olmesartan carries a rare risk of severe sprue-like enteropathy, and the combination can cause hypotension and renal impairment, especially in volume-depleted or elderly patients.

Monitoring

Monitor blood pressure, renal function and serum electrolytes including sodium, potassium and where relevant urate after initiation and dose adjustment.

Counselling the patient

Report persistent severe diarrhoea or unexplained weight loss, which can rarely be linked to this medicine.
Stay adequately hydrated, particularly in hot weather or intercurrent illness.
Inform your doctor at once if you become pregnant.

Evidence & guidelines

Adding a thiazide to an angiotensin-receptor blocker is a recognised step in NICE hypertension management, and fixed-dose combinations support adherence and blood-pressure control.

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).

Curated clinical cross-links plus same-class fallbacks.

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