Co-Diovan

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Co-Diovan on Prescriptsy

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Co-Diovan is a combination antihypertensive medicine containing valsartan, an angiotensin II receptor blocker (ARB), and hydrochlorothiazide, a thiazide diuretic.

It is licensed in the United Kingdom for the treatment of essential hypertension in adults whose blood pressure is not adequately controlled by either active substance alone.

High blood pressure affects approximately one in three adults in the UK and is the single largest modifiable risk factor for cardiovascular disease, stroke, and chronic kidney disease.

By combining two complementary blood pressure-lowering mechanisms in a single tablet, Co-Diovan simplifies treatment, improves adherence, and delivers more effective blood pressure reduction than either monotherapy.

This page provides a comprehensive clinical overview of how Co-Diovan works, correct dosing, monitoring requirements, side effects, safety warnings, and how to obtain a prescription in the UK.

Important safety information about Co-Diovan

Before reading further, note the following essential safety points. Co-Diovan is a prescription-only medicine (POM) in the UK and must only be taken under medical supervision.

• Co-Diovan must not be taken during pregnancy. It can cause serious harm to the developing baby, particularly in the second and third trimesters. If you become pregnant, stop Co-Diovan immediately and contact your doctor.
• Regular blood tests (kidney function, electrolytes, uric acid) are required during treatment.
• Do not take Co-Diovan with an ACE inhibitor or with aliskiren if you have diabetes or significant kidney impairment.
• The hydrochlorothiazide component may increase sensitivity to sunlight and, with long-term use, the risk of non-melanoma skin cancer. Use sun protection and report any suspicious skin changes.
• Seek emergency medical attention if you develop swelling of the face, lips, tongue, or throat (angioedema).

Understanding high blood pressure (hypertension)

Blood pressure is the force exerted by circulating blood on the walls of the arteries.

It is measured in millimetres of mercury (mmHg) and expressed as two numbers: systolic (pressure during a heartbeat) over diastolic (pressure between heartbeats).

The NICE threshold for diagnosing hypertension is a clinic reading of 140/90 mmHg or above, confirmed by ambulatory blood pressure monitoring (ABPM) with a daytime average of 135/85 mmHg or above.

Hypertension is usually asymptomatic and is often detected incidentally during routine health checks.

Uncontrolled hypertension damages arterial walls over years, accelerating atherosclerosis and increasing the risk of myocardial infarction, ischaemic and haemorrhagic stroke, heart failure, chronic kidney disease, retinopathy, and vascular dementia.

The NHS Health Check programme aims to identify hypertension early in adults aged 40 to 74.

NICE guideline NG136 (Hypertension in adults) recommends a stepwise approach to treatment.

For most patients, first-line therapy is an ACE inhibitor or ARB (for patients under 55 or with diabetes) or a calcium channel blocker (for patients aged 55 and over, or of Black African or African-Caribbean origin).

If blood pressure remains above target on monotherapy, combination treatment is recommended at step 2.

Co-Diovan represents a rational combination for patients already on an ARB who require the addition of a diuretic.

How Co-Diovan works: mechanism of action

Valsartan: angiotensin II receptor blockade

The renin-angiotensin-aldosterone system (RAAS) is a key regulator of blood pressure and fluid balance.

Renin, released by the kidneys in response to low blood pressure or reduced renal perfusion, converts angiotensinogen to angiotensin I.

Angiotensin-converting enzyme (ACE) then converts angiotensin I to angiotensin II, a potent vasoconstrictor that also stimulates aldosterone secretion from the adrenal cortex.

Aldosterone promotes renal sodium and water retention, further increasing blood volume and pressure.

Valsartan selectively blocks the AT1 receptor through which angiotensin II exerts its vasoconstrictive, aldosterone-releasing, and growth-promoting effects.

Unlike ACE inhibitors, ARBs do not inhibit the breakdown of bradykinin, which means they are less likely to cause the dry cough that is a common side effect of ACE inhibitors.

Valsartan provides 24-hour blood pressure control with once-daily dosing.

Hydrochlorothiazide: thiazide diuresis

Hydrochlorothiazide inhibits the sodium-chloride co-transporter in the distal convoluted tubule of the nephron.

This prevents the reabsorption of approximately 5 to 8% of filtered sodium, promoting its excretion in the urine along with water.

The initial blood pressure reduction is primarily due to decreased plasma volume, but with continued treatment, the mechanism shifts to reduced peripheral vascular resistance.

Synergistic combination

Diuretics activate the RAAS as a compensatory response to volume depletion.

By simultaneously blocking the AT1 receptor, valsartan prevents the counterproductive vasoconstrictive and sodium-retaining effects of this reflex activation.

The combination therefore produces additive and in some cases synergistic blood pressure reduction. Additionally, valsartan partially counteracts the potassium-lowering effect of hydrochlorothiazide, reducing the need for potassium supplementation.

Clinical evidence

The efficacy of valsartan/hydrochlorothiazide has been established in multiple randomised controlled trials.

In a pivotal dose-ranging study, the combination of valsartan 160 mg and hydrochlorothiazide 25 mg reduced sitting diastolic blood pressure by approximately 14 to 15 mmHg, compared with 8 to 9 mmHg for either component alone.

Additional studies have demonstrated sustained blood pressure control over 12 months with good tolerability.

The VALUE trial (Valsartan Antihypertensive Long-term Use Evaluation) compared valsartan-based therapy with amlodipine-based therapy in over 15,000 high-risk hypertensive patients.

While amlodipine provided slightly faster blood pressure reduction in the first 6 months, outcomes were comparable once blood pressure was equalised.

Notably, valsartan was associated with a lower incidence of new-onset diabetes.

NICE NG136 supports the use of ARB plus thiazide-like diuretic combinations as a rational step 2 strategy.

Although NICE has a preference for indapamide or chlorthalidone as the thiazide-like diuretic, hydrochlorothiazide remains widely used in fixed-dose combinations and is supported by extensive clinical data.

Dosage and administration

Co-Diovan is taken as one tablet once daily, at the same time each day, with or without food. The tablet should be swallowed whole with water.

Co-Diovan is available in three strength combinations: 80/12.5 mg, 160/12.5 mg, and 160/25 mg (valsartan/hydrochlorothiazide).

The choice of starting strength depends on the patient's existing therapy.

Patients already receiving valsartan 80 mg who need additional blood pressure reduction may be switched to Co-Diovan 80/12.5 mg.

Patients on valsartan 160 mg may switch to 160/12.5 mg, with the option to increase to 160/25 mg after 4 or more weeks if blood pressure remains above target.

Blood pressure response should be assessed after at least 4 weeks at each dose level before titrating upward.

The maximum recommended daily dose is valsartan 320 mg with hydrochlorothiazide 25 mg.

However, fixed-dose Co-Diovan tablets are available only up to 160/25 mg; higher valsartan doses require separate prescriptions.

Special populations

No dose adjustment is required for elderly patients, though treatment initiation should be cautious due to an increased risk of postural hypotension and volume depletion.

Patients with mild to moderate renal impairment (GFR above 30 mL/min) require no dose adjustment but should have renal function monitored regularly.

Co-Diovan is contraindicated in severe renal impairment and anuria.

Patients with mild to moderate hepatic impairment without cholestasis should not exceed valsartan 80 mg daily. Co-Diovan is contraindicated in severe hepatic impairment, biliary cirrhosis, and cholestasis.

Side effects of Co-Diovan

Common side effects

Commonly reported adverse effects include dizziness (especially on standing), headache, fatigue, and increased urination in the first few days of treatment.

The thiazide component may cause electrolyte disturbances, most notably hypokalaemia (low potassium), which can manifest as muscle cramps, weakness, or palpitations.

Other electrolyte changes include low sodium (hyponatraemia), low magnesium, and elevated calcium. These are usually detected through routine blood tests rather than symptoms.

Uncommon and rare side effects

Uncommon effects include postural hypotension, nausea, diarrhoea, raised uric acid (which may trigger gout in predisposed individuals), elevated blood glucose, photosensitivity, and muscle cramps.

Rare but serious effects include angioedema (swelling of face, lips, tongue, or throat), acute renal impairment, jaundice, interstitial nephritis, pancreatitis, blood dyscrasias (including thrombocytopenia and agranulocytosis), and severe cutaneous adverse reactions such as Stevens-Johnson syndrome.

When to seek medical advice

Seek emergency care (call 999 or attend A&E) if you experience swelling of the face, lips, tongue, or throat, difficulty breathing, or a severe blistering skin rash.

Contact your GP or NHS 111 if you develop persistent dizziness, fainting, muscle weakness, cramps, irregular heartbeat, excessive thirst, dark urine, or signs of gout.

Report any suspected adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

Warnings and precautions

Pregnancy and breastfeeding

Co-Diovan is absolutely contraindicated in pregnancy.

Exposure to ARBs during the second and third trimesters is associated with foetal renal failure, oligohydramnios, skull ossification defects, limb contractures, and neonatal death.

Even first-trimester exposure cannot be considered safe. Women of childbearing potential must use reliable contraception throughout treatment.

If pregnancy is confirmed or suspected, stop Co-Diovan immediately and seek specialist obstetric advice. Co-Diovan is not recommended during breastfeeding.

Renal function monitoring

Both components of Co-Diovan affect renal haemodynamics.

ARBs reduce glomerular filtration pressure and may cause a rise in serum creatinine, particularly in patients with renal artery stenosis or pre-existing renal impairment.

Thiazides become less effective and potentially harmful as renal function declines.

Renal function and electrolytes should be measured before starting treatment and monitored regularly, at minimum annually for stable patients and more frequently during dose changes or illness.

Dual RAAS blockade

The concurrent use of Co-Diovan with an ACE inhibitor or aliskiren is not recommended due to an increased risk of hypotension, hyperkalaemia, and renal impairment.

This combination is specifically contraindicated in patients with diabetes mellitus or moderate to severe renal impairment (GFR below 60 mL/min/1.73 m2).

Skin cancer risk

Hydrochlorothiazide has been associated with a dose-dependent increase in the risk of non-melanoma skin cancer, specifically basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).

Patients should be advised to limit sun and UV exposure, use sunscreen with high SPF, and report any new or changing skin lesions promptly.

Regular skin checks are recommended for patients on long-term thiazide therapy.

How to get a Co-Diovan prescription in the UK

Co-Diovan is a prescription-only medicine.

It is typically prescribed by your GP or a hospital specialist (cardiologist, nephrologist) as part of a structured hypertension management plan in accordance with NICE NG136.

Your clinician will confirm your diagnosis of hypertension using ambulatory or home blood pressure monitoring, assess cardiovascular risk, and check baseline blood tests before starting treatment.

Authorised online prescribers registered with the GPhC may also prescribe Co-Diovan following a comprehensive online consultation including verification of diagnosis, current medication review, and recent blood test results.

The standard NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Living with hypertension: lifestyle management

Medication is most effective when combined with lifestyle modifications.

NICE recommends reducing dietary salt intake to below 6 g per day, eating a balanced diet rich in fruit, vegetables, and whole grains, achieving and maintaining a healthy weight (BMI 18.5 to 24.9), exercising for at least 150 minutes of moderate-intensity activity per week, limiting alcohol to within recommended guidelines (14 units per week), and stopping smoking.

Regular home blood pressure monitoring (using a validated upper-arm device) helps track treatment response and supports informed clinical decisions at review appointments.

When to seek urgent medical advice

Contact your GP or NHS 111 if you experience persistent dizziness, fainting, a significant change in urine output, or symptoms of electrolyte imbalance.

Seek emergency care (call 999 or attend A&E) if you develop swelling of the face or throat, chest pain, sudden severe headache, visual disturbance, or weakness on one side of the body, as these may indicate angioedema, a hypertensive emergency, or stroke.

Report adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

Sources

• Co-Diovan 160/25 mg Film-coated Tablets, Summary of Product Characteristics (EMC)
• Valsartan with hydrochlorothiazide, British National Formulary (BNF)
• NICE NG136: Hypertension in adults: diagnosis and management
• High blood pressure (hypertension), NHS
• MHRA Yellow Card Scheme