Co-Tenidone

Managing high blood pressure often requires a combination of medicines that work through different mechanisms. Co-tenidone tablets are a prescription combination product containing atenolol, a cardioselective beta blocker, and chlortalidone, a thiazide-like diuretic. Together they provide complementary antihypertensive effects in a single once-daily tablet, supporting blood pressure control in adults with hypertension. Because co-tenidone contains a beta blocker, it must not be stopped suddenly, and it carries important contraindications, including asthma. A prescription can only be issued following a clinical consultation with a registered prescriber.

Co-tenidone tablets are an oral prescription combination medicine containing two active ingredients: atenolol and chlortalidone. Atenolol is a cardioselective beta-1 adrenoceptor blocker and chlortalidone is a thiazide-like diuretic. The two components are available as a fixed-dose combination in two strengths: 100mg atenolol with 25mg chlortalidone, and 50mg atenolol with 12.5mg chlortalidone per tablet.

Co-tenidone is licensed in the United Kingdom for the treatment of hypertension (high blood pressure) in adults. It is suitable for patients whose blood pressure is adequately managed by the doses of atenolol and chlortalidone present in the combination tablet, and for patients who would benefit from the convenience of a single tablet. Co-tenidone is not licensed for angina or heart failure. Because it contains a beta blocker, the contraindications and precautions relevant to atenolol apply in full.

All clinical information on this page is drawn from the current UK Summary of Product Characteristics for co-tenidone tablets.

Important: Do not stop taking co-tenidone suddenly without speaking to your prescriber first. Abrupt withdrawal of the atenolol component can cause a rebound increase in heart rate and blood pressure and may trigger serious cardiac events in some patients. Your prescriber will advise on a gradual dose reduction if treatment needs to be stopped.

Co-tenidone lowers blood pressure through the combined and complementary actions of its two active ingredients.

Atenolol: Beta Blocker Action

Atenolol selectively blocks beta-1 adrenoceptors in the heart, which are normally stimulated by adrenaline and noradrenaline. This reduces heart rate and the force of cardiac contraction, lowering cardiac output and the pressure at which blood is pumped through the arteries. Atenolol is cardioselective, meaning it preferentially targets beta-1 receptors in the heart rather than beta-2 receptors in the airways and blood vessels. This makes it less likely to cause bronchoconstriction than non-selective beta blockers, though it remains contraindicated in asthma and significant bronchospasm.

Chlortalidone: Thiazide-like Diuretic Action

Chlortalidone acts on the distal tubule of the kidney to inhibit the reabsorption of sodium and chloride. This increases sodium and water excretion in urine, reducing the volume of fluid circulating in the blood vessels. The resulting reduction in blood volume lowers blood pressure. Chlortalidone is a thiazide-like diuretic with a longer duration of action than older thiazides such as bendroflumethiazide, supporting sustained blood pressure control with once-daily dosing.

Combined Antihypertensive Effect

The combination of a beta blocker and a thiazide-like diuretic provides additive blood pressure lowering through two distinct mechanisms. The reduced cardiac output from atenolol complements the reduced blood volume from chlortalidone. This combination approach is supported in the management of hypertension and may be appropriate when monotherapy with either component has not achieved adequate blood pressure control. Electrolyte and metabolic monitoring is recommended because both components can affect potassium and other metabolic parameters.

Always take co-tenidone exactly as your prescriber instructs. The information below summarises key points from the current UK SmPC. Read the Patient Information Leaflet supplied with your medicine before starting treatment.

• Take co-tenidone once daily, in the morning. Taking it in the morning means any increase in urination from the chlortalidone component occurs during the day rather than disrupting sleep.
• Co-tenidone can be taken with or without food.
• Swallow the tablet whole with a glass of water.
• If you miss a dose, take it as soon as you remember on the same day. If you only remember the following day, skip the missed dose and continue with your normal schedule. Do not take two doses on the same day.
• Never stop taking co-tenidone suddenly without medical advice. Abrupt withdrawal of the atenolol component can cause a rebound increase in heart rate and blood pressure. Your prescriber will advise on a gradual reduction if treatment needs to be stopped.
• Attend all blood test and monitoring appointments arranged by your prescriber. Co-tenidone affects electrolytes and metabolic parameters, and these should be reviewed periodically.

Co-tenidone tablets are available in two fixed-dose combination strengths through this service. The doses are expressed as atenolol/chlortalidone. The appropriate strength will be determined by your prescriber based on your blood pressure, previous monotherapy response, kidney function, and clinical history.

Co-tenidone 50mg/12.5mg Tablets

Each tablet contains 50mg of atenolol and 12.5mg of chlortalidone. This is the lower strength combination. It is appropriate for patients who require a moderate antihypertensive effect, for older patients who may be more sensitive to antihypertensive treatment, or for those in whom the 100mg/25mg strength provides more effect than is clinically required. Your prescriber will advise whether this strength is appropriate for your circumstances.

Co-tenidone 100mg/25mg Tablets

Each tablet contains 100mg of atenolol and 25mg of chlortalidone. This is the standard strength combination and corresponds to commonly prescribed doses of atenolol and chlortalidone. It is appropriate for patients requiring a greater antihypertensive effect whose blood pressure is not adequately controlled on lower doses. All dosing decisions are made by your prescriber. Do not change your strength without medical advice.

Like all medicines, co-tenidone can cause side effects. Because it contains two active ingredients, it carries the potential side effects of both atenolol and chlortalidone. The information below is based on the current UK SmPC. Refer to the Patient Information Leaflet for the full list.

Common Side Effects (may affect up to 1 in 10 people)

• Bradycardia (a slow heart rate) - Atenolol reduces heart rate as part of its therapeutic action. If the heart rate falls excessively, contact your prescriber.
• Cold or numb hands and feet, caused by reduced blood flow to the extremities.
• Fatigue and tiredness.
• Dizziness or lightheadedness, particularly when standing up quickly (postural hypotension).
• Increased frequency of urination, particularly in the first few hours after taking the tablet.
• Low potassium levels (hypokalaemia) from the chlortalidone component, which can cause muscle cramps, weakness, and an irregular heartbeat.
• Raised blood uric acid levels from chlortalidone, which may trigger or worsen gout in susceptible patients.

Uncommon Side Effects (may affect up to 1 in 100 people)

• Sleep disturbance or vivid dreams.
• Low mood or depression.
• Nausea or gastrointestinal discomfort.
• Raised blood glucose, which may affect patients with or at risk of diabetes.
• Skin rash or itching.
• Raised blood cholesterol or triglycerides with longer-term chlortalidone use.

Serious Side Effects: Seek Urgent Medical Attention

Contact your prescriber or go to your nearest accident and emergency department promptly if you experience any of the following:

• A very slow or irregular heartbeat, or sudden severe breathlessness.
• Worsening breathlessness or wheezing, particularly if you have any respiratory condition - even though atenolol is cardioselective, it can occasionally worsen airway function in susceptible individuals.
• Signs of a serious allergic reaction, such as sudden swelling of the face, lips, tongue, or throat, difficulty breathing, or a severe skin reaction.
• Severe muscle weakness or cramps, which may indicate significant low potassium.
• Sudden severe joint pain, redness, and swelling, which may indicate a gout attack.

Report any suspected side effect to your prescriber or pharmacist or via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.

Co-tenidone Tablets May Be Suitable If You:

• Are an adult with hypertension whose blood pressure is adequately managed by the doses of atenolol and chlortalidone present in the combination tablet.
• Have been established on separate atenolol and chlortalidone tablets at doses that correspond to one of the available co-tenidone strengths and would benefit from a single tablet.
• Are already prescribed co-tenidone and require a repeat prescription through an online prescribing service.

Co-tenidone Tablets Are Not Suitable If You:

• Have asthma or a history of bronchospasm - the atenolol component is contraindicated in patients with asthma, even though atenolol is cardioselective.
• Have second or third degree heart block (unless you have a functioning pacemaker).
• Have sick sinus syndrome or sinoatrial block.
• Have severe bradycardia.
• Have cardiogenic shock or uncontrolled heart failure.
• Have untreated phaeochromocytoma.
• Have severe peripheral artery disease or severely symptomatic Raynaud's phenomenon.
• Have metabolic acidosis.
• Have severe kidney impairment or are anuric.
• Have severe liver disease.
• Have refractory hypokalaemia (low potassium that cannot be corrected), hypercalcaemia, or hyponatraemia.
• Have gout.
• Are pregnant or breastfeeding.
• Have a known allergy to atenolol, chlortalidone, sulfonamide-derived medicines, or any excipient in the SmPC.
• Are under 18 years of age (this service is for adults only).

Cautions

Caution is required in patients with COPD, as even cardioselective beta blockers may worsen airway obstruction in some individuals. Patients with diabetes should be aware that atenolol can mask some symptoms of hypoglycaemia, particularly palpitations, and that chlortalidone can raise blood glucose levels. Older patients are at greater risk of electrolyte disturbances, dehydration, and postural hypotension. Patients with mild to moderate kidney impairment require monitoring of electrolytes and kidney function. Chlortalidone raises uric acid levels and should be used with particular care in patients with a history of raised uric acid.

Important Drug Interactions

Co-tenidone can interact with a number of commonly prescribed medicines. Tell your prescriber about all medicines you take, including over-the-counter products and herbal supplements. The following interactions are of particular clinical importance:

• Calcium channel blockers of the verapamil or diltiazem type: combining these with the atenolol component can cause a significant slowing of the heart rate and marked reduction in blood pressure. This combination should generally be avoided unless under close specialist supervision.
• Digoxin: electrolyte changes caused by chlortalidone, particularly low potassium, increase the risk of digoxin toxicity. Monitoring is essential in patients taking both medicines.
• Lithium: chlortalidone can increase lithium levels, raising the risk of lithium toxicity. Close monitoring is required.
• Antidiabetic medicines including insulin: atenolol can mask some hypoglycaemia warning signs, and chlortalidone can raise blood glucose. Both effects require careful management in diabetic patients.
• NSAIDs such as ibuprofen: these can reduce the antihypertensive effect of both components and increase the risk of kidney problems.
• Clonidine: if both co-tenidone and clonidine are to be stopped, atenolol should be withdrawn several days before clonidine to avoid a rebound rise in blood pressure.

This is not a complete list of interactions. Your prescriber will carry out a full clinical assessment, including a review of your current medicines, before any prescription is considered.

Co-tenidone is a prescription-only medicine. The clinical consultation is the essential first step. A prescription will only be issued if a registered prescriber determines, based on their individual assessment of your circumstances, that co-tenidone is clinically appropriate for you.

During your online consultation with Pharmacy Planet, a registered prescriber will review your clinical information. This includes your blood pressure readings, heart rate, kidney function, electrolyte levels, current medicines, and relevant medical conditions, including any history of asthma, COPD, diabetes, gout, or peripheral artery disease. The prescriber will also assess whether the fixed-dose combination corresponds to doses of both components that are clinically appropriate for your individual circumstances.

Not all consultations will result in a prescription being issued. The prescriber may recommend a different strength, the individual components at separately adjusted doses, or suggest that a face-to-face appointment with your GP is more appropriate. This process is designed to ensure your safety.

If you are already being managed for hypertension by your GP or a specialist, please keep them informed of all medicines you are taking, including any prescribed through online services.

• Store below 25°C.
• Store in the original packaging to protect from light and moisture.
• Keep out of the sight and reach of children.
• Do not use after the expiry date printed on the packaging.
• Do not dispose of medicines via household waste or wastewater. Return unused or out-of-date tablets to your pharmacist for safe disposal.

Full storage instructions are provided in the Patient Information Leaflet supplied with your medicine.

The table below compares beta blocker tablets available at Pharmacy Planet. Beta blockers reduce heart rate and cardiac output to lower blood pressure. They differ in cardioselectivity, additional properties, and licensed indications.

Important: This comparison is for general information only and does not replace medical advice. A prescriber will decide which treatment is suitable for you following an online consultation.

Pharmacy Planet is a GPhC-registered online pharmacy providing access to prescription medicines through a clinically led consultation process. Our registered prescribers and pharmacists are committed to patient safety, clinical accuracy, and responsible prescribing.

We follow GPhC standards, MHRA guidance, and ASA advertising regulations in all aspects of our service. Every prescription is reviewed and dispensed by qualified healthcare professionals. We provide clear, factual information to help patients understand their antihypertensive medication and make informed decisions about their health.

If you have questions about co-tenidone, combination blood pressure treatment, or cardiovascular therapy, our pharmacy team is available to help. We are committed to transparent, patient-centred care.

References

1. Electronic Medicines Compendium (eMC). Co-tenidone 100mg/25mg and 50mg/12.5mg Tablets — Summary of Product Characteristics. https://www.medicines.org.uk/emc. Accessed August 2026.
2. National Institute for Health and Care Excellence (NICE). Hypertension in adults: diagnosis and management. NICE guideline NG136. https://www.nice.org.uk/guidance/ng136. Accessed August 2026.
3. Joint Formulary Committee. British National Formulary (BNF). Atenolol with chlortalidone. BMJ Group and Pharmaceutical Press. https://bnf.nice.org.uk. Accessed August 2026.
4. NHS. Atenolol. https://www.nhs.uk/medicines/atenolol. Accessed August 2026.
5. Medicines and Healthcare products Regulatory Agency (MHRA). Yellow Card — report a side effect. https://yellowcard.mhra.gov.uk. Accessed August 2026.