Atenolol, chlortalidone (Tenoret 50)
How does it work?
Tenoret 50 tablets contain two active ingredients, atenolol, which is a type of medicine called a beta-blocker and chlortalidone, which is a type of medicine called a thiazide diuretic. This combination of medicines is sometimes called co-tenidone and is also available without a brand name, ie as the generic medicine.
Atenolol blocks beta receptors that are found in the heart. This reduces the action of adrenaline and noradrenaline on the heart, causing it to beat more slowly and with less force. In turn, this reduces the pressure at which the blood is pumped out of the heart and around the body, which helps to reduce blood pressure. Atenolol can therefore be used to lower high blood pressure.
Chlortalidone works by causing the kidneys to increase the amount of salts such as potassium and sodium that are filtered out of the blood and into the urine. When these salts are filtered out of the blood by the kidneys, they draw water alongside them. As diuretics increase the removal of salts from the blood, they also cause more water to be drawn out of the blood and into the urine.
Removing water from the blood decreases the volume of fluid circulating through the blood vessels. This subsequently decreases the pressure within the blood vessels. Diuretics such as chlortalidone can therefore be used to lower high blood pressure.
Atenolol and chlortalidone have a combined effect on lowering blood pressure.
What is it used for?
- High blood pressure (hypertension).
How do I take it?
- Tenoret 50 tablets can be taken either with or without food.
- Tenoret 50 tablets should be swallowed with a drink of water. The recommended dose is usually one tablet daily. This should be taken in the morning.
- As diuretics cause your kidneys to produce more urine, you may find that if you take a dose too late in the day that you need to get up in the night to visit the toilet. For this reason, it is recommended that you take this medicine in the morning. Seek further advice from your doctor or pharmacist.
- It is important that you don't suddenly stop taking this medicine unless your doctor tells you to.
- This medicine may cause fatigue and dizziness. You should take care when performing potentially hazardous activities, such as driving or operating machinery, until you know how this medicine affects you and are sure you can perform such activities safely.
- You should not stop taking this medicine suddenly, particularly if you have ischaemic heart disease (inadequate flow of blood to the heart, eg angina). When treatment with this medicine is stopped it should be done gradually, usually over one to two weeks, following the instructions given by your doctor.
- While taking this medicine you may need to have regular blood tests to monitor your kidney function and the levels of salts such as potassium and sodium in your blood.
- If you experience any of the following symptoms while taking this medicine you should inform your doctor promptly, so that the amount of fluids and salts in your body can be checked: thirst, lethargy, confusion, weakness, drowsiness, muscle cramps, scanty production of urine, abnormal heart rhythm, seizures, nausea and vomiting.
- If you go into hospital or to the dentist to have an operation you should tell the person treating you that you are taking this medicine. This is because your blood pressure may fall too low if you are given certain types of anaesthetics while taking this medicine.
Use with caution in
- Elderly people.
- Decreased liver function.
- Decreased kidney function.
- People with a history of heart failure or a weak heart.
- People with slowed conduction of electrical messages between the chambers of the heart (1st degree heart block).
- A severe form of chest pain not caused by exertion (Prinzmetal's or variant angina).
- Chronic obstructive pulmonary disease (COPD).
- History of asthma, wheezing or any other breathing difficulties.
- People with poor blood circulation in the arteries of the extremities, eg hands and feet (avoid if problems are severe - see below).
- Diabetes (this medicine may mask the symptoms of low blood sugar, such as increased heart rate and tremor, and the dose of your diabetes medicine may need adjusting).
- People with a history of sudden drops in blood sugar levels (hypoglycaemia).
- Overactive thyroid gland (this medicine may mask the symptoms of a thyroid storm or thyrotoxicosis).
- Abnormal muscle weakness (myasthenia gravis).
- People with a history of allergies (beta-blockers may increase sensitivity to allergens and result in more serious allergic reactions; they may also reduce the response to adrenaline used to treat anaphylactic shock).
Not to be used in
- Severe liver disease.
- Kidney failure.
- People whose kidneys are not producing urine.
- People allergic to sulphonamides.
- People with a low level of potassium or sodium in their blood that is not responding to treatment.
- People with high levels of calcium in their blood.
- Addison's disease.
- People with a serious defect in the heart's electrical message pathways, resulting in decreased function of the heart (2nd or 3rd degree heart block).
- Uncontrolled heart failure.
- People with a very slow heart rate (bradycardia).
- A problem common in the elderly, related to poor control of the working of the heart (sick sinus syndrome).
- Failure of the heart to maintain adequate circulation of blood around the body (cardiogenic shock).
- Low blood pressure (hypotension)
- Severe conditions involving poor blood circulation in the arteries of the extremities, eg hands and feet (peripheral arterial disorders such as Raynaud's syndrome or intermittent claudication).
- People with an increase in the acidity of the blood (metabolic acidosis).
- Untreated tumour of the adrenal gland (phaeochromocytoma). If you are being treated for phaeochromocytoma you will be given another medicine called an alpha-blocker in combination with this one.
- This medicine is not recommended for children.
This medicine should not be used if you are allergic to any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.
If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.
Pregnancy and breastfeeding
Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
- This medicine should not be used during pregnancy. Beta-blockers reduce blood flow to the placenta, which could increase the chance of premature delivery or death of the foetus. They may also slow the baby's heart beat, cause its blood sugar to drop, or restrict its growth in the womb. Thiazide diuretics may also have harmful effects on the baby in the womb. If you think you could be pregnant while taking this medicine, or want to try for a baby, it is important to seek medical advice from your doctor. It is important that you don't stop taking this medicine suddenly.
- This medicine may pass into breast milk in small amounts. As this could potentially cause the baby's heart rate to slow down or its blood sugar to fall, it is recommended that this medicine is not used by breastfeeding mothers. The chlortalidone component may also reduce production of breast milk. Seek medical advice from your doctor.
- Do not stop taking this medication except on your doctor's advice.
Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.
Common (affect between 1 in 10 and 1 in 100 people)
- Feeling tired.
- Cold hands and feet.
- Slower than normal heart beat (bradycardia).
- Increased level of uric acid in the blood (hyperuricaemia) - this may cause kidney problems and gout.
- Decreased level of potassium in the blood (hypokalaemia).
- Low blood sodium level (hyponatraemia).
- Disturbances of the gut such as nausea, abdominal discomfort or pain.
Uncommon (affect between 1 in 100 and 1 in 1000 people)
Rare (affect between 1 in 1000 and 1 in 10,000 people)
- Mood changes.
- Dizziness (particularly when standing up, which may sometimes cause fainting).
- Sensation of pins and needles in hands and feet.
- Narrowing of the blood vessels in the hands leading to periods of white, painful hands (Raynaud's disease).
- Cramping pain in the leg (calf) muscles on exertion (intermittent claudication).
- Dry or irritated eyes.
- Visual disturbances.
- Dry mouth.
- Problems with the electrical pathways that control the pumping action of the heart (heart block).
- Inability of the heart to pump blood efficiently (heart failure).
- Breathing difficulties due to a narrowing of the airways (bronchospasm).
- A drop in blood pressure that occurs when going from lying down to sitting or standing, which results in dizziness and lightheadedness (postural hypotension)
- Sexual problems such as impotence.
- Hair loss.
- Reduced platelet count in the blood (thrombocytopenia).
- Low levels of a type of white blood cell (neutrophils) in the blood (neutropenia).
- Decrease in the number of white blood cells (leukopenia),
The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.
For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.
How can this medicine affect other medicines?
It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to make sure that the combination is safe.
This medicine is likely to have an additive effect with other medicines that decrease blood pressure, particularly medicines that are used to treat high blood pressure (antihypertensives). This may cause dizziness, which can usually be relieved by lying down until the symptoms pass. If you feel dizzy while taking this medicine in combination with other medicines that can lower blood pressure you should let your doctor know, as your doses may need adjusting. Other medicines that decrease blood pressure include the following:
- ACE inhibitors, eg enalapril
- alpha-blockers such as prazosin
- angiotensin II receptor antagonists such as losartan
- antipsychotics such as chlorpromazine
- benzodiazepines, eg temazepam, diazepam
- other beta-blockers such as propranolol
- calcium channel blockers such as verapamil, nifedipine. (If atenolol is taken with calcium channel blockers such as verapamil, nifedipine or diltiazem, there may also be an increased risk of slow heart rate and heart failure. Verapamil must not be given as an injection into a vein (intravenously) to people being treated with atenolol.)
- clonidine. (If atenolol is taken in combination with clonidine there is also a risk of a rebound increase in blood pressure if the clonidine is suddenly stopped. If you are taking both these medicines it is important to keep taking both of them unless otherwise directed by your doctor. When stopping treatment, the atenolol should be stopped several days before slowly stopping the clonidine.)
- diuretics, eg furosemide
- dopamine agonists, eg bromocriptine, apomorphine
- MAOI antidepressants, eg phenelzine
- nitrates, eg glyceryl trinitrate
There may be an increased risk of slow heart rate and heart block if atenolol is used in combination with the following medicines:
- medicines for irregular heartbeats (anti-arrhythmics), eg amiodarone, flecainide, quinidine
There may be an increased risk of coldness, numbness or tingling of the hands and feet if ergot derivatives such as ergotamine or methysergide (used to treat migraines) are taken in combination with atenolol.
This medicine may reduce the blood sugar lowering effect of some medicines used to treat diabetes. People with diabetes should carefully monitor their blood sugar while taking this medicine, as atenolol can also mask some of the signs of low blood sugar, such as increased heart rate and tremor.
Chlortalidone can decrease the amount of potassium in the blood. If it is used in combination with any of the following medicines, which can also lower potassium in the blood, the risk of a low blood potassium level (hypokalaemia) is increased:
- corticosteroids, such as hydrocortisone and prednisolone
- beta 2 agonists, eg salbutamol, terbutaline
- other diuretics, eg furosemide
If the level of potassium in your blood falls during treatment, this can increase the risk of side effects on the heart from various other medicines, including digoxin, certain antipsychotics and medicines for abnormal heart rhythms (anti-arrhythmics), eg amiodarone.
Chlortalidone can increase the amount of calcium in your blood. If you are taking calcium supplements, or regularly take large amounts of calcium-containing antacids, your doctor may want to monitor the level of calcium in your blood. Taking occasional antacids should not cause any problems.
Chlortalidone reduces the ability of the body to remove the medicine lithium, which can cause the level of lithium in the blood to rise too high. If you are taking lithium your lithium level should be checked after you start and stop treatment with this medicine, as well as after any dose changes. Your lithium dose may need adjusting.
The following medicines may reduce the blood pressure lowering effect of this medicine:
- corticosteroids, such as dexamethasone or prednisolone
- oestrogens, such as those in the contraceptive pill
- regular use of non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, diclofenac or indomethacin (occasional painkilling doses are unlikely to have a significant effect).
Other medicines containing the same active ingredients
Co-tenidone tablets are also available without a brand name, ie as the generic medicine.