How does it work?
Tenormin tablets, Tenormin LS tablets, Tenormin syrup and Tenormin injection all contain the active ingredient atenolol, which is a type of medicine called a beta-blocker. Atenolol is also available without a brand name, ie as the generic medicine.
Beta-blockers work by blocking beta receptors that are found in various parts of the body, including the heart. Blocking the beta receptors prevents the action of two hormones that are produced naturally by the body, called noradrenaline and adrenaline. These hormones are often referred to as the 'fight or flight' chemicals, because they are responsible for the body's reaction to stressful situations.
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.
Atenolol's action in slowing the rate and force of the heartbeat also reduces the energy used by the heart to pump blood around the body. This reduces the heart's need for oxygen, which means that atenolol can also be used in the management of angina. Angina is chest pain that occurs because the heart does not get enough oxygen to meet demand, for example during exercise. This is usually as a result of hardening or narrowing of the arteries that supply blood to the heart. Atenolol reduces the workload of the heart and so decreases the amount of oxygen that it needs to pump blood around the body. This helps to prevent attacks of angina.
As atenolol causes the heart to beat more slowly and with less force, it also allows the electrical signals in the heart to fire more regularly. This means it can be used to treat irregular heartbeats (arrhythmias), which occur when electrical activity in the heart is disturbed.
Atenolol is also used for this reason in the period immediately after a heart attack. It has been shown to reduce irregular heartbeats and the risk of further heart attacks, and thus improve survival.
What is it used for?
- Angina pectoris (as a regular long-term treatment to help prevent attacks).
- High blood pressure (hypertension).
- Irregular heartbeats (arrhythmias).
- Reducing the risk of further heart attacks immediately after a heart attack and improving survival.
How do I take it?
- Atenolol tablets and syrup can be taken either with or without food. The tablets should be swallowed with a drink of water.
- The dose prescribed and how often the medicine needs to be taken depends on the condition being treated. Atenolol is usually taken once or twice a day. It is important to follow the instructions given by your doctor. These will be printed on the dispensing label your pharmacist has put on the packet of medicine.
- 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.
- 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
- 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.
- 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.
- The manufacturer states that this medicine should not be used during pregnancy unless considered essential by your doctor. 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 heartbeat, cause its blood sugar to drop, or restrict its growth 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 passes into breast milk. 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. 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).
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.
- 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).
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 ensure that the combination is safe.
Atenolol 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, bendroflumethiazide
- dopamine agonists, eg bromocriptine, apomorphine
- MAOI antidepressants, eg phenelzine
- nitrates, eg glyceryl trinitrate
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.
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
- verapamil (also see above).
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.
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 ingredient
Atenolol tablets are also available without a brand name, ie as the generic medicine.
Tenoret 50, Tenoretic and co-tenidone all contain atenolol in combination with chlortalidone.
Kalten contains atenolol in combination with amiloride and hydrochlorothiazide.
Tenif and Beta-adalat both contain atenolol in combination with nifedipine.