Bronchodilatateurs oraux

What is a bronchodilator?

Bronchodilators are medicines that are used to treat breathing problems in people with lung diseases such as asthme et maladie pulmonaire obstructive chronique (MPOC). They help to relieve symptoms such as coughing, wheezing and shortness of breath.

Bronchodilators are usually used as inhaled medicines, in inhalers or nebulisers. This is because they usually work better when inhaled than when taken orally: as inhaled medicines, they get directly to the airways, and there are fewer side-effects. However, in some situations, oral bronchodilators might also be used.

There are two types (groups) of oral bronchodilators available to prescribe in the UK. These are:

• Beta₂ agonists (salbutamol, bambuterol et terbutaline).

• Methylxanthines (theophylline et aminophylline).

Aminophylline is a 2:1 mixture of theophylline and ethylenediamine. Ethylenediamine is used to improve how well theophylline dissolves in water. Oral bronchodilators are available as capsules, tablets and oral liquids. Aminophylline is also available as an injection; this is usually given in hospital. They all come in various different brand names.

Two other bronchodilators called ephedrine and orciprenaline are also licensed in the UK. However, they are very rarely used nowadays to treat breathing problems because they can cause serious side-effects such as an irregular heartbeat.

Bronchodilators may also be either:

• Short-acting bronchodilators - these are used for quick relief of symptoms

• Long-acting bronchodilators - these are used to treat asthma symptoms and enhance the anti-inflammatory effect of inhaled corticosteroids in order to improve lung function.

Bronchodilators are also available as inhaled medicines. These are much more commonly used bronchodilators. However, the rest of this leaflet only discusses the use of oral bronchodilators (that is, bronchodilators that you take by mouth as capsules, tablets or liquids). See also the separate leaflets called Asthma Inhalers et Inhalers for COPD (including Inhaled Steroids).

The word bronchodilator means to widen (dilate) the bronchi. Bronchodilators work by opening the air passages (bronchi and bronchioles) wider so that air can flow into the lungs more freely. The two different types of bronchodilators work in a slightly different way to one another.

Beta₂ agonists

Work by stimulating receptors called beta₂ receptors in the muscles that line the air passages. This relaxes these muscles, which can make the air passages widen which can make it easier to breathe.

Beta-2 agonists come in short--acting and long-acting forms. For example, salbutamol is a short-acting beta-2 agonist, and bambuterol is a long-acting beta-2 agonist.

Methylxanthines

It is still not known exactly how these medicines work. However, it is thought that they stop a substance in the body, called phosphodiesterase, from working. This then relaxes the muscles in the air passages, leading to easier breathing. Unfortunately, when phosphodiesterase is blocked this can lead to other effects such as low blood pressure, a fast heartbeat, headache and nausea.

As stated above, bronchodilator medicines are usually prescribed for people who have lung-related problems that mean they have difficulty breathing. They are most commonly prescribed in cases of asthma and COPD. Most people with asthma do not need an oral bronchodilator. This is because inhalers usually work well.

In some cases a tablet (liquid form for children) form of beta₂ agonist is prescribed, especially for young children and for the elderly. However, inhaled bronchodilators are more effective and have fewer side-effects.

Methylxanthines are normally prescribed for people who have stable COPD rather than in an acute exacerbation. An aminophylline injection is sometimes prescribed by hospital doctors if you have a very severe asthma attack.

Salbutamol tablets are normally taken three or four times a day. Terbutaline is usually taken three times a day, whereas bambuterol is taken once a day at bedtime (adults only).

Theophylline tablets and capsules may be taken either once a day or twice a day, depending on which brand your doctor has prescribed. It is important always to stick to the same brand of theophylline. This is because, the amount of theophylline absorbed by the body varies greatly between brands. If you start taking a different brand to the one you normally have, you may be having too much or too little theophylline. Aminophylline is usually taken twice a day.

The dose prescribed usually depends on how well you respond to treatment and how old you are. Normally your doctor will start off with a low dose and increase this (if necessary) over a number of weeks until you find the right dose.

Getting the dose of theophylline and aminophylline just right can be tricky. The body breaks down (metabolises) theophylline in the liver. This metabolism varies from person to person. The blood levels of the medicine, therefore, can vary enormously. This is particularly the case in smokers, people with liver damage or impairment and in heart failure. In some conditions, the breakdown is reduced and blood levels increase. In other conditions, the breakdown is increased and so blood levels of theophylline fall. This is very important, as the toxic (dangerous) dose for theophylline is only just above the dose that is needed for the medicine to work well. When you first start treatment with one of these medicines your doctor will take some blood tests to make sure you are getting the right amount of medicine. This blood test measures how much theophylline is in your blood. Ideally the amount of theophylline in the blood is kept between 10 and 20 mg/L. Once you are settled on treatment your doctor may do more blood tests from time to time to check how much theophylline is in your blood.

If bronchodilators help your symptoms then they are usually prescribed long-term. Your doctor or practice nurse will monitor your breathing regularly and review your need for these medicines. If a bronchodilator is used in hospital when you are acutely and seriously ill (very ill for a short period of time) then it may not need to be continued when you go home.

As with all medicines, oral bronchodilators have a number of common side-effects. Listed below are some of the more common side-effects:

• Beta₂ agonists - common side-effects include: fine tremor (for example, shaking of the hands), nervous tension, headache, muscle cramps and the sensation of having a 'thumping heart' (palpitations).

• Methylxanthines - these commonly cause side-effects such as: palpitations, feeling sick (nausea), headache and occasionally abnormal irregular heartbeat (arrhythmia) or even fits (convulsions).

For a more detailed list see the leaflet that came with your medicine.

There are very few medicines that cannot be taken with salbutamol. However, there are quite a few medicines that can affect theophylline. For example, cimetidine, ciprofloxacin, erythromycin, fluvoxamine, and St John's wort (which can be bought from pharmacies and health food shops as a treatment for stress or anxiety) can increase the amount of theophylline in your blood. In addition, some medicines such as phenytoin, carbamazepine, or rifampicin decrease the amount of theophylline in your blood.

If you start taking a medicine that can interfere with the amount of theophylline in your blood, your doctor may need to increase or decrease your theophylline (or aminophylline) dose.

If you take a methylxanthine such as theophylline or aminophylline, always ask your pharmacist for advice regarding which medicines it is safe to take.

If you are a smoker and decide to stop smoking, you may need to have your dose of theophylline or aminophylline reduced. This is because people who smoke break this medicine down quickly (compared with people who do not smoke) and usually need a higher dose, compared with people who do not smoke. Your practice nurse or pharmacist will advise.

No - you cannot buy oral bronchodilators; you need a prescription to obtain these medicines.

The vast majority of people are able to take an oral bronchodilator.