These are drugs which make the bronchial muscles relax, and are therefore useful in asthma. There are three types of bronchodilators: |32-adrenoceptor agonists, xanthines and anticholinergics.
? 2-adrenoceptor agonists
Antagonists are drugs such as antihistamines which bind to receptors and block the effect of the natural messenger (eg histamine) that normally binds to the receptor. Agonists have the opposite effect. They bind to receptors and stimulate the cell, in the same way that the natural messenger would – in other words, they mimic the effects of that natural messenger.
The (32-adrenoceptor agonists mimic the effects of adrenaline on the bronchial muscles, by binding to receptors for adrenaline. These are called (52 adrenoceptors, hence the name of the drugs. They include salbutamol (Ventolin,
Ventodisks, Volmax, Cobutolin, Salbulin, Salbuvent, Asmaven, Aerolin-Auto), terbutaline (Bricanyl, Monovent), fenoterol (Berotec), pirbuterol (Exirel), reproterol (Bronchodil), rimiterol (Pulmadil). Sometimes such drugs are combined with corticosteroids (see below), as in Ventide, which contains salbutamol.
Of all the bronchodilators, these drugs have the most specific effects on the bronchi. They are now preferred to isoprenaline (Iso-Autohaler and Medihaler-Iso) which has a less specific effect, and tends to combine with adrenaline receptors in the heart muscles as well as those in the bronchi, sometimes causing irregular heartbeat, flushing and headaches. Isoprenaline is combined with a sympathomimetic, phenylephrine in Duo-Autohaler and Medihaler-Duo. ,
Isdetharine (Numotac) is another nonspecific 6-agonist. It is combined with phenylephrine in Bronchilator.Orciprenaline (Alupent) is a drug of the same type that is partially selective for bronchial muscles, and has similar side-effects.
Side-effects can also occur with the specific p2-adrenoceptor agonists, such as salbutamol, although they are generally less of a problem. They include tremor, nervous tension, headache, flushing and dry mouth. Taking the drugs from an inhaler reduces the side-effects by targeting the drug on the bronchi – this allows a much lower dose to be used than if the drugs were taken by mouth.
The effects of these drugs lasts for up to six hours, and the timing of doses should be geared to the patient’s needs. Learning how to operate the inhaler properly is very important, as the drug can be ineffective if the inhaler is misused.
Even if they are used at quite high doses over long periods of time there seem to be no serious ill-effects with these drugs. On the other hand, they do not reduce the sensitivity of the bronchi, as sodium cromoglycate does, so once they are discontinued their beneficial effects cease. A combination of the two drugs is sometimes used.
*425\180\8*
Posted in
Allergies Tags:
Allergies
Janet was 40 years old and had been ill in various ways since she was twelve, with rhinitis, severe migraine, urinary problems and pain in the region of her kidneys. During her thirties she had also developed depression which had led to two suicide attempts and resulted in electroconvulsive therapy. Over the past six years she had made over 100 visits to her family doctor, spent 63 days in hospital, visited outpatients 49 times and taken 34 courses of drugs.
Janet was then tried on an elimination diet which excluded all commonly eaten foods. This provoked the
worst migraine she had ever experienced at first, but then left her feeling a great deal better. On testing, a glass of milk produced sneezing, rhinitis and headache, whereas wheat left her depressed with a severe migraine. Eggs produced a headache, nausea and pain around the kidneys. Eating maize resulted in nausea and fatigue. By avoiding these four foods, Janet has remained very well. In the six years since her treatment she has visited her doctor five times, spent only two days in hospital and not required any drugs – a striking contrast to her previous six years.
*378\180\8*
Posted in
Allergies Tags:
Allergies
The final step takes us to the least rigorous form of elimination diet, in which most fruits, vegetables, fish and meats are allowed, but wheat and other cereals, milk, eggs and other common offenders are excluded. This diet is quite good enough for many people, but those with multiple sensitivities tend to slip through the net because they are still eating some foods which cause symptoms.
One other form of elimination diet should be mentioned here. This uses elemental diets during the exclusion phase, rather than any foods. Elemental diets are made from various ordinary foods, but these are treated to break down the food molecules into smaller pieces. They are similar to the hydrolysate formulas used for babies who are sensitive to cow’s milk but they are designed to be eaten – or rather drunk – by adults. In theory, the molecules that remain in the elemental diet are too small to cause any allergic reactions or other problems. In practice, some people with established food sensitivity do react to them, because the fragments of molecules they contain are too reminiscent of the original molecules. For many people, however, they are very effective.
Various drawbacks are associated with elemental diets. Firstly they taste dreadful. Secondly they are very expensive – the cost of living on them and nothing else is about £20 per day. Although they are available on the National Health, they are classified as ‘borderline substances’ which means that they can only be prescribed for certain named illnesses – suspected food sensitivity is not one of these. The elemental diet that most doctors prefer to use is Vivo-nex, and this is only available on prescription. Another form of elemental diet, Elemental 028, is available without prescription, but this contains sugar (sucrose) to which some people are sensitive. Nevertheless, it might be useful as a last resort for someone who is intolerant of a great many foods and has therefore not succeeded with an elimination diet. You should not try out an elemental diet without the help and advice of your doctor.
*331\180\8*
Posted in
Allergies Tags:
Allergies
The timing of responses in the diet varies. Most children recover within a week or two on the initial stages of the diet, but others take up to three weeks. Foods should only be tested once there is a noticeable and sustained improvement. If this does not occur, then revert to the normal diet and consider other options. It may be that your child has chemical sensitivities – reading Chapter Nine should help you to assess this possibility. Be prepared to reconsider the likelihood of emotional stresses and strains.
The procedure for testing foods is slightly different for hyperkinetic syndrome. Although a few may take up to a week of daily feeding with the culprit food before they respond, this is probably fairly unusual. The response time for most is between 15 minutes and four hours. Reintroduced foods should be fed in the morning, and again in the afternoon, if there was no reaction, or only a slight reaction, to the first feeding. A normal-sized portion should be eaten, except in children who have asthma or urticaria, where a very small amount should be tried first, in case there is a severe reaction. If, by the morning after, there is no reaction to the food, then it can be incorporated into the diet, and testing begun on a new food. As always, in an elimination diet, it is important not to eat too much of any one food.
Assuming the diet is effective, and you discover what foods or additives cause the problems, then you have to decide on a plan of action. Again, you should discuss this with your doctor. Avoiding the foods in question may be quite difficult, especially at school or with friends, and you may wish to reconsider other options, especially if your child is not affected all that severely or if he reacts to a great many foods. Drugs are one option, and you should discuss the pros and cons of these with your doctor. Another, more controversial form of treatment, is neutralization therapy. Although this is not accepted widely among the medical profession, there are many reports of it being used successfully for the treatment of hyperactive children. If you decide on avoidance of the food, bear in mind that the child’s sensitivity may disappear in time. The culprit foods should be retested at one- or two-yearly intervals, to see if they still produce the same symptoms.
*281\180\8*
Posted in
Allergies Tags:
Allergies
IgE molecules are just as specific for their antigen as other antibody isotypes but they operate in a rather different way. Their main function is to defend the body against parasites such as ringworms and flukes – these are much larger than bacteria and viruses so the body has different strategies for killing them. In the tropics, where parasites are common, quite high levels of IgE may be found even in non-allergic people. Cooler conditions are not as favourable to parasites and they are far less of a health problem – in non-allergic people living in temperate climates, the level of IgE is usually very low.
Like other antibodies, IgE molecules are produced by B cells. But once they have been produced, the IgE molecules behave difference from most other antibodies in that they attach themselves to mast cells and basophils. These two types of cell look slightly different under the microscope, and whereas basophils are found floating in the blood, mast cells are embedded in the solid tissues of the body. Mast cells are better known and understood, so we will conveniently ignore the basophils from here onwards: the two types of cell probably work in much the same way.
Although the stem of the IgE molecule is attached to the mast cell, the antigen-binding sites are still free. So when the right, antigen comes along, it will bind to the IgE molecules. This is the signal the mast cell has been waiting for. Packets of chemicals inside the cell are suddenly released to the outside, where they act as messengers, causing major changes in the cells and tissues around them.
*32\180\8*
Posted in
Allergies Tags:
Allergies