Title: Allergy Treatments
Key words: antihistamines, H1 receptors, itching, sneezing, redness, corticosteroids, steroids, anti-inflammatory, osteoporosis, sodium cromoglycate, emollients, allergy relief market
Date: Sept 2000
Category: 16. Food Intolerance/Allergy
Author: DJE Candlish
The symptoms of allergic disorders depend on the part of the body that is affected, so the treatment depends, to some degree, on the condition involved. Anti-histamines, however, are useful in most allergic conditions, because histamine is so important as a cause of symptoms.
Anti-histamines do not prevent the release of histamine; instead they compete with histamine for specific histamine receptors on the surface of cells. The receptors involved in allergy are known as H1 receptors. This competitive antagonism effectively blocks the effects of histamine on blood vessels and inflammatory cells and quickly provides relief of symptoms.
Anti-histamines can be taken orally, in the form of tablets or syrups, they can be injected or they can be applied topically, i.e. direct to the skin, in a cream or ointment. There are two groups of anti-histamine, the traditional type and so-called 'second generation', or 'non-sedating' anti-histamines. The traditional anti-histamines have a long history of use with a well-established safety record.
The only important side-effect of the traditional anti-histamines is drowsiness or sedation. There is a wide degree of variation in this effect between the different drugs in the group. There is also a wide variation from individual to individual in the sedative effects of any one of these drugs.
Traditional histamines include:
Clemastine, diphenhydramine, promethazine, trimeprazine, dimenhydrinate, cyclizine, mequitazine and chlorpheniramine
Of these, chlorpheniramine, cyclizine and mequitazine are described in the British National Formulary No. 30 Sept 1995 as the least sedating and promethazine, trimeprazine and dimenhydrinate the most sedating.
The second generation anti-histamines are:
Acrivistine, astemizole, cetirizine, loratidine and terfenadine.
These cause less sedation than the traditional anti-histamines. Concerns over the safety of both terfenadine and, to a lesser extent, astemizole have been raised recently, however.
A minor side-effect of both the traditional and the newer anti-histamines is mild anti-cholinergic activity. This may cause dry mouth, blurring of vision and constipation in some people.
Efficacy in Allergic Conditions
In hay fever, anti-histamines stop or reduce the itching and sneezing and help dry up the running nose. They are less effective in relieving a blocked nose. The antihistamines are usually given in the form of tablets for hay fever. These can take several hours from the first dose to reach effective concentrations in the blood and the affected tissues of the nose.
Anti-histamines can help relieve the itching, watering and redness of the eyes in hay fever and allergic conjunctivitis. Anti-histamines can also be applied topically in the form of eye drops. In this form, however, they can only be used for short periods as they may themselves cause sensitisation in atopic individuals.
For asthma, anti-histamines are less effective, as the smooth muscle contraction and much of the inflammation are not dependent on histamine.
For skin conditions, traditional anti-histamines like chlorpheniramine are extremely effective in reducing itch, especially in urticaria. They are particularly effective when taken at night, as the mild sedation they can cause in some people enables them to have an undisturbed night's sleep. For mild skin rashes, where the skin is unbroken, an anti-histamine cream can help relieve itching and inflammation.
Evidence for the effectiveness of the newer anti-histamines in skin conditions is at best contradictory and some studies have indicated that they are of little benefit. For insect bites and stings, a small amount of an anti-histamine preparation applied to the skin helps reduce the inflammatory response and relieves itching. Oral anti-histamines may be more effective if the bites or stings affect large areas of the skin. The sedative effects of the traditional anti-histamines may also be useful in helping sufferers sleep.
Synthetic corticosteroids have very potent anti-inflammatory effects and can be extremely useful in the treatment of allergic disorders. They also have potentially dangerous side-effects and should therefore be used with care. Most steroids are only available with a doctor's prescription.
Corticosteroids can be taken as tablets or applied topically in the form of creams, ointments, nasal sprays, asthma inhalers or eye drops and ointments.
For hay fever, steroids are usually taken in the form of low-dose nasal sprays, which both relieve existing symptoms and prevent symptoms recurring. Treatment should start a few days before hay fever symptoms are expected, and should continue throughout the season. Corticosteroid nasal sprays are not recommended for children under 12 years old. When used for the relatively short hay fever season, these products are considered safe and effective.
For perennial allergic rhinitis, there is still some debate about their safety in the long term. Some of the dose administered to the nasal lining is absorbed and can cause systemic effects. Oral steroids are best avoided for the same reason, unless the condition is severe, when they may be given in short courses.
The potential systemic effects of steroids include:
· weight gain
· osteoporosis (weakening of the bones)
· retarded growth in children
· delayed wound healing
· skin atrophy (wasting)
· reduced resistance to infection
Steroid eye drops can be used for severe allergic inflammation of the eye but they are not normally used for hay fever. The main danger in their use is that they can interfere with local immune defences. This can allow bacteria to cause secondary infections or worsen viral and fungal infections (if present). Other risks include thinning of the cornea and raised intraocular pressure.
Steroids, particularly inhaled steroids, are the mainstay of treatment for asthma as they deal with the inflammation present in the airways, regardless of its cause. This reduces the secretion of mucus and the swelling of the lining of the airways, which cause the sufferer's breathing difficulties. Another type of medication, called a bronchodilator, may also be needed to relieve the airway smooth muscle constriction that also occurs in asthma.
For skin conditions, steroids are also extremely effective, usually applied topically as cream or ointment. A wide range of steroids with different potencies is available. Because of the risk of skin atrophy and secondary infection, the weakest concentration of the mildest possible steroid should always be used. Steroids reduce the swelling, itching and overall inflammation of the affected skin in all forms of atopic skin disease.
Sodium cromoglycate was developed from a naturally occurring compound present in a plant called khellin (Ammni visnaga). Its mode of action is not fully understood, but it is known to stabilise mast cells when applied direct to the affected tissue. This prevents the release of inflammatory mediators (including histamine). Sodium cromoglycate is not absorbed when taken orally. It can only be applied direct to the tissue as a spray or in drops.
Sodium cromoglycate nasal sprays and eye drops should be used for the prevention of the symptoms of hay fever. Treatment should start before the season begins and must be taken regularly throughout the season to avoid symptoms occurring. Even when symptoms have developed, sodium cromoglycate prevents further mediator release and so is useful in resolving established symptoms.
Cromoglycate's outstanding safety record allows it to be used in all age groups. However, cromoglycate eye drops should not be used by people who have glaucoma or who wear contact lenses.
Cromoglycate has no place in the treatment of atopic skin conditions except where these are known to be due to food allergy. Oral administration of cromoglycate has been shown to help some patients in this situation, presumably by an effect on the lining of the digestive tract.
Emollients are fats and oils that are used in the treatment of atopic skin disorders. They have a soothing and softening effect when applied to the skin and also help the skin to retain moisture. This can be helpful in the treatment of skin inflammation.
Emollients are also used as the base for ointments and creams containing other active ingredients, such as steroids and antibiotics.
Emollient skin preparations can contain vegetable oils, animal fats (such as lanolin [wool fat]), paraffin and related chemicals and waxes.
The Allergy Relief Market
The use of allergy relief products has grown dramatically in recent years, for a number of reasons. The most important of these is the increasing incidence of allergic disorders. In 1996, the British Allergy Foundation stated that:
"Over the last 30 years, there has been an extraordinary increase in all allergic diseases and this world-wide increase is showing no signs of slowing."
Awareness of allergies is also increasing, both among the healthcare professions and the public. The importance of house dust mites as a major allergen in atopic diseases in the developed world has become widely accepted and food allergy is increasingly recognised as being the cause of many previously unexplained allergic symptoms.
Not only are more individuals being affected by hay fever, but also the hay fever season itself appears to be extending year on year. This may be due to increased pollution and poorer air quality or other environmental factors, as yet unknown.
At the same time there is a drive towards making individuals take more responsibility for their health, as represented by the Health of the Nation report produced by the last government in 1992. This was intended to drive a change in individual and group behaviour towards healthier lifestyles. Linked to this was the increase in products allowed to move from prescription only status (POM) to pharmacy sale (P), encouraging consumers to self-medicate. GPs are also recommending OTC products more frequently, as part of a drive to reduce the NHS drugs bill.
These factors have combined to nearly double the size of the allergy relief market in the UK over the past four or five years. In 1996, it was estimated to be worth nearly £30 million.