The word 'allergic' is often used loosely and has become almost a part of our general conversation. In a way it has become synonymous with 'dislike'. Many ailments which cannot be immediately diagnosed are incorrectly attributed to allergy. In fact, allergy is an unusual response of the body caused by substances like foods, pollens, house dust, feathers, fungus, insecticides, drugs, and chronic infection.

The common allergic diseases are allergic rhinitis and hay fever, and the common cause is pollen. Allergy is due to abnormal antibodies of the IgE type which are formed only in some -susceptible individuals. Normally the antibodies are supposed to be protective. But the abnormal antibodies are fixed on special allergic cells called mast cells and on coming into contact with an allergen such as a pollen, release chemical agents such as histamine, serotonin, and slow-reacting substances. The release of these substances produce symptoms of allergy characterized by a running nose, itching, rash, and breathing difficulty.

Treatment

The management of allergic reactions includes specific treatment aimed at removing the cause, blocking allergic reaction by immuno-therapy, and symptomatic treatment. Some examples of allergen-avoidance are stopping use of such drugs, installation of air filters in air conditioners, keeping pets out of living room and removing dust collecting furniture and carpets.

Specific Treatment

Specific treatment consists of removal of the offending agents. This is done by 'allergen testing'. Various extracts of possible offending agents are available and these are injected into the skin to detect the causative agent. However, in most cases it is difficult to identify the causative agent, but if it is found, desensitization of the individual can be carried out by injecting its doses. It has been found that through desensitization, the abnormal antibodies, that is, the IgE antibodies, are reduced or completely abolished, and protective antibodies, that is, the IgG anibodies are developed.

Symptomatic Treatment

The aim of symptomatic treatment is to check the release or antagonize the action of released chemical mediators of allergic reactions. The most important of these chemical mediators is believed to be histamine. For this reason antihistaminics are employed in almost all cases of allergy. Sometimes decongestants are combined with antihistaminics to enhance effects. Only in extremely severe cases are corticosteroids used.

Uses of Antihistaminics

Besides their use in allergy, antihistaminics are useful for prophylaxis and treatment of motion (travel) sickness and vomiting during pregnancy or following radiation. They are beneficial in the symptomatic treatment of Parkinsonism but ineffective in bronchial asthma. They are quite often used to treat common cold. In this condition anti-cholinergic effects of these drugs afford symptomatic relief by decreasing secretions of nose and respiratory passages.

Adverse Effects: The most common adverse effects are drowsiness and sedation which interfere with daytime activity, mental alertness, and reflex actions. Other side-effects include giddiness, ringing in the ears, weariness, fatigue, loss of appetite, nausea, vomiting, rapid pulse, a slight fall in BP, constipation, abdominal pain, dryness of mouth, urinary hasitancy and blurring of vision. Very high doses may induce fever. These adverse effects are more common in elderly people.

Precautions

Alcohol is forbidden with these drugs as sedation of a dangerous level may occur.

Driving and operating any kind of machine should be avoided after taking these drugs as they cause drowsiness.

If taken after a meal, the intensity of side-effects can be minimized.

Drugs containing chlorcyclizine and meclizine which are also antihistaminic, should not be self used by a pregnant woman. These may cause some adverse effects on the foetus.

Ointments containing these drugs should not be used for a prolonged period; allergic reactions have been found to be more common on local application of these drugs. (At times these anti-allergic drugs, when taken orally or more commonly, when applied on the skin, may cause allergic reaction. Is this not a paradox?)

Other Drugs for Symptomatic Treatment

Ketotifen (Ketovent, Ketotif)

This drug stabilizes the cell membranes of mast cells and thus prevents the release of histamine. Besides having antihistaminic properties, it is useful in preventing an attack of asthma. It does, however, cause drowsiness, a dry mouth, dizziness, nausea and weight gain.

Cromolyn Sodium (Ifiral, Fintal)

Used as eye drops (2%) in allergic conjunctivitis, nasal spray (2%) in allergic rhinitis and metered dose inhaler (1 to 2 mg/puff) in bronchial asthma.

Nedocromil

This drug is used 2 puffs, twice a day, in place of cromolyn.

Topical steroids like flunisolide (SYNTARIS) and budesonide (BUDECORT) are nasal spray.

Non-Sedative Antihistaminics for Symptomatic Treatment

These new generation anti-allergic drugs do not reach the brain and do not produce sedation (cetirizine causes some sedation) which is common adverse effects of all the drugs available in this group. These are therefore used more widely. They do not impair psychomotor activities such as driving and do not enhance effects of alcohol or diazepam. They are useful in allergic rhinitis, allergic conjunctivitis, urticaria, drug allergies and atopic eczema. They are not effective in motion sickness, vertigo and should not be used in pregnancy. These agents are less effective than older drugs in common cold.

Decongestants Used in Symptomatic Treatment

These agents reduce the swelling of mucous membranes (shrinking effect) in allergic diseases by constricting small blood vessels. Some drugs are used by mouth such as pseudoephedrine (PSEUDAFED 60 mg tab) and phenylpropanolamine. The latter is rarely used alone.