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Allergies to medicines

26. 3. 2009

A true drug allergy is sometimes difficult to distinguish from other reactions, such as toxic effects, overdose, simple intolerance and others. Drug allergy, unlike these other manifestations, is caused by an immune reaction. This can be either immediate, occurring within an hour of the allergen, or delayed.


26.3.2009

Even medicines can trigger an allergic reaction

The immediate reaction is caused by "allergic" antibodies of the IgE class. The mechanism of the reaction is the same as in pollen or food allergy. The risk factor for drug allergy is younger age (20-50 years), when immune reactivity is generally higher. Female sex (most likely hormonal influences), hereditary predispositions or chemical properties of the drug also have an influence. A large molecule is easily sensitised, a small molecule binds readily to proteins and is also more easily sensitised in this form.

Previous use of the same drug is also a risk factor. This may sensitise the patient, but sometimes a reaction occurs after the first administration of the drug, due to cross-reactivity of the drug with other allergens that the patient has already encountered in the past. The route of administration also influences the risk of reaction. Direct administration into a vein is more risky; the disease for which the drug is administered may also be a factor. AIDS patients are known to have reactions after sulphonamide administration, and patients with infectious mononucleosis often have reactions after ampicillin antibiotics.

Combinations with other drugs may also increase the risk of an allergic reaction. Cross-reactions to drugs and pollen or mite allergens are not very common. They have mostly been observed only when herbal extracts are administered or when foreign proteins are part of the medication, as is the case with some vaccines or hormones of animal origin.

Various herbal preparations are often used in alternative medicine, which is widely believed to be a 'natural' treatment and therefore free of harmful side effects. Unfortunately, this is not quite true. Both toxic and allergic reactions have been described after administration of, for example, homeopathic remedies. People suffering from pollen or other allergies are more prone to such reactions. For example, sensitisation to Asteraceae, which include the plant Echinacea, often used in homeopathy, or the frequently used chamomile, is common among pollen allergy sufferers.

Natural remedies made from royal jelly may contain traces of pollen, and the same applies to honey, often used in home medicine. Some vaccines are produced on chicken embryos and so contain traces of egg protein. Others may contain admixtures of antibiotics or yeast. If the patient is allergic to these ingredients, vaccines containing them can cause severe reactions.

Other dangers may lurk not in the drugs themselves, but in their adulterants and packaging. Capsules may contain gelatine, dyes, lactose, starch. These adulterants can be a hidden cause of allergic and intolerant reactions to drugs, sometimes causing difficulties in diagnosis.

(van)

Source:

U Lékaře.cz