Immunotherapy for allergic asthma
In many people who have asthma, it is closely linked to an allergy. Their asthma attacks are mainly triggered by allergy-causing substances (allergens), such as pollen, dust mites or animal fur. Allergen-specific immunotherapy is a treatment option for this kind of asthma.
The goal of allergen-specific immunotherapy is to reduce allergy symptoms in the medium to long term and to prevent asthma attacks. It has to be repeated regularly and takes quite a long time to start working. This treatment is also known as desensitization. It aims to do exactly that: make the immune system less sensitive. In people who are allergic to something, their body is oversensitive or hypersensitive to an allergen. They produce antibodies to fight the allergen, even though it is harmless. These antibodies are part of a chain reaction that leads to allergy symptoms.
In allergen-specific immunotherapy, people are given allergen extracts to try to train their body to react differently: It’s a bit like being “vaccinated” against your own allergy. The allergen extracts can be injected or taken as tablets or drops.
Which allergies can be treated using allergen-specific immunotherapy?
Allergen-specific immunotherapy can't be used for every allergy. It is called "specific" because the allergen extract has to be tailored to the individual person's allergic response. These allergen extracts aren’t available for every allergy trigger. There are currently allergen extracts that have been approved for the treatment of allergies caused by
It's also possible to do immunotherapy with allergen extracts that haven't been approved – for example, if you're allergic to cats or mold. But unlike with the approved allergen extracts, there's no guarantee that unapproved ones will be effective enough.
What does the treatment involve?
In specific immunotherapy, the person is repeatedly given a very small amount of the allergen. To allow their body to get used to the allergen, only a very small amount of the substance is used at first. This dose is increased gradually until their personal maximum dose is reached, which is then given at regular intervals. It should be as high as possible without causing too much of an allergic reaction. So both the person getting the treatment and the doctor need to watch very carefully for reactions.
There are two types of immunotherapy:
- Subcutaneous immunotherapy (SCIT): The allergens are injected into the skin.
- Sublingual immunotherapy (SLIT): The allergens are given in the form of drops or tablets, and are kept under your tongue (sublingual) for one or two minutes before they are swallowed.
People who have subcutaneous immunotherapy (injections) have to go to the doctor regularly. The allergen is given every week or two at first. Later on it's given less often, usually once a month. The drops or tablets for sublingual immunotherapy are typically taken once a day.
How effective is immunotherapy?
Research has shown that people who have asthma can benefit from allergen-specific immunotherapy. Both treatment approaches – placing the extract solution under the tongue and injecting the extract – can help relieve the symptoms and prevent asthma attacks. Research on subcutaneous immunotherapy (injections) found that:
- Without immunotherapy: Asthma symptoms got worse after a few years in about 60 out of 100 people who did not have immunotherapy.
- With immunotherapy: Symptoms got worse in about 30 out of 100 people who had immunotherapy.
In other words, allergen-specific immunotherapy prevented asthma from getting worse in 30 out of 100 people.
The treatment also had another effect: About 20 out of 100 people who had allergen-specific immunotherapy needed less asthma medication overall.
The effect of allergen-specific immunotherapy can last for several years. It then wears off in some people.
What are the possible side effects?
Mild and temporary side effects are very common in allergen-specific immunotherapy. This is to be expected when a person is given a substance that they are usually allergic to. The likelihood of side effects depends on things like
- how sensitive they are to the allergen,
- how high the dose is, and
- which drug is used.
About 10 to 60 out of 100 people develop a mild skin rash at the site of injection. When allergens are placed under the tongue, itching and swelling in the mouth are common. Up to 50 out of 100 people have allergic reactions such as sneezing, watery eyes or asthma symptoms at least once. Tiredness and headaches can occur too. These side effects are usually mild and temporary. They only rarely need to be treated.
If severe side effects occur, the dose is reduced again. It is then a good idea to rule out other possible causes too. Should other causes of these symptoms be found and treated, the dose might be increased again.
How common are anaphylactic reactions?
The biggest concern is that allergen-specific immunotherapy will cause an extreme allergic response called an anaphylactic reaction (sometimes referred to as "anaphylactic shock"). Among other things, this can lead to severe itching, nausea, breathing difficulties, circulation problems, and may even result in circulatory shock (not enough blood flowing through the body). In the worst case, anaphylactic reactions can be life-threatening. More severe reactions require immediate medical attention. An adrenaline (epinephrine) injection is usually given in order to quickly limit the dangerous overreaction occurring in the body.
Anaphylactic reactions are very rare in people who are otherwise healthy. There are only rough estimates of the risk. In studies, fewer than 1 out of 1,000 people who were given injections had a reaction that needed to be treated with adrenaline. Because of this small risk, precautionary measures are taken: People who are given an allergen extract have to stay at the doctor's office for at least 30 minutes afterwards. Your doctor should describe the symptoms of an anaphylactic reaction to you, and make sure your family is informed too. If you then start showing signs of this reaction, you can seek medical help immediately.
The risk of an anaphylactic reaction is much higher in some people. For instance, certain heart problems can increase the risk, and if you're taking beta blockers it's harder to treat possible side effects. So people with cardiovascular (heart and blood vessel) disease can usually only have allergen-specific immunotherapy if beta blockers can be replaced with other medications. People with severe asthma can have immunotherapy if their asthma is well controlled and stable. If you have had an allergic reaction to an injection in the past, it's important to tell your doctor about it before starting allergen-specific immunotherapy.
Which is more effective: Injections or tablets/drops?
It's not yet possible to say for sure whether one type of allergen-specific immunotherapy is better than the other. Several studies have compared the two treatment approaches with each other. They suggest that injections could relieve the symptoms somewhat more effectively than medication placed under the tongue in the form of tablets or drops. But because the treatment approaches are at least similarly effective, the treatment decision can be based on personal preferences.
Abramson MJ, Puy RM, Weiner JM. Injection allergen immunotherapy for asthma. Cochrane Database Syst Rev 2010; (8): CD001186.
Calderon MA, Alves B, Jacobson M, Hurwitz B, Sheikh A, Durham S. Allergen injection immunotherapy for seasonal allergic rhinitis. Cochrane Database Syst Rev 2007; (1): CD001936.
Lin SY, Erekosima N, Suarez-Cuervo C, Ramanathan M, Kim JM, Ward D et al. Allergen-Specific Immunotherapy for the Treatment of Allergic Rhinoconjunctivitis and/or Asthma: Comparative Effectiveness Review. March 2013. (AHRQ Comparative Effectiveness Reviews; Volume 111).
Normansell R, Kew KM, Bridgman AL. Sublingual immunotherapy for asthma. Cochrane Database Syst Rev 2015; (8): CD011293.
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