Allergies and Hypersensitivity Reactions!

What are allergies?

Allergies and hypersensitivity reactions are overreactions by the immune system to a foreign substance which is otherwise harmless.

On the PTCB exam, students may be asked questions on allergies, allergens, hypersensitivity classes, or common medicines used to treat allergies. If you have taken PTCB practice test questions, you may already have come across this topic. If not, here we have put together a comprehensive summary of the facts about allergies and hypersensitivity reactions that you need to know.

Allergies are very common.

Many people suffer from allergies – up to 50 million people in the United States suffer from some form of allergy each year. As pharmacy technicians, it’s important that – as a front-line healthcare professional – you understand this illness and what measures and medicines are used to help patients control their symptoms. Let’s begin by learning more about the most common triggers of the allergic response.

Substances that trigger allergic reactions are called allergens.

Common kinds of allergens include:

• Animal sources: pet dander, insect waste, cockroaches
• Medicines: Sulfa-based drugs and penicillin allergies
• Foodstuffs: shellfish, nuts, and milk are among the most typical
• Stings: wasps and bees, as well as mosquitoes
• Spores: spores from fungal growths can spread in the air and cause allergies
• Greenery: pollen is the most common cause of allergies. Not only that, but resins from specific plants – such as poison ivy/oak – are also common, too.
• Fabrics: some people are allergic to latex – often found in condoms or gloves.
• Metals: many people are allergic to metals, such as nickel.

How do allergies form?

Allergies typically do not develop from first exposure to the allergen. Instead, multiple exposures are needed for the body to create antibodies that can then trigger an immune response to future exposures of the allergen.

This process is known as sensitization.

In an allergic response, specific cells – known as mast cells – release histamine.

Antibodies are responsible for breaking down these mast cells and releasing this neurotransmitter into the body.

Symptoms of an Allergy

When histamine is released, it is responsible for allergy symptoms, including:

• Runny nose and eyes
• Sneezing
• Itching
• Abdominal cramps
• Nausea
• Sinus pain
• Shortness of breath
• Wheezing
• Rash
• Cough
• Swelling

Skin allergies often display local symptoms such as rash, eczema, burning sensation, and hives – along with many of the listed symptoms above.

In some cases, an allergic reaction can produce a potentially fatal reaction known as anaphylaxis. In anaphylaxis, the entire body is affected and includes more serious symptoms such as:

• Severe swelling of the mouth and throat, making it difficult to breathe or speak.
• Extensive body rash and itch.
• Extreme weakness and collapsing into unconsciousness due to a rapid reduction in blood pressure (hypotension).

In cases of anaphylaxis, emergency treatment is required.

Allergies have a genetic element, too.

Parents can pass down the allergic response to their children. This does not mean that parents can pass down a specific allergy. For example – if a mother has an allergy to peanuts, it does not mean the child will suffer from a peanut allergy, too.

Instead, it is the susceptibility to a general allergic response that can be passed down.

Coombs and Gell Hypersensitivity Classes

There are many kinds of allergy and they do not all product the same response.

A classification system was created to differentiate between these different kinds of allergic reactions – a system sometimes referred to as the Coombs and Gell hypersensitivity classification system.

In this system, there are 4 types of hypersensitivity allergic reaction:

• Type I – immediate-response to the allergen that does not take hours or days to develop. Examples include asthma reactions and anaphylaxis caused by pollen, insect stings, or certain kinds of food or drug. Most of the common allergies – such as allergic rhinitis (runny nose etc.) – are type 1 reactions.
• Type II – hypersensitivity reaction that can occur with an organ transplant rejection. In this case, the body refuses to accept the donor organ, and any cells which are tagged with IgM or IgG (both types of antibody) are bound for cell destruction. Type II reactions are also seen in conditions such as autoimmune hemolytic anemia, rheumatic heart disease, and thrombocytopenia.
• Type III – referred to as “immune complex” where the complex is formed between the antibody and the antigen. This leads to a series of inflammatory states that damage tissues. Examples include rheumatoid arthritis, lupus, and glomerulonephritis.
• Type IV – referred to as the “delayed” hypersensitivity reaction. Here, it takes several hours or days for the allergic response to manifest. That’s because white blood cells – known as T-helper cells – are involved. Contact dermatitis is the most common example.

To summarize – Type 1 reactions form the vast majority of common allergic reactions to foreign substances; Type 4 reactions are delayed, occurring many hours or days after exposure; whereas Type 2 reactions refer to organ transplant rejection; and Type 3 reactions refer to an antibody-antigen complex that damages tissue in autoimmune conditions such as rheumatoid arthritis.

Medicines used to treat Allergies

Treatment of allergies is symptomatic.

There are many effective medicines that can control symptoms. Medicines are available as either over the counter (OTC) or by prescription. The drug of choice depends on the symptoms the patient displays and their severity.

Medicines used to treat allergies and hypersensitivity reactions include:

• Antihistamines – loratadine, desloratadine, cetirizine, levocetirizine, fexofenadine, chlorpheniramine, diphenhydramine.
• Corticosteroids
• Cromolyn sodium – which works to stabilize mast cells, thereby preventing release of histamine.
• Decongestants – such as pseudoephedrine found in medicines such as Sudafed and oxymetazoline, found in medicines such as Afrin.
• Antileukotriene agents – such as the drug montelukast found in the medicine Singulair. Leukotrienes are substances produced by the immune system which, when released by cells in the body, cause inflammation, bronchoconstriction, and mucus secretion.

Severe or life-threatening emergency allergies are treated using an epinephrine shot – which is found in medicines such as EpiPen or Twinject. IV fluids and corticosteroids may also be required as part of the treatment plan once the patient has stabilized from the anaphylactic response.

Review

For the PTCB exam, students should have a working knowledge of:

• The definition of an allergy
• Why allergic reactions take place
• Symptoms of an allergic response
• Definition and symptoms of anaphylaxis
• Differences between the 4 types of hypersensitivity reaction
• Common medicines used to treat allergies and hypersensitivity reactions

As a pharmacy technician, it is important that you understand the differences between standard allergic symptoms and anaphylaxis, and the means through which allergic reactions take place. Technicians should also know the medicines that are frequently used to treat cough and cold.

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