Allergy versus side effects: The Confusion Must Stop (FL INITIAL Autonomous Practice - Pharmacology)

Anaphylactic Reactions are immunologically-mediated instead of reactions secondary to drug interactions, drug overdose, direct toxicity, or pharmacologic idiosyncrasies (Cosco et al., 2017). Anaphylaxis is a type 1 immediate hypersensitivity reaction. Type 1 reactions are IgE-mediated and produce responses in end organs such as urticaria in the skin, angioedema and bronchospasm in the respiratory system, vasodilation, and increased capillary permeability in the cardiovascular system (Cosco et al., 2017).

On the other hand, anaphylactoid reactions can have an identical clinical response, but they are not mediated by IgE or an antigen-antibody process (Cosco et al., 2017). Examples of anaphylactoid reactions include hypersensitivity to radiocontrast dye and angiotensin-converting enzyme inhibitors. Anaphylactoid reactions tend to activate the complement system. The complement system is usually activated in one of two pathways, the classical pathway or the alternative pathway. The classical pathway is initiated through IgG or IgM. The alternative pathway is mediated by endotoxins or directly by the allergen, such as the drug in question. Anaphylactoid reactions cannot be predicted with pretesting; Only IgE-mediated reactions can be predicted with pretesting (Cosco et al., 2017).

Patients with a past medical history of atopic conditions such as eczema, asthma, and seasonal allergies do not have an increased risk of anaphylactic reactions. However, they have an increased risk of having more severe reactions.

When an allergen binds IgE antibodies on the surface of basophils and mast cells, eosinophilic chemotactic factors and histamine are released from storage granules in the cell (Cosco et al., 2017). Once this happens, other chemical mediators are rapidly synthesized and released, such as kinins, platelet-activating factors, adenosine, and leukotrienes, which are slow-acting reactants involved in anaphylaxis (Cosco et al., 2017). Clinically, the patient experiences the first wave of symptoms, usually vasodilation and a sense of imminent doom (Cosco et al., 2017).

In a sensitized patient, the onset of signs and symptoms can be experienced almost immediately, but it may be delayed by 2 to 15 minutes (Cosco et al., 2017). Occasionally the allergic reactions can be delayed by up to two and a half hours after exposure to the allergen. Mast cell activation and proliferation promote the production of cytokines which perpetuate the allergic reaction even after the allergen is no longer present, lasting up to 6 to 8 hours. The clinical symptoms of an allergic reaction to a drug may vary widely. A generalized allergic reaction may appear similar to serum sickness reactions or immune-complex reactions.

Serum sickness and serum sickness-like reactions occur approximately 7-10 days after the primary exposure to an allergen, in this case, the drug, and are characterized by urticaria (hives), polyarthralgia (joint pain involving multiple joints), fever, and lymphadenopathy (swollen lymph nodes) (Rowe & Gaeta, 2016). Occasionally the patients may have systemic venalities’ (inflammation of the veins during intravenous drug administration), which may progress into a full-blown systemic vasculitis.

Serum sickness and serum sickness-like reactions can also occur after secondary exposure to heterologous proteins (classic serum sickness) or after secondary exposure to non-protein drugs such as sulfa-based drugs or penicillin-based antibiotics (serum sickness-like reactions) (Rowe & Gaeta, 2016).

Most transfusion reactions occur due to the formation of immune complexes, which usually result in serum sickness. Transfusion-based allergic reactions usually occur secondary to IgE and IgG antibodies against IgA and mast cell-mediated reactions. Angioedema is initiated by histamine release, but its effects are sustained by peptide kinins unaffected by antihistamines (Katzung, 2015).

Some patients are more susceptible to the release of histamines and other immunologic mediators with the administration of certain drugs. Some believe that there are environmental and hereditary factors that contribute to this predisposition to allergic reactions (Cosco et al., 2017).

First-generation antihistamines are commonly used over-the-counter drugs for the management of allergic conditions. However, they commonly have sedative effects and, as such, second-generation antihistamines (H1 antagonists) are increasingly more frequently used.

Antihistamines are often the first drugs used to prevent or treat allergic reactions. In allergic rhinitis, the H1 antagonists are used after the administration of intranasal steroids. In urticaria, histamines are responsible for mediating the allergic response. For that reason, antihistamines are the drug of choice. In urticaria, antihistamines tend to be more effective if they are administered before exposure to the allergen (Katzung, 2015).

In asthma, there are multiple mediators of allergic reactions; therefore, antihistamines are mostly ineffective (Katzung, 2015). In patients with atopic dermatitis, antihistamines are usually administered for their sedative effects to reduce the patient’s awareness of itching.

In some cases, such as anaphylactoid reactions to intravenous contrast agents, pretreatment with antihistamines (diphenhydramine) has been shown to prevent or ameliorate the reaction (Katzung, 2015).

• Obtain a thorough medical history, including an updated allergies list with the reported reaction
• Premedicate patients with any risk of an anaphylactoid reaction (antihistamines, steroids, and iv fluids)
• In cases when the diagnosis is unclear, blood levels of chemical mediators, especially tryptase, can be used to clarify the diagnosis

Factors that affect the extent to which an allergic reaction manifests include the following: the amount of the allergen, the route of entry (oral versus dermic versus intravenous), the persistence of the antigen, and the end-organ response to vasoactive mediators.

Other signs and symptoms of allergic reactions are nausea, vomiting, diarrhea, and colicky abdominal pain (gastrointestinal manifestations), dyspnea, wheezing and chest tightness (respiratory manifestations), and peripheral vasodilation, hypotension, and tachycardia (cardiovascular manifestations) (Cosco et al., 2017).

Patients who present with severe wheezing, hypotension, stridor, hoarseness of voice, and shortness of breath should be treated as a medical emergency (Cosco et al., 2017). The primary focus is to secure the airway and cardiopulmonary resuscitation. Patients who respond to treatment immediately should be observed as inpatients for 24 hours. Those who respond to therapy more slowly or inadequately should be observed in an intensive care unit, where they are generally intubated for any severe laryngeal edema. Occasionally, the patients may have severe hypotension refractory to the treatment, thereby warranting intensive care monitoring (Cosco et al., 2017).

Although the mechanism of allergic reactions remains the same in outpatient and inpatient settings, certain triggers are specific to a hospital setting, such as latex. Additionally, in the hospital setting, intravenous medications are more frequently administered, and they have been linked to more service allergic reactions compared to oral ingestions.

Mrs. Tabe is admitted to a medical/surgical unit with Congestive Heart Failure (CHF) and pneumonia. You are the nurse completing the admission and initial assessment. Upon reviewing her medical record, you note that she has an allergy to sulfa drugs and morphine. What are the missing components of her allergy history? How would you proceed to clarify her allergy history?

Nurses play a critical role in obtaining and verifying allergy histories. As such, a thorough and detailed approach is necessary. In some cases, the patient may need to be educated about the difference between side effects and allergies, as detailed in the case above. It is important to enter a note in the medical record explaining details in the allergy history before updating the clinical record.

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