An infusion reaction is an adverse event that occurs during or shortly after the intravenous administration of a medication or biological product. These reactions represent the body’s unfavorable response to the drug, which can involve the rapid activation of the immune system or other physiological effects. While often associated with therapies like chemotherapy or monoclonal antibodies, reactions can occur with various infused agents. The severity of these events varies widely, and it is often difficult to predict which patients may experience a reaction.
Recognizing the Signs of a Reaction
Symptoms of an infusion reaction range from mild discomfort to life-threatening emergencies, making quick recognition paramount. Mild reactions often manifest as localized or systemic symptoms such as itching, flushing, urticaria (hives), chills, or fever. These signs may appear 30 to 120 minutes after the infusion begins and sometimes resolve on their own.
Moderate reactions signal a more pronounced systemic response, involving symptoms like chest tightness, shortness of breath, or a significant change in blood pressure. Other signs include back pain, nausea, vomiting, or dizziness. If symptoms progress beyond a mild state, the medical team typically interrupts the infusion and administers supportive medications.
The most severe form of reaction is anaphylaxis, a medical emergency characterized by a rapid onset of life-threatening airway, breathing, or circulation problems. Signs include laryngeal edema (causing a hoarse voice or stridor), severe hypotension, and an inability to breathe. Recognizing these severe symptoms, which can occur within minutes of starting the infusion, is necessary for immediate intervention.
Triggers and Mechanisms of Infusion Reactions
Infusion reactions are broadly categorized based on their underlying biological mechanisms: immunologic and non-immunologic pathways. Immunologic reactions are true hypersensitivity responses, where the immune system mistakenly identifies the infused drug as a threat. These reactions are often mediated by Immunoglobulin E (IgE) antibodies, which trigger the release of inflammatory chemicals like histamine from mast cells. This IgE-mediated response is a classic allergic reaction that can lead to anaphylaxis.
Non-immunologic reactions do not involve IgE antibodies and are related to the direct pharmacological properties of the drug or the rate of infusion. A common example is Cytokine Release Syndrome (CRS), where the medication causes a widespread activation of immune cells. This results in a rapid release of signaling molecules called cytokines, leading to symptoms such as fever, tachycardia, and low blood pressure.
Pseudoallergic reactions are also non-immunologic and occur when the drug directly stimulates immune cells to release mediators like histamine without antibody involvement. While symptoms of immunologic and non-immunologic reactions often overlap, the distinction in mechanism guides the choice of preventative measures and treatment. Non-immunologic reactions are frequently seen with the first dose of certain agents, such as monoclonal antibodies, due to their direct cellular effects.
Immediate Management During a Reaction
When an infusion reaction is suspected, the initial step is to immediately stop the drug infusion to prevent further exposure. Medical staff will then quickly assess the patient’s vital signs, including blood pressure, heart rate, oxygen saturation, and respiratory status. This assessment determines the severity of the reaction and guides the subsequent course of treatment.
For mild-to-moderate reactions, supportive medications are administered to counteract inflammatory chemicals. This typically involves intravenous antihistamines, such as diphenhydramine, to block histamine’s effects. Corticosteroids like dexamethasone may also be given to suppress the inflammatory response and stabilize cell membranes. Oxygen may be applied to support breathing, and IV fluids may be started to manage blood pressure changes.
In cases of severe reactions or anaphylaxis, the immediate administration of epinephrine is necessary, as it acts rapidly to reverse bronchospasm and raise blood pressure. After symptoms have completely resolved (which may take an hour or more), the medical team may cautiously attempt to restart the infusion. Re-initiation is typically done at a significantly slower rate, such as 50% of the rate at which the reaction occurred, with careful monitoring for any return of symptoms.
Strategies for Minimizing Risk
Several proactive steps are taken to reduce the likelihood of an infusion reaction before and during therapy. Premedication is a standard preventative strategy, where patients are given medications prior to the infusion to dampen the inflammatory response. Common regimens include administering an oral or intravenous antihistamine and acetaminophen, which acts as an antipyretic.
Corticosteroids are frequently added to the premedication protocol for specific drugs to further reduce the risk of both immunologic and non-immunologic reactions. Another method involves starting the drug infusion at a very slow rate, allowing for gradual exposure to the medication. If the patient tolerates this initial slow rate, the speed is gradually increased in a process called titration.
A thorough review of a patient’s medical history for previous drug sensitivities or allergies is an important step in risk assessment. Identifying risk factors helps the healthcare team determine the most appropriate premedication strategy and level of monitoring required throughout the treatment. This careful preparation and slow initial rate mitigate the risk, especially during the first few treatment cycles where reactions are most common.