Biphasic

Biphasic Reaction
Synonyms	N/A
Pronounce	N/A
Specialty	N/A
Symptoms	Initial allergic reaction followed by a second phase of symptoms
Complications	Anaphylaxis
Onset	Minutes to hours after initial reaction
Duration	Can last several hours
Types	N/A
Causes	Allergic reactions, often to foods, medications, or insect stings
Risks	Previous allergic reactions, asthma
Diagnosis	N/A
Differential diagnosis	N/A
Prevention	N/A
Treatment	Epinephrine, antihistamines, corticosteroids
Medication	N/A
Prognosis	Good with prompt treatment
Frequency	Varies
Deaths	N/A

Overview

A biphasic reaction is a type of allergic reaction that occurs in two distinct phases. The first phase is the initial allergic response, which can range from mild to severe. The second phase occurs after a symptom-free interval and can vary in severity. Biphasic reactions are most commonly associated with anaphylaxis, a severe and potentially life-threatening allergic reaction.

Pathophysiology

Biphasic reactions are thought to occur due to the complex interplay of immune system mediators. During the initial phase, exposure to an allergen triggers the release of histamine and other inflammatory mediators from mast cells and basophils. This leads to the classic symptoms of an allergic reaction, such as urticaria, angioedema, and bronchospasm.

The second phase of a biphasic reaction is believed to be due to the continued release or delayed release of inflammatory mediators, or the recruitment of additional immune cells to the site of the reaction. This can result in a recurrence of symptoms after a period of apparent resolution.

Clinical Presentation

The clinical presentation of a biphasic reaction can vary widely. The initial phase typically occurs within minutes to hours of exposure to the allergen and can include:

• Hives (urticaria)
• Swelling (angioedema)
• Difficulty breathing (bronchospasm)
• Hypotension
• Gastrointestinal symptoms such as nausea, vomiting, or diarrhea

The second phase can occur anywhere from 1 to 72 hours after the initial reaction, although it most commonly occurs within 8 to 10 hours. Symptoms of the second phase can be similar to or different from the initial phase and can range from mild to severe.

Diagnosis

The diagnosis of a biphasic reaction is primarily clinical, based on the history of exposure to a known allergen and the characteristic two-phase pattern of symptoms. It is important to differentiate biphasic reactions from protracted anaphylaxis, where symptoms persist without a symptom-free interval.

Management

The management of biphasic reactions involves the treatment of both the initial and second phases of the reaction. Immediate treatment of the initial phase typically includes:

• Administration of epinephrine
• Antihistamines to reduce itching and hives
• Corticosteroids to reduce inflammation
• Oxygen therapy and intravenous fluids for severe reactions

Patients who experience an initial allergic reaction should be observed for an extended period, typically 4 to 6 hours, to monitor for the development of a biphasic reaction. In some cases, longer observation or admission to a hospital may be warranted.

Prevention

Preventing biphasic reactions involves avoiding known allergens and being prepared to treat allergic reactions promptly. Patients with a history of severe allergic reactions should carry an epinephrine auto-injector and be educated on its use.

Prognosis

The prognosis for biphasic reactions is generally good with prompt recognition and treatment. However, severe biphasic reactions can be life-threatening, underscoring the importance of early intervention and appropriate management.

See Also

• Anaphylaxis
• Allergic reaction
• Mast cell

External Links

• American Academy of Allergy, Asthma & Immunology
• American College of Allergy, Asthma & Immunology