Is this anaphylaxis in a 38-year-old female with iron deficiency anemia, chronic hepatitis B, and chronic hepatitis D, taking tenofovir disoproxil and Bulevirtide, who developed malaise, anterior chest pressure, lower abdominal pain, facial flushing, hypotension, chills, and decreased peripheral oxygen saturation after receiving a subcutaneous injection of drug a and drug b?

Yes, This is Anaphylaxis

This patient experienced anaphylaxis based on the acute onset of multisystem involvement (cardiovascular, respiratory, and cutaneous symptoms) occurring within minutes of drug administration, meeting established diagnostic criteria. 1

Diagnostic Criteria Met

This case fulfills the clinical definition of anaphylaxis through multiple criteria:

• Acute onset (1-2 minutes post-injection) with rapid progression of symptoms involving multiple organ systems 1
• Cardiovascular compromise: Hypotension (95/55 mmHg from baseline) represents a mean arterial pressure decrease requiring active treatment 1
• Respiratory involvement: Hypoxemia with SpO2 86% (confirmed at 85% on blood gas analysis) 1
• Cutaneous manifestations: Facial flushing, which is present in approximately 80% of anaphylaxis cases 2
• Additional systemic symptoms: Malaise, chest pressure, abdominal pain, and chills 1

The temporal relationship is critical here—symptoms began within 1-2 minutes of subcutaneous drug administration, which is characteristic of immediate hypersensitivity reactions and strongly supports anaphylaxis diagnosis. 1

Clinical Features Supporting Anaphylaxis

The combination of hypotension with respiratory compromise and cutaneous symptoms within minutes of drug exposure is pathognomonic for anaphylaxis. 3, 2

Key supporting features include:

• Immediate response to epinephrine: The patient's improvement with IM adrenaline 0.3 mL is characteristic of anaphylaxis, as epinephrine is the definitive first-line treatment 1, 4
• Hypoxemia severity: SpO2 of 86% (85% on ABG) indicates significant respiratory compromise, a life-threatening feature of anaphylaxis 1, 2
• Cardiovascular instability: The hypotension requiring fluid resuscitation and epinephrine represents the intravascular volume redistribution characteristic of anaphylactic shock 1

Important Diagnostic Considerations

The absence of urticaria does not exclude anaphylaxis—cutaneous symptoms are absent in up to 20% of cases, particularly in rapidly progressive reactions. 5, 2

This patient presented with:

• Facial flushing (a cutaneous manifestation) but no documented urticaria or angioedema 2
• Predominantly cardiovascular and respiratory symptoms, which is more typical of drug-induced anaphylaxis in adults 6
• Chest pressure and abdominal pain, which are recognized features of anaphylaxis involving smooth muscle contraction 1

The elevated D-dimer (2.17 mg/L) may reflect the systemic inflammatory response and vascular permeability changes that occur during anaphylaxis, though this is not a diagnostic criterion. 1

Differential Diagnosis Exclusions

This presentation is not consistent with vasovagal syncope, which would typically present with bradycardia rather than the hemodynamic instability seen here. 1

Key distinguishing features:

• Vasovagal reaction: Would present with bradycardia, pallor, and diaphoresis without respiratory compromise or flushing 1
• Cytokine release syndrome: Typically occurs hours after drug administration, not within 1-2 minutes 1
• Cardiac event: Serial EKGs showed no clinically significant abnormalities, making primary cardiac etiology unlikely 1

Management Appropriateness

The immediate treatment provided was appropriate and likely life-saving:

• IM epinephrine 0.3 mL was correctly administered as first-line therapy 1, 4
• Supplemental oxygen addressed the hypoxemia appropriately 1, 7
• IV fluid resuscitation (250 mL normal saline) was appropriate for the hypotension, though larger volumes (1-2 L bolus) are often required 1
• Corticosteroids (hydrocortisone 200 mg) were appropriately given after acute stabilization to potentially prevent biphasic reactions 1

Required Follow-Up Actions

This patient requires mandatory referral to an allergy/immunology specialist for comprehensive investigation to identify the causative agent. 1, 5

Essential next steps include:

• Skin testing should be performed once the patient has fully recovered and antihistamine effects have worn off (typically 4-7 days) 1
• Serum tryptase levels should be obtained at 1-2 hours and 2-4 hours post-reaction, with a baseline level at least 24 hours after resolution 5
• Extended observation for minimum 6 hours is appropriate given the severity of this reaction 5
• Documentation of all drugs administered (drug a and drug b) with exact timing must be provided to the specialist center 1
• Patient education on anaphylaxis recognition and provision of self-injectable epinephrine prescription before discharge 5, 2

Risk Factors Present

This patient has several risk factors that may have contributed to the severity:

• Female gender (though males typically have more severe drug-induced anaphylaxis, this patient still experienced significant symptoms) 6
• Drug-induced anaphylaxis carries higher risk for severe cardiovascular symptoms compared to food-induced reactions 6
• Subcutaneous route allows for rapid systemic absorption of the trigger agent 1

The hypokalemia (2.8 mmol/L) likely represents a secondary effect from epinephrine administration and stress response rather than a primary feature of anaphylaxis. 8