What is the immediate treatment for an adult or child experiencing anaphylaxis shock due to a bite?

Immediate Treatment for Anaphylaxis from a Bite

Administer intramuscular epinephrine 0.3-0.5 mg (1:1000 concentration) into the anterolateral thigh immediately—this is the only first-line treatment and must never be delayed or replaced by antihistamines or corticosteroids. 1, 2, 3

Initial Emergency Actions (First 60 Seconds)

Epinephrine Administration:

• Adults and children ≥30 kg: 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) intramuscularly into the anterolateral thigh 2, 3
• Children <30 kg: 0.01 mg/kg (maximum 0.3 mg) intramuscularly into the anterolateral thigh 1, 3
• Repeat every 5-15 minutes as needed if symptoms persist or worsen 4, 1, 2
• The anterolateral thigh is superior to subcutaneous or deltoid administration because it achieves faster and higher plasma levels 1

Positioning:

• Place patient supine with legs elevated (unless respiratory distress prevents this position) 1
• For pregnant women, perform left uterine displacement to avoid aortocaval compression 1

Immediate Supportive Measures:

• Establish intravenous access 1, 2
• Administer supplemental oxygen 1, 2
• Monitor vital signs continuously 2

Fluid Resuscitation (Within First 5 Minutes)

The reduction in preload from vasodilation and capillary leak requires aggressive fluid replacement 1:

• Grade II reactions: Initial bolus of 0.5 L crystalloids 1
• Grade III reactions: Initial bolus of 1 L crystalloids 1
• Repeat boluses as needed, up to 20-30 mL/kg, based on clinical response 1

Second-Line Adjunctive Treatments (ONLY After Epinephrine)

These medications are never substitutes for epinephrine and should only be administered after initial epinephrine dose 1, 2:

Antihistamines (for cutaneous symptoms only):

• H1 antihistamines: Diphenhydramine 25-50 mg IV (or 1-2 mg/kg in children) 1, 2
• H2 antihistamines: Ranitidine 50 mg IV in adults (1 mg/kg in children) 1, 2

Bronchodilators (if bronchospasm persists despite epinephrine):

• Albuterol 2.5-5 mg nebulized in 3 mL saline, repeated as necessary 2

Corticosteroids (to prevent biphasic reactions):

• Methylprednisolone 1-2 mg/kg/day IV every 6 hours 2
• These do not help in acute treatment but may prevent protracted or biphasic anaphylaxis 4, 2

Management of Refractory Anaphylaxis

If symptoms persist after 2-3 doses of intramuscular epinephrine 1, 2:

Intravenous Epinephrine:

• Grade II reactions: 20 μg IV 1
• Grade III reactions: 50-100 μg IV 1
• Grade IV reactions (cardiac arrest): 1 mg IV following ACLS guidelines 1

Epinephrine Infusion (when >3 boluses administered):

• Prepare by adding 1 mg (1 mL) of 1:1000 epinephrine to 250 mL D5W (concentration 4.0 μg/mL) 4, 2
• Infuse at 0.05-0.1 μg/kg/min (or 1-4 μg/min in adults, increasing to maximum 10 μg/min) 4, 1, 2

Alternative Vasopressors:

• Consider norepinephrine, vasopressin, phenylephrine, or metaraminol for persistent hypotension 1

Special Consideration for Beta-Blocker Patients:

• Administer glucagon 1-2 mg IV if patient is on beta-blockers and not responding to epinephrine 1, 2

Post-Anaphylaxis Observation

Observation Period:

• Minimum 6 hours in a monitored area or until stable and symptoms are regressing 1, 2
• Grade III-IV reactions typically require ICU admission 1
• High-risk patients (severe anaphylaxis, required >1 dose epinephrine) may need extended observation up to 6 hours or more 1

Tryptase Sampling:

• First sample at 1 hour after reaction onset 1
• Second sample at 2-4 hours after onset 1
• Baseline sample at least 24 hours post-reaction for comparison 1

Critical Discharge Requirements

Epinephrine Autoinjectors (Mandatory):

• Prescribe two epinephrine autoinjectors before discharge 1
• Dosing: 0.15 mg for 10-25 kg; 0.3 mg for ≥25 kg 1
• For infants >7.5 kg where 0.1 mg autoinjector unavailable, use 0.15 mg dose 1

Written Anaphylaxis Emergency Action Plan:

• Must include common symptoms/signs, clear instructions, and list of known triggers 1
• Include plan for monitoring autoinjector expiration dates 1

Referral:

• Arrange allergist evaluation to identify triggers and assess ongoing risk 1

Critical Pitfalls to Avoid

• Never use antihistamines or corticosteroids as first-line treatment instead of epinephrine—this is the most common fatal error 2, 5
• Never inject epinephrine into buttocks, digits, hands, or feet due to risk of tissue necrosis 3
• Never delay epinephrine administration—delayed epinephrine is directly associated with anaphylaxis fatalities 1, 6
• Never discharge patients too early—biphasic reactions can occur hours later 1, 2
• Never administer IV epinephrine in non-arrest situations without appropriate hemodynamic monitoring 4, 2
• There are no absolute contraindications to epinephrine in anaphylaxis, even in elderly patients with cardiovascular disease 1