Can you provide a detailed explanation of each medication, beginning with epinephrine?

Epinephrine: Detailed Medication Overview for Anaphylaxis

Epinephrine is the first-line, life-saving medication for anaphylaxis and must be administered immediately—it is nearly always effective when given promptly, while delayed administration is associated with fatality. 1

Why Epinephrine is the Drug of Choice

Epinephrine works through multiple critical mechanisms that directly reverse the pathophysiology of anaphylaxis:

• α1-adrenergic effects: Causes vasoconstriction, reversing hypotension and shock
• β1-adrenergic effects: Increases cardiac output and heart rate (positive inotropy and chronotropy)
• β2-adrenergic effects: Produces bronchodilation, relieving airway obstruction
• Mast cell stabilization: Prevents further release of inflammatory mediators 2

No other medication possesses this comprehensive profile of actions needed to treat anaphylaxis. Antihistamines and glucocorticoids lack vasoconstrictive, bronchodilatory, ionotropic, and mast cell stabilization properties 2.

Dosing and Administration

In Healthcare Settings:

• Dose: 0.01 mg/kg intramuscularly (IM)
  • Maximum: 0.3 mg in prepubertal children
  • Maximum: 0.5 mg in teenagers and adults 1
• Route: IM injection in the mid-outer thigh achieves peak concentrations promptly and is safer than IV bolus 1

In Community Settings (Autoinjectors):

• 0.15 mg dose: For patients weighing 7.5-25 kg (16.5-55 lbs)
  • Although not ideal for those <15 kg, this is preferred over delayed or inaccurate dosing 1
• 0.3 mg dose: For patients ≥25 kg (≥55 lbs) 1

Repeat Dosing:

• Administer every 5-15 minutes for persistent anaphylaxis 3
• Treatment should never be withheld for ongoing symptoms 2
• After 2-3 doses, prepare IV epinephrine infusion for refractory cases 3

Physical Properties and Storage

Epinephrine (adrenaline) is supplied as a clear, colorless, sterile solution at 1 mg/mL concentration 4. The solution contains:

• 1 mg epinephrine per mL
• Sodium chloride, sodium metabisulfite, tartaric acid, and other stabilizers
• pH range: 2.2-5.0 4

Critical storage requirements 4:

• Store at 20-25°C (68-77°F)
• Protect from light and freezing
• Epinephrine deteriorates rapidly when exposed to air or light, turning pink (oxidation to adrenochrome) then brown (melanin formation) 4
• Do not use if colored, cloudy, or contains particulate matter 4
• Multi-dose vials must be discarded 30 days after initial use 4

Timing is Critical

The onset of action for epinephrine is rapid when given IM, while antihistamines take 30-120 minutes to reach peak plasma concentrations and require an additional 60-90 minutes for tissue diffusion—far too slow for the rapid, potentially fatal progression of anaphylaxis 2.

Delayed epinephrine injection is associated with poor outcomes including death, while prompt injection is nearly always effective 1, 5.

What Epinephrine is NOT Replaced By

Antihistamines:

• Only treat cutaneous symptoms (urticaria, pruritus, flushing)
• Poorly effective for cardiovascular and respiratory symptoms (hypotension, bronchospasm)
• Too slow onset of action for acute anaphylaxis
• Should never be given before or instead of epinephrine 2, 1

Glucocorticoids:

• Work through slow genomic mechanisms (hours to days)
• No proven role in acute anaphylaxis treatment
• May reduce hospital length of stay but do not prevent biphasic reactions
• Should never be given before or instead of epinephrine 2

Bronchodilators (Albuterol):

• Only address bronchospasm
• Do not treat hypotension, shock, or other systemic manifestations
• Provide adjunctive treatment only, never replace epinephrine 1

Patient Positioning

After epinephrine administration:

• Position supine with legs elevated (default position)
• If respiratory distress: Allow patient to sit upright with legs extended and elevated
• Never force a patient flat if they are in respiratory distress 3

Post-Administration Management

All patients require observation in an emergency department after epinephrine use in community settings, not because epinephrine is dangerous, but to monitor the anaphylactic episode itself 1.

Standard observation period is 4-6 hours, though recent evidence suggests biphasic reactions occur either within 150 minutes or many hours later (10-33 hours), questioning the utility of fixed observation periods 6.

Who Needs an Epinephrine Autoinjector Prescription

Prescribe autoinjectors for all patients who have experienced anaphylaxis and may re-encounter their trigger in community settings 1. High-risk patients without prior anaphylaxis may also warrant prescription in specific circumstances 1.

Autoinjectors should be prescribed with written, personalized emergency action plans that prioritize: calling 911, injecting epinephrine, and proper positioning 1.

Common Pitfalls to Avoid

1. Waiting to see if symptoms resolve: Delayed administration kills—give epinephrine immediately when anaphylaxis is suspected
2. Giving antihistamines or steroids first: These are adjunctive only and waste critical time
3. Using IV epinephrine as first-line: IM is safer and achieves adequate concentrations promptly 1
4. Underdosing or failing to repeat doses: Epinephrine can be given every 5-15 minutes as needed 5, 3
5. Using discolored epinephrine: Pink or brown solutions are oxidized and ineffective 4