EpiPen Formulation
The EpiPen auto-injector contains epinephrine (adrenaline) in a 1:1000 concentration (1 mg/mL) as a sterile aqueous solution, with EpiPen delivering 0.3 mg in 0.3 mL and EpiPen Jr delivering 0.15 mg in 0.3 mL. 1
Active and Inactive Ingredients
Each 0.3 mL solution in both EpiPen formulations contains:
Active ingredient:
- EpiPen: 0.3 mg epinephrine
- EpiPen Jr: 0.15 mg epinephrine
Inactive ingredients (identical in both formulations):
- 1.8 mg sodium chloride
- 0.5 mg sodium metabisulfite (as preservative/antioxidant)
- Hydrochloric acid (for pH adjustment)
- Water for Injection
- pH range: 2.2–5.0 1
Chemical Structure and Stability
Epinephrine is chemically designated as (-)-3,4-Dihydroxy-α-[(methylamino)methyl]benzyl alcohol, a sympathomimetic catecholamine. 1 The solution deteriorates rapidly when exposed to air or light, turning pink from oxidation to adrenochrome and brown from melanin formation. Discard the device if the solution appears discolored (pinkish or brown), cloudy, or contains particles. 1
Clinical Dosing Context
The fixed-dose formulations reflect standard anaphylaxis dosing of 0.01 mg/kg intramuscularly, with the 0.15 mg dose designed for children weighing approximately 15 kg (33 lbs) and the 0.3 mg dose for those weighing approximately 30 kg (66 lbs) or more. 2 Both doses are dispensed across nearly the entire pediatric age range in practice, though this creates potential for over- or underdosing in infants and adolescents. 2, 3
Important caveat: The sodium metabisulfite preservative may cause allergic-type reactions including anaphylaxis in susceptible individuals, particularly those with asthma. However, there is no absolute contraindication to epinephrine use in anaphylaxis, as the benefit outweighs this theoretical risk. 1