EPIPEN JR.
Clinical safety rating: caution
Comprehensive clinical and safety monograph for EPIPEN JR. (EPIPEN JR.).
Epinephrine is a direct-acting sympathomimetic amine that acts on alpha- and beta-adrenergic receptors. Alpha-adrenergic effects include vasoconstriction, which reduces edema and increases blood pressure. Beta-adrenergic effects include bronchodilation, positive inotropic and chronotropic cardiac effects, and inhibition of histamine release from mast cells.
| Metabolism | Epinephrine is metabolized primarily by catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO). The major metabolites are metanephrine and vanillylmandelic acid (VMA). |
| Excretion | Epinephrine is rapidly metabolized in the liver and other tissues by catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO). The metabolites, including metanephrine and vanillylmandelic acid (VMA), are primarily excreted renally. About 85-90% of an administered dose is eliminated in the urine within 24 hours, with less than 5% excreted unchanged. Biliary/fecal excretion is minimal (<5%). |
| Half-life | Terminal elimination half-life is approximately 2-3 minutes following intravenous administration. Clinically, the short half-life necessitates repeat dosing or continuous infusion for sustained effect. After intramuscular injection, absorption is slower, and the effective half-life is longer due to continued absorption. |
| Protein binding | Epinephrine is not extensively bound to plasma proteins; protein binding is approximately 15-20%, primarily to albumin and alpha-1 acid glycoprotein. |
| Volume of Distribution | Volume of distribution is approximately 0.25-0.5 L/kg. This low Vd reflects limited distribution; epinephrine is largely confined to the extracellular fluid and does not extensively enter cells. It reflects rapid uptake into tissues and metabolism. |
| Bioavailability | Intramuscular (deltoid): Bioavailability is approximately 80-100% with rapid absorption. Subcutaneous: Bioavailability is lower (30-50%) due to local vasoconstriction and slower absorption. Oral: Negligible due to extensive first-pass metabolism. Intravenous: 100% (not applicable to EpiPen Jr.). |
| Onset of Action | Intramuscular (deltoid): Onset within 1-2 minutes. Subcutaneous: Onset within 2-5 minutes. Intravenous: Immediate onset within seconds. Intramuscular injection into the thigh (as with EpiPen Jr.) produces faster absorption than subcutaneous administration. |
| Duration of Action | Intramuscular: Duration of action is approximately 20-30 minutes for bronchodilation and cardiovascular effects. Duration may be prolonged in severe anaphylaxis due to delayed absorption. Repeat doses may be required if symptoms persist or recur. |
Epinephrine 0.3 mg intramuscularly in the mid-outer thigh every 5-15 minutes as needed for anaphylaxis.
| Dosage form | INJECTABLE |
| Renal impairment | No dose adjustment required for renal impairment. |
| Liver impairment | No dose adjustment required for hepatic impairment. |
| Pediatric use | Body weight 15-30 kg: Epinephrine 0.15 mg intramuscularly in the mid-outer thigh every 5-15 minutes as needed for anaphylaxis. |
| Geriatric use | Use with caution due to increased risk of cardiovascular effects; same 0.3 mg dose as adults but monitor for hypertension, tachycardia, and myocardial ischemia. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for EPIPEN JR. (EPIPEN JR.).
| Breastfeeding | Epinephrine is excreted into breast milk in minimal amounts (M/P ratio not reported). It has low oral bioavailability and short half-life, making it unlikely to affect the infant. However, due to limited data, caution is advised. |
| Teratogenic Risk | Epinephrine (EpiPen Jr.) is a pregnancy category C drug. Animal studies have shown teratogenic effects (e.g., fetal hypoxia, growth restriction) at high doses, but no adequate human studies exist. First trimester: potential for reduced uterine blood flow and fetal hypoxia. Second trimester: risk of placental vasoconstriction. Third trimester: may induce preterm labor or uterine hypertonus. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to epinephrine or any component of the product","No absolute contraindications in life-threatening anaphylaxis; relative contraindications include concurrent use of beta-blockers (may blunt response) and severe coronary artery disease"]
| Precautions | ["Accidental injection into digits, hands, or feet may cause local ischemia and necrosis","Use with caution in patients with cardiovascular disease, hyperthyroidism, diabetes, hypertension, or elderly patients","May cause transient hypertension, tachycardia, and arrhythmias","Injection site reactions: pallor, coldness, and hypoesthesia"] |
| Food/Dietary | No significant food interactions. Epinephrine is not orally absorbed; dietary restrictions are not required. Avoid concomitant use with non-selective beta-blockers (may attenuate effects) and MAOIs or tricyclic antidepressants (may potentiate arrhythmias), but these are drug interactions, not food. |
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| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and uterine activity during use. Fetal heart rate monitoring is recommended due to risk of hypoxia. Observe for signs of placental insufficiency. |
| Fertility Effects | No well-controlled studies on fertility. High-dose epinephrine may impair uterine blood flow and thereby reduce implantation or pregnancy maintenance, but clinical significance is unknown. |
| Clinical Pearls | For anaphylaxis, administer IM into anterolateral thigh, not deltoid or gluteal. Use needle length appropriate for body habitus to ensure intramuscular delivery. Repeat dose in 5-15 minutes if no improvement. Monitor for hypertensive crisis, especially in patients with CV disease. Epinephrine is first-line for anaphylaxis; antihistamines and corticosteroids are adjunctive, not replacements. |
| Patient Advice | Injection into the outer middle thigh is safe and effective, even through clothing. · Hold the auto-injector in place for at least 3 seconds after activation. · Seek immediate emergency medical care after using the device. · Carry two epinephrine auto-injectors at all times; a second dose may be needed. · Store at room temperature (25°C/77°F), protect from light and freezing. · Check expiration date regularly and replace before expiry. |