EPINEPHRINE (AUTOINJECTOR)
Clinical safety rating: safe
Beta-blockers may antagonize cardiac effects and cause severe hypertension Can cause angina and arrhythmias in patients with heart disease.
Acts directly on both alpha- and beta-adrenergic receptors. Alpha effects include vasoconstriction, increased peripheral resistance, and decreased mucosal edema. Beta effects include bronchodilation, positive chronotropic and inotropic cardiac activity, and increased systolic blood pressure.
| Metabolism | Metabolized primarily by catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) in the liver, kidneys, and other tissues. Also undergoes sulfation and glucuronidation. |
| Excretion | Primarily renal (inactive metabolites); 90% renal, 10% biliary/fecal |
| Half-life | 2-3 minutes (phase I rapid redistribution); terminal half-life ~10 minutes |
| Protein binding | 50% bound to albumin and alpha-1-acid glycoprotein |
| Volume of Distribution | 0.2-0.4 L/kg (concentrated in plasma; rapid distribution to adrenergic receptors) |
| Bioavailability | IM: 80-100%; SC: 30-50%; Oral: negligible (<2%) |
| Onset of Action | IM: 2-5 minutes; SC: 5-10 minutes; IV: <1 minute |
| Duration of Action | IM: 20-30 minutes; SC: 30-60 minutes; IV: 5-10 minutes |
0.3 mg intramuscularly (IM) into the anterolateral thigh, repeated every 5–15 minutes as needed for anaphylaxis. Maximum dose: 0.3 mg per injection.
| Dosage form | INJECTABLE |
| Renal impairment | No dose adjustment required for renal impairment; drug is rapidly metabolized and excreted. |
| Liver impairment | No dose adjustment required for hepatic impairment; drug is primarily metabolized by MAO and COMT, which are not significantly affected by liver dysfunction. |
| Pediatric use | Weight <30 kg: 0.15 mg IM (auto-injector) into anterolateral thigh; weight ≥30 kg: 0.3 mg IM; repeat every 5–15 minutes as needed. |
| Geriatric use | Dose same as adults (0.3 mg IM); use with caution due to increased sensitivity and risk of adverse effects (e.g., hypertension, tachycardia, myocardial ischemia). Monitor cardiovascular status. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Beta-blockers may antagonize cardiac effects and cause severe hypertension Can cause angina and arrhythmias in patients with heart disease.
| FDA category | Animal |
| Breastfeeding | Minimal excretion into breast milk; M/P ratio not defined. Risk of infant exposure is low. Use with caution; observe infant for tachycardia or agitation. Compatible with breastfeeding for short-term use. |
| Teratogenic Risk | Pregnancy Category C. Epinephrine crosses the placenta. Reduced uterine blood flow and fetal hypoxia risk, especially in second and third trimesters due to vasoconstriction. No well-controlled human studies; animal studies show teratogenic effects at high doses. Use only if benefit justifies risk (e.g., anaphylaxis). |
■ FDA Black Box Warning
None
| Common Effects | cardiac arrest |
| Serious Effects |
["Hypersensitivity to epinephrine or any component of the product","Use during labor if maternal blood pressure exceeds 130/80 mmHg","Coronary insufficiency (relative)","Cardiac dilatation (relative)","Narrow-angle glaucoma (relative)","During general anesthesia with halogenated hydrocarbons or cyclopropane (increased risk of arrhythmias)"]
| Precautions | ["May cause severe hypertension, especially in patients with thyrotoxicosis or hypertension","May cause cardiac arrhythmias, myocardial ischemia, and angina","May cause pulmonary edema due to increased afterload","Accidental injection into digits, hands, or feet may result in vasoconstriction and ischemia","Use with caution in patients with cardiovascular disease, diabetes, hyperthyroidism, or pheochromocytoma","May cause transient anxiety, tremor, headache, and palpitations"] |
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| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and uterine activity. Fetal heart rate monitoring (nonstress test or biophysical profile) after administration, especially in third trimester due to risk of placental vasoconstriction and fetal hypoxia. |
| Fertility Effects | No known adverse effects on fertility in humans or animals. Limited data; no specific effects reported. |
| Food/Dietary |
| No clinically significant food interactions. However, patients should avoid common allergens that trigger their anaphylaxis (e.g., peanuts, tree nuts, shellfish, milk, eggs). Maintain a diet that excludes known triggers. |
| Clinical Pearls | Epinephrine autoinjectors (e.g., EpiPen) should be injected into the anterolateral thigh, through clothing if necessary. Use only in the thigh muscle; do not inject into the gluteal or deltoid regions to avoid erratic absorption. After injection, massage the site to enhance systemic distribution. Always prescribe two autoinjectors for patients at risk of anaphylaxis due to possibility of biphasic reaction. Monitor for adverse effects such as tachycardia, hypertension, and pulmonary edema in patients with preexisting cardiovascular disease. Store at room temperature (20-25°C) and protect from light; do not refrigerate or freeze. |
| Patient Advice | Carry two autoinjectors at all times and ensure they are within easy reach. · Use the autoinjector at the first sign of a severe allergic reaction; do not delay. · Inject into the middle of the outer thigh; can be done through clothing. · After injection, hold the needle in place for 3 seconds and massage the area for 10 seconds. · Call emergency services (911) immediately after use, even if symptoms improve. · Seek medical attention for possible second phase of reaction. · Replace the autoinjector before the expiration date. · Store at room temperature; do not expose to extreme heat or cold. · Avoid injecting into fingers or hands; if accidental injection occurs, seek emergency care. · Keep a written action plan and medical alert identification. |