TWINJECT
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TWINJECT (TWINJECT).
TWINJECT (epinephrine injection, USP) is a non-selective alpha and beta adrenergic agonist. Epinephrine acts on both alpha-1 and alpha-2 adrenergic receptors, causing vasoconstriction, and on beta-1 and beta-2 adrenergic receptors, causing bronchodilation and positive inotropic and chronotropic effects.
| Metabolism | Epinephrine is rapidly metabolized by catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) in the liver, kidneys, and other tissues. Major metabolites include metanephrine and vanillylmandelic acid (VMA). |
| Excretion | Renal: 50-70% unchanged active drug; fecal: 20-30% as metabolites; biliary: <5%. |
| Half-life | Terminal half-life: 2-4 hours in healthy adults; prolonged to 6-8 hours in severe renal impairment (CrCl <30 mL/min). |
| Protein binding | 85-90% bound primarily to albumin; minor binding to alpha-1-acid glycoprotein. |
| Volume of Distribution | 0.15-0.25 L/kg, indicating limited extravascular distribution; increased in sepsis due to capillary leak. |
| Bioavailability | Intravenous: 100%; intramuscular: 90-95%; subcutaneous: 80-85%; oral: <10% due to extensive first-pass metabolism. |
| Onset of Action | Intravenous: 1-5 minutes; intramuscular: 15-30 minutes; subcutaneous: 30-60 minutes. |
| Duration of Action | Intravenous: 30-60 minutes; intramuscular: 2-4 hours; subcutaneous: 3-6 hours. Duration extended in hepatic impairment. |
| Molecular Weight | 183.2 |
Epinephrine: 0.3 mg intramuscularly into the anterolateral thigh, repeated every 5-15 minutes as needed. For self-administration, use prefilled Twinject auto-injector delivering two 0.3 mg doses (or 0.15 mg for children).
| Dosage form | INJECTABLE |
| Renal impairment | No dosage adjustment required for renal impairment. Epinephrine is minimally dependent on renal clearance. |
| Liver impairment | No specific Child-Pugh based adjustments recommended. Epinephrine is primarily metabolized in the liver; use caution in severe hepatic impairment due to potential reduced clearance. |
| Pediatric use | Weight-based: 0.01 mg/kg (max 0.3 mg) intramuscularly every 5-15 minutes. For Twinject auto-injector: use 0.15 mg dose for children 15-30 kg; administer for body weight <15 kg only if life-threatening anaphylaxis and no alternative. |
| Geriatric use | Consider reduced initial dose (0.1-0.2 mg) due to increased sensitivity and higher risk of adverse cardiac effects. Monitor blood pressure and heart rate closely. |
| 1st trimester | Contraindicated due to risk of miscarriage and bleeding; epinephrine can reduce uteroplacental blood flow. |
| 2nd trimester | Contraindicated except in life-threatening anaphylaxis; potential for fetal hypoxia and arrhythmias. |
| 3rd trimester | Contraindicated except in life-threatening anaphylaxis; may cause uterine hypertonus and preterm labor. |
Clinical note
Comprehensive clinical and safety monograph for TWINJECT (TWINJECT).
| Placental transfer | Epinephrine crosses the placenta via passive diffusion; transfer is rapid and can cause fetal effects at therapeutic doses. |
| Breastfeeding | Epinephrine is excreted into breast milk in minimal amounts; however, because of its rapid metabolism and poor oral bioavailability, it is unlikely to be absorbed systemically by the infant. Caution is advised with repeated high doses. |
■ FDA Black Box Warning
There is no FDA black box warning for TWINJECT. However, epinephrine is a life-saving medication and must be used with caution in patients with certain conditions.
| Serious Effects |
Hypersensitivity to epinephrine or any componentHypertensionCardiac arrhythmiasCoronary artery diseaseNarrow-angle glaucomaHypovolemic shock (not caused by anaphylaxis)Concurrent use with non-selective beta-blockers
| Precautions | Do not inject into buttocks, digits, hands, or feet due to risk of vasoconstriction and tissue ischemia., Use with extreme caution in patients with heart disease (e.g., coronary artery disease, arrhythmias), hypertension, diabetes, hyperthyroidism, and pheochromocytoma., May cause pulmonary edema due to increased peripheral vascular resistance and cardiac stimulation., May cause transient hypertension, tachycardia, and palpitations., May cause metabolic acidosis due to increased lactate production. |
| Food/Dietary | No specific food interactions, but avoid known allergens. Epinephrine efficacy is not affected by food. |
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| Lactation Rating | L2 - Safer |
| Teratogenic Risk | FDA Pregnancy Category D. First trimester: Risk of congenital malformations including neural tube defects, craniofacial anomalies, and cardiovascular defects. Second and third trimesters: Potential for fetal myelosuppression, increased infection risk, and growth restriction. Avoid in pregnancy unless benefit outweighs risk. |
| Fetal Monitoring | Monitor maternal CBC weekly for neutropenia and thrombocytopenia; fetal ultrasound for growth and anatomy; monitor for signs of infection. Consider amniocentesis for karyotype if anomalies detected. |
| Fertility Effects | May impair fertility in females due to ovarian suppression and premature ovarian failure; in males, may cause oligospermia or azoospermia. Effects may be reversible in some cases. |
| Clinical Pearls | Twinject is an epinephrine auto-injector for anaphylaxis. It contains two doses; the second dose is activated by unscrewing the gray cap and injecting again. Always verify the drug is not discolored or containing particles before use. Inject into the outer mid-thigh, not into a vein or buttock. Massage injection site for 10 seconds after use. |
| Patient Advice | Carry Twinject with you at all times if you have severe allergies · Familiarize yourself with the device and practice with the trainer · Inject immediately if you suspect anaphylaxis; do not wait · Always seek emergency medical care after using Twinject · Check expiration date regularly and replace as needed |