Epinephrine
**Epinephrine** (commonly known as adrenaline) is a potent, endogenous catecholamine produced by the adrenal medulla. It is the primary "fight or flight" hormone of the sympathetic nervous system. In veterinary medicine, it is a critical, life-saving emergency drug used primarily for: * **Cardiopulmonary Cerebral Resuscitation (CPCR):** To restore spontaneous circulation during cardiac arrest (asystole). * **Severe Anaphylaxis:** To rapidly reverse life-threatening allergic reactions by inducing bronchodilation and vasoconstriction. * **Local Anesthesia Adjunct:** Added to local anesthetics (like lidocaine) to induce local vasoconstriction, thereby delaying systemic absorption, prolonging the anesthetic effect, and reducing bleeding at the site. > **Clinical Pearl:** Epinephrine is highly potent and has a very narrow therapeutic index. Extreme care must be taken to ensure the correct concentration is used. **Never confuse the 1:1,000 (1 mg/mL) concentration with the 1:10,000 (0.1 mg/mL) concentration.**
Mechanism: Epinephrine is a direct-acting, non-selective adrenergic agonist that stimulates both alpha (ฮฑ) and beta (ฮฒ) receptors via G-protein coupled pathways (activating **adenylyl cyclase** โ โ **cAMP**). * **ฮฑ1-receptors:** โ Induces profound smooth muscle contraction and vasoconstriction, increasing systemic vascular resistance and blood pressure. * **ฮฒ1-receptors:** โ Directly stimulates the heart, increasing both chronotropy (heart rate) and inotropy (contractility), which increases cardiac output and myocardial oxygen demand. * **ฮฒ2-receptors:** โ Relaxes smooth muscle, leading to profound bronchodilation (relieving bronchospasm in anaphylaxis), vasodilation in skeletal muscle, and increased glycogenolysis (raising blood sugar). * **Histamine Antagonism:** Physiologically antagonizes the effects of histamine released during anaphylaxis. *Hemodynamic effects depend on the route and rate of administration:* Rapid IV injection causes direct cardiac stimulation and increased systolic BP. Slow IV infusion produces a modest rise in systolic pressure, a decrease in diastolic pressure, and decreased total peripheral resistance due to dominant ฮฒ2 effects.
Dosing by species
- Anaphylaxis ยท 0.5-1 mL/100 lbs. body weight of 1:1,000 (dilute to 1:10,000 if using IV) ยท SC, IM, IV ยท may be repeated at 15 minute intervals ยท Often used in conjunction with corticosteroids and diphenhydramine.
- Anaphylaxis ยท 0.5-1 mL/100 lbs. body weight of 1:1,000 (dilute to 1:10,000 if using IV) ยท SC, IM, IV ยท may be repeated at 15 minute intervals ยท Often used in conjunction with corticosteroids and diphenhydramine.
- Cardiac resuscitation (asystole) ยท 0.01 mg/kg ยท IV ยท Repeat every 3-5 minutes if no return of spontaneous circulation (ROSC) ยท Part of CPCR protocol after ABCs. Vasopressin may be alternated.
- Cardiac resuscitation ยท 0.1-0.2 mg/kg (high dose) or 0.01-0.02 mg/kg (low dose) ยท IV or IO ยท Repeat at 3-5 minute intervals if no response ยท Low dose generally attempted first.
- Cardiac resuscitation ยท 0.01-0.02 mg/kg (IV) or 0.03-0.1 mg/kg (IT) ยท IV, IT ยท every 3-5 minutes ยท For IT, dilute in 5-10 mL of sterile water or normal saline.
- Neonatal resuscitation (when respiratory support/compressions fail) ยท 0.1-0.3 mg/kg ยท IV or IO
- Anaphylaxis ยท 0.01-0.02 mg/kg ยท IV, IT, IM, SC ยท Dosage may be doubled and given via endotracheal tube if IV line not established. Less severe cases may use IM or SC.
- Anaphylaxis ยท 0.2-0.5 mg (total dose) ยท SC or IM
Routes of administration
Contraindications
- Narrow-angle glaucoma
- Hypersensitivity to epinephrine
- Shock due to non-anaphylactoid causes
- During general anesthesia with halogenated hydrocarbons or cyclopropane
- During labor (may delay the second stage)
- Cardiac dilatation or coronary insufficiency
- Conditions where vasopressors are contraindicated (e.g., thyrotoxicosis, diabetes, hypertension, toxemia of pregnancy)
- Injection with local anesthetics into small appendages (toes, ears, etc.) due to risk of necrosis
Adverse effects
- Anxiety and fear
- Tremors and excitability
- Vomiting
- Hypertension (especially with overdosage)
- Cardiac arrhythmias (especially with pre-existing heart disease)
- Hyperuricemia
- Lactic acidosis (with prolonged use or overdose)
- Tissue necrosis and sloughing at the injection site (with repeated injections or injection into small appendages)
Drug interactions
- Alpha-blockers (phentolamine, phenoxybenzamine, prazosin) ยท May negate the therapeutic effects of epinephrine.
- Alpha-2 agonists (detomidine, dexmedetomidine, xylazine) ยท Do NOT use epinephrine to treat cardiac effects caused by alpha-2 agonists; may worsen hemodynamics.
- General Anesthetics (halogenated hydrocarbons, cyclopropane) ยท Increased risk of developing severe arrhythmias. Propranolol may be used to treat if they occur.
- Antihistamines (diphenhydramine, chlorpheniramine) ยท May potentiate the effects of epinephrine.
- Beta-blockers (propranolol) ยท May potentiate hypertension and antagonize epinephrine's cardiac and bronchodilating effects.
- Digoxin ยท Increased risk of arrhythmias if used concurrently.
- Nitrates ยท May reverse the pressor effects of epinephrine.
- Levothyroxine ยท May potentiate the effects of epinephrine.
- Oxytocic agents ยท Hypertension may result if used concurrently. ยท moderate
- Other Sympathomimetic agents (isoproterenol) ยท Should not be administered together as increased toxicity may result.
- Phenothiazines ยท May reverse the pressor effects of epinephrine.
- Reserpine ยท May potentiate the pressor effects of epinephrine.
Monitoring
- Cardiac rate and rhythm (ECG)
- Respiratory rate and auscultation (especially during anaphylaxis)
- Urine flow (if possible)
- Blood pressure
- Blood gases (if indicated and possible)
Overdose
Clinical signs of overdosage or inadvertent IV administration of SC/IM doses include: * Sharp rises in systolic, diastolic, and venous blood pressures * Cardiac arrhythmias * Pulmonary edema and dyspnea * Vomiting, headache, and chest pain * Cerebral hemorrhages (due to severe hypertension) * Renal failure, metabolic acidosis, and cold skin **Treatment:** Because epinephrine has a relatively short duration of effect, treatment is mainly supportive. If necessary, an alpha-adrenergic blocker (e.g., phentolamine) or a beta-adrenergic blocker (e.g., propranolol) can be used to treat severe hypertension and cardiac arrhythmias. Prolonged periods of hypotension may follow, requiring treatment with norepinephrine.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.