Ephedrine

Overview

Ephedrine is a sympathomimetic drug with both alpha- and beta-adrenergic activity, commonly used in veterinary medicine as a vasopressor to manage anesthesia-associated hypotension in dogs and cats. It increases blood pressure by enhancing cardiac output and promoting peripheral vasoconstriction.

Because it stimulates both alpha- and beta-receptors, ephedrine raises blood pressure while also increasing heart rate and cardiac output; in anaesthetized dogs it has been shown to increase mean arterial pressure, cardiac index and systemic vascular resistance. Its duration of action is relatively longer than many other vasopressors when given intravenously.

Mechanism of Action (MOA): Ephedrine acts both directly and indirectly on the sympathetic nervous system. It directly stimulates alpha- and beta-adrenergic receptors and indirectly increases the release of endogenous norepinephrine from presynaptic neurons while reducing its breakdown. These combined effects lead to increased heart rate, cardiac output, and vasoconstriction, resulting in elevated blood pressure. Additional effects include mild central nervous system stimulation, bronchodilation, increased urethral sphincter tone and relaxation of the bladder muscle.

Indications

Ephedrine is primarily used in dogs and cats as a vasopressor and sympathomimetic agent in situations where increasing blood pressure or improving vascular tone is required. It is most commonly indicated in anesthetized patients with hypotension that does not adequately respond to fluid therapy.

• Anesthesia-associated hypotension: Used to increase blood pressure during general anesthesia by improving cardiac output and systemic vascular resistance, particularly when hypotension is not responsive to fluid boluses.
• Adjunct in anesthetic management: During anaesthesia, ephedrine may support blood pressure by increasing cardiac index and systemic vascular resistance.
• Urinary incontinence (urethral sphincter hypotonus): Ephedrine has been used orally for the management of urethral sphincter mechanism incompetence (USMI); however, its use has declined because of limited product availability and the availability of safer and more effective alternatives.
• Nasal congestion (decongestant): Ephedrine has been proposed as a nasal decongestant in dogs and cats and may provide some benefit in cats with influenza.

Dosage (Reference)

Dog

In dogs, ephedrine is used primarily to treat anesthesia-associated hypotension. It is typically administered as intermittent IV boluses for rapid effect, although continuous rate infusion (CRI) may be used in some cases.

Cat

In cats, ephedrine is used similarly to dogs for the management of anesthesia-associated hypotension. Careful titration is essential to avoid excessive cardiovascular stimulation.

Warnings & Precautions

Ephedrine is a sympathomimetic agent with significant cardiovascular and central nervous system effects. Careful patient selection, dose titration, and monitoring are essential to avoid serious adverse outcomes, especially in compromised patients.

• Cardiovascular disease: Contraindicated in patients with severe cardiovascular disease, particularly those with arrhythmias.
• Hypertension risk: May cause significant increases in blood pressure; use cautiously in patients with pre-existing hypertension or conditions where elevated blood pressure is undesirable.
• Endocrine and metabolic disorders: Use with caution in patients with hyperthyroidism, diabetes mellitus, hypercortisolism or other metabolic disorders.
• Exclude polyuria first (urinary incontinence): Before using ephedrine for urinary incontinence, exclude polyuria and its underlying causes, because several polyuric disorders would be made worse by ephedrine.
• Glaucoma and prostatic hypertrophy: Contraindicated in animals with glaucoma. Use with caution in animals with prostatic hypertrophy or partial urethral obstruction.
• Tachyphylaxis: Repeated dosing may lead to reduced effectiveness due to depletion of endogenous norepinephrine stores; clinical response may diminish over time.
• Renal impairment: Reduced renal function may prolong drug elimination and increase the risk of prolonged or exaggerated effects.
• Pregnancy and lactation: Avoid use in pregnant or lactating animals. Ephedrine crosses the placenta and is excreted in milk; if treatment is unavoidable during lactation, consider using a milk replacer for nursing offspring.
• Neonatal monitoring (Caesarean): After maternal ephedrine exposure during a Caesarean section, monitor neonates for signs of metabolic acidosis.
• IV administration considerations: Administer as controlled, diluted IV boluses; for an IV bolus a drug concentration of 5–10 mg/mL is cited (extrapolated from human data).
• Drug confusion risk: Do not confuse ephedrine with epinephrine, as they have different pharmacologic profiles and clinical uses.
• Handler safety (PPE): People who are or may become pregnant should not handle this drug; follow appropriate handling precautions.

Drug Interactions

Most clinically relevant interactions with ephedrine are related to additive cardiovascular stimulation, altered adrenergic responses, or interference with norepinephrine pathways. Review the reported and theoretical interactions below before concurrent use; whether monitoring or dose adjustment is needed depends on the specific interaction.

• Alpha-adrenergic antagonists (e.g., prazosin, phentolamine): May reduce or inhibit the pressor effects of ephedrine.
• Alpha-2 agonists (e.g., dexmedetomidine, xylazine, clonidine): May enhance the pressor response and increase the risk of excessive hypertension.
• Atropine: May augment the cardiovascular (pressor) effects of ephedrine.
• Beta-blockers (e.g., atenolol, propranolol): May decrease the effectiveness of both drugs and blunt the expected cardiovascular response.
• Cardiac glycosides (e.g., digoxin): Increased risk of arrhythmias when used concurrently.
• Epidural anesthesia: Ephedrine may reduce the effectiveness of epidural anesthesia.
• Monoamine oxidase inhibitors (e.g., selegiline, amitraz): Avoid use within 2 weeks due to risk of severe hypertension and hyperthermia.
• Oxytocin: May result in additive hypertensive effects.
• Phenothiazines (e.g., acepromazine): May antagonize the effects of ephedrine and increase the risk of arrhythmias; combination should be avoided.
• Propofol: May enhance the pressor effects of ephedrine.
• Quinidine: May reduce the effectiveness of both drugs.
• Reserpine: May inhibit the pressor effects of ephedrine.
• Sodium bicarbonate: May decrease drug elimination and increase the risk of toxicity.
• Other sympathomimetics (e.g., phenylpropanolamine): Avoid concurrent use with other sympathomimetic agents unless the potential benefits outweigh the risks. If combination therapy is considered, monitor closely for additive cardiovascular and central nervous system adverse effects.
• Theophylline / aminophylline: Increased risk of CNS and gastrointestinal toxicity.
• Tricyclic antidepressants (e.g., amitriptyline, clomipramine): May decrease the pressor response of ephedrine; concurrent use with amitriptyline may also cause arrhythmias.
• Urinary alkalinizers (e.g., carbonic anhydrase inhibitors, citrates): May reduce urinary excretion and prolong the drug’s duration of action.
• Vasopressin: May cause additive hypertensive effects.
• Volatile / inhalant anaesthetics: Volatile (inhalant) anaesthetics enhance the myocardium’s sensitivity to the effects of ephedrine.
• Y-site incompatibilities: Y-site incompatible with conventional amphotericin, diazepam and pantoprazole.

Side Effects & Overdose

Side Effects

Adverse effects of ephedrine reflect excessive adrenergic (sympathomimetic) activity. Most effects involve cardiovascular stimulation or central nervous system excitation.

• CNS stimulation: Restlessness or irritability may occur.
• Tachycardia: Increased heart rate is common due to beta-adrenergic stimulation.
• Hypertension: Blood pressure may rise.
• Arrhythmias: Cardiac rhythm disturbances, including atrial fibrillation, may occur, particularly in susceptible patients.
• Gastrointestinal effects: Nausea and vomiting may be observed.
• Anorexia: Reduced appetite may occur in some animals.
• Additional sympathetic effects: Generalized sympathetic stimulation may also cause panting, mydriasis (dilated pupils), peripheral vasoconstriction and reduced intestinal motility and tone; reflex bradycardia has also been reported.

Overdose

Overdose of ephedrine results in excessive sympathomimetic stimulation, leading to severe cardiovascular and neurologic complications. Clinical signs typically represent an exaggerated form of its pharmacologic effects.

• Severe hypertension: May progress to rebound hypotension in advanced cases.
• Cardiac disturbances: Includes bradycardia or tachycardia, arrhythmias, and potential cardiovascular collapse.
• CNS effects: Marked CNS stimulation progressing to coma in severe toxicity.
• Management: Primarily supportive care with close monitoring of cardiovascular status and blood pressure.
• Decontamination (oral exposure): Consider gastrointestinal decontamination with activated charcoal and cathartics when appropriate.
• Antihypertensive therapy: May be required to control severe hypertension.
• Poison-control consultation: After a known or suspected overdose, consult a 24-hour poison-control service that provides veterinary-specific guidance.

Key Notes

Practical clinical points that help optimize the safe and effective use of ephedrine in dogs and cats in everyday veterinary practice:

• Prefer bolus over CRI: For anaesthesia-related hypotension, intermittent IV boluses are recommended rather than a continuous rate infusion.
• Effective in fluid-refractory hypotension: Particularly useful when hypotension persists despite appropriate crystalloid boluses.
• Balanced hemodynamic effect: By stimulating both alpha- and beta-receptors, ephedrine supports both cardiac output and vascular tone rather than vasoconstriction alone.
• Monitor response closely: Administer diluted, incremental IV boluses and reassess the blood-pressure response.
• Limited outpatient use: Current injectable use is primarily for acute blood-pressure support; oral and nasal uses are also described, although oral products are scarce.
• Short-term use preferred: Repeated vasopressor doses may become less effective (tachyphylaxis), so injectable use is best suited to short-term, acute blood-pressure support.
• Urinary pH influence: Drug elimination may vary depending on urinary pH, which can affect duration of action in some patients.
• Consider electrolyte effects: Beta-adrenergic activity may reduce serum potassium levels; monitor in susceptible or critical patients.
• Useful with concurrent bradycardia: During anaesthesia, ephedrine’s positive inotropic and heart-rate-raising effects can help when hypotension is accompanied by bradycardia.
• Preparation / dilution: The 50 mg/mL product may be diluted 1:10 in 5% dextrose, 0.9% sodium chloride or lactated Ringer’s solution; do not dilute the premixed 5 mg/mL product.
• Storage: Store at room temperature (25°C; excursions 15–30°C), protect from light, and discard any unused portion.
• Laboratory interference: Ephedrine may produce a false-positive amphetamine result on an EMIT immunoassay.
• Discharge timing: After in-clinic administration, ensure the drug’s clinical effects have resolved before the animal is discharged.
• Historical CNS-stimulant use: Ephedrine has historically been used as a CNS stimulant, though the references give no small-animal dosing regimen for this use.
• Less rebound than stronger decongestants: As a nasal decongestant, ephedrine causes less rebound congestion than more powerful sympathomimetics such as oxymetazoline or xylometazoline.
• Active metabolite (norephedrine): In dogs, ephedrine is rapidly N-demethylated to norephedrine, and much of its activity is thought to be mediated by this metabolite.