Procaine with Epinephrine
Procaine is a short-acting ester-type local anesthetic. Epinephrine (adrenaline) is added as a vasoconstrictor to prolong the duration of action and reduce the rate of systemic absorption, thereby decreasing the risk of systemic toxicity. **Clinical Pearl:** Procaine is rapidly hydrolyzed by plasma pseudocholinesterases, making it relatively safe but very short-acting without the addition of epinephrine. It is primarily used for local infiltration and nerve blocks.
Mechanism: Procaine causes a reversible blockade of the **voltage-gated sodium channels** → prevents the influx of sodium → inhibits the propagation of action potentials along the nerve fiber. Sensory nerve fibers are blocked before motor nerve fibers, allowing a selective sensory blockade at low doses. Epinephrine stimulates **alpha-1 adrenergic receptors** → local vasoconstriction → delays systemic absorption of procaine, increasing its local duration of action.
Routes of administration
Contraindications
- Intravenous administration
- Use in areas supplied by end-arteries (e.g., tail, ears, digits) due to risk of ischemic necrosis
- Known hypersensitivity to ester-type local anesthetics or PABA
- Epidural use (depending on specific formulation preservatives)
Adverse effects
- Local tissue irritation
- Ischemia or tissue necrosis (due to epinephrine)
- CNS excitation followed by depression (at toxic doses)
- Cardiovascular depression, hypotension, or arrhythmias (at toxic doses)
- Allergic reactions (ester anesthetics are metabolized to PABA, a known allergen)
Drug interactions
- Sulfonamide antibiotics · Procaine is metabolized to PABA, which competitively antagonizes the antibacterial effect of sulfonamides. · major
- Alpha-adrenergic blockers · May antagonize the vasoconstrictive effects of epinephrine. · moderate
- Halothane · Sensitizes the myocardium to catecholamines; increased risk of arrhythmias with epinephrine. · major
Monitoring
- Heart rate and rhythm
- Blood pressure
- Signs of CNS toxicity (tremors, seizures)
- Tissue perfusion at the injection site
Overdose
Overdose or accidental IV injection can lead to systemic toxicity. * **CNS signs:** Restlessness, tremors, seizures, followed by severe CNS depression. * **Cardiovascular signs:** Arrhythmias, hypotension, and cardiovascular collapse. * **Treatment:** Supportive care, oxygen therapy, control seizures with diazepam or midazolam, and manage arrhythmias. Intravenous lipid emulsion (ILE) therapy may be considered for severe local anesthetic systemic toxicity (LAST).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.