Drug Classifications: Local Anesthetics Flashcards

Local Anesthetics Overview

• Local anesthetics suppress pain by blocking impulse conduction along axons.
• Blockage of sodium channels in the axon membrane is crucial for stopping nerve conduction.

Advantages and Classifications

• Local anesthesia provides pain relief without causing generalized nervous system depression, unlike inhalation anesthesia.
• Two main types of local anesthetics:
  • Ester-type (e.g., procaine)
  • Amide-type (e.g., lidocaine)

Differences Between Ester and Amide Types

• Differ in two key aspects:
  • Method of inactivation
  • Potential for allergic responses

Mechanisms and Administration

• Termination of local anesthesia occurs as the anesthetic molecules diffuse out of neurons and are absorbed into the bloodstream.
• Often administered with a vasoconstrictor to reduce blood flow, delaying systemic absorption.

Benefits of Delaying Systemic Absorption

• Prolongs anesthesia duration.
• Reduces risk of toxicity.

Metabolism of Anesthetics

• Ester-type anesthetics are metabolized by enzymes called esterases in the blood.
• Amide-type anesthetics undergo metabolism in the liver by liver enzymes.

Allergic Reactions

• Ester-type anesthetics are more likely to cause allergic reactions than amide-type.
• Procaine can lead to allergic reactions due to its metabolism by esterases.

Cardiac and Vascular Effects

• Absorbed local anesthetics can suppress myocardial and conducting system excitability.
• Signs of cardiac effects include bradycardia, heart block, reduced contractile force, and possible cardiac arrest.
• Hypotension is a noted effect on blood vessels.

Placental Transfer and Labor

• Local anesthetics can cross the placenta and may prolong labor.

Historical Context

• Cocaine was the first local anesthetic, categorized as an ester-type.

Surface Anesthetics

• Common surface anesthetics include lidocaine, tetracaine, and cocaine.

Minimizing Topical Anesthetic Absorption

• To reduce risks:
  • Use the smallest effective amount.
  • Avoid large area applications.
  • Exclude broken or irritated skin in applications.
  • Refrain from strenuous exercise, wrapping the site, or heating, as these increase absorption.

Neuron Sensitivity

• Smaller, nonmyelinated neurons are blocked more rapidly than larger, myelinated ones.

Systemic Toxicity Concerns

• Key concerns include cardiac dysrhythmias and central nervous system effects.
• CNS effects of toxicity may include seizures, unconsciousness, and coma.

Risk Reduction Strategies

• Minimize systemic toxicity by using smaller amounts, avoiding large areas, and not applying to broken skin.
• Avoid strenuous exercise and heat application post-application.