Local anesthetics

Two types-esters and amides.

Esters include tetracaine, procaine, cocaine and chloroprocaine.

Amides include lidocaine, mepivacaine, bupivacaine, and etidocaine.

Esters, such as procaine, are metabolized by plasma cholinesterase and are then excreted by the kidney.

Amides, such as lidocaine and bupivacaine, are metabolized by the liver and then in the kidney.

Because amides are metabolized more slowly than esters, they have a longer duration of action.

Work by diffusing through the plasma membrane of nerves and causes blockade of sodium channels, prevents the nerve from depolarizing and inhibits axonal conduction.

In the presence of acidosis at the tissue level (as occurs with inflammation and infection) slows the onset and decreases analgesic intensity by causing local anesthetic molecules to become positively charged and less able to diffuse into nerves.

Can lead to CNS toxicity and cardiovascular toxicities.

May cause mental status alteration, dizziness, perioral numbness, tinnitus, visual changes, metallic taste and seizure activity.

May cause decreased cardiac output, hypotension and cardiovascular collapse.

The use of epinephrine 1:200,000 mixed in with local anesthetic solutions can prolong the duration of neural blockade and reduce the risk of systemic absorption.

Use of the addition of epinephrine is contraindicated in areas where arterial spasms can lead to tissue necrosis.

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