Local anesthetic

A local anesthetic is a drug that inhibits the propagation of signals along nerves. When it is used on specific nerve pathways, effects such as analgesia (loss of pain sensation) and paralysis (loss of muscle power) can be achieved.

While many drugs have some local anesthetic action as a side effect, the substances that are clinically used belong to one of two related classes: aminoamide and aminoester local anesthetics. All of these are structurally related to cocaine, which was the first drug to be used as a local anesthetic. Aminoamide and aminoester local anesthetics are also classified as synthetic local anesthetics. These drugs differ from cocaine mainly in that they have no abuse potential and do not act on the sympathoadrenergic system, i.e. they do not produce hypertension or local vasoconstriction.

Mechanism of action

Local anesthetic drugs act mainly by inhibiting sodium influx through specific sodium channels in the cell membrane of neurons. When the influx of sodium is interrupted, an action potential cannot build up and thus signal conduction is inhibited. The receptor site is thought to be located at the cytoplasmic (inner) portion of the transmembrane sodium channel.

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Undesired effects

The conduction of electric impulses follows a similar mechanism in peripheral nerves, the central nervous system, smooth muscle, and the heart. The effects of local anesthetics are therefore not specific for the signal conduction in peripheral nerves. However, toxicity usually occurs only at plasma levels which are rarely reached if proper anesthetic techniques are adhered to.

Central nervous system

Cardiovascular system

Smooth muscle

Hypersensitivity