Local Anesthetics and its Ideal properties

Local Anesthetics and its Ideal properties

Local anesthetics are applied topical and its target injection cause reversible loss of sensory perception, especially of pain, in a restricted area of the body. They block generation and conduction of nerve impulse at any part of the neuron with which they come in contact, without causing any structural damage. Thus, not only sensory but also motor impulses are interrupted when a local anesthetic is applied to a mixed nerve, resulting in muscular paralysis and loss of autonomic control as well.

CLASSIFICATION

Injectable anesthetic

Low potency, short duration

Procaine

Chloroprocaine

Intermediate potency and duration

Lidocaine (Lignocaine)

Prilocaine

High potency, long duration

Tetracaine (Amethocaine)

Bupivacaine

Ropivacaine

Dibucaine (Cinchocaine)

Surface anesthetic

Soluble                          Insoluble

Cocaine                           Benzocaine

Lidocaine                        Butylaminobenzoate

Tetracaine                      (Butamben)

Benoxinate                      Oxethazaine

The clinically useful local anesthetics are weak bases with amphiphilic property. A hydrophilic tertiary or secondary amine on one side and a lipophilic aromatic residue on the other are joined by an alkyl chain through an ester or amide linkage.

Ester-linked Las- Cocaine, procaine, chloroprocaine, tetracaine, benzocaine.

Amide-linked Las- Lidocaine, bupivacaine, dibucaine, prilocaine, ropivacaine.

Because of their short duration, less intense analgesia and higher risk of hypersensitivity, the ester-linked local anesthetics are rarely used for infiltration or nerve block but are still used topically on mucous membranes.

Ideal properties of LocalAnesthetics

•   Duration of action should be enough to allow time for the surgical procedure.
•   It should be effective both when injected into tissue and when applied topically to mucous   membranes.
•  It should be effective oral as well as intravenous.
•   It should have low toxicity.
•   It should not deteriorate by the heat of sterilization.
•   Its effects should be completely reversible.
•   Rapid onset of action and short duration of action.
•   The local anesthetics should be non-irritating.
•   The local anesthetic should be soluble in water and stable in solution.
•   The onset of action should be quick.