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Local Anesthetics (Med Chem:- 2) Notes Download


Local anaesthetic agents act locally to abolish the sensory perception over a
local area . They vary in their pharmacological properties and are used in the
following local anaesthesia techniques:
1) Topical anaesthesia (surface),
2) Infiltration,
3) Plexus block,
4) Epidural (extradural block), and
5) Spinal anaesthesia (subarachnoid block).
Local anaesthetics bind to cell membrane sodium channels and inhibit sodium
ion passage, thus prevent the membrane depolarisation of nerve cells. Sodium
channel is liable to local anaesthetic binding in the open state; therefore the
frequently stimulated nerves are blocked easily. The ability of local anaesthetics
to block a nerve depends on the length of the nerve ex posed, nerve diameter,
myelination, and the anaesthetic used.
17.1.2. Classification
Local anaesthetics are classified as follows:
1) Natural Agents: Cocaine.
2) Synthetic Nitrogenous Compounds
i) Derivatives of benzoic acid.
ii) Derivatives of para-amino benzoic acid
a) Freely Soluble: Procaine and Amethocaine.
b) Poorly Soluble: Benzocaine and Orthocaine.
iii) Derivatives of Acetanilide: Lignocaine, Mepivacaine, Bupivacaine,
Prilocaine, and Etidocaine.
iv) Derivatives of Quinoline: Cinchocaine and Dimethisoquin.
3) Synthetic Non-Nitrogenous Agents: Benzyl alcohol and Propanediol.
4) Miscellaneous Drugs with Local Action: Clove oil, Phenol,
Chlorpromazine and Diphenhydramine.
Based on Duration of Action
1) Injectable Anaesthetics
i) Low Potency and Short Duration: Procaine and Chloroprocaine.

1) Local anaesthetic agents act locally to abolish the sensory perception over
a local area.
2) Benzoic acid is an aromatic carboxylic acid found naturally in plant and
animal tissues.
3) Cocaine is a benzoyl methylecgonine hydrochloride (a benzoic acid ester).
It is an alkaloid and is extracted from the leaves of coca tree ( Erythroxylum
4) Hexylcaine (or cyclaine or osmocaine) is a short -acting local anaesthetic. It
acts by blocking the sodium channel conduction.
5) Meprylcaine (or epirocaine or oracaine) is a local anaesthetic having
stimulant properties. Its structure is related to dimethocaine.
6) Cyclomethycaine is a benzoate ester. It is used as a local anaesthetic for
surface application, and infiltration or nerve block.
7) Piperocaine is a benzoate ester. It is a local anaesthetic developed in the
8) Aminobenzoic acid is an organic acid with UV absorption and anti -fibrotic

9) Benzocaine is a surface anaesthetic which prevents the transmission of
impulses on nerve fibres and at nerve endings.
10) Butamben is a local anaesthetic that occurs in the form of n -butyl-p-
11) Procaine is an ester type local anaesthetic.
12) Butacaine is a white crystalline benzoate ester used as a local anaesthetic.
13) Propoxycaine is a local anaesthetic of the ester type. It has a rapid onset of
action and a longer duration of action than procaine.
14) Tetracaine is an ester -type local anaesthetic. Currently, it is available as a
cream and patch in combination with lidocaine.
15) Benoxinate (or oxybuprocaine) is a local anaesthetic.
16) Lidocaine is a local anaesthetic and cardiac depressant.
17) Lignocaine (or lidocaine and xylocaine) produces temporary loss of sensory,
motor, and autonomic function wh en injected or applied close to neural
18) Mepivacaine is local anaesthetic. Chemically, it is related to bupivacaine,
however pharmacologically it is related to lidocaine.
19) Prilocaine is a local anaesthetic and is pharmacologically similar to
20) Etidocaine is a local anaesthetic. It is injected during surgical procedures
and labour and delivery.
21) Phenacaine is an aromatic ether. It exists as white coloured, odourless and
crystalline powder.
22) Diperodon is a carbamate ester. It is structurally similar to anilides, in which
the aromatic ring is attached to sp2 carbon via nitrogen bridge.
23) Dibucaine is a local anaesthetic of amide type. It is used for surface

Subject:- Medicinal chemistry 2

Semester:- Sem 5

Course:- Bachelor of pharmacy