Local Anaesthetics

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LOCAL ANAESTHETICS Presented by Mr.Rupesh S. Ranpise Guide by Ms.Shital S. Bhandari Sitabai Thite College of Pharmacy, Shirur

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Defination of local Anaesthetics Local anaesthetic agents can be defined as drugs which are used clinically to produce reversible loss of sensation in a circumscribed area of the body. At high concentrations, many drugs that are used for other purposes possess local anaesthetic or membrane stabilising properties. These include Beta-adrenoceptor antagonists, opioid analgesics, anticonvulsants and antihistamines.

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There are 2 classes of local anaesthetic drugs defined by the nature of the carbonyl-containing linkage group. Most of the clinically useful local anaesthetic agents consist of an aromatic ring linked by a carbonyl containing moiety through a carbon chain to a substituted amino group.

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History of Local Anesthetics Cocaine isolated 1856 1884 cocaine used in occular surgery 1880’s Regional anesthesia plexus 1898 cocaine used in spinal anesthesia 1905 1st synthetic LA (procaine) introduced 1943 lidocaine synthesized Mepivacaine (1957), Bupiv (’63), Ropiv (’96)

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Different technique Surface anesthesia - application of local anesthetic spray, solution or cream to the skin or a mucous membrane. The effect is short lasting and is limited to the area of contact. Infiltration anesthesia - injection of local anesthetic into the tissue to be anesthetized. Surface and infiltration anesthesia are collectively topical anesthesia. Field block - subcutaneous injection of a local anesthetic in an area bordering on the field to be anesthetized. Peripheral nerve block - injection of local anesthetic in the vicinity of a peripheral nerve to anesthetize that nerve's area of innervation. Plexus anesthesia - injection of local anesthetic in the vicinity of a nerve plexus, often inside a tissue compartment that limits the diffusion of the drug away from the intended site of action.

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Epidural anesthesia - a local anesthetic is injected into the epidural space where it acts primarily on the spinal nerve roots. Depending on the site of injection and the volume injected, the anesthetized area varies from limited areas of the abdomen or chest to large regions of the body. Spinal anesthesia - a local anesthetic is injected into the cerebrospinal fluid, usually at the lumbar spine (in the lower back), where it acts on spinal nerve roots and part of the spinal cord. The resulting anesthesia usually extends from the legs to the abdomen or chest. Intravenous regional anesthesia (Bier's block) -. The drug fills the limb's venous system and diffuses into tissues where peripheral nerves and nerve endings are anesthetized. The anesthetic effect is limited to the area that is excluded from blood circulation and resolves quickly once circulation is restored. Local anesthesia of body cavities (e.g. intrapleural anesthesia, intraarticular anesthesia)

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The mechanism of local anesthetics connects with the ion channels, nerve, and depolarization. Local anesthetics block the conduction in peripheral nerves that inhibited the nerve to excited and created anesthesia. The anesthetic is a reversible reaction. It binds and activates the sodium channels. The sodium influx through these channels and depolarizes the nerve cell membranes. It also created high impulses along the way. As a result, the nerve loses depolarization and the capacity to create the impulse, the patient loses sensation in the area supplied by the nerve. Mechanism

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Classification of local anaesthetics 1.ESTER- a.Ester of benzoic acid ex. Cocaine. b.Ester of p-amino benzoic acid ex. Benzocaine procaine. 2.AMIDES- a. Anilide amides ex. Xylocaine (lignocaine) b. Non- Anilide amides Ex. Cinchocaine 3.MISCELLANEOUS- ex. Phenol , Chlorobutanol, Eugenol, Benzyl alcohol.

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Properties It is ethyl ester of p- amino benzoic acid. Colourless crystal & white crystalline powder. Odourless & gas bitter taste followed by sensation of numbness Slightly soluble in water but freely soluble in alcohol & soluble in dilute acid . Stability & storage It is stable in air but affected by light hence it is store in well closed light resistance container.

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Uses It is local anaesthetics & used as : To relieve pain associated with ulcer wounds & mucous surface. Orally to relieve pain of gastric carcinoma . For symtomic treatment of tuberculosis laryngitis. To treat pruritus ,anal fissures & haemorrhoids. To prevent nausea & vomiting. Dosage form Benzocaine Lozenges IP & BP , Benzocaine ointment IP & BP, Benzocaine spray IP & BP , Benzocaine creams IP & BP, Benzocaine lotions IP & BP, Benzocaine aerosols IP & BP. Brand names Vicks formula 44, Soliwax ear ,Healex spray.

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PROCAINE (NOVOCAINE , ETHOCAINE) STRUCTURE:- Chemical name:- 2-diethylamino ethyl , 4-amino benzoate

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Physical properties :- It is official as it’s hydrochloride salt which occurs as colourless crystal or white crystalline power. Odourless &has salty & bitter taste . Freely soluble in water , soluble in alcohol & very slightly soluble in chloroform. Stability & Storage :- Aq. Solution are most stable at pH 3.5. Store in well closed light resistant container.

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Uses :- a) It is primarily used for it’s local anaesthetics activity and used for : 1.Infiltration. 2.Peripheral nerve block. 3.Spinal anaesthesia. 4.Producing regional analgesia. b) Its salt with benzyl penicillin is given to increase duration of action of benzyl penicillin Dosage Forms :- Procaine & adrenaline injection. IP & BP Procaine benzyl penicillin injection. IP & BP Fortified procaine penicillin injection. IP & BP Procaine hydrochloride. IP & BP Brand Name :- Novocaine , Planocaine , Pronestyl.

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LIGOPCAINE (LIDOCAINE , XYLOCAINE) STRUCTURE:- N-diethylamino acetyl 2,6 xylidine or 2-diethylamino, N-(2,6-dimethyl phenyl) acetamide. Chemical name:-

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Properties :- It’s hydrochloride salt which occurs as white crystalline power. Odourless &has slightly bitter taste . Very soluble in water ,freely soluble in alcohol & soluble in chloroform. Stability & Storage :- Stable compound & is not oxidized by air & oxygen. Store in well closed container.

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Uses:- a) It is used for it’s local anaesthetics activity and used for : 1.Infiltration. 2. Nerve block. 3.Topical use. 4.To Producing dental analgesia. b) used for prevention & treatment of ventricular arrhythmia. Dosage Forms :- 1. Ligocaine hydrochloride IP & BP . 2. Ligocaine Eye drops. 3.Ligocaine hydrochloride gels. IP & BP 4. Ligocaine hydrochloride injection. BP . Brand Names:- Otek , Otosil – C , Trox , Kebutacaine .

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Lipid solubility All local anesthetics have weak bases. Increasing the lipid solubility leads to faster nerve penetration, block sodium channels, and speed up the onset of action. The more tightly local anesthetics bind to the protein, the longer the duration of onset action. Local anesthetics have two forms, ionized and nonionized. The nonionized form can cross the nerve membranes and block the sodium channels. So, the more nonionized presented, the faster the onset action. pH influence Usually at range 7.6 – 8.9 Decrease in pH shifts equilibrium toward the ionized form, delaying the onset action. Lower pH, solution more acidic, gives slower onset of action Factors Affect the Reaction of Local Anesthetics

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Vasodilation Vasoconstrictor is a substance used to keep the anesthetic solution in place at a longer period and prolongs the action of the drug vasoconstrictor delays the absorption which slows down the absorption into the bloodstream Lower vasodilator activity of a local anesthetic leads to a slower absorption and longer duration of action Vasoconstrictor used the naturally hormone called epinephrine (adrenaline). Epinephrine decreases vasodilator. Side effects of epinephrine Epinephrine circulates the heart, causes the heart beat stronger and faster, and makes people feel nervous. Factors Affect the Reaction of Local Anesthetics

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Toxicity light headedness shivering or twitching seizures hypotension (low blood pressure) numbness

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