local anesthetics and techniques

Sadaqat Ali

Definition How local anesthetic work Moa Classification Pharmacokinetics Clinical uses Lidocaine Diylocinine Spinal cord anesthesia

Contents:

DEFINITION: Local anesthesia is defined as a

loss of sensation in a circumscribed area of the body caused by depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves

LOSS OF SENSATION WITHOUT

INDUCING LOSS OF CONSCIOUSNESS.

Introduction

Altering the basic potential of nerve membrane Altering the threshold Decreasing the rate of depolarization Prolonging the rate of repolarization

How local anesthetics work

Local anesthetics inhibit depolarization of the nerve membrane by interfering with both Na+ and K+ currents.

The action potential is not propagated because the threshold level is never attained.

Local anesthetics act at the cell membrane to prevent the generation and the conduction of nerve impulses

Mechanism of action

Esters: Cocaine, Procaine. Chloroprocaine , Tetracaine. Amides: Lidocaine, Mepivacaine, Prilocaine, Articaine,

Popivacaine, Etidocaine. Ketones: Dyclonine. Quinoline: Centbucridine

LOCAL ANESTHETICS CALSIFICATION

Following injection into the area of nerve fibers to be blocked, local anesthetics are absorbed into blood.

Ester-linked local anesthetics are quickly hydrolyzed by butyrylcholinesterase in blood.

Amide-linked local anesthetics can be widely distributed via circulation. Amide- linked local anesthetics are hydrolyzed by liver microsomal enzymes.

Thus, half lifes of these drugs are significantly longer and toxicity is more likely to occur in patients with impaired liver function.

Pharmacokinetics:

Absorption of local anesthetics is affected by following factors:

– dosage, – site of injection – drug-tissue-binding and – Presence of vaso-constricting drugs

Absorption:

Analgesia  Regional anesthesia  Prevention and treatment of cardiac arrhythmias  Prevention/management: increased intracranial

pressure Treatment of grand mal seizure

Clinical Uses

CNS Low doses: tremors and oral numbness, with possible dizziness, confusion and agitation (exception = cocaine) Mod. doses: convulsions (immediately preceded by muscle twitching); prevented by injection of anti-convulsant High doses: possible respiratory depression

Adverse Effects

Cardiovascular:vasodilation (exception = cocaine) - less often, myocardial depression- ventricular contraction possibly leading to reduced cardiac output, in the worst case, ventricular arrhythmias and

cardiac arrest unintentional high plasma levels of LAs, but

can occur with normal IV doses of bupivacaine

Hypersensitivity: local dermatitis with some topical; rare systemic allergic response with injected esters (due to metabolite)

Smooth Muscle• Depress contractions in the intact bowel• Relax vascular and bronchial smooth muscle• May increase the resting tone• Decrease the contractions of isolated human

uterine muscle.

Proto type drugs and their specifications

Cocaine, an ester of benzoic acid and methylecognine, occurs in abundance in the leaves of the coca shrub.

Cocaine

Cocaine produces anesthesia by inhibiting excitation of nerve endings or by blocking conduction in peripheral nerves. This is achieved by reversibly binding to and inactivating sodium channels. Sodium influx through these channels is necessary for the depolarization of nerve cell membranes and subsequent propagation of impulses along the course of the nerve.

Cocaine is the only local anesthetic with vasoconstrictive properties.

Mechanism of action:

This is a result of its blockade of norepinephrine reuptake in the autonomic nervous system. Cocaine binds differentially to the dopamine, serotonin, and norepinephrine transport proteins and directly prevents the re-uptake of dopamine, serotonin, and norepinephrine into pre-synaptic neurons. Its effect on dopamine levels is most responsible for the addictive property of cocaine.

PHARMACOKNIETICS Absorption Cocaine is absorbed from all sites of application,

including mucous membranes and gastrointestinal mucosa. By oral or intra-nasal route, 60 to 80% of cocaine is absorbed.

Metabolism Hepatic. Cocaine is metabolized to

benzoylecgonine and ecgonine methyl ester, which are both excreted in the urine.

Indication For the introduction of local (topical) anesthesia of

accessible mucous membranes of the oral, laryngeal and nasal cavities.

A local anesthetic and cardiac depressant used as an anti arrhythmia agent.

Its actions are more intense and its effects more prolonged than those of procaine.

its duration of action is shorter than that of bupivacaine or prilocaine.

Lidocaine

Mechanism of actionLidocaine stabilizes the neuronal membrane by

inhibiting the ionic fluxes required for the initiation and conduction of impulses thereby effecting local anesthetic action. Lidocaine alters signal conduction in neurons by blocking the fast voltage gated sodium (Na+) channels in the neuronal cell membrane that are responsible for signal propagation.

With sufficient blockage the membrane of the postsynaptic neuron will not depolarize and will thus fail to transmit an action potential. This creates the anesthetic effect by not merely preventing pain signals from propagating to the brain but by aborting their birth in the first place.

Absorption information derived from diverse formulations,

concentrations and usages reveals that lidocaine is completely absorbed following parenteral administration, its rate of absorption depending, for example, upon various factors such as the site of administration and the presence or absence of a vasoconstrictor agent.

Metabolism Primarily hepatic.

Route of elimination Lidocaine and its metabolites are excreted by the

kidneys. Half life 109 minutes Toxicity convulsions, hypoxia, acidosis, bradycardia,

arrhythmias and cardiac arrest

Indication For production of local or regional anesthesia by

infiltration techniques such as percutaneous injection and intravenous regional anesthesia by peripheral nerve block techniques such as

brachial plexus and intercostal and by central neural techniques such as lumbar and caudal epidural blocks.

Dyclonine is an oral anesthetic found in Sucrets, an over the counter throat lozenge.

It is also found in some varieties of the Cepacol sore throat spray.

Dyclonine

Mechanism of action Local anesthetics block both the initiation and

conduction of nerve impulses by decreasing the neuronal membrane's permeability to sodium ions. This reversibly stabilizes the membrane and inhibits depolarization, resulting in the failure of a propagated action potential and subsequent conduction blockade.

Absorption Readily absorbed through mucous membranes

into the systemic circulation. Half life Approximately 30 to 60 minutes. Toxicity cardiovascular system depression, CNS toxicity,

and methemoglobinemia

Indication Used to provide topical anesthesia of accessible mucous

membranes prior to examination, endoscopy or instrumentation, or other procedures involving the esophagus, larynx, mouth, pharynx or throat, respiratory tract or trachea, urinary tract, or vagina.

Also used to suppress the gag reflex and/or other laryngeal and esophageal reflexes to facilitate dental examination or procedures (including oral surgery), endoscopy, or intubation.

Also used for relief of canker sores, cold sores or fever blister.

Topical application: Lidocaine (ointment) SC injections

Anesthesia techniques

Topical application Anesthesia of mucous membrane of nose, mouth

throat can be produced by direct application of salts of many local anesthetics or by suspension of poorly soluble drugs like tetracain 2 % or lidocain2 %

techniques of anasthesia

It is the injection of local anesthetic directly into the tissue without taking into consideration the course of nerve

Lidocain Procain Bupivacaine

Infiltration anesthesia:

Is produced by SC injection of a solution of LA in order to anesthetize the region distal to the injection.

Nerve blockinjection of a LA into or about individual peripheral

nerve or peripheral plexuses.

Field block anesthesia

Nerve blocked Trigeminal nerve is blocked Anesthetic Cartridges + syringes

Dental procedure

Intervertibral space CSF withdrawal Injection procedure

Spinal cord anesthesia

Goodman and Gilman’s the pharmacological Basis of therapeutics 12th Edition Chapter no 20

www.drugbank.com www.link.springer.com

REFERENCES

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