Local Anaesthetics

LOCAL ANAESTHETICS

Dr. VINODHINI, B.Pharm, M.Sc,Ph.d, D.Acu Lecturer Department of Pharmacology SRM Dental College, Ramapuram LOCAL ANAESTHETICS

Reversible loss of all sensations by blocking nerve conduction near the site of application or injection without loss of consciousness

CLASSIFICATION I. BASED ON THE ROUTE OF ADMINISTRATION • LIDOCAINE /LIGNOCAINE BUTAMBEN • TETRACAINE BENOXINATE SURFACE • BENZOCAINE DYCLONINE • OXETHAZINE DIBUCAINE • PROPARACAINE CLASSIFICATION I. BASED ON THE ROUTE OF ADMINISTRATION • LIDOCAINE / LIGNOCAINE ROPIVACAINE • BUPIVACAINE MEPIVACAINE • CHLORPROCAINE INJECTABLES ARTICAINE • PRILOCAINE ETIDOCAINE • TETRACAINE • PROCAINE

II. BASED ON CHEMICAL STRUCTURE

• LIDOCAINE MEPIVACAINE • BUPIVACAINE ARTICAINE • PRILOCAINE AMIDES ETIDOCAINE • DIBUCAINE OXETHAZINE • ROPIVACAINE DYCLONINE

II. BASED ON CHEMICAL STRUCTURE

•CHLORPROCAINE BENZOCAINE ESTERS •TETRACAINE BUTAMBEN •PROCAINE

VOLTAGE GATED SODIUM CHANNEL

RESTING - CLOSED STATE Na+

LA LA - Local Anaesthetics IG AG - Activation Gate IG - Inactivation Gate Receptor VOLTAGE GATED SODIUM CHANNEL

ACTIVATED - OPEN STATE Na+

LA LA - Local Anaesthetics Na+ AG - Activation Gate IG - Inactivation Gate Receptor VOLTAGE GATED SODIUM CHANNEL

INACTIVATED - BLOCKED STATE Na+

BH + B

LA Receptor B BH +

LA - Local Anaesthetics AG - Activation Gate IG - Inactivation Gate Unionised Local anesthetic Diffuse through cell membrane into the nerve fibre

Ionisation of Local anesthetic

Ionised form of Local anesthetic binds to specific receptor in sodium channel

Inactivation ( Blockade ) of sodium channel

Blockade of generation and transmission of impulses

LOCAL ANESTHESIA

TECHNIQUES OF ADMINISTERING LOCAL ANAESTHETICS • SURFACE ANAESTHESIA • INFILTRATION ANAESTHESIA • CONDUCTION BLOCK - FIELD BLOCK - NERVE BLOCK • SPINAL ANAESTHESIA • EPIDURAL ANAESTHESIA • IV REGIONAL ANAESTHESIA LOCAL ANAESTHETICS + ADRENALINE Rationale for combining Epinephrine with Lidocaine Epinephrine having vasoconstrictor action, retards the diffusion and limits the absorption of Lidocaine. LA – Lidocaine, Bupivacaine, Procaine Vasoconstrictors – Adrenaline, Phenylephrine, Fellypressin, Levonordefrine.

1. Prolongs the duration of action of Lidocaine. 2. Decreases systemic toxicity of Lidocaine. 3. Increases the intensity of nerve block. 4. Provides a more bloodless field for surgery. 5. Also combats any hypersensitivity reaction of Lidocaine. This combination is contraindicated in 1. End organs – digits, ear, nose, penis, scrotum, since they have minimal collateral circulation, hypoxia and gangrene may be produced. 2. Patients having cardiovascular disorders. 3. Hyperthyroidism. 4. Intravenous regional anesthesia.

1. SURFACE ANAESTHETICS

Blocks the sensory nerve endings in the skin or mucous membrane

USED IN: • Oral cavity - Recurrent aphthous stomatitis, Post herpetic neuralgia, Prior to intraoral injection of local anaesthetic, Oral mucositis pain after radiation or chemotherapy, sore throat, cold sores.

• Eye – tonometry, cataract and other ocular surgery. • Nose, ear – painful lesions, polyps. • Respiratory tract – endoscopy, endotracheal intubation, tonsillectomy.

• Esophagus, stomach – gastritis, esophagitis, heartburn • Anal canal – fissure, haemorrhoids, proctoscopy. • Abraded skin – ulcer, burns.

• Intact skin – skin graft harvesting, venipuncture, excision, electrodessication and shave biopsy of skin lesions. Eutectic mixture of local anesthetics – EMLA - Lidocaine + Prilocaine/Tetracaine LA + ADRENALINE – NOT EFFECTIVE

2. INFILTRATION ANESTHETICS

Produced by injection of local anesthetic into and around the field of surgery, without identifying individual nerves.

USED IN: Tooth extraction, root canal treatment, periodontal procedures. suturing, incision, excision. Drugs used Lidocaine, Bupivacaine, Procaine.

Disadvantage – large amount of local anesthetic is needed to anesthetize small areas. LA + ADRENALINE – COMBINATION USED

3. CONDUCTION BLOCK

Conduction block is produced by injection of local anesthetic around nerve trunks and the area distal to injection is anesthetized and paralysed.

FIELD BLOCK Produced by injection of local anesthetic subcutaneously, so all the nerves of a particular field are blocked. Local anesthetic is injected near the larger terminal nerve endings.

USED IN: Root canal treatment. Appendicectomy, scalp stitching, operation on forearms and legs. Drugs used: Lidocaine, Bupivacaine, Procaine.

LA + ADRENALINE – COMBINATION USED

NERVE BLOCK Produced by injection of local anesthetic into or around a peripheral nerve or plexus supplying the part to be anesthetized.

• Brachial plexus, cervical plexus, ulnar, phrenic, sciatic, femoral nerve block, pudendal block

Drugs used Lidocaine, Prilocaine, Bupivacaine, Ropivacaine, Mepivacaine.

• LA + ADRENALINE – COMBINATION USED

4. SPINAL/ SUBARACHNOID/ INTRATHECAL ANAESTHESIA

Produced by injection of local anesthetic within the spinal

subarachnoid space, between L2-3 and L3-4 causing temporary paralysis of the nerves with which it comes into contact.

USED IN : Surgeries of lower half of body – obstetric procedures, lower limbs, pelvis, lower abdomen. DRUGS USED : Lidocaine, Bupivacaine

LA + ADRENALINE – COMBINATION USED

Complications of spinal anaesthesia • Hypotension due to decreased cardiac output and venodilatation secondary to sympathetic block. • Bradycardia or heart block. • Headache due to leakage of cerebrospinal fluid • Backache • Cauda equina syndrome characterised by bladder and bowel dysfunction - urinary retention and incontinence, fecal incontinence, impotence. • Septic meningitis.

5. EPIDURAL ANAESTHESIA Produced by injection of local anesthetic into the epidural space in the lumbar, sacral (caudal block), thoracic or cervical regions

USED IN : Obstetric and surgical procedures. Drugs used : Bupivacaine, Lidocaine, Ropivacaine.

LA + ADRENALINE – COMBINATION USED

• Royal college of Obstetrics and Gynaecologists (RCOG) – Recommendation Epidural – Bupivacaine is the ‘gold standard’ for obstetric analgesia. 6. INTRAVENOUS REGIONAL ANAESTHESIA (BIER’S BLOCK) Produced by injection of local anesthetic into a vein of the limb after exsanguination and application of a tourniquet.

Used in : Orthopedic surgery. Drugs used : Prilocaine, Lidocaine Bupivacaine is contraindicated due to it’s cardiotoxicity. LA + ADRENALINE – CONTRAINDICATED

ADVERSE DRUGS REACTIONS OF LOCAL ANAESTHETICS

• Hypersensitivity reactions. • CNS effects Excitation of CNS manifested as restlessness, excitement, nervousness, paresthesias, dizziness, light headedness, visual and auditory disturbances, muscle twitching, tremors and convulsions. Excitation is followed by depression with drowsiness, respiratory failure and coma.

• CVS effects Hypotension and bradycardia due to myocardial depression and peripheral vasodilatation. • Blood Methemoglobinemia is more common with Prilocaine due to metabolism of the aromatic ring to O-toluidine.

Preparations of Lidocaine • Injection • Surface Oral patch, Oral solution Gel, Lozenges, Spray, Ointment,Cream Eyedrops, Rectal preparation Transdermal patch – Lidocaine

Combinations EMLA – Lidocaine+Prilocaine/Tetracaine Lidocaine + Hydrocortisone

Cardiac use of Lidocaine Prophylaxis for ventricular arrhythmias in acute myocardial infarction.