Local anesthetics

Local anestheticsLocal anestheticsDR.SOBAN SADIQDR.SOBAN SADIQ

ClassificationClassification

EstersEstersCocaineCocaineBenzocaineBenzocaineProcaineProcaineTetracaineTetracaineChloroprocaineChloroprocaine

Am”i”desAm”i”desBupBupiivacainevacaineLLiidocainedocaineRopRopiivacainevacaineEtEtiidocainedocaineMepMepiivacainevacaine

Mechanism of action

• Block voltage gated sodium (Na+) channels in the axonal membrane preventing influx of Na which is required for neuronal conduction

• Local anesthetics bind Local anesthetics bind directlydirectly to the to the intracellularintracellular voltage-dependent sodium voltage-dependent sodium channelschannels

Limit influx of sodium, thereby limiting Limit influx of sodium, thereby limiting propagation of the action potential.propagation of the action potential.

Clinical usesClinical uses• 1-Topical local anesthesia is used for 1-Topical local anesthesia is used for

eye,ear,nose and throat procedureseye,ear,nose and throat procedures• Use drug that is capable of rapid Use drug that is capable of rapid

penetration across skin or mucosa with penetration across skin or mucosa with limited tendency to diffuse away from site limited tendency to diffuse away from site of applicationof application

• Cocaine has excellent penetration and Cocaine has excellent penetration and local vasoconstrictor effect but its short local vasoconstrictor effect but its short acting and irritating.acting and irritating.

• Anesthesia of mucous membranes of the Anesthesia of mucous membranes of the nose, mouth, throat, tracheobronchial nose, mouth, throat, tracheobronchial tree, esophagus, and genitourinary tract tree, esophagus, and genitourinary tract can be produced by direct application of can be produced by direct application of aqueous solutions of salts of many local aqueous solutions of salts of many local anestheticsanesthetics

• Infiltration anesthesia is the injection of Infiltration anesthesia is the injection of local anesthetic directly into tissue without local anesthetic directly into tissue without taking into consideration the course of taking into consideration the course of cutaneous nerves. Infiltration anesthesia cutaneous nerves. Infiltration anesthesia can be so superficial as to include only the can be so superficial as to include only the skin. It also can include deeper structures, skin. It also can include deeper structures, including intra-abdominal organs, when including intra-abdominal organs, when these too are infiltratedthese too are infiltrated

• Nerve Block AnesthesiaNerve Block Anesthesia Brachial plexus blocks are particularly Brachial plexus blocks are particularly useful for procedures on the upper useful for procedures on the upper extremity and shoulder. Intercostal nerve extremity and shoulder. Intercostal nerve blocks are effective for anesthesia and blocks are effective for anesthesia and relaxation of the anterior abdominal wallrelaxation of the anterior abdominal wall. .

• Spinal AnesthesiaSpinal Anesthesia

Spinal anesthesia follows the Spinal anesthesia follows the injection of local anesthetic into the injection of local anesthetic into the cerebrospinal fluid (CSF) in the cerebrospinal fluid (CSF) in the lumbar space.lumbar space.

ToxicityToxicity1-CNS(1-CNS(IMPORTANT TOXIC EFFECTS ARE IN CNS)IMPORTANT TOXIC EFFECTS ARE IN CNS) Low doses: Low doses:

Sleepiness, Light headedness, visual and Sleepiness, Light headedness, visual and auditory disturbances, restlessness, auditory disturbances, restlessness, tongue numbness.tongue numbness.--

Higher doses:Higher doses: Nystagmus, Muscular twitching, Nystagmus, Muscular twitching, convulsions, CNS depressionconvulsions, CNS depression..

2-2-Peripheral nervous systemPeripheral nervous system(Neurotoxicity(Neurotoxicity))

• sensory and motor deficits following spinal anesthesia

3-Cardiovascular System3-Cardiovascular System• Block cardiac sodium channels Block cardiac sodium channels • Depress abnormal cardiac pacemaker Depress abnormal cardiac pacemaker

activityactivity, , Excitability and conductionExcitability and conduction..• At very high concentration Also block CaAt very high concentration Also block Ca++++

channel. channel. Depress strength of cardiac contraction

Bupivacaine is most cardio-toxic

• CocaineCocaine • vasoconstriction -------------Hypertension • Vasoconstriction ------ ischemia, ulceration

of mucous membrane• In chronic users (addictors,snuffers)-------

Damage to nasal septum

4-Blood4-Blood• Prilocaine (large doses > 10 mg/kg) during

regional anesthesia-------- accumulation of metabolite ,

0 – toluidine -----------

• convert hemoglobin to methemoglobin• Patient may appear Cyanotic• Methemoglobinaemia can cause

decompensation in patients with cardiac or pulmonary disease

5-Allergic reaction5-Allergic reaction

• Ester type : metabolized to p – amino benzoic acid derivatives ------ allergy

• Amide type : do not metabolized to PABA