Local Anaesthetics

Local anaesthetics (L.A’s) are drugs that produce reversible inhibition of conduction along nerves Small sensory nerves are most affected, but in large doses large nerves (motor nerves) could be affected

L.A’s methods of application: - Direct application to mucus membranes and skin - Intradermal, local infiltration or S.C - Epidural injection, spinal or subararachnoid injection - I.V extremity block

L.A’s dosage forms: Creams, pastes, ointments, oral lozenges, suppositories and solutions for injection... Use of vasoconstrictors with L.A’s: Most commonly used AD (EP) or felypressin (ADH-like drug) Major purpose of adding a vasoconstrictor: - To extend DOA of L.A - To limit bleeding and to decrease or inhibit LA systemic absorption

L.A’s side effects: Allergy, convulsions, cardiac & respiratory depression Lidocaine (lignocaine; xylocaine) Most widely used L.A in all types of local anaesthesia Also has an antiarrhythmic effect (given I.V) used in certain types of cardiac arrhythmia

Prilocaine Similar to lidocaine but has longer DOA, widely used in dentistry Has unique side effect: Methemoglobinemia Bupivacaine Widely used in epidural anaesthesia Has slower OOA as compared to lidocaine

Amethocaine & oxybuprocaine Toxic L.A’s only used as L.A’s in the eye Cocaine Has marked CNS stimulant effect and sympathomimetic effects Produces vasoconstriction and euphoria Used as a surface anaesthesia in eye, throat and nasal surgery It produces addiction (major disadvantage)