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Questions 1.

Write short notes on the pharmacology and side effects of local anaesthetic agents. Attempted by 20 candidates PASS RATE 95 %

  • Pharmacokinetics Behaviour of the drug in the body (what the body does to the drug). Half life, volume, distribution

  • 􏰟 Pharmacodynamics Effects on the body (what the drug does to the body) Absorption, distribution, metabolism, excretion, metabolism. Esters and amides, absorption, toxicity, systemic blood levels, duration of action.

  • 􏰟 Patient Factors Site of administration. Intercostal greater than caudal, greater than brachial plexus. Tissue Ph, pregnancy, paediatrics.

  • 􏰟 Drug Factors pKa, ionisation, lipid solubility, protein binding.

􏰀 Routes of administration: topical, eye drops, amethocaine (ester), EMLA to skin, buckle, mucosa, urethral. Subcutaneous, nerve blocks, intravenous regional anaesthesia/analgesia. 􏰀 Role of local anaesthetics in neuropathic pain. Intravenous infusions, headaches. Local anaesthetic oral analogues, mexiletine. 􏰀 Toxicity: Allergic - esters, amides rare. Local myotoxicity if large intra muscular doses Systemic toxicity related to blood level - related to rate of absorption, related to site of injection, Volume and concentration of drug = dose central nervous system, mechanism unclear but neuronal desynchronisation leading to seizure then inhibition of inhibitory and facilitatory pathways and generalised CNS depression. Circumoral tingling, fitting coma, cardiotoxicity, Na channel block conduction slowing widening QRS complex arrhythmia, cardiac arrest. Treatment: prevention, supportive care Ability to provide CPR/ALS when using doses of local anaesthetic Possible role for intralipid Prevention: maximum doses in any four hour period: Lignocaine 4 mg per kg. Lignocaine with adrenaline 7 mg per kg, Bupivacaine 2.0 mg per kg, Faculty of Pain Medicine 2006 Examination Report

Cardiotoxicity: Lignocaine, ropivacaine, bupivacaine, isomer (levo bupivacaine) safer then bupivacaine, Also include maximum safe doses for prolonged infusion e.g. 400mcg/kg/hr Comment that these levels only safe if there are likely to be normal AAG levels etc

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