Local anaesthetics Flashcards
Describe mechanism of action of local anaesthetics
Reversibly block conduction of impulses along nerve axons, and other excitable membranes that utilize sodium channels.
Sodium ions then become unable to pass through the channels blocked by anaesthetics, and impulses are not conducted.
Local anaesthetics are used to
Block pain sensation from sympathetic vasoconstrictor impulses to specific areas of the body.
What was the first local anaesthetic drug?
Cocaine
Application methods for local anaesthesia:
- Topical/surface
- Infiltration
- Intravenous regional
- Nerve block
- Spinal
- Epidural
- Injection into trigger points in horses with recurrent limb pain
Two types of local anaesthesia:
Esters
* cocaine, procaine, benzocaine and tetracaine
* Short half-life, broken down by cholinesterase enzyme in the extracellular fluid
Amides
* trimecaine, lidocaine, bupivacaine and mepivacaine
* longer acting, broken down by liver
Describe use, risks and mechanism of action of cocaine
Ester
Use: nasal and lacrimal duct surgery in horses
Risk of cardiovascular toxicity
Mechanism of action: intense vasoconstrictor
Describe use, risks, effects and mechanism of action of procaine
Ester
Use and effect: Infiltration and nerve block
1% in small animals and 2% in large animals
Not very effective for surface anaesthesia
Describe use, risks, effects and mechanism of action of benzocaine
Ester
Use: dentistry and cutaneous, numb larynx prior to intubation
Low solubility - can remain localized in wounds to provide long analgesia
Describe use, risks, effects and mechanism of action of tetracaine
Ester
Use: eye, nose and throat, spinal.
Rapid adsorption from mucosa increases the risk for cardiovascular toxicity.
Patch application system and gel preparation –> percutaneous analgesia with favourable results
Describe use, risks, effects and mechanism of action of trimecaine (mesocaine)
Amide
Topical, infiltrational anaesthesia
Prophylaxis and therapy of arrhytmia in myocardial infarction
Antiarrhytmics - block sodium channels
Describe use, risks, effects and mechanism of action of lidocaine/lignocaine
Amide
Used for all types of local anaesthesia
Adrenalin prolongs the effects and decrease the bleeding
Antiarrhytmic agent - 4mg/kg in dogs
Supplement to general anaesthesia
Injected near nerves so nerves cannot conduct signals to or from the brain
What are keratoplastics and keratolytics
Keratoplastics are substances that support the formation of the corneal layer of the skin.
Keratolytics dissolve this layer.
Salisylic acid and its compounds act as:
Keratoplastics at conc. <3%
Keratolytics at higher conc. <10%
Depilatories are:
Capable of dissolving hair
Keratoplastics and keratolytics are used to:
Soften keratin
Improve skin moisture binding capacity
Remove warts, calluses and other lesions
