6th lecture - local anesthetics Flashcards
local anesthetics are
Substances that cause reversible local anaesthesia by affectingg sensory nerve fibres and endings, inducing absence of sensation.
They prevent the conduction of nerve impulses from the peripheral nervous system to the brain.
All types of sensation are switched off, including the sensation of pain.
The order in which sensation disappears:
pain, cold, warmth, touch and pressure sensation.
local anesthetic substances can be divided into (2)
esters & amides
local anesthetic esters (3)
Cocaine (not a medicinal product anymore)
Procaine (novocaine)
Tetracaine (Dicaine)
local anesthetic amides (4)
lidocaine
mepivacaine
bupivacaine
ropivacaine
Mechanism of action of local anesthetics
They inhibit the function of various ion channels.
Most important is the prevention of the movement of Na+ ions, which increases the depolarization threshold.
Depending on the pH of tissue, local anaesthetics in the organisms mainly take the form of cations.
Non-ionised forms are capable of penetrating cell membranes.
local anesthetics reduce the permeability of the cell membrane to
Na+ ions, closing Na+ channels, thereby preventing membrane depolarization, this leads to anaesthesia.
According to some theories Ca2+ ions are also involved in the mechanism of action.
Pharmacokinetics of local anesthetics
Metabolized in the
liver and in blood plasma by way of hydrolysis, catalyzed by non-specific pseudocholinesterase.
After metabolism, local anesthetics are excreted through the kidneys. Excretion depends on
urine pH.
Excretion is slowed down in alkaline urine because metabolites are not ionized.
Excretion is enhanced in case of acidic urine.
Describe Procaine
was the most used local anaesthetic before the amide-type local anesthetics were launched on the market (procaine is an ester), lately authorised again, used widely.
Reduces cardiac excitability, has an antiarrhythmic effect.
In case of large doses, a sharp decrease in blood pressure will occur.
Procaine is used to perform what type of anesthesia?
infiltration, epidural and paravertebral anaesthesia.
What is infiltration anesthesia?
Infiltration anesthesia is accomplished with administration of the local anesthetic solution intradermally (ID), subcutaneously (SC), or submucosally across the nerve path that supplies the area of the body that requires anesthesia.
e.g. local blocking a surgical wound
When procaine is used in combination with penicillin intramuscularly, it does what
it slows/prolongs the release of the penicillin.
lidocaine Effect is 2 times stronger than that of
novocaine.
Lidocaine is used for
infiltration, epidural and topical anaesthesia.
Lidocaine metabolism occurs in the
liver, excretion with urine. It quickly penetrates the placental barrier.
Lidocaine sideffects/signs of overdose
Muscular tremor,
hypotension,
nausea,
vomiting and
cramping may occur in case of overdose.
The toxicity of lidocaine increases depending on concentration.
What substance increases the toxic effect of lidocaine.
Pentobarbitone (pentobarbital)
Which local anesthetic substance can be used to treat heart rhythm disorders in dogs.
Lidocaine because it Has a strong antiarrhythmic effect
what is Etidocaine
A long-acting derivative of lidocaine.
It is suitable as a component of surgical anaesthesia, its postoperative analgetic effect is weaker.
Rarely used in veterinary medicine.
describe Mepivacaine
Its effect is similar to that of lidocaine but it is less toxic.
Onset of action is slower and duration of activity is longer than that of lidocaine.
It is not an effective topical anesthetic.
describe Bupivacaine
Long duration of action.
It is 4 times more potent than lidocaine but more toxic.
It is used for infiltration, nerve blocks, spinal and intrathecal techniques.
Because of cardiotoxicity its use in intravenous regional anaesthesia is contraindicated.
liquid nitrogen also known as?
Chloroethane
has been used as a local anesthetic for small areas of skin. used for removal of small skin lesions too.
describe local anesthetic toxicity/ side effects
Primarily related to systemic toxicity or hypersensitivity.
Toxic doses also cause a decreased cardiac output, slowdown in impulse transmission, decrease in blood pressure, dysarrhythmias (although lidocaine is used for stabilizing ventricular dysarythmias).
Cause of death is respiratory arrest.
