Local Anaesthetic agents Flashcards
Local anaesthesia function?
prevents transmission of
the nerve impulse in the
region to which it is
applied, without affecting
consciousness
LA Irr/revsersible?
revsersible
Local anaesthetics?
Local anaesthetics are drugs which upon topical application or local
administration causes reversible loss of sensory perception,
especially pain in a localized area of the body
No structural damage to neurons
Local anaesthetics chemical structure?
-Weak bases
-Lipophilic ring
-Hydrophilic amine
-Intermediate chain: amide or ester
Local anaesthetic topical drugs?
Local TOP Benzo’s
Lignocaine
Tetracaine
Oxybuprocaine
Prilocaine
Benzocaine
Local anaesthetic injectable drugs?
My Role Leaves Lover Boys
Mepivacaine
Ropivacaine
Lignocaine
Levobupivacine
Bupivacaine
Local anaesthetic MOA?
block voltage-gated sodium channels & reduce influx of sodium
ions
preventing depolarization of the membrane blocking conduction
of the action potential
LA bases or acids?
All LA agents are weak bases
What are the two forms that LA exist in?
Unionised and ionised
The importance of pKa of a LA?
The pKa of a weak base defines the pH at which both forms exist
in equal amounts
As the pH of tissues differs from the pKa of the specific drug,
more of the drug exists either in its charged or uncharged form
Relationship of pKa and ionisation for local anaesthetics
Decrease in pKA, increases ionisation
Infected tissue pH variations?
Infected tissue reduced pH
Fraction of unionised LA is reduced –> effect
reduced/ineffective
Infected tissue increased blood supply - more LA removed
from local area before it can have an effect on the neuron
What makes LA more potent-explain the chemistry too?
-Longer hydrocarbon chain length
more lipophilic
-More lipophilic more potent:
penetrates the cell membrane
more easily to exert effect
-Bupivacaine high potency
What affects LA tissue binding ability?
-More protein binding. More protein bound, the tighter is binds and longer the duration of action.
Different types of nerve fibres of LA?
Type A:(heavy myelination)
Alpha: Proprioception, Motor
Beta: Touch, pressure
Gamma: Muscle Spindle
Delta: Pain, temperature
Type B:(light myelination)
Preganglionic autonomic
Type C:
Dorsal Root-pain(zero myelination)
Sympathetic-post ganglionic(zero myelination)
Influence of LA blocking based on diameter?
Small diameter nerve fibers (e.g. C-fibers) are more readily blocked
than large fibers
Influence of LA blocking based on myelination?
Myelinated fibers are more susceptible to blockade than unmyelinated fibers of the same size (mechanism not clear)
What order are fibres blocked in?
- Sympathetic and pain
- Temperature
- Light touch and proprioception
- Motor
What order does recovery of drugs occur in?
- Motor
- Light touch and proprioception
- Temperature
- Sympathetic and pain
Benefit of motor being last order of LA blockage?
This is exploited to produce analgesia with minimal or no motor block,
by using lower concentrations of LA
Addition of vasoconstrictor on LA?
Increases duration of action added to injectables
Localize the anaesthetic at desired site
Prolongs duration of action of LA
Reduce local haemorrhage
Reduce amnt of LA absorbed into
systemic circ
Decrease toxicity
What are the drug interactions precautions to use of vascoconstrictors?
Tricyclic antidepressants (e.g.: Amitriptyline)
potentiates hypertensive effect
Non selective beta blockers (e.g.: Propranolol)
increase BP, reflex decr HR, monitor BP
Cocaine, methamphetamine abusers
increase risk HT crisis, stroke, MI , postpone 24 hours
Digoxin
narrow TI, may ppt cardiac arrythmias
Undergoing general anaesthesia (e.g.: Halothane)
increase dysrhythmic effects of
Contraindications of vasoconstrictors?
Severe heart disease
Uncontrolled hyperthyroidism
Sulphite allergies
Asthmatics (corticosteroid-dependant)
Pheochromocytoma-releases and increase overstimulate CNS
LA P/K?
LA administered to areas to be
blocked: skin, s.c tissues, intrathecal, epidural spaces
Some of the drug will be
absorbed into systemic
circulation
Intrinsic effects of drugs
Vascularity of tissue/area
Additives
Pharmacokinetics
High vascularity to low:
IV > tracheal > intercostal > caudal > epidural > brachial > sciatic > s.c
Metabolism P/K?
ESTERS
Metabolism
Plasma cholinesterase’s to
inactive compounds
Shorter time
AMIDES
Metabolism
In Liver hepatic cytochromes
Longer process
Administration of LA formulation for oral and injections?
Water solubility of a LA is greatest in its ionised form
Injectionable preparations are formulated as HCL salts
Increasing alkalinity of injection solution increases the speed of acti
Several administrations of LA?
- Topical
- Infiltration
- Peripheral nerve block
- Central nerve block (epidural and spinal)
- Intravenous regional
Topical Anaesthesia?
High concentrations of LA in an oily vehicle slowly penetrate the
skin or mucous membrane
Topical Anaesthesia duration?
Provides short term pain relief
Topical Anaesthesia drugs?
Long TOP’s Benzo
Lignocaine
Tetracaine
Oxybuprocaine
Prilocaine
Benzocaine
Examples of topical administration of LA?
o Creams
o Gels
o Lozenges
o Sprays
o Eye drops
o Patches
Infiltration of LA?
LA is injected intradermally or subcutaneously by the area to be
anaesthetised
Infiltration of LA time?
Produces numbness faster than topical anaesthesia
Infiltration of LA usuage now?
Used extensively in dentistry – lignocaine is the most widely
used injected anaesthetic
Infiltration drugs?
Mouth Really Be Laughing
Mepivacaine
Ropivacaine
Bupivacaine
Lignocaine
Peripheral Nerve Block Anaesthesia?
Injection of LA solution around a nerve trunk
Produces fields of anaesthesia distal to site of injection
Peripheral Nerve block usuage?
E.g. a brachial plexus block is used to anaesthetise the whole
arm
Peripheral Nerve Usuage drugs?
Bupivacaine
Lignocaine
Mepivacaine
Ropivacaine
Central nerve block anaesthesia ?
LA is injected near the spinal cord
Produces anaesthesia above and below site of injection
Epidural anaesthesia used extensively during labo
Central nerve block anaesthesia drugs?
Bupivacaine
Lignocaine
Ropivacaine
Intravenous regional anaesthesia?
LA is injected into a limb after application of tourniquet
Intravenous uses?
Used for manipulation of fractures and minor surgical
procedures
Intravenous IV drug?
lignocaine
Local Anaesthetic Systemic Toxicity (LAST)?
SAMS
Slurred or difficult speech
Altered Central Nervous System
Muscle Twitching
Seizures
LA systemic toxicity CNS?
Symptoms:
Tingling of lips
Slurred speech
Reduces level of consciousness
Sezures
LA systemic toxicity Prevention?
Prevention/Treatment
Oxygen for loss of conciousness
Benzodiazepines thiopentone for seizures
LA respiratory toxicity mean?
Respiratory Arrest
LA respiratory toxicity symptoms ?
Reduced myocardial
contractility
Arrythmias
Hypotension
Ventricular fibrillation -
bupivacaine
LA prevention for hypotension?
Vasopressors
(ephedrine/ phenylephrine)
Inotropes
(adrenaline)
Prevention of toxicity?
Use max safe dose
Aspirate regularly during injection
Adrenaline if appropriate
Test doses
Stabilise needle carefully
Monitor patients vitals
Amides -Bupivacaine P/K?
Long-acting LA {doa usually 3 hours, peripheral blocks: 2-24hrs: dose & site}
Slow onset of action: 30 mins
Bupivacaine is a potent LA capable of producing prolonged anaesthesia
Widely used during labour or postoperatively
Amides -Bupivacaine I?
Local infiltration, regional block, spinal & epidural anaesthesia
Chiefly used for surgical anaesthesia (0.5%)
Useful in providing several days of Analgesia (admin. via indwelling
catheters & continuous infusions)
Amides Metabolism?
Liver
Amides toxicity?
Cardiotoxic
Amides-lignocaine indications?
INDICATIONS:
Local/topical
Infiltration
Intravenous regional anaesthesia (biers block)
Epidural anaesthesia
Eye block
Amides-lignocaine P/K?
Onset of action: rapid
Duration: Intermediate
Amides-lignocaine CI?
Heart block and conduction disturbance
Amides-lignocaine DI?
-Cimetidine/Beta Blockers
Mepivacaine I?
INDICATIONS:
Infiltration and nerve blocks
Metabolism: Liver enzymes
Mepivacaine Duration?
Intermediate acting
Ropivacaine duration?
LONG ACTING LA
Ropivacaine indications?
Epidural anaesthesia
Local nerve block
Infiltration
Analgesia
Ropivacain metabolism and cautions?
METABOLISM: Liver enzymes
CAUTIONS: partial or complete
heart block, elderly, liver dysfunction
Amides-articane I?
Infiltration
Nerve block
Amides-articaine P/K?
An amide but contains ester side chain which is hydrolysed - plasma esterases
Elimination half life: 20-40min
High lipid solubility - thiophene ring
Rapid onset
Prilocaine P/K?
Topical anaesthesia
Available in combination with lignocainE
Prilocaine skin P/K?
Mucosa: apply and leave unoccluded for 10-15min
Intact skin: apply a thick layer and cover
with an occlusive dressing for 1-2 hours
(analgesia: for +/-2 hrs after removal of
dressing)
Lignocaine P/K?
Topical spray: larynx
Jelly: urethral anaesthesia &
haemorrhoids
Patch: (5%, S4) neuropathic
pain relief (PHN)
Tetracaine uses?
Uses:
Topical cream: pain relief in
haemorrhoids and minor skin burns
Eye drops: ophthalmology in
tonometry, foreign body removal,
suture removal
Oral gel: pain relief of mucous
membranes of mouth, lips, gums
Benzocaine uses?
Topical gel: dentistry injection
sites: minimize sensation
Lozenge: Surface anaesthetic -
pain relief of sore throats
Throat spray
Throat gargl
Oxybuprocaine
Uses:
Eye drops: ophthalmology in
tonometry, foreign body removal,
suture removal
Has additive bactericidal activity
