Pharmacology To LA Flashcards
What topical preparions For la are there?
Lidocaine
Benzocaine
What are the two types of LA techniques?
Topical: provides LA to soft tissues
Injectable: provides nerve block and infiltration
How can topical LA affect dose absorbed?
Lidocaine: well absorbed so must be included in max dose to pt
Benzocaine: poorly absorbed and works faster and have choice of flavours, less important in total dose
How far dose topical anaesthetise to?
2-3mm depth
What type of tissue does topical work on?
Non keratinised so little use on palate
Why is topical not effective on keratinised mucosa?
Tissues deeper tha 2-3 means thr pain is produced by rapid rate of injection
How long should you leave topical to work?
2 mins
What is the difference between anaesthesia and analgesia ?
Anaesthesia: absence of all sensation
Analgesia: abscence of pain sensation
Which LA do we mainly use as dentists in UK?
Lidocaine
Which anaesthetic agents do we use as dentists?
- Lidocaine 2% with adrenaline 1:80,000
- Prilocaine 3% with felypressin 0.031IU/ml
- Articaine 4% adrenaline 1: 1/2/400,000
What is the max dose of lidocaine?
4.4mg/kg up to 300mg
When would u use Prilocaine?
When epinephrine contraindicated but not as effective as lidocaine
Hat is the max dose for Prilocaine?
8mg/kg
400mg
What is the issue with felypressin?.
Can cause coronary artery constrictionso limit dose in patients with IHD to 3 cartridges
Not to be used in preg
T/Farticaine has a short half life?
T
What is the max dose of Articaine?
7mg/kg
T/F Articaine can be used for ID block
T
However until further evidence should use other anaesthitics
T/F LA is inherently water soluble?
F
to make it water soluble it is combined with HCL
What is the purpose of adding adrenlaine?
vasconstricor
pronlongs duration
What s the effect of adrenlaine?
this causes the pH of the anaestehtic to drop even more and become smore acidic which means aneasthetic stings upon entry and it has a slower onset
What is pKa?
this is the dissociation constant
the pH at which 50% of the LA will be in the ioned form and 50% will be in the unionesed for,
What form iones or unionised does LA need to be in to cross across the nerve membrame?
un ionised
if the pKa of lidocaine is 7.9 what does this mean?
below 7.9 more than 50% will be ionised
above 7.9 less then 50% will be ionsed i.e more unionsed
What is adde to the LA solution to help try an increase the number of unionsed particles?
Sodium bicarbonate
What is an alternative to adrenalin?
Felypressin
Allergies
Cocaine users
What is blocked by the LA?
LA blocks the sodium poassium voltage gated channels. it binds to the sodium portion and prevents sodium from rushing inside also by membrane expansion (10% of effect)
two therories: non specific and specific
non: membrane expansion, where the lipophilic aromatic ring is incoporated into the nerve cell membrane, this then causes the nerve cell memenrae to swell and makes the sodium channells smaller and thus harder for sidum to pass through
specific: charged hydrophilic portion binds to the some areas os the sodum channel to obstucy sodum ion passage
What is the resting potentil of the nerve membrane?
-70mV
What happens when an action potental is fired?
sodium rush in making the rsting potentil more postive to +40mV(depolarisation)
postassium rush out in the repolarisation making it more negative again (repolarisation)
What is the threshold value for depolarisation?
-55mV
What is the molecular structure of LA?
Aromatic ring
intermidiate linkage (amids or ester)
terminal amine
Wwhich portion is lipophilic?
AROMATIC RING
Which portion is hydrophilic?
terminal amine
WHich LA are amides?
Lidocaine
prilocaine
mepivaein
bupivicaine
Where are amides metabolised?
liver
What LA are esters?
articane
procaine
Benxocaine (topical)
Wheere are esters matbalised/
plasta cholinesterarses
Whcih LA is both amide and ester?
articaone
What is the half life, time of onset and duration of action for lidocaine?
Onset – 2-5 mins
Half life 90 mins
Duration pulpal – 45 - 60 mins
soft tissue - 2- 3 hrs
What is the half life, time of onset and duration of action for articaine?
Onset 1-6 mins
Half life 20 mins*
Duration pulpal – 75 mins
soft tissue – 20 to 175 mins
What is the half life, time of onset and duration of action for prolicaine
Half life 90 mins
Duration pulpal – 60-90 mins
soft tissue – 2-4 hrs
What are the contents of LA?
LA base HCL salt Vasocontrictor buffering agents eg sodium bicarbonate preservatives eg methyl paraben, soduim suplphite which stabilises adrenaline
Name an example of a catecholamine vasocontrcirt?
aderenaline
NAme an example of a non catecholamine vaso?
felyprssin
Why is LA less effective in infeted tissues?
infmaked tissues: acidic therefore less LA is ionised form
increased vasculaiurty: which means more solution is removed away
prostaglandins lower the threshold for nerve firing and higher concentration of LA is needed
Why do children with abscess on upper molars always present with faciall sweeling?
because they have a low attatchent of buccinator
