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M3: LA > Pharmacology of Dental LA > Flashcards

Pharmacology of Dental LA Flashcards

1
Q

What is in a cartridge?

A
  • usually 2.2ml or 1.8ml
  • anaesthetic agent
  • vasoconstrictor
  • stabiliser/preservative
  • isotonic carrier medium - same concentration as tissue fluids
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2
Q

List some common preparations and their trade name:

A

Lidocaine and adrenaline - lignospan special

Mepivacaine - scandonest

Prilocaine and Felypressin - citanest

Prilocaine Plain (no vasoconstrictor) - citanest plain

Articaine and adrenaline - septanest

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3
Q

What is the general structure of a local anaesthetic agent?

A
  • aromatic ring (lipophilic)
  • intermediate chain
  • hydrophilic tail
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4
Q

What determines the type of LA?

What are the two types and how are they distinguished?

A

Structure of intermediate chain determines type of LA

  • ester - COO -
  • amide - NHCO -
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5
Q

List examples of esters?

Which drugs are classified as amides?

A
  • procaine and benzocaine

Amides: drugs by injection

  • lidocaine
  • prilocaine
  • mepivacaine
  • bupivacaine
  • articaine
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6
Q

How do LAs work?

What are the two theories on how they actually work?

A

LA works to block action potentials by reversibly blocking NA+ channels

  • Membrane expansion theory
  • Specific receptor theory
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7
Q

What does the membrane expansion theory suggest?

A
  • LA diffuses into axon membrane and expands membrane
  • Prevents sodium channels opening, as they are squashed together
  • Not likely
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8
Q

Explain the specific receptor theory:

A
  • LA binds to the sodium channel (reversibly)
  • Inactivates sodium channel, holding it shut

LA accesses Na+ channel from inside so:

  • LA must pass through phospholipid membrane
  • LA must be able to bind to Na channel
  • hence the lipophilic and hydrophilic ends
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9
Q

Explain some dissociation and solubility LA properties:

A
  • LA drugs poorly soluble in aqueous environment
  • Exists in 2 states: uncharged lipid soluble - pass through axon membrane, charged - binds to sodium channel

Proportion of charged vs uncharged depends upon:

  • pKA of the drug
  • pH of the environment
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10
Q

If a drug has a low pKA, how does this affect it?

Low pH? What can cause low pH?

A

Low pKa:

  • more uncharged drug
  • passes through nerve membrane rapidly

Low pH results in a slow onset as there are more charged molecules and can lead to failure

Low pH can be due to inflammation and infection

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11
Q

What are protein binding LA properties?

A

Protein binding:

  • increases duration
  • provides a pool of LA
  • drugs with high protein binding include bupivacaine and articaine
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12
Q

How is vasodilation a property of LA?

A
  • all are vasodilators
  • increases rate of systemic uptake
  • least vasodilatory are prilocaine and mepivacaine (plain preparations with no vasoconstrictor)
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13
Q

What type of nerves are easier to block and lasts longest?

A
  • C fibres are easiest (smallest and most commonly associated with pain)
  • A-delta
  • A-beta
  • A-alpha are most difficult (largest)
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14
Q

Name the types of local anaesthetics:

A
  • lidocaine - gold standard
  • priloccaine - an alternative
  • mepivacaine - an alternative - least vasodilatory
  • bupivacaine - high protein binding –> long acting
  • articaine - relatively new witha unique selling point: diffusability
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15
Q

What is absorption?

What does this depend on?

A
  • uptake from site of deposition into bloodstream, loss of LA activity

Depends on:

  • dose
  • vasoactivity of LA
  • vascularity of tissues
  • vasodilator effect vs use of vasoconstrictor
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16
Q

Where can LA be distributed?

A
  • unbound LA may enter any organ
  • in particular, organs that are highly perfused: brain, liver, kidneys, placenta
17
Q

How can LA affect other organs?

A

CNS: initial stimulation, depression of CNS with increasing dose

Peripheral vessels: vasodilation, overdose –> hypotension

Respiratory system: low doses - bronchodilation, high dise: CNS depression

Myocardium: reduces excitability and conductivity, used in acute cardiac care

These side effects only occur when you over-prescribe dose of LA

18
Q

Where are LAs metabolised?

What are the half lives of lidocaine, prilocaine and articaine?

A
  • amidases breakdown LA drugs in the liver
  • important to recognise patients with liver disease as you must reduce dose of LA

Prilocaine is broken down in the lungs

Articaine is broken down in plasma

Half life of lidocaine and prilocaine - 1.6 hours

Articaine - 0.5 hours

19
Q

Why do we use vasoconstrictors?

A
  • increase speed of onset
  • counteract vasodilatory effects of LA agent
  • extend duration of anaesthesia
  • improve depth of anaesthesia
  • lower blood levels of LA
  • reduces haemorrhage
20
Q

What are the types of vasoconstrictors?

A

Adrenaline: sympathomimetic amines

  • acts on alpha 1 receptors causing vasoconstriction
  • concentration usually 1:80,000 = 12.5 micrograms/ml
  • 2.2ml cartridge contains 27.5 micrograms
  • requires a preservative to maintain shelf life

Felypressin: synthetic polypeptides

  • 0.03 IU/ml = 0.54 micrograms/ml
  • analogous to vasopressin
  • works on venous side
  • vasocontrictive potency is half that of adrenaline
  • poor haemostasis compared to adrenaline
21
Q

Is there any contra-indications of any vasoconstrictors in pregnancy?

A

Felypressin and pregnancy

  • mild toxic effect
  • theoretical risk of interfering woth placental circulation and uterine tone
  • however dose used in dentistry is small: need ~100 cartridges to induce labour
  • despite low risk, should avoid in pregnancy
22
Q

What % anaesthetic is in Lidocaine hydrochloride?

  • Vasoconstrictor?
  • Preservative?
  • Maximum Anaesthetic Dose?
A
  • 2% = 20mg/ml (44mg in a 2.2ml cartridge)
  • Vasoconstrictor: adrenaline, 1:80,000 = 12.5micrograms/ml
  • Preservative: sodium or potassium metabisulphite

Maximum Anaesthetic Dose:

  • 4.4mg/kg upto a maximum of 300mg = 6.8 cartridges!
23
Q

How is maximum anaesthetic dose of 2% lidocaine and adrenaline calculated for a 70kg healthy adult?

Explain another way to work this out:

Are there any important points to note regarding maximum dose?

A

4.4mg/kg upto a max of 300mg

max dose = 70 x 4.4 = 308mg but max dose is 300mg

  • 2.2ml cartridge contains 44mg
    so: 300/44 = 6.8 cartridges
  • very rarely need more than 3 cartridges

Another way to calculate: a tenth of a cartridge per kg for healthy patients

e.g. cartridge for every 10kg of body weight up to a max of 6.8 cartridge

Once max dose reached, do not switch to another LA drug as it uses same metabolic pathways, resulting in a high level of anaesthetic in bloodstream!!

24
Q

What is the concentration of anaesthetic in mepivacaine hydrochloride?

Vasoconstrictor?

Preservative?

Max Dose?

A
  • 3% = 30mg/ml (66mg in a 2.2ml cartridge)
  • No vasoconstrictor
  • No preservative

Maximum anaesthetic dose:

  • 4.4mg/kg (absolute max 300mg)
25
Q

Concentration of Prilocaine?

Vasoconstrictor?

Preservative?

Maximum dose?

A
  • 3% = 30mg/ml (66mg in a 2.2ml cartridge)
  • vasoconstrictor: Felypressin - 0.03IU/ml = 0.54micrograms/ml
  • No preservative

Maximum Anaesthetic Dose:

  • 6mg/kg (absolute max 400mg)
26
Q

What LA should you use for majority of procedures?

When should this not be used?

A

Lidocaine/Adrenaline should be used as it results in effective haemostasis, anaesthesia, and is safe.

Do not use if patient has:

  • unstable angina
  • severe cardiac dysrhythmia
  • allergy to any components

Caution with other cardiac conditions

  • avoid or reduce dose
27
Q

When would you use prilocaine?

Mepivacaine?

Articaine?

A

Prilocaine:

  • wish to avoid adrenaline
  • preservative allergy
  • avoid prilocaine in pregnancy

Mepivacaine:

  • use as an alternative to prilocaine
  • short acting

Articaine:

  • USP: diffusability, especially through bone
  • potential alternative to inferior alveolar blocks
28
Q

What type of patients should you reduce dose of LA?

Are any drugs contraindicated with use of adrenaline?

A
  • liver disease: impaired metabolism
  • beta blockers
  • calcium channel blockers
  • drug abusers

Reduce dose or use alternative (prilocaine) in patients who take tricyclic antidepressants and mono-amine oxidase inhibitors as use of adrenaline was thought to be contraindicated

29
Q

What are the main features of articaine?

A
  • classified as an amide but contains an ester group (helps systemic safety)
  • lipophilic component is a thiophene ring which increases lipid solubility (better diffusivity and imporves efficacy)
30
Q

Concentration of articaine?

Vasoconstrictor?

Preservative?

Maximum Anaesthetic Dose?

When should this not be used?

A
  • 4% - 40mg/ml (88mg in a 2.2ml cartridge)
  • vasoconstrictor: adrenaline, 1:100,000 = 10micrograms/ml
  • preservative: sodium metabisulphite

Maximum Anaesthetic Dose:

  • 7mg/kg (upto a max of 300mg)

Do not use in children under 4 years

31
Q

How is articaine metabolised?

A
  • Plasma: plasma esterase enzymes break ester bonds and deactivate drug when enters bloodstream
  • Liver: hepatic amidase enzymes break amide bond
  • Elimination via kidneys
  • rapid breakdown –> low systemic toxicity –> safe
  • mothers should not breastfeed for 48 hours following anaesthesia as effects are unknown
32
Q

What are the three things to consider whether you adopt something new/else?

What is special regarding articaine?

A
  • Efficacy - is it as good as the others?
  • Is it better than the others? Any USP?
  • Is it safe?

Articaine USP:

  • ability to diffuse through bone
  • can achieve anaesthesia of lower posterior teeth by infiltration
33
Q

What are the safety points of articaine?

A
  • rapid metabolism (plasma and liver)
  • high protein binding: less of drug free to float around body
  • lower adrenaline concentrations - 1:100,000 or 1:200,000
  • higher anaesthetic concentrations (4%)
  • no serious adverse effects
34
Q

What causes paraesthesia?

A
  • physical trauma to nerve trunk
  • not likely due to articaine itself as it has the lowest neurotoxicity when compared to other drugs at the same concentration
  • likelihood of nerve damage following regional LA apears to be more likely when LA concentration is increased
35
Q

What is the advise for articaine and IANB?

A
  • IAN block dependent on technique, anatomy, not diffusability through bone
  • avoid articaine for IAN block injections
  • consider using it by infiltration for: failed IANB, supplementary IANB, as a potential alternative to IANB

M3: LA (4 decks)

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