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Exodontia > LA - pharmacology > Flashcards

LA - pharmacology Flashcards

1
Q

Analgesia definition

A

Loss of pain alone

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2
Q

Anaesthesia definition

A

Loss of all forms of sensation

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3
Q

Local anaesthesia definition

A

Loss of sensation in a circumscribed areas of the body by a depression of excitation in nerve endings or an inhibition of conduction process in peripheral nerves

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4
Q

LA uses

A 
Controlling operative pain
Control post-operative pain
Controlling operative haemorrhage
Diagnosis of pain
Relief of orofacial pain - topical and injection
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5
Q

History of LA drugs

A

1855 - Gardeke - extracted cocaine = leaves chewed with lime by natives of Bolivia and Peru
1884 - Carl Koeller - synthesised procaine
1943 - Nils Lofgren - synthesised lignocaine
1963 - Prilocaine

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6
Q

History of LA administration

A

1827 - Nov Neuner - seveloped syringe for vet use
1884 - Zophar Jayne - used syringe in man through incision
Nov 1884 - William Halstead - blocked IAN by injection of 4% cocaine
1917 - Harvey COok - devised cartridge system

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7
Q

Chemistry of LAs

A

All weak bases with general formula
Aromatic group - intermediate chain - 2. or 3. amine
-aromatic group is lipophilic i.e. dissolve in lipid sheath around nerve
-intermediate chain are esters or now amides
-amino terminal is hydrophilic (1. soluble and 2 transfer through interstitial fluids)

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8
Q

Ester or amide

A

Early: cocaine, procaine and amethocaine aromatic and intermediate groups were ester
-disadvantages: unstable in soln, not autoclavable, antigenic/ allergy
Lignocaine, prilocaine and all other are amides
-advantages: more stable, autoclavable and very rarely antigenic

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9
Q

Example of long acting LA

A

Bupivocaine

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10
Q

Example of short acting LA

A

Procaine (ester, don’t use it anymore)

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11
Q

How is drug administered so it dissolves

A

LAs are weak organic bases - poorly soluble in H2O
Drug combined with strong acid to form water soluble salt (usually hydrochloride)
Therefore ionises to cationic form (pH in cartridge approx 2-6)
Active form is non-ionised base formed in tissues and is lipid soluble (therefore penetrates lipid membranes and tissue barriers)
Therefore, at physiological pH (extra-cellular fluid = 7.4), need reasonable conc. of non-ionised form (lignocaine approx 25%, procaine approx 2.5%, therefore lignocaine better)

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12
Q

Mode of action

A

Nerve conduction
Depolarisation by receptor potential/ chemical etc. –> a.p.
At rest nerve cell membrane largely impermeable to sodium ions
If stimulus reduces electro- charge to around -55mV (firing level) then membrane becomes highly permeable to sodium ions - a.p.
LA binding site is inside nerve cell - hence need for LA to be non-charged
Once inside nerve it re-equilibrates into mixed charged and non-charged forms. Charged form binds to specific receptor (specific receptor theory)
Non-specific action of LA is lipophilic portion of molecule may cause swelling of membrane (non-specific theory)
Initially high threshold for excitation, then conduction block

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13
Q

Henderson-Hasselbach equation

A

Look at graphs on slides

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14
Q

Anaesthetic drug - non-ionised form penetrates

A

Epineurium
Perineurium
Endoneurium

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15
Q

Two theories of mode of action

A

Once inside nerve it re-equilibrates into mixed charged and non-charged forms. Charged form binds to specific receptor (specific receptor theory)
Non-specific action of LA is lipophilic portion of molecule may cause swelling of membrane (non-specific theory)

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16
Q

What does LA effect

A

Affects all fibre types (not function specific), but small (pain and T) first and large (motor, proprioceptive) last
Vasomotor (BV wall) effects:
-blocks sympathetic vasoconstrictors (therefore dilation)
-direct effect on smooth muscle of vessels is variable (cocaine constricts, lignocaine dilates)

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17
Q

Detoxification of esters

A

Esters - esterases in blood and liver –> benzoic acids and alcohol –> urine
1:2800 of pop. lack peudocholineserase (plasma) - problems with suxamethonium (GA) but OK with amide LAs

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18
Q

Detoxofication of amides

A

Mainly broken down in liver, oxidised, some conjugated with glucuronic acid, all –> urine
Therefore if severe liver disease
Lignocaine half life 90 mins
Articaine (amide) undergoes initial breakdown by esterases in the plasma. Rapid breakdown - half life 20 minutes

19
Q

Ideal characteristics

A

Produce complete LA without damaging or other local tissues
Rapid onset with predictable and appropriate duration
Isotonic
Non-toxic sytemically
Readily soluble and stable in soln. (adequate shelf-life - usually 2-2 1/2 years)
Sterilisable (esters not autoclavable)
Non-addictive (not cocaine)

20
Q

Citonest

A

Trade name of prilocaine

21
Q

Intermediate duration LAs

A

Lignocaine
Prilocaine
Mepivacaine
Articaine

22
Q

Vasoconstrictors advantages

A

Delay removal from site
More rapid onset of anaesthesia
Prolongs and enhances effect
Reduces operative bleeding

23
Q

Vasoconstrictors disadvantages

A

Prolonged soft tissue anaesthesia unpopular with pxs e.g. dentala analgesia from lignocaine 2% with 1:80,000 adrenaline = approx 1/3 - 1 hour; soft tissue approx 3 hours
Without adrenaline, analgesia = 5-20 mins; soft tissue = approx 1 hour
Potential systemic effects (e.g. heart palputations) with intravascular injection

24
Q

Adrenaline

A

Usually used as 1:80,000 (12.5µg/ml) with lignocaine
Systemically, affects α and beta receptors, with +ve inotropic (force) and chronotropic (rate) effects and > potential for arrythmias
In practice, these effects are usually insignificant

25
Q

Adrenaline with affect

A 
Blood pressure
-vasodilation of muscles
-vasoconstriction of skin
Heart rate
->rate and force of contractions
Blood glucose
-> glucose
Plasma potassium
-< potassium
26
Q

Noradrenaline

A

Can cause > BP and lead to CVA (stroke)

Never used in UK

27
Q

Felypressin (octapressin)

A

Synthetic polypeptide. similar to vasopressin
Usually used as 0.03 i.u. with prilocaine (citanest)
Less likely to produce CV effects than adrenaline
Action on uterus - beware preganncy

28
Q

Why do we avoid esters

A

Can cause allergies

29
Q

Reducing agent

A

Sodium metabisulphate to prevent oxidisation of vasoconstrictors (brown discolouration)

30
Q

Preservative

A

e.g. Methyl paraben

May be responsible for allergic reactions (no longer used by Dentsply)

31
Q

Fungicide

A

e.g. thymol or fungi, may cause cloudiness

32
Q

Modified Ringer’s solution

A

Isotonic

33
Q

Cocaine

A

Rarely used
May cause idiosyncratic reactions in some people
Sometimes used by anaesthetists to aid nasal intubation (vasoconstrictor effet)
Systemically causes exhiliration and overcomes fatigue but is addictive and toxic with overdose
Can lead to tremors, convulsions, hallucinations, etc
Categorised as a dangerous drug

34
Q

Procaine

A

1905-1940s
Ester, slow onset, short duration, poor penetration of tissues
Superseded

35
Q

Amethocaine

A

Ester, potent and long-acting and highly effective as a surface anaesthetic
Not used routinely

36
Q

Lignocaine trade names

A

Lidocaine, xylocaine, xytolox, lignostab

37
Q

Lignocaine

A

Most widely used LA drug
2% soln usually with 1:80,000 adrenaline
Max total dose approx. 4.4mg/kg in healthy adult (approx 7 cartridges)
Rapid onset - good penetration

38
Q

Other application %s of lignocaine

A

5% ointment, 4% or 10% spray or 2% gel, for topical use (ulcers etc.)

39
Q

Mepivacaine (Carbocaine)

A

Similar to lignocaine
3% plain (without vasoconstrictor) is better than plain lignocaine and so good for short procedures
2% with 1:80,000 adrenaline is indistinguishable from lignocaine

40
Q

Bupivacaine (Marcain)

A

0.5% solution, 1:200,000 adrenaline
Slow onset but very long duration (approx 2x lignocaine)
Used for major surgery or short term relief for trigeminal neuralgia

41
Q

Prilocaine (Citonest)

A

4% plain or 3% with felypressin
Rapid onset, good penetration
Used if avoiding adrenaline
Used with lignocaine as EMLA (Eutectic Mixture of LAs) for venepuncture in children

42
Q

Articaine (Ultracaine)

A

4% with adrenaline
Claimed to diffuse widely
Not yet in routine use and may cause > incidence of nerve damage
Avoid use for nerve blocks

43
Q

Ropivacaine (naropin)

A

Long acting agent, recently launched in UK

Not yet in routine use

44
Q

Maximum recommended dose - lignocaine

A

Lignocaine 4.4mg/kg - healthy px
2% lignocaine will contain 20mg/ml
65kg man may have total of 65x4.4mg = 286mg
14.3ml of 2%
6.5 x 2.2ml cartridges
One tenth of a cartridge per kg in weight

Exodontia (21 decks)

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