Local anaesthetic MCQ
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Adrenaline added to local anaesthetic at 1:200,000. The concentration is?
c) 0.1mcg/mL (etc)
- 1% = 10mg/mL
- 1g in 1mL --> 1 in 1,000
- 1g in 10mL --> 1 in 10,000
- 1mcg in 1mL = 1 in 1,000,000
- (0.001mg in 1 mL = 0.0001%)
Bupivacaine has pKa of 8.1, what is its pH when ratio of ionised to unionised fraction is 100:1?
- bupiv is basic drug pKa = 8.1
- basic drugs fraction unionised/ionised
- acidic drugs fraction ionised /unionised
- simple way to remember is BASES BELOW, ACIDS ABOVE - referring to ionised portion
- pH = pKa + log (1/100)
Bupivacaine 0.5% 20mLs given intracascularly over 30sec in a 30 y/o pregnant woman of 60kg. Most likely effects?
a) tinnitus and sinus tachy
b) grand mal seizure and hypotension
c) focal seizures and atrial ectopics
d) muscle twitches and AV block
e) confusion and something else
- b) grand mal seizure and hypotension??
- doesn't cause sinus tachy
- doesn't cause focal seizures
- muscle twitches and AV block - happens at lower doses????
a) Toxicity probably due to sodium channel blockade in the heart
b) More toxic as evident by higher cv:cns ratio is lower = bad = as soon as you get CNS toxicity, starting to get CVS toxicity (2:1)
c) Lignocaine has got a higher ratio for CVS toxicity (7:1)
- a) Toxicity probably due to sodium channel blockade in the heart
- Bupivacaine CC:CNS ratio is 4-5:1
- Ropivacaine ratio is 5:1
a) Direct sympathetic activity
b) Strong central dopamine activity
- b) Strong central dopamine activity (blocks reuptake)
Levobupivacaine and Ropivacaine?
a) Levo is an L isomer, Ropi is an R isomer
b) Levo hydrophilic portion confer greater potency - butyl chain compared with propyl chain makes less hydrophilic
c) Levo hydrophobic portion confer greater potency
d) Levo amide links confer greater potency
- b) Levo hydrophilic portion confer greater potency - butyl chain compared with propyl chain makes less hydrophilic
Ropi is S NOT R
Which of the following is an amide local anaesthetic?
A solution of LA contains 1:200,000 adrenaline. How much adrenaline has been added?
- 1:100,000 = 1mg in 100mL= 10mcg/mL
- 1:200,000 = half the same strength
a) not absorbed via GIT
- poor bioavailability but still absorbed a little
Systemic absorption of LA given epidurally depended on all except?
a) adrenaline added
b) intrinsic vasoconstrictor activity
c) hepatic metabolism
d) renal clearance
- d) renal clearance - minimal of unchanged drug
hepatic metabolism is wrong as increases gradient of drug diffusing into plasma
LA order of potency?
a) bupivacaine > levo > ropi > Lig
b) bupiv = levo > ropi > lig
c) ropi > levo > bupiv > lig
- b) bupiv = levo > ropi > lig
Lignocaine has pKa of 7.9, the % ionised at pH 6.9 is?
using hendersen hasselbach eqn model
- 6.9 - 7.9 = -1
- log of 1/10 = -1
- therefore the fraction unionised /ionised is 1/10
- therefore fraction of ionised/both union and ion = 10/11 = 91%
Order of protein binding, from highest to lowest?
a) bupiv > procaine > lignocaine > prilocaine
d) bupiv > lign > procaine > prilocaine
e) bupiv > procaine > prilocaine > lignocaine
- Levo - ??98%
- Bupiv 95- 96%
- Ropiv 94%
- Etidocaine - 94%
- Tetracaine - 75%
- Lignocaine - 70%
- Prilo - 55%
- Procaine - 5%
none of the options are right
a) with a pKa of 7.9 is 24% ionised at pH 7.4
b) has a clearance independent of liver blood flow
- a) at pH 7.4 with pKa 7.9 - (bases below) more will be ionised than unionised.
- -0.5 equivalent to log 1/3
- therefore 3/4 is ionised = 75%
b) wrong, extensively reliant on metabolism in liver
a) cocaine toxicity is similar to amphetamine toxicity
b) central effects are due to noradrenaline
d) maximal effect within 5 minutes
- a) cocaine toxicity is similar to amphetamine toxicity
a) Blocks reuptake of dopamine and noradrenaline
b) central effects are due to noradrenaline
c) crosses lipid soluble membranes because its pKa is 2.8
d) Is not metabolised by plasma pseudocholinesterase
e) Rapidly absorbed by nasal mucosa
- a) blocks reuptake of dopamine and noradrenaline
- b is wrong, peripheral effects
- c is wrong pKa of cocaine is 8.6
- d is wrong - portion of cocaine IS metabolised by PchE
- e is wrong - it is well absorbed, but NOT rapidly
a) produces greater motor block than bupivacaine
b) is prepared as the r enantiomer
c) is less lipid soluble than lignocaine
d) has the same cardiotoxicity as lignocaine
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