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21 Cards in this Set
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LA01 [Mar96] [Mar97] [Jul97] [Mar99] [Jul01] Lignocaine has a pKa of 7.9 At pH 6.9, the percentage ionised is:
A. 1% (or 5%) B. 10% C. 50% D. 90% E. 99% |
ANSWER D
Acids are predominantly ionised Above their pKa ; Bases are predominantly ionised Below their pKa For each ph unit 1 - 90% 2 - 96% 3 - 99% |
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LA02 [Mar96] [Jul04] Cocaine:
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 |
ANSWER A
* A. Blocks reuptake of dopamine and noradrenaline - True for both - Cocaine's "euphoric properties are due primarily to inhibition of catecholamine uptake, particularly dopamine, in the CNS." (Goodman and Gilman) * B. Central effects are due to noradrenaline - False: see A * C. Crosses lipid soluble membranes because its pKa is 2.8 - False pKa 8.7 * D. Is not metabolised by plasma pseudocholinesterase - False "Ester-type local anesthetics are hydrolyzed very rapidly in the blood by circulating butyrylcholinesterase (pseudocholinesterase) to inactive metabolites." Katzung online ed. * E. Rapidly absorbed by nasal mucosa - not sure, definitely absorbed |
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LA03 [Mar96] [Mar03] Ropivacaine:
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 E. 94% protein bound to alpha 1 acid glycoprotein |
ANSWER E
Ropivacaine: * A. Produces greater motor block than bupivacaine - False "the motor anaesthesia produced by ropivacaine is less intense and of shorter duration" (than bupivacaine) p.175 Stoelting 3rd ed * B. Is prepared as the R enantiomer - FALSE "Ropivacaine has been developed as a pure S enantiomer" Stoelting p159 3rd ed. * C. Is less lipid soluble than lignocaine - FALSE Both bupivacaine and ropivacaine are more lipid soluble than lignocaine * D. Has the same cardiotoxicity as lignocaine - FALSE CC:CNS ratio is 5 cf lignocaine's 7 |
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LA03b [Mar97] [Feb00] Ropivacaine
A. Is a pure R isomer B. Is an isomer of bupivacaine C. Provides more motor block than bupivacaine D. Has more toxicity than bupivacaine E. Has similar physico-chemical properties to bupivacaine |
ANSWER E
Ropivacaine * A. Is a pure R isomer - False see above * B. Is an isomer of bupivacaine - false * C. Provides more motor block than bupivacaine FALSE Don't we use ropivacaine in epidurals to try to reduce the motor block?? * D. Has more toxicity than bupivacaine false * E. Has similar physico-chemical properties to bupivacaine - true similar protein binding and pKa |
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LA03c [Mar98] [Jul98] Ropivacaine differs from bupivacaine mainly by:
A. More motor blockade than bupivacaine B. Mainly affecting A beta rather than A delta fibres C. Lower cardiac toxicity than bupivacaine D. Better neonatal outcomes with ropivacaine E. None of the above |
ANSWER C
Ropivacaine differs from bupivacaine mainly by: * A. More motor blockade than bupivacaine - false * B. Mainly affecting A beta rather than A delta fibres - false affects A delta and C fibres * C. Lower cardiac toxicity than bupivacaine true higher CC:CNS ratio * D. false: There was no significant difference between the two drugs in mode of delivery, maternal satisfaction, or neonatal outcomes. * E. None of the above |
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LA04 [Mar96] [Mar99] Bupivacaine:
A. Is an aminoester local anaesthetic B. Is formed by substituting butyl for methyl on amino group of mepivacaine C. ?Less/more toxic than tetracaine D. Adrenaline solution contains sodium metabisulphite E. Equipotent to etidocaine in causing motor block |
ANSWER B D
* A. False - Bupivacaine is an amino-amide LA * B. Correct - Mepivicaine has a methyl group on the piperidine nitrogen atom, which is replaced by a butyl group in Bupivacaine (stoelting 4th pg 180 or p159 in 3rd ed) Tip/Historical note: Mepivacaine has a methyl group; (p)ropivacaine has a propyl group; bupivacaine has a butyl group * C. More toxic. CNS toxicity index Bupivacaine: 2.9, Tetracaine 2.0 (p522 Evers&Maze) * D. is true * E. False - "Compared to bupivacaine, etidocaine produces preferential motor blockade." Goodman and Gilman Ch 14 online ed. |
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LA05 [Jul97] With regard to molecular weight of local anaesthetics, which is the correct sequence?
A. Cinchocaine > bupivacaine > lignocaine > prilocaine B. Bupivacaine > lignocaine > cinchocaine > prilocaine C. Bupivacaine > lignocaine > prilocaine > cinchocaine D. Prilocaine > bupivacaine > cinchocaine > lignocaine E. Lignocaine>bupivacaine>prilocaine>cinchocaine |
ANSWER A
* Molecular weights for the above local anaesthetics are as follows: 1. Cinochocaine: MW 379.9 (C20.H3.0.Cl.N3.O2) 2. Bupivacaine: MW 288.4 (C18.H28.N2.O) 3. Lignocaine: MW 234.3 (C14.H22.N2.O) 4. Prilocaine: MW 220.3 (C13.H20.N2.O) * Hence the correct answer is [A] - Cinochocaine > Bupivacaine > Lignocaine > Prilocaine |
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LA06 [Jul97] [Jul04] Lignocaine works by:
A. Altering Na+ permeability B. Altering membrane structure C. Reduced Ca++ permeability D. Increased K+ permeability E. Ca++ binding to tropomyosin |
ANSWER A
Lignocaine acts by selectively binding to Na channel in the inactivated states,local anaesthestics molecule stablize these channels in this configuration and prevents there changes to rested closed and active open. It also bind to specificed sites located in the inner portion of Na channels(H gates)and well as physically obstruct the external opening of the channel & maintain them inactive closed state |
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LA07 [Jul97] Lignocaine:
A. Has ?% uptake in lung B. Is 24% ionised at physiological pH C. Reduces Na+ conductance (?) D. ? |
ANSWER C
As a side note.... Lung Uptake: Alfentanyl 80% Fentanyl 75% Propranolol 75% Pethidine 65% Lignocaine 60& Thio 14% morphine 3-5% Lignocaine is 25% UNionized at physiologic pH |
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LA08 [Jul97] Lignocaine:
A. Has active metabolites B. Metabolism faster in females because of progesterone C. Metabolism is independent of liver blood flow D. ? |
ANSWER A
* A. Has active metabolites - TRUE: they are responsible for preventing cardiac arrhythmias when the infusion of lignocaine is stopped * B. Metabolism faster in females because of progesterone * C. Metabolism is independent of liver blood flow - FALSE "hepatic disease or decreases in hepatic blood flow... can decrease the rate of metabolism" Stoelting p 164 3rd ed |
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LA10 [Mar98] Local anaesthetics are metabolized in the following order:
A. Bupivacaine>ropivacaine>lignocaine>prilocaine>procaine B Ropivaine>ligocaine>Bupivacaine>procaine>prilocaine C Prilocaine>Bupivacaine>ropivacaine>lignocaine>procaine |
ANSWER A
I'd go by t1/2 beta where longest to shortest is bupivacaine, ropivacaine, lignocaine, prilocaine and procaine... no specific reference as stoelting does not have value for prilocaine while Peck + Williams says lignocain = prilocaine |
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LA11 [Mar98] Saxitoxin site on sodium channel is:
A. Inside channel B. Outside channel C. On membrane outside D. ? |
ANSWER B
Saxitoxin site on sodium channel is: * A. Inside channel - FALSE * B. Outside channel - True (see below) * C. On membrane outside - FALSE Saxitoxin and tetrotoxin are bio-toxins which both block the neural voltage-gated sodium channel by binding to a specific site at the extracellular side of the channel. |
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LA12 [Jul98] The site of action of benzocaine is:
A. Same site as saxitoxin B. Inside Na+ channel /OR: At the channel mouth C. At axoplasmic end of Na+ channel D. At Ca++ channel E. In the cell membrane |
Option "E In the cell membrane" would be the best answer.
Benzocaine is an ester local anaesthetic which is a secondary amine. It is unique among clinically useful LA's. As a weak base with a low pKa (3.5) - therefore at physiological pH exists primarily in an unionized form rendering it lipid soluble (& water-insoluble). Because of this it is suitable for topical anaesthesia of mucus membranes (in concentrations up to 20%). Its systemic toxicity is also diminished because of rapid hydrolysis. It has a very rapid onset |
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LA13 [Jul98] EMLA cream contains:
A. Soluble in water at >16 degrees C B. 20% ionised at pH C. 80% ionised at pH D. 10% amount of ionised drug E. All of the above |
EMLA cream contains:
* A. Soluble in water at >16 degrees C - FALSE: looks like a trick answer; melting point for the eutectic mixture of lignocaine and prilocaine is 17 degrees (cf lignocaine 67 and prilocaine 37 individually) * B. 20% ionised at pH ?? - perhaps true; the mixture is buffered with NaOH to a high pH of ~9.6 to increase the non-ionised fraction to over 90% (sorry, no reference apart from a medal winner's model answers!) * C. 80% ionised at pH ??.. OR: Base contains 80% local anaesthetic * D. ?? amount of ionised drug * E. All of the above Are there no correct answers in the above options? Considering how widely this cream is now used, it is surprising that there is only one MCQ about it. Its use is not without risk. EMLA = Eutectic Mixture of Local Anaesthetic 5% EMLA is a mixture of crystalline bases of 2.5% lignocaine and 2.5% prilocaine in an emulsion of white oil:water. One of the metabolites of prilocaine, o-toludine may cause methaemoglobinaemia. Therefore its use should be avoided in patients with methaemaglobinaemia (congenital or idiopathic) or in those taking other drugs associated with an increased risk of methaemoglobinaemia (eg sulphonamides or phenytoin). In contrast to the eutectic mixture, I understand that AnGel cream (Royal Children's Hospital Formulation) is 4% amethocaine, an ester local anaesthetic used for topical anaesthesia. Some paediatric departments appear to be favouring this over EMLA, perhaps due to its lack of association with methaemoglobinaemia? Topical amethocaine has a faster onset of action, producing good topical anaesthesia in 30mins, unlike EMLA which needs to be on for one hour. The extra speed is great when attempting to canulate a sick child! |
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LA14 [Mar99] [Mar03] What factor does not influence the peak plasma levels after epidural injection of local anaesthetic?
A. Vasoconstrictor B. Natural vasoconstrictor activity of the drug C. Hepatic clearance D. Renal clearance |
ANSWER D
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LA15 [Mar99] [Mar03] Which ONE of the following is an amide?
A. Tetracaine B. Procainamide C. Procaine D. Prilocaine E. Cinchocaine |
ANSWER B, D and E
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LA15b [Jul01] The following are all amides except:
A. Bupivicaine B. Prilocaine C. Etidocaine D. Tetracaine E. Dibucaine |
ANSWER D
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LA16 [Jul99] Lignocaine:
A. Anti-arrhythmic effect - ??Na channel /open & inactivated state B. Prolongs QRS C. Class 1a antiarrythmic D. An ester E. Metabolised by non specific esterases |
ANSWER A
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LA17 [Jul99] [Feb00] [Jul00] [Jul01] [Jul03]
A solution of local anaesthetic contains 1:100,000 adrenaline. How much adrenaline has been added? A. 0.01% B. 0.1% C. 10 mcg/ml D. 100 mcg/ml E. 1000 mcg/ml |
ANSWER C
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LA19 [Jul00] [Jul01] Regarding local anaesthetic plasma protein binding
A. Is predominantly by albumin B. Is predominantly by alpha-1 acid glycoprotein C. Is greater for tetracaine than for bupivacaine D. Neonates have a greater number of binding sites E. Plasma binding is directly proportional to local anaesthetic concentration. |
ANSWER B
Lignocaine is 65% PPB predominately to alpha-1 acid glycoprotein The percentage of local aneasthetic bound to protein is INVERSELY related to plasma concentration of drug |
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LA20 [Jul01] For a local anaesthetic agent at a given concentration:
A. Effect is dependent on resting membrane potential B. Faster onset with increasing frequency of stimulation of nerve C. Unionised form blocks the surface receptor D. Agent blocks the channel in the inactivated state E. Faster onset with more negative resting membrane potential. |
ANSWER B
A - False, it is NOT dependent on resting membrane potential B - true; LAs cause a frequency dependent blockade C - false; ionised form is effective at blocking the channel. It is non-ionised to get to the channel but the ionised form blocks it, on the cytoplasmic side of the membrane (internal or H gate) D - False; blocks Na channel in activated-open and inactive-closed but not resting-closed state E - unsure |
