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100 Cards in this Set
- Front
- Back
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Almost all LA allergies are to what class?
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Esters
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First synthetic LA
Ester Low toxicity and potency (32:1 C:B) Hydrolyzed to PABA Uses: infiltration, spinal & different spinal block |
Procaine
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C:B 13:1
a.k.a. pontocaine Uses: spinal and topical Rapid onset Profound motor and sensory block >10x potency of procaine |
Tetracaine
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C:B 49:1
Ester 2x potency of procaine (is procaine derivative) Uses: OB epidural Short onset and rapid hydrolysis |
2-chloroprocaine
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Ester
Cardiac problems; caution when given with Epi vasoconstrictor - prevents reuptake of NE into postganglionic nerve endings Pure levorotary isomer Topical anesthetic ENT uses frequently Abuse potential |
Cocaine
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Very low pKa
C:B = all base Ester Topical Uncharged and hydrophobic Should reach receptor by alternate pathway Does NOT produce frequency-dependent block. Very potent, need small amount Access to receptor site is independent of channel kinetics (dissolves in lipid membrane and diffuses toward channel protein) |
Benzocaine
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What is ester with highest potency?
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Tetracaine
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C:B 3:1
1st amide LA in use Versatile, rapid onset with 1-2 hr duration Uses: 1) IV, peripheral, spinal & epidural, topical oint & LTA spray 2) antidysrhythmic - inhibits phase 3 repolarization & suppresses ventricular ectopy 3) systemic anelgesic |
Lidocaine
(know 3 uses) |
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C:B 2:1 Fast onset!
Amide Uses: inflitration, peripheral& epidural blocks Short latency & intermediate duration Longer duration than Lidocaine |
Mepivacaine
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C:B 5:1
Amide Racemic mix 1:1 R:S enantiomers; molecules are chiral a.k.a. Sensorcaine & Marcaine Uses: infiltration, periph nerve blocks, epidural & SAB Potent, long lasting LA CV toxicity >> CNS toxicity and CV seen first! |
Bupivacaine
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C:B 5:1
Amide: developed and approved in 1996 a.k.a. Naropin Uses: OB continuous epidural Single S enantiomer of Bupivacaine "Walking epidurals" - blocks sensory, but less motor effect Propyl replaces butyl chain at tertiary amine. Much less CV tox than Bupivicaine, d/t slow uptake of this drug... |
Ropivacaine
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C:B 5:1
Amide a.k.a. Chirocaine S enantiomer (optical isomer) of racemic bupivacaine Less CV tox than Levobupivacaine, similar potency |
Levobupivacaine
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C:B 2:1
Amide a.k.a. Duranest MOST RAPID ONSET LA CV toxicity ~ similar to bupivacaine Prolonged duration and profound motor blockade > sensory Longer motor blockade Uses: infiltration, sensory nerve blocks & epidurals |
Etidocaine
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Due to long motor blockade this LA is bad for outpatient surgeries or patients that need to walk later that day.
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Etidocaine
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Two amides with severe, and about equal, CV toxicity.
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Bupivacaine
Etidocaine |
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C:B 3:1
Amide Similar to Lidocaine -- << vasodilation, useful w/o Epi Metabolized to o-toluidine |
Prilocaine
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Methemoglobinemia w/ doses >600 mg
(treat with 1mg/kg Methylene blue) |
Prilocaine
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Same pKa & toxicity as lidocaine
Metabolized differently Very short half life, < 1/4 Lido and 1/5 Mepivacaine Great for dental procedures |
Articaine
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Really rapid onset, duration ~1hr
Great for dental procedures |
Articaine
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Mix of crystalline substances
Made of two LAs, together melting point is < either of its individual components |
EMLA cream
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1 gm of EMLA cream contains
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25 mg Lidocaine
25 mg Prilocaine (both amides) |
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What is max prilocaine dose (w/ regards to EMLA)?
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7 mg/kg
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How much EMLA would you apply and what is onset?
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1-2 grams of EMLA cream per 10 cm/skin, cover with occlusive dressing
onset 45-60 min |
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EMLA cream is more effective than other topicals d/t...
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High conc. of uncharged base... up to 80%
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T/F - Enantiomers are just two chiral stereoisomers.
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True.
(Lucky guess) |
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Name the four LAs that are NOT 1:1 racemic mixtures.
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Cocaine - pure levorotary S, isomer
Lidocaine - achiral (looks same in mirror) Ropivacaine - S enantiomer, (stereoisomer) of bupivacaine Levobupivacaine - S enantiomer (isomer) of bupivacaine |
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L = levo isomer = ???
R = dextro isomer = ??? |
L = levo = S-sinister = CCW
R = dextro = R-rectus = CW |
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What fraction of all synthetic drugs are chiral?
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1/3
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More carbons = ____ fat solubility (up to a point), and ____ potency
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more Cs = more fat soluble = more potent
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Why is pt's pH important w/ regard to LAs?
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LAs are basic and acidotic pt will ionize LAs making less base form available, decreasing efficacy.
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Drugs with highest percentage available in base form (at pH 7.4)
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Benzocaine (100%)
Mepivacaine (39%) Etidocaine (33%) Lidocaine (24%) Bupivacaine (17%) Tetracaine (14%) Procaine (3%) 2-chloroprocaine (2%) |
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An ester Pam said is "good for hip blocks" because it is long acting
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Tetracaine
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LAs with > binding affinity for proteing ..
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increase duration of blockade because they stay in channel longer (bound to protein)
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primary plasma protein LAs bind...
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Alpha-1-acid glycoprotein (not albumin)
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What increases alpha-1-acid glycoprotein levels an thus increasing LA duration of action?
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trauma
CA uremia MI |
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Two conditions that decrease protein binding of LA, resulting in more free LA...
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pregnancy
oral contraceptives |
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T/F = LA absorption into tissue uniform regardless of age.
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False. Extremes of age see FASTER absorption.
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What LAs have decreased clearance when taken with other drugs that decrease hepatic blood flow?
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Amides
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CHF, cirrhosis, orthostatic hypotension will likely cause pts to have ________ rate of clearance of _____ LAs.
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DECREASED rate of clearance of AMIDE LAs.
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High vascularity has __ LA uptake, while areas with low vascularity have __ LA uptake.
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High vascularity = fast LA uptake.
Fat/poor vascularity have slower uptake. |
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High volume of LA injected will result in...
Will this change onset, intensity or duration? None of the above? |
Large volumes will diffuse to cover a larger area with NO effect on onset, duration, intensity.
To block large area, use large volume of low conc. LA To block small area, use smaller volume with higher conc. of LA. |
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When using epi or other vasoconstrictor with LAs, where should you NOT inject it?
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distal areas, digits, any place without collateral blood flow as vasoconstriction will eliminate blood supply (no fingertips, toes)
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T/F: A fresh ester is poorly soluble in water and unstable in air.
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False. An AMINE is poorly soluble in H2O and unstable in air.
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As pKa of drug approaches pH more LA is in _____ form.
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BASE form.
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Is LA salt H2O soluble? Stable?
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Yes. LA salt is VERY WATER SOLUBLE AND STABLE!
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Cation & Base ratio governed by 2 things..
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1) ambient and variable pH (infected wound vs. normal pH patient)
2) Drug's fixed pKa |
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How can you minimize tachyphylaxis with regards to LAs?
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Keep pain levels stady, high peaks and valleys = bad.
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_______ ____ is key to development of tachyphylaxis.
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Breathrough pain... more likely to result in tachyphylaxis to LAs
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Two LAs most likely to result in tachyphylaxis... and what about these two predisposes this?
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Lidocaine & Mepivacaine
Their pKa's are closer to physiologic pH. |
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T/F: Adding Bicarb to LA brings onset 5 minutes faster and makes duration 5 minutes longer.
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False... Onset comes 5 minutes earlier.
Block wears off 5 minutes FASTER. |
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What is the rate-limiting factor regarding LA plasma concentrations?
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Regional blood flow.
More blood flow = higher concentration |
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LA absorption decrease (from highest absorption to lowest)
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Interpleural: vascular
Intercostal Caudal Epidural space Brachial plexus Sciatic and femoral nerve Subarachnoid space Infiltration |
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LAs always VASOCONSTRICT when...
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given at toxic doses.
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Lidocaine, Mepivacaine >> vasodilator than Prilocaine
Which will have faster absorption? |
Lido & Mepi will be faster because they are stronger vasodilators and will INCREASE blood flow.
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What is an "epi wash?"
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Fill the syringe with epi, then shoot it out.
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Epi conc of 1:200K
How many mcg/mL? |
5 mcg/mL
(1:100K = 10 mcg/mL) |
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Why is it better to add epi right before injection rather than prepackaged with LA?
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Prepackaged LA + epi will become acidic and decrease base (active) form of LA
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What LA is significant exception regarding common vasodilatory properties that most LAs share?
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Cocaine -- vasoconstricts
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No epi in ______ nerve block
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Peripheral
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What is max dose of Epi for CV patients?
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200 mcg
(So if 1:200K epi conc., may only give 40 mL) |
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What is phase 1 of LA metabolism?
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Oxidation.
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Ester hydrolysis of LAs done by...
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plasma esterases.
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What types of patients may develop LA toxicity or prolonged apnea d/t impaired metabolism?
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1) atypical pseudocholinesterase
2) liver disease 3) pregnant 4) on oral contraceptive |
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Amides or esters: which is more resistant to hydrolysis?
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Amides
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What is purpose of phase 2 LA metabolism? What is the reaction?
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Reaction: conjugation
Purpose: conjugating phase 1 products decrease toxicity until excretion |
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Which amide is a unique secondary amine and what is different about its metabolism?
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Prilocaine
Does not require dealkylation! |
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Amide metabolism rates... Faster to slowest
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Prilocaine > Etidocaine > Lidocaine > Mepivacaine > Bupivacaine
(PELMB) |
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Why would renal failure decrease of drugs half life?
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Renal failure --> anemia --> higher cardiac output
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Prilocaine - why do we worry about metabolism of this drug?
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Metabolites oxidize Hgb to Methgb.
O-toludine (oxidant) transforms ferric (Fe+2) to ferrous (Fe+3) CONSISTENTLY decrease blood O2 carrying capacity w/ occasional cyanosis (may ne symptomatic in CAD pt.) |
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Recommended max dose fo Prilocaine?
Why? |
600 mg
Methemoglobinemia |
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pKa = ??
Lipid sol = ?? protein binding = ?? chemical linkage = ?? Higher concentration = ? |
LOW pKa = FASTER onset
high lipid sol = high POTENCY high protein binding = long duration chemical linkage determines metabolism higher concentration also speeds onset d/t mass effect |
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LAs work on ___ ion channels causing 3 nerve effects.
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Na+ ion channels
1) slowed conduction 2) decrease rate of rise of AP 3) Inc threshold for excitation |
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Does LA have higher affinity for Na+ channels in resting state or open or inactive state?
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Open * inactive = highest affinity
O > I > R (LA affinity for Na+ ion channels) |
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Stabilized excitable tissue in the application region prevents normal function of ______ neurons.
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Afferent
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Stabilizing property of LAs can lead to negative effects like..
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CV & CNS tox
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Systemic tox of LAs can result in higher PCO2 levels which does what to CNS?
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Increases CBF and therefore increasing CNS tox
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First signs of CNS tox often convulsions and/or seizures. How would you treat?
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Midazolam
Ativan Barbs |
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How does LA tox in CNS result in CNS excitation?
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LA causes blockade of inhibitory pathways in cerebral cortex --> CNS excitation, eventually depression of CNS neurons.
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3 things influencing CNS toxicity
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1) potency
2) Rapidity of increase in systemic blood levels 3) Acidosis |
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Generally, how much more LA needed to cause CV tox compared to CNS tox?
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3x more LA needed to cause CV tox
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LA induced CV toxic affects:
inotropic effects? automaticity? Rhythmicity & conductivity? Unidirectional block of conduction paths? Peripheral smooth musc? |
Negative inotropic
Minimal/zero automaticity effects (SA node resistant) VT/VFib may be seen with sub-convulsant doses of Bupivacaine Unidirectional block may generate re-entrant arrhythmias, difficult to treat Low dose LA --> vasoconstrict peripheral smooth musc High dose LA --> vasodilate |
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Normal progression of LA toxicity
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1) Circumoral numbness, metallic taste
2) Tinnitus, dizziness, agitation 3) Sedation, unconscious 4) Seizures, coma 5) Resp arrest 6) CV depression |
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What is contact toxicity?
What end results? |
Direct injection of LA into nerve. Would cause intense pain upon injection. Later post-traumatic neuropathy.
Goal is to "bathe" nerve. |
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What does hyperbaric mixture refer to with LAs?
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High sugar/dextrose mixture.
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What is cauda equina syndrome?
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Prolonged bowel and bladder dysfunction caused by pooling of LA in small area affecting few nerves long term.
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If pt reports LA allergy, use ____-free.
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preservative-free
*Most allergies from esters. |
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During convulsions:
O2 consumtion.... and ventilation... |
O2 consumption goes up and ventilation is compromised
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Treatment of LA toxicity.
What is primary concern? Treatment includes? What about long convulsions? |
CNS is primary concern
Treat: 1) ABCs 2) O2 & airway protection Long convulsions: 1) Thiopental 50-100mg or other ultra-short barbs 2) Benzos (Midaz) 3) Sux (for intubation & musc relax) |
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Treatment of LA induced CV tox?
Basically follow.... |
ACLS protocol for arrhythmias.
Hypotension: ephedrine 15-30 mg atropine 0.4mg Dopamine if severe |
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What does lipid infusion increase when treating CV tox?
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Lipid infusion increases resistance to Bupivacaine induced asystole.
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What is single injection dose of Chloroprocaine? With epi?
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11(14)
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What is single injection dose of Lidocaine? With epi?
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4(7)
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What is single injection dose of Mepivacaine? With epi?
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4(7)
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What is single injection dose of Prilocaine? With epi?
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7 (8.5)
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What is single injection dose of Bupivacaine? With epi?
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2.5 (3.2)
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What is single injection dose of Etidocaine? With epi?
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6 (8)
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What is single injection dose of Ropivacaine? With epi?
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3 (3.5)
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What is single injection dose of Levobupivacaine? With epi?
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2.5 (3.2)
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What is single injection dose of Cocaine? With epi?
In kids? |
1-3
1mg in kids |
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example..
0.5% bupivacain = ___ mg/mL |
5 mg/mL
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