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Pharm1Test3LA

Pharm1 Test3 Local Anesthetics

QuestionAnswer
Local anesthetics reversibly block the <blank> and <blank> of nerve impulses. Generation and propagation.
What is bi-directional blockade? Can block function in all excitable cells; thus can alter both sensory and motor function.
LA's level of effect depends on what four factors? Agent used, route of administration, drug concentration at site, and lipophilicity.
What are the routes of LA administration? Used topically on skin or mucous membranes, or peripheral, central and spinal via parenteral route. Also occasional use rectally or ophthalmically.
LA are some of the world's most widely used drugs. Some are also used as... Antiarrhythmics.
The lipophilicity of the aromatic group controls the LA's ability to... Penetrate the nerve sheath and enter the nerve membrane.
Most LA are weak bases that can exist in what two forms(will alter function at site)? Freebase and positively charged form.
Most solutions are weakly acidic and alkalinization prior to use increases free base form which... Increases lipid solubility and shortens onset time.
LA have lipophilic and hydrophilic regions. What is the lipophilic group? Aromatic ring.
What is the LA's hydrophilic region? Usually an amine (ionizable).
The LA's lipophilic and hydrophilic regions are joined by an amide or an ester, which is important for... Metabolism and allergies.
Increasing lipid solubility <blank> onset time and <blank> duration. Decreases, increases.
All usable LA have pKa's between... 7.5-9.0
LA act to decrease the permeability of the membrane to sodium ions. How? These agents bind to sites in the Na+ channel of the voltage gated Na+ channels, thus inhibiting Na+ inflow during depolarization.
Low conc. of LA's decreases both the rate of rise and the height of the action potential. Higher concentrations can... Abolish it totally.
What do LA do to the firing threshold and propagation time? Increase them.
In myelinated fibers, where do LA's attack? At the Nodes of Ranvier.
True or false. Sodium channel made up of an alpha subunit comprised of 16 additional subunits, and additional beta subunits. False. Sodium channel made up of an alpha subunit comprised of 4 additional subunits, and additional beta subunits.
Where in the Sodium channel is the Sodium pore? The alpha subunit.
LA bind to what kind of Sodium channel? The closed, inactivated channel, freezing it in that form.
How is K ion flow affected by LA? K+ outflow may also be inhibited somewhat, but not nearly to the extent of Na+.
How do LA's act? Most act by binding to inner portion of Na+ channel.
In LA, small diameter nerves are affected first, then larger diameter nerves due to... The number of channels to be blocked (greater in large fibers).
In LA, more rapidly stimulated fibers are also blocked first due to more frequent opening of Na+ channels, and the ability of the LA's to get into channel to bind. True or false? True.
Sensory fibers tend to be triggered more frequently than motor fibers, and so tend to be... Blocked first by LA.
What is the order of fibers affected by LA? Autonomic, then sensory, then motor.
What are some natural toxins that kill by blocking Na channels? Tetrodotoxin - from pufferfish and saxitoxin – from red tide microorganisms (paralytic shellfish poisoning), work by similar mechanism, blocking outer mouth of Na+ channel.
What is the order of recovery from fibers affected by LA? Motor, sensory, autonomic.
How do LA work as antiarhythmics? Due to the blockade of Na+ channels in myocardial tissues, with an effective decrease in firing rate, and passage of signals through conductive fibers.
How are LA used topically? Decrease pain of wounds, burns, mucous membrane.
How are LA used via infiltration? Injected around area - i.e. - for surgery.
How are LA used for regional nerve block? Injected close to nerve that innervates the area to be anesthetized.
How are LA used for spinals? Injected into lumbar subarachnoid space to get to nerves in that area going to various body sites.
How are LA used for epidurals? Given inside spine above the dura mater.
How are LA used IV? Usually for surgery on a specific limb.
Onset of anesthesia with LA is usually fastest with what two agents? Lidocaine and Prilocaine. Procaine and tetracaine are slower.
Why is epi given with LA? To attempt to increase duration. This is not always effective.
What locals have the shortest duration? Procaine and Chloroprocaine (15-30 mins).
What locals have intermediate duration? Lidocaine and Prilocaine (30-90 mins).
What local has the longest duration? Tetracaine (2-3 hours).
Benzocaine shows the fastest onset when applied to mucous membranes, then... Lidocaine and cocaine.
Duration for topical LA? 30-60 mins.
Sensitivity reactions are more common with what kind of LA? Esters.
Some LA preps include what additives that increase sensitivity risk? Tartrazine and sulfites.
Systemic absorption of LA can lead to cardiotoxicity and what CNS symptoms? Sedation, dizziness, disorientation, tremors, seizures, respiratory arrest.
Neurotoxicity is more common in what kinds of LA? Epidural and subarachnoid.
Cauda equina syndrome can occur from epidurals and spinals. What is this? Severe compression of the cauda equina resulting in loss of bowel or bladder function, loss of sensation in the buttocks and groin, and weakness in the legs.
What topical LA can cause methhemoglobinemia? Prilocaine, Benzocaine, Lidocaine, Cetacaine.
What happens in methhemoglobinemia? Oxidization of hemoglobin.
Except for allergic or hypersensitivity reactions, actual risk for most patients is fairly low. Why? Due to their use in small amounts in a localized area for most procedures.
What is the metabolism of LA amides? Primarily via hepatic microsomal enzymes. Metabolism via multiple steps
What is the metabolism of LA esters? Metabolized by plasma and other esterases.
How are the LA classified? By their structure, depending on whether the compound has an ester or amide linkage (or neither).
What are the LA esters? Benzocaine (Oragel), Procaine (Novocain), Chloroprocaine (Nesacaine), Tetracaine (Pontocaine), Cocaine, and Cetacaine (Cetylite).
Why is Benzocaine(Oragel) only used topically? It's poorly water soluble.
Excessive absorption of Benzocaine(Oragel) can lead to what? Methemoglobinemia.
What is the pKa of Benzocaine(Oragel)? 3.5.
What was the first synthetic LA? Procaine(Novocaine).
Procaine(Novocaine) has a slower onset with <blank> duration and <blank> potency Short, weak.
True or false: Procaine(Novocaine) is highly systemically toxic. False. Fairly low systemic toxicity.
Procaine(Novocaine) is best used for... Infiltration and nerve blocks.
Procaine(Novocaine)'s use has been superseded by what better agents? Amides.
Chloroprocaine (Nesacaine) has a low systemic toxicity, a <blank> onset and <blank> duration. rapid, short.
Since toxicity is low, Chloroprocaine(Nesacaine) is used in what concentrations? High concentrations.
How is Chloroprocaine(Nesacaine) used? Infiltration, nerve block, IV and epidurals.
Tetracaine(Ponticaine) is ten times more potent than Procaine, but also... Ten times more toxic.
Tetracaine(Ponticaine) has a <blank> duration with <blank> onset. Long, slow.
Why is Tetracaine(Ponticaine) mainly used in spinal anesthesia? Barriers decrease diffusion and decrease toxicity risk.
Tetracaine(Ponticaine) is active topically, but what limits its use? Absorption across mucous membranes.
Cocaine is derived from what part of the coca plant? The leaves.
What level controlled substance is Cocaine? C-II.
Cocaine is too toxic for use other than... Topically.
In addition to its LA effect, Cocaine has potent... Vasoconstrictive and addictive effects.
When do we usually use Cocaine in anesthesia? Topically on mucous membranes, such as nasal cavities or oropharyngeal cavities prior to surgery, and packed post-op to decrease bleeding and pain.
Cetacaine (Cetylite) is a topical agent for local skin disorders and is used on various mucous membranes, except... The eye.
Cetacaine(Cetylite) is a mixture of what three drugs? Benzocaine, Tetracaine, and Butyl Aminobenzoate.
When do we use Cetacaine(Cetylite)? Topically, rectally or as a spray to inhibit the gag reflex (during bronchoscope exam, etc).
What are the LA amides? Lidocaine (Xylocaine), Prilocaine (Citanest), Mepivacaine (Carbocaine), Bupivacaine (Marcaine), Articaine (Septocaine), and Ropivacaine (Naropin).
What is the most commonly used LA? Lidocaine(Xylocaine).
Lidocaine(Xylocaine) has <blank> onset with <blank> duration Rapid, intermediate.
Lidocaine(Xylocaine) causes vasodilation, so many formulations contain... Epinephrine.
Prilocaine (Citanest) is similar to Lidocaine in properties, but less... Vasodilation.
Prilocaine(Citanest) has <blank> onset with <blank> duration. Rapid, intermediate.
True or false: Prilocaine(Citanest) causes methemoglobinemia most often of the amides. False. It is the least toxic of the amides, but can still cause methemoglobinemia.
Mepivacaine(Carbocaine) is used similarly to Lidocaine. How is it used? Infiltration, nerve block, epidural.
True or false. Mepivacaine(Carbocaine) is a topical anesthetic. False. Has no topical effect.
Why don't we use Mepivacaine(Carbocaine) in OB? Biotransformation in fetus is prolonged.
Mepivacaine(Carbocaine) is a racemic mixture. It is similar to what other two anesthetics? Bupivacaine and Ropivacaine.
True or false: Bupivacaine(Marcaine) is a highly potent drug with a long duration and slower onset. True.
How does the toxicity of Bupivacaine(Marcaine) compare to Lidocaine(Xylocaine)? It is much more toxic(cardiotoxic).
How is Bupivacaine(Marcaine) used? Infiltration nerve block, epidural and spinal anesthesia.
Bupivacaine(Marcaine) is more likely to cause... Adverse effects.
Articaine (Septocaine) is only available in U.S. in combination with... Epinephrine.
Articaine(Septocaine) has a rapid onset and short duration. When is it used? Dental and periodontal procedures.
Why does Articaine(Septocaine) have such rapid metabolism? It has both an ester and an amide group.
Articaine(Septocaine) has a low toxicity due to its... Rapid metabolism.
Ropivacaine (Naropin) has a long duration, similar to Bupivacaine, but less... Cardiotoxic.
Bupivacaine's cardiotoxicity is due to what isomer? R-isomer.
Ropivicaine(Naropin) is purified and contains only what isomer? S-isomer.
Less lipid soluble, and more rapidly <blank> than Bupivacaine. Metabolized.
How do we use Ropivicaine(Naropin)? Infiltration, nerve block, epidural, spinal.
What LA is neither an amide nor an ester? Pramoxine (Proctofoam).
How is Pramoxine(Proctofoam) used? Topical agent for relief of hemorrhoids, rectal pain and itching of skin disorders (pruritus).
What is Pramoxine(Proctofoam) commonly mixed with? Many products (ex. Hydrocortisone, calamine).
True or false: Pramoxine(Proctofoam) is used to abolish the gag reflex. False. It has a weak potency and will not completely obliterate the gag reflex.
Created by: Chelsea Leigh Jones Chelsea Leigh Jones on 2010-04-18



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