Pharm1 Test3 Local Anesthetics
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| Local anesthetics reversibly block the <blank> and <blank> of nerve impulses. | Generation and propagation.
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| What is bi-directional blockade? | Can block function in all excitable cells; thus can alter both sensory and motor function.
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| LA's level of effect depends on what four factors? | Agent used, route of administration, drug concentration at site, and lipophilicity.
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| 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.
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| LA are some of the world's most widely used drugs. Some are also used as... | Antiarrhythmics.
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| The lipophilicity of the aromatic group controls the LA's ability to... | Penetrate the nerve sheath and enter the nerve membrane.
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| Most LA are weak bases that can exist in what two forms(will alter function at site)? | Freebase and positively charged form.
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| Most solutions are weakly acidic and alkalinization prior to use increases free base form which... | Increases lipid solubility and shortens onset time.
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| LA have lipophilic and hydrophilic regions. What is the lipophilic group? | Aromatic ring.
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| What is the LA's hydrophilic region? | Usually an amine (ionizable).
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| The LA's lipophilic and hydrophilic regions are joined by an amide or an ester, which is important for... | Metabolism and allergies.
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| Increasing lipid solubility <blank> onset time and <blank> duration. | Decreases, increases.
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| All usable LA have pKa's between... | 7.5-9.0
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| 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.
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| Low conc. of LA's decreases both the rate of rise and the height of the action potential. Higher concentrations can... | Abolish it totally.
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| What do LA do to the firing threshold and propagation time? | Increase them.
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| In myelinated fibers, where do LA's attack? | At the Nodes of Ranvier.
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| 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.
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| Where in the Sodium channel is the Sodium pore? | The alpha subunit.
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| LA bind to what kind of Sodium channel? | The closed, inactivated channel, freezing it in that form.
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| How is K ion flow affected by LA? | K+ outflow may also be inhibited somewhat, but not nearly to the extent of Na+.
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| How do LA's act? | Most act by binding to inner portion of Na+ channel.
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| 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).
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| 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.
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| Sensory fibers tend to be triggered more frequently than motor fibers, and so tend to be... | Blocked first by LA.
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| What is the order of fibers affected by LA? | Autonomic, then sensory, then motor.
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| 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.
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| What is the order of recovery from fibers affected by LA? | Motor, sensory, autonomic.
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| 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.
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| How are LA used topically? | Decrease pain of wounds, burns, mucous membrane.
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| How are LA used via infiltration? | Injected around area - i.e. - for surgery.
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| How are LA used for regional nerve block? | Injected close to nerve that innervates the area to be anesthetized.
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| How are LA used for spinals? | Injected into lumbar subarachnoid space to get to nerves in that area going to various body sites.
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| How are LA used for epidurals? | Given inside spine above the dura mater.
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| How are LA used IV? | Usually for surgery on a specific limb.
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| Onset of anesthesia with LA is usually fastest with what two agents? | Lidocaine and Prilocaine. Procaine and tetracaine are slower.
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| Why is epi given with LA? | To attempt to increase duration. This is not always effective.
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| What locals have the shortest duration? | Procaine and Chloroprocaine (15-30 mins).
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| What locals have intermediate duration? | Lidocaine and Prilocaine (30-90 mins).
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| What local has the longest duration? | Tetracaine (2-3 hours).
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| Benzocaine shows the fastest onset when applied to mucous membranes, then... | Lidocaine and cocaine.
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| Duration for topical LA? | 30-60 mins.
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| Sensitivity reactions are more common with what kind of LA? | Esters.
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| Some LA preps include what additives that increase sensitivity risk? | Tartrazine and sulfites.
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| Systemic absorption of LA can lead to cardiotoxicity and what CNS symptoms? | Sedation, dizziness, disorientation, tremors, seizures, respiratory arrest.
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| Neurotoxicity is more common in what kinds of LA? | Epidural and subarachnoid.
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| 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.
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| What topical LA can cause methhemoglobinemia? | Prilocaine, Benzocaine, Lidocaine, Cetacaine.
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| What happens in methhemoglobinemia? | Oxidization of hemoglobin.
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| 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.
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| What is the metabolism of LA amides? | Primarily via hepatic microsomal enzymes. Metabolism via multiple steps
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| What is the metabolism of LA esters? | Metabolized by plasma and other esterases.
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| How are the LA classified? | By their structure, depending on whether the compound has an ester or amide linkage (or neither).
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| What are the LA esters? | Benzocaine (Oragel), Procaine (Novocain), Chloroprocaine (Nesacaine), Tetracaine (Pontocaine), Cocaine, and Cetacaine (Cetylite).
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| Why is Benzocaine(Oragel) only used topically? | It's poorly water soluble.
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| Excessive absorption of Benzocaine(Oragel) can lead to what? | Methemoglobinemia.
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| What is the pKa of Benzocaine(Oragel)? | 3.5.
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| What was the first synthetic LA? | Procaine(Novocaine).
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| Procaine(Novocaine) has a slower onset with <blank> duration and <blank> potency | Short, weak.
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| True or false: Procaine(Novocaine) is highly systemically toxic. | False. Fairly low systemic toxicity.
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| Procaine(Novocaine) is best used for... | Infiltration and nerve blocks.
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| Procaine(Novocaine)'s use has been superseded by what better agents? | Amides.
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| Chloroprocaine (Nesacaine) has a low systemic toxicity, a <blank> onset and <blank> duration. | rapid, short.
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| Since toxicity is low, Chloroprocaine(Nesacaine) is used in what concentrations? | High concentrations.
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| How is Chloroprocaine(Nesacaine) used? | Infiltration, nerve block, IV and epidurals.
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| Tetracaine(Ponticaine) is ten times more potent than Procaine, but also... | Ten times more toxic.
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| Tetracaine(Ponticaine) has a <blank> duration with <blank> onset. | Long, slow.
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| Why is Tetracaine(Ponticaine) mainly used in spinal anesthesia? | Barriers decrease diffusion and decrease toxicity risk.
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| Tetracaine(Ponticaine) is active topically, but what limits its use? | Absorption across mucous membranes.
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| Cocaine is derived from what part of the coca plant? | The leaves.
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| What level controlled substance is Cocaine? | C-II.
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| Cocaine is too toxic for use other than... | Topically.
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| In addition to its LA effect, Cocaine has potent... | Vasoconstrictive and addictive effects.
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| 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.
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| Cetacaine (Cetylite) is a topical agent for local skin disorders and is used on various mucous membranes, except... | The eye.
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| Cetacaine(Cetylite) is a mixture of what three drugs? | Benzocaine, Tetracaine, and Butyl Aminobenzoate.
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| When do we use Cetacaine(Cetylite)? | Topically, rectally or as a spray to inhibit the gag reflex (during bronchoscope exam, etc).
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| What are the LA amides? | Lidocaine (Xylocaine), Prilocaine (Citanest), Mepivacaine (Carbocaine), Bupivacaine (Marcaine), Articaine (Septocaine), and Ropivacaine (Naropin).
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| What is the most commonly used LA? | Lidocaine(Xylocaine).
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| Lidocaine(Xylocaine) has <blank> onset with <blank> duration | Rapid, intermediate.
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| Lidocaine(Xylocaine) causes vasodilation, so many formulations contain... | Epinephrine.
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| Prilocaine (Citanest) is similar to Lidocaine in properties, but less... | Vasodilation.
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| Prilocaine(Citanest) has <blank> onset with <blank> duration. | Rapid, intermediate.
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| 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.
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| Mepivacaine(Carbocaine) is used similarly to Lidocaine. How is it used? | Infiltration, nerve block, epidural.
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| True or false. Mepivacaine(Carbocaine) is a topical anesthetic. | False. Has no topical effect.
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| Why don't we use Mepivacaine(Carbocaine) in OB? | Biotransformation in fetus is prolonged.
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| Mepivacaine(Carbocaine) is a racemic mixture. It is similar to what other two anesthetics? | Bupivacaine and Ropivacaine.
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| True or false: Bupivacaine(Marcaine) is a highly potent drug with a long duration and slower onset. | True.
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| How does the toxicity of Bupivacaine(Marcaine) compare to Lidocaine(Xylocaine)? | It is much more toxic(cardiotoxic).
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| How is Bupivacaine(Marcaine) used? | Infiltration nerve block, epidural and spinal anesthesia.
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| Bupivacaine(Marcaine) is more likely to cause... | Adverse effects.
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| Articaine (Septocaine) is only available in U.S. in combination with... | Epinephrine.
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| Articaine(Septocaine) has a rapid onset and short duration. When is it used? | Dental and periodontal procedures.
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| Why does Articaine(Septocaine) have such rapid metabolism? | It has both an ester and an amide group.
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| Articaine(Septocaine) has a low toxicity due to its... | Rapid metabolism.
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| Ropivacaine (Naropin) has a long duration, similar to Bupivacaine, but less... | Cardiotoxic.
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| Bupivacaine's cardiotoxicity is due to what isomer? | R-isomer.
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| Ropivicaine(Naropin) is purified and contains only what isomer? | S-isomer.
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| Less lipid soluble, and more rapidly <blank> than Bupivacaine. | Metabolized.
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| How do we use Ropivicaine(Naropin)? | Infiltration, nerve block, epidural, spinal.
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| What LA is neither an amide nor an ester? | Pramoxine (Proctofoam).
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| How is Pramoxine(Proctofoam) used? | Topical agent for relief of hemorrhoids, rectal pain and itching of skin disorders (pruritus).
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| What is Pramoxine(Proctofoam) commonly mixed with? | Many products (ex. Hydrocortisone, calamine).
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| 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.
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