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42 Cards in this Set
- Front
- Back
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What is a local anesthetic?
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A drug that causes reversible blockade of nerve impulse when applied locally to nerve tissue
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What are the two main classifications of local anesthetics?
How are they different? |
Amides and Esters
Amides- longer acting, b/c highly bound to plasma proteins Esters- shorter acting, b/c less tightly bound to plasma proteins |
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What are the effects of local anesthetics on the brain?
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minimal effects
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How can you distinguish between amide and Ester drugs?
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Amides have the letter I before the suffix caine
Esters do not |
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What is the order of blockage from fastest to slowest when dealing with local anesthetics?
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Small autonomic, pain, small myelinated
Lg. sensory Motor |
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What is the mechanism of action of local anesthetics?
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Bind to voltage dependent Na channels receptors in the nerve membrane thereby preventing an influx of Na ions
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Which type of fiber is usually blocked first with a local anesthetics?
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Small first
myelinated are blocked before unmyelinated Pain first (small) motor last (larger) |
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What can you see clinically with an over dose in local anesthetics?
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seizures
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What is the main pharmacological effect of local anesthetics?
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Cardiac depression
vasodilation at large doses |
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Which local anesthetic can be used as an antiarrhythmic?
Tachyarrhythias? |
Lidocaine (ventricular tachy)
Bupivicaine & etidocaine |
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What is the effect of lidocaine on the intestines?
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Prokinetic = increase intestinal motility
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Which of the Amides are highly protein bound?
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Bupivicaine
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How does blood flow effect systemic absorption?
What drug would you give to keep a local anesthetic around longer? |
Areas of high blood flow systemic absorption is increased which decreases the duration of local anesthetic
Epinephrine- causes Vasoconstriction |
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Which drug do you use topically on the eye?
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Proparacaine
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Do esters have a long or short half-life? What are they broken down to?
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Short - less bound to plasma proteins
PABAs -> allergic reactions (may cause histamine release do to PABA breakdown) |
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Are Local anesthetics basic or acidic drugs?
Are the acidic or basic in solution? These drugs are more ionized in what type of environment? |
Basic
Acidic Acidic - this is relevant if you want to increase elimination |
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How are amides metabolized? Esters?
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Amide- liver
Esters- plasma pseudocholenesterases |
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What is lidocaine mixed with when used in topical creams?
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Prilocaine
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What is the biggest factor in determining potency?
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Lipid solubility
It is more potent when it is more lipid soluble Water solubility increases diffusion to the side of action. Pregnancy may increase potency, possibly to hormone changes |
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Will a drug with a pKa close to the fluid pH be more or less potent? Why?
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More potent
Because it will remain nonionized and move into the tissues What factors determine the onset of action of local anesthetics? Increased lipid solubility Ionization If pKa is close to the pH of 7.4 it will have greater solubility due to increase non ionized molecules. Most locals have a pKa in the range of 7.5 to 9 |
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What can you add to lidocaine to decrease pain during injection?
How does this effect solubility? |
Sodium bicarbonate
Increases lipid solubility b/c it's basic and will not ionize the LA |
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What is the ONSET of action of Prilocaine, Bupivicaine, Lidocaine and Procaine?
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Lidocaine & Prilocaine = fast (1-2 min)
Bupivicaine= intermediate Procaine= Slow |
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What is the DURATION of action of Prilocaine, Bupivicaine, Lidocaine, and Procaine?
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Short 15-30 min= Procaine
Intermediate 30- 1.5 = Lidocaine & Prilocaine Long 2-3 hrs= Bupivicaine |
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What can be blocked when local anesthetics are administered epidurally?
What can this cause? |
Sympathetic nervous system
Hypotension |
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What is the main use for Procaine?
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Slow down the absorption of Penicillin G to prolong the action
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What are examples of amide anesthetics?
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Lidocaine, bupivicaine, mepiviacaine, prilocaine, etidocaine, ropivicaine
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What are examples of ester anesthetics?
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Procaine, Chloroprocaine, cocaine, tetracaine, benzocaine, proparacaine
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What is the main mechanism by which local anesthetics cause neuronal blockade?
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They cross the lipid membrane of the nerve cell to reach the cytoplasm and bind to voltage gated Na channels -> decrease influx of Na which prevents depolarization and blocks action potential
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How is cocaine different compared to other local anesthetics in regards to overdose?
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cases vasoconstriction due to increased catecholamines
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What are some differences in lidocaine and bupivicaine?
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Bupivicaine is longer acting and more toxic than lidocaine
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Which local anesthetic is approved and commonly used in horse?
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Mepivacaine
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What are some important elimination concerns with local anesthetics?
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Ester local anesthetics have short half lives due to rapid metabolism plasma cholinesterases
Cocaine is an exception and has significant hepatic metabolism Amide local anesthetics have long half lives (2-6 hours) Local anesthetics are basic drugs so acidic urine with increase elimination Many metabolites are excreted in urine |
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How long does it take most topical cream anesthetics to work?
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30-60 minutes for ophthalmic creams
Proparacaine will work the fastest |
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Which commonly used local anesthetics given as an injectable are fast acting and which are intermediate and which are slow?
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Lidocaine and Mepivacaine = fast
Bupivicaine = intermediate Tetracaine = slow |
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How long do most topical local anesthetics last?
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1 -2 hours for creams
Lidocaine patches last about 12 hours |
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What are the side effects of local anesthetics?
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CNS stimulation, convulsive seizures followed by CNS depression and death from respiratory failure.
CNS stimulation is often seen before cardiac depression but can be seen together like with the use of bupivicaine. Cocaine does not cause cardiac depression but bupivicaine and causes the most Local anesthetics can cause vasodilation Methemoglobinemia due to the toxic metabolites with prilocaine and benzocaine and a cats are the most sensitive |
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How can epidural administration of a local anesthetics cause hypotension?
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Local anesthetic goes cranially the sympathetic system can be blocked resulting in hypotention
Sometimes glucose is added to solutions to make them heavier then the CNS fluid and less likely to ascend the spine and causes sympathetic inhibition |
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Which local anesthetic is more toxic, bupivicaine or lidocaine?
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Bupivicaine is toxic at lower doses and is more likely to be proarrhythmic
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Which species are more sensitive to local anesthetics?
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Horses are the most sensitive and cats are more sensitive than dogs
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What are problems with intravenous regional local anesthesia and epidural anesthesia?
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IV may cause sudden increase in blood concentration, therefore more toxic local anesthetics are not recommended by this route (bupivicaine)
Epidural can migrate cranially and cause hypotension (add glucose) |
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What are good ways to prevent toxic effects of local anesthetics?
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Do not exceed toxic dose
Use vasoconstrictor to decrease toxicity Use monoisometric compounds |
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How is local anesthetic toxicity treated?
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Anticonvulsants such as valium, propofol, pentobarbital to control seizures
Ventilate patients with respiratory arrest Include fluids and vasopressors for hypotention associated with vasodilation and atropine for positive inotropes in cases with decreased cardiac contractility and heart rate Tachyarrythmias caused by bupivacaine is often refractory to treatment with antiarrythmics. Lipid infusions may help bind the lipid soluble bupivacaine to decrease the levels of free drug |
