Term
| What are the amide local anesthetics? |
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Definition
Lidocaine, Bupivacaine, and Ropivacaine are the amide anesthetics.
They are the more commonly used local anesthetics |
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Term
| What are the ester local anesthetics? |
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Definition
Procaine and Tetracaine are the ester local anesthetics.
(also: benzocaine) |
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Term
| By what mechanism do local anesthetics work? |
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Definition
| Local anesthetics block Na+ channels (mainly inactivated) |
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Term
| What is a liposome preparation? |
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Definition
| A liposome preparation is a slow release preparation of the local asesthetic. Liposomes are lipid bilayers that act as a barrier to drug diffusion and thereby prolong their action. |
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Term
What is the order of conduction blockade in the following neurons?
Pain fibers
ANS fibers
Motor Fibers
Sensory/Proprioception fibers |
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Definition
Symp. and parasymp. are blocked first. This is followed by pain fibers then other sensory fibers. The motor fibers are the last to be blocked.
ANS
Pain
Proprioception
Motor |
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Term
| How does a local anesthetic's vasodilatory action relate to its duration of action? |
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Definition
These are inversely related. The greater the vasodilatory effect of a local anesthetic, the faster the drug is cleared from the area and the shorter its duration of action.
Ex: Lidocaine has a greater vasodilatory action than mepivocaine, so it's duration of action is less. |
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Term
| Which drugs cross the placenta more easily: Ester or amide local anesthetics? |
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Definition
The amide anesthetics cross the placenta more easily. Ester anesthetics are rapidly hydrolyzed by plasma esterases, so they are inactivated quickly.
The ease with which amide anesthetics cross the placenta is inversely proportional to the degree that they are protein bound.
(amides are metabolized by the liver/CYP450 system) |
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Term
| Why can a large dose of local anesthetic lead to seizure? |
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Definition
| A large dose may allow the local anesthetic to exert systemic effects. In the CNS they preferentially depress the inhibitory neurons, which can lead to overexcitation of the brain and seizures. |
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Term
| Which local anesthetics are used topically? |
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Definition
| The ester anesthetics Tetracaine and benzocane... and the amide anesthetic Lidocaine are the only local anesthetics that are used topically. |
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Term
| Which local anesthetic is NOT used for local infiltration? |
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Definition
Tetracaine is the only anesthetic not used for local infiltration (local injection). It is metabolized slowly, and therefore has a greater risk of systemic toxicity!
(also not used for peripheral nerve block)
Benzocaine is also not injectable...but this one was not covered in class |
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Term
| What anesthetics are used for epidural anesthesia? |
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Definition
The amide anesthetics are the main drugs for epidural anesthesia.
(With the exception of chloroprocaine, the ester anesthetics are not used in epidural anesthesia) |
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Term
| Which anesthetic can cause methemoglobinemia? |
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Definition
| Prilocaine can cause methemoglobinemia |
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Term
| What are uses for tetracaine? |
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Definition
Tetracaine is only used topically or in spinal anesthesia.
Recall, tetracaine is metabolized slowly so it is more likely to cause systemic effects. Because of this it is not injected into tissues or for peripheral nerve blockade. |
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Term
| Why is epinephrine added to local anesthetics? |
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Definition
| Epinephrine is a peripheral vasoconstrictor. This maintains a higher concentration of the anesthetic locally, prolonging its duration of action. It also prevents diffusion of the drug into systemic circulation, thereby minimizing systemic effects. |
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Term
| if local anesthetics are absorbed too rapidly into systemic circulation, what are some side effects you may observe? |
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Definition
| Drowsiness, anxiety, nystagmus, respiratory depression, muscle twitching, convulsions, Hypotension, arrhythmias, cardiovascular collapse (bupivacaine), methemoglobinemia (prilocaine). |
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Term
| Which local anesthetic agent is cardiotoxic? |
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Definition
| Bupivacaine, an amide local anesthetic with long duration, is the most cardiotoxic of all local anesthetics. |
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Term
| Administration of ester anesthetics has what effect on sulfonamide antibiotics? |
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Definition
| Local ester anesthetics inhibit the antimicrobial effects of sulfonamides. This is because they are esters of Para-aminobenzoic acid (PABA). Their metabolism releases PABA, a reagent in tetrahydrofolic acid synthesis. Sulfonamide antibiotics inhibit THF synthesis in bacteria. But with the ester anesthetics, now you have an increased amount of rectant (PABA) pushing the process forward and counteracting the effect of the sulfonamide drug. |
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Term
| How does pH affect the diffusion of local anesthetics into the cell? |
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Definition
Local anesthetics are weak bases. At low pH, they become protonated into their ionized form. This decreases their lipid solubility and hinders their ability to diffuse into the cells.
(sites of infection have lowered pH = decreased solubility of local anesthetics!) |
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Term
| Why does benzocaine make a good topical local anesthetic? |
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Definition
Benzocaine has a very low pKa, so it is almost insuluble in water. It therefore cannot be injected. Instead, it makes a great topical anesthetic because it remains where it was applied for a long time (doesn't diffuse away) and produces a sustained anesthetic action.
Other topical anesthetics are lidocaine and tetracaine. |
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Term
| An allergy to para-aminobenzoic acid (PABA) contraindicates what local anesthetics? |
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Definition
Allergies to PABA contraindicate all ester type local anesthetics, as they are all esters of PABA. The ester anesthetics include:
Procaine
Tetracaine
Benzocaine |
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Term
| Why would you not include epinephrine with an injection of a local anesthetic? |
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Definition
| Don't use Epi when a patient has cardiac arrhythmias. |
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