Local Anesthetics Flashcards
Benzocaine
Procaine
Cat: Short acting ester LA (benzocaine = topical, procaine = infiltrate, epidural)
MOA: Blocks activated/inactivated Na channels
Adverse: allergy to PABA, anxiety, convulsions (GABA block - tx w/diazepam), CV collapse
Cocaine
Cat: short acting ester for nose/throat
MOA: block activated/inactivated Na channels, use dependent
SE: PABA allergy, anxiety, convulsions (GABA block - tx w/ diazepam), inc HR/contraction, VFib, hypertension
Beware of drug abuse
Lidocaine
Ropivacaine
Cat: long acting amide LA
MOA: block activated and inactivated Na channels, use dependent
SE: anxiety, convulsions d/t GABA, CV collapse (bradycardia, hypotension)
Which LA has reduced affinity for cardiac sodium channels and is therefore associated with less cardiac toxicity?
S-isomer of ropivacaine
Locations of use of lidocaine vs ropivacaine
Lidocaine: infiltration, Bier block, peripheral, epidural, spinal
Ropivacaine: peripheral
Epinephrine
Reduces systemic absorp of local anesthetics via vasoconstriction via alpha 1 adrenergic activation
SE: localized tissue necrosis
Increases LA action by 50%
Clonidine
Used with LAs for epidural and spinal admin to further reduce pain transmission
MOA: prevents NT release at C and Ad fibers via presynaptic alpha 2
Diazepam
Treat convulsions d/t systemic absorption of LA into CNS by activating GABA receptors in CNS
3 characteristics that determine level of lipophilic
- # of hydrocarbon chains and length
- Length of intermediate connecting chain
- # /length of aromatic ring hydrocarbons
A delta fibers
Fast pain
Glutamate to NMDA
Neospinthalmic neurons
Myelinated
C fibers
Second pain
Substance P to P receptors
Paleospinothalmic neurons
Esters
One “i”
Short duration of action
Metab by plasma/live pseudocholinesterases
Allergies: PABA derivatives
Amides
Two Is
Longer duration of action
Metab: liver p450
Why don’t local anesthetics work well in infected tissue?
Lower pH means that the LA is more charged, leaving it unable to cross the cell membrane leading to decreased potency and longer onset time
Fiber types most susceptible to LA
Small diameter
Myelinated
Firing a lot
Exterior fibers