Local Anesthetics Flashcards
What is the mechanism of local anesthetics?
The mechanism is similar to that of Class 1b anti-arrhythmic drugs in that they inhibit local Na+ fast channels in the inactive state.
Are local anesthetics classified as anti-arrhythmic Class 1b drugs?
Though similar MOAs, lidocaine is the only local anesthetic also classified as an anti-arrhythmic Class 1b drug.
How can you differentiate ester local anesthetics and amide local anesthetics when reading the name?
Esters have one “i” in their name while amides have 2 “i”s in their name.
Which nerve gets blocked first (is most sensitive to the local anesthetic) and as a result causes vasodilation?
Sympathetic post ganglion fiber (type C fiber, no myelination)
What is the order of nerve block after initially blocking the sympathetic post ganglion fiber (most sensitive to least sensitive)?
Dull pain (dorsal root, type C fiber, no myelination), sharp pain (delta, type A fiber, heavy myelination), and lastly motor (alpha, type A fiber, heavy myelination)
What is MOA of local anesthetics on neuronal tissue?
Ionized local anesthetics (LAH+) bind to inactivated state and inhibit fast-sodium channels / inhibit depolarization of the nerve
What is the nomenclature by which local anesthetics are classified & why?
LAs are classified as either Esters or Amides. LAs have lipophilic aromatic portion, an intermediate chain, and a hydrophilic amine portion. The intermediate chain either possess an ester linkage or an amide linkage.
If patient is allergic to ester anesthetics, what do you use for local anesthesia?
Amide LA
Why do ester anesthetics have allergy?
Esters are associated with a higher incidence of allergic reactions due to a p-aminobenzoic acid (PABA) metabolite. Amide agents do not undergo such metabolism.
What are the advantages to adding a vasoconstrictor to a local anesthesia (short acting lidocaine, procaine)?
To prolong LA’s effects and avoid systemic absorption, Decrease systemic toxicity (decrease blood level up to 1/3), Decrease local bleeding (improve visualization of surgical field)
What are the side effects if a local anesthetic is absorbed?
- CNS effects (Circumoral, tongue numbness, metallic taste - earliest sign, Nystagmus, muscle twitching, Seizures, Depression / Loss of Consciousness)
- Cardiotoxic (cardiac arrest, CV collapse)
Which local anesthetic is most cardiac toxic?
Bupivacaine is most cardiotoxic, contraindicated in epidural anesthesia in Obstetrics.
How do you treat cardiac arrest after LA?
Lipid emulsion treats cardiotoxicity.
How do you treat CNS toxicity of LA?
Diazepam/Midazolam/Propofol (for seizures), succinylcholine, O2
What are the differences between the ester and amide linked local anesthetics?
Esters are metabolized by tissue and blood butyrylcholinesterase (peudocholinesterase). Amides are metabolized by liver amidase
(long T1/2 1.5-2h), and liver diseases affect.
