Local Anesthetics Flashcards
What is the difference between LA and GA?
LA is as effective but safer than GA!
What is a local anesthetic?
A local anesthetic is a drug that causes reversible local anesthesia and a loss of nociception by blocking afferent activity in the peripheral and CNS produced by stimulation of specialised nociceptors or “pain receptors” that only respond to tissue damage caused by intense chemical, mechanical or thermal stimulation.
What are the various techniques of local anesthesia?
Administered to the site of action using:
- Topical Anesthesia (surface)
- Infiltration (into subcutaneous tissue)
- Plexus block (bundle of nerves)
- Epidural (Extradural) block
- Spinal anesthesia (subarachnoid block)
4 and 5 are for lower limb/abdomen
Which technique of local anesthesia is most commonly used by dentist?
Infiltration
What are the effects of LA?
Analgesia (loss of pain sensation) and Paralysis (loss of muscle power)
What are the adverse effects of LA?
Depends on: LA, method, site of administration
- Localised prolonged anesthesia or Paresthesia
Caused by Infection, hematoma, excessive fluid pressure in a confined cavity, severing of nerves and support tissue during injection - Systemic reactions - when LA is accidentally injected into the bloodstream
Causes depressed CNS syndrome, allergic reaction, vasovagal episode, and cyanosis due to local anesthetic toxicity
What is the pKa of LA?
8-9 (weak base)
What are examples of LA which are part of the amide group?
Lidocaine Mepivacaine Bupivacaine Etidocaine Prilocaine
What are examples of LA which are part of the ester group?
Cocaine
Procaine
Chloroprocaine
Tetracaine
What is the chemical structure of LA?
A lipophilic group connected via an amide or ester link to an ionisable group
Why do ester LAs have a shorter duration of action?
This is because ester links are more prone to hydrolysis
Which form of LAs is most active
The charged form of LAs are the most active, as it cannot readily exit closed Na channels
What is the uncharged form of LA good for?
The uncharged form of LAs is important for rapid penetration of the lipid membranes.
Why are LAs less effective when injected into acidic tissues? (Inflamed or ischemic tissues)
This is because a smaller proportion of it will be unionsed and available for diffusion into nerves. Only uncharged forms of LAs can rapidly penetrate into lipid membranes.
What does absorption and distribution of LA determine?
Offset of action and systemic toxicity
This is because LA is usually injected around nerves.