• How does the sensitivity for blockade by a LA compare regarding the following types of fibres:

(a) myelinated fibres with unmyelinated fibres; and

smaller and myelinated fibers are blocked easier than larger and unmyelinated fibers

(b) pressure/touch nerves with the dorsal nerves that transmit pain impulses?

Dorsal nerves (type C fiber) that transmit pain impulses have a higher sensitivity to be blocked by local anaesthetics than pressure/touch nerves (type A fiber)

• Make a list of the effects of LA on other tissues.

Heart: class 1 antiarrhythmic drugs like lidocaine, blocks sodium channels in the heart, shortens the duration of action potential and increases the refractory period.

Weak blocking effects on skeletal neuromuscular junction and thus as no clinical application

Mood elevation induced by cocaine reflects actions on dopamine or other amine-mediated transmission in CNS rather than a local anaesthetic action on membranes.

• What is the basis for the selection of a LA?

1. The type of procedure that is being done
2. The type of tissue that the local anesthetic should be used on
3. The duration of the numbing effect that is needed

• Why are LA solutions sometimes saturated with CO₂?

CO₂ acidifies the solution; a lower pH increases the concentration of the active cationic protonated forms of the local anesthetic. Adding COD thus potentiates the effects of the LA by increasing the concentration of the ionised form of the drug that is more effective in blocking of the Na ion channel and enhances/ increases the onset of the pharmacological action

Which of the LA are typically used for surface anaesthesia?

• Benzocaine
• Cocaine
• oxybuprocaine

Brand, L. 2021. Local Anesthetics. Study Unit 6 [PowerPoint Presentation]. Unpublished Lecture Notes on eFundi. FKLG 312. Potchefstroom:NWU

https://pubmed.ncbi.nlm.nih.gov/9026253/