LA pharmacology: Basics Flashcards
What is the purpose of stabiliser in cartridge?
- prolongs shelf life
what is the purpose of isotonic carrier medium?
- same osmotic conc. as tissue fluids so no net movement of fluid therefore cell doesnt change in size
Name the five LA drug names used in the UK and each of their trade name (incl. vasoconstrictor name)
- Lidocaine and adrenaline (Vc) - Lignospan special / Xylocaine / Utilycaine
- Mepivacaine - scandonest
- Prilocaine and Felypressin (Vc) - citanest
- Prilocaine Plain - citanest plain
- Articaine and adrenaline (Vc) - Septanest / Bartinest
What is the general structure of a local anaesthetic?
- aromatic ring gives lipophilic end: likes lipid
- Intermediate chain - two types - structure determines type of LA it is
- Hydrophilic end: likes water - charged element
What are the two types of intermediate linkages?
- Ester linkage
- Amide linkage
What do we classify local aesthetics based on?
- wether it is an ester or an amide
Which local anaesthetics are esters? What are they each used for?
- procaine: first LA made - no longer used
- benzocaine: only in topical anaesthesia
what are the five local anaesthetics classified as amides?
- Lidocaine
- Mepivicaine
- Prilocaine
- Bupivacaine
- Articaine
what is one characteristic that is the same amongst all amide local anaesthetics?
- they’re all used for injections
what is one characteristic that is the same amongst all amide local anaesthetics?
- they’re all used for injections
What is the structure of an ester local anaesthetic?
- has an ester bond in intermediate chain
what is the structure of an amide local anaesthetic?
- has an amide bond in the intermediate chain
Explain how action potentials work
- action potential is a nerve impulse that allows nerves to communicate and for a response e.g. gland secretes hormones or muscle contracts
- when there is a stimulus such as pain, it causes change in cell membranes of neurones which initiates a nerve impulse
- In resting state, the charge inside the neurone is more negative than outside of cell
- within the membrane, there are voltage gated sodium and potassium channels which are closed in resting state
- following stimulus, some sodium channels open and sodium ions flow into the neurone
- this causes potential difference across membrane, if this difference reaches the threshold, it propagates an action potential
- more sodium channels open, sodium flows in and this causes depolarisation
- potassium channels open and flow out of the neurone, this causes repolarisation
- they remain open for a while after a nerve impulse, extra potassium ions flow out and cause inside of membrane to become more negative than resting state - hyper polarised
- takes time for recovery - refractory period - no further nerve impulses initiated in this time
- channels opening is propagated along the nerve and allows impulse to travel and reach target
how do local anaesthetics work ?
- They target sodium channels, they prevent them opening and imitating a nerve impulse ie. preventing pain being felt
What is the name of the two theories of how local anaesthetics work?
- membrane expansion theory
2. specific receptor theory
