pharm of LA Flashcards
Define anaesthesia
Without feeling or sensation
Define local anaesthesia
Loss of feeling restricted to a particular region
When is local anaesthesia used?
To enable minor or major operative procedures to be carried out To provide relief from prolonged severe pain
What can local anaesthesia be produced by?
- Local anaesthesia can be produced by:2. Cooling with ethyl chloride (block of neuronal conduction at 8-10°C)3. Pressure (used to reduce discomfort from injection in palatal tissue)4. Hypoxia5. Irreversible blockade (phenol ethanol, radiofrequency lesion)6. true local anesthetics
Give examples of irreversible blockers used as local anaesthetics
Phenol ethanol| Radiofrequency lesion
Describe true local anaesthetics
A substance applied to any nerve fibre in sufficient concentration will produce reversible blockade of axonal conduction without depolarisation
What is a local anaesthetic?
A local anaesthetic is a drug that causes reversible local anaesthesia and a loss of nociception (the neural processes of encoding and processing noxious stimuli)
Define nociception
The neural processes of encoding and processing noxious stimuli
How do local anaesthetics work?
They reversibly block impulse conduction along nerve axons and other excitable membranes that utilise sodium channels as the primary means of generating action potentials
What is the result of using local anaesthetics on specific nerve pathways?
Effects such as analgesia and paralysis can be achieved
Define analgesia
Loss of pain sensation
Loss of pain sensation
Loss of muscle power
Name some techniques local anaesthetics are used in?
- Topical application2. Subcutaneous injection 3. Nerve block 4. Epidural 5. Intrathecal
Where is a topical anaesthetic applied?
Around the gums, cornea and skin prior to venipuncture
What is a Subcutaneous injection?
An infiltration anesthesia can be one or more injections
Where is a nerve block applied?
Around the nerve
Where is an epidural given?
Into the epidural space; child birth
Where is an intrathecal anesthetic given?
Into subarachnoid space| It is a form of spinal anesthesia
List some ideal properties of local anesthetic
- stable in solution, (requires no additive)* non-irritating to tissues* no permanent damage to nerves* no systemic toxicity* no allergic response* potent* rapid onset of action* predictable duration of action* Must be a sensory not a motor block* Must have no active metabolites
On what day is the first recorded use of general anaesthetics?
October 16th 1846
What did Dr Karl koller notice?
That the end of his tongue went numb when he tasted cocaine| He then dropped some cocaine dissolved in water into his eye – noticed its tissue-numbing capabilities
What did Dr Koller demonstrate in 1884?
The potential for cocaine to be used as a local anaesthetic in eye surgery
What is Dr Kollers nick name?
Coca Koller
What replaced cocaine as a local anaesthetic and when?
In the 20th century, other agents such as lidocaine replaced cocaine as a local anaesthetic
What is the aromatic terminal of LA’s described as and why?
Lipophilic as is contains no positive or negative charges
Define lipophilic
Lipid soluble
Why is the aromatic terminal essential for LA’s?
In order for them to penetrate fatty tissues such as the lipid sheath of nerves in order to gain access to the nerve cell membranes to reach its site of action
What is the amino terminal in local anaesthetics described as?
Water soluble or hydrophilic
Why is solubility in water essential for LA’s?
- To allow for the dissolution in a solvent to permit injection 2. To allow penetration through interstitial fluid allowing administration
How does the amide structure of articaine differ from other local anaesthetics?
The amide structure is similar but the molecular structure differs through the presence of a thiophene ring instead of a benzene ring
Name some ester linked agents
Cocaine| Procaine
Describe what cocaine does and when it was used?
It was first used in 1884, It is a good penetratorIt is not used as much now as it is a drug of abuse, It blocks sodium re uptake
What are the major disadvantages of cocaine?
Cocaine is an intense vasoconstrictor and has a potential to cause cardiovascular toxicity
Describe what procaine does and when it was used?
First used in 1905 as a nerve blockerHas low potent and last for a short duration Not used much now