Pharmacology: local anaesthetics Flashcards
3 structural components of local anaesthetics?
Aromatic ring
Ester bond or amide bond (defines the two classes of local anaesthetics)
Amino side chain
Local anaesthetic structure
- What is the significance of the amino group?
They are weak bases - which enables local anaesthetics to penetrate the nerve sheath and the axon
Local anaesthetics: ester bond class
Metabolism
- How are they metabolised?
- Thus, are they longer or shorter acting?
- 2 examples?
By pseudocholinesterases in the blood - occurs quickly.
Hence, they are shorter acting.
Examples: cocaine, procaine
Local anaesthetics: amide bond
Metabolism
- How are they metabolised?
- Thus, are they longer or shorter acting? Wider or more narrowly distributed/
By hepatic CYP enzymes - which takes longer than pseudocholinesterases in the blood.
They are longer acting and more widely distributed
Lidocaine
Local anaesthetics
- Mechanism of action?
Reversibly bind to and block Na+ influx channels.
Reduced Na+ influx –> stops AP firing.
Occurs in sensory neurons, including noiciceptive neurons
Additionally,promotes sustained K+ efflux –> increased refractory period –> decreased AP firing rate
Local anaesthetics
- Describe use dependence
Hydrophobic local anaesthetics - can block the inside of the sodium channel without it being opened; so, they are not use dependent.
Hydrophilic local anaesthetics - can only block the inside of the sodium channel once it has been opened - hence, it is use dependent.
Local anaesthetics
- Two additional effects?
- Anti dysrhythmic
- Anti epileptic
Local anaesthetics
- Why are vasoconstrictors sometimes given along with a local anaesthetic?
Becuase it confines the local anaesthetic to the target site; prevents it from escaping local area (which can lead to ADRs)
3 CNS related ADRs?
Restlessness (due to anti epileptic effect)
Metallic taste
Respiratory depression
3 CV related ADRs?
Myocardial depression
Conduction block
Vasodilation
