Changes

==Mechanism of Action==

==Mechanism of Action==

The mechanism of action of all local anaesthetic drugs is similar. The salt of the anaesthetic base (RNH⁺Cl^–) is an ionizable quaternary amine with little or no anaesthetic properties of its own because it is not lipid soluble and therefore not absorbed through the nerve membrane. After deposition in tissue that is slightly alkaline and has considerable buffering capacity, the anaesthetic base is liberated as follows:<br><br>

The mechanism of action of all local anaesthetic drugs is similar. The salt of the anaesthetic base (RNH⁺Cl^–) is an ionizable quaternary amine with little or no anaesthetic properties of its own because it is not lipid soluble and therefore not absorbed through the nerve membrane. After deposition in tissue that is slightly alkaline and has considerable buffering capacity, the anaesthetic base is liberated as follows:<br><br>

<font color="red">RNH⁺Cl^– <--> Cl^– + RNH⁺ <-->  Cl^– + RN + H⁺</font color><br><br>

RNH⁺Cl^– <--> Cl^– + RNH⁺ <-->  Cl^– + RN + H⁺<br><br>

The free anaesthetic base (RN) is absorbed in the outer lipid nerve membrane, where anaesthetic action takes place. If sufficient local buffering capacity exists to remove the dissociated H⁺, this reaction proceeds to the right, and an active base is liberated which exerts an anaesthetic effect. In inflamed or infected tissue, however, the pH is acidic and the result is that only small amounts of free base dissociate from the anaesthetic salt, resulting in poor local anaesthesia.<br><br>

The free anaesthetic base (RN) is absorbed in the outer lipid nerve membrane, where anaesthetic action takes place. If sufficient local buffering capacity exists to remove the dissociated H⁺, this reaction proceeds to the right, and an active base is liberated which exerts an anaesthetic effect. In inflamed or infected tissue, however, the pH is acidic and the result is that only small amounts of free base dissociate from the anaesthetic salt, resulting in poor local anaesthesia.<br><br>

In human dentistry and oral surgery, vasoconstrictors (adrenaline, L-noradrenaline) are routinely used in combination with the local anaesthetic. The main reason is to delay systemic absorption of the local anaesthetic, thus reducing the toxicity and increasing the margin of safety. Local anaesthetics produce analgesia when given in small doses intravenously, but are potent proconvulsants and can induce marked myocardial depression and cardiac dysrythmias when administered systemically. The addition of vasoconstrictors, by reducing systemic absorption of the local anaesthetic, also increase intensity and prolong anaesthetic activity. However, they may increase the risk of [[:Category:Arrhythmia|cardiac arrhythmias]] and ventricular fibrillation. In veterinary dentistry and oral surgery, local anaesthetics are generally used without the addition of vasoconstrictors.

In human dentistry and oral surgery, vasoconstrictors (adrenaline, L-noradrenaline) are routinely used in combination with the local anaesthetic. The main reason is to delay systemic absorption of the local anaesthetic, thus reducing the toxicity and increasing the margin of safety. Local anaesthetics produce analgesia when given in small doses intravenously, but are potent proconvulsants and can induce marked myocardial depression and cardiac dysrythmias when administered systemically. The addition of vasoconstrictors, by reducing systemic absorption of the local anaesthetic, also increase intensity and prolong anaesthetic activity. However, they may increase the risk of [[:Category:Arrhythmia|cardiac arrhythmias]] and ventricular fibrillation. In veterinary dentistry and oral surgery, local anaesthetics are generally used without the addition of vasoconstrictors.

[[Category:Dental and Oral Medication]]

[[Category:Dental and Oral Medication]]

[[Category:Analgesia]]

[[Category:Analgesia]]

[[Category:To Do - Dentistry questions]]

[[Category:Waltham reviewing]]