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. |