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All local anesthetic drugs:

  • Are potentially toxic, you must know the maximum safe dose
  • May depress the central nervous system
  • May cause drowsiness, which may progress to unconsciousness with twitching and possibly convulsions
  • May cause hypotension related to extensive sympathetic blockade or direct depression of cardiac function.
  • These reactions are most likely to occur if the drug is accidentally injected into a vein or if an overdose is
    given by using either too high a concentration or too large a volume of drug.


Rate of drug absorption can be reduced by injection with a vasoconstrictor drug, such as:

- epinephrine

  • most often used in dilution of 5 mg/ml (1:200 000)
  • for infiltration, 2.5 mg/ml (1:400 000) generally sufficient

To make a 1:200 000 dilution of epinephrine (adrenaline):

- add 0.1 ml of 1:1000 epinephrine to 20 ml local anaesthetic solution

Pre-mixed ampoules of local anaesthetic, epinephrine often available

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