Commercial local anaesthetic solutions have an acidic pH to maximise their water solubility and chemical stability.This increases their shelf-life.immediately before injection, alkali can be added to raise the pH towards the physiological pH.This is called 'alkalinisation' or 'buffering' of the solution.Anaesthetic activity is dependent on having both the ionised and non-ionised forms of the drug present after injection.Alkalinisation increases the proportion of non-ionised drug and this could be advantageous.Care must be taken, because if too much alkali is added, the local anaesthetic will precipitate.when used for infiltration anaesthesia or block of small nerves, alkalinised solutions of local anaesthetic are less painful when injected.The onset of local anaesthesia may also be slightly quicker.For epidural anaesthesia or block of large nerves the amount of time saved is minimal and so alkalinisation is not practically useful for these procedures.