Local anaesthetic with maximum ionized form at physiological pH
Local anaesthetics with pKa value closest at physiological pH (7.4) will have a higher concentration of nonionized (unionized) base. Thus, the agent with pKa value away from physiological pH will have more concentration of ionized formChloroprocaine has highest pKa value, hence maximum ionized form at physiological pH.(Refer: Morgan and Mikhail's Clinical Anaesthesiology, 5th edition, pg no.268-270)
Lignocaine
Etidocaine
Bupivacaine
Chloroprocaine
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