The structural domain of LAs responsible for their lipophilicity is the aromatic group. The lipid solubility or partition coefficient of LAs determine their ability to pass through biological membranes and reach their sites of action.2-10 Therefore, the primary determinant of an agent’s potency is its partition coefficient. A LA with higher potency will require a lower dose to achieve the same degree of neuronal blockade as that achieved by an agent with lower potency (Table 2).

Table 2. Lipid solubility determines a LA’s relative potency, which is reflected in the drug’s formulation.
  Lidocaine Mepivacaine Prilocaine Articaine Bupivacaine
Lipid solubility 43 21 25 17 346
Relative potency ≈2 ≈1 ≈1 ≈1 ≈8
Formulations 2% 2% or 3% 4% 4% 0.5%
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