Lidocaine plasma concentrations following administration of intraoral lidocaine solution

Seventeen healthy male volunteers received 15 mL of 2% solution (300 mg) of lidocaine hydrochloride every three hours for eight consecutive doses. Modes of administration were as follows: (A) each dose washed throughout the oral cavity, then spit out without swallowing; (B) each dose washed, then swallowed; and (C) each dose swallowed directly. Plasma levels of lidocaine and its two metabolites (monoethylglycinexylidide [MEGX] and glycinexylidide [GX]) were measured during and after the period of dosage. In trial A, levels of all three compounds were very low, in no case exceeding 0.3 microgram/mL. During trial C, the mean peak levels of lidocaine and MEGX, respectively, were 0.5 and 0.6 microgram/mL after the first dose, and 0.8 and 1.3 microgram/mL after the eighth dose. Both compounds were essentially undetectable by 12 hours after the last dose. Levels in trial B were very similar to those in trial C. Thus, recommended topical oral cavity use of 2% lidocaine leads to negligible systemic levels of lidocaine and metabolites. Even when doses are swallowed, systemic levels do not approach a toxic range.