Lidocaine plasma concentrations following administration of intraoral lidocaine solution

D. J. Greenblatt, D. M. Benjamin, C. R. Willis, J. S. Harmatz and M. A. Zinny

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.