Serum lidocaine and MEGX concentrations after pharyngeal anesthesia for gastroscopy

In 20 patients undergoing topical anesthesia for gastroscopic examination, serum concentrations of lidocaine and its metabolite, monomethylglycinexylidide (MEGX), were measured. Patients were divided randomly into two groups: a gel group, in which 5 ml of 2% lidocaine gel was applied to the throat for 20 minutes; and a solution group, in which 40 ml of 2% lidocaine solution was administered by gargling for five minutes. The effect of oropharyngeal anesthesia was comparable in both groups. In the gel group, the serum levels of lidocaine and MEGX were not elevated at 15 minutes after application of the anesthetic. However, in the solution group, a rise in both serum lidocaine and MEGX at 15 minutes after anesthesia was detected in some of the patients (40%). Increased serum MEGX concentrations, which correlated well with serum lidocaine concentrations, were associated with the age of the patient (r = 0.606; p < 0.05), but not with height or weight. As a topical anesthetic for endoscopic examination, we prefer lidocaine gel to lidocaine solution, because the latter might be absorbed more rapidly and unpredictably in some, especially aged patients.