Effect of Epinephrine on the Absorption of Lidocaine Following Application to the Oral Mucosa in Rats

Abstract Objective We investigated the role of epinephrine in prolonging the localization of a topical anesthetic on oral mucosa and inhibiting its absorption in blood. Methods We used 7–8-week-old specific-pathogen-free Wistar male rats (n = 128) for our study. We divided them into lidocaine and lidocaine with epinephrine groups and applied 5 µL of 14C-labeled lidocaine hydrochloride gel and 10 µg/mL 14C-labeled lidocaine hydrochloride gel with added epinephrine to the palatal mucosae of the rats, respectively. The amount of lidocaine was measured by radioactivity and was observed using autoradiograms. Results After 4 min, the values were significantly lower in the lidocaine with epinephrine group (1040.0 ± 142.8 vs. 701.2 ± 109.0 ng/mg [20 min]). After 40 min, the lidocaine level became significantly higher in the lidocaine with epinephrine group (586.8 ± 112.4 vs. 1131.3 ± 155.2 ng/mg [40 min]). Similar results were observed in the palatine bone and mucosa and serum. Conclusion Epinephrine prolonged the localization of lidocaine applied to the mucosa and inhibited its absorption into the bloodstream. Clinical studies are required to evaluate the use of epinephrine-containing topical anesthetics on the oral mucosa.