Methods: Approval from the Animal Experiment Committee of our university was obtained, and all procedures were performed according to the prescribed regulations. Subjects were Wistar-strain male rats, 7-8 week-old, weighing 250-270g. (n=5) Five μl of 2%14C-lidocaine gel (L) or 2%14C-lidocaine gel with 10μg/ml adrenaline (LA) was applied on the center of palatine mucosa using an applicator (Bore:2mm) under general anesthesia. The maxilla was removed at 0.5, 2, 4, 7, 10, 20, 30, 40, 50 and 60 minutes after application and the topical anesthetic was wiped away. The part of maxilla where 14C-lidocaine was applied was extracted. We separated the part into palatine mucosa and palatine bone. Blood samples were taken from femoral vein. Radioactivity in the tissue and serum was measured by an γ-counter. The amount of lidocaine in maxillary tissue (ng/mg wet weight) was calculated based on the specific radioactivity.
Results: The amount of lidocaine peaked at 10min after topical application in L and at 40min in LA both in mucosa and bone. The amount of lidocaine in palatine bone reflected that in palatine mucosa. Approximately 1/100 of lidocaine in mucosa infiltrated into bone. The serum lidocaine concentration reached the highest 20min and 50min after application of lidocaine in L and LA respectively.
Conclusions: Adrenaline prolonged local stagnation of topical lidocaine and prevented rapid increase of blood lidocaine concentration. It was suggested that adrenaline prolonged the duration of topical anesthesia and reduced a risk of intoxication.