Effect of Adrenaline on Pharmacokinetics of Local Anesthetics in Pulp

Method: 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 weeks old, weighing 250-300g. (n=5) Twenty μl of 2% ¹⁴C-labeled lidocaine or 0.5% ³H-labeled ropivacaine with and without 10μg/ml adrenaline (LA-, L-, RA- and R-group, respectively) were injected into the maxilla under general anesthesia. The maxilla and the right three molars were removed at 2, 5, 10, 20, 30, 40 and 60 minutes after the injection. Radioactivity in the maxillary tissue and pulp was measured by an γ-counter. The amount of local anesthetics (maxillary tissue: ng/mg wet weight, pulp: ng/pulp) was calculated based on the specific radioactivity

Result: In lidocaine, the kinetics in the pulp, which was similar to that in the maxillary tissue both in L-group and in LA-group, might directly reflect the change of concentrations in the maxillary tissue. The concentration of ropivacaine   reached the maximum 8 minutes later in the pulp than in the maxillary tissue both in R-group and in RA-group. The pulpal concentrations markedly increased in RA-group. The rates of increase in the pulpal concentration 20 minutes after the injection in the first and second molars were 1.3 and 16.8 times higher in RA-group than in R-group. The effect of adrenaline reached to the third molar in RA-group.

Conclusion: Retention of local anesthetics in the pulp induced by adrenaline was more significant in ropivacaine than in lidocaine.