Effects of Adrenaline on the Distribution of Lidocaine in Rats

Objective: Adrenaline is added to lidocaine for dental use in order to improve its anesthetic efficacy and duration. The aim of this study was to investigate the effects of adrenal ine on the distribution of supraperiosteally injected lidocaine in maxilla.

Method: 20ěl of 14C-lidocaine 2% without (L-group) or with adrenaline 1:100,000 (LA-group) were injected proximal to the right maxillary molars of rats under general anesthesia with 50mg/kg pentobarbital intraperitoneally. The rats were sacrificed at 2, 5, 10, 20, 30 and 60min after the injection. The palatal mucosa and maxilla were taken. The palatal mucosa was cut into 2-pieces along the median line, and the maxilla was divided into 6-parts (the division including injection site: right maxilla part). The radioactivity in each sample (100-300mg wet weight) was measured by liquid scintillation counting (dpm), and was converted into quantity of lidocaine (ng/mg tissue wet weight).

Result: In the right palatal mucosa, radioactivity in both L- and LA-groups was highest at 2min and gradually reduced as time passed. Changes of the quantity of lidocaine in L and LA-groups were parallel. In the right maxilla part, while lidocaine gradually reduced and disappeared 30min late in L-group, Almost a constant value was kept in LA-group until 20min after the injection and lidocaine disappeared 60min later. The quantity of lidocaine at the peak in L-group in the left maxilla part was about 1/10 compared to one in the right maxilla part. Lidocaine disappeared 30min later in L-group. In LA-group, nearly the same value was kept from 5 to 30min after the injection in the left maxilla part.

Conclusions: The results suggested lidocaine was kept in maxilla until 20min after the injection, and that the distribution of lidocaine after maxillary injection in L- and LA-groups reflected the duration of pulpal anesthesia with and without adrenaline.