Neo Vitacain Injection containing 0.1% dibucaine hydrochloride (D), 0.3% sodium salicylate (S) and 0.2% calcium bromide (B) is a widely used analgesic preparation in the fields of anesthesiol. and orthopedics.Regarding the significance of the prescription of this drug. inconsistent results were obtained in non-clin. studies.In this study, we investigated the influences of S and/or B on the local anesthetic effect of D using the infiltration anesthesia test model in guinea pigs.ED50 values were estimated as the concentration of D in D alone and in combination (D+S, D+B and D+S+B).Using these ED50 values, the potency ratios were calculatedAs for the significance of combination with S, the potency ratio between D+S+B and D alone was 2.00 [95% confidence limit (CL); 1.29-3.09, 40 min after treatment], and that between D + S and D alone was 1.67 [CL; 1.11-2.44, 25 min].Moreover, in both cases the durations of infiltration anesthetic effect were prolonged.As for the significance of combination with B, the potency ratio between D+B and D alone was 0.90-1.10 [1.10 (CL; 0.63-2.04, 20 min), 1.00 (CL; 0.66-1.52, 25 min) and 0.90 (CL; 0.53-1.53, 30 min)], and that between D+S+B and D+S was 1.20 [CL; 0.73-2.13, 20 min].In conclusion, the local anesthetic potency of D by S was enhanced in this study.This enhancement is considered to be due by the increased intracellular concentration of ionized D (active form) to S through the acidification of the intracellular pH.As for B, further studies are required to clarify the effectiveness of this preparation