Figure 3. Time-related effects of epidural and intrathecal n-butyl-p-aminobenzoate (closed squares) and bupivacaine (open squares) in the rat. Median effective doses and 95% confidence interval expressed in nanomoles (log scale) are plotted against time after administration. Best-fitting quadratic functions are included. Significant difference between the median effective doses of n-butyl-p-aminobenzoate and bupivacaine at any time are indicated by *P < 0.01 and **P < 0.001.