Change from baseline and subsequent mean values for thermal pain and pressure pain was performed 15 min after each injection (4-, 4-, 8-, and 16-mg individual doses given 90 min apart, corresponding to cumulative doses of 4, 8, 16, and 32 mg, respectively), as well as 90 and 180 min after final drug administration. Repeated-measures ANOVA with Bonferroni correction was used to examine pairwise comparisons at each time point. Bars represent sample means, and error bars represent standard deviations. No significant differences were found in these pain testing modalities.