Antinociceptive Effects and Interaction Mechanisms of Intrathecal Pentazocine and Neostigmine in Two Different Pain Models in Rats

Figure 4

Shows the interaction between intrathecal pentazocine and neostigmine in phases I (a) and II (b) of the formalin tests and the plantar incisional pain model (c) which were analyzed using an isobologram. The x- and y-axes represent the ED₅₀ dose of pentazocine and neostigmine, respectively. The lines connecting the ED₅₀ points are the theoretical additive lines and the theoretical additive points for the drug combinations. The theoretical additive value was significantly higher than the experimental ED₅₀ value of the combination of the two drugs. The experimental ED₅₀ values were significantly below the lines of additivity, indicating a synergistic interaction.

(a)

(b)

(c)