Influence of bile acid derivates on tramadol analgesic effect in mice

Influence of two newly synthesized bile acids derivates, namely sodium salt of monoketocholic acid MKH-Na and methyl ester of monoketocholic acid MKH-Me on tramadol (12.5 mg/kg oral and intramuscular) analgesic effect was examined in this research. Analgesic effect was measured by antinociceptive hot plate method. Interaction was estimated by detection of changes in analgesic effect of tramadol combined with bile acids (subcutaneous administration of 4 mg/kg 20 min before tramadol) compared to analgesic effect of the same dose of tramadol given alone. Hydrosoluble sodium salt of monoketocholic acid did not show interaction with tramadol, regardless of the route of administration of tramadol. However, methyl ester of monoketocholic acid increased the analgesic effect of tramadol when it was given intra-muscularly. After oral administration of tramadol, methyl ester of monoketocholic acid decreased the analgesic effect of tramadol. According to the time point when interaction reached statistically significant difference, it can be presumed that after intramuscular administration of tramadol, methyl ester of monoketocholic acid increases tramadol absorption and transport to brain and in that way increases its analgesic effect. The analgesic effect of tramadol after oral administration was decreased, which could be explained by the induction of tramadol metabolism in the liver, but should be examined in more details.