Binding Studies of Lamotrigine with Sera of Different Animal Species

Purpose: The serum protein-binding characteristic of lamotrigine with sera from various species (horse, rat, rabbit and goat) was studied at different dielectric constants and temperatures to obtain an insight into the mechanism of interaction, evaluate the effect of dielectric constant on binding affinity, and to determine the effect of species variation on drug plasma-protein interaction. Method: Binding data were generated by evaluating equilibrium dialysis of lamotrigine in methanolwater solvent (1:1 and 1:3) with horse serum at 20, 28 and 37 0 C The equilibrium dialysis evaluation of lamotrigine with sera of other animal species rabbit, goat and rat was also performed at 37 0 C. Results: A Rosenthal plot obtained with the binding data at different temperatures showed that binding constant decreased with increasing temperature and that binding of lamotrigine to horse serum appeared to be saturation binding. The results also indicated that the binding process was characterized by negative ∆H 0 value and a small positive ∆S 0 values. The binding constant decreased as dielectric constant rose. Conclusions: The results obtained suggest that hydrophobic interaction may have occurred and that van der Waals’ forces were responsible for binding in the hydrophobic region. Data obtained for lamotrigine binding with horse, goat, rabbit and rat sera show that there are no significant changes in plasma protein binding in the above-mentioned species.