Abstract: Aim To study the exchange reaction characteristics of anion exchange resin for diclofenac sodium. Methods The drug-resin complexes were prepared by a batch method with diclofenac sodium as the model drug and the strong anion exchange resin (201 × 7) as the carrier. The effects of different forms (OH^- and Cl^-) of the strong anion exchange resin, the particle size of the resin, and the reaction temperature on the exchange behavior were described. The exchange kinetic profiles were fitted. The related exchange reaction rate constants, exchange activation energy, and selectivity coefficients were determined. The exchange thermodynamic parameters, such as Δ_rG^θ_m, Δ_rH^θ_m andΔ_rS^θ_m, were evaluated. Results The anion exchange resin in the Cl^- and OH^- form had the same exchange capacity of diclofenac sodium. When the size of resin particle decreased or the temperature increased, the rate of exchange reaction increased. The exchange reaction between the drug and resin was accorded with first order kinetics. The exchange activation energy was about 60.68 kJ·mol^-1. The exchange thermodynamics parameters achieved at 303K, 313K and 323K were all satisfied with the following results: Δ_rG^θ_m<0, Δ_rH^θ_m>0 and Δ_rS^θ_m>0. Conclusion The exchange process of drug-resin complexes was mainly influenced by the size of the resin and the reaction temperature. The exchange reaction was an endothermic and spontaneous reaction as the temperature increased.

Key words: diclofenac sodium, diclofenac sodium, anion exchange resin, anion exchange resin, exchange kinetics, exchange kinetics, exchange thermodynamics, exchange thermodynamics