Characterization of the Effect of Drug-Drug Interaction on Protein Binding in Concurrent Administration of Sulfamethoxazol and Diclofenac Sodium Using Bovine Serum Albumin

This project was aimed to determine the effect of concurrent administration of sulfamethoxazole and diclofenac sodium.
Equilibrium dialysis method was adopted to study different protein binding aspects of sulfamethoxazole and diclofenac sodium.
Sulfamethoxazole showed two types of association constants; high affinity constant 29.0±0.20×106 M-1 with lower number of binding sites of 0.7±1 and low affinity constant 1.13±0.20×106 M-1 with higher number of binding sites of 3.45±1 at pH 7.4 and 40 °C temperature. Diclofenac sodium showed high affinity constant 33.66±0.20×106 M-1 with lower number of binding sites of 1.01±1 and low affinity constant 1.72±0.20×106 M-1 with higher number of binding sites of 6.40±1 at the same condition. Site specific probe displacement data implied that site-I, warfarin sodium site, was the high affinity site, while site-II, diazepam site, was the low affinity site for these drugs. During concurrent administration, sulfamethoxazole increased the free concentration of diclofenac sodium from 17.5±0.14% to 70.0±0.014% in absence and from 22.5±0.07% to 83.0±0.014% in presence of site-I specific probe. Diclofenac sodium also increased the free concentration of sulfamethoxazole from 2.8±0.07% to 52.0±0.14% and from 8.5±0.014% to 64.4±0.07% in absence and presence of site-I specific probe respectively.
The study revealed that the concurrent administration of sulfamethoxazole and diclofenac sodium may result drug concentration alteration in blood.