Binding of Betamethasone, Prednisolone and Theophylline to Bovine Serum Albumin: Plausible Explanations for Mode of Binding and Drug-drug Interactions

The binding of betamethasone sodium phosphate and prednisolone, two steroidal antiinflammatory drugs and theophylline sodium glycinate, a bronchodilator, to bovine serum albumin (BSA), has been studied by equilibrium dialysis (ED) method at different temperature and pH values for characterizing the binding of these drugs to BSA. Binding was exothermic, entropically driven and spontaneous, as indicated by the thermodynamic analysis. The major part of the binding energy at site II results from electrostatic and hydrophobic interactions. The free fraction of either betamethasone or prednisolone in the presence of theophylline sodium glycinate and vice versa was monitored in the presence and absence of site specific probes. The free fraction of betamethasone sodium phosphate by theophylline sodium glycinate and vice versa was increased during concurrent administration causing reduced binding of these drugs to BSA. This increment of free fraction was more prominent in the presence of site I specific probe, which suggested that in the absence of site I specific probe, betamethasone after being displaced by theophylline from its high affinity site rebound to its low affinity site. Similar type of result was observed in case of prednisolonetheophylline interaction.