Complexes of penicillins and human serum albumin studied by static light scattering

The complex formed by the interaction of the structurally similar surface active penicillin drugs cloxacillin and dicloxacillin, and human serum albumin (HSA) in water at 25 °C has been investigated using static light scattering. The colloidal dispersion has been considered as a binary system in which water and drug molecules (at concentrations below their critical aggregation concentration) are regarded as the solvent for the HSA–drug complex. A maximum in the size of the HSA–cloxacillin complex was found corresponding to the binding of approximately 2100 penicillin molecules per HSA molecule. In contrast, the size of the HSA–dicloxacillin complex increased gradually with dicloxacillin concentration over the same concentration range.