Abstract

Dialysis and microcalorimetric methods were used to calculate the binding parameters of some cephalosporins to human serum albumin (HSA) and to study the nature of the interactions involved in the binding process. Dialysis results agree with microcalorimetric data for cephapirin, cephradin, cefamandole, and cefazolin. Binding forces seem to be principally electrostatic. The parts of the drug molecule involved in HSA drug binding have been identified by high-resolution NMR. The major binding site for cephalosporins with high HSA affinity is thought to be the electron-rich heterocyle fixed on the methylene at position 3. Four classes of cephalosporin have been defined: (a) very weak affinity for HSA (cephalexin, cephradin); (b) moderate affinity (cephapirin, cefoxitin, and cefotaxime) in which binding to the protein involves the heterocycle substituent of the acetamide chain carbon atom; (c) strongly binding (cefamandole), in which binding to HSA is by means of the methyltetrazole ring; and, finally (d), cefazolin, with two classes of binding sites for protein, showing strong and moderate affinity.