The binding of antibiotics to serum proteins.

ultrafiltration Visking dialysis tubing. Preliminary experiments indicated that there was no significant difference between the extent of binding in plasma obtained from heparinized blood and that in serum. The antibiotic present in the protein-free ultrafiltrate was measured by microbiological assay and this quantity represented the free, unbound, fraction of antibiotic in serum. The amount of antibiotic bound to protein was derived by subtracting the level of free antibiotic from the known total concentration in serum. Before comparative experiments were made to measure the extent to which different antibiotics were bound to the proteins of human serum, preliminary investigations were carried out into the effects of various experimental factors thought likely to influence the extent of binding. These included the effects of antibiotic concentra- tion, nature of protein, temperature, individual variation, rate of binding and nature of