[Influence of protamine sulfate as neutralizer of heparin on a vancomycin assay in serum]

Levels of vancomycin (VCM), measured with cobas 6000 c501(c501), were low when blood-collecting tubes for heparinized blood (SQH) were used. It was determined that the phenomenon was due to the effects of protamine sulfate, a heparin neutralizer. VCM levels decreased by approximately 10% when the concentration of protamine sulfate was 0.01 mg/ml, and were undetectable when the concentration was 0.045 mg/ml. However, the effects of protamine sulfate, with the dose being up to approximately twice, were not seen in the presence of heparin. There were no such effects if specimens in SQH were maintained at a specified volume. The phenomenon was characteristic of the measurement of VCM levels using c501. Measurements of other agents such as valproic acid, which is measured in the same manner as VCM, using the same equipment did not lead to the identification of any effect. In addition, when VCM levels were measured with reagents of INTEGRA 800, no effect was seen. It is difficult to elucidate the mechanisms of action, as the manufacturer has not provided detailed information regarding reagents. Protamine sulfate is estimated to partially influence the antigen-antibody reaction involving anti-VCM antibodies in reagents of c501. Protamine sulfate is also used as an injection, and, hence, the influence of the agent on VCM levels measured with c501 cannot be ruled out even if other blood collecting tubes are used. Attachment to separating mediums presents problems when measuring blood concentrations of drugs, but there has been no report regarding a heparin neutralizer, as seen in this case. This is a new influential factor that requires attention.