Validation and quality assurance program for monitoring tacrolimus (FK 506) concentrations in plasma and whole blood.

Tacrolimus (FK 506), an investigational immunosuppressant drug, is undergoing several trials for various transplantations where protocols call for monitoring plasma and/or whole blood 12-h trough concentrations. Initially, the FK 506 Central Laboratory (FCL) adapted an established enzyme immunoassay (EIA) for FK 506 in plasma and provided clinical monitoring services for hepatic transplantation trials. Within 1 year, 16 clinical sites participating in these trials began direct use of the immunoassay for plasma and whole blood. A five step validation sequence facilitated rapid training and implementation of proficient assay services. All laboratories utilized common reagents, standards, and procedures. Participation in a quality assurance program involved monthly analysis of the three proficiency unknowns supplied by the FCL and reciprocal analysis of five patient samples (cross-checks) by the FCL. The quality of the data produced was assessed by proficiency scores, bivariate regression analysis, and correlations that demonstrated the concordance of their assay results for FK 506 in plasma and whole blood.