Pitfalls in monitoring tacrolimus (FK 506)

• Published in: Therapeutic drug monitoring Vol. 19; no. 6; p. 628
• Main Authors: Braun, F, Schütz, E, Christians, U, Lorf, T, Schiffmann, J H, Armstrong, V W, Schröter, W, Sewing, K F, Oellerich, M, Ringe, B
• Format: Journal Article
• Language: English
• Published: United States 01.12.1997
• Subjects: Adolescent; Chromatography, High Pressure Liquid; Drug Monitoring - methods; Enzyme-Linked Immunosorbent Assay; Female; Humans; Immunosuppressive Agents - blood; Immunosuppressive Agents - metabolism; Immunosuppressive Agents - pharmacokinetics; Liver Transplantation; Mass Spectrometry; Tacrolimus - blood; Tacrolimus - metabolism; Tacrolimus - pharmacokinetics
• ISSN: 0163-4356
• DOI: 10.1097/00007691-199712000-00004

Tacrolimus (FK 506) is a new, potent immunosuppressive drug for primary and rescue therapy in liver and kidney transplantation. Therapeutic drug monitoring is essential for this drug because of its narrow therapeutic window. Blood levels are monitored routinely by enzyme linked immunoassay (ELISA) or by microparticle enzyme immunoassay (MEIA). In a 13-year-old recipient of a liver transplant who had poor hepatic function during the first postoperative week, the authors observed unusually high tacrolimus blood concentrations using either the ELISA (26.6 to 49.0 microg/l) or MEIA (58.5 to 64.5 microg/l). Parent drug levels measured in the same blood samples by high-performance liquid chromatography/mass spectrometry (HPLC/MS) were up to 10-fold lower (5.1 to 9.0 microg/l). The discrepancies between the immunoassay and HPLC/MS results could not be attributed to any of the known metabolites of tacrolimus.