Evaluation of 2 immunoassays for monitoring low blood levels of tacrolimus.

The objective of this study was to evaluate the analytical performance of 2 new tacrolimus immunoassays (Dade Dimension Xpand and Abbott ARCHITECT) for therapeutic drug monitoring as possible replacements for the current method in our laboratory, the Abbott IMx tacrolimus assay. Attending physicians at our institute desire to minimize calcineurin inhibitor therapy in kidney allograft recipients to prolong graft survival and improve the quality of life of their patients. Proposed future target trough levels of tacrolimus in whole blood are in the range of 2-4 ng/mL, which requires an assay with a limit of quantification (LOQ) below this range, ideally around 1 ng/mL (European Consensus Recommendation from the Committee on Tacrolimus Optimization). Method comparison analysis of the Dade and ARCHITECT assays showed good correlation to the IMx assay, with correlation coefficients of 0.94 and 0.96, respectively. Both assays reported tacrolimus concentrations lower on average than IMx as demonstrated by slopes of 0.83 (Dade) and 0.93 (ARCHITECT). LOQ for both Dade instruments tested was >4 ng/mL, whereas the LOQ for the ARCHITECT i2000 and i1000 instruments was 0.8 and 0.5 ng/mL, respectively (upper 95% confidence limit). Values reported from both Dade instruments were observed to shift over time, whereas the values on the IMx and ARCHITECT instruments were stable. The Abbott ARCHITECT Tacrolimus assay is a sensitive and precise assay that meets the new LOQ recommendation, 1 ng/mL, for monitoring tacrolimus in whole blood.

Sublingual tacrolimus: a pharmacokinetic evaluation pilot study.

STUDY OBJECTIVE: To evaluate and compare the pharmacokinetic parameters of sublingual and oral tacrolimus in the presence and absence of a drug that interacts with tacrolimus at the intestinal level. DESIGN: Prospective, randomized, open-label, parallel-group pilot study. SETTING: Large, urban, academic medical center. PATIENTS: Six adults with end-stage renal disease who were awaiting kidney transplantation; five completed the study. INTERVENTION: Patients were randomized in a 1:1 ratio to receive tacrolimus plus a clotrimazole troche (a drug that interacts with tacrolimus at the intestinal level) or tacrolimus plus nystatin suspension. For the tacrolimus route of administration, patients first received sublingual tacrolimus for five doses; after a 2-day washout period, they received oral tacrolimus for five doses. MEASUREMENTS AND MAIN RESULTS: Demographic characteristics, concomitant medications, tacrolimus dosing information, and steady-state venous whole blood specimen values after tacrolimus administration were collected. Noncompartmental pharmacokinetics were calculated from the tacrolimus blood concentrations in samples collected at multiple time points after drug administration. The area under the concentration-time curve from 0-6 hours for sublingual and oral tacrolimus ranged from 27.2-66 and 32.4-76 mg·hour/L, respectively, in the tacrolimus plus clotrimazole group and from 9.3-63 and 4.9-23.2 mg·hour/L, respectively, in the tacrolimus plus nystatin group. The average maximum concentration was higher during sublingual administration than during oral administration: 16.7 versus 12.9 ng/ml in the tacrolimus plus clotrimazole group and 9.5 versus 6 ng/ml in the tacrolimus plus nystatin group. CONCLUSION: An oral-to-sublingual tacrolimus dose conversion should be evaluated on an individual basis. A 1:1 dose conversion may be appropriate in the presence of clotrimazole, whereas a 2:1 oral-to-sublingual conversion may be appropriate when there are no concomitantly interacting drugs. These findings should be investigated further in pharmacokinetic studies conducted in solid organ transplant recipients.