Tacrolimus levels in adult patients with renal transplant

Tacrolimus, a macrolide immunosuppressant agent, is indicated for the prophylaxis of organ rejection in patients receiving allogenic liver or kidney transplantation. Successful therapy is complicated by both intra- and inter-patient variability in drug absorption, coupled with the drug's narrow therapeutic index. Moreover, clearance, is significantly affected by co-administration with food and with additional factors such as length of posttransplantation time. At the National Institute of Cardiology, Mexico, the measure of tacrolimus levels is carried out as a common analysis on patients who have been transplanted as a measure to make empiric doseage adjustments. The purpose of this study was to investigate whether tacrolimus levels exceed the desired therapeutic range in adult patients being initiated on a dosage regimen and to establish the use of pharmacokinetic concepts to avoid organ rejection and other complications related to tacrolimus over-exposure. The patients were followed from 1 week to 6 months after transplantation and a mean of 12 samples were collected (11.92 +/- 2.59 ng/mL) from each patient. Modeling was used to establish the correlation between the doses administered per kilogram of body weight, the tacrolimus level measured and the post-transplantation time. Of 155 tacrolimus measurements, only 48.4% were found within the therapeutic range (5-10 ng/mL); 7.1% below and 44.5% with elevated levels. Tacrolimus has proven its usefulness in solid organ transplants, but this study demonstrates that it is essential to carry out close monitoring through the application of pharmacokinetic concepts to optimize therapy.