The purpose of the study is to identify factors that may influence tacrolimus (TAC) pharmacokinetics, and the impact of gene polymorphism (ABCB1, CYP3A4, CYP3A5, POR) on pharmacokinetics of TAC in Taiwanese.

TAC is one of the most important immunosuppressive agents for organ transplantation. In some patients the dose and concentration of TAC are difficult to adjust because of its narrow therapeutic index and variable pharmacokinetics.

Many factors affect the pharmacokinetics of TAC. Literature suggests that ABCB1, CYP3A4, CYP3A5, POR gene polymorphisms may affect the pharmacokinetics of TAC. In addition, the distribution of TAC is affected by hematocrit and albumin concentrations. The pharmacokinetics of TAC may also be affected by total protein, total bilirubin, creatinine, AST, ALT, gender, age, drug interactions, and so on.

This study intends to analyze the influence of various factors, including drugs, on the pharmacokinetics of TAC.

Inclusion Criteria:

• kidney transplants or liver transplants
• 20 - 65 years old
• receiving tacrolimus as immunosuppressive drugs

Exclusion Criteria:

• Human immunodeficiency virus-positive status
• Retransplantation or multiorgan transplantation
• non-Asian

Renal or liver transplant recipients who underwent transplantation at National Taiwan University Hospital, and were treated with tacrolimus.