The pharmacokinetics and immunosuppressive response of tacrolimus in paediatric renal transplant recipients

The aims of our trial were to study the pharmacokinetics of tacrolimus in paediatric kidney transplant recipients. The study comprised 25 patients (median age 13 years, range 2–20 years) followed for 12 months; five pharmacokinetics profiles (within the first and second week and after 1 month, 6 months and 12 months) were obtained. Patients were divided into two groups: six children <6 years old and 19 older children. Tacrolimus was given at an initial dose of 0.15 mg/kg twice a day. Blood samples were drawn before and 1 h, 2 h, 3 h, 4 h, 6 h, 9 h and 12  h after drug administration. Patient and kidney survival rates were 100% at 1 year. At 6 months and 12 months creatinine clearance was 68.5±16.3 ml/min per 1.73 m² and 64.0±15.2 ml/min per 1.73 m² body surface area, respectively. Tacrolimus trough levels were 7.8±1.9 ng/ml and 7.3±2.5 ng/ml. The area under the concentration–time curve for 0 h to 12 h (AUC_0–12) normalised to a dose of 0.15 mg/kg, increased with time from the kidney transplantation and stabilised after the 6th month post-transplantation. During the first month after transplantation the normalised tacrolimus concentration–time profiles were significantly greater in the older children (P<0.05); the actual doses were significantly greater in the younger children (P<0.05). In conclusion, initial doses of 0.15 mg/kg twice a day orally are safe and guarantee a satisfactory degree of immunosuppression, with our therapeutic regimen. Children <6 years old need to start with a 50% higher tacrolimus dose to achieve the same pharmacokinetic and immunosuppressive results.