Background The management of immunosuppression in kidney transplant (KT) is divided into: induction from 0 to 3 months, early maintenance (EM) from 3 to 6 months and late maintenance (LM) from 6 months. During the induction, more intense immunosuppression is required to prevent acute rejection of the graft.

Purpose To assess the mean concentration, the intra-patient variability (IPV) of tacrolimus plasmatic levels (FKplasm) and their evolution during the different periods of KT.

Material and methods Observational retrospective study included kidney transplanted patients since January 2015, with a minimum post-transplant follow-up of 2 years.

The clinical data was collected from the hospital’s medical records, including: kind of transplant, surgery date and FKplasm from the transplantation date to 2 full years of follow-up.

The variables of the study were calculated considering the different stages of KT: induction, EM and LM: 6–12 months (LM1), 1–2 years (LM2) and 2–3 years (LM3). The mean of FKplasm, the number of analytical determinations performed and the percentage of patients with concentrations lower than 5 ng/mL were calculated. The therapeutic range of FKplasm value was 5–20 ng/mL.

To describe the IPV of FKplasm, the coefficient of variation (CV) was calculated. The IPV was considered inadequate when the CV values were higher than 30%.

The statistical analysis was carried out using SPSS, and to compare population means the variance analysis and Fisher–Snedecor’s F distribution were used.

Results Two-hundred and twelve patients and 4180 measures of FKplasm were included. The values of the variables analysed were expressed in the temporal order of induction, EM, LM1, LM2 and LM3:

Mean FKplasm: 9.63 ng/ml (95% CI: 9.33 to 9.92), 8.57 ng/ml (95% CI: 8.26 to 8.88), 8.01 ng/ml (95% CI: 7.71 to 8.31) and 7.61 ng/ml (95% CI: 7.35 to 7.87). Mean number of plasmatic determinations: 13.71 (95% CI: 12.89 to 14.54), 4.72 (95% CI: 4.18 to 5.26), 5.24 (95% CI: 4.66 to 5.83) and 5.45 (95% CI: 4.87 to 6.04). Percentage of concentrations lower than 5 ng/ml: 13.51% (95% CI: 11.28 to 15.74), 9.28% (95% CI: 6.49 to 12.06), 13.12% (95% CI: 9.73 to 16.51) and 12.81% (95% CI: 9.35 to 16.27). Mean CV: 43.55% (95% CI: 41.29 to 45.81), 25.41% (95% CI: 23.09 to 27.74), 25.38% (95% CI: 22.99 to 27.77) and 24.43% (95% CI: 22.11 to 26.75). Percentage of patients with CV >30%: 80.25% (95% CI: 75.21 to 85.29), 31.75% (95% CI: 25.42 to 38.09), 29.86% (95% CI: 23.63 to 36.08) and 30.48% (95% CI: 23.82 to 37.14).

Conclusion FKplasm and IPV during induction are higher than in EM and LM. However, patients with CV >30% remain in the maintenance periods between 29.9% and 31.8%, and with values<5 ng/ml between 9.3% and 13.1% which would justify a greater need for pharmacokinetic monitoring and therapeutic control, in order to preserve a longer graft survival and to minimise the events of pharmacological adverse reactions.

References and/or acknowledgements Thanks to all authors for their involvement.

No conflict of interest.