RESUMO
BACKGROUND: Mycophenolic acid is widely used to treat lupus nephritis (LN). However, it exhibits complex pharmacokinetics with large interindividual variability. This study aimed to develop a population pharmacokinetic (popPK) model and a 3-sample limited sampling strategy (LSS) to optimize therapeutic drug monitoring in Indian patients with LN. METHODS: Five blood samples from each LN patient treated with mycophenolic acid were collected at steady-state predose and 1, 2, 4, and 6 hours postdose. Demographic parameters were tested as covariates to explain interindividual variability. PopPK analysis was performed using Monolix and the stochastic approximation expectation-maximization algorithm. An LSS was derived from 500 simulated pharmacokinetic (PK) profiles using maximum a posteriori Bayesian estimation to estimate individual PK parameters and area under the curve (AUC). The LSS-calculated AUC was compared with the AUC calculated using the trapezoidal rule and all the simulated samples. RESULTS: A total of 51 patients were included in this study. Based on the 245 mycophenolic acid concentrations, a 1-compartmental model with double absorption using gamma distributions best fitted the data. None of the covariates improved the model significantly. The model was internally validated using diagnostic plots, prediction-corrected visual predictive checks, and bootstrapping. The best LSS included samples at 1, 2, and 4 hours postdose and exhibited good performances in an external dataset (root mean squared error, 21.9%; mean bias, -4.20%). CONCLUSIONS: The popPK model developed in this study adequately estimated the PK of mycophenolic acid in adult Indian patients with LN. This simple LSS can optimize TDM based on the AUC in routine practice.
RESUMO
Tacrolimus is a narrow therapeutic index drug. As a result, regulatory agencies worldwide recommend stringent bioequivalence evaluation criteria for approval of generics. Despite this, the professional transplantation societies have raised concerns over the safety and efficacy of generic substitutions. We conducted this pragmatic real-life bioequivalence study to assess the effect of generic substitutions of tacrolimus. This was an observational study including recipients of renal transplantation who were considered for generic medication substitution. Transplanted organs were from living-related donors and were performed at least 1 month before the study. Time of administration of the drug, time of dosing with respect to meals, and time of blood sample collection were controlled; however, the lot number of the generic drugs was not controlled. The participants were allowed to use their usual supplies irrespective of the lot number. Concentration (C0) was quantified by liquid chromatography with tandem mass spectrometry after the generic substitution from ABC brand to XYZ brand. The average C0 ± SD with generic ABC was 11.09 ± 4.26 ng/mL and generic ABC was 9.7 ± 4.12 ng/mL. Though there was no statistically significant difference observed between the concentrations, when the individual patient data was examined, 2 patients were found to have a very high concentration of tacrolimus and at least 7 patients fell below the therapeutic range. These derangements called for retitration with the new generic tacrolimus (40%). The results of our study suggest that generic-to-generic substitutions should be carried out very carefully in a closely observed setting in patients with renal transplants. The strength of our study is that it matched the real clinical practice setting as much as possible unlike a bioequivalence study. Therefore, we recommend repeating C0 at least 3 times over a period of 7 to 10 days with a generic substitution to prevent untoward consequences.