While the existing literature extensively covers the topic of tacrolimus variability, it remains crucial to gather data that are tailored to the Tunisian population. Our primary goal was to assess the variability in tacrolimus bioavailability using the Cp(0)/weight dosage ratio in Tunisian kidney transplant patients. We also aimed to determine the correlations between blood trough level (Cp(0)) and the area under the concentration–time curve (AUC0–12h) in this cohort. This retrospective study included patients treated with oral tacrolimus for the prevention of organ rejection between 2009 and 2023. The correlation between parameters was analyzed through a Pearson coefficient and a regression model. We assessed the inter- and intraindividual variability by calculating the coefficient of variation for patients with at least 3 samples. Analysis of 2124 samples revealed a weak correlation (R = 0.121) between Cp(0) and weight dosage. We found that 79.3% of patients exhibited high variability in the Cp(0)/weight dosage ratio. A strong correlation (R = 0.797) was found between Cp(0) and the AUC0–12h. We also found that 47.6% of patients showed high variability in the AUC0–12h/ Cp(0) ratio. This study underscores the necessity for individualized therapeutic drug monitoring in Tunisian kidney transplant recipients due to the high variability in the Cp(0)/weight dosage ratio. The AUC0–12h/Cp(0) ratio is proposed as a more consistent parameter for therapeutic drug monitoring, offering potential improvements in tacrolimus therapy management.

Keywords: therapeutic drug monitoring, tacrolimus, bioavailability, blood trough level, the area under the concentration–time curve.