The potential impact of hematocrit correction on evaluation of tacrolimus target exposure in pediatric kidney transplant patients

• Published in: Pediatric nephrology (Berlin, West) West), 2019-03, Vol.34 (3), p.507-515
• Main Authors: Schijvens, Anne M., van Hesteren, Fransje H. S., Cornelissen, Elisabeth A. M., Bootsma-Robroeks, Charlotte M. H. H. T., Brüggemann, Roger J. M., Burger, David M., de Wildt, Saskia N., Schreuder, Michiel F., ter Heine, Rob
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Age Factors; Area Under Curve; Blood levels; Calcineurin Inhibitors - pharmacokinetics; Calcineurin Inhibitors - therapeutic use; Child; Child, Preschool; Complications and side effects; Dosage and administration; Drug Monitoring - methods; Erythrocytes; Female; Graft Rejection - immunology; Graft Rejection - prevention & control; Hematocrit; Hematocrit - standards; Humans; Immunosuppression; Infant; Kidney transplantation; Kidney Transplantation - adverse effects; Kidney transplants; Male; Medicine; Medicine & Public Health; Nephrology; Original; Original Article; Patient outcomes; Pediatrics; Physiological aspects; Reference Values; Retrospective Studies; Tacrolimus; Tacrolimus - pharmacokinetics; Tacrolimus - therapeutic use; Therapeutic drug monitoring; Transplants & implants; Urology; What’s New in Renal Transplantation
• ISSN: 0931-041X; 1432-198X
• DOI: 10.1007/s00467-018-4117-x

Background Tacrolimus is an important immunosuppressive agent with high intra- and inter-individual pharmacokinetic variability and a narrow therapeutic index. As tacrolimus extensively accumulates in erythrocytes, hematocrit is a key factor in the interpretation of tacrolimus whole blood concentrations. However, as hematocrit values in pediatric kidney transplant patients are highly variable after kidney transplantation, translating whole blood concentration targets without taking hematocrit into consideration is theoretically incorrect. The aim of this study is to evaluate the potential impact of hematocrit correction on tacrolimus target exposure in pediatric kidney transplant patients. Methods Data were obtained from 36 pediatric kidney transplant patients. Two hundred fifty-five tacrolimus whole blood samples were available, together responsible for 36 area under the concentration-time curves (AUCs) and trough concentrations. First, hematocrit corrected concentrations were derived using a formula describing the relationship between whole blood concentrations, hematocrit, and plasma concentrations. Subsequently, target exposure was evaluated using the converted plasma target concentrations. Ultimately, differences in interpretation of target exposure were identified and evaluated. Results In total, 92% of our patients had lower hematocrit (median 0.29) than the reference value of adult kidney transplant patients. A different evaluation of target exposure for either trough level, AUC, or both was defined in 42% of our patients, when applying hematocrit corrected concentrations. Conclusion A critical role for hematocrit in therapeutic drug monitoring of tacrolimus in pediatric kidney transplant patients is suggested in this study. Therefore, we believe that hematocrit correction could be a step towards improvement of tacrolimus dose individualization.