Pharmacokinetics, Pharmacodynamics, and Pharmacogenomics of Immunosuppressants in Allogeneic Hematopoietic Cell Transplantation: Part II

Part I of this article included a pertinent review of allogeneic hematopoietic cell transplantation (alloHCT), the role of postgraft immunosuppression in alloHCT, and the pharmacokinetics, pharmacodynamics, and pharmacogenomics of the calcineurin inhibitors and methotrexate. In this article (Part II), we review the pharmacokinetics, pharmacodynamics, and pharmacogenomics of mycophenolic acid (MPA), sirolimus, and the antithymocyte globulins (ATG). We then discuss target concentration intervention (TCI) of these postgraft immunosuppressants in alloHCT patients, with a focus on current evidence for TCI and on how TCI may improve clinical management in these patients. Currently, TCI using trough concentrations is conducted for sirolimus in alloHCT patients. Several studies demonstrate that MPA plasma exposure is associated with clinical outcomes, with an increasing number of alloHCT patients needing TCI of MPA. Compared with MPA, there are fewer pharmacokinetic/dynamic studies of rabbit ATG and horse ATG in alloHCT patients. Future pharmacokinetic/dynamic research of postgraft immunosuppressants should include '-omics'-based tools: pharmacogenomics may be used to gain an improved understanding of the covariates influencing pharmacokinetics as well as proteomics and metabolomics as novel methods to elucidate pharmacodynamic responses

A Limited Sampling Schedule to Estimate Mycophenolic Acid Area Under the Concentration-Time Curve in Hematopoietic Cell Transplantation Recipients

Mycophenolate mofetil (MMF) is a key component of post-grafting immunosuppression in hematopoietic cell transplant (HCT) recipients. The plasma area under the curve (AUC) of its active metabolite, mycophenolic acid (MPA), is associated with MMF efficacy and toxicity. This study developed a population pharmacokinetic model of MPA in HCT recipients and created limited sampling schedules (LSS) to enable individualized pharmacotherapy. A retrospective evaluation of MPA concentration-time data following a 2 hr MMF intravenous (IV) infusion was conducted in 77 HCT recipients. The final model consisted of one and two compartments for MMF and MPA pharmacokinetics, respectively. The mean estimated values (coefficient of variation, %) for total systemic clearance, distributional clearance, and central and peripheral compartment volumes of MPA were 36.9 L/h (34.5%), 15.3 L/h (80.4%), 11.9 L (71.7%), and 182 L (127%), respectively. No covariates significantly explained variability among individuals. Optimal LSS were derived using a simulation approach based on the scaled mean squared error. A five-sample schedule of 2, 2.5, 3, 5, and 6 hr from the start of the infusion precisely estimated MPA AUC(0–12 hr) for Q12 hr IV MMF. A comparable schedule (2, 2.5, 3, 4 and 6 hr) similarly estimated MPA AUC(0–8hr) for Q8 hr dosing

High prevalence of potential drug interactions affecting mycophenolic acid pharmacokinetics in nonmyeloablative hematopoietic stem cell transplant recipients

Objective: Mycophenolic acid (MPA) exposure is associated with clinical outcomes in hematopoietic cell transplant (HCT) recipients. Various drug interaction studies, predominantly in healthy volunteers or solid organ transplant recipients, have identified medications which impact MPA pharmacokinetics. Recipients of nonmyeloablative HCT, however, have an increased burden of comorbidities, potentially increasing the number of concomitant medications and potential drug interactions (PDI) affecting MPA exposure. Thus, we sought to be the first to characterize these PDI in nonmyeloablative HCT recipients. Materials and methods: We compiled PDI affecting MPA pharmacokinetics and characterized the prevalence of PDI in nonmyeloablative HCT recipients. A comprehensive literature evaluation of four databases and PubMed was conducted to identify medications with PDI affecting MPA pharmacokinetics. Subsequently, a retrospective medication review was conducted to characterize the cumulative PDI burden, defined as the number of PDI for an individual patient over the first 21 days after allogeneic graft infusion, in 84 nonmyeloablative HCT recipients. Results: Of the 187 concomitant medications, 11 (5.9%) had a PDI affecting MPA pharmacokinetics. 87% of 84 patients had one PDI, with a median cumulative PDI burden of 2 (range 0 – 4). The most common PDI, in descending order, were cyclosporine, omeprazole and pantoprazole. Conclusion: Only a minority of medications (5.9%) have a PDI affecting MPA pharmacokinetics. However, the majority of nonmyeloablative HCT recipients had a PDI, with cyclosporine and the proton pump inhibitors being the most common. A better understanding of PDI and their management should lead to safer medication regimens for nonmyeloablative HCT recipients

Supplementary Figures from Busulfan in Infant to Adult Hematopoietic Cell Transplant Recipients: A Population Pharmacokinetic Model for Initial and Bayesian Dose Personalization

PDF file 181K, Figures of 1) the association of dosing weight to actual and predicted total body weights; and 2) prediction corrected visual predictive checks</p

Supplementary Table 1 from Busulfan in Infant to Adult Hematopoietic Cell Transplant Recipients: A Population Pharmacokinetic Model for Initial and Bayesian Dose Personalization

PDF file 62K, Prior population pharmacokinetic models and initial dosing for children receiving IV busulfan</p

Supplementary Table 3 from Busulfan in Infant to Adult Hematopoietic Cell Transplant Recipients: A Population Pharmacokinetic Model for Initial and Bayesian Dose Personalization

PDF file 34K, Acknowledgement of the institutions who used the FHCRC (1999-2001) or the SCCA Busulfan Pharmacokinetics Laboratory (2002-2011)</p

Supplementary Tables 4 through 6 from Busulfan in Infant to Adult Hematopoietic Cell Transplant Recipients: A Population Pharmacokinetic Model for Initial and Bayesian Dose Personalization

PDF file 45K, Empirical estimates of allometric exponents; correlation of between subject and between occasion variabilities of pharmacokinetic parameters; and evaluation of alternative models created from pediatric datasets</p

Supplementary Materials and Methods from Busulfan in Infant to Adult Hematopoietic Cell Transplant Recipients: A Population Pharmacokinetic Model for Initial and Bayesian Dose Personalization

PDF file 34K, Additional description of data incorporation and quality assurance procedures</p

Nonrelapse Mortality and Mycophenolic Acid Exposure in Nonmyeloablative Hematopoietic Cell Transplantation

AbstractWe evaluated the pharmacodynamic relationships between mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), and outcomes in 308 patients after nonmyeloablative hematopoietic cell transplantation. Patients were conditioned with total body irradiation ± fludarabine, received grafts from HLA-matched related (n = 132) or unrelated (n = 176) donors, and received postgrafting immunosuppression with MMF and a calcineurin inhibitor. Total and unbound MPA pharmacokinetics were determined to day 25; maximum a posteriori Bayesian estimators were used to estimate total MPA concentration at steady state (Css). Rejection occurred in 9 patients, 8 of whom had a total MPA Css less than 3 μg/mL. In patients receiving a related donor graft, MPA Css was not associated with clinical outcomes. In patients receiving an unrelated donor graft, low total MPA Css was associated with increased grades III to IV acute graft-versus-host disease and increased nonrelapse mortality but not with day 28 T cell chimerism, disease relapse, cytomegalovirus reactivation, or overall survival. We conclude that higher initial oral MMF doses and subsequent targeting of total MPA Css to greater than 2.96 μg/mL could lower grades III to IV acute graft-versus-host disease and nonrelapse mortality in patients receiving an unrelated donor graft