A toxicity reduced conditioning regimen containing Treosulfan (Treo), fludarabine (Flu), thiotepa for high risk Thal Major (TM) has been used since 2009 at our centre that has significantly improved transplant outcomes of these patients compared to the historical cohort of patients receiving busulfan/ cyclophosphamide based myeloablative regimen (Mathews et al, 2013). Limited knowledge is available on the pharmacokinetics (PK), pharmacogenetics (PG) and pharmacodynamics of fludarabine and treosulfan, especially in non-malignant hematological disorders like TM. We describe here the PK of Flu and Treo in patients with TM undergoing HSCT, the factors influencing the inter-individual variability in PK and the role of these factors on HSCT outcome. Seventy one patients diagnosed with TM undergoing HSCT with Flu/Treo based conditioning regimen between January 2012 and January 2015 were included (Table: Patient demographics). Selected functional polymorphisms in the NT5E, DCK, hENT1 and GST genes that are involved in fludarabine or treosulfan metabolism were screened. All patients received Flu 40mg/m2/day x 4 days as an 1hr infusion on days 1 and 4 and Treo as 14g/m2/day x 3 days at the rate 5g/hr. Plasma was separated from the peripheral blood collected at predetermined time points after the infusion of Flu and Treo PK analysis. Plasma Flu was analyzed using a LC-MS/MS method and the concentration was expressed as mMole/ml while Treo was analyzed using a HPLC-RI method and concentration was expressed as mg/L. Flu and Treo PK was estimated using nonlinear mixed effects modeling via Monolix 4.3.3. The covariates tested for both PK were: age, sex, body weight, BSA, ferritin, and polymorphisms in NT5E, hENT1, dCK and GST genes. The PK parameters AUC, CL, V and k were estimated on day 1 for Treo and on day 1 and day 4 for Flu (Table). The influence of Flu and Treo PK and PG on graft rejection, early transplant related mortality (TRM) & chimerism status was estimated using logistic regression analysis. Wide inter-individual variation in Flu and Treo PK was noted (7 and 9 fold Vs 5 and 8 fold respectively for Day 1 & 4 Flu AUC & Cl; 33 & 31 fold variation in Treo AUC and Cl) (Table). Flu CL was significantly higher on day 4 compared to day1 (Figure A). The variation in Flu PK was explained by genetic variants in NT5E and dCK. Patients having variant genotype for the SNPs in NT5E (rs2295890) and dCK (rs11544786) showed significantly lower plasma Flu clearance compared to those with wild type genotype (p=0.006 & p=0.05 respectively) (Figure B). This is consistent with our previous report in patients with aplastic anemia undergoing HSCT (Mohanan et al. 2014; Blood: 124 (21)). None of the genetic variants in the GST genes explained the variation in Treo PK. Day21 mortality was seen in 6/71 patients (8.5%) and graft rejection in 3/66 evaluable patients (4.5%). Analysis of the influence of PK and PG variables on transplant outcome showed significantly high first dose Flu AUC to be associated with D21 mortality upon Univariate analysis (median 42.5, range 32.1-63.7 compared to 31.8, range 15.2-111 mMole*h/mL, in those with and without TRM respectively; p=0.043); none of these parameters were significantly associated with graft rejection or mixed chimerism. There was no association between Treo PK parameters and graft rejection or TRM. The influence of Flu and Treo PK on regimen related toxicity is yet to be evaluated. The lack of the influence of PK on transplant outcome could be due to lower incidence of rejection and TRM in this cohort. Further analysis in a larger cohort of patients will be done once we enroll more patients for PK analysis. Our results demonstrate that Flu PK is influenced by genetic variants in NT5E and dCK, the enzymes involved in Flu biotransformation. The relationship between high-plasma Flu exposure and TRM and given the fact that multiple factors influence TRM, we can extrapolate that the plasma Flu AUC may be a surrogate marker of overall preparative regimen intensity as reported previously (Long-Boyle et al, Bone Marrow Transplant, 2011). The lack of association of genetic variants in GST genes in explaining the inter-patient variability in treosulfan exposure suggests the involvement of other drug metabolizing genes on treosulfan PK. We are currently evaluating the role of genetic variants in a large panel of drug metabolizing genes on explaining this inter-individual variability in Treo PK. Disclosures No relevant conflicts of interest to declare.
Pharmacokinetic (PK)-targeted dose adjustment of oral Bu has been shown to minimize the toxicity and treatment related mortality following hematopoietic stem cell transplantation (HSCT). Intravenous busulfan (IV Bu) based myeloablative conditioning regimen has significantly reduced the inter-patient variability, ease of administration and reduced toxicities compared to oral Bu. However due to challenges in availability and cost of original formulation (Busulfex, Otsuka Pharmaceuticals) has resulted in the increased use of generic versions of the drug worldwide. Also, in many parts of the world, regulatory approval for generic drugs is obtained only with bioequivalence studies without a clinical trial or PK data. From June 2010 to December 2014, our center has used generic IV busulfan Bucelon™ (Celon Labs, Hyderabad, India) with routine therapeutic drug monitoring and dose adjustment. Since January 2015, Buslera™ (Biem Pharmaceuticals, Ankara, Turkey), a newer generic IV busulfan formulation, is being used in patients undergoing HSCT in our centre due to non-availability of Bucelon™. We prospectively analyzed the PK of IV Buslera™ and compared the systemic exposure and targeted dose adjustment pattern with our experience with Bucelon™. Eighteen patients underwent HSCT with IV Buslera™ based conditioning regimen between January and July 2015. Twelve patients received once daily Bu dose (Q24H; 40mg/m2/day x 4 days) and 6 received every 6 hour dosing (Q6H; 0.8mg/kg/dose x 4 days). In the historical cohort, 135 patients (30 Q6H and 105 Q24H) received Bucelon™ (Mohanan et al, Blood 2013; 122:3280). Demographics of the patients in both groups are depicted in the Table. Blood samples were collected at predetermined time points on day 1 and 3 & busulfan plasma concentrations analyzed using previously published method (Desire et al, 2013). Further doses of busulfan were adjusted to achieve target busulfan AUC (4500-5500 mmoles*min for Q24H and 900-1350 mmoles*min for Q6H). In patients receiving Q24H IV Buslera, the median busulfan AUC on day 1 was 6516 mMoles*min (3908-14064 mMoles*min). The Buslera dose was reduced in 8 patients (median dose reduction 13%; range: 7-18%), increased in one (9%) and 3 patients did not require any dose adjustment. In patients receiving Q6H IV Bu, the AUC on day 1 was 784 mMoles*min (446-960 mMoles*min). Five out of 6 patients required a moderate increase in dose (median dose increase 5%; range: 5-8%) and one did not require any dose adjustment. This data is strikingly different when compared to the historical cohort of patients receiving IV Bucelon™ where 60% patients receiving Q24h dose required dose increase, while with Buslera™ only 9% of patients needed dose increase (p<0.001) to achieve target AUC of busulfan. In general, we noticed that the median clearance of Buslera™ was significantly lower compared to Bucelon™ (Figure) Our study strongly suggests the need for routine therapeutic drug monitoring and targeted dose adjustment of busulfan, especially when different generic busulfan formulations are used. TDM with generic busulfan is even more relevant in markets where approval of generics is done only based on bioequivalence studies with PK data in an appropriate clinical setting and without a clinical trial. Disclosures No relevant conflicts of interest to declare.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.