Background Information on the pharmacokinetics of tacrolimus during pregnancy is limited to case reports despite the increasing number of pregnant women being prescribed tacrolimus for immunosuppression. Methods Blood, plasma and urine samples were collected over one steady-state dosing interval from women treated with oral tacrolimus during early to late pregnancy (n = 10) and postpartum (n = 5). Total and unbound tacrolimus as well as metabolite concentrations in blood and plasma were assayed by a validated LC/MS/MS method. A mixed effect linear model was used for comparison across gestational age and using postpartum as the reference group. Results The mean oral clearance (CL/F) based on whole blood tacrolimus concentration was 39% higher during mid- and late-pregnancy compared to postpartum (47.4 ± 12.6 vs. 34.2 ± 14.8 L/h, P < 0.03). Tacrolimus free fraction increased by 91% in plasma (fP) and by 100% in blood (fB) during pregnancy (P = 0.0007 and 0.002, respectively). Increased fP was inversely associated with serum albumin concentration (r = − 0.7, P = 0.003), which decreased by 27% during pregnancy. Pregnancy related changes in fP and fB contributed significantly to the observed gestational increase in tacrolimus whole blood CL/F (r2 = 0.36 and 0.47 respectively, P < 0.01). In addition, tacrolimus whole blood CL/F was inversely correlated with both hematocrit and red blood cell counts, suggesting that binding of tacrolimus to erythrocytes restricts its availability for metabolism. Treating physicians increased tacrolimus dosages in study participants during pregnancy by an average of 45% in order to maintain tacrolimus whole blood trough concentrations in the therapeutic range. This led to striking increases in unbound tacrolimus trough concentrations and unbound AUC, by 112% and 173%, respectively during pregnancy (P = 0.02 and 0.03, respectively). Conclusions Tacrolimus pharmacokinetics are altered during pregnancy. Dose adjustment to maintain whole blood tacrolimus concentration in the usual therapeutic range during pregnancy increases circulating free drug concentrations, which may impact clinical outcomes.
Summary Pregnancy following solid organ transplantation, although considered high risk for maternal, fetal and neonatal complications, has been quite successful. Tacrolimus pharmacokinetic changes during pregnancy make interpretation of whole blood trough concentrations particularly challenging. There are multiple factors that can increase the fraction of unbound tacrolimus, including but not limited to low albumin concentration and low RBC count. The clinical titration of dosage to maintain whole blood tacrolimus trough concentrations in the usual therapeutic range can lead to elevated unbound concentrations and possibly toxicity in pregnant women with anemia and hypoalbuminemia. Measurement of plasma or unbound tacrolimus concentrations for pregnant women might better reflect the active form of the drug, though these are technically-challenging and often unavailable in usual clinical practice. Tacrolimus crosses the placenta with in utero exposure being approximately 71% of maternal blood concentrations. The lower fetal blood concentrations are likely due to active efflux transport of tacrolimus from the fetus toward the mother by placental P-glycoprotein. To date, tacrolimus has not been linked to congenital malformations, but can cause reversible nephrotoxicity and hyperkalemia in the newborn. In contrast, very small amounts of tacrolimus are excreted in the breast milk and are unlikely to elicit adverse effects in the nursing infant.
Chimeric antigen receptor (CAR)‐T cell therapy has achieved considerable success in treating B‐cell hematologic malignancies. However, the challenges of extending CAR‐T therapy to other tumor types, particularly solid tumors, remain appreciable. There are substantial variabilities in CAR‐T cellular kinetics across CAR‐designs, CAR‐T products, dosing regimens, patient responses, disease types, tumor burdens, and lymphodepletion conditions. As a “living drug,” CAR‐T cellular kinetics typically exhibit four distinct phases: distribution, expansion, contraction, and persistence. The cellular kinetics of CAR‐T may correlate with patient responses, but which factors determine CAR‐T cellular kinetics remain poorly defined. Herein, we developed a cellular kinetic model to retrospectively characterize CAR‐T kinetics in 217 patients from 7 trials and compared CAR‐T kinetics across response status, patient populations, and tumor types. Based on our analysis results, CAR‐T cells exhibited a significantly higher cell proliferation rate and capacity but a lower contraction rate in patients who responded to treatment. CAR‐T cells proliferate to a higher degree in hematologic malignancies than in solid tumors. Within the assessed dose ranges (107‒109 cells), CAR‐T doses were weakly correlated with CAR‐T cellular kinetics and patient response status. In conclusion, the developed CAR‐T cellular kinetic model adequately characterized the multiphasic CAR‐T cellular kinetics and supported systematic evaluations of the potential influencing factors, which can have significant implications for the development of more effective CAR‐T therapies.
Simultaneous and accurate measurement of circulating vitamin D metabolites is critical to studies of the metabolic regulation of vitamin D and its impact on health and disease. To that end, we developed a specific LC-MS/MS method that permits the quantification of major circulating vitamin D3 metabolites in human plasma. Plasma samples were subjected to a protein precipitation, liquid-liquid extraction and Diels-Alder derivatization procedure prior to LC-MS/MS analysis. Importantly, in all human plasma samples tested, we identified a significant dihydroxyvitamin D3 peak that could potentially interfere with the determination of 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3] concentrations. This interfering metabolite has been identified as 4β,25-dihydroxyvitamin D3 [4β,25(OH)2D3] and was found at concentrations comparable to 1α,25(OH)2D3. Quantification of 1α,25(OH)2D3 in plasma required complete chromatographic separation of 1α,25(OH)2D3 from 4β,25(OH)2D3. An assay incorporating this feature was used to simultaneously determine the plasma concentrations of 25OHD3, 24R,25(OH)2D3, 1α,25(OH)2D3, and 4β,25(OH)2D3 in healthy individuals. The LC-MS/MS method developed and described here, could result in considerable improvement in the quantification of 1α,25(OH)2D3, as well as monitoring the newly identified circulating metabolite, 4β,25(OH)2D3.
Recent clinical trials indicate that the use of azithromycin is associated with the emergence of macrolide resistance. The objective of our study was to simultaneously characterize free target site concentrations and correlate them with the MIC 90 s of clinically relevant pathogens. Azithromycin (500 mg once daily [QD]) was administered orally to 6 healthy male volunteers for 3 days. The free concentrations in the interstitial space fluid (ISF) of muscle and subcutaneous fat tissue as well as the total concentrations in plasma and polymorphonuclear leukocytes (PMLs) were determined on days 1, 3, 5, and 10. All concentrations were modeled simultaneously in NONMEM 7.2 using a tissue distribution model that accounts for nonlinear protein binding and ionization state at physiological pH. The model performance and parameter estimates were evaluated via goodness-of-fit plots and nonparametric bootstrap analysis. The model we developed described the concentrations at all sampling sites reasonably well and showed that the overall pharmacokinetics of azithromycin is driven by the release of the drug from acidic cell/tissue compartments. The model-predicted unionized azithromycin (AZM) concentrations in the cytosol of PMLs (6.0 ؎ 1.2 ng/ml) were comparable to the measured ISF concentrations in the muscle (8.7 ؎ 2.9 ng/ml) and subcutis (4.1 ؎ 2.4 ng/ml) on day 10, whereas the total PML concentrations were >1,000-fold higher (14,217 ؎ 2,810 ng/ml). The total plasma and free ISF concentrations were insufficient to exceed the MIC 90 s of the skin pathogens at all times. Our results indicate that the slow release of azithromycin from low pH tissue/cell compartments is responsible for the long terminal half-life of the drug and thus the extended period of time during which free concentrations reside at subinhibitory concentrations.
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.