Pharmacokinetics of tacrolimus during pregnancy

Physiologically-based pharmacokinetic modeling to predict the exposure and provide dosage regimens of tacrolimus in pregnant women with infection disease

Tacrolimus is extensively used for the prevention of graft rejection following solid organ transplantation in pregnant women. However, knowledge gaps in the dosage of tacrolimus for pregnant patients with different CYP3A5 genotypes and infection conditions have been identified. This study aimed to develop a pregnant physiologically based pharmacokinetic (PBPK) model to characterize the maternal and fetal pharmacokinetics of tacrolimus during pregnancy and explore and provide dosage adjustments. We developed PBPK models for nonpregnant patients and validated them via data from previous clinical studies using PK-Sim and Mobi software. To extrapolate to pregnancy, we considered anatomical, physiological, and metabolic alterations and simulated tacrolimus by adding six groups of IL-6 concentrations (0, 5, 25, 50, 500, and 5000 pg/mL). Models were verified by assessing goodness-of-fit plots and ratios of predicted-to-observed pharmacokinetic parameters. The developed PBPK models adequately describe the available clinical data; the fold errors of the predicted and observed values of the area under the curve and peak plasma concentration were between 0.59 and 1.64, and the average folding error and the absolute average folding error values for all concentration-time data points were 1.15 and 1.36, respectively. The simulation results indicated that the area under the steady-state concentration‒time curve and trough concentrations decreased from the first to the third trimester of pregnancy. The trough concentrations were not within the therapeutic range (4-11 ng/mL) in pregnant patients with the CYP3A5 genotype for most of the infection conditions and exceeded its effective concentration in all the CYP3A5 nonexpressers. Based on the model-derived dosing regimen, the tacrolimus trough concentration in pregnant patients with different CYP3A5 genotypes could fall into the therapeutic window, which provided a clinical practice reference for dosage adjustments during pregnancy.

Myasthenia gravis complicated by pure red cell aplasia with clonal large granular lymphocytosis in the absence of thymoma: a rare case report and literature review

In 2013, a young woman during her early pregnancy was repeatedly hospitalized due to respiratory and swallowing difficulties. The pregnancy was terminated due to recurrent severe lung infections. She was later diagnosed with myasthenia gravis (MG) based on positive acetylcholine receptor antibodies. Her muscle weakness was subsequently well-controlled with pyridostigmine bromide, azathioprine, and prednisone. Notably, in the seventh year after her MG diagnosis (2021), the patient developed severe anemia (hemoglobin: 44 g/L). Bone marrow analysis revealed a rare combination of pure red cell aplasia (PRCA) with clonal expansion of large granular cells. Further examinations excluded thymoma. Considering the possibility of drug-induced PRCA, azathioprine was replaced with tacrolimus. Remarkably, the anemia resolved within 1 month, and her MG remained well-controlled. It is well-established that abnormal thymic hyperplasia within thymomas can alter the distribution and function of peripheral T lymphocytes, leading to the development of autoimmune diseases such as MG and PRCA. In this unique case without thymoma, we discussed the mechanisms and associations of PRCA with MG, medication, and clonal large granular T cells. This unique case highlights the unprecedented association of MG and PRCA without thymoma, underscoring the complexity of the disease spectrum. The patient's subsequent successful delivery in June 2023 adds another dimension to the multifaceted clinical course, warranting attention and exploration into potential connections between these conditions.

Alternate Sampling Matrices for Therapeutic Drug Monitoring of Immunosuppressants

BACKGROUND

Immunosuppressant (IS) therapeutic drug monitoring (TDM) relies on measuring mostly pharmacologically inactive erythrocyte-bound and/or plasma protein-bound drug levels. Variations in hematocrit and plasma protein levels complicate interpretation of blood calcineurin inhibitor (CNI) and inhibitors of the molecular target of rapamycin (mTORi) concentrations. Variable binding of mycophenolic acid (MPA) to albumin similarly complicates its TDM in plasma. A different matrix may improve IS concentration-response relationships and better reflect exposures at sites of action.

METHODS

This review explores the evidence for IS TDM using peripheral blood mononuclear cell (PBMC), graft tissue, and total or unbound plasma concentrations.

RESULTS

Tandem mass spectrometry provides the sensitivity for assessing these matrices. But several challenges must be addressed, including minimizing hemolysis during blood collection, preventing IS efflux during PBMC preparation, and determining the need for further purification of the PBMC fraction. Assessing and reducing nonspecific binding during separation of unbound IS are also necessary, especially for lipophilic CNIs/mTORi. Although TDM using PBMC or unbound plasma concentrations may not be feasible due to increased costs, plasma CNI/mTORi levels may be more easily integrated into routine TDM. However, no validated TDM targets currently exist, and published models to adjust blood CNI/mTORi concentrations for hematocrit or to predict PBMC, and total and unbound plasma IS concentrations have yet to be validated in terms of measured concentrations or prediction of clinical outcomes.

CONCLUSIONS

Even if CNI/mTORi measurements in novel matrices do not become routine, they may help refine pharmacokinetic-pharmacodynamic relationships and improve mathematical models for TDM using whole blood. Notably, there is evidence to support measuring unbound MPA in patients with severe renal dysfunction, hypoalbuminemia, and hyperbilirubinemia, with some proposed TDM targets.

Immunosuppressant drug tacrolimus inhibits HUVEC angiogenesis and production of placental growth factor

BACKGROUND

Tacrolimus is a cornerstone of immunosuppression in solid organ transplants, but its use is linked with the development of endothelial dysfunction. Pregnant solid organ transplant recipients are four to six times more likely to develop preeclampsia, which is also associated with endothelial dysfunction. Therefore, this in vitro study investigated the acute effects of tacrolimus on the expression of common angiogenic factors related to preeclampsia, and effects on angiogeneis in primary human tissues.

METHODS

Primary human umbilical vein endothelial cells (HUVECs) were exposed to tacrolimus (0, 5, 20, 50 ng/mL) for 24h alone, or in combination with tumour necrosis factor (TNF, 10 ng/mL) and high dose glucose (25 mM). Cell culture concentrations of sFlt-1, PlGF and activin A were measured. In addition, the effect of tacrolimus on markers of endothelial dysfunction and permeability were assessed, as were the effect of tacrolimus on tube formation. Angiogenic factors and mRNA markers of oxidative stress and inflammation were also assessed in primary placental tissue after an acute 24 h exposure to tacrolimus.

RESULTS

Tacrolimus exposure significantly reduced HUVEC secretion of PlGF, increased production of activin A, andreduced tubular structure formation without impacting cell permeability or viability. There was no change in ICAM1 or VCAM1 expression in HUVECs treated with tacrolimus treatment alone, however co-culture with TNF significantly increased expression of ICAM1 and VCAM1. In placental explants tacrolimus did not change angiogenic factor production or markers of inflammation or oxidative stress.

CONCLUSION

An acute tacrolimus exposure reduced PlGF secretion and impaired angiogenesis in primary endothelial cells, without affecting. These findings provide a potential mechanistic basis for tacrolimus to contribute to the endothelial dysfunction contributing to preeclampsia.

An Immune-Independent Mode of Action of Tacrolimus in Promoting Human Extravillous Trophoblast Migration Involves Intracellular Calcium Release and F-Actin Cytoskeletal Reorganization

We have previously reported that the calcineurin inhibitor macrolide immunosuppressant Tacrolimus (TAC, FK506) can promote the migration and invasion of the human-derived extravillous trophoblast cells conducive to preventing implantation failure in immune-complicated gestations manifesting recurrent implantation failure. Although the exact mode of action of TAC in promoting implantation has yet to be elucidated, the integral association of its binding protein FKBP12 with the inositol triphosphate receptor (IP3R) regulated intracellular calcium [Ca2+]i channels in the endoplasmic reticulum (ER), suggesting that TAC can mediate its action through ER release of [Ca2+]i. Using the immortalized human-derived first-trimester extravillous trophoblast cells HTR8/SVneo, our data indicated that TAC can increase [Ca2+]I, as measured by fluorescent live-cell imaging using Fluo-4. Concomitantly, the treatment of HTR8/SVneo with TAC resulted in a major dynamic reorganization in the actin cytoskeleton, favoring a predominant distribution of cortical F-actin networks in these trophoblasts. Notably, the findings that TAC was unable to recover [Ca2+]i in the presence of the IP3R inhibitor 2-APB indicate that this receptor may play a crucial role in the mechanism of action of TAC. Taken together, our results suggest that TAC has the potential to influence trophoblast migration through downstream [Ca2+]i-mediated intracellular events and mechanisms involved in trophoblast migration, such as F-actin redistribution. Further research into the mono-therapeutic use of TAC in promoting trophoblast growth and differentiation in clinical settings of assisted reproduction is warranted.

Steroid-tacrolimus drug-drug interaction and the effect of CYP3A genotypes

AIMS

Tacrolimus, metabolized by CYP3A4 and CYP3A5 enzymes, is susceptible to drug-drug interactions (DDI). Steroids induce CYP3A genes to increase tacrolimus clearance, but the effect is variable. We hypothesized that the extent of the steroid-tacrolimus DDI differs by CYP3A4/5 genotypes.

METHODS

Kidney transplant recipients (n = 2462) were classified by the number of loss of function alleles (LOF) (CYP3A5*3, *6 and *7 and CYP3A4*22) and steroid use at each tacrolimus trough in the first 6 months post-transplant. A population pharmacokinetic analysis was performed by nonlinear mixed-effect modelling (NONMEM) and stepwise covariate modelling to define significant covariates affecting tacrolimus clearance. A stochastic simulation was performed and translated into a Shiny application with the mrgsolve and Shiny packages in R.

RESULTS

Steroids were associated with modestly higher (3%-11.8%) tacrolimus clearance. Patients with 0-LOF alleles receiving steroids showed the greatest increase (11.8%) in clearance compared to no steroids, whereas those with 2-LOFs had a negligible increase (2.6%) in the presence of steroids. Steroid use increased tacrolimus clearance by 5% and 10.3% in patients with 1-LOF and 3/4-LOFs, respectively.

CONCLUSIONS

Steroids increase the clearance of tacrolimus but vary slightly by CYP3A genotype. This is important in individuals of African ancestry who are more likely to carry no LOF alleles, may more commonly receive steroid treatment, and will need higher tacrolimus doses.

Adverse Pregnancy Outcomes in Solid Organ Transplant Recipients: A Systematic Review and Meta-Analysis

Importance

Transplant recipients experience high rates of adverse pregnancy outcomes; however, contemporary estimates of the association between solid organ transplantation and adverse pregnancy outcomes are lacking.

Objective

To evaluate the association between solid organ transplantation and adverse pregnancy outcomes and to quantify the incidence of allograft rejection and allograft loss during pregnancy.

Data Sources

PubMed/MEDLINE, EMBASE and Scopus databases were searched from January 1, 2000, to June 20, 2024, and reference lists were manually reviewed.

Study Selection

Cohort and case-control studies that reported at least 1 adverse pregnancy outcome in pregnant women with solid organ transplantation vs without solid organ transplant or studies that reported allograft outcomes in pregnant women with solid organ transplantation were included following independent dual review of abstracts and full-text articles.

Data Extraction and Synthesis

Two investigators abstracted data and independently appraised risk of bias using the Newcastle Ottawa Scale. A random-effects model was used to calculate overall pooled estimates using the DerSimonian-Laird estimator. Reporting followed the Meta-analysis of Observational Studies in Epidemiology (MOOSE) reporting guideline.

Main Outcomes and Measures

Primary pregnancy outcomes were preeclampsia, preterm birth (<37 weeks), and low birth weight (<2500 g). Secondary pregnancy outcomes were live birth rate, gestation, very preterm birth (<32 weeks), very low birth weight (<1500 g), and cesarean delivery. Allograft outcomes were allograft loss and rejection during pregnancy.

Results

Data from 22 studies and 93 565 343 pregnancies (4786 pregnancies in solid organ transplant recipients) were included; 14 studies reported adverse pregnancy outcomes, and 13 studies provided data for allograft outcomes. Pregnancies in organ transplant recipients were associated with significantly increased risk of preeclampsia (adjusted odds ratio [aOR], 5.83 [95% CI, 3.45-9.87]; I2 = 77.4%), preterm birth (aOR, 6.65 [95% CI, 4.09-12.83]; I2 = 81.8%), and low birth weight (aOR, 6.51 [95% CI, 2.85-14.88]; I2 = 90.6%). The incidence of acute allograft rejection was 2.39% (95% CI, 1.20%-3.96%; I2 = 68.5%), and the incidence of allograft loss during pregnancy was 1.55% (95% CI, 0.05%-4.44%; I2 = 69.2%).

Conclusions and Relevance

In this systematic review and meta-analysis, pregnancies in recipients of a solid organ transplant were associated with a 4 to 6 times increased risk of preeclampsia, preterm birth, and low birth weight during pregnancy. There was a low overall risk of graft rejection or loss during pregnancy.

Change in Tacrolimus Concentration Measured in Whole Blood Correlates With Changes in Red Blood Cell Parameters After Red Blood Cell Transfusion in Kidney Transplant Recipients

BACKGROUND

Tacrolimus (TAC) is a narrow therapeutic range drug that requires therapeutic drug monitoring. TAC concentration is measured using whole blood owing to its high red blood cell (RBC) transfer rate of 95%. The distribution and whole-blood TAC concentration may be affected by the transfusion of red cell concentrates (RCCs); however, this has not been studied in kidney transplant recipients (KTR). Therefore, we investigated the relationship between changes in whole-blood TAC concentration and RBC parameters before and after RCC transfusion in KTR.

METHODS

Fifteen KTR who received TAC and RCC transfusions were enrolled. The change rates of RBC parameters (RBC count, hemoglobin [Hgb], hematocrit [Hct]), and TAC concentration/dose before and after transfusion were calculated. The correlation between each RBC parameter and the TAC rate was evaluated.

RESULTS

The TAC concentration and rate increased after RCC transfusion. Moreover, the TAC rate showed a significant and strong correlation with RBC count, Hgb, and Hct, with RBC count showing the highest correlation coefficient (r = 0.811, 0.766, and 0.764, respectively; p < .01). Serum creatinine and potassium levels remained stable, suggesting the absence of typical adverse effects associated with TAC, such as acute kidney injury or hyperkalemia.

CONCLUSION

Changes in whole-blood TAC concentration and RBC parameters were correlated, and whole-blood TAC concentration increased after RCC transfusion. Therefore, the TAC dose should be adjusted accordingly.

Immunosuppressant Medications in Pregnancy

Pregnant patients are often on immunosuppressant medications, most commonly to manage transplantation or autoimmune disorders. Most immunosuppressant agents, including tacrolimus, corticosteroids, azathioprine, and calcineurin inhibitors, are safe during pregnancy and lactation. However, mycophenolic acid is associated with higher risks of birth defects and should be avoided in pregnancy. Tacrolimus, the commonly used drug in transplantation medicine and autoimmune disorders, requires monitoring of serum levels for dose adjustment, particularly during pregnancy. Although no pregnancy-specific therapeutic range exists, the general target range is 5-15 ng/mL, and pregnant patients may require higher doses to achieve therapeutic levels. Adherence to prescribed immunosuppressive regimens is crucial to prevent graft rejection and autoimmune disorder flare-ups. This review aims to provide essential information about the use of immunosuppressant medications in pregnant individuals. With a rising number of pregnant patients undergoing organ transplantations or having autoimmune disorders, it is important to understand the implications of the use of these medications during pregnancy.

Pharmacokinetics of Tacrolimus in Pregnant Solid-Organ Transplant Recipients: A Retrospective Study

Data on the pharmacokinetics of tacrolimus during pregnancy are limited. Therefore, the aim of this retrospective study was to characterize the whole-blood pharmacokinetics of tacrolimus throughout pregnancy. In this single-center retrospective cohort study, whole-blood tacrolimus trough concentrations corrected for the dose (concentration-to-dose [C/D] ratios) were compared before, monthly during, and after pregnancy in kidney, liver, and lung transplant recipients who became pregnant and gave birth between 2000 and 2022. Descriptive statistics and linear mixed models were used to characterize changes in tacrolimus C/D ratios before, during, and after pregnancy. The total study population included 46 pregnancies (31 pregnant women). Nineteen, 21, and 6 pregnancies were following kidney, liver, and lung transplantation, respectively. Immediate-release or extended-release formulations were used in 54.5% and 45.5% of the women, respectively. Tacrolimus C/D ratios significantly (P < .001) decreased (-48%) compared to the prepregnancy state at 7 months of pregnancy. These ratios recovered within 3 months postpartum (P = .002). C/D ratios tended to be lower during treatment with an extended-release formulation than with an immediate-release formulation (P = .071). Transplantation type did not significantly affect C/D ratios during pregnancy (P = .873). In conclusion, we found that tacrolimus whole-blood pharmacokinetics change throughout pregnancy, with the lowest C/D ratios (48% decrease) in the 7th month of pregnancy. In general, the decrease in C/D ratios seems to stabilize from month 4 onward compared to prepregnancy.

Modelling changes in the pharmacokinetics of tacrolimus during pregnancy after kidney transplantation: A retrospective cohort study

AIMS

Pregnancy after kidney transplantation is realistic but immunosuppressants should be continued to prevent rejection. Tacrolimus is safe during pregnancy and is routinely dosed based on whole-blood predose concentrations. However, maintaining these concentrations is complicated as physiological changes during pregnancy affect tacrolimus pharmacokinetics. The aim of this study was to describe tacrolimus pharmacokinetics throughout pregnancy and explain the changes by investigating covariates in a population pharmacokinetic model.

METHODS

Data of pregnant women using a twice-daily tacrolimus formulation following kidney transplantation were retrospectively collected from 6 months before conception, throughout gestation and up to 6 months postpartum. Pharmacokinetic analysis was performed using nonlinear mixed effects modelling. Demographic, clinical and genetic parameters were evaluated as covariates. The final model was evaluated using goodness-of-fit plots, visual predictive checks and a bootstrap analysis.

RESULTS

A total of 260 whole-blood tacrolimus predose concentrations from 14 pregnant kidney transplant recipients were included. Clearance increased during pregnancy from 34.5 to 41.7 L/h, by 15, 19 and 21% in the first, second and third trimester, respectively, compared to prior to pregnancy. This indicates a required increase in the tacrolimus dose by the same percentage to maintain the prepregnancy concentration. Haematocrit and gestational age were negatively correlated with tacrolimus clearance (P ≤ 0.01), explaining 18% of interindividual and 85% of interoccasion variability in oral clearance.

CONCLUSIONS

Tacrolimus clearance increases during pregnancy, resulting in decreased exposure to tacrolimus, which is explained by gestational age and haematocrit. To maintain prepregnancy target whole-blood tacrolimus predose concentrations during pregnancy, increasing the dose is required.

Calcineurin inhibitors in the management of recurrent miscarriage and recurrent implantation failure: Systematic review and meta-analysis

Recurrent miscarriage (RM) affects up to 2.5% of couples of reproductive age. Up to 10% of couples using assisted reproductive technology experience recurrent implantation failure (RIF). Immunosuppressive drugs, such as calcineurin inhibitors (CNIs), has been proposed for RM and RIF management. This systematic review and meta-analysis (SRMA) aimed to evaluate the efficacy and safety of CNIs in RM and RIF treatment. We searched in the three databases. Review Manager 5.4.1 was used for statistical analysis. This review included 8 studies involving 1042 women (485 women in the CNIs group and 557 women in the control group). CNI treatment (cyclosporine [CsA] and tacrolimus [TAC]) increases live birth rate (LBR, odds ratio [OR]: 2.52; 95% confidence interval [CI]: 1.93-3.28, p < 0.00001) and clinical pregnancy rate (OR: 2.25; 95% CI: 1.54-4.40, p < 0.0001) and decreases miscarriage rate (OR: 0.45 95% CI: 0.32-0.63, p < 0.00001) when compared to the control. Side effects and obstetric and neonatal complications was similar in both groups. In conclusion, CNIs increased LBR in women with RM and RIF but there is a moderate risk of bias. Subgroup analysis revealed that CNIs improved LBR in women with RM with a low risk of bias. However, in women with RIF, with moderate to high risk of bias. The use of CsA and TAC, in low doses and for a short period, for managing reproductive failures in women seems to be safe, not causing serious side effects nor increasing the risk of obstetric and neonatal complications.

Total and Free Blood and Plasma Concentration Changes in Pregnancy for Medicines Highly Bound to Plasma Proteins: Application of Physiologically Based Pharmacokinetic Modelling to Understand the Impact on Efficacy

Free drug concentrations are generally considered the pharmacologically active moiety and are important for cellular diffusion and distribution. Pregnancy-related changes in plasma protein binding and blood partitioning are due to decreases in plasma albumin, alpha-1-acid glycoprotein, and haematocrit; this may lead to increased free concentrations, tissue distribution, and clearance during pregnancy. In this paper we highlight the importance and challenges of considering changes in total and free concentrations during pregnancy. For medicines highly bound to plasma proteins, such as tacrolimus, efavirenz, clindamycin, phenytoin, and carbamazepine, differential changes in concentrations of free drug during pregnancy may be clinically significant and have important implications for dose adjustment. Therapeutic drug monitoring usually relies on the measurement of total concentrations; this can result in dose adjustments that are not necessary when changes in free concentrations are considered. We explore the potential of physiologically based pharmacokinetic (PBPK) models to support the understanding of the changes in plasma proteins binding, using tacrolimus and efavirenz as example drug models. The exposure to either drug was predicted to be reduced during pregnancy; however, the decrease in the exposure to the total tacrolimus and efavirenz were significantly larger than the reduction in the exposure to the free drug. These data show that PBPK modelling can support the impact of the changes in plasma protein binding and may be used for the simulation of free concentrations in pregnancy to support dosing decisions.

Long-term Course of Kidney Function in Uterus Transplant Recipients Under Treatment With Tacrolimus and After Transplantectomy: Results of the First Clinical Cohort

Background

Chronic kidney disease is common after non-renal solid organ transplantation, mainly secondary to calcineurin inhibitors toxicity. Uterus transplantation (UTx) is an innovative treatment for women with absolute uterine factor infertility. UTx is exclusive because it is transient with the absence of lifelong immunosuppression and is performed in young healthy participants. Therefore, UTx provides a unique setting for evaluating the effect of time-limited calcineurin inhibitors treatment on recipients' kidney function.

Methods

In the first UTx cohort worldwide, we studied kidney function using estimated glomerular filtration rate (eGFR) in 7 women over a median follow-up of 121 (119-126) mo.

Results

Median eGFR (mL/min/1.73 m2) of the cohort was 113 at UTx, which declined to 74 during month 3, 71 at months 10-12, 76 at hysterectomy (HE), and 83 at last follow-up. Median duration of tacrolimus exposure was 52 (22-83) mo, and median trough levels (µg/L) were 10 during month 3 and 5.8 at HE. Between UTx and month 3, decline in kidney function was observed in all 7 participants with a median eGFR slope for the whole cohort of -24 mL/min/1.73 m2, which declined further by -4 mL/min/1.73 m2 until months 10-12. Thereafter, eGFR slope improved in 3 participants, remained stable in 3, and worsened in 1 until HE/tacrolimus discontinuation, after which it improved in 2. Eventually, between UTx and last follow-up, 4 of 7 participants had a decline in their eGFR, the median annual eGFR slope being negative at -1.9 mL/min/1.73 m2/y for the whole group.

Conclusions

Kidney function declined in all recipients early after UTx followed by a persistent long-term decrease in majority, despite transplantectomy and discontinuation of immunosuppression. Thus, UTx may incur an increased risk of chronic kidney disease even in this young and healthy population, highlighting the importance of close surveillance of kidney function and minimization of tacrolimus exposure.

Use of Physiologically Based Pharmacokinetic Modeling for Hepatically Cleared Drugs in Pregnancy: Regulatory Perspective

Physiologically based pharmacokinetic modeling could be used to predict changes in exposure during pregnancy and possibly inform medicine use in pregnancy in situations in which there is currently limited or no available clinical PK data. The Medicines and Healthcare Product Regulatory Agency has been evaluating the available models for a number of medicines cleared by hepatic clearance mechanisms. Models were evaluated for metoprolol, tacrolimus, clindamycin, ondansetron, phenytoin, caffeine, fluoxetine, clozapine, carbamazepine, metronidazole, and paracetamol. The hepatic metabolism through cytochrome P450 (CYP) contributes significantly to the elimination of these drugs, and available knowledge of CYP changes during pregnancy has been implemented in the existing pregnancy physiology models. In general, models were able to capture trends in exposure changes in pregnancy to some extent, but the magnitude of pharmacokinetic change for these hepatically cleared drugs was not captured in each case, nor were models always able to capture overall exposure in the populations. A thorough evaluation was hampered by the lack of clinical data for drugs cleared by a specific clearance pathway. The limited clinical data, as well as complex elimination pathways involving CYPs, uridine 5'-diphospho-glucuronosyltransferase and active transporter for many drugs, currently limit the confidence in the prospective use of the models. Pregnancy-related changes in uridine 5'-diphospho-glucuronosyltransferase and transport functions are emerging, and incorporation of such changes in current physiologically based pharmacokinetic modeling software is in progress. Filling this gap is expected to further enhance predictive performance of models and increase the confidence in predicting PK changes in pregnant women for hepatically cleared drugs.

Design Considerations for Pharmacokinetic Studies During Pregnancy

Most of the interventions performed by obstetric providers involve the administration of drugs. Pregnant patients are pharmacologically and physiologically different from nonpregnant young adults. Therefore, dosages that are effective and safe for the general public may be inadequate or unsafe for the pregnant patient and her fetus. Establishing dosing regimens appropriate for pregnancy requires evidence generated from pharmacokinetic studies performed in pregnant people. However, performing these studies during pregnancy often requires special design considerations, evaluations of both maternal and fetal exposures, and recognition that pregnancy is a dynamic process that changes as gestational age advances. In this article, we address design challenges unique to pregnancy and discuss options for investigators, including timing of drug sampling during pregnancy, appropriate selection of control groups, pros and cons of dedicated and nested pharmacokinetic studies, single-dose and multiple-dose analyses, dose selection strategies, and the importance of integrating pharmacodynamic changes into these protocols. Examples of completed pharmacokinetic studies in pregnancy are provided for illustration.

Optimizing Therapeutic Drug Monitoring in Pregnant Women: A Critical Literature Review

BACKGROUND

More than 90% of pregnant women take at least one drug during pregnancy. Drug dose adjustments during pregnancy are sometimes necessary due to various pregnancy-induced physiological alterations frequently associated with lower plasma concentrations. However, the clinical relevance or benefits of therapeutic drug monitoring (TDM) in pregnant women have not been specifically studied. Clinical pharmacokinetic studies in pregnant women are incredibly challenging for many reasons. Despite this, regulatory agencies have made efforts to encourage the inclusion of this population in clinical trials to achieve more information on the pharmacotherapy of pregnant women. This review aims to provide support for TDM recommendations and dose adjustments in pregnant women.

METHODS

The search was conducted after a predetermined strategy on PubMed and Scopus databases using the MeSH term "pregnancy" alongside other terms such as "Pregnancy and dose adjustment," "Pregnancy and therapeutic drug monitoring," "Pregnancy and PBPK," "Pregnancy and pharmacokinetics," and "Pregnancy and physiological changes."

RESULTS

The main information on TDM in pregnant women is available for antiepileptics, antipsychotics, antidepressants, antibiotics, antimalarials, and oncologic and immunosuppressive drugs.

CONCLUSIONS

More data are needed to support informed benefit-risk decision making for the administration of drugs to pregnant women. TDM and/or pharmacokinetic studies could ensure that pregnant women receive an adequate dosage of an active drug. Mechanistic modeling approaches potentially could increase our knowledge about the pharmacotherapy of this special population, and they could be used to better design dosage regimens.

Fetal endothelial colony-forming cell impairment after maternal kidney transplantation

BACKGROUND

Successful pregnancies are nowadays possible after kidney transplantation but are associated with a higher incidence of maternal and fetal complications. Immunosuppressive therapy causes cardiovascular side effects but must be maintained during pregnancy. Little is known about the consequences of maternal kidney transplantation on offspring's endothelial health. Endothelial colony forming cells (ECFCs) represent a highly proliferative subtype of endothelial progenitor cells and are crucial for vascular homeostasis, repair and neovascularization. Therefore, we investigated whether maternal kidney transplantation affects fetal ECFCs' characteristics.

METHODS

ECFCs were isolated from umbilical cord blood of uncomplicated and post-kidney-transplant pregnancies and analyzed for their functional abilities with proliferation, cell migration, centrosome orientation and angiogenesis assays. Further, ECFCs from uncomplicated pregnancies were exposed to either umbilical cord serum from uncomplicated or post-kidney-transplant pregnancies.

RESULTS

Post-kidney-transplant ECFCs showed significantly less proliferation, less migration and less angiogenesis compared to control ECFCs. The presence of post-kidney-transplant umbilical cord serum led to similar functional aberrations of ECFCs from uncomplicated pregnancies.

CONCLUSIONS

These pilot data demonstrate differences in ECFCs' biological characteristics in offspring of women after kidney transplantation. Further studies are needed to monitor offspring's long-term cardiovascular development and to assess possible causal relationships with immunosuppressants, uremia and maternal cardiovascular alterations.

IMPACT

Pregnancy after kidney transplantation has become more common in the past years but is associated with higher complications for mother and offspring. Little is known of the impact of maternal kidney transplantation and the mandatory immunosuppressive therapy on offspring vascular development. In this study we are the first to address and detect an impairment of endothelial progenitor cell function in offspring of kidney-transplanted mothers. Serum from post-transplant pregnancies also causes negative effects on ECFCs' function. Clinical studies should focus on long-term monitoring of offspring's cardiovascular health.

Reproductive health after thoracic transplantation: An ISHLT expert consensus statement

Pregnancy after thoracic organ transplantation is feasible for select individuals but requires multidisciplinary subspecialty care. Key components for a successful pregnancy after lung or heart transplantation include preconception and contraceptive planning, thorough risk stratification, optimization of maternal comorbidities and fetal health through careful monitoring, and open communication with shared decision-making. The goal of this consensus statement is to summarize the current evidence and provide guidance surrounding preconception counseling, patient risk assessment, medical management, maternal and fetal outcomes, obstetric management, and pharmacologic considerations.

Principles of Obstetric Pharmacology: Maternal Physiologic and Hepatic Metabolism Changes

Since the recognition of pregnancy as a special pharmacokinetic population in the late 1990s, investigations have expanded our understanding of obstetric pharmacology. Many of the basic physiologic changes that occur during pregnancy impact on drug absorption, distribution, or clearance. Activities of hepatic metabolizing enzymes are variably altered by pregnancy, resulting in concentrations sufficiently different for some drugs that efficacy or toxicity may be affected. Understanding these unique pharmacologic changes will better inform our use of medications for our pregnant patients.

Immunosuppression in Uterus Transplantation: Experience From the Dallas Uterus Transplant Study

BACKGROUND

Uterus transplantation is a temporary transplant allowing women with absolute uterine factor infertility to experience pregnancy and childbirth. The degree of immunosuppression (IS) required to prevent rejection while minimizing toxicity to the recipient and fetus remains an area of investigation.

METHODS

In this article, we describe immunosuppressive therapy, rejection episodes, infections, and adverse events in 14 uterus transplant recipients. Induction consisted of antithymocyte globulin and methylprednisolone. Ten recipients (71%) received no steroids postoperatively, and 4 (29%) had steroids tapered off at 42 d. All received oral tacrolimus, either immediate release (n = 2, 14%) or extended release (n = 12, 86%). Mycophenolate was used in 4 cases (29%), de novo azathioprine in 9 (64%), and de novo everolimus in 1 (7%).

RESULTS

Sixteen clinically silent, treatment-responsive rejection episodes occurred in 10 recipients. Five recipients (36%) experienced acute kidney injury. In 3 recipients, IS was discontinued due to renal dysfunction. Eleven infection episodes were noted in 7 recipients. No babies had congenital abnormalities.

CONCLUSIONS

Our experience demonstrates that safe IS regimens can be used for uterus transplant recipients before and during pregnancy.

Co-administration of tacrolimus and low molecular weight heparin in patients with a history of implantation failure and elevated peripheral blood natural killer cell proportion

AIM

To investigate the therapeutic effect of co-administration of tacrolimus (TAC) and low-molecular-weight heparin (LMWH) or LMWH only on pregnancy outcomes in the female with a history of implantation failure and elevated peripheral blood natural killer (pNK) cell proportion in frozen-thawed embryo transfer cycles.

METHODS

To evaluate the pregnancy parameters for 249 patients with ≥2 implantation failures and pNK cell proportion ≥12% by analyzing a retrospective observational cohort study. Sixty patients had received the co-administration TAC and LMWH (TAC & LMWH group), 85 others had only taken LMWH (LWMH group), and the rest did not take any particular drugs (control group).

RESULTS

The experimental finding indicated that the TAC & LMWH group and the LMWH group showed higher clinical pregnancy rates than the control group (p < 0.05), and TAC & LMWH group had a much higher live birth rate. According to the binary logistic regression analysis, the combination of TAC and LMWH was conducive to clinical pregnancy and live birth rate and reduced the possibility of miscarriage. It would not affect the result of spontaneous abortion and live birth, although the LMWH was only beneficial to clinical pregnancy. In addition, these findings were similar for these three groups' obstetrical and neonatal outcomes.

CONCLUSIONS

The combination of TAC and LMWH can improve clinical pregnancy and live birth rates and reduce the risk of spontaneous miscarriage in patients with a history of implantation failure and elevated pNK ratio. LMWH is also beneficial to clinical pregnancy.

Pharmacokinetic data in pregnancy: A review of available literature data and important considerations in collecting clinical data

Pregnancy-related physiological changes can alter the absorption, distribution, metabolism and excretion of medicines which may affect the safety and efficacy of the medicines administered in pregnancy. Pharmacokinetic data can thus be instrumental in supporting dose adjustments required in this population. This review considers the availability of published pharmacokinetic data for over 200 medicines of interest for use in pregnancy in the UK, to identify whether sufficient data currently exists, in principle, for any medicine or group of medicines to support dose adjustments to maintain maternal health through pregnancy. Very limited data was found for many of the medicines of interest. Nevertheless, well documented, large changes of exposure for some drugs, where data is available, highlights the urgent need to collect more data of good quality to inform appropriate doses, when needed, in this population. In addition, clinical study methodology can have an impact on the usefulness of the data and key clinical design aspects are highlighted for consideration in future clinical study design.

Autoimmune hepatitis in pregnancy: Pearls and pitfalls

Autoimmune hepatitis (AIH) in pregnancy has many unique considerations. Evidence provided from single center studies with patient level data and nationwide population studies provide valuable insight into this complex situation. Because a planned pregnancy is a safer pregnancy, preconception counseling is a crucial opportunity to optimize care and risk stratify women with AIH. Women with chronic liver disease who receive preconception advice and counseling are more likely to achieve stable liver disease at conception and undergo appropriate variceal surveillance. Loss of biochemical response in pregnancy is associated with adverse outcomes in unstable disease. New onset AIH in pregnancy should be managed with classical treatment regimens. The continued use of immunosuppression in pregnancy, with the exception of mycophenolate mofetil, has not shown to adversely affect the rates of stillbirth or congenital malformation. Previously adopted immunosuppression withdrawal paradigms in pregnancy should no longer be considered advantageous, because remission loss postdelivery is likely (12%-86%). Population studies, report improved outcomes with preterm birth rates falling from 20% to 9%-13% in AIH pregnancies over a 20-year period. Newer data have also demonstrated an increased risk of gestational diabetes and hypertensive complications in AIH pregnancy, which has implications for management and preeclampsia prevention with aspirin use. This review aims to provide the framework to guide and manage pregnancy in AIH outlining pearls and pitfalls to ensure optimal outcomes for mother, baby and to reduce variation in practice.

Development and Validation of the New Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Unbound Tacrolimus in the Plasma Ultrafiltrate of Transplant Recipients

(1) Background: Only unbound tacrolimus particles are considered to be active and capable of crossing cellular membranes. Thus, the free-drug concentration might be better associated with clinical effects than the total drug concentration used for dosage adjustment. We propose a new, fully validated online liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for unbound tacrolimus concentration measurement. (2) Methods: The determination of the unbound tacrolimus concentration in plasma ultrafiltrate was performed with the Nexera LC system with LCMS-8050 triple quadrupole MS using ascomycin as an internal standard. Chromatographic separation was made using a HypurityC18 analytical column. MS/MS with electrospray ionization and positive-ion multiple-reaction monitoring was used. The unbound tacrolimus level was determined in 36 patients after solid organ transplantation (n = 140). (3) Results: A lower limit of quantification 0.1 pg/mL was achieved, and the assay was linear between 0.1 and 20 pg/mL (R2 = 0.991). No carry-over was detected. The within-run and between-run accuracies ranged between 97.8–109.7% and 98.3–107.1%, while the greatest imprecision was 10.6% and 10.7%, respectively. Free tacrolimus in patients’ plasma ultrafiltrate varied between 0.06 and 18.25 pg/mL (median: 0.98 pg/mL). (4) Conclusions: The proposed method can be easily implemented. The significance of the unbound tacrolimus concentration needs to be investigated. This may facilitate the individualization and optimization of immunosuppressive treatment.

Autoimmune hepatitis and pregnancy: considerations for the clinician

INTRODUCTION

Autoimmune hepatitis (AIH) is an immune mediated inflammatory disease of the liver which affects females of reproductive age. AIH poses unique challenges in pregnancy and historically was associated with adverse pregnancy outcomes.

AREAS COVERED

This report aims to review the current evidence for AIH pregnancy outcomes and the use of medical therapies in pregnancy. The disease course of AIH in pregnancy including loss of biochemical response (LOBR) and hepatic decompensation is also reviewed. The importance of preconception counselling and continued monitoring into the post-partum phase are reinforced.

EXPERT OPINION

The lack of prognostic markers and targeted immunosuppression are some of the areas for future development, as this will aid the move towards individualised risk stratification and personalised care.

Impact of Pregnancy on GFR Decline and Kidney Histology in Kidney Transplant Recipients

Introduction

Women with advanced kidney disease are advised to wait until after transplant to pursue pregnancy, but the impact of pregnancy on estimated glomerular filtration rate (eGFR) decline and kidney histology is unclear.

Methods

We identified a cohort of women aged 18 to 44 years at transplant from 1996 to 2014 at our 3-site program (N = 816) and determined whether they had a pregnancy >20 weeks gestation post-transplant by chart review. Outcomes included rate of change in eGFR after pregnancy, changes in kidney histology before and after pregnancy, graft failure, and 50% reduction in eGFR.

Results

There were 37 women with one or more pregnancies lasting longer than 20 weeks gestation post-transplant. Comparing women with and without pregnancy post-transplant, there was a significant increase in the rate of eGFR decline after pregnancy (−2.4 ml/min per 1.73 m² per year vs. −1.9 ml/min per 1.73 m² per year in women with no pregnancy, P < 0.001). Pregnancy did not affect the risk of graft failure, death-censored graft failure, or 50% reduction in eGFR.

Conclusion

Pregnancy affects the rate of eGFR decline in the allograft. Postpregnancy biopsy findings revealed an increase in vascular injury, which could be a potential mechanism. We did not find a significant increase in risk of graft failure or reduction in eGFR by 50% owing to pregnancy.

Maternal, Decidual, and Neonatal Lymphocyte Composition Is Affected in Pregnant Kidney Transplant Recipients

Pregnancy after renal transplantation is associated with an increased risk of complications. While a delicately balanced uterine immune system is essential for a successful pregnancy, little is known about the uterine immune environment of pregnant kidney transplant recipients. Moreover, children born to kidney transplant recipients are exposed in utero to immunosuppressive drugs, with possible consequences for neonatal outcomes. Here, we defined the effects of kidney transplantation on the immune cell composition during pregnancy with a cohort of kidney transplant recipients as well as healthy controls with uncomplicated pregnancies. Maternal immune cells from peripheral blood were collected during pregnancy as well as from decidua and cord blood obtained after delivery. Multiparameter flow cytometry was used to identify and characterize populations of cells. While systemic immune cell frequencies were altered in kidney transplant patients, immune cell dynamics over the course of pregnancy were largely similar to healthy women. In the decidua of women with a kidney transplant, we observed a decreased frequency of HLA-DR⁺ Treg, particularly in those treated with tacrolimus versus those that were treated with azathioprine next to tacrolimus, or with azathioprine alone. In addition, both the innate and adaptive neonatal immune system of children born to kidney transplant recipients was significantly altered compared to neonates born from uncomplicated pregnancies. Overall, our findings indicate a significant and distinct impact on the maternal systemic, uterine, and neonatal immune cell composition in pregnant kidney transplant recipients, which could have important consequences for the incidence of pregnancy complications, treatment decisions, and the offspring's health.

Unbound Plasma, Total Plasma, and Whole-Blood Tacrolimus Pharmacokinetics Early After Thoracic Organ Transplantation

BACKGROUND AND OBJECTIVE

Therapeutic drug monitoring of tacrolimus whole-blood concentrations is standard care in thoracic organ transplantation. Nevertheless, toxicity may appear with alleged therapeutic concentrations possibly related to variability in unbound concentrations. However, pharmacokinetic data on unbound concentrations are not available. The objective of this study was to quantify the pharmacokinetics of whole-blood, total, and unbound plasma tacrolimus in patients early after heart and lung transplantation.

METHODS

Twelve-hour tacrolimus whole-blood, total, and unbound plasma concentrations of 30 thoracic organ recipients were analyzed with high-performance liquid chromatography-tandem mass spectrometry directly after transplantation. Pharmacokinetic modeling was performed using non-linear mixed-effects modeling.

RESULTS

Plasma concentration was < 1% of the whole-blood concentration. Maximum binding capacity of erythrocytes was directly proportional to hematocrit and estimated at 2700 pg/mL (95% confidence interval 1750-3835) with a dissociation constant of 0.142 pg/mL (95% confidence interval 0.087-0.195). The inter-individual variability in the binding constants was considerable (27% maximum binding capacity, and 29% for the linear binding constant of plasma).

CONCLUSIONS

Tacrolimus association with erythrocytes was high and suggested a non-linear distribution at high concentrations. Monitoring hematocrit-corrected whole-blood tacrolimus concentrations might improve clinical outcomes in clinically unstable thoracic organ transplants.

CLINICAL TRIAL REGISTRATION

NTR 3912/EudraCT 2012-001909-24.

Case Report: Low Hematocrit Leading to Tacrolimus Toxicity

Tacrolimus is a calcineurin inhibitor characterized by a narrow therapeutic index and high intra- and inter-individual pharmacokinetic variability. Therapeutic drug monitoring in whole-blood is the standard monitoring procedure. However, tacrolimus extensively binds to erythrocytes, and tacrolimus whole-blood distribution and whole-blood trough concentrations are strongly affected by hematocrit. High whole-blood tacrolimus concentrations at low hematocrit may result in high unbound plasma concentrations and increased toxicity. We present the case of a 16-year-old girl with kidney and liver transplant in whom low concentrations of tacrolimus in the context of low hematocrit led to significant increase in the dosage of tacrolimus and participate, along with a genetic polymorphism of ABCB1, in nephrotoxicity.

Usage of Tacrolimus and Mycophenolic Acid During Conception, Pregnancy, and Lactation, and Its Implications for Therapeutic Drug Monitoring: A Systematic Critical Review

BACKGROUND

Conception, pregnancy, and lactation following solid organ transplantation require appropriate management. The most frequently used immunosuppressive drug combination after solid organ transplantation consists of tacrolimus (Tac) plus mycophenolic acid (MPA). Here, the effects of Tac and MPA on fertility, pregnancy, and lactation are systematically reviewed, and their implications for therapeutic drug monitoring (TDM) are discussed.

METHODS

A systematic literature search was performed (August 19, 2019) using Ovid MEDLINE, EMBASE, the Cochrane Central Register of controlled trials, Google Scholar, and Web of Science, and 102 studies were included. Another 60 were included from the reference list of the published articles.

RESULTS

As MPA is teratogenic, women who are trying to conceive are strongly recommended to switch from MPA to azathioprine. MPA treatment in men during conception seems to have no adverse effect on pregnancy outcomes. Nevertheless, in 2015, the drug label was updated with additional risk minimization measures in a pregnancy prevention program. Data on MPA pharmacokinetics during pregnancy and lactation are limited. Tac treatment during conception, pregnancy, and lactation seems to be safe in terms of the health of the mother, (unborn) child, and allograft. However, Tac may increase the risk of hypertension, preeclampsia, preterm birth, and low birth weight. Infants will ingest very small amounts of Tac via breast milk from mothers treated with Tac. However, no adverse outcomes have been reported in children exposed to Tac during lactation. During pregnancy, changes in Tac pharmacokinetics result in increased unbound to whole-blood Tac concentration ratio. To maintain Tac concentrations within the target range, increased Tac dose and intensified TDM may be required. However, it is unclear if dose adjustments during pregnancy are necessary, considering the higher concentration of (active) unbound Tac.

CONCLUSIONS

Tac treatment during conception, pregnancy and lactation seems to be relatively safe. Due to pharmacokinetic changes during pregnancy, a higher Tac dose might be indicated to maintain target concentrations. However, more evidence is needed to make recommendations on both Tac dose adjustments and alternative matrices than whole-blood for TDM of Tac during pregnancy. MPA treatment in men during conception seems to have no adverse effect on pregnancy outcomes, whereas MPA use in women during conception and pregnancy is strongly discouraged.

Determination of tacrolimus, three mono-demethylated metabolites and a M1 tautomer in human whole blood by liquid chromatography - tandem mass spectrometry

The immunosuppressant tacrolimus is the primary drug used in kidney transplantation to prevent organ rejection. A sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed to measure tacrolimus and its three known mono-demethylated metabolites 13-O-desmethyl tacrolimus (M1), 31-O-desmethyl tacrolimus (M2), 15-O-desmethyl tacrolimus (M3). By generating the metabolites to use as standards after incubation of tacrolimus with rat liver microsomes, we discovered multiple M1 peaks which we identified as two tautomers of M1. The M1 tautomer II was also successfully validated in this method. The separation and purification of the metabolites and tautomers were performed by semi-preparative liquid chromatography with UV-detection, while confirmation was done by UPLC-MS/MS and Nuclear Magnetic Resonance. For quantification an easy sample preparation was performed with zinc sulfate and acetonitrile as cell lyses and precipitation. Detection was performed in positive electrospray ionization. By better characterization of the metabolites and the tautomers, we could possibly explain insight into the clinical condition and thus adjust the immunosuppressant therapy individually per patient. Calibration curves were linear for all compounds. Precision was assessed according to the NCCLS EP5-T guideline, being below 15 % and mean recoveries were between 93 and 110 % for tacrolimus, its three metabolites and the M1 tautomer II. The validated method was successfully applied in a cohort of 20 patients after kidney transplantation.

Comparison of hospitalization outcomes for delivery and resource utilization between pregnant women with kidney transplants and chronic kidney disease in the United States

BACKGROUND

This study aimed to assess outcomes of delivery hospitalizations, including acute kidney injury (AKI), obstetric and foetal events and resource utilization among pregnant women with kidney transplants compared with pregnant women with no known kidney disease and those with chronic kidney disease (CKD) Stages 3-5.

METHOD

Hospitalizations for delivery in the US were identified using the enhanced delivery identification method in the National Inpatient Sample dataset from the years 2009 to 2014. Diagnoses of CKD Stages 3-5, kidney transplantation, along with obstetric events, delivery methods and foetal events were identified using ICD-9-CM diagnosis and procedure codes. Patients with no known kidney disease group were identified by excluding any diagnoses of CKD, end stage kidney disease, and kidney transplant. Multivariable logistic regression accounting for the survey weights and matched regression was conducted to investigate the risk of maternal and foetal complications in women with kidney transplants, compared with women with no kidney transplants and no known kidney disease, and to women with CKD Stages 3-5.

RESULT

A total of 5, 408, 215 hospitalizations resulting in deliveries were identified from 2009 to 2014, including 405 women with CKD Stages 3-5, 295 women with functioning kidney transplants, and 5, 405, 499 women with no known kidney disease. Compared with pregnant women with no known kidney disease, pregnant kidney transplant recipients were at higher odds of hypertensive disorders of pregnancy (OR = 3.11, 95% CI [2.26, 4.28]), preeclampsia/eclampsia/HELLP syndrome (OR = 3.42, 95% CI [2.54, 4.60]), preterm delivery (OR = 2.46, 95% CI [1.75, 3.45]), foetal growth restriction (OR = 1.74, 95% CI [1.01, 3.00]) and AKI (OR = 10.46, 95% CI [5.33, 20.56]). There were no significant differences in rates of gestational diabetes or caesarean section. Pregnant women with kidney transplants had 1.30-times longer lengths of stay and 1.28-times higher costs of hospitalization. However, pregnant women with CKD Stages 3-5 were at higher odds of AKI (OR = 5.29, 95% CI [2.41, 11.59]), preeclampsia/eclampsia/HELLP syndrome (OR = 1.72, 95% CI [1.07, 2.76]) and foetal deaths (OR = 3.20, 95% CI [1.06, 10.24]), and had 1.28-times longer hospital stays and 1.37-times higher costs of hospitalization compared with pregnant women with kidney transplant.

CONCLUSION

Pregnant women with kidney transplant were more likely to experience adverse events during delivery and had longer lengths of stay and higher total charges when compared with women with no known kidney disease. However, pregnant women with moderate to severe CKD were more likely to experience serious complications than kidney transplant recipients.

Drug development research in pregnant and lactating women

Pregnant and lactating women are considered "therapeutic orphans" because they generally have been excluded from clinical drug research and the drug development process owing to legal, ethical, and safety concerns. Most medications prescribed for pregnant and lactating women are used "off-label" because most of the clinical approved medications do not have appropriate drug labeling information for pregnant and lactating women. Medications that lack human safety data on use during pregnancy and lactation may pose potential risks for adverse effects in pregnant and lactating women as well as risks of teratogenic effects to their unborn and newborn babies. Federal policy requiring the inclusion of women in clinical research and trials led to considerable changes in research design and practice. Despite more women being included in clinical research and trials, the inclusion of pregnant and lactating women in drug research and clinical trials remains limited. A recent revision to the "Common Rule" that removed pregnant women from the classification as a "vulnerable" population may change the culture of drug research and drug development in pregnant and lactating women. This review article provides an overview of medications studied by the Obstetric-Fetal Pharmacology Research Units Network and Centers and describes the challenges in current obstetrical pharmacology research and alternative strategies for future research in precision therapeutics in pregnant and lactating women. Implementation of the recommendations of the Task Force on Research Specific to Pregnant Women and Lactating Women can provide legislative requirements and opportunities for research focused on pregnant and lactating women.

Clinical Pharmacokinetics and Impact of Hematocrit on Monitoring and Dosing of Tacrolimus Early After Heart and Lung Transplantation

The calcineurin inhibitor tacrolimus is an effective immunosuppressant and is extensively used in solid organ transplantation. In the first week after heart and lung transplantation, tacrolimus dosing is difficult due to considerable physiological changes because of clinical instability, and toxicity often occurs, even when tacrolimus concentrations are within the therapeutic range. The physiological and pharmacokinetic changes are outlined. Excessive variability in bioavailability may lead to higher interoccasion (dose-to-dose) variability than interindividual variability of pharmacokinetic parameters. Intravenous tacrolimus dosing may circumvent this high variability in bioavailability. Moreover, the interpretation of whole-blood concentrations is discussed. The unbound concentration is related to hematocrit, and changes in hematocrit may increase toxicity, even within the therapeutic range of whole-blood concentrations. Therefore, in clinically unstable patients with varying hematocrit, aiming at the lower therapeutic level is recommended and tacrolimus personalized dosing based on hematocrit-corrected whole-blood concentrations may be used to control the unbound tacrolimus plasma concentrations and subsequently reduce toxicity.

Sources of Interindividual Variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in others. A significant source of this variability in drug response is drug metabolism, where differences in presystemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C_max, and/or C_min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is recognized that both intrinsic factors (e.g., genetics, age, sex, and disease states) and extrinsic factors (e.g., diet , chemical exposures from the environment, and the microbiome) play a significant role. For drug-metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, upregulation and downregulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less predictable and time-dependent manner. Understanding the mechanistic basis for variability in drug disposition and response is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that will improve outcomes in maintaining health and treating disease.

Pregnancy in Kidney Transplant Recipients

Women with end-stage kidney disease commonly have difficulty conceiving through spontaneous pregnancy, and many suffer from infertility. Kidney transplantation restores the impairment in fertility and increases the possibility of pregnancy. In addition, the number of female kidney transplant recipients of reproductive age has been increasing. Thus, preconception counseling, contraceptive management, and family planning are of great importance in the routine care of this population. Pregnancy in kidney transplant recipients is complicated by underlying maternal comorbidities, kidney allograft function, the effect of pregnancy on the transplanted kidney, and the effect of the maternal health on the fetus, in addition to immunosuppressive medications and their potential teratogenesis. Given the potential maternal and fetal risks, and possible complications during pregnancy, pretransplant and prepregnancy counseling for women of reproductive age are crucial, including delivery of information regarding contraception and timing for pregnancy, fertility and pregnancy rates, the risk of immunosuppression on the fetus, the risk of kidney allograft, and other maternal complications. In this article, we discuss aspects related to pregnancy among kidney transplant recipients and their management.

Case study of tacrolimus as an effective treatment for idiopathic membranous glomerulonephritis in pregnancy

BACKGROUND

Tacrolimus has been used in pregnant women following transplantation and for management of lupus nephritis. We report a case of successful control of nephrotic syndrome due to membranous glomerulonephritis during pregnancy using tacrolimus.

CASE REPORT

A 26-year-old female presented with severe nephrotic syndrome in her first pregnancy. Post-partum renal biopsy confirmed idiopathic membranous glomerulonephritis. She had persistent proteinuria of 6 g/day with hypoalbuminaemia despite angiotensin receptor blockade. Treatment with tacrolimus monotherapy led to remission of proteinuria, three months prior to conceiving again. She maintained remission with tacrolimus therapy in pregnancy, resulting in a successful birth outcome.

CONCLUSIONS

Membranous glomerulonephritis can be successfully and safely managed with tacrolimus monotherapy during pregnancy. This provides an alternative immunosuppressant with a favourable side effect profile suitable for use in women planning a pregnancy when other immunosuppressive drugs should be avoided.

Drug dosing during pregnancy-opportunities for physiologically based pharmacokinetic models

Drugs can have harmful effects on the embryo or the fetus at any point during pregnancy. Not all the damaging effects of intrauterine exposure to drugs are obvious at birth, some may only manifest later in life. Thus, drugs should be prescribed in pregnancy only if the expected benefit to the mother is thought to be greater than the risk to the fetus. Dosing of drugs during pregnancy is often empirically determined and based upon evidence from studies of non-pregnant subjects, which may lead to suboptimal dosing, particularly during the third trimester. This review collates examples of drugs with known recommendations for dose adjustment during pregnancy, in addition to providing an example of the potential use of PBPK models in dose adjustment recommendation during pregnancy within the context of drug-drug interactions. For many drugs, such as antidepressants and antiretroviral drugs, dose adjustment has been recommended based on pharmacokinetic studies demonstrating a reduction in drug concentrations. However, there is relatively limited (and sometimes inconsistent) information regarding the clinical impact of these pharmacokinetic changes during pregnancy and the effect of subsequent dose adjustments. Examples of using pregnancy PBPK models to predict feto-maternal drug exposures and their applications to facilitate and guide dose assessment throughout gestation are discussed.

Clinical Pharmacokinetic Studies in Pregnant Women and the Relevance of Pharmacometric Tools

BACKGROUND

In clinical pharmacokinetic (PK) studies, pregnant women are significantly underrepresented because of ethical and legal reasons which lead to a paucity of information on potential PK changes in this population. As a consequence, pharmacometric tools became instrumental to explore and quantify the impact of PK changes during pregnancy.

METHODS

We explore and discuss the typical characteristics of population PK and physiologically based pharmacokinetic (PBPK) models with a specific focus on pregnancy and postpartum.

RESULTS

Population PK models enable the analysis of dense, sparse or unbalanced data to explore covariates in order to (partly) explain inter-individual variability (including pregnancy) and to individualize dosing. For population PK models, we subsequently used an illustrative approach with ketorolac data to highlight the relevance of enantiomer specific modeling for racemic drugs during pregnancy, while data on antibiotic prophylaxis (cefazolin) during surgery illustrate the specific characteristics of the fetal compartments in the presence of timeconcentration profiles. For PBPK models, an overview on the current status of reports and papers during pregnancy is followed by a PBPK cefuroxime model to illustrate the added benefit of PBPK in evaluating dosing regimens in pregnant women.

CONCLUSIONS

Pharmacometric tools became very instrumental to improve perinatal pharmacology. However, to reach their full potential, multidisciplinary collaboration and structured efforts are needed to generate more information from already available datasets, to share data and models, and to stimulate cross talk between clinicians and pharmacometricians to generate specific observations (pathophysiology during pregnancy, breastfeeding) needed to further develop the field.

Pregnancy outcomes in heart transplant recipients

BACKGROUND

The population of female heart transplant recipients of reproductive age is growing, and counseling regarding reproductive decisions is important. We describe maternal and fetal outcomes of pregnancy in the Transplant Pregnancy Registry International.

METHODS

Data regarding pregnancies between 1987 and 2016 were collected via questionnaires, phone interviews, and medical records review. Demographics, comorbidities, changes in immunosuppressive regimens, rejection episodes during pregnancy, data on maternal retransplants, and deaths were recorded.

RESULTS

A total of 91 patients reported 157 pregnancies. Mean maternal age at conception was 27 ± 5.6 years. The most common indications for transplant were congenital heart disease (22%) and viral myocarditis (18%). Average transplant to conception interval was 7 ± 6.1 years. Immunosuppression was calcineurin inhibitor-based in almost all patients, with 20% of recipients taking mycophenolic acid (MPA) while pregnant. Complications during pregnancy included pre-eclampsia (23%) and infections (14%). Rejection was reported during 9% of pregnancies and within 3 months postpartum in 7%. Livebirths occurred in 69%, with no neonatal deaths. Miscarriages occurred in 26% of pregnancies, 49% of which had MPA exposure. Mean follow-up post pregnancy was 8.9 ± 6.5 years. At last follow-up, 30 recipients had died, an average of 9.4 ± 6.2 years after pregnancy. The most common causes included allograft vasculopathy and rejection.

CONCLUSIONS

This is the largest reported series of pregnancies in heart transplant recipients and demonstrates that two thirds of pregnancies reported are successful. MPA exposure is associated with increased risk of teratogenicity and miscarriage. Pre-pregnancy counseling should include discussions of risk of MPA exposure, rejection, graft dysfunction, and maternal survival.

Toward a robust tool for pharmacokinetic-based personalization of treatment with tacrolimus in solid organ transplantation: A model-based meta-analysis approach

AIMS

The objective of this study is to develop a generic model for tacrolimus pharmacokinetics modelling using a meta-analysis approach, that could serve as a first step towards a prediction tool to inform pharmacokinetics-based optimal dosing of tacrolimus in different populations and indications.

METHODS

A systematic literature review was performed and a meta-model developed with NONMEM software using a top-down approach. Historical (previously published) data were used for model development and qualification. In-house individual rich and sparse tacrolimus blood concentration profiles from adult and paediatric kidney, liver, lung and heart transplant patients were used for model validation. Model validation was based on successful numerical convergence, adequate precision in parameter estimation, acceptable goodness of fit with respect to measured blood concentrations with no indication of bias, and acceptable performance of visual predictive checks. External validation was performed by fitting the model to independent data from 3 external cohorts and remaining previously published studies.

RESULTS

A total of 76 models were found relevant for meta-model building from the literature and the related parameters recorded. The meta-model developed using patient level data was structurally a 2-compartment model with first-order absorption, absorption lag time and first-time varying elimination. Population values for clearance, intercompartmental clearance, central and peripheral volume were 22.5 L/h, 24.2 L/h, 246.2 L and 109.9 L, respectively. The absorption first-order rate and the lag time were fixed to 3.37/h and 0.33 hours, respectively. Transplanted organ and time after transplantation were found to influence drug apparent clearance whereas body weight influenced both the apparent volume of distribution and the apparent clearance. The model displayed good results as regards the internal and external validation.

CONCLUSION

A meta-model was successfully developed for tacrolimus in solid organ transplantation that can be used as a basis for the prediction of concentrations in different groups of patients, and eventually for effective dose individualization in different subgroups of the population.

Acute Kidney Injury in Pregnant Patient With Pancreas-Kidney Transplant Caused by Abdominal Compartment Syndrome: A Case Presentation, Review of Literature, and Proposal of Diagnostic Approach

Rationale:

With increasing number of complex medical patients with renal transplant who get pregnant, clinicians need to be aware of abdominal compartment syndrome which may masquerade as acute renal allograft injury in pregnancy.

Presenting concerns of the patient:

A 34-year-old nulliparous Caucasian female with end-stage renal disease (ESRD) due to type 1 diabetes mellitus who received a simultaneous pancreas-kidney transplant (SPK) in 2006 and then after rejection of renal allograft another, kidney-only allograft from a donation after circulatory death became pregnant in May 2013 with dichorionic, diamniotic twins without reproductive technology, and during pregnancy, she developed two episodes of acute injury to the renal allograft.

Diagnoses:

End-stage renal disease secondary to type I diabetes, acute renal allograft injury, tacrolimus toxicity, abdominal pain.

Interventions (including prevention and lifestyle):

She received intravenous hydration, medications contributing to renal failure were held, and pain and nauseas were controlled appropriately. Abdominal compartment syndrome was managed by maintaining intravascular pressure and optimizing regional and systemic vascular perfusion by appropriate fluid balance, evacuating intraluminal contents by decompressing gastrointestinal system, and improving abdominal wall compliance by using appropriate analgesics, sedation, and patient positioning.

Outcomes:

With advancing pregnancy, the patient developed progressive abdominal pain, nausea, leg edema, and rising creatinine that were not responsive to ongoing therapies and required delivery via Cesarean section at 31 weeks of gestational age.

Lessons learned:

In the era of increasing number of pregnant renal transplant patients with multiple medical issues, we need organized approach to diagnosis of acute renal allograft injury in pregnancy and we need to consider abdominal compartment syndrome as one of the causes.

Management of reproductive health after cardiac transplantation

Pregnancy after cardiac transplantation poses immense challenges. Maternal risks include hypertensive disorders of pregnancy, rejection, and failure of the cardiac allograft that may lead to death. Fetal risks include potential teratogenic effects of immunosuppression and prematurity. Because of the high-risk nature of pregnancy in a heart transplant patient, management of reproductive health after cardiac transplantation should include preconception counseling to all women in the reproductive age group before and after cardiac transplantation. Reliable contraception is vital as nearly half of the pregnancies in this population are unintended. Despite the associated risks, successful pregnancies after cardiac transplantation have been reported. A multidisciplinary approach proposed in this review is essential for successful outcomes. A checklist for providers to guide management is provided.

Immunomodulatory drugs in pregnancy and lactation

Pregnancy presents challenges for women with autoimmune diseases. It is associated with significant physiological, hormonal and immunomodulatory changes which are complex and vary according to the stage of pregnancy

Pregnancy planning and counselling should be offered

Autoimmune diseases such as rheumatoid arthritis tend to improve in pregnancy while systemic lupus erythematosus may increase in activity

During pregnancy the chosen regimen should control or prevent underlying disease activity and minimise risk to the fetus. Ideally, women should be on a stable regimen before conception

Poorly controlled disease is associated with poor outcomes for both mother and fetus, such as higher risks of pre-eclampsia, early delivery and growth restriction of the fetus

Postpartum, there is a sudden fall in hormone concentrations, and a switch to a pro-inflammatory state. This increases the risk of relapse of many autoimmune diseases in particular rheumatoid arthritis, Crohn’s disease and autoimmune hepatitis

Many drugs are compatible with breastfeeding, but there are limited data on many of the new drugs