Pharmacokinetics of tacrolimus during pregnancy

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

BACKGROUND

Tacrolimus is an important immunosuppressive agent with high intra- and inter-individual pharmacokinetic variability and a narrow therapeutic index. As tacrolimus extensively accumulates in erythrocytes, hematocrit is a key factor in the interpretation of tacrolimus whole blood concentrations. However, as hematocrit values in pediatric kidney transplant patients are highly variable after kidney transplantation, translating whole blood concentration targets without taking hematocrit into consideration is theoretically incorrect. The aim of this study is to evaluate the potential impact of hematocrit correction on tacrolimus target exposure in pediatric kidney transplant patients.

METHODS

Data were obtained from 36 pediatric kidney transplant patients. Two hundred fifty-five tacrolimus whole blood samples were available, together responsible for 36 area under the concentration-time curves (AUCs) and trough concentrations. First, hematocrit corrected concentrations were derived using a formula describing the relationship between whole blood concentrations, hematocrit, and plasma concentrations. Subsequently, target exposure was evaluated using the converted plasma target concentrations. Ultimately, differences in interpretation of target exposure were identified and evaluated.

RESULTS

In total, 92% of our patients had lower hematocrit (median 0.29) than the reference value of adult kidney transplant patients. A different evaluation of target exposure for either trough level, AUC, or both was defined in 42% of our patients, when applying hematocrit corrected concentrations.

CONCLUSION

A critical role for hematocrit in therapeutic drug monitoring of tacrolimus in pediatric kidney transplant patients is suggested in this study. Therefore, we believe that hematocrit correction could be a step towards improvement of tacrolimus dose individualization.

Retrospective analysis of the correlation between tacrolimus concentrations measured in whole blood and variations of blood cell counts in patients undergoing allogeneic haematopoietic stem cell transplantation

Objective

Tacrolimus is administered to patients undergoing haematopoietic stem cell transplantation (HSCT) as prophylaxis for graft-versus-host disease. As a high blood tacrolimus concentration within a narrow therapeutic range must be maintained after HSCT, therapeutic drug monitoring (TDM) is necessary. We investigated the correlation between blood tacrolimus concentration and blood cell count in HSCT patients to assess how changes in blood cell count affect tacrolimus TDM.

Methods

A retrospective analysis was performed for 24 patients who underwent allogeneic HSCT and received tacrolimus. The correlation between variations in blood tacrolimus concentration and blood cell count was evaluated for three consecutive weeks, starting 1 week after HSCT.

Results

Variations in blood tacrolimus concentration were significantly correlated with variations in red blood cell (RBC) count, haemoglobin level and haematocrit value, but not with variations in white blood cell or platelet counts. Further, the above variations were significantly correlated in patients undergoing cord blood transplantation and peripheral blood stem cell transplantation, but not in those undergoing bone marrow transplantation.

Conclusions

These findings demonstrate that RBC count is associated with variations in blood tacrolimus concentration, with the relevance of this association depending on the source of transfused stem cells. Thus, variations in RBC count might be useful for tacrolimus TDM.

Changes in the blood level, efficacy, and safety of tacrolimus in pregnancy and the lactation period in patients with systemic lupus erythematosus

OBJECTIVES

We investigated the efficacy and safety of tacrolimus (TAC) by monitoring its serum concentration for mothers and infants in pregnant patients with systemic lupus erythematosus (SLE).

METHODS

We measured trough concentrations of TAC in 25 pregnant patients with SLE to assess influence of TAC on the disease activity. Additionally, we measured the concentrations of TAC in umbilical arterial blood, breast milk, and breastfed infants to investigate the safety of TAC for the mothers and infants.

RESULTS

The trough concentrations of TAC in the mothers significantly decreased in the second trimester as compared with those before pregnancy. However, the decrease in the trough concentrations of TAC did not lead to the deterioration of SLE. When examined, the doses of TAC were significantly lower in the second trimester and postpartum in the deteriorating group than those in the non-deteriorating group. There were no adverse events by TAC in mothers and fetuses. The concentrations of TAC in the umbilical cord blood were lower than those in the maternal blood. The relative infant dose in breastfed infants of TAC was < 1%. The level of TAC in infant bloods was below detectable limits.

CONCLUSION

These findings suggest that TAC is one of the most effective and safest immunosuppressive drugs for use in pregnant patients with SLE.

A Mechanism-Based Population Pharmacokinetic Analysis Assessing the Feasibility of Efavirenz Dose Reduction to 400 mg in Pregnant Women

BACKGROUND

Reducing the dose of efavirenz can improve safety, reduce costs, and increase access for patients with HIV infection. According to the World Health Organization, a similar dosing strategy for all patient populations is desirable for universal roll-out; however, it remains unknown whether the 400 mg daily dose is adequate during pregnancy.

METHODS

We developed a mechanistic population pharmacokinetic model using pooled data from women included in seven studies (1968 samples, 774 collected during pregnancy). Total and free efavirenz exposure (AUC24 and C12) were predicted for 400 (reduced) and 600 mg (standard) doses in both pregnant and non-pregnant women.

RESULTS

Using a 400 mg dose, the median efavirenz total AUC24 and C12 during the third trimester of pregnancy were 91 and 87% of values among non-pregnant women, respectively. Furthermore, the median free efavirenz C12 and AUC24 were predicted to increase during pregnancy by 11 and 15%, respectively.

CONCLUSIONS

It was predicted that reduced-dose efavirenz provides adequate exposure during pregnancy. These findings warrant prospective confirmation.

Pregnancy in Renal Transplant Recipients and Donors

Women with renal transplants have restoration of fertility with improved kidney function; however, pregnancy rates in renal transplant recipients appear to be lower than the general population, which might be influenced by patient choice. Women with renal transplants need to evaluate potential neonatal outcomes, graft outcomes, and risks to their own health to make informed decisions about conception. Pregnancy should be carefully planned in renal transplant recipients to reduce risk for graft loss, optimize pregnancy outcomes, and ensure immunosuppression regimes are nonteratogenic. Neonatal outcomes remain significantly worse for women with renal transplants than healthy controls, particularly for those with reduced graft function, hence prepregnancy, antenatal, and postpartum care of women with renal transplants should be guided by a multidisciplinary team of nephrologists and specialist obstetricians.

Reproductive health in women following abdominal organ transplant

Fertility is commonly impaired in women with end-stage kidney and liver disease, although most women will have restoration of fertility within 1 year of transplant. Family planning is therefore critical to discuss with reproductive-aged transplant recipients in the early posttransplant period, in order to ensure timely initiation of contraception, and optimal timing for conception. For women seeking pregnancy, the risks to the mother, graft, and baby should be discussed, including evaluation of immunosuppression safety and potential for adjusting medications prior to conception. With an increasing number of transplant patients now breastfeeding, immunosuppression safety in lactation continues to carry great importance.

Ribavirin-induced anaemia reduced tacrolimus level in a hepatitis C patient receiving haemodialysis

A 37-year-old man with hepatitis C virus (HCV) genotype 3A developed renal failure. In 2007, the patient received a renal transplant and started receiving tacrolimus (Tac); the transplant subsequently failed. In April 2015, the patient restarted haemodialysis and in May initiated sofosbuvir 400 mg and ribavirin 400 mg daily. Baseline Tac level was 6.6 ng/mL and haemoglobin (Hb) was 10.3 g/dL. The patient then left the country for vacation and Hb was found to be dramatically low at 3.7 g/dL on return on 5 August. Ribavirin was put on hold, while darbepoetin dose was increased. On 23 August, Tac level was found undetectable; hence, dosage was increased. Hb eventually bounced back to >10 g/dL in October and Tac to 7.2 ng/mL; ribavirin was restarted at 200 mg three times weekly. HCV RNA level was undetectable at 3 months and remained undetectable 12 weeks after therapy finished.

Placental disposition of the immunosuppressive drug tacrolimus in renal transplant recipients and in ex vivo perfused placental tissue

Currently, tacrolimus is the most potent immunosuppressive agent for renal transplant recipients and is commonly prescribed during pregnancy. As data on placental exposure and transfer are limited, we studied tacrolimus placental handling in samples obtained from renal transplant recipients. We found transfer to venous umbilical cord blood, but particularly noted a strong placental accumulation. In patient samples, tissue concentrations in a range of 55-82 ng/g were found. More detailed ex vivo dual-side perfusions of term placentas from healthy women revealed a tissue-to-maternal perfusate concentration ratio of 113 ± 49 (mean ± SEM), underlining the placental accumulation found in vivo. During the 3 h ex vivo perfusion interval no placental transfer to the fetal circulation was observed. In addition, we found a non-homogeneous distribution of tacrolimus across the perfused cotyledons. In conclusion, we observed extensive accumulation of tacrolimus in placental tissue. This warrants further studies into potential effects on placental function and immune cells of the placenta.

Pregnancy and Glomerular Disease: A Systematic Review of the Literature with Management Guidelines

During pregnancy, CKD increases both maternal and fetal risk. Adverse maternal outcomes include progression of underlying renal dysfunction, worsening of urine protein, and hypertension, whereas adverse fetal outcomes include fetal loss, intrauterine growth restriction, and preterm delivery. As such, pregnancy in young women with CKD is anxiety provoking for both the patient and the clinician providing care, and because the heterogeneous group of glomerular diseases often affects young women, this is an area of heightened concern. In this invited review, we discuss pregnancy outcomes in young women with glomerular diseases. We have performed a systematic review in attempt to better understand these outcomes among young women with primary GN, we review the studies of pregnancy outcomes in lupus nephritis, and finally, we provide a potential construct for management. Although it is safe to say that the vast majority of young women with glomerular disease will have a live birth, the counseling that we can provide with respect to individualized risk remains imprecise in primary GN because the existing literature is extremely dated, and all management principles are extrapolated primarily from studies in lupus nephritis and diabetes. As such, the study of pregnancy outcomes and management strategies in these rare diseases requires a renewed interest and a dedicated collaborative effort.

Practical Recommendations for Long-term Management of Modifiable Risks in Kidney and Liver Transplant Recipients: A Guidance Report and Clinical Checklist by the Consensus on Managing Modifiable Risk in Transplantation (COMMIT) Group

Short-term patient and graft outcomes continue to improve after kidney and liver transplantation, with 1-year survival rates over 80%; however, improving longer-term outcomes remains a challenge. Improving the function of grafts and health of recipients would not only enhance quality and length of life, but would also reduce the need for retransplantation, and thus increase the number of organs available for transplant. The clinical transplant community needs to identify and manage those patient modifiable factors, to decrease the risk of graft failure, and improve longer-term outcomes.COMMIT was formed in 2015 and is composed of 20 leading kidney and liver transplant specialists from 9 countries across Europe. The group's remit is to provide expert guidance for the long-term management of kidney and liver transplant patients, with the aim of improving outcomes by minimizing modifiable risks associated with poor graft and patient survival posttransplant.The objective of this supplement is to provide specific, practical recommendations, through the discussion of current evidence and best practice, for the management of modifiable risks in those kidney and liver transplant patients who have survived the first postoperative year. In addition, the provision of a checklist increases the clinical utility and accessibility of these recommendations, by offering a systematic and efficient way to implement screening and monitoring of modifiable risks in the clinical setting.

Pregnancy-related pharmacokinetic changes

The pharmacokinetics of many drugs are altered by pregnancy. Drug distribution and protein binding are changed by pregnancy. While some drug metabolizing enzymes have an apparent increase in activity, others have an apparent decrease in activity. Not only is drug metabolism affected by pregnancy, but renal filtration is also increased. In addition, pregnancy alters the apparent activities of multiple drug transporters resulting in changes in the net renal secretion of drugs.

Basic obstetric pharmacology

Pregnancy is associated with a variety of physiological changes that can alter the pharmacokinetics and pharmacodynamics of several drugs. However, limited data exists on the pharmacokinetics and pharmacodynamics of the majority of the medications used in pregnancy. In this article, we first describe basic concepts (drug absorption, bioavailability, distribution, metabolism, elimination, and transport) in pharmacokinetics. Then, we discuss several physiological changes that occur during pregnancy that theoretically affect absorption, distribution, metabolism, and elimination. Further, we provide a brief review of the literature on the clinical pharmacokinetic studies performed in pregnant women in recent years. In general, pregnancy increases the clearance of several drugs and correspondingly decreases drug exposure during pregnancy. Based on current drug exposure measurements during pregnancy, alterations in the dose or dosing regimen of certain drugs are essential during pregnancy. More pharmacological studies in pregnant women are needed to optimize drug therapy in pregnancy.

Safety of tacrolimus in pregnancy

QUESTION

I have a 30-year-old patient who had a kidney transplant 2 years ago. She is now planning a pregnancy. She has been treated with tacrolimus since her transplant. Will it be safe for the fetus if she continues to take it during the pregnancy or should she switch to a different antirejection medication?

ANSWER

If your patient is stable while taking tacrolimus, there is no reason to switch. The current available information does not suggest that tacrolimus increases the risk of major congenital malformations above the baseline risk in the general population. Premature birth and low birth weight are often reported in this population; however, these effects are frequently reported in pregnant transplant patients treated with other immunosuppressant agents and probably reflect the effects of the maternal condition. As there are some reports of hyperkalemia and renal impairment in infants exposed to tacrolimus in utero, kidney function and electrolytes should be monitored in exposed neonates.

Breast-feeding after transplantation

Transplantation affords recipients the potential for a full life and, for some, parenthood. Female transplant recipients must continue to take immunosuppression during pregnancy and breast-feeding. This article reviews case and series reports regarding breast-feeding in those taking transplant medications. Avoidance of breast-feeding has been the customary advice because of the potential adverse effects of immunosuppressive exposure on the infant. Subsequent studies have demonstrated that not all medication exposure translates to risk for the infant, that the exposure in utero is greater than via breast milk and that no lingering effects due to breast-feeding have been found to date in infants who were breast-fed while their mothers were taking prednisone, azathioprine, cyclosporine, and/or tacrolimus. Thus, except for those medications where clinical information is inadequate (mycophenolic acid products, sirolimus, everolimus, and belatacept), the recommendation for transplant recipients regarding breast-feeding has evolved into one that is cautiously optimistic.

Tacrolimus placental transfer at delivery and neonatal exposure through breast milk

AIM(S)

The current investigation aims to provide new insights into fetal exposure to tacrolimus in utero by evaluating maternal and umbilical cord blood (venous and arterial), plasma and unbound concentrations at delivery. This study also presents a case report of tacrolimus excretion via breast milk.

METHODS

Maternal and umbilical cord (venous and arterial) samples were obtained at delivery from eight solid organ allograft recipients to measure tacrolimus and metabolite bound and unbound concentrations in blood and plasma. Tacrolimus pharmacokinetics in breast milk were assessed in one subject.

RESULTS

Mean (±SD) tacrolimus concentrations at the time of delivery in umbilical cord venous blood (6.6 ± 1.8 ng ml(-1)) were 71 ± 18% (range 45-99%) of maternal concentrations (9.0 ± 3.4 ng ml(-1)). The mean umbilical cord venous plasma (0.09 ± 0.04 ng ml(-1)) and unbound drug concentrations (0.003 ± 0.001 ng ml(-1)) were approximately one fifth of the respective maternal concentrations. Arterial umbilical cord blood concentrations of tacrolimus were 100 ± 12% of umbilical venous concentrations. In addition, infant exposure to tacrolimus through the breast milk was less than 0.3% of the mother's weight-adjusted dose.

CONCLUSIONS

Differences between maternal and umbilical cord tacrolimus concentrations may be explained in part by placental P-gp function, greater red blood cell partitioning and higher haematocrit levels in venous cord blood. The neonatal drug exposure to tacrolimus via breast milk is very low and likely does not represent a health risk to the breastfeeding infant.

The challenge of pregnancy for patients with SLE

Pregnancy poses an important challenge for doctors looking after women with systemic lupus erythematosus. Knowledge about safety of medications, the effect of pregnancy on such disease, and vice versa, together with multidisciplinary team care, are basic cornerstones needed to provide the best obstetric and medical care to these women. Pre-conceptional counselling constitutes the ideal scenario where a patient's previous obstetric history, organ damage, disease activity, serological profile and additional medical history can be summarized. Important issues regarding medication adjustment, planned scans and visits, and main risks discussion should also be raised at this stage. Planned pregnancies lead to better outcomes for both mothers and babies. Close surveillance throughout pregnancy and the puerperium, and tailored management approach guarantee the highest rates of successful pregnancies in these women.

Pregnancy and pharmacogenomics in the context of drug metabolism and response

It is well-known that profound physiological and biochemical changes occur throughout the course of pregnancy. At the same time, the role of pharmacogenomics in modulating the metabolism and response profile to numerous medications has been elucidated. Yet, the clinical impact of pharmacogenomics during pregnancy is less well understood. We present an overview of factors modulating the pharmacokinetics and pharmacodynamics of medications throughout the time span of pregnancy while providing insights on how pharmacogenomics may contribute to interindividual variability in drug metabolism and response amongst pregnant women.

Inflammatory bowel disease in women of reproductive age

Management of inflammatory bowel disease in women of reproductive age requires special attention. Even though fertility in women without previous pelvis surgery is similar to the general population, active disease at conception and during pregnancy can lead to unfavorable pregnancy and fetal outcomes. In general, most medications needed to treat inflammatory bowel disease are low risk during pregnancy and breastfeeding. Achieving and maintaining disease remission, patient education, and a multidisciplinary team approach is the key to a successful pregnancy.

Obstetric Pharmacokinetic Dosing Studies are Urgently Needed

Use of pharmacotherapy during pregnancy is common and increasing. Physiologic changes during pregnancy may significantly alter the overall systemic drug exposure, necessitating dose changes. A search of PubMed for pharmacokinetic clinical trials showed 494 publications during pregnancy out of 35,921 total pharmacokinetic published studies (1.29%), from the late 1960s through August 31, 2013. Closer examination of pharmacokinetic studies in pregnant women published since 2008 (81 studies) revealed that about a third of the trials were for treatment of acute labor and delivery issues, a third included studies of infectious disease treatment during pregnancy, and the remaining third were for varied ante-partum indications. Approximately, two-thirds of these recent studies were primarily funded by government agencies worldwide, one-quarter were supported by private non-profit foundations or combinations of government and private funding, and slightly <10% were supported by pharmaceutical industry. As highlighted in this review, vast gaps exist in pharmacology information and evidence for appropriate dosing of medications in pregnant women. This lack of knowledge and understanding of drug disposition throughout pregnancy place both the mother and the fetus at risk for avoidable therapeutic misadventures - suboptimal efficacy or excess toxicity - with medication use in pregnancy. Increased efforts to perform and support obstetric dosing and pharmacokinetic studies are greatly needed.

Update on pregnancy and breastfeeding in the era of biologics

Inflammatory bowel diseases are chronic conditions that frequently affect patients during their childbearing years. Considering the characteristics of disease and the medications used to treat it, several issues arise in the care of these patients when they attempt or achieve conception. We review the most current evidence concerning fertility and pregnancy outcomes in patients with inflammatory bowel diseases. With the exception of those women who undergo pelvic surgery, patients with inflammatory bowel diseases have no decreased fertility. Sulfasalazine decreases fertility in men. When looking at obstetrical outcomes, active disease at conception is associated with an increased risk of preterm delivery and low birth weight. While most medications used to treat inflammatory bowel diseases are low risk, some precautions need to be taken and the risk-to-benefit ratio needs to be considered on an individualized basis. In general, aminosalicylates and thiopurines should be continued, but methotrexate is contraindicated. Anti-tumour necrosis factor agents are considered safe to continue but full monoclonal antibodies do cross the placenta. As a general rule, the it is important to counsel women that conception is optimal when disease is in remission, as adverse obstetrical outcomes are directly associated with disease activity. Clinicians need to educate patients before, during and after conception, emphasizing treatment compliance.

Women and transplantation: fertility, sexuality, pregnancy, contraception

Since 1958, thousands of women with kidney transplants have become pregnant. Although most pregnancies in kidney transplant recipients are successful, they are high-risk endeavors. This seems more a function of the associated issues and comorbidities that often affect individuals with kidney transplants (eg, hypertension) or immunosuppression side effects rather than the kidney transplant per se. Regardless of the underlying pathophysiology, these pregnancies are associated with a high rate of preeclampsia diagnoses, preterm deliveries, Cesarean sections, and small-for-gestational-age babies. Given these risks, it is critical to counsel and inform transplant recipients and prospective transplant recipients of childbearing age and their partners regarding many aspects of pregnancy, including the need for contraception to prevent pregnancy after transplant, immunosuppression concerns, and the potential effect of pregnancy on the outcome of the mother, baby, and kidney transplant.

Interpreting tacrolimus concentrations during pregnancy and postpartum

Pregnancy after 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 red blood cell 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, although 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.

Pregnancy management and outcome in women with chronic kidney disease

An increasing number of pregnancies occur in the presence of chronic kidney diseases (CKD), mainly including chronic glomerulonephritis (GN), diabetic nephropathy (DN), and lupus nephritis (LN). The most important factor affecting fetal and maternal prognosis is the degree of renal function at conception. In the majority of patients with mild renal function impairment, and well-controlled blood pressure, pregnancy is usually successful and does not alter the natural course of maternal renal disease. Conversely, fetal outcome and long-term maternal renal function might be seriously threatened by pregnancy in women with moderate or severe renal function impairment. The last few years, advances in our knowledge about the interaction of pregnancy and renal function resulted in the improvement of fetal outcome in patients with chronic renal failure and also in the management of pregnant women with end-stage renal disease (ESRD) maintained on dialysis. However, women with impaired renal function and those on dialysis should be carefully counseled about the risks of pregnancy.

Drug metabolism and transport during pregnancy: how does drug disposition change during pregnancy and what are the mechanisms that cause such changes?

There is increasing evidence that pregnancy alters the function of drug-metabolizing enzymes and drug transporters in a gestational-stage and tissue-specific manner. In vivo probe studies have shown that the activity of several hepatic cytochrome P450 enzymes, such as CYP2D6 and CYP3A4, is increased during pregnancy, whereas the activity of others, such as CYP1A2, is decreased. The activity of some renal transporters, including organic cation transporter and P-glycoprotein, also appears to be increased during pregnancy. Although much has been learned, significant gaps still exist in our understanding of the spectrum of drug metabolism and transport genes affected, gestational age-dependent changes in the activity of encoded drug metabolizing and transporting processes, and the mechanisms of pregnancy-induced alterations. In this issue of Drug Metabolism and Disposition, a series of articles is presented that address the predictability, mechanisms, and magnitude of changes in drug metabolism and transport processes during pregnancy. The articles highlight state-of-the-art approaches to studying mechanisms of changes in drug disposition during pregnancy, and illustrate the use and integration of data from in vitro models, animal studies, and human clinical studies. The findings presented show the complex inter-relationships between multiple regulators of drug metabolism and transport genes, such as estrogens, progesterone, and growth hormone, and their effects on enzyme and transporter expression in different tissues. The studies provide the impetus for a mechanism- and evidence-based approach to optimally managing drug therapies during pregnancy and improving treatment outcomes.