In vivo higher glucuronidation of mycophenolic acid in male than in female recipients of a cadaveric kidney allograft and under immunosuppressive therapy with mycophenolate mofetil

Women's health and kidney protective medications

PURPOSE OF REVIEW

We discuss the sex-based differences in the pharmacokinetics and pharmacodynamics of kidney protective medications and their implications on women's health.

RECENT FINDINGS

A critical examination of adverse drug reactions highlights the underrepresentation of women in clinical trials for kidney and cardiovascular protective drugs, such as SGLT2 inhibitors, ACE inhibitors, and endothelin receptor antagonists. This underscores the need for sex-specific analyses in clinical studies to accurately assess medication efficacy and safety.

SUMMARY

The research demonstrates that women are more likely to experience adverse events and less likely to benefit from certain treatments, emphasizing the urgent need for healthcare providers to adopt a sex-informed approach in prescribing practices. Future research should prioritize sex differences from the outset to enhance understanding and improve clinical outcomes for women with chronic kidney disease and cardiovascular conditions.

Gender and kidney transplantation

Kidney transplantation provides the best form of kidney replacement therapy with improvement in quality of life and longevity. However, disparity exists in its availability, utilisation and outcomes, not only due to donor availability or financial constraints but also arising from the influence of biological sex and its sociocultural attribute i.e., Gender. Women make up the majority of kidney donors but are less likely to be counselled regarding transpantation, be waitlisted or receive living/deceased donor kidney. Biological differences also contribute to differences in kidney transplantation among the sexes. Women are more likely to be sensitised owing to pregnancy, especially in multiparous individuals, complicating donor compatibility. A heightened immune system in women, evidenced by more autoimmune illnesses, increases the risk of allograft rejection and loss. Differences in the pharmacokinetics of transplant drugs owing to biological variances could also contribute to variability in outcomes. Transgender medicine is also increasingly becoming a relevant topic of study, providing greater challenges in the form of hormonal manipulations and anatomic changes. It is thus important to determine and study transplantation and its nuances in this backdrop to be able to provide relevant sex and gender-specific interventions and design better practices for optimum kidney transplant utilisation and outcomes.

Sex and Gender Differences in Kidney Transplantation

Sex and gender often are used interchangeably, but are two distinct entities, with sex being the biological attribute and gender including the social, psychological, and cultural aspects of one's identity. Kidney transplantation has been proven to be the best treatment for end-stage kidney disease, improving both quality of life and life-expectancy for most patients. However, gender disparities in access to and outcomes of kidney transplantation remain despite the plethora of evidence showing the advantages of kidney transplantation to our patients. Data have shown that women are less likely to be waitlisted for a kidney transplant and to receive a deceased donor or a living donor kidney. On the other hand, women are more likely than men to become living kidney donors. Although some state the latter is the result of the female gender to nurture and care for loved ones, others believe this observation is because women often are incompatible with their spouse or child because pregnancy is a strong sensitizing event, which stems from the biological rather than the social differences between the sexes. Influence of sex and gender is not limited to access to kidney transplantation, but rather exist in other areas of transplant medicine, such as the difference observed in transplant outcomes between the sexes, variability in immunosuppression metabolism, and even in more contemporary areas such as recent data showing sex-based differences in outcomes of kidney transplant recipients with coronavirus disease-2019, with males having an increased incidence of acute kidney injury and death.

Malignancy following heart transplantation: differences in incidence and prognosis between sexes - a multicenter cohort study

Male patients are at increased risk for developing malignancy postheart transplantation (HT); however, real incidence and prognosis in both genders remain unknown. The aim of this study was to assess differences in incidence and mortality related to malignancy between genders in a large cohort of HT patients. Incidence and mortality rates were calculated for all tumors, skin cancers (SCs), lymphoma, and nonskin solid cancers (NSSCs) as well as survival since first diagnosis of neoplasia. 5865 patients (81.6% male) were included. Total incidence rates for all tumors, SCs, and NSSCs were lower in females [all tumors: 25.7 vs. 44.8 per 1000 person-years; rate ratio (RR) 0.68, (0.60-0.78), P < 0.001]. Mortality rates were also lower in females for all tumors [94.0 (77.3-114.3) vs. 129.6 (120.9-138.9) per 1000 person-years; RR 0.76, (0.62-0.94), P = 0.01] and for NSSCs [125.0 (95.2-164.0) vs 234.7 (214.0-257.5) per 1000 person-years; RR 0.60 (0.44-0.80), P = 0.001], albeit not for SCs or lymphoma. Female sex was associated with a better survival after diagnosis of malignancy [log-rank p test = 0.0037; HR 0.74 (0.60-0.91), P = 0.004]. In conclusion, incidence of malignancies post-HT is higher in males than in females, especially for SCs and NSSCs. Prognosis after cancer diagnosis is also worse in males.

Differential effects of antiretroviral drug toxicity in male versus female children who are HIV-exposed but uninfected

: In recent years, widespread use of antiretroviral therapy (ART) during pregnancy has been increasingly effective in reducing risk of vertical transmission of HIV, with over 80% of pregnant women living with HIV now accessing ART, and a 41% reduction in new infections in children between 2010 and 2018. Despite these strides, the developmental toxicity of widely administered antiretroviral drugs (ARVs) remains poorly described and existing literature often fails to account for fetal and infant sex as a variable. Recent reports have identified associations between in-utero exposure to commonly used antiretroviral regimens and alteration in neurodevelopment, growth, and metabolism amongst children who are HIV-exposed but uninfected, with findings of sex differences in the prevalence and severity of ARV toxicity. These differences are potentially explained by variable exposure to ARV drugs in utero or exacerbation of existing sex-linked risk factors. Fetal ARV exposure is mediated by placental and fetal drug transporters and metabolic enzymes, which may contribute to the manifestation of sex differences. Existing evidence of sex differences in ARV toxicity in fetal development is concerning, and demands further research to guide optimal treatment options for maternal health and prevention of vertical HIV transmission.

Influence of Calcineurin Inhibitor and Sex on Mycophenolic Acid Pharmacokinetics and Adverse Effects Post-Renal Transplant

Tacrolimus or cyclosporine is prescribed with mycophenolic acid posttransplant and contributes to interpatient variability in mycophenolic acid pharmacokinetics and response. Cyclosporine inhibits enterohepatic circulation of the metabolite mycophenolic acid glucuronide, which is not described with tacrolimus. This study investigated mycophenolic acid pharmacokinetics and adverse effects in stable renal transplant recipients and the association with calcineurin inhibitors, sex, and race. Mycophenolic acid and mycophenolic acid glucuronide area under the concentration-time curve from 0 to 12 hours (AUC0-12h ) and apparent clearance were determined at steady state in 80 patients receiving cyclosporine with mycophenolate mofetil and 67 patients receiving tacrolimus with mycophenolate sodium. Gastrointestinal adverse effects and hematologic parameters were evaluated. Statistical models evaluated mycophenolic acid pharmacokinetics and adverse effects. Mycophenolic acid AUC0-12h was 1.70-fold greater with tacrolimus (68.9 ± 30.9 mg·h/L) relative to cyclosporine (40.8 ± 17.6 mg·h/L); P < .001. Target mycophenolic acid AUC0-12h of 30-60 mg·h/L was achieved in 56.3% on cyclosporine compared with 34.3% receiving tacrolimus (P < .001). Mycophenolic acid clearance was 48% slower with tacrolimus (10.6 ± 4.7 L/h) relative to cyclosporine (20.5 ± 10.0 L/h); P < .001. Enterohepatic circulation occurred less frequently with cyclosporine (45%) compared with tacrolimus (78%); P < 0.001; with a 2.9-fold greater mycophenolic acid glucuronide AUC0-12h to mycophenolic acid AUC0-12h ratio (P < .001). Race did not affect mycophenolic acid pharmacokinetics. Gastrointestinal adverse effect scores were 2.2-fold higher with tacrolimus (P < .001) and more prominent in women (P = .017). Lymphopenia was more prevalent with tacrolimus (52.2%) than cyclosporine (22.5%); P < 0.001. Calcineurin inhibitors and sex contributed to interpatient variability in mycophenolic acid pharmacokinetics and adverse effects post-renal transplant, which could be attributed to differences in enterohepatic circulation.

Sex differences in the pharmacology of itch therapies-a narrative review

BACKGROUND

Chronic itch is the most common skin-related condition, associated with a high psychosocial and economic burden. In recent years, increasing evidence of sex differences in the perception, clinical presentation and treatment requirements of itch points towards potential benefits when using sex-adapted therapies. It is well-known that body composition, absorption, metabolism, elimination and adverse drug reactions (ADRs) differ between sexes, but only little is known about the impact of sex in the pharmacology of itch treatments, which could help to rationalise sex-adapted treatment strategies.

AIM

To evaluate and review sex effects in the pharmacokinetics and /-dynamics of drugs used to treat itch.

METHODS

In this narrative review we performed a PubMed and MEDLINE (Ovid) search using the terms (itch OR pruritus) AND (gender OR sex) AND (drug OR medication OR pharmacokinetics OR pharmacodynamics). Additional searches were performed for the topical and systemic drugs recommended by the European Guideline on Chronic Pruritus.

RESULTS

We found numerous reports with variable levels of evidence of sex effects with respect to the pharmacokinetics and/or pharmacodynamics of 14 drug classes used for the treatment of itch, including a total of 19 systemic and 3 topical drugs. Women seem to present higher plasma levels of several drugs used in itch treatment, including tri- and tetracyclic antidepressants (e.g. doxepin, amitriptyline, mirtazapine), serotonin reuptake inhibitors (e.g. paroxetine, sertraline, fluoxetine), immunosuppressive drugs (e.g. cyclosporine, mycophenolate mofetil), serotonin receptor antagonists (e.g. ondansetron) and betablockers (e.g. propranolol). Adverse drug reactions (ADRs) were generally more common in women. Being female was reported to be an independent risk factor for QTc-prolongation associated with antihistamines and tetracyclic antidepressants. Additionally, women seem to be more prone to sedative effects of antihistamines, and to suffer from a higher frequency as well as severity of side effects with systemic calcineurin inhibitors, opioid agonists, and opioid antagonists. Women were also sensitised more often to topically applied drugs. Of note, apart from only one experimental study with capsaicin, none of these reports were designed specifically to assess the effect of sex (and gender) in the treatment of itch.

DISCUSSION/CONCLUSION

Our review supports previous reports that sex is of importance in the pharmacokinetics and /-dynamics of several drugs used to treat itch although those drugs were mostly evaluated for non-itch indications. However, the results are limited by methodological limitations evident in most studies such as underrepresentation of women in clinical trials. This emphasises the need to study the impact of sex (and gender) in future itch trials to yield better outcomes and prevent ADRs in both sexes.

Adverse effects of mycophenolic acid in renal transplant recipients: gender differences

Background Mycophenolic acid is widely used immunosuppressive drug, associated with adverse effects which increase patient morbidity and decrease medication adherence. Objective To evaluate the adverse effects in renal transplant recipients under mycophenolate treatment with respect to gender. Setting University Clinical Centre of Nis, Clinic of Nephrology, Serbia. Method This research included 96 renal transplant recipients, who received immunosuppressive regimen, based on tacrolimus or cyclosporin A, prednisone and mycophenolic acid. The high-performance liquid chromatography method combined with protein precipitation was used for the analysis of mycophelate concentration in human plasma. Drug concentration and dose-adjusted concentration were determined with respect to the patients' gender. An adverse effect scoring system developed by nephrologists within the University of Buffalo Nephrology/Transplant Program was used to monitor adverse effects of therapy. Main outcome measure Individual and scores of adverse effects in relation to the dosing regimen and gender. Results Results showed statistically lower dose and concentrations in men compared to the women in our investigation group. Also, female patients demonstrated higher mean scores (cumulative and subscores) within the same dosing regimens of mycophenolic acid. The gastrointestinal score was significantly higher in women who received a dose greater than 720 mg compared to men (0.20 ± 0.12 vs 0.12 ± 0.12). Women demonstrated higher individual adverse effects such as diarrhea and skin changes (41.7 vs 17.0; p = 0.038 and 62.5 vs 30.2; p = 0.037, respectively). Conclusions The results of our research showed that recipients' gender may play an important role in pharmacokinetic profile of mycophenolic acid, suggesting that women had higher concentration of mycophenolic acid and more serious side effects.

Development of a Formula to Correct Particle-Enhanced Turbidimetric Inhibition Immunoassay Values so That it More Precisely Reflects High-Performance Liquid Chromatography Values for Mycophenolic Acid

Background

Mycophenolic acid (MPA) concentration measured by homogeneous particle-enhanced turbidimetric inhibition immunoassay (PETINA) may be overestimated due to its cross-reactivity with pharmacologically inactive MPA glucuronide (MPAG), as well as other minor metabolites, accumulated with renal function impairment or co-administered cyclosporine A. In contrast, high-performance liquid chromatography (HPLC) is precise because it can exclude the cross-reactivity. In this study, we assumed HPLC values for MPA (HPLC-MPA) as a reference and aimed to develop a formula correcting PETINA values for MPA (PETINA-MPA) to more precisely reflect HPLC-MPA.

Methods

MPA trough concentrations were measured both by HPLC-UV and PETINA in 39 samples issued from 39 solid-organ transplant recipients. MPAG concentrations were also measured using HPLC UV assay. We determined the impacts of renal function and coadministered calcineurin inhibitor on concentrations of MPA and MPAG measured by HPLC. Then, we evaluated the difference between PETINA-MPA and HPLC-MPA. Finally, we develop a formula to reflect HPLC-MPA by using multilinear regression analysis.

Results

MPAG concentration was negatively correlated with estimated glomerular filtration rate (eGFR) (R² = 0.376, P < 0.001), although MPA was not correlated with eGFR. There were no significant differences in MPA or MPAG concentrations per dose between the patients who were co-administered tacrolimus versus cyclosporine A. Finally, we developed the formulas to reflect HPLC-MPA:Formula 1: Estimated MPA concentration = 0.048 + 0.798 × PETINA-MPAFormula 2: Estimated MPA concentration = - 0.059 + 0.800 × PETINA-MPA + 0.002 × eGFRHowever, there was no significant improvement in the coefficient of determination with addition of eGFR in the formula, suggesting that HPLC-MPA can be well predicted by only 1 variable, PETINA-MPA.

Conclusions

This study developed a formula so that PETINA-MPA can be corrected to more precisely reflect HPLC-MPA.

Pharmacokinetic Variability of Mycophenolic Acid in Pediatric and Adult Patients With Hematopoietic Stem Cell Transplantation

The aim of this study was to evaluate the pharmacokinetic variations of mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), in both pediatric and adult patients following hematopoietic stem cell transplantation (HSCT). Twenty pediatric patients with a median age of 3 years (range 0.2-12 years) and 13 adult patients with a median age of 54 years (range 18-63 years) were enrolled. Blood samples were collected on days 0, 7, 14, 21, and 30 after allogeneic HSCT. Total and free (unbound) MPA as well as MPA 7-O-glucuronide (MPAG) were quantified using a validated LC-MS/MS assay. The plasma protein binding of MPA and MPAG did not change significantly in pediatric patients over the 1-month sampling period post-HSCT. However, it increased in adult patients from day 7 to day 30 post-HSCT, from 97.3 ± 0.8% to 98.3 ± 0.6% for MPA (P < .05), and 74.6 ± 9.4% to 82.9 ± 8.1% for MPAG (P < .05). The plasma protein binding of MPA was significantly higher in males compared to females in both pediatric (98.3 ± 1.1% vs 97.4 ± 1.1%) and adult (98.1 ± 0.7% vs 97.4 ± 1.2%) patients (P < .05). The MPAG/MPA ratios on a milligram-per-kilogram dose basis in adult patients were significantly higher than those in pediatric patients (4.3 ± 3.4 vs 2.4 ± 2.6; P < .05). Time-dependent plasma protein binding and age-related differences in MPA metabolism at least in part impact the reported large intra- and interindividual variability in MPA pharmacokinetics. These patient and pharmacologic factors, if incorporated into MMF regimen design and modification, may contribute to the rational dose selection of MMF in HSCT patients.

Sex differences in transplantation

Sex plays a role in the incidence and progression of a wide variety of diseases and conditions related to transplantation. Additionally, a growing body of clinical and experimental evidence suggests that sex can impact the pharmacokinetics and pharmacodynamics of several commonly used immunosuppressive and anti-infective drugs in transplant recipients. A better understanding of these sex differences will facilitate advances in individualizing treatment for patients and improve outcomes of solid organ transplantation. Here, we provide a review of sex-related differences in transplantation and highlight opportunities for future research directions.

Influence of sex and race on mycophenolic acid pharmacokinetics in stable African American and Caucasian renal transplant recipients

BACKGROUND AND OBJECTIVES

No evaluation of sex and race influences on mycophenolic acid (MPA) pharmacokinetics and adverse effects (AEs) during enteric-coated mycophenolate sodium (ECMPS) and tacrolimus immunosuppression are available. The primary objective of this study was to investigate the influence of sex and race on MPA and MPA glucuronide (MPAG) pharmacokinetics in stable renal transplant recipients receiving ECMPS and tacrolimus

METHODS

The pharmacokinetics of MPA and MPAG and their associated gastrointestinal AEs were investigated in 67 stable renal transplant recipients: 22 African American males (AAMs), 13 African American females (AAFs), 16 Caucasian males (CMs), and 16 Caucasian females (CFs) receiving ECMPS and tacrolimus. A validated gastrointestinal AE rating included diarrhea, dyspepsia, vomiting, and acid-suppressive therapy was completed. Apparent clearance, clearance normalized to body mass index (BMI), area under the concentration-time curve from time zero to 12 h (AUC12) and dose-normalized AUC12 (AUC*) were determined using a statistical model that incorporated gastrointestinal AE and clinical covariates.

RESULTS

Males had more rapid apparent MPA clearance (CMs 13.8 ± 6.27 L/h vs. AAMs 10.2 ± 3.73 L/h) than females (CFs 8.70 ± 3.33 L/h and AAFs 9.71 ± 3.94 L/h; p = 0.014) with a race-sex interaction (p = 0.043). Sex differences were observed in MPA clearance/BMI (p = 0.033) and AUC* (p = 0.033). MPA AUC12 was greater than 60 mg·h/L in 57 % of renal transplant recipients (RTR) with 71 % of patients demonstrating gastrointestinal AEs and a higher score noted in females. In all patients, females exhibited 1.40-fold increased gastrointestinal AE scores compared with males (p = 0.024). Race (p = 0.044) and sex (p = 0.005) differences were evident with greater MPAG AUC12 in AAFs and CFs.

CONCLUSION

Sex and race differences were evident, with females having slower MPA clearance, higher MPAG AUC12, and more severe gastrointestinal AEs. These findings suggest sex and race should be considered during MPA immunosuppression.

Effects of amoxicillin/clavulanic acid on the pharmacokinetics of valproic acid

Valproic acid (VPA) is mainly metabolized via glucuronide, which is hydrolyzed by β-glucuronidase and undergoes enterohepatic circulation. Amoxicillin/clavulanic acid (AMC) administration leads to decreased levels of β-glucuronidase-producing bacteria, suggesting that these antibiotics could interrupt enterohepatic circulation and thereby alter the pharmacokinetics of VPA. This study aimed to evaluate the effects of AMC on the pharmacokinetics of VPA. This was an open-label, two-treatment, one-sequence study in 16 healthy volunteers. Two treatments were evaluated; treatment VPA, in which a single dose of VPA 500 mg was administered, and treatment AMC + VPA, in which multiple doses of AMC 500/125 mg were administered three times daily for 7 days and then a single dose of VPA was administered. Blood samples were collected up to 48 hours. Pharmacokinetic parameters were calculated using noncompartmental methods. Fifteen subjects completed the study. Systemic exposures and peak concentrations of VPA were slightly lower with treatment AMC + VPA than with treatment VPA (AUC_last, 851.0 h·mg/L vs 889.6 h·mg/L; C_max, 52.1 mg/L vs 53.0 mg/L). There were no significant between-treatment effects on pharmacokinetics (95% confidence interval [CI]) of AUC_last and C_max (95.7 [85.9–106.5] and 98.3 [91.6–105.6], respectively). Multiple doses of AMC had no significant effects on the pharmacokinetics of VPA; thus, no dose adjustment is necessary.

Pharmacokinetics of mycophenolic acid and its phenyl glucuronide metabolite in kidney transplant recipients with renal impairment

INTRODUCTION

The aim of the study was to analyse the influence of renal impairment on the pharmacokinetic parameters (PK) of mycophenolic acid (MPA) and its glucuronide metabolite (MPAG) in renal transplant recipients.

MATERIAL AND METHODS

The study included 43 adult patients during the maintenance period (> 6 months) following renal transplantation, treated with mycophenolate mofetil (MMF), calcineurin inhibitors (CNI) (tacrolimus or cyclosporine) and steroids. The study compared patients with normal renal function (n = 17; creatinine clearance (C(cr)) > 60 ml/min) and with renal impairment (n = 26; C(cr) < 60 ml/min). Areas under the 4-h curve (AUC(0-4 h)) of MPA and MPAG were determined using a validated HPLC method.

RESULTS

The renal impairment group showed significantly increased AUC(0-4 h) and pre-dose (C(0)) for MPAG compared to patients with normal renal function and increased MPA C(0). However, there was no significant difference in MPA AUC(0-4 h) between patients with renal impairment and patients with normal renal function. In multivariate analysis some MPA and MPAG PK parameters were correlated with sex, CNI co-administered and body weight.

CONCLUSIONS

Although MPAG is an inactive metabolite, its accumulation in patients with renal impairment can be unfavourable. The results of our study indicate that solely MPA C(0) determination in patients receiving MMF may be insufficient in clinical practice because of great inter-patient variability of this PK parameter caused mainly by enterohepatic recirculation.

Steady-state mycophenolate mofetil pharmacokinetic parameters enable prediction of systemic lupus erythematosus clinical flares: an observational cohort study

Introduction

The aim of this study was to determine whether mycophenolate mofetil (MMF) pharmacokinetics (PK) under combined MMF and prednisone remission-maintenance therapy can predict systemic lupus erythematosus (SLE) clinical flares.

Methods

At inclusion, steady-state PK parameters of the MMF active form, mycophenolic acid (MPA), and its glucuronide metabolite (MPAG) were determined for 25 stable SLE patients without renal manifestations. Disease activity was assessed during 6 months of follow-up. Potential relationships between those entry MMF-PK variables and clinical outcome were analyzed.

Results

MMF controlled disease activity in 17 patients (successes) and failed to do so for 8 others (failures). For failures and successes, respectively, entry MPA areas under the time-concentration curve between 0 and 12 hours (AUC_{0-12 h}) (medians: 37.7 vs 73.1 mg/h/L, P = 0.003) and MPA 12-hour trough concentrations (C_{12 h}) (medians: 1.5 vs 3.7 mg/L, P = 0.008) were significantly lower, and inclusion MPAG/MPA C_{12 h} ratios (medians: 18.7 vs 10.2, P = 0.02) were significantly higher. According to our receiver operating characteristics curve analysis, MPA C_{12 h} was best able to discriminate a flare during follow-up (93% sensitivity, 85% specificity). A 3-mg/L cut-off had 92% negative-predictive value for developing a flare during follow-up.

Conclusions

For our SLE patients without renal manifestations, clinical flares developing under maintenance therapy were associated with steady-state inclusion MPA C_{12 h} < 3 mg/L.

Therapeutic drug monitoring of mycophenolic acid: does it improve patient outcome?

Treatment with the immunosuppressive agent mycophenolate mofetil (MMF) decreases the risk of rejection after renal transplantation and improves graft survival compared with azathioprine. The exposure to the active metabolite mycophenolic acid (MPA) is correlated to the risk of developing acute rejection. The interpatient variability in exposure of MPA is wide relative to the proposed therapeutic window of the MPA AUC(0 12) (30 - 60 mg.h/l). The pharmacokinetics of MPA are influenced by patient characteristics such as gender, time after transplantation, serum albumin concentration, renal function, comedication and pharmacogenetic factors. Therapeutic drug monitoring is likely to reduce inter-patient variability. Limited sampling strategies are used to predict the full AUC(0 12). Three prospective randomised studies compared concentration controlled MMF therapy to a fixed-dose regimen. Preliminary outcomes of these studies showed conflicting results and longer follow up is needed to further clarify the role of therapeutic drug monitoring in increasing the therapeutic potential of MMF.

Clinical pharmacokinetics and pharmacodynamics of mycophenolate in solid organ transplant recipients

This review aims to provide an extensive overview of the literature on the clinical pharmacokinetics of mycophenolate in solid organ transplantation and a briefer summary of current pharmacodynamic information. Strategies are suggested for further optimisation of mycophenolate therapy and areas where additional research is warranted are highlighted. Mycophenolate has gained widespread acceptance as the antimetabolite immunosuppressant of choice in organ transplant regimens. Mycophenolic acid (MPA) is the active drug moiety. Currently, two mycophenolate compounds are available, mycophenolate mofetil and enteric-coated (EC) mycophenolate sodium. MPA is a potent, selective and reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), leading to eventual arrest of T- and B-lymphocyte proliferation. Mycophenolate mofetil and EC-mycophenolate sodium are essentially completely hydrolysed to MPA by esterases in the gut wall, blood, liver and tissue. Oral bioavailability of MPA, subsequent to mycophenolate mofetil administration, ranges from 80.7% to 94%. EC-mycophenolate sodium has an absolute bioavailability of MPA of approximately 72%. MPA binds 97-99% to serum albumin in patients with normal renal and liver function. It is metabolised in the liver, gastrointestinal tract and kidney by uridine diphosphate gluconosyltransferases (UGTs). 7-O-MPA-glucuronide (MPAG) is the major metabolite of MPA. MPAG is usually present in the plasma at 20- to 100-fold higher concentrations than MPA, but it is not pharmacologically active. At least three minor metabolites are also formed, of which an acyl-glucuronide has pharmacological potency comparable to MPA. MPAG is excreted into the urine via active tubular secretion and into the bile by multi-drug resistance protein 2 (MRP-2). MPAG is de-conjugated back to MPA by gut bacteria and then reabsorbed in the colon. Mycophenolate mofetil and EC-mycophenolate sodium display linear pharmacokinetics. Following mycophenolate mofetil administration, MPA maximum concentration usually occurs in 1-2 hours. EC-mycophenolate sodium exhibits a median lag time in absorption of MPA from 0.25 to 1.25 hours. A secondary peak in the concentration-time profile of MPA, due to enterohepatic recirculation, often appears 6-12 hours after dosing. This contributes approximately 40% to the area under the plasma concentration-time curve (AUC). The mean elimination half-life of MPA ranges from 9 to 17 hours. MPA displays large between- and within-subject pharmacokinetic variability. Dose-normalised MPA AUC can vary more than 10-fold. Total MPA concentrations should be interpreted with caution in patients with severe renal impairment, liver disease and hypoalbuminaemia. In such individuals, MPA and MPAG plasma protein binding may be altered, changing the fraction of free MPA available. Apparent oral clearance (CL/F) of total MPA appears to increase in proportion to the increased free fraction, with a reduction in total MPA AUC. However, there may be little change in the MPA free concentration. Ciclosporin inhibits biliary excretion of MPAG by MRP-2, reducing enterohepatic recirculation of MPA. Exposure to MPA when mycophenolate mofetil is given in combination with ciclosporin is approximately 30-40% lower than when given alone or with tacrolimus or sirolimus. High dosages of corticosteroids may induce expression of UGT, reducing exposure to MPA. Other co-medications can interfere with the absorption, enterohepatic recycling and metabolism of mycophenolate. Most pharmacokinetic investigations of MPA have involved mycophenolate mofetil rather than EC-mycophenolate sodium therapy. In population pharmacokinetic studies, MPA CL/F in adults ranges from 14.1 to 34.9 L/h (ciclosporin co-therapy) and from 11.9 to 25.4 L/h (tacrolimus co-therapy). Patient bodyweight, serum albumin concentration and immunosuppressant co-therapy have a significant influence on CL/F. The majority of pharmacodynamic data on MPA have been obtained in patients receiving mycophenolate mofetil therapy in the first year after kidney transplantation. Low MPA AUC is associated with increased incidence of biopsy-proven acute rejection. Gastrointestinal adverse events may be dose related. Leukopenia and anaemia have been associated with high MPA AUC, trough concentration and metabolite concentrations in some, but not all, studies. High free MPA exposure has been identified as a risk factor for leukopenia in some investigations. Targeting a total MPA AUC from 0 to 12 hours (AUC12) of 30-60 mg.hr/L is likely to minimise the risk of acute rejection and may reduce toxicity. IMPDH monitoring is in the early experimental stage. Individualisation of mycophenolate therapy should lead to improved patient outcomes. MPA AUC12 appears to be the most useful exposure measure for such individualisation. Limited sampling strategies and Bayesian forecasting are practical means of estimating MPA AUC12 without full concentration-time profiling. Target concentration intervention may be particularly useful in the first few months post-transplant and prior to major changes in anti-rejection therapy. In patients with impaired renal or hepatic function or hypoalbuminaemia, free drug measurement could be valuable in further interpretation of MPA exposure.

Concentrations of Mycophenolic Acid and Glucuronide Metabolites Under Concomitant Therapy With Cyclosporine or Tacrolimus

Mycophenolate mofetil [MMF, the prodrug of mycophenolic acid (MPA)] is usually administered at double doses with cyclosporine than with tacrolimus because it is believed that MPA exposure is lower during cyclosporine therapy. This study aimed to compare 12 hour, steady-state concentration-time profiles of MPA and its phenol- and acyl-glucuronide metabolites (MPAG and AcMPAG, respectively) in stable kidney transplant recipients maintained either on cyclosporine (n = 12) or tacrolimus (n = 12). During the absorption phase in the cyclosporine group, dose-normalized concentrations of total and free MPA were significantly higher but the overall area under the concentration-time curve (AUC0-12) was not significantly different. Additionally, exposure to AcMPAG was higher in the cyclosporine group (P < 0.05). Ten of 12 patients in the cyclosporine group were on ketoconazole therapy; however, the exposure to MPA or MPAG was not different when MMF was given orally to Sprague-Dawley rats with or without ketoconazole. In conclusion, cyclosporine modulates the disposition of MPA and metabolites differently from tacrolimus; however, patients on cyclosporine may not require double doses of MMF to achieve the same exposure.

Gender-Related Differences in Mycophenolate Mofetil-Induced Gastrointestinal Toxicity in Rats

Mycophenolate mofetil (MMF), the prodrug of mycophenolic acid (MPA), is included in current combination immunosuppressive regimens following organ transplant. Treatment with MMF often results in dose-limiting gastrointestinal (GI) side effects. The underlying mechanisms responsible for these side effects are not fully understood, but exposure of the intestinal epithelia to MPA during enterohepatic recycling may be involved. The present study demonstrated that female rats are more susceptible to MMF-induced GI toxicity than male rats. Female Sprague-Dawley rats treated chronically with an oral dose of 50 mg of MPA equivalents/kg/day experienced greater GI toxicity than male rats, as measured by diarrhea grade and weight loss. Intestinal microsomes harvested from the upper jejunum of female rats had approximately 3-fold lower MPA glucuronidation rates compared with male rats. In the remaining areas of the small and large intestine, there was also a trend toward decreased glucuronidation in the female rats. The area under the plasma concentration-time curve (AUC) for MPA following an oral dose of 50 mg of MPA equivalents/kg was roughly similar between genders, whereas the AUC for mycophenolic acid phenolic glucuronide (MPAG) was significantly lower in female rats. Female rats also excreted half of the biliary MPAG as male rats. The greater susceptibility of female rats to MMF-induced gastrointestinal toxicity, despite diminished intestinal MPA exposure via reduced biliary excretion of MPAG, may result from reduced protection of enterocytes by in situ glucuronidation. Likewise, susceptibility to MMF-induced GI toxicity in humans may also result from variable intestinal glucuronidation due to UDP glucuronosyltransferase polymorphisms or differential expression.

Pharmacogenetic differences and drug-drug interactions in immunosuppressive therapy

With the advent of new immunosuppressants and formulations, the elucidation of molecular targets and the evolution of therapeutic drug monitoring, the field of organ transplantation has witnessed significant reductions in acute rejection rates, prolonged graft survival and improved patient outcome. Nonetheless, challenges persist in the use of immunosuppressive medications. Marked interindividual variability remains in drug concentrations and drug response. As medications with narrow therapeutic indices, variations in immunosuppressant concentrations can result in acute toxicity or transplant rejection. Recent studies have begun to identify factors that contribute to this variability with the promise of tailoring immunosuppressive regimens to the individual patient. These advances have uncovered differences in genetic composition in drug-metabolising enzymes, drug transporters and drug targets. This review focuses on commonly used maintenance immunosuppressants (including cyclosporin, mycophenolate mofetil, tacrolimus, sirolimus, everolimus, azathioprine and corticosteroids), examines current studies on pharmacogenetic differences in drug-metabolising enzymes, drug transporters and drug targets and addresses common drug-drug interactions with immunosuppressant therapies. The potential role of drug-metabolising enzymes in contributing to these drug-drug interactions is briefly considered.

Determinants of mycophenolic acid levels after renal transplantation

There are data suggesting an association between mycophenolic acid (MPA) levels and acute rejection and toxicity in renal transplant recipients treated with mycophenolate mofetil (MMF), and therefore, knowledge of factors determining MPA levels may aid in accurate adjustment of MMF dosage. A total of 4970 samples taken 12 hours postdose were analyzed for MPA by immunoassay at regular intervals from the first week posttransplantation in 117 renal transplant patients immunosuppressed with MMF and tacrolimus in a steroid-sparing regimen (prednisolone for the first 7 days only). MPA levels rose in the first 3 months and stabilized thereafter; dose-normalized MPA levels rose throughout the first 12 months and subsequently stabilized. Multivariate analysis by means of a population-averaged linear regression showed positive associations between MPA level and total daily dose (P < 0.001) but not individual dose or total daily dose corrected for body weight. Positive associations were also seen with serum albumin (P = 0.01), tacrolimus trough level (P = 0.01), and female gender (P = 0.002). The association with tacrolimus levels diminished with time. Negative associations were seen between MPA level and higher estimated creatinine clearance (P < 0.001), and also with increasing alanine transaminase levels (P = 0.002), the use of oral antibiotics (P < 0.001), and infective diarrhea (P < 0.001). The latter findings may be related to changes in enterohepatic recirculation of MPA. Many clinical variables show associations with trough MPA levels. An understanding of these factors may aid therapeutic monitoring of MMF.

Cardiovascular drug therapy in women

Cardiovascular disease has been the leading cause of morbidity and mortality in American women; yet, until recently, there was no mandate to specifically include women in clinical trials of the major cardiovascular drugs. Despite new regulations, there is still a lack of readily available data for the clinician to use when planning drug therapy for women, as many of the drugs in use today were developed and tested prior to the new regulations being in effect. The purpose of this article is to provide advanced practice nurses with the most current information on the use of cardiovascular drugs in women. Information on the unique biological features of women is first presented to provide background material for subsequent sections. This is followed by an explanation of pharmacokinetic processes in women to include information on absorption, distribution, and clearance of drugs. A brief review of the effects of the phases of the menstrual cycle on drug therapy is given and then issues related to the profound physiologic changes in pregnancy and subsequent effects on drug therapy are reviewed. An analysis of the strength of the available evidence on drug therapies in women from the major trials on acute coronary syndromes, heart failure, dyslipidemia, atrial fibrillation, and hypertension is provided. Finally, implications for practice, including recommendations for drug prescription, are summarized.

IDENTIFICATION OF THE UDP-GLUCURONOSYLTRANSFERASE ISOFORMS INVOLVED IN MYCOPHENOLIC ACID PHASE II METABOLISM

Mycophenolic acid (MPA), the active metabolite of the immunosuppressant mycophenolate mofetil is primarily metabolized by glucuronidation. The nature of UDP-glucuronosyltransferases (UGTs) involved in this pathway is still debated. The present study aimed at identifying unambiguously the UGT isoforms involved in the production of MPA-phenyl-glucuronide (MPAG) and MPA-acylglucuronide (AcMPAG). A liquid chromatography-tandem mass spectrometry method allowing the identification and determination of the metabolites of mycophenolic acid was developed. The metabolites were characterized in urine and plasma samples from renal transplant patients under mycophenolate mofetil therapy and in vitro after incubation of mycophenolic acid with human liver (HLM), kidney (HKM), or intestinal microsomes (HIM). The UGT isoforms involved in MPAG or AcMPAG production were investigated using induced rat liver microsomes, heterologously expressed UGT (Supersomes), and chemical-selective inhibition of HLM, HKM, and HIM. The three microsomal preparations produced MPAG, AcMPAG, and two mycophenolate glucosides. Among the 10 UGT isoforms tested, UGT 1A9 was the most efficient for MPAG synthesis with a K(m) of 0.16 mM, close to that observed for HLM (0.18 mM). According to the chemical inhibition experiments, UGT 1A9 is apparently responsible for 55%, 75%, and 50% of MPAG production by the liver, kidney, and intestinal mucosa, respectively. Although UGT 2B7 was the only isoform producing AcMPAG in a significant amount, the selective inhibitor azidothymidine only moderately reduced this production (approximately -25%). In conclusion, UGT 1A9 and 2B7 were clearly identified as the main UGT isoforms involved in mycophenolic acid glucuronidation, presumably due to their high hepatic and renal expression.

The influence of calcineurin inhibitors on mycophenolic acid pharmacokinetics

Despite the fact that concentrations of mycophenolic acid (MPA) are not routinely measured, accumulating data suggest the usefulness of this monitoring to optimize therapy. The aim of this study was to assess the influence of CsA and tacrolimus on MPA pharmacokinetics. Concentrations of MPA were measured using HPLC. An assay was performed before dose (the C(0)), as well as at 40 minutes and 1, 2, 4, 6, 8, 10, 12 hours after administration of mycophenolate mofetil (MMF). MPA profiles were assessed in 51 patients receiving tacrolimus at a dose of 1.0 g/d and prednisone as well as in 97 patients receiving CsA (2.0 g/d) and prednisone. Significant correlations of MPA levels with serum albumin and GFR were observed in both groups. Women presented with higher levels of MPA than men. C(0) MPA level among the tacrolimus group were significantly higher than those in CsA group: 3.18 +/- 2.21 microg/mL versus 1.68 +/- 1.03 microg/mL (P </=.001). The level of MPA AUC((0-12)) in the tacrolimus group was nonsignificantly higher than that in the CsA group. There was no second peak of MPA level in a group of patients receiving CsA. We developed a limited sampling strategy to estimate MPA AUC((0-12)) in both tacrolimus and CsA groups. We observed a correlation between C(0) MPA and C(0) CsA (r =.35; P </=.001) as well as, between tacrolimus dose and MPA C(40) and MPA C(max) (r =.24; P </=.05; r =.27; P </= 0.05, respectively). No relationship between MPA pharmacokinetics and tacrolimus blood concentrations was noticed. Tacrolimus and CsA both affect the pharmacokinetics of MPA; high MPA concentrations in patients treated with tacrolimus justify MMF dose reduction in this group. Alterations of CsA concentrations must be used to guide MMF dose adjustments.

Gender-specific implications for cardiovascular medication use in the elderly optimizing therapy for older women

Sex should be considered during the selection of cardiovascular medications and dosages of cardiovascular medications. There is mounting evidence that clinically important differences between the sexes exist in the pharmacokinetic processes that determine drug concentrations and in the pharmacodynamic processes that determine physiologic responses to pharmacologic agents. Although aging also affects these processes, aging does not eliminate the sex-related differences. The major pharmacokinetic differences between the sexes, on average, are lower weight and distribution volumes in women compared with men and lower renal drug clearance in women compared with men. Sex-related differences in hepatic drug clearance are less predictable. Pharmacodynamic responses that differ between the sexes include increased adverse cardiovascular drug effects in women compared with men (torsade de pointes arrhythmias, increased risk of hemorrhagic consequences of anticoagulation or thrombolytic therapy, electrolyte abnormalities with diuretics, myopathy with HMG Co-A reductase inhibitors, cough with ACE inhibitors, and increased incidence of thrombosis). Recommendations for optimizing cardiovascular drug therapy for the older women include individualization of drug selection to minimize the number of medications and side effects; dosage adjustment based on age, size, and sex; close monitoring for side effects; and consideration of cost and access to medications. Optimal care for the older woman with cardiovascular disease will also require investigation of cardiovascular medications in older women and of therapies for cardiovascular diseases that are more common in women than men.

Automated determination of free mycophenolic acid and its glucuronide in plasma from renal allograft recipients

Mycophenolic acid, the active moiety of mycophenolate mofetil, inhibits the enzyme inosine monophosphate dehydrogenase. The main metabolite, mycophenolic acid glucuronide, has no immunosuppressive effect. Reported protein bindings are 97% for mycophenolic acid and 82% for mycophenolic acid glucuronide. Considerable intraindividual and interindividual variability in mycophenolic acid pharmacokinetics has been observed. Data on the variability of mycophenolic acid free fraction in plasma are sparse but may be relevant when discussing whether therapeutic drug monitoring of this drug is warranted. The authors describe a fully automated method for the determination of free concentrations by dialysis across a membrane followed by concentration of the dialysate on a trace enrichment column and liquid chromatography. Total concentrations are measured by protein precipitation and direct injection on the trace enrichment column. Plasma concentrations as low as 6 ng/mL free mycophenolic acid and 1 microg/mL free mycophenolic acid glucuronide can be measured with between-day coefficient of variation less than 15% and 6%, respectively. Stability testing confirmed that plasma samples could be stored for 14 days at 4 degrees C or -20 degrees C and at room temperature for approximately 12 hours without significant changes in free concentrations. Predose total and free concentrations of mycophenolic acid and mycophenolic acid glucuronide were determined in 27 samples from stable renal allograft recipients treated with mycophenolate mofetil, cyclosporin, and steroids. Total concentrations ranged from 0.57 to 16.2 microg/mL mycophenolic acid and 36 to 199 microg/mL mycophenolic acid glucuronide. Free concentrations ranged from 13 to 210 ng/mL mycophenolic acid and 8 to 58 microg/mL mycophenolic acid glucuronide. The method presented here has been successfully applied to measure free mycophenolic acid and free mycophenolic acid glucuronide in clinical samples. Further investigations may provide important data to support the identification of principles and target ranges for the monitoring of mycophenolic acid in the immunosuppressive therapy of organ transplant recipients.

Pharmacokinetics of mycophenolate mofetil in patients with autoimmune diseases compared renal transplant recipients

Mycophenolate mofetil (MMF), being effectively used as immunosuppressant in transplant medicine, has recently attracted interest as therapeutic agent for autoimmune diseases (AID). For these patients, no pharmacokinetic (PK) data are available. This study is an investigation of single-dose concentration-time profiles of 1 g off MMF in 16 patients with AID, including 10 patients with ANCA-associated vasculitis and 6 patients with systemic lupus erythematosus, and compares them with profiles of 16 renal transplant recipients (RTX). Mycophenolic acid (MPA) blood levels were measured by both HPLC and EMIT, and MPA-glucuronide was determined by HPLC. In AID, mean MPA concentrations at 12 h were significantly higher compared with RTX (4.1 +/- 3.27 versus 1.8 +/- 1.15 mg/L; P = 0.018), whereas peak concentrations were lower (P = 0.017). However, mean MPA-AUC at 12 h as well as at 24 h were comparable between both groups. In contrast to RTX, there was an association in AID between MPA trough levels at 12 h and at 24 h with AUC(0-12) (P < 0.05 and P < 0.01). MPA trough concentrations at 24 h provided an estimation of AUC(0-24 h) in both patient groups (P < 0.001 and P < 0.01; AID and RTX, respectively). Compared with RTX, MPA-PK seems to be less affected in AID by renal function. Inter-individual variability of PK parameters was high in both groups. These data indicate that there are differences of MPA-PK between RTX and AID. The use of therapeutic drug monitoring in patients with AID appears to be clinically practicable and may be valuable to optimize individual immunosuppressive therapy.

How important are gender differences in pharmacokinetics?

Gender-related differences in pharmacokinetics have frequently been considered as potentially important determinants for the clinical effectiveness of drug therapy. The mechanistic processes underlying gender-specific pharmacokinetics can be divided into molecular and physiological factors. Major molecular factors involved in drug disposition include drug transporters and drug-metabolising enzymes. Men seem to have a higher activity relative to women for the cytochrome P450 (CYP) isoenzymes CYP1A2 and potentially CYP2E1, for the drug efflux transporter P-glycoprotein, and for some isoforms of glucuronosyltransferases and sulfotransferases. Women were suggested to have a higher CYP2D6 activity. No major gender-specific differences seem to exist for CYP2C19 and CYP3A. The often-described higher hepatic clearance in women compared with men for substrates of CYP3A and P-glycoprotein, such as erythromycin and verapamil, may be explained by increased intrahepatocellular substrate availability due to lower hepatic P-glycoprotein activity in women relative to men. Physiological factors resulting in gender-related pharmacokinetic differences include the generally lower bodyweight and organ size, higher percentage of body fat, lower glomerular filtration rate and different gastric motility in women compared with men. Although gender disparity in pharmacokinetics has been identified for numerous drugs, differences are generally only subtle. For a few drugs, e.g. verapamil, beta-blockers and selective serotonin reuptake inhibitors, gender-related differences in pharmacokinetics have been shown to result in different pharmacological responses, but their clinical relevance remains unproven. In contrast, gender differences of clinical importance have clearly been identified for pharmacodynamic processes such as QTc prolongation, and intensive future research efforts are needed to assess the full scope and impact of pharmacodynamic gender disparity on applied pharmacotherapy.

Endoscopic and histological features of mycophenolate mofetil colitis in patients after solid organ transplantation

BACKGROUND

Mycophenolate mofetil (MMF) is an immunosuppressive agent commonly used after organ transplantation. Gastrointestinal side effects occur in approximately 45% of patients. The spectrum of histologic features associated with MMF colitis has been well described, but data on the endoscopic features is lacking. The aim of the study was to describe the endoscopic features of MMF colitis in solid organ transplant recipients (SOTRs) as well as the frequency of histologic features and identify associated risk factors.

METHODS

A retrospective review of all SOTRs taking MMF and who underwent colonoscopy between 2000 and 2010 was performed. 36 cases of MMF colitis were identified and 361 patients served as controls. Descriptive statistics and data analysis looking for associated risk factors were performed.

RESULTS

Among SOTRs taking MMF who underwent colonoscopy, MMF colitis was diagnosed in 9%. Endoscopic findings ranged from erythema (33%) to erosions/ulcers (19%). 47% of patients had a normal colonoscopy and everyone had rectal sparing. Histological findings included acute colitis-like findings (50%), inflammatory bowel disease-like characteristics (36%), ischemia-like findings (5.6%), and graft-versus-host disease-like features (8.3%). Diarrhea occurred in 83%. Kidney transplantation was associated with a higher risk of MMF colitis (OR 5.8 [2.86-11.86], P<0.0001) whereas liver transplantation was associated with a lower risk (OR 0.06 [0.03-0.16], P<0.0001).

CONCLUSION

MMF colitis is fairly prevalent in SOTRs taking MMF who undergo colonoscopy. Diarrhea is the most common reason for colonoscopy referral (83%) and up to 47% of patients have normal colonoscopy, suggesting the need for routine biopsies to help confirm the diagnosis.