Optimal Practice for Vancomycin Therapeutic Drug Monitoring: Position Statement From the Anti-infectives Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology.

ABSTRACT: Individualization of vancomycin dosing based on therapeutic drug monitoring (TDM) data is known to improve patient outcomes compared with fixed or empirical dosing strategies. There is increasing evidence to support area-under-the-curve (AUC24)-guided TDM to inform vancomycin dosing decisions for patients receiving therapy for more than 48 hours. It is acknowledged that there may be institutional barriers to the implementation of AUC24-guided dosing, and additional effort is required to enable the transition from trough-based to AUC24-based strategies. Adequate documentation of sampling, correct storage and transport, accurate laboratory analysis, and pertinent data reporting are required to ensure appropriate interpretation of TDM data to guide vancomycin dosing recommendations. Ultimately, TDM data in the clinical context of the patient and their response to treatment should guide vancomycin therapy. Endorsed by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology, the IATDMCT Anti-Infectives Committee, provides recommendations with respect to best clinical practice for vancomycin TDM.

Personalized Therapy for Mycophenolate: Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology.

ABSTRACT: When mycophenolic acid (MPA) was originally marketed for immunosuppressive therapy, fixed doses were recommended by the manufacturer. Awareness of the potential for a more personalized dosing has led to development of methods to estimate MPA area under the curve based on the measurement of drug concentrations in only a few samples. This approach is feasible in the clinical routine and has proven successful in terms of correlation with outcome. However, the search for superior correlates has continued, and numerous studies in search of biomarkers that could better predict the perfect dosage for the individual patient have been published. As it was considered timely for an updated and comprehensive presentation of consensus on the status for personalized treatment with MPA, this report was prepared following an initiative from members of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT). Topics included are the criteria for analytics, methods to estimate exposure including pharmacometrics, the potential influence of pharmacogenetics, development of biomarkers, and the practical aspects of implementation of target concentration intervention. For selected topics with sufficient evidence, such as the application of limited sampling strategies for MPA area under the curve, graded recommendations on target ranges are presented. To provide a comprehensive review, this report also includes updates on the status of potential biomarkers including those which may be promising but with a low level of evidence. In view of the fact that there are very few new immunosuppressive drugs under development for the transplant field, it is likely that MPA will continue to be prescribed on a large scale in the upcoming years. Discontinuation of therapy due to adverse effects is relatively common, increasing the risk for late rejections, which may contribute to graft loss. Therefore, the continued search for innovative methods to better personalize MPA dosage is warranted.

Monoclonal Antibody Monitoring: Clinically Relevant Aspects, A Systematic Critical Review.

Monoclonal antibody (mAb) therapy does not usually lead to a clinical response in all patients and resistance may increase over time after repeated mAb administration. This lack or loss of response to the treatment may originate from different and little-known epigenetic, biomolecular, or pathophysiological mechanisms, although an inadequate serum concentration is perhaps the most likely cause, even if not widely recognized and investigated yet. Patient factors that influence the pharmacokinetics (PK) of a mAb should be taken into account. Multiple analyses of patient-derived PK data have identified various factors influencing the clearance of mAbs. These factors include the presence of antidrug antibodies, low serum albumin, high serum levels of C-reactive protein, high body weight, and gender differences among others. The same clearance processes involved in systemic clearance after intravenous administration are also involved in local first-pass catabolism after subcutaneous administration of mAbs. Therapeutic drug monitoring has been proposed as a way to understand and respond to the variability in clinical response and remission. For both classes of mAbs with anti-inflammatory and antitumor effects, dose-guided optimization based on the measurement of serum concentrations in individual patients could be the next step for a personalized and targeted mAb therapy.

Pharmacologic Treatment of Transplant Recipients Infected With SARS-CoV-2: Considerations Regarding Therapeutic Drug Monitoring and Drug-Drug Interactions.

BACKGROUND: COVID-19 is a novel infectious disease caused by the severe acute respiratory distress (SARS)-coronavirus-2 (SARS-CoV-2). Several therapeutic options are currently emerging but none with universal consensus or proven efficacy. Solid organ transplant recipients are perceived to be at increased risk of severe COVID-19 because of their immunosuppressed conditions due to chronic use of immunosuppressive drugs (ISDs). It is therefore likely that solid organ transplant recipients will be treated with these experimental antivirals. METHODS: This article is not intended to provide a systematic literature review on investigational treatments tested against COVID-19; rather, the authors aim to provide recommendations for therapeutic drug monitoring of ISDs in transplant recipients infected with SARS-CoV-2 based on a review of existing data in the literature. RESULTS: Management of drug-drug interactions between investigational anti-SARS-CoV-2 drugs and immunosuppressants is a complex task for the clinician. Adequate immunosuppression is necessary to prevent graft rejection while, if critically ill, the patient may benefit from pharmacotherapeutic interventions directed at limiting SARS-CoV-2 viral replication. Maintaining ISD concentrations within the desired therapeutic range requires a highly individualized approach that is complicated by the pandemic context and lack of hindsight. CONCLUSIONS: With this article, the authors inform the clinician about the potential interactions of experimental COVID-19 treatments with ISDs used in transplantation. Recommendations regarding therapeutic drug monitoring and dose adjustments in the context of COVID-19 are provided.

Posaconazole oral dose and plasma levels in pediatric hematology-oncology patients.

BACKGROUND: Posaconazole is a triazole with limited pharmacokinetic information in children. This study assessed the correlation between posaconazole oral solution daily dosage/kg/body weight and trough plasma level. METHODS: A total of 97 hematology-oncology pediatric patients with ≥1 posaconazole plasma concentration level (PPC) assessment in the first 6 weeks after the start of posaconazole treatment were included. RESULTS: Posaconazole was used as prophylaxis in 84 of 97 (87%) patients and as therapy in 13 of 97 (13%). The median daily dose/kg/bw ranged from 10 to 12 mg in the prophylaxis group and 12.5 to 16.5 mg in the therapy group. The median value of PPC for the prophylaxis group was 0.9 and 0.8 µg/mL at the first and second/third determinations, respectively. Posaconazole prophylaxis failed in 4 of 84 patients (5%). The median value of PPC for the therapy group was 1.5 and 1.4 µg/mL at the first/second and the third determination, respectively. Posaconazole-related side effects were reported in 6 patients and all regressed with the suspension of the drug. In the prophylaxis group, the use of proton-pump inhibitors was significantly associated with a lower PPC, P = 0.04. CONCLUSIONS: Posaconazole may be a valuable antifungal agent in children despite the incomplete knowledge of its pharmacokinetic characteristics.

Bioequivalence of a New Oral Levosulpiride Formulation Compared With a Standard One in Healthy Volunteers.

BACKGROUND: A monocentric, single-dose, open-label, 2-way, crossover randomized study was conducted by the San Matteo Phase I Clinical Trial Unit and Experimental Therapy (Pavia, Italy) to assess the bioequivalence and the systemic tolerability of a new oral formulation of levosulpiride (tablet 25 mg: test) versus a commercially available formulation on the Italian market (tablet 25 mg: reference). METHODS: Thirty-five healthy adult volunteers, men (n = 19) and women (n = 16), aged between 18 and 55 years were screened and 32 of them were enrolled in the study. After having signed the written informed consent, each subject received a single oral dose of Test or Reference product with 250 mL of natural mineral water, in fasting conditions, interspersed with a 6-day washout period Blood samples were collected up to 36 hours after drug administration: the drug plasma levels were determined by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. The pharmacokinetic parameters included peak plasma concentration (Cmax), time corresponding to Cmax (tmax), area under the plasma concentration-time curve from zero to infinity (AUC0-∞) or to the last sampling time assessment (AUC0-36), the elimination rate constant (ke), and the terminal half-life (t1/2). Safety was measured by pre- and post-treatment specific biochemical investigations, physical examination, electrocardiogram, occurrence of adverse events, and any information on patients' withdrawal. RESULTS: The geometric mean ratio Test/Reference (90% confidence interval) for levosulpiride was 103.0% (95.8-110.8) for AUC0-36, 103.6% (95.9-111.9) for AUC0-∞, and 104.3% (94.9-114.6) for Cmax. ke and t1/2 were 0.07 (SD: 0.02) and 9 hours (8-12) for both the formulations. Clearance (L/h) was 29.6 (±13.5) and 30.7 (±14.2) for the test and the reference product, respectively. CONCLUSIONS: Because the acceptance criteria required by the drug regulatory agency (European Medicines Agency, EMA) for bioequivalence prescribe limits of 80%-120% for untransformed data and 80%-125% for "ln" transformed data, we can confirm that the 2 formulations are bioequivalent, in terms of the rate and extent of absorption.

Hydroxychloroquine Blood Concentrations Can Be Clinically Relevant Also After Drug Discontinuation.

BACKGROUND AND OBJECTIVE: Hydroxychloroquine was widely used during the severe acute respiratory syndrome coronavirus 2 pandemic as an antiviral drug. Most previous pharmacokinetic/pharmacodynamic studies on hydroxychloroquine were conducted on healthy volunteers or patients receiving long-term therapy. There are no studies on the elimination of hydroxychloroquine after short-term treatments. Hydroxychloroquine is known to have a pro-arrhythmic effect through QT interval prolongation, but data in this setting are not conclusive. Our aims were to estimate the time needed for hydroxychloroquine concentrations (CHCQ) to drop to a safe concentration (500 ng/mL) after a short-term therapeutic cycle and to correlate the corrected QT interval with CHCQ. METHODS: We collected blood samples and electrocardiograms of patients who underwent short-term therapy with hydroxychloroquine during drug intake and after discontinuation. Hydroxychloroquine concentrations were determined by high-performance liquid chromatography-tandem mass spectrometry and analysed with a linear regression model to estimate the elimination time of the drug after its discontinuation. We conducted a multivariate analysis of the corrected QT interval correlation with CHCQ. RESULTS: Our data suggest that short-term hydroxychloroquine courses can generate significant CHCQ persisting above 500 ng/mL up to 16 days after discontinuation of treatment. Corrected QT interval prolongation significantly correlates with CHCQ. CONCLUSIONS: The study confirms the long half-life of hydroxychloroquine and its effect on the corrected QT interval even after short-term courses of the drug. This can inform the clinician using hydroxychloroquine treatments that it would be safer to start or re-initiate treatments with corrected QT interval-prolonging potential 16 days after hydroxychloroquine discontinuation.

Inosine monophosphate dehydrogenase variability in renal transplant patients on long-term mycophenolate mofetil therapy.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: * Mycophenolic acid (MPA) is a potent, selective and reversible inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme for de novo guanosine triphosphate biosynthesis. * The large IMPDH interindividual variability could be responsible for the differences in therapeutic effects and side-effects observed with MPA. * Induction of IMPDH activity has been observed in whole blood during immunosuppressive therapy. WHAT THIS STUDY ADDS: * Our data were acquired in long-term mycophenolate mofetil-treated renal transplant recipients on different combinations of immunosuppressive agents (ciclosporin, tacrolimus, sirolimus) and with different treatment duration (up to 8.8 years post transplant). * The increasing trend in IMPDH activity that we observed throughout our 12-month observation period was significantly higher in rejecting than in nonrejecting subjects. AIMS: Long-term mycophenolate mofetil (MMF) therapy may induce inosine 5'-monophosphate dehydrogenase (IMPDH) activity in peripheral blood mononuclear cells (PBMCs), thus decreasing MMF immunosuppressive properties. Pharmacodynamic monitoring was used to investigate whether biological activity is altered after long-term therapy. METHODS: IMPDH activity was measured in PBMC samples from 54 stable kidney transplant patients, already on MMF (for at least 3 months), before (t(0)) and 2 h after (t(2)) MMF morning dose administration; levels were monitored for up to 15 months, together with total mycophenolic acid (MPA) and free MPA concentrations. RESULTS: During the 15 months' monitoring, t(0) IMPDH activity in transplant recipients increased from 5.9 +/- 3.7 nmol h(-1) mg(-1)[95% confidence interval (CI) 4.9, 6.9] to 9.0 +/- 3.9 nmol h(-1) mg(-1) (95% CI 7.2, 10.8), with an intra- and interpatient variability of 28% and 42%. Five patients experienced acute rejection during the follow-up: t(0) IMPDH activity was increased during rejection vs. nonrejection, and the trend was significantly higher in rejecting than in nonrejecting subjects for the whole monitoring period. CONCLUSIONS: Even though a correlation has been found between IMPDH activity and rejection, its efficacy as a predictive tool in long-term transplant outcomes may be affected by high interpatient variability; on the other hand, continuous monitoring of the IMPDH trend could make an effective prognostic parameter of rejection. Other trials also including pre-transplant data on both IMPDH expression and activity are warranted to better assess their role as biomarkers for MPA effect in clinical practice.

Development and validation of a combined enzymatic-digestion/mass spectrometry assay for Tacrolimus quantitation in cardiac biopsies.

Recent studies report strategies for analysing immunosuppressive drugs in brain, liver and renal tissue, mostly in animals: we developed and validated a two steps combined enzymatic digestion/mass spectrometry assay to quantify Tacrolimus (TAC) in heart biopsies. Our aims were to avoid sample loss and sample contamination during the laboratory preparation, and to limit matrix effects in the electrospray ionization source (ESI) of the mass spectrometer. Enzymatic tissue digestion followed by a liquid-liquid drug extraction in the same vial of reaction allowed us to reach both our aims. The assay was assessed for selectivity, matrix effect, linearity, Lower Limit of Quantification (LLOQ) and Detection (LOD), accuracy and precision, according to the "Guideline on Bioanalytical Method Validation (EMA). A stable isotopically labelled (SIL) analogue (13CD2-TAC) was used as internal standard. The chromatographic separation of the analyte took 6 min. The observed linear range of quantification was 0.0162-0.520 ng in terms of TAC added to the biopsies (by 50 µL of the corresponding working solutions). The limit of detection and the lower limit of quantification (LLOQ) were 0.008 and 0.0162 ng, respectively. Both the mobile phases contained ammonium acetate and formic acid that promote the formation of ammoniated precursor ions that can be easily fragmented ([M + NH4]+, TAC m/z 821.3; 13CD2-TAC m/z 824.3). The calibration curves were generated by plotting analyte-to-internal standard peak area ratios versus TAC amount (ng) added to the biopsies, and using a weighted (1/x) linear regression. Curves were not forced to pass through the origin. Swine hearts were employed as blank matrix for all the analytical method validation procedures but, after approval by the ethics committee (by "Fondazione IRCCS Policlinico San Matteo": Protocol 20190032933), TAC was also quantified in endomyocardial biopsies from informed and consenting heart transplant patients. The study was funded by Fondazione IRCCS Policlinico San Matteo (RC08017617), as a part of the clinical studies on the maintenance of immunosuppressive therapy in cardiac transplant patients. Tacrolimus concentrations in patients biopsies were expressed as ratio between the detected amount of TAC (ng) in the tissue and the weight of the tissue itself (mg).

Efficacy of intraventricular amikacin treatment in pan-resistant Pseudomonas aeruginosa postsurgical meningitis.

BACKGROUND: We describe a case of pan-resistant Pseudomonas aeruginosa postsurgical meningitis associated with the presence of an external ventricular device. We changed therapy twice; finally, by using amikacin and a continuous infusion of cefepime, we obtained clinical improvement. CASE PRESENTATION: A female patient, who underwent surgery for a cavernous angioma, presented with meningitis. Cerebrospinal fluid culture revealed a multidrug-resistant Pseudomonas aeruginosa, initially sensitive only to colistin. We successfully used intrathecal amikacin and intravenous cefepime continuous infusion plus intravenous amikacin after two previous ineffective therapeutic approaches. CONCLUSION: The evaluation of the antibiotic concentration and the bactericidal activity in cerebrospinal fluid may contribute to the choice of the drug in cases of multidrug-resistant meningitis.

In vitro and in vivo quantification of chloroprocaine release from an implantable device in a piglet postoperative pain model.

BACKGROUND: The pharmacokinetic properties and clinical advantages of the local anesthetic chloroprocaine are well known. Here, we studied the pharmacokinetic profile of a new hydrogel device loaded with chloroprocaine to investigate the potential advantages of this new strategy for postoperative pain (POP) relief. MATERIALS AND METHODS: We performed both in vitro and in vivo analyses by considering plasma samples of four piglets receiving slow-release chloroprocaine. To quantify chloroprocaine and its inactive metabolite 4-amino-2-chlorobenzoic acid (ACBA), a HPLC-tandem mass spectrometry (HPLC-MS/MS) analytical method was used. Serial blood samples were collected over 108 hours, according to the exposure time to the device. RESULTS: Chloroprocaine was consistently found to be below the lower limit of quantification, even though a well-defined peak was observed in every chromatogram at an unexpected retention time. Concerning ACBA, we found detectable plasma concentrations between T0 and T12h, with a maximum plasma concentration (Cmax) observed 3 hours after the device application. In the in vitro analyses, the nanogel remained in contact with plasma at 37°C for 90 minutes, 3 hours, 1 day, and 7 days. Chloroprocaine Cmax was identified 1 day following exposure and Cmin after 7 days, respectively. Additionally, ACBA reached the Cmax following 7 days of exposure. CONCLUSION: A thorough review of the literature indicates that this is the first study analyzing both in vivo and in vitro pharmacokinetic profiles of a chloroprocaine hydrogel device and is considered as a pilot study on the feasibility of including this approach to the management of POP.

Human Genetic Variability Contributes to Postoperative Morphine Consumption.

UNLABELLED: High interindividual variability in postoperative opioid consumption is related to genetic and environmental factors. We tested the association between morphine consumption, postoperative pain, and single nucleotide polymorphisms (SNPs) within opioid receptor µ 1 (OPRM1), catechol-O-methyltransferase (COMT), uridine diphosphate glucose-glucuronosyltransferase-2B7, and estrogen receptor (ESR1) gene loci to elucidate genetic prediction of opioid consumption. We analyzed 20 SNPs in 201 unrelated Caucasian patients who underwent abdominal surgery and who were receiving postoperative patient-controlled analgesia-administered morphine. Morphine consumption and pain intensity were dependent variables; age and sex were covariates. A haplotype of 7 SNPs in OPRM1 showed significant additive effects on opioid consumption (P = .007); a linear regression model including age and 9 SNPs in ESR1, OPRM1, and COMT explained the highest proportion of variance of morphine consumption (10.7%; P = .001). The minimal model including 3 SNPs in ESR1, OPRM1, and COMT explained 5% of variance (P = .007). We found a significant interaction between rs4680 in COMT and rs4986936 in ESR1 (P = .007) on opioid consumption. SNPs rs677830 and rs540825 of OPRM1 and rs9340799 of ESR1 were nominally associated with pain Numeric Rating Scale scores. Combinations of genetic variants within OPRM1, COMT, and ESR1 better explain variability in morphine consumption than single genetic variants. Our results contribute to the development of genetic markers and statistical models for future diagnostic tools for opioid consumption/efficacy. PERSPECTIVE: This article presents the efforts dedicated to detect correlations between the genetic polymorphisms and the clinical morphine effect self-administered by patients using a patient-controlled analgesia pump after major surgery. The clinical effect is expressed in terms of morphine consumption and pain scores. REGISTERED ON CLINICALTRIALS.GOV: NCT01233752.

Genetic Screening of Anderson-Fabry Disease in Probands Referred From Multispecialty Clinics.

BACKGROUND: Anderson-Fabry disease (AFD) is a rare X-linked lysosomal storage disease, caused by defects of the alpha-galactosidase A (GLA) gene. AFD can affect the heart, brain, kidney, eye, skin, peripheral nerves, and gastrointestinal tract. Cardiology (hypertrophic cardiomyopathy), neurology (cryptogenic stroke), and nephrology (end-stage renal failure) screening studies suggest the prevalence of GLA variants is 0.62%, with diagnosis confirmation in 0.12%. OBJECTIVES: This study sought to expand screening from these settings to include ophthalmology, dermatology, gastroenterology, internal medicine, pediatrics, and medical genetics to increase diagnostic yield and comprehensively evaluate organ involvement in AFD patients. METHODS: In a 10-year prospective multidisciplinary, multicenter study, we expanded clinical, genetic, and biochemical screening to consecutive patients enrolled from all aforementioned clinical settings. We tested the GLA gene and α-galactosidase A activity in plasma and leukocytes. Inclusion criteria comprised phenotypical traits and absence of male-to-male transmission. Screening was extended to relatives of probands harboring GLA mutations. RESULTS: Of 2,034 probands fulfilling inclusion criteria, 37 (1.8%) were carriers of GLA mutations. Cascade family screening identified 60 affected relatives; clinical data were available for 4 affected obligate carriers. Activity of α-galactosidase A in plasma and leukocytes was diagnostic in male subjects, but not in female subjects. Of the 101 family members harboring mutations, 86 were affected, 10 were young healthy carriers, and 5 refused clinical evaluation. In the 86 patients, involved organs or organ systems included the heart (69%), peripheral nerves (46%), kidney (45%), eye (37%), brain (34%), skin (32%), gastrointestinal tract (31%), and auditory system (19%). Globotriaosylceramide accumulated in organ-specific and non-organ-specific cells in atypical and classic variants, respectively. CONCLUSIONS: Screening probands with clinically suspected AFD significantly increased diagnostic yield. The heart was the organ most commonly involved, independent of the clinical setting in which the patient was first evaluated.

Effects of recombinant growth hormone on visceral fat accumulation: pilot study in human immunodeficiency virus-infected adolescents.

CONTEXT: Recombinant human GH (rhGH) reduces excess accumulation of intraabdominal adipose tissue (IAT) in lipodystrophic HIV-infected adults, whereas data in pediatric patients are lacking. OBJECTIVE: The objective of this study was to assess the efficacy of rhGH treatment on lipodystrophy in HIV-infected adolescents. DESIGN: The study is a prospective, 24-wk open-label study of rhGH. SETTING: The study was conducted at a referral center for pediatric HIV infection. PATIENTS AND OTHER PARTICIPANTS: Eight HIV-infected adolescents (ages, 13.7-18.5 yr), with abnormal IAT accumulation (>41 cm(2) at L4-magnetic resonance imaging) and 97 healthy controls (HC) (ages, 9.5-19.9 yr) were enrolled. INTERVENTION: rhGH was given by sc injection at a daily dose of 0.028 mg/kg. MAIN OUTCOME MEASURES: The main outcome was change in IAT at L4-magnetic resonance imaging. Body composition by dual-energy x-ray absorptiometry, glucose and lipid metabolism, and IGF-I changes were also evaluated. RESULTS: All patients completed the study period; none of them showed adverse event, and no change in the daily dose of rhGH was required. The treatment was associated with a mean height increase of 2.4 cm. From baseline to wk 24, IAT area decreased significantly by a median of 34.5% (-19.2 to -70%). Fat mass decreased significantly in patients, compared with HC, with a median loss of total, trunk, and arm and leg fat mass of 10.4, 10.9, 12.7, and 5.4%, respectively. Total, arm, and leg lean masses increased significantly, compared with HC. IGF-I increased significantly, but supraphysiological values of mild degree (2-23% over the upper normal limit) were detected in only nine of 24 samples. No significant effects on glucose metabolism, triglyceride, and cholesterol levels were observed. CONCLUSIONS: Our data showed that rhGH 0.028 mg/kg daily for 24 wk in HIV-infected adolescents reduces IAT, trunk, and also limb fat and increases lean mass. Overall, short-term rhGH is well tolerated and is not associated with a worsening of glucose and lipid metabolism.

Monitoring of inosine monophosphate dehydrogenase activity and expression during the early period of mycophenolate mofetil therapy in de novo renal transplant patients.

Measurement of inosine-monophosphate dehydrogenase (IMPDH) activity or gene expression was used as a further approach in pharmacokinetics (PK)/pharmacodynamic (PD)-guided mycophenolate mofetil (MMF) therapy. Forty-four de novo kidney transplant patients were enrolled; 35 of these completed the study, and were followed for 24 weeks for clinical status, PK parameters, IMPDH activity and IMPDH1/2 gene expression. IMPDH activity and expression were measured in peripheral blood mononuclear cells before transplant and at week 2,4,12 and 24, drawn before (t0) and 2 h (t2 h) after MMF administration. No significant correlation was found between IMPDH activity/expression and PK parameters. For both genes, significant enhancement in t2 h expression was observed, then decreases towards week 24 with a trend following steroid dosages. Seven patients experienced acute rejection (AR) and exhibited significantly higher pre-transplant expression of both IMPDH1 (median 3.42 vs. 0.84; p=0.0025), and IMPDH2 genes (135 vs. 104; p=0.0218) with respect to non-rejecting patients. A significant association was also found between pre-transplant IMPDH1 mRNA and haematological complications (p=0.032). This study suggests that high steroid dosages may influence IMPDH1/2 expression, hampering their use as a PD biomarker, particularly during the early post-transplant period. The measurement of pre-transplant levels of IMPDH1/2 may contribute to prediction of individual drug responsiveness to improve the clinical management of patients in MMF therapy.