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.

Use of two validated in vitro tests to assess the embryotoxic potential of mycophenolic acid

Mycophenolate mofetil is a widely used immunosuppressive drug that recently has been categorized as a human teratogen. Animal experiments indicate a teratogenic potential of the drug, but so far, it has not been studied in embryotoxicity in vitro assays. The aim of this study was to evaluate the in vitro embryotoxic potential of mycophenolic acid and investigate the ability of such tests to detect its embryotoxic potential. We used two validated assays: the rat whole embryo culture and the murine embryonic stem cell test. Rat embryos cultured from gestational day 9.5 for 48 h with the drug showed dysmorphogenic development already at a concentration of 250 microg mycophenolic acid/l medium. At concentrations of 750 microg/l and more, all rat embryos exhibited malformations. The main effects were defective yolk sac blood circulation, neural tube defects (open cranial neural pore), malformations of the head with missing eye anlagen and heart anomalies. Moreover, the exposed embryos showed a concentration-dependent decrease in protein content, crown-rump length, number of somites and morphological score. The murine embryonic stem cell test was slightly more sensitive. Proliferation and differentiation of the ES-D3-cells were significantly impaired at concentrations of 31 and 125 microg mycophenolic acid/l medium, respectively. In the differentiation assay, at a concentration of 125 microg mycophenolic acid/l medium and more, the number of wells with differentiated cardiomyocytes significantly decreased. Additionally, a cytotoxicity assay with balb/c 3T3 mouse fibroblasts was used to compare the proliferation and vitality of embryonic cells with adult cells. In the balb/c 3T3 cytotoxicity assay, the number of vital mouse fibroblasts significantly decreased at a mycophenolic acid concentration of 62 microg/l and more. In conclusion, by using the two validated in vitro tests, we showed that mycophenolic acid exhibits a pronounced embryotoxic potential at cytotoxic concentrations. This result from validated in vitro tests is of special interest, because it supports the use of the tests to detect human teratogens.

Calcineurin inhibitor sparing in paediatric solid organ transplantation : managing the efficacy/toxicity conundrum

Despite their efficacy, the calcineurin inhibitors (CNIs) ciclosporin and tacrolimus carry a risk of debilitating adverse effects, especially nephrotoxicity, that affect the long-term outcome and survival of children who are given organ transplants. Simple reduction in dosage of CNI has little or no long-term benefit on their adverse effects, and complete withdrawal without threatening graft outcome may only be possible after liver transplantation. Until the last decade, the only option was to increase corticosteroid and/or azathioprine doses, which imposed additional long-term hazards. Considered here are the emerging generation of new agents offering an opportunity for improving long-term graft survival, minimizing CNI-related adverse events and ensuring patient well-being.A holistic, multifaceted strategy may need to be considered - initial selection and optimized use and monitoring of immunosuppressant regimens, early recognition of indicators of patient and graft dysfunction, and, where applicable, early introduction of CNI-sparing regimens facilitating CNI withdrawal. The evidence reviewed here supports these approaches but remains far from definitive in paediatric solid organ transplantation. Because de novo immunosuppression uses CNI in more than 93% of patients, reduction of CNI-related adverse effects has focused on CNI sparing or withdrawal.A recurring theme where sirolimus and mycophenolate mofetil have been used for this purpose is the importance of their early introduction to limit CNI damage and provide long-term benefit: for example, long-term renal function critically reflects that at 1 year post-transplant. While mycophenolic acid shows advantages over sirolimus in preserving renal function because the latter is associated with proteinuria, sirolimus appears the more potent immunosuppressant but also impairs early wound healing. The use of CNI-free immunosuppressant regimens with depleting or non-depleting antibodies plus sirolimus and mycophenolic acid needs much wider investigation to achieve acceptable rejection rates and conserve renal function. The adverse effects of the alternative immunosuppressants, particularly the dyslipidaemia associated with sirolimus, needs to be minimized to avoid replacing one set of adverse effects (from CNIs) with another. While we can only conjecture that judicious combinations with the second generation of novel immunosuppressants currently in development will provide these solutions, a rationale of low-dose therapy with multiple immunosuppressants acting by complementary mechanisms seems to hold the promise for efficacy with minimal toxicity until the vision of tolerance achieves reality.