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      A Review on Therapeutic Drug Monitoring of Immunosuppressant Drugs

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          Abstract

          Immunosuppressants require therapeutic drug monitoring because of their narrow therapeutic index and significant inter-individual variability in blood concentrations. This variability can be because of factors like drug-nutrient interactions, drug-disease interactions, renal-insufficiency, inflammation and infection, gender, age, polymorphism and liver mass. Drug monitoring is widely practiced especially for cyclosporine, tacrolimus, sirolimus and mycophenolic acid.

          Cyclosporine

          Therapeutic monitoring of immunosuppressive therapy with cyclosporine is a critical requirement because of intra- and inter-patient variability of drug absorption, narrow therapeutic window and drug induced nephrotoxicity.

          Mycophenolic acid (MPA)

          Some reasons for therapeutic drug monitoring of MPA during post-transplant period include: relationship between MPA pharmacokinetic parameters and clinical outcomes, Inter-patient pharmacokinetic variability for MPA despite fixed MMF doses, alternations of MPA pharmacokinetics during the first months after transplantation, drug- drug interaction and influence of kidney function on MPA pharmacokinetic.

          Sirolimus

          A recent review of the pharmacokinetics of sirolimus suggested a therapeutic range of 5 to 10 μg l −1 in whole blood. However, the only consensus guidelines published on the therapeutic monitoring of sirolimus concluded that there was not enough information available about the clinical use of the drug to make recommendations.

          Tacrolimus

          Sudies have shown, in kidney and liver transplant patients, significant associations of low tacrolimus concentrations with rejection and of high concentrations with nephrotoxicity. Although the feasibility of a limited sampling scheme to predict AUC has been demonstrated, as yet, trough, or pre-dose, whole blood concentration monitoring is still the method of choice.

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          Most cited references131

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          The natural history of chronic allograft nephropathy.

          With improved immunosuppression and early allograft survival, chronic allograft nephropathy has become the dominant cause of kidney-transplant failure. We evaluated the natural history of chronic allograft nephropathy in a prospective study of 120 recipients with type 1 diabetes, all but 1 of whom had received kidney-pancreas transplants. We obtained 961 kidney-transplant-biopsy specimens taken regularly from the time of transplantation to 10 years thereafter. Two distinctive phases of injury were evident as chronic allograft nephropathy evolved. An initial phase of early tubulointerstitial damage from ischemic injury (P<0.05), prior severe rejection (P<0.01), and subclinical rejection (P<0.01) predicted mild disease by one year, which was present in 94.2 percent of patients. Early subclinical rejection was common (affecting 45.7 percent of biopsy specimens at three months), and the risk was increased by the occurrence of a prior episode of severe rejection and reduced by tacrolimus and mycophenolate therapy (both P<0.05) and gradually abated after one year. Both subclinical rejection and chronic rejection were associated with increased tubulointerstitial damage (P<0.01). Beyond one year, a later phase of chronic allograft nephropathy was characterized by microvascular and glomerular injury. Chronic rejection (defined as persistent subclinical rejection for two years or longer) was uncommon (5.8 percent). Progressive high-grade arteriolar hyalinosis with luminal narrowing, increasing glomerulosclerosis, and additional tubulointerstitial damage was accompanied by the use of calcineurin inhibitors. Nephrotoxicity, implicated in late ongoing injury, was almost universal at 10 years, even in grafts with excellent early histologic findings. By 10 years, severe chronic allograft nephropathy was present in 58.4 percent of patients, with sclerosis in 37.3 percent of glomeruli. Tubulointerstitial and glomerular damage, once established, was irreversible, resulting in declining renal function and graft failure. Chronic allograft nephropathy represents cumulative and incremental damage to nephrons from time-dependent immunologic and nonimmunologic causes. Copyright 2003 Massachusetts Medical Society
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            Clinical pharmacokinetics of tacrolimus.

            Tacrolimus, a novel macrocyclic lactone with potent immunosuppressive properties, is currently available as an intravenous formulation and as a capsule for oral use, although other formulations are under investigation. Tacrolimus concentrations in biological fluids have been measured using a number of methods, which are reviewed and compared in the present article. The development of a simple, specific and sensitive assay method for measuring concentrations of tacrolimus is limited by the low absorptivity of the drug, low plasma and blood concentrations, and the presence of metabolites and other drugs which may interfere with the determination of tacrolimus concentrations. Currently, most of the pharmacokinetic data available for tacrolimus are based on an enzyme-linked immunosorbent assay method, which does not distinguish tacrolimus from its metabolites. The rate of absorption of tacrolimus is variable with peak blood or plasma concentrations being reached in 0.5 to 6 hours; approximately 25% of the oral dose is bioavailable. Tacrolimus is extensively bound to red blood cells, with a mean blood to plasma ratio of about 15; albumin and alpha 1-acid glycoprotein appear to primarily bind tacrolimus in plasma. Tacrolimus is completely metabolised prior to elimination. The mean disposition half-life is 12 hours and the total body clearance based on blood concentration is approximately 0.06 L/h/kg. The elimination of tacrolimus is decreased in the presence of liver impairment and in the presence of several drugs. Various factors that contribute to the large inter- and interindividual variability in the pharmacokinetics of tacrolimus are reviewed here. Because of this variability, the narrow therapeutic index of tacrolimus, and the potential for several drug interactions, monitoring of tacrolimus blood concentrations is useful for optimisation of therapy and dosage regimen design.
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              Relationship of FK506 whole blood concentrations and efficacy and toxicity after liver and kidney transplantation.

              FK506 (tacrolimus) is a safe and effective immunosuppressant for the prevention of organ rejection after organ transplantation. FK506 has a relatively narrow therapeutic index and the correlation of dose to blood concentration is poor as a result of moderate variability in pharmacokinetic parameters between patients. Therapeutic monitoring of whole blood FK506 drug concentrations has been used in an effort to determine whether a relationship exists between concentrations of FK506 in the blood and the development of toxicity or the risk for organ rejection. An analysis of the relationship between FK506 blood levels and the occurrence of toxicity and rejection was carried out using data from four recent clinical trials. Trough FK506 levels within a 7-day window before the onset of rejection or toxicity were analyzed using logistic regression models. In kidney transplant patients (n=92), a significant correlation between FK506 levels and the incidence of both toxicity (P=0.01) and rejection (P=0.02) was seen. In liver transplant patients from three clinical trials, FK506 levels correlated well with the incidence of toxicity (P < or = 0.01); however, there was no significant relationship between FK506 levels and the incidence of rejection. It is concluded that therapeutic monitoring of whole blood FK506 levels may be useful for minimizing the risks of both toxicity and rejection in kidney transplant patients and for minimizing the risk of toxicity in liver transplant recipients.
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                Author and article information

                Journal
                Iran J Basic Med Sci
                Iran J Basic Med Sci
                IJBMS
                Iranian Journal of Basic Medical Sciences
                Mashhad University of Medical Sciences (Mashhad, Iran )
                2008-3866
                2008-3874
                Nov-Dec 2011
                : 14
                : 6
                : 485-498
                Affiliations
                [1 ] Department of Microbiology, School of Medicine, Islamic Azad University, Mashhad Branch, Mashhad, Iran
                [2 ] Zakariya Research Centre, Islamic Azad University, Mashhad Branch, Mashhad, Iran
                [3 ] Department of Pharmacodinamy and Toxicology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran
                [4 ] Pharmaceutical Research Centre, Mashhad University of Medical Sciences, Mashhad, Iran
                [5 ] Department of Biotechnology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran
                Author notes
                [* ]Corresponding author: Tel: +98-511-8823255; Fax: +98-511-8823251; email: mohamadpoorah@mums.ac.ir
                Article
                JBMS-14-485
                3586862
                23493821
                806dd71b-5ec7-4fe6-9a75-33157e1b9330
                © 2011: Iranian Journal of Basic Medical Sciences

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License, ( http://creativecommons.org/licenses/by/3.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 11 October 2010
                : 27 March 2011
                Categories
                Review Article

                cyclosporine,mycophenolic acid,sirolimus,tacrolimus,therapeutic drug monitoring

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