Mycophenolate mofetil (MMF) is a purine analogue. Mycophenolic Acid Pharmacokinetics in Pediatric Liver Transplant Recipients

Transcription

1 Mycophenolic Acid Pharmacokinetics in Pediatric Liver Transplant Recipients Marion M. Aw, Nigel W. Brown, Toshi Itsuka, Christopher E. Gonde, Jemimah E. Adams, Nigel D. Heaton, J. Michael Tredger, Giorgina Mieli-Vergani, and Anil Dhawan The aim of this study is to study mycophenolic acid (MPA) pharmacokinetics in stable pediatric liver transplant recipients and determine which times best represent the area under the concentration versus time curve (AUC) of MPA plasma concentrations. MPA pharmacokinetic profiles were determined in 21 liver transplant recipients (age, 2 to 15 years; 12 boys) administered mycophenolate mofetil (MMF) for at least 6 months. Ten patients were coadministered cyclosporine A (CsA), and 11 patients were coadministered tacrolimus (Tac). Plasma MPA levels were analyzed by enzyme-multiplied immunoassay technique in blood samples at 0, 0.33, 0.67, 1.25, 2, 3.5, 5, and 7 hours after MMF administration. The AUC of plasma concentrations to 7 hours (AUC 0-7 ) was calculated using the linear trapezoidal rule. MPA plasma trough concentration (C 0 ), maximal concentration, and AUC 0-7 values ranged 9- to 14-fold at a median of 1.81 mg/l (range, 0.4 to 3.7 mg/l), 10.5 mg/l (range, 2.8 to 40.0 mg/l), and 30.2 mg/l.hr (range, 9.3 to 80.3 mg/l.hr), respectively. AUC 0-7 correlated significantly with MMF dose (r 0.552; P.010) and C 0 (r 0.844; P <.001). Median AUC 0-7 (29.6 v 31.4 mg/l.hr; P.918) was similar in children comedicated with CsA or Tac. Median MMF dose was greater in the CsA group (500 v 250 mg; P.006). Consequently, median AUC 0-7 was significantly lower in the CsA group when equalized for dose and body weight (2.02 v 3.85 g/l.hr per mg of MMF dose per kg of weight; P.002). Variations of MPA pharmacokinetics in pediatric liver transplant recipients suggest that monitoring MPA plasma levels is required. C 0 correlates closely with AUC. Comedication with CsA increased MMF dosage requirements compared with children on Tac therapy. (Liver Transpl 2003;9: ) Mycophenolate mofetil (MMF) is a purine analogue first approved for use in the prophylaxis of organ rejection after renal transplantation. 1,2 It is the ester prodrug of mycophenolic acid (MPA), which acts as a potent reversible inhibitor of inosine monophosphate dehydrogenase, the key enzyme in the de novo purine biosynthesis of proliferating T and B lymphocytes. 3 Its main advantage is its nonnephrotoxic profile. It has been used with increasing frequency in solidorgan transplantation and has an adjuvant immunosuppressive effect when used with the calcineurin inhibitors cyclosporine (CsA) and tacrolimus (Tac) in both the prevention of acute rejection 1,2,4 and treatment of resistant or chronic rejection. 5-7 The pharmacokinetics of MPA, the major metabolite and active component of MMF, has been studied in healthy adult subjects, as well as adult and pediatric renal transplant recipients. 8,9 Despite its increasing use in pediatric liver transplant recipients, 7,10,11 pharmacokinetic studies of MPA in this population are lacking. Aims of this study are to: (1) describe the pharmacokinetics of MPA in a group of stable pediatric liver transplant recipients, (2) define whether single time points can reliably estimate total drug exposure, and (3) identify determinants of pharmacokinetic variability, including comedication with CsA and Tac. Patients and Methods Patient inclusion criteria were: (1) age between 2 and 16 years, (2) stable liver graft function in the preceding 3 months, (2) MMF administration for at least 6 months without dose alteration for at least 1 week before the pharmacokinetic study, and (4) no new medication in the preceding week. Informed (parental) assent was obtained. The study was approved by the local hospital research ethics committee. Twenty-one children (12 boys) were recruited. Median age at the time of the study was 9.5 years (range, 2.1 to 15.3 years). Reasons for transplantation were biliary atresia (7 patients), acute liver failure (4 patients), 1 -antitrypsin deficiency (3 patients), Alagille syndrome (2 patients), cystic fibrosis (1 patient), congenital hepatic fibrosis (1 patient), Crigler-Najjar syndrome (1 patient), progressive intrahepatic cholestasis (1 patient), and neonatal sclerosing cholangitis (1 patient). Median interval from transplantation was 4.7 years (range, 1.3 to 11.4 years). Median time of treatment with MMF was 30 months (range, 9 to 49 months). Reasons for the addition of MMF were for its nephrotoxicity-sparing effect in 8 children and the treatment of resistant From the Institute of Liver Studies, King s College Hospital, London, UK. Presented in part at the 52nd American Association for the Study of Liver Diseases, Dallas, TX, Address reprint requests to Anil Dhawan, MD, Paediatric Liver Service, King s College Hospital, Denmark Hill, London SE5 9RS, UK. Telelephone: ; FAX: ; anil.dhawan@kcl.ac.uk Copyright 2003 by the American Association for the Study of Liver Diseases /03/ $30.00/0 doi: /jlts Liver Transplantation, Vol 9, No 4 (April), 2003: pp

2 384 Aw et al rejection in 13 children. In general, MMF was started at a dose of 10 mg/kg/d administered twice daily and increased to 20 mg/kg/d administered twice daily, to a maximum of 1 g twice daily. MMF dose was adjusted according to the presence of side effects (namely, leukopenia and diarrhea), not to a target MMF level. If the child remained well and graft function was stable, MMF dose was not adjusted for increases in body weight. At the time of these studies, median MMF dose was 25.1 mg/kg/d (range, 11.9 to 37.5 mg/kg/d), administered in two divided daily doses. Absolute median dose was 375 mg (range, 65 to 1,000 mg). Of 21 children, 10 children were coadministered with CsA (all administered prednisolone), and 11 patients were administered Tac (9 patients also administered prednisolone). Blood samples were collected in EDTA anticoagulant before and at 0.33, 0.67, 1.25, 2, 3.5, 5, and 7 hours after the morning dose of MMF. Patients were fasted overnight before the morning dose of MMF. All were allowed to take their usual diet (breakfast and lunch) for the duration of the study. Other medications were withheld, except for pancreatin (two children), anticonvulsant (one child), and warfarin (one child). Samples were stored at 4 C overnight, plasma was separated, and MPA was assayed the following day using an enzyme-multiplied immunoassay technique (EMIT; Dade Behring; San Jose, CA) on the Cobas Mira analyzer (Roche, Nutley, NJ), which is the preferred method at this institution for routine monitoring. Interassay coefficients of variation for MPA were 10% to 11.3% over the concentration range of 0.3 to 15 mg/l. The EMIT assay shows good agreement with a high-performance liquid chromatography (HPLC) method (r 0.98, with EMIT 1.12 HPLC 0.04 for samples from pediatric liver transplant recipients; N. Brown, unpublished observation) and has been used effectively in previous pharmacokinetic studies of MPA. 12,13 Time and magnitude (C max ) of maximal plasma MPA concentrations were noted. The area under the concentration-time curve (AUC) of plasma concentrations to 7 hours (AUC 0-7 ) was calculated using the linear trapezoid rule. AUC 0-12 was calculated based on the assumption that plasma concentration at 12 hours was the same as that for trough concentrations (C 0 ). Complete blood count, international normalized ratio, serum electrolyte and creatinine levels, and liver function tests (aspartate aminotransferase [AST], -glutamyl transpeptidase, and bilirubin levels) were checked at the same time. CsA whole-blood levels were assayed using the Abbott AxSYM Cyclosporine monoclonal fluorescent polarization immunoassay (Abbott Diagnostics [UK] Ltd, Maidenhead, United Kingdom), whereas Tac whole-blood levels were assayed using the Abbott IMx Tacrolimus II microparticle enzyme immunoassay. Serum AST levels were elevated in 7 of 21 children, with a median value of 66 U/L (range, 55 to 80 U/L). Serum -glutamyl transpeptidase levels were elevated in 3 children (48, 85, and 160 U/L), all of whom had elevated AST levels. Median serum bilirubin level for the entire group was 6 mol/l (range, 2 to 15 mol/l). Of children with elevated liver enzyme levels, 2 children had been diagnosed to have posttransplantation de novo autoimmune hepatitis, 2 children had ischemic changes on biopsy, 2 children had mild abnormalities on cholangiography, and 1 child had a normal liver biopsy result. Median calculated creatinine clearance was 85 ml/min/ 1.73 m 2 (range, 41 to 140 ml/min/1.73 m 2 ). All except two children had a calculated creatinine clearance greater than 70 ml/min/1.73 m 2, and their values were 41 and 54 ml/min/ 1.73 m 2. Median CsA and Tac C 0 s were 45 g/l (range, 15 to 88 g/l) and 5.8 g/l (range, 3.4 to 6.7 g/l), respectively. Five of the 21 children experienced MMF-related side effects. Three children had diarrhea soon after MMF therapy was started. In two children, this could have been coincidental viral gastroenteritis, and symptoms resolved without MMF dose alteration. The third child had persistent loose stools, and MMF dose was not increased beyond 25 mg/kg/d. Two children experienced neutropenia that resolved when MMF doses were decreased from 37.5 and 40 to 25 and 20 mg/kg/d, respectively. Correlations between pharmacokinetic data were analyzed using Spearman s rank analysis, and Mann Whitney U test was used to compare results obtained between children comedicated with CsA and those comedicated with Tac. P less than.05 is considered statistically significant. Results MPA plasma concentrations for C 0 (0.36 to 3.7 mg/l), C max (2.8 to mg/l), AUC 0-7 (9.3 to 80.3 mg/l.hr), and AUC 0-12 (12.3 to mg/l.hr) ranged 9-, 14-, 9-, and 9-fold, respectively (Fig. 1). C max occurred at a median time of 0.83 hours (range, 0.33 to 3.5 hours). AUC 0-7 correlated best with C 0 (r 0.84; P.001) and C 3 (r 0.87; P.001) and worst with C 1 (r 0.39; P.08) and C 2 (r 0.57; P.008). In addition, AUC 0-7 correlated with actual MMF dose (r 0.55; P.01) rather than MMF dose corrected for body weight of the child (r 0.29; P.2; Fig. 2). There was no significant difference in median weights of children comedicated with CsA (median, 32.3 kg; range, 20 to 80 kg) compared with Tac (median, 26.9 kg; range, 9.4 to 42 kg; P.2), although the CsA group tended to be heavier. The CsA group was administered significantly greater (absolute) doses of MMF (median, 500 mg; range, 250 to 1,000 mg v 250 mg; range, 65 to 500 mg, respectively; P.006). However, median C 0 (CsA, 1.80 v 1.81 mg/l for Tac; P 1.0) and AUC 0-7 values (CsA, 29.6 v 31.4 mg/l.hr for Tac; P.918) were similar in both groups of children. Consequently, the median dose C 0 ratio was significantly greater (384.2 v 153.8; P.002) and median AUC 0-7 equalized for dose and body weight

3 MPA in Pediatric Liver Transplantation 385 Figure 1. Graphs of C 0,C max, time to maximum concentration (T max ), and AUC 0-7 in stable pediatric liver transplant recipients comedicated with either CsA or Tac. was significantly lower in the CsA group (2.02 v 3.85 ug/l.hr per mg of MMF dose per kg; P.002; Fig. 3). Discussion Our data show that in stable pediatric liver transplant recipients, there are large interindividual variations in MPA pharmacokinetic parameters. This reinforces the need for therapeutic drug monitoring and individualized dosing, especially in light of increasing evidence of good pharmacokinetic/pharmacodynamic correlations with MMF treatment Studies of adult renal transplant recipients have shown a definite relationship between MPA AUC 0-12 and allograft rejection; as AUC 0-12 of MPA increased, the probability of acute allograft rejection decreased. 14 An AUC 0-12 of 30 mg/l.hr achieved a 50% reduction in rejection, whereas a 90% reduction in rejection was associated with an AUC 0-12 greater than 55 mg/l.hr. 14 Median MPA AUC 0-12 achieved by our pediatric liver transplant recipients comedicated with CsA was 40.6 mg/l.hr (range, 14 to 75.3 mg/l.hr). This is similar to the median MPA AUC 0-12 (45 mg/l.hr) of stable adult renal transplant recipients administered CsA, glucocorticoids, and MMF (dose adjusted to 2 g/d). 18 Figure 2. Graphs of AUC 0-7 versus (A) MMF dose and (B) MMF dose adjusted for body weight of child.

4 386 Aw et al Figure 3. Graph showing the difference in MMF dose per kilogram, AUC 0-7, and AUC 0-7 equalized for dose and body weight between children comedicated with CsA and Tac. It has been shown that MMF side effects are associated with the use of greater MMF doses, 15 as well as greater MPA levels. 16 Patients who experienced MPArelated side effects had significantly greater MPA AUC 0-12 values than those who did not ( v mg/l.hr). 16 Median MMF dose for the children in our study was 13.3 mg/kg/dose administered twice daily (range, 10.5 to 18.8 mg/kg/dose administered twice daily), equivalent to the adult dose of 1 g twice daily (assuming adult weight of 70 kg). Only two children required dose reductions because of neutropenia. This suggests that an MMF dose of approximately 15 mg/kg/dose (30 mg/kg/d) could be the most suitable dose for pediatric liver transplant recipients, but this needs confirming in a larger cohort of patients. Differences in renal function are not likely to contribute to the interindividual variations observed because all except two children had normal renal function. In addition, studies of the renal transplant population have shown that the pharmacokinetics of parent MPA are not affected by glomerular filtration rate until almost end-stage renal function is reached. 19,20 Performing 12-hour MPA AUC profiles is not only time consuming and costly, but also less practical and more difficult in children. Full AUC profiles may be valuable in patients in whom specific problems are encountered, but in the majority, there is a strong rationale for using a surrogate marker that best reflects AUC or performing abbreviated AUC profiles. Our study shows good correlation with AUC 0-7 at C 0 (r 0.844). This result differs from corresponding data for both adult and pediatric renal transplant recipients that show poor correlations with predose MPA concentrations (r 0.38 to 0.65 and r 0.48, respectively). 21,22 Our data therefore suggest that immediate predose levels may permit effective MPA monitoring in pediatric liver transplant recipients. We also found close correlations of AUC with C 3 (r 0.87) and C max (r 0.77) in the pediatric liver cohort, similar to those in renal patients in whom close correlations with postdose levels at C max (r 0.63 to 0.76) and 2 (r 0.59) to 3 hours (r 0.52) favor these times for optimal monitoring. 22,23 Consistent with both observations is an absence from all profiles we obtained in liver transplant recipients of a late second peak in MPA plasma levels associated previously with enterohepatic recirculation of MPA glucuronide. 19 We propose that liver graft recipients without a gall bladder may lack this bolus of biliary MPA glucuronide and the second peak, which adds variability to the magnitude of predose MPA levels and reduces their correlation with AUC. Studies of renal transplant recipients have reported pharmacokinetic interactions when patients are comedicated with either CsA or Tac. In general, for the same MMF dose, MPA levels appear lower with CsA comedication and higher with Tac. 12,23-25 Our study shows a significantly lower dose-normalized AUC 0-7 and a correspondingly higher dose-c 0 ratio in the CsAcomedicated group. A study of pediatric renal transplant recipients administered 600 mg/m 2 of MMF gave similar results, with a trend toward a lower dose-normalized AUC in those comedicated with CsA compared with those comedicated with Tac or without calcineurin inhibitors. 12 An additional study of adult renal transplant recipients found that MPA C 0 almost doubled at 9 months after transplantation after the discon-

5 MPA in Pediatric Liver Transplantation 387 tinuation of CsA at 6 months. 23 Two possibilities have been suggested to underlie these drug interactions: (1) Tac augments the bioavailability of MMF through inhibition of MPA glucuronidation, the primary metabolic pathway for MPA 26 ; and (2) CsA inhibits enterohepatic recycling of MPA. 27 Our additional studies on the pharmacokinetics of mycophenolate glucuronide suggest both these mechanisms may apply and are reported elsewhere. 28 These drug interactions have definite implications for patients because conversion from comedication with CsA to Tac could result in a sudden increase in MPA levels and potential toxicity. At the same time, MPA monitoring would be important when one is considering withdrawal of either calcineurin inhibitor, especially Tac, because it could result in significant changes in MPA levels and possible underimmunosuppression. In conclusion, variable MPA pharmacokinetics in pediatric liver graft recipients suggests that monitoring MPA plasma levels is required. MPA C 0 correlated closely with AUC in our small cohort of pediatric liver transplant recipients and may be ideal for drug monitoring. Comedication of MMF with CsA increased dosage requirements compared with children comedicated with Tac to achieve similar MPA C 0 s. These drug interactions as a result of comedication make monitoring MPA levels particularly crucial at times when calcineurin inhibitor conversion or withdrawal is being considered. References 1. The European Mycophenolate Mofetil Co-operative Study Group. Placebo-controlled study of mycophenolate mofetil combined with cyclosporin and corticosteroids for prevention of acute rejection. Lancet 1995;1: Sollenger HW for the US Renal Transplant Mycophenolate Mofetil Study Group. Mycophenolate mofetil for the prevention of acute rejection in primary cadaveric renal allograft recipients, the US Renal Transplant Mycophenolate Mofetil Study Group. Transplantation 1995;60: Eugui EM, Allison AC. Immunosuppressive activity of mycophenolate mofetil. Ann NY Acad Sci 1993;685: Sterneck M, Fisher L, Gahlemann C, Gundlach M, Rogiers X, Broelsch C. Mycophenolate mofetil for prevention of liver allograft rejection: Initial results of a controlled clinical trial. Ann Transplant 2000;5: Herbert MF, Ascher NL, Lake JR, Emond J, Nikolai B, Linna TJ, Roberts JP. Four-year follow-up of mycophenolate mofetil for graft rescue in liver allograft recipients. Transplantation 1999;67: The Mycophenolate Mofetil Renal Refractory Rejection Study Group. Rescue therapy with mycophenolate mofetil. Clin Transplant 1996;10: Chardot C, Nicoluzzi JE, Janssen M, Sokal E, Lerut J, Otte JB, Reding R. Use of mycophenolate mofetil as rescue therapy after pediatric liver transplantation. Transplantation 2001;71; Bullingham RES, Nicholls AJ, Kamm BR. Clinical pharmacokinetics of mycophenolate mofetil. Clin Pharmacokinet 1998;34: Weber LT, Shipkova M, Lamersdorf T, Shipkova M, Niedmann P, Oellerich M, et al. Pharmacokinetics of mycophenolic acid (MPA) and determinants of MPA free fraction in pediatric and adult renal transplant recipients. J Am Soc Nephrol 1998;9: Aw MM, Samaroo B, Baker AJ, Verma A, Rela M, Heaton ND, et al. Calcineurin-inhibitor related nephrotoxicity Reversibility in paediatric liver transplant recipients. Transplantation 2001;72: Renz JF, Lightdale J, Mudge C, Bacchetti P, Watson J, Ascher ND, et al. Mycophenolate mofetil, microemulsion cyclosporine, and prednisone as primary immunosuppression for pediatric liver transplant recipients. Liver Transpl Surg 1999;5: Filler G, Zimmering M, Mai I. Pharmacokinetics of mycophenolate mofetil are influenced by concomitant immunosuppression. Pediatr Nephrol 2000;14: Vidal E, Cantarell C, Capdevila L, Monforte V, Roman A, Pou L. Mycophenolate mofetil pharmacokinetics in transplant patients receiving cyclosporine or tacrolimus in combination therapy. Pharmacol Toxicol 2000;87: Bullingham RES, Nicolls A, Hale M. Pharmacokinetics of mycophenolate mofetil (RS61443): A short review. Transplant Proc 1996;28: Van Gelder T, Hilbrands LB, Vanrenterghem Y, Weimar W, De Fijter JW, Squifflet JP, et al. A randomised double-blind, multicenter plasma concentration controlled study of the safety and efficacy of oral mycophenolate mofetil for the prevention of acute rejection after kidney transplantation. Transplantation 1999;68: Mourad M, Malaise J, Chaib Eddour D, De Meyer D, Konig J, Schepers R, et al. Correlation of mycophenolic acid pharmacokinetic parameters with side effects in kidney transplant patients treated with mycophenolate mofetil. Clin Chem 2001;47: Shaw LM, Korecka M, DeNofrio D, Brayman KL. Pharmacokinetic, pharmacodynamic and outcome investigations as the basis for mycophenolic acid therapeutic drug monitoring in renal and heart transplant patients. Clin Biochem 2001;34: Shaw LM, Nicholls A, Hale M, Armstrong VW, Ollerich M, Yatscoff R, et al. Therapeutic monitoring of mycophenolic acid. A consensus panel report. Clin Biochem 1998;31: Weber LT, Lamersdorf T, Shipkova M, Niedmann PD, Wiesel M, Zimmerhackl LB, et al. Area under the plasma concentration time curve for total but not free mycophenolic acid increases in the stable phase after renal transplantation: A longitudinal study in pediatric patients. Ther Drug Monit 1999;21: Shah J, Bullingham R, Rice P, Tsina I, Swan S, Halstenson C. Pharmacokinetics of oral mycophenolate mofetil and metabolites in renally impaired patients [abstract]. Clin Pharmacol Ther 1995;57:149A. 21. Brunet M, Martorell J, Oppenheimer F, Vilardell J, Millan O, Carrillo M, et al. Pharmacokinetics and pharmacodynamics of mycophenolic acid in stable renal transplant recipients treated with low doses of mycophenolate mofetil. Transpl Int 2000; 13(suppl 1):S301-S Filler G, Mai I. Limited sampling strategy for mycophenolic acid area under the curve. Ther Drug Monit 2000;22:

6 388 Aw et al 23. Gregoor PJ, de Sevaux RG, Hene RJ, Hesse CJ, Hilbrands LB, Vos P, et al. Effect of cyclosporine on mycophenolic acid trough levels in kidney transplant recipients. Transplantation 1999;68: Gregoor PJ, van Gelder T, Hesse CJ, van der Mast BJ, van Besouw NM, Weimar W. Mycophenolic acid plasma concentrations in kidney allograft recipients with or without cyclosporin: A cross-sectional study. Nephrol Dial Transplant 1999;14: Hubner GI, Eismann R, Sziegoleit W. Drug interaction between mycophenolate mofetil and tacrolimus detectable within therapeutic mycophenolic acid monitoring in renal transplant patients. Ther Drug Monit 1999;21: Zucker K, Tsaroucha A, Olson L, Esquenazi V, Tzakis A, Miller J. Evidence that tacrolimus augments the bioavailability of mycophenolate mofetil through the inhibition of mycophenolic acid glucuronidation. Ther Drug Monit 1999;21: van Gelder T, Klupp J, Barten M, Christians U, Morris RE. Comparison of the effects of tacrolimus and cyclosporine on the pharmacokinetics of mycophenolic acid. Ther Drug Monit 2001;23: Brown N, Aw MM, Mieli-Vergani G, Dhawan A, Tredger JM. Mycophenolic acid and mycophenolic acid glucuronide pharmacokinetics in pediatric liver transplant recipients: Effect of cyclosporine and tacrolimus co-medication. Ther Drug Monit 2002; 24: