Marsha R. Honaker

The Effect of CYP3A5 and MDR1 Polymorphic Expression on Cyclosporine Oral Disposition in Renal Transplant Patients

Variability in CYP3A (CYP3A4/5) and P‐glycoprotein (human MDR1 gene product) activity underlies interindividual differences in oral cyclosporine (CsA) bioavailability. Racial differences in polymorphic expression of CYP3A5 and MDR1 may explain observed interracial variability in oral bioavailability. Our objective was to evaluate the effect of CYP3A5 and MDR1 polymorphic expression on CsA oral disposition. Steady‐state plasma concentration profiles (n = 19) were sampled in renal transplant recipients receiving concentration‐adjusted CsA maintenance therapy. CsA plasma concentrations were measured by fluorescence polarization immunoassay. CYP3A5 and MDR1 genotypes were determined by real‐time polymerase chain reaction. Noncompartmental pharmacokinetic analysis and nonlinear mixed‐effects modeling (NONMEM) were performed to assess the effect of genotype on CsA pharmacokinetics. MDR1 C3435T genotype was identified as the best predictor of CsA systemic exposure. CsA oral clearance was significantly higher in subjects who carried at least one 3435T allele compared to homozygous wild‐type individuals (40.0 ± 2.2 vs. 26.4 ± 3.1 L/h, p = 0.007). MDR1 C3435T genotype accounted for 43% of the interindividual variability of CsA oral clearance in the study population after accounting for interoccasion variability. The authors were unable to independently assess whether CYP3A5 correlated with any CsA pharmacokinetic parameter since all CYP3A5 nonexpressors were also 3435T allele carriers. MDR1 3435T allele carriers have enhanced oral clearance compared to individuals with the CC genotype. The frequency of the 3435T allele is lower in African Americans compared to Caucasians. Thus, the MDR1 C3435T genotype offers a potential mechanistic basis to explain interracial differences in CsA oral bioavailability. Further studies are needed to explore the relationship between CYP3A5 and MDR1 genotype and phenotype.

Evolving experience of hepatitis B virus prophylaxis in liver transplantation

Abstract: Passive immunoprophylaxis with hepatitis B immunoglobulin (HBIG) is important to prevent recurrence of hepatitis B virus (HBV) after orthotopic liver transplantation (OLT) for chronic HBV cirrhosis. With availability of lamivudine (3TC), the use of combination prophylaxis with long‐term HBIG/3TC has been shown to prevent short‐term HBV recurrence. This report compares HBV recurrence rates between groups receiving no/short‐term HBIG, long‐term HBIG alone, or HBIG/3TC prophylaxis, and describes HBIG requirements during the first 6 and 12 months in the latter two groups. This study involved patients undergoing OLT at the University of Tennessee‐Memphis between May 1990 and July 2001. During this period, 388 liver transplants were performed at our center. All hepatitis B surface antigen (HBsAg)‐positive recipients (n = 27) were included in this retrospective analysis. The groups were similar with regard to pre‐transplant demographic characteristics such as age, gender, weight, and pre‐transplant diagnosis. Owing to the retrospective study design, median follow‐up was longer for the no‐prophylaxis (5.6 years) and the HBIG‐alone (6.0 years) groups compared to the HBIG/3TC group (4.2 years). Patient survival was 50% in the no‐prophylaxis and 71% in the HBIG‐alone groups compared to 100% in the HBIG/3TC group (P = 0.09). When censored for death with a functioning graft, graft survival was 50% in the no‐prophylaxis and 86% in the HBIG‐alone group compared to 100% in the HBIG/3TC group (P = 0.07). The overall incidence of HBV recurrence in the no‐prophylaxis era was 100% and 21% in the HBIG‐alone era compared to 0% in the HBIG/3TC era (P < 0.001), despite similar mean and median HBIG trough titers in the HBIG‐alone and HBIG/3TC groups. The incidence of HBV recurrence in HBV DNA‐positive recipients was 100% in the no‐prophylaxis era, 30% in the HBIG‐alone era, and 0% in the HBIG/3TC era (P < 0.001). Recipients in the HBIG‐alone group had a nearly two‐fold increase in HBIG requirement at 6 and 12 months in order to maintain similar HBIG trough titers post‐transplant compared to recipients in the HBIG/3TC group despite similar pre‐transplant HBV serology. This increased HBIG requirement in the HBIG‐alone group resulted in a marked increase in the mean overall cost of HBV prophylaxis in this group (

Detection of MDR1 single nucleotide polymorphisms C3435T and G2677T using real-time polymerase chain reaction: MDR1 single nucleotide polymorphism genotyping assay.

47,367 at 6 months;

Renal allograft loss as the result of polyomavirus interstitial nephritis after simultaneous kidney-pancreas transplantation: results with kidney retransplantation.

84,280 at 12 months) compared to the HBIG/3TC group (

Retrospective evaluation of the risk of hepatitis B virus reactivation after transplantation

25,931 at 6 months;

Impact of hepatitis C virus status in pancreas transplantation: a case controlled study

49,599 at 12 months). These data demonstrate an improvement in patient and graft survival rates in the group receiving combination HBIG/3TC prophylaxis compared to the HBIG‐alone and no‐prophylaxis groups. There was a significant reduction in HBV recurrence in the group receiving combination HBIG/3TC when compared to the groups receiving HBIG alone or no prophylaxis. Furthermore, we demonstrated that the addition of 3TC to the long‐term HBIG regimen led to elimination of the disparity previously described in HBV recurrence rates between HBV DNA‐positive and HBV DNA‐negative recipients. Importantly, our data demonstrates a complete lack of HBV recurrence in the HBIG/3TC group at a median follow‐up of 4.2 years. Additionally, the data show that the addition of 3TC to the post‐operative prophylaxis regimen resulted in a reduction in the requirement of HBIG at 6 and 12 months, which markedly reduced the overall cost of post‐transplant HBV prophylaxis.

Thymoglobulin for induction or rejection therapy in pancreas allograft recipients: a single centre experience.

The objective of this study was to develop a real-time polymerase chain reaction (PCR) method to detect MDR1 (human multidrug resistance gene) single nucleotide polymorphisms (SNPs) C3435T and G2677T. C3435T and G2677T are linked to MDR1 *2, which is associated with enhanced efflux activity in vitro. Using the Smart Cycler, an allele-specific real-time PCR-based genotyping method was developed to detect C3435T and G2677T. The MDR1 genotype of human genomic DNA templates was determined by direct DNA sequencing. PCR reactions for genotyping C3435T and G2677T by using allele-specific primers were conducted in separate tubes. An additional nucleotide mismatch at the third position from the 3′ end of each allele-specific primer was used to abrogate nonspecific PCR amplification. The fluorescence emitted by SYBR Green I was monitored to detect formation of specific PCRproducts. PCR growth curves exceeding the threshold cycle were considered positive. Fluorescence melt-curve analysis was used to corroborate results from PCR growth curves. Using PCR growth curves, our assay accurately determined hetero- and homozygosity for C3435T and G2677T. Genotype assignments based on PCR growth curve, melt-curve analysis, agarose gel electrophoresis, and direct DNA sequencing results of PCR products were in perfect agreement. We have developed a rapid MDR1 genotyping method that can be used to assess the contribution of MDR1 *2 to pharmacokinetic and pharmacodynamic variability of P-glycoprotein substrates.

Short-term outcomes of Thymoglobulin induction in pediatric renal transplant recipients

Background. Polyomavirus (PV) infection in kidney transplant patients has been reported to cause interstitial nephritis and subsequent graft loss. The cornerstone of current therapy is a reduction in immunosuppression, which can subsequently lead to kidney allograft rejection. This dilemma becomes even more challenging in the setting of simultaneous kidney-pancreas transplantation, because a reduction in immunosuppression may result in rejection of the pancreas allograft. Antiviral therapy has not been shown to be clinically successful in decreasing the risk of graft loss secondary to PV infection. Furthermore, because of limited experience, the decision to perform retransplantation in patients who lost their primary kidney grafts to PV interstitial nephritis becomes a difficult one. Methods. Retrospective review and case studies. Results. We report two successful living donor kidney retransplants in simultaneous kidney-pancreas transplant patients who lost their first kidney grafts to PV infection. Both patients are receiving rimantadine therapy and performing well, with functioning kidney and pancreas grafts and no evidence of recurrent PV interstitial nephritis 22 and 37 months after retransplantation. Conclusions. Although follow-up is limited, our initial experience would indicate that graft loss secondary to PV interstitial nephritis is not an absolute contraindication for kidney retransplantation.

Renal allograft outcomes in African American versus Caucasian transplant recipients in the tacrolimus era.

Abstract: Numerous case reports describe patients with previously documented immunity developing active hepatitis B virus (HBV) infection after transplantation. However, the risk of reactivation of HBV under long‐term immunosuppression in hepatitis B core antibody (HBcAb)‐positive, hepatitis B surface antigen (HBsAg)‐negative transplant recipients has not been clearly described. Herein, we present a long‐term follow‐up for 49 HBcAb‐positive, HBsAg‐negative recipients (27 liver, 18 kidney, 4 pancreas) transplanted between June 1996 and April 2001. Among these, 37 recipients (76%) were HBsAb positive at transplantation. Immunosuppression consisted of various antibody induction regimens in 20 (41%) of the recipients with either tacrolimus (33 [67%])‐ or cyclosporine (16 [33%])‐based maintenance immunosuppression. The incidence and duration of HBV prophylaxis was not significant. No patient received hepatitis B immunoglobulin (HBIG) before or after transplantation. Additionally, only two patients received lamivudine, which was started post transplant without clinical indication. The mean length of follow‐up was 3.1±1.4 years. At the last follow‐up, overall patient and graft survival were 98% and 96%, respectively. Patient survival was 96% in liver, 100% in kidney, and 100% in pancreas transplant recipients. The graft survival for each organ type was 93% in liver, 100% in kidney, and 75% in pancreas transplant recipients at the end of follow‐up. There was no incidence of HBV reactivation defined as recurrence of HBsAg and/or HBV DNA positivity. These data suggest that the risk of reactivation of HBV in HBcAb‐positive, HBsAg‐negative transplant recipients under immunosuppression is negligible, regardless of immunosuppressive regimen, lamivudine prophylaxis, or HBsAb status. These patients should have access to transplantation as they enjoy excellent patient and graft survival rates.

Tacrolimus: A "heads up" on potential drug interactions

Available data suggest that hepatitis C virus positive (HCV+) renal transplant patients may be at an increased risk of morbidity and mortality compared with HCV− patients. Limited data are available regarding the impact of HCV status in pancreas transplant patients. We compared the outcomes of 10 HCV+ patients undergoing pancreas transplantation (seven simultaneous kidney‐pancreas, one pancreas after kidney, two pancreas alone) between 1/96 and 10/99 with 20 HCV− recipients that were matched for age, race, gender, timing of transplant, type of pancreas transplant, and surgical technique. Length of follow‐up was not significantly different between the HCV+ group compared with the HCV− group (24 ± 14 vs. 20 ± 13 months; p=0.45). There was a trend toward a higher incidence of all cause mortality in HCV+ recipients compared with HCV− recipients, 30 vs. 10%, respectively (p=0.17). Additionally, the HCV+ recipients had a trend toward a higher incidence of sepsis‐related mortality compared with HCV− recipients, 20 vs. 5%, respectively (p=0.19). Renal allograft survival was 50% in the HCV+ group compared with 94% in the HCV− group (p=0.02). Pancreas allograft survival was not significantly different between the groups, 60 vs. 80%, respectively (p=0.24). At 3, 6, 12 months, and end of follow‐up, there were no differences in serum creatinine, amylase, C‐peptide, or fasting glucose levels. However, there was a significantly higher incidence of proteinuria at last follow‐up in the HCV+ recipients with a renal allograft when compared with HCV− recipients, 50 vs. 12.5%, respectively (p=0.05). In order to maintain comparable glycemic control between the groups, there was a significant increase in oral hypoglycemic requirement in HCV+ recipients compared with HCV− recipients, 33 vs. 0%, respectively (p=0.01). These data suggest that HCV+ pancreas transplant patients may be at an increased risk of graft dysfunction and morbidity. Further studies with more patients and longer follow‐up are needed to fully define the impact of HCV status on pancreas graft survival and function.