Genetic and clinical determinants of mizoribine pharmacokinetics in renal transplant recipients.

AIM: Mizoribine (MZR) is an immunosuppressant for the prevention of allograft rejection in Asian countries, but the great variability in pharmacokinetics (PK) limits its clinical use. This study was to explore genetic and clinical factors that affect the MZR PK process. METHODS: Blood samples and clinical data were collected from 60 Chinese renal transplant recipients. MZR plasma concentration was measured at pre-dose (0 h) and 0.5, 1, 2, 3, 4, 5, 6, 8, and 12 h post-dose by high performance liquid chromatography with an ultraviolet detector. PK parameters were calculated by non-compartmental analysis. High-throughput sequenced single nucleotide polymorphism was applied screening possible genetic factors. RESULTS: Extensive inter-individual MZR PK differences were reflected in the process of elimination (ke, CL/F, MRT and t1/2) and intestinal absorption (Cmax and Tmax), as well as in the dose-normalized exposure (AUC0-12h/D). From 146 SNPs within 39 genes screened, AUC0-12h/D was found higher in recipients with CREB1 rs11904814 TT than with G allele carriers (3.135 ± 0.928 versus 2.084 ± 0.379 µg h ml-1 mg-1, p = 0.007). Recipients with SLC28A3 rs10868138 TT had lower t1/2 as compared to C allele carriers (0.728 ± 0.189 versus 0.951 ± 0.196 h, p = 0.001). Serum creatinine (SCr) explained 35.5% of C0/D variability (p < 0.001). Pure effects of genotypes CREB1 and SLC28A3 were 13.7% (p = 0.004) and 17.5% (p = 0.001) for AUC0-12h/D and t1/2, respectively. When additionally taking SCr into models, CREB1 and SLC28A3 genotypes explained 20.0% (p = 0.038) and 46.5% (p < 0.001) of AUC0-12h/D and t1/2 variability, respectively. CONCLUSION: CREB1 and SLC28A3 genotypes, as well as SCr, are identified as determinants in predicting inter-individual MZR PK differences in renal transplant recipients.

Prediction of mizoribine pharmacokinetic parameters by serum creatinine in renal transplant recipients.

PURPOSE: Mizoribine (MZR) is an immunosuppressive agent with extensive inter-individual differences in pharmacokinetics (PK). Here, we investigated the PK characteristics of MZR in renal transplant recipients and gave equations for prediction of some critical PK parameters. METHODS: A total of 40 renal transplant recipients participated in this prospective study and were administered MZR orally twice daily in the range of 1.1-8.9 mg kg-1 day-1. Steady-state concentrations of MZR were detected before (0 h) and 0.5, 1, 2, 3, 4, 5, 6, 8, and 12 h after administration by high-performance liquid chromatography method. Another 38 patients with newly detected trough concentration (C0) were enrolled to validate the obtained C0 predictive equation. RESULTS: Significant inter-individual differences in MZR PK parameters were observed. Patients with decreasing creatinine clearance rate (CCr) had significantly decreased terminal elimination rate constant (kel) and apparent total body clearance (Cl/F), while other PK parameters including apparent terminal half-life (t1/2), peak time (Tmax), peak concentration (Cmax), area under the curve (AUC0-12h), apparent volume of distribution (V/F), and mean residence time (MRT) were significantly increased. Correlation coefficients between AUC0-12h and C0/Cmax were 0.894 and 0.916, respectively (both p < 0.001). A serum creatinine (SCr)-based predictive C0 equation [C0 = (2.160 × SCr - 54.473) × Dose] was established and validated by C0 from another 38 patients. Besides, significant linear correlations between kel/t1/2 and CCr were also found (r2 = 0.668 and 0.484, respectively), and equations predicting kel/t1/2 were also obtained (kel = 0.015 + 0.002 × CCr, t1/2 = 13.601 - 0.139 × CCr). CONCLUSIONS: Renal function plays as an essential factor that contributes to great inter-individual MZR PK variation. Both C0 and Cmax are suitable for evaluating MZR exposure in the body. SCr could be applied to predict C0 and t1/2 of MZR.

Mizoribine therapy combined with steroids and mizoribine blood concentration monitoring for idiopathic membranous nephropathy with steroid-resistant nephrotic syndrome.

BACKGROUND: We designed a prospective and randomized trial of mizoribine (MZR) therapy combined with prednisolone (PSL) for idiopathic membranous nephropathy (IMN) with steroid-resistant nephrotic syndrome (SRNS). METHODS: Patients with IMN were divided into 2 groups, and MZR combined with PSL was administered for 2 years. PSL was initially prescribed at 40 mg/day and tapered. MZR was given once-a-day at 150 mg and 3-times-a-day at 50 mg each to groups 1 and 2. Serum MZR concentrations from 0 to 4 h after administration were examined within one month of treatment. The concentration curve and peak serum level (C max) of MZR were estimated by the population pharmacokinetic (PPK) parameters of MZR. RESULTS: At 2 years, 10 of 19 patients (52.6 %) in group 1 and 7 of 18 patients (38.9 %) in group 2 achieved complete remission (CR). The time-to-remission curve using the Kaplan-Meier technique revealed an increase in the cumulative CR rate in group 1, but no significant difference between the groups. Meanwhile, there was a significant difference in C max between groups 1 and 2 (mean ± SD: 1.20 ± 0.52 vs. 0.76 ± 0.39 µg/mL, p = 0.04), and C max levels in CR cases were significantly higher than those in non-CR cases. Receiver operating characteristic analysis showed that C max more than 1.1 µg/mL was necessary for CR in once-a-day administration. CONCLUSION: Administration of MZR once a day is useful when combined with PSL for treatment of IMN with SRNS. In addition, it is important to assay the serum concentration of MZR and to determine C max, and more than 1.1 µg/mL of C max is necessary for CR.

Population pharmacokinetics of mizoribine in pediatric patients with kidney disease.

BACKGROUND: The present study aimed to obtain information enabling optimisation of the clinical effect of mizoribine (MZR) in pediatric patients with kidney disease. METHODS: A total of 105 pediatric patients with kidney disease treated at our institutions were enrolled. Kidney transplant patients were excluded. Population pharmacokinetic analysis of MZR was performed based on serum concentration data. Area under the curve from time zero to infinity (AUC∞) and maximal concentration (C max) were calculated by Bayesian analysis. RESULTS: In children, the appearance of MZR in the blood tended to be slower and the subsequent rise in blood concentration tended to be more sluggish, compared to healthy adults. Apparent volume of distribution and oral clearance were also higher in children compared to adults. A significant positive correlation was observed between patient age and AUC∞. There were significant differences of AUC∞ and C max by age group. No relationship was observed between the administration method of MZR and serum concentration. CONCLUSION: The pharmacokinetics of MZR was different in children compared to adults. To obtain the expected clinical efficacy, the regular MZR dosage schedule (2-3 mg/kg/day) might be insufficient for pediatric patients. In particular, younger patients might require a higher dosage of MZR per unit body weight.

Chronopharmacology of mizoribine in collagen-induced arthritis rats.

We previously reported that higher therapeutic effects were obtained in rheumatoid arthritis (RA) patients and RA model animals when the dosing-times of methotrexate and tacrolimus were chosen according to the 24-h rhythms of the inflammatory response. Mizoribine (MZR) is an immunosuppressive agent and is used against RA in the same manner as methotrexate and tacrolimus. In this study, we examined whether a dosing-time dependency of the therapeutic effect of MZR could be detected in collagen-induced arthritis (CIA) rats. To measure C-reactive protein (CRP) and tumor necrosis factor (TNF)-α levels, blood was collected from CIA rats at different times. MZR was administered at two different dosing-times based on these findings and its effects and toxicity were examined. CRP and TNF-α concentrations in blood showed significant 24-h rhythms. The exacerbation of arthritis and excessive increase in leukocytes in CIA rats were markedly lower in the group treated with MZR at the dark phase than those of the group treated with MZR at the light phase. These findings suggest that the therapeutic index of RA therapy may be improved by administering MZR at a time in the day when the inflammatory reaction begins to activate.

Therapeutic effect of mizoribine on pemphigus vulgaris and pemphigus foliaceus.

We evaluated the effectiveness of mizoribine, a newly developed immunosuppressive agent, as an adjuvant therapy in the treatment of both pemphigus vulgaris and pemphigus foliaceus. Eleven pemphigus patients (eight pemphigus vulgaris and three pemphigus foliaceus) received the combination therapy of prednisolone and mizoribine. Complete remission was observed in three of the eight patients with pemphigus vulgaris and in one of the three patients with pemphigus foliaceus. The four patients with complete remission had a rapid clinical response and achieved remission at a median of 11.8 months. Partial remission was achieved in two of the three patients with pemphigus foliaceus. The median time to achieve partial remission was 16.0 months. Six (55.6%) of the 11 patients with pemphigus had complete or partial remission and were able to taper their prednisolone. The cumulative probability of having a complete remission was 64.3% at 19 months of follow-up using Kaplan-Meier analysis. The effectiveness of the additional mizoribine therapy could be attributed to its corticosteroid-sparing properties as well as its immunosuppressive effects. The serum concentration titer of mizoribine was around 1.0 µg/mL 2 hours after administration. Patients who were not improved by the additional mizoribine might require a continuously higher dose of mizoribine to achieve effective therapy.

Effect of single-dose oral mizoribine pulse therapy twice per week for frequently relapsing steroid-dependent nephrotic syndrome.

AIM: To evaluate the efficacy of single-dose oral mizoribine (MZB) pulse therapy given twice weekly for frequently relapsing steroid-dependent nephrotic syndrome (FR-SDNS). METHODS: The subjects were 8 patients with FR-SDNS with a median age of 6.9 years old (range 3.1 - 18.0 y). The study was performed as a Phase II trial. The MZB dose was adjusted to achieve a peak blood level of 3 - 5 µg/ml (3.9 - 15.9 mg/kg/d, maximum dose: 750 mg) using a single dose given twice weekly before a meal. The therapeutic benefits of MZB pulse therapy were assessed based on a comparison of the incidence of relapse and the required daily dosage of prednisolone (PSL) in the 12 months prior to and following therapy. RESULTS: The incidence of relapse after therapy was significantly lower than that before therapy (2.5 ± 1.4 vs. 4.3 ± 0.5, p < 0.01) and the required daily dosage of prednisolone (PSL) after therapy was lower than that before therapy (0.48 ± 0.23 vs. 0.52 ± 0.32 mg/kg/d, not significant). However, this therapy was not effective for 3 out of 4 patients treated with cyclosporine. During follow-up, discontinuation of PSL was possible in 4 of 5 patients who showed a decreased rate of relapse after therapy. The peak blood concentration of MZB in these patients was significantly higher than that in 3 patients who did not show a decreased rate of relapse (3.95 ± 0.11 vs. 3.05 ± 0.21 µg/ml, p < 0.01). No adverse effects were observed in any patients. CONCLUSION: Our results show that single-dose oral MZB pulse therapy is effective in decreasing the frequency of relapse in some pediatric patients with FR-SDNS. A peak concentration of MZB of ~3.8 - 4.0 µg/ ml may be required for FR-SDNS therapy.

An investigation of the correlation between blood concentration of mizoribine and its efficacy in treatment of rheumatoid arthritis based on indices of drug survival and improvement in DAS28-CRP.

OBJECTIVES: The efficacy of mizoribine (MZR) in treatment of rheumatoid arthritis (RA) was retrospectively investigated in terms of drug survival, improvement in Disease Activity Score-28 (DAS28)-C-reactive protein (CRP), and blood MZR concentration obtained 3 h after dosing (MZR-C3). METHODS: To compare the efficacy of MZR administered via different regimens, the subjects were divided into 2 groups: those receiving a single dose of MZR at 100-150 mg every other day (group A) and those receiving 2 or 3 divided doses of the drug on consecutive days, which is the usual dosing method of the drug (group B). RESULTS: Group A had significantly higher MZR-C3 levels compared with group B, as well as significantly greater improvement in DAS28-CRP. Moreover, drug survival was significantly longer in group A. The primary regression equation suggested that the effective blood MZR concentration in RA treatment is MZR-C3 of 1.47 µg/mL or more. CONCLUSIONS: The results of the present study indicate that it is possible to increase the efficacy of MZR in a blood concentration-dependent manner, and also to control RA over a prolonged period, using single administration of MZR on alternate days at an increased dose.

An association study of ABCG2 rs2231142 on the concentrations of allopurinol and its metabolites.

ABCG2 is a gene that codes for the human breast cancer resistance protein (BCRP). It is established that rs2231142 G>T, a single nucleotide polymorphism of the ABCG2 gene, is associated with gout and poor response to allopurinol, a uric acid-lowering agent used to treat this condition. It has also been suggested that oxypurinol, the primary active metabolite of allopurinol, is a substrate of the BCRP. We thus hypothesized that carrying the rs2231142 variant would be associated with decreased oxypurinol concentrations, which would explain the lower reduction in uric acid. We performed a cross-sectional study to investigate the association between the ABCG2 rs2231142 variant and oxypurinol, allopurinol, and allopurinol riboside concentrations in 459 participants from the Montreal Heart Institute Hospital Cohort. Age, sex, weight, use of diuretics, and estimated glomerular filtration rate were all significantly associated with oxypurinol plasma concentration. No association was found between rs2231142 and oxypurinol, allopurinol and allopurinol riboside plasma concentrations. Rs2231142 was not significantly associated with daily allopurinol dose in the overall population, but an association was observed in men, with T carriers receiving higher doses. Our results do not support a major role of ABCG2 in the pharmacokinetics of allopurinol or its metabolites. The underlying mechanism of the association between rs2231142 and allopurinol efficacy requires further investigation.

Population pharmacokinetics of mizoribine in adult recipients of renal transplantation.

BACKGROUND: The aim of the present study was to estimate the population pharmacokinetic parameters of mizoribine in adult recipients of renal transplantation using a nonlinear mixed effects model (NONMEM) program. METHODS: Pharmacokinetic data for population analysis were retrospectively collected from 114 recipients (66 males and 48 females) routinely treated with oral administration of mizoribine (25-450 mg/day). The range of creatinine clearance (CL(cr)) was 7.6-136.1 mL/min (mean 49.2 mL/min). RESULTS: The pharmacokinetics of mizoribine in adult recipients of renal transplantation was well described by a 1-compartment model with first-order absorption. The mean value of the absorption lag time (ALAG) and absorption rate constant (KA) was estimated to be 0.581 and 0.983 h(-1), respectively. Apparent volume of distribution (V/F) was modeled as a function of body weight (WT), and the mean value was estimated to be 0.858 × WT L. Oral clearance (CL/F) was modeled as a function of creatinine clearance (CL(cr)), and the mean value was estimated to be 1.80 × CL(cr) × 60/1000 L/h. In addition, there was a strong correlation between CL(cr)-corrected CL/F and WT-corrected V/F in the adult recipients, indicating large interindividual variability in bioavailability (F) of mizoribine. CONCLUSION: The present findings suggested that not only the rate of renal excretion but also the extent of intestinal absorption of mizoribine is responsible for the large interindividual pharmacokinetic variability of the drug.

Development and validation of LC/MS/MS method for Triciribine and its monophosphate metabolite in plasma and RBC: Application to mice pharmacokinetic studies.

Triciribine (TCN) is a tricyclic nucleoside analog of adenosine and an inhibitor of Akt kinase. Triciribine 5'-monophosphate (TCNP) is a water-soluble analog of Triciribine and has progressed to Phase I and II clinical trials in oncology. TCNP is also an endogenous anabolite of TCN similar to other nucleoside phosphates. Clinical development of TCNP has been hampered by high pharmacokinetic variability due to complex interplay of TCN-TCNP conversion and reconversion in plasma, erythrocytes (RBC) and peripheral organs. TCN has been demonstrated to be an efficacious agent in mice models of acute lung injury at low doses (0.5 mg/kg/day) although its pharmacokinetic-pharmacodynamic (PK/PD) relationship remained unclear. We have developed and validated a sensitive, specific and robust LC/MS/MS assay for quantitation of TCN and TCNP in plasma and RBC. Using a simple protein precipitation method, quantitation of these analytes was accomplished with recoveries exceeding 85% and with a run time of 4 min. This assay was used to determine the pharmacokinetic parameters of TCN and TCNP in mice after single dose intravenous administration at 1, 3 and 10 mg/kg. TCNP accumulates in RBC, has low clearance and a half-life of 18 to 23 h. Unlike other nucleoside phosphates, TCNP was found to be relatively stable in mice plasma serving as a secondary depot. TCN levels were low and with high clearance relative to hepatic blood flow. A combination of sustained levels of TCNP in RBC and plasma serves as a depot for TCN to elicit robust therapeutic activity in acute lung injury mice models.

Maribavir prophylaxis for prevention of cytomegalovirus infection in allogeneic stem cell transplant recipients: a multicenter, randomized, double-blind, placebo-controlled, dose-ranging study.

The anti-cytomegalovirus (CMV) activity and safety of oral maribavir in CMV-seropositive allogeneic stem-cell transplant recipients were evaluated in a randomized, double-blind, placebo-controlled, dose-ranging study. After engraftment, 111 patients were randomized to receive CMV prophylaxis with maribavir (100 mg twice daily, 400 mg once daily, or 400 mg twice daily) or placebo. Within the first 100 days after transplantation, the incidence of CMV infection based on CMV pp65 antigenemia was lower in each of the respective maribavir groups (15%, P = .046; 19%, P = .116; 15%, P = .053) compared with placebo (39%). Similarly, the incidence of CMV infection based on plasma CMV DNA was lower in each of the respective maribavir groups (7%, P = .001; 11%, P = .007; 19%, P = .038) compared with placebo (46%). Anti-CMV therapy was also used less often in patients receiving each respective dose of maribavir (15%, P = .001; 30%, P = .051; 15%, P = .002) compared with placebo (57%). There were 3 cases of CMV disease in placebo patients but none in the maribavir patients. Adverse events, mostly taste disturbance, nausea, and vomiting, were more frequent with maribavir. Maribavir had no adverse effect on neutrophil or platelet counts. These results show that maribavir can reduce the incidence of CMV infection and, unlike ganciclovir, does not cause myelosuppression.

A sensitive and practical LC-MS/MS method for the determination of mizoribine in human serum and its bioequivalence study on Chinese healthy volunteers.

A high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) method was developed and validated for the determination of mizoribine in human serum using thiamphenicol as internal standard (IS). The serum samples of mizoribine were precipitated with acetonitrile and separated by HPLC on a reversed phase C18 column with a mobile phase of 0.1% ammonium acetate water solution-methanol (47:53, v/v). Mizoribine and IS were detected in the multiple reaction monitoring mode with precursor/product ion transitions of m/z 258.2/126.0 and 354.1/185.2, respectively. The calibration curves were linear over the range of 0.02-2 microg mL(-1) for mizoribine. The limit of quantification (LOQ) was 0.02 microg mL(-1) with acceptable precision and accuracy. The validated method was successfully applied for the evaluation of a bioequivalence study on Chinese healthy volunteers. The main pharmacokinetics parameters after oral administration of 100 mg mizoribine test or reference formulation were as follows: Cmax (1.00 +/- 0.21), (1.00 +/- 0.22) microg mL(-1); AUC(0-infinity) (6.72 +/- 1.39), (6.48 +/- 1.44) microg h mL(-1); t1/2 (2.77 +/- 0.26), (2.66 +/- 0.29) h; tmax (2.95 +/- 0.78), (2.84 +/- 0.50) h.

Mizoribine therapy in a patient with lupus nephritis: the association between mizoribine concentration and peritoneal dialysis.

We describe a 20-year-old female with systemic lupus erythematosus (SLE) who developed renal failure during continuous ambulatory peritoneal dialysis (CAPD). The patient was treated with mizoribine (MZR). MZR peak concentration was 1.8 mug/ml and was sufficient for clinical efficacy as measured by serological data. Treatment with MZR was safe and useful even while undergoing CAPD. Achieving optimal MZR blood concentration was important for treatment of SLE, even though the patient was in end-stage renal failure.

Effects of Maribavir on P-Glycoprotein and CYP2D6 in Healthy Volunteers.

Maribavir is an investigational drug being evaluated in transplant recipients with cytomegalovirus infection. To understand potential drug-drug interactions, we examined the effects of multiple doses of maribavir on cytochrome P450 (CYP) 2D6 and P-glycoprotein (P-gp) activity using probe substrates in healthy volunteers. During this phase 1 open-label study (NCT02775240), participants received the probe substrates digoxin (0.5 mg) and dextromethorphan (30 mg) before and after maribavir (400 mg twice daily for 8 days). Serial plasma samples were analyzed for digoxin, dextromethorpha, dextrorphan, and maribavir concentrations. Pharmacokinetic parameters were calculated (noncompartmental analysis) and analyzed with a linear mixed-effects model for treatment comparison to estimate geometric mean ratios (GMRs) and 90% confidence intervals (CIs). CYP2D6 polymorphisms were genotyped using polymerase chain reaction. Overall, 17 of 18 participants (94.4%) completed the study. All participants were genotyped as CYP2D6 intermediate/extensive metabolizers. GMR (90%CI) of digoxin Cmax , AUClast , and AUC0-∞ with and without maribavir was 1.257 (1.139-1.387), 1.187 (1.088-1.296), and 1.217 (1.110-1.335), respectively, outside the "no-effect" window (0.8-1.25). GMR (90%CI) of dextromethorphan AUClast and AUClast ratio of dextromethorphan/dextrorphan were 0.877 (0.692-1.112) and 0.901 (0.717-1.133), respectively, marginally outside the no-effect window, although large variability was observed in these pharmacokinetic parameters. Pharmacokinetic parameters of dextrorphan were unaffected. Maribavir inhibited P-gp activity but did not affect CYP2D6 activity. Maribavir's effect on the pharmacokinetics of P-gp substrates should be evaluated individually, and caution should be exercised with P-gp substrates with narrow therapeutic windows.

Alterations of Proximal Tubular Secretion in Autosomal Dominant Polycystic Kidney Disease.

BACKGROUND AND OBJECTIVES: In autosomal dominant polycystic kidney disease (ADPKD), the GFR often remains normal despite significant nephron loss. Proximal tubular secretory clearance may be reduced in ADPKD before detectable changes in GFR. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We used targeted mass spectrometry to quantify secretory solutes from blood and urine samples from 31 patients with ADPKD and preserved GFR (mean eGFR =111±11 ml/min per 1.73 m2) and 25 healthy control individuals as well as from 95 patients with ADPKD and reduced GFR (mean eGFR =53±21 ml/min per 1.73 m2) and 92 individuals with non-ADPKD CKD. We used linear regression to compare the fractional excretion of each solute between ADPKD and control groups. Among 112 patients with ADPKD, we used linear regression to determine associations of solute fractional excretion with height-adjusted total kidney volume. RESULTS: After adjusting for demographics, clinical characteristics, and kidney function measures, the fractional excretions of three secretory solutes were lower in patients with ADPKD and preserved GFR compared with healthy individuals: 52% lower cinnamoylglycine excretion (95% confidence interval, 24% to 70%), 53% lower tiglylglycine excretion (95% confidence interval, 23% to 71%), and 91% lower xanthosine excretion (95% confidence interval, 83% to 95%). In addition to lower excretions of tiglylglycine and xanthosine, patients with ADPKD and reduced GFR also demonstrated 37% lower dimethyluric acid excretion (95% confidence interval, 21% to 50%), 58% lower hippurate excretion (95% confidence interval, 48% to 66%), 48% lower isovalerylglycine excretion (95% confidence interval, 37% to 56%), and 31% lower pyridoxic acid excretion (95% confidence interval, 16% to 42%) compared with patients with non-ADPKD CKD and comparable eGFR. Among patients with ADPKD, solute fractional excretions were not associated with differences in kidney volume. CONCLUSIONS: Patients with ADPKD and preserved and reduced GFR demonstrate lower tubular secretory solute excretion compared with healthy controls and patients with non-ADPKD CKD. Our results suggest that tubular secretion is impaired in ADPKD independent of GFR.

A simple HPLC method for the quantification of mizoribine in human serum: pharmacokinetic applications.

A simple high-performance liquid chromatographic (HPLC) method was developed and validated for the quantification of mizoribine in human serum. After the addition of 70% perchloric acid and 3-methylxanthine (50 microg/mL, internal standard) to human serum, the samples were mixed and centrifuged at 12,000 rpm (1432 g) for 10 min. The supernatant was injected onto a C(18) column eluted with a mobile phase of 20 mm Na2HPO4 and methanol (93:7, v/v, pH 3) containing 0.04% octanesulfonic acid and detected utilizing an ultraviolet detector at 275 nm. The linear calibration curve was obtained in the concentration range of 0.1-4.0 microg/mL and the lower limit of quantification was 0.1 microg/mL. This method was validated with selectivity, linearity, precision and accuracy. In addition, the method was successfully applied to estimate the pharmacokinetic parameters of mizoribine in Korean subjects following an oral administration of 100 mg mizoribine (two Bredinine 50 mg tablets). The maximum serum concentration (C(max)) of 2.30 +/- 0.83 microg/mL was reached 2.27 +/- 0.66 h after an oral dose. The mean AUC(0-12 h) and the elimination half-life (t(1/2)) were 13.2 +/- 4.79 microg h/mL and 3.10 +/- 0.74 h, respectively.

Population Pharmacokinetic Analysis of Mizoribine in Chinese Renal Transplant Recipients.

BACKGROUND: We calculated the population pharmacokinetics of mizoribine in adult Chinese patients and compared the parameters with those of Japanese patients to determine whether there are any ethnic differences in blood concentration transition between these 2 populations. METHODS: The blood concentrations of mizoribine in 21 Chinese patients who were administered mizoribine after renal transplantation were measured at 304 time points. The absorption lag time, absorption rate constant, apparent distribution volume, and oral clearance were thereafter calculated and compared with the respective Japanese references. RESULTS: The absorption lag time, absorption rate constant, and apparent distribution volume calculated in this study were, respectively, 0.353 hour, 0.856 hour-1, and 0.776 L/kg. The oral clearance was calculated as 2.18 times the creatinine clearance using creatinine clearance as a function. The absorption rate constant, apparent distribution volume, and oral clearance are determinants of the maximum blood concentration, trough, and area under the blood concentration time curve. The relative absorption rate constant, apparent distribution volume, and oral clearance were 0.9-, 0.9-, and 1.2-fold, respectively, in Chinese patients compared with those in Japanese patients. These values are within the confidence limit, suggesting that there is no significant PK difference between the 2 ethnic groups. CONCLUSIONS: Results of this study showed no ethnic difference in blood mizoribine concentration transition between Chinese and Japanese patients. In addition, the population pharmacokinetic parameters obtained in this study are useful in determining the initial dosage or in the Bayesian analysis of mizoribine concentrations using scarce time points.

Pharmacokinetics of maribavir, a novel oral anticytomegalovirus agent, in subjects with varying degrees of renal impairment.

The effect of renal function on the pharmacokinetics of maribavir, a novel anticytomegalovirus agent, was evaluated in 12 adults with normal renal function (creatinine clearance [CrCl] >80 mL/min) and 19 adults with renal impairment classified as mild (n = 5), moderate (n = 5), or severe (n = 9), as measured by CrCl 50-80, 30-49, and <30 mL/min, respectively. After a single oral dose of maribavir 400 mg, the pharmacokinetics of maribavir, based on total and unbound plasma concentrations, showed no statistically significant difference between subjects with normal renal function and subjects with mild/moderate or severe renal impairment. Renal impairment was associated with an increase in area under the plasma concentration-time curve (AUC) values for an inactive metabolite of maribavir, VP 44469. Results were consistent with those of previous studies, which showed that very little maribavir was excreted unchanged in urine, whereas about 22% of an oral dose of maribavir is recovered in urine as VP 44469.