Impact of changing from cyclosporine to tacrolimus on pharmacokinetics of mycophenolic acid in renal transplant recipients with diabetes

The rate of mycophenolic acid (MPA) absorption after oral administration of mycophenolate mofetil (MMF) is delayed in patients with diabetes. Cyclosporine (CsA) decreases MPA exposure by inhibiting enterohepatic recirculation of MPA/MPA glucuronide, and tacrolimus (TRL) may alter the rate and extent of MPA absorption due to its prokinetic properties especially in patients with diabetic gastroparesis. This study evaluated the effect of changing from CsA to TRL on pharmacokinetics of MPA in stable renal transplant recipients with long-standing diabetes. Eight patients were switched from a stable dose of CsA to TRL while taking MMF 1 g twice daily. The 12-hour steady-state total plasma concentration-time profiles of MPA and MPA glucuronide were obtained after oral administration of MMF on 2 occasions: first while taking CsA and second after changing to TRL. Pharmacokinetic parameters of MPA were calculated by the noncompartmental method. Changing from CsA to TRL resulted in significantly increased MPA exposure (area under the concentration-time curve from 0 to 12 hours, AUC0-12) by 46 +/- 32% (P = 0.012) and MPA predose concentration (C0) by 121 +/- 67% (P = 0.008). The magnitude of change in MPA exposure did not correlate well with MPA-C0 or CsA trough concentration. Switching to TRL had minimal impact on peak concentration of MPA (15.0 +/- 6.9 mg/L with CsA versus 16.1 +/- 9.7 mg/L with TRL, P = 0.773) and time to reach the peak concentration (1.0 +/- 0.4 hours with CsA versus 1.2 +/- 0.8 hours with TRL, P = 0.461). Highly variable and unpredictable changes in MPA exposure among renal transplant patients with diabetes do not support a strategy of preemptively adjusting MMF dose when switching calcineurin inhibitors in this population.     

Intake of grapefruit juice alters the metabolic pattern of cyclosporin A in renal transplant recipients

OBJECTIVE: The aim of the present study was to investigate the effect of grapefruit juice on the pharmacokinetics of cyclosporin A (CsA), as Sandimmun Neoral, and its main metabolites, M1, M9 and M4N, in renal transplant recipients. METHODS: Ten renal transplant recipients, on CsA-based immunosuppressive therapy, were included in this open, randomized crossover study. Patients were given their individualized morning dose of CsA, administered with either 250 ml water or 250 ml grapefruit juice and 12-hour CsA pharmacokinetic investigations were performed. The 2 investigation days were separated by at least 7 days. RESULTS: Administration of CsA with grapefruit juice compared with water significantly increased the area under the whole blood concentration versus time curve in the interval from 0-12 hours (AUC(0-12)) of CsA, by an average of 25 +/- 19% (p = 0.002). Intake of grapefruit juice did not have any significant influence on maximum whole blood concentration (Cmax) or time to Cmax (tmax) of CsA. AUC(0-12) and Cmax of M9 decreased significantly with intake of grapefruit juice, on average 22 +/- 11% (p = 0.0007) and 36 +/- 6% (p = 0.0001), respectively. AUC(0-12) of M1, however, was on average 13 +/- 14% (p = 0.02) higher upon co-administration of CsA with grapefruit juice as compared with water. The level of M4N was below the limit of quantification in most samples, and an effect of co-administration of CsA with grapefruit juice could not be determined for this metabolite. CONCLUSION: The present study shows that co-administration of grapefruit juice with CsA compared with water affects the formation and/or elimination of the 2 metabolites M1 and M9 differently. In addition, administration of CsA with grapefruit juice compared with water induced a moderate, but significant increase in systemic exposure of CsA in renal transplant recipients.     

Population pharmacokinetics and bayesian estimator of cyclosporine in pediatric renal transplant patients

Cyclosporine A (CsA) is an immunosuppressive drug widely used in pediatric renal graft recipients. Its large interindividual pharmacokinetic variability and narrow therapeutic index render therapeutic drug monitoring necessary. However, information about CsA pharmacokinetics is scarce and no population pharmacokinetic (popPK) studies in these populations have been reported so far. to the objectives of this study were 1) to develop a PKpop model and identify the individual factors influencing the variability of CsA pharmacokinetics in pediatric kidney recipients; and 2) to build a Bayesian estimator allowing the estimation of the main PK parameters and exposure indices to CsA on the basis of a limited sampling strategy (LSS). The popPK analysis was performed using the NONMEM program. A total of 256 PK profiles of CsA collected in 98 pediatric renal transplant patients (mean age 9.7 +/- 4.5 years old) within the first year posttransplantation were studied. A 2-compartment model with first-order elimination, and Erlang distribution to describe the absorption phase, fitted the data adequately. For Bayesian estimation, the best LSS was determined based on its performance in estimating area under the concentration-time curve (AUC0-12h) and validated in an independent group of 20 patients. The popPK analysis identified body weight and posttransplant delay as individual factors influencing the apparent central volume of distribution and the apparent clearance, respectively. Bayesian estimation allowed accurate prediction of AUC0-12h using predose, C1h, and C3h blood samples with a mean bias between observed and estimated AUC of 0.5% +/- 11% and good precision (root mean square error = 10.9%). This article reports the first popPK study of CsA in pediatric renal transplant patients. It confirms the reliability and feasibility of CsA AUC estimation in this population. The body weight and the posttransplantation delay were identified to influence PK interindividual variability of CsA and were included in the Bayesian estimator developed, which could be helpful in further clinical trials.     

Flecainide pharmacokinetics after multiple dosing in patients with impaired renal function

Study objective: To determine the pharmacokinetics of oral flecainide acetate after single and multiple doses in patients with impaired renal function. Design: Paired study of single followed by multiple oral doses. Setting: Patients enrolled in a Veterans Administration Hospital renal subspecialty clinic and dialysis unit. Patients: Twenty men and one woman between the ages of 33 and 74 years with impaired renal function including ten patients with end-stage renal disease receiving maintenance hemodialysis. Interventions: All patients received a single, oral, 200-mg dose of flecainide acetate followed by sequential venous blood sampling. Seven to 14 days after the single-dose study, each patient received 100 mg of flecainide acetate by mouth every 12 hours or every 24 hours for 10 days. Venous blood samples were drawn periodically during multiple dosing and sequentially after the last dose. Measurements and primary results: Peak flecainide acetate concentrations (micrograms/L) were 330 +/- 104 micrograms/L (mean +/- SD) after the single dose and 687 +/- 505 micrograms/L after multiple doses. Time to peak occurred at 3.3 +/- 2.3 hours and 2.7 +/- 1.2 hours after single and multiple doses, respectively. The apparent volume of distribution was 8.2 +/- 2.9 L/kg and 9.2 +/- 5 L/kg after single and multiple dose studies, respectively. Plasma elimination half-life after the single dose (20.4 +/- 9.0 hours) was significantly shorter (P less than .001) than after multiple doses (37.8 +/- 39.7 hours), as was total body clearance: 391 +/- 154 mL/min versus 302 +/- 194 mL/min. There were no statistically significant differences between pharmacokinetic measurements determined for patients on chronic hemodialysis when compared with nondialysis patients during the multiple-dose study.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of cytochrome P4502D6 in the metabolism of brofaromine

Summary The intraindividual variability and circadian variation of oral cyclosporine (CsA) pharmacokinetics were studied over 24 h in 18 renal transplant recipients at steady state, and in 10 of the patients during a second 24 h period.The absolute percentage intraindividual difference in daytime AUC (0–12 h) ranged from 2% to 54% (mean 30%), and the corresponding variability in nighttime AUC (0–12 h) ranged from 5% to 80% (mean 34%). The pharmacokinetic variables t_1/2, t_max and C_max were more variable than the AUC (0–12 h) both during the day and at night. The evening trough level was significantly lower than the morning trough level; 185 ng · ml^–1 versus 223 ng · ml^–1. This, together with a significantly longer t_1/2 in the night than the day, suggested circadian variability in the pharmacokinetics of CsA.In a separate retrospective study in 162 renal transplant recipients given CsA by constant intravenous infusion, repeated CsA blood concentration measurements at steady state showed lower concentrations during the day than the night, suggesting higher CsA clearance during daytime.It is concluded that CsA pharmacokinetics in renal transplant recipients, besides the well-known interindividual variability, also displays large intraindividual variability as well as circadian variation. Our findings further emphasize the necessity and difficulty of pharmacological monitoring in the clinical use of CsA in organ transplantation.     

Cyclosporin C2hour monitoring after renal transplantation

Therapeutic drug monitoring of cyclosporin A (CsA) is essential because of its variable pharmacokinetics in individual patients and its narrow therapeutic window. In the past, standard trough level (C0) monitoring has been used, and although this method is currently the routine strategy, it has been shown that a single blood concentration measurement 2 hours after CsA administration (C2hour) is a significantly more accurate predictor of drug exposure and clinical events than trough concentrations. The CsA absorption profiling, in particular the measurement of C2hour, is a much more sensitive approach to assessing the pharmacokinetics and predicting the clinical effect in the individual patient. However, there are limited prospective data available examining the risks and benefits of C2hour monitoring in renal transplant recipients. Most studies focus on the early post-transplant phase, but there is little experience with C2hour monitoring in maintenance patients. Our experience in 127 stable long-term renal allograft recipients suggests that the therapeutic window for C2hour levels in patients during maintenance is lower than previously anticipated. Repeat determinations of both C0 and C2hour levels in 46 patients to determine precision of C2hour monitoring showed a high intrapatient variability. We observed only a slightly better coefficient of variation for C2hour than for C0 in repeat determinations. This suggests that drug monitoring using C2hour levels in transplant patients may provide a more accurate and reliable measure of drug exposure in the individual patient. However, CsA absorption showed only a weak correlation with dose during repeated measurements, suggesting high variability in absorption in these stable patients. We conclude that an adequate C2hour level soon after transplantation is associated with a reduced risk of acute rejection in adult renal transplant recipients. It is important to identify slow and poor absorbers in the initial phase after transplantation in order to avoid inappropriate increases in CsA dose. In maintenance patients, C2hour values between 500 and 600 ng/ml are effective and safe for providing effective rejection prophylaxis. Although mean C2hour levels do not seem to identify patients at risk of rejection, they may help to identify excessive immunosuppression and to improve long-term survival by reducing CsA toxicity.     

肾移植术后服用环孢素A2h血药浓度峰值监测及治疗窗浓度探讨

目的探讨肾移植术后国内患者服用环孢素A(CsA)2h血药浓度峰值在不同时期的监测范围。方法用荧光偏振免疫法(FPIA)同时测定92例肾移植受者CsA谷浓度(C0)和服药2h后峰浓度(C2),并观察排斥反应的发生及肝、肾毒性反应。结果肾移植术后CsA C2在不同时期监测范围建议0mo~1mo为1000~1300μg/L,2mo~3mo为950~1250μg/L,4mo~6mo为900~1100μg/L,7mo~12mo为750~1000μg/L,12mo以上为600~800μg/L。结论在上述治疗窗浓度范围,CsA既能达到满意的免疫抑制效果,又能减少排斥反应和肝、肾毒性的发生。     

Effects of Carbamazepine on Cyclosporine Metabolism in Pediatric Renal Transplant Recipients

This study documents a pharmacokinetic interaction between carbamazepine and cyclosporine (CsA) in pediatric renal transplant recipients. Noncompartmental steady-state CsA pharmacokinetics were determined in three pediatric renal transplant recipients who were receiving both CsA and carbamazepine as long-term therapy (carbamazepine group) and in three matched renal transplant subjects who were not receiving carbamazepine (control group). Even though the mean daily dosage of CsA was consistently higher in the carbamazepine group than in the control group (16.2 mg/kg/24 hrs vs 10.8 mg/kg/24 hrs, respectively), the predose trough CsA blood concentrations were significantly lower in the carbamazepine group (57 ng/ml vs 162 ng/ml, respectively; p=0.0023). Mean average steady-state blood concentrations of CsA (C_av) per mg of CsA administered were less than 50% in the carbamazepine group compared with the control group. This reflects either an induction of CsA hepatic metabolism or a reduced systemic bioavailability (possible induction of pre-hepatic metabolism) by concurrent use of carbamazepine.     

Cyclosporine monitoring with 2-hour postdose levels in heart transplant recipients

Cyclosporine therapeutic drug monitoring based on 2-hour postdose concentration (C2) compared with conventional trough concentration (C0) can improve clinical outcomes for de novo renal and liver transplant patients. However, in heart transplant patients, published studies are limited. To determine the clinical significance of C2 compared with C0 following orthotopic heart transplantation, the authors measured CsA at C0 and C2 and estimated CsA area under the curve (AUC) using Bayesian estimation and 4 sparse sample algorithms in a cross section of 31 adult patients receiving triple-drug immunosuppression with CsA, mycophenolate mofetil (MMF), and prednisone. CsA was measured using a validated HPLC method. Endomyocardial biopsies were graded based on the ISHLT system. Mean +/- SD values for CsA dose, C0, and C2 were 4.8 +/- 1.4 mg/kg/d, 240 +/- 62 microg/L, and 1319 +/- 469 microg/L, respectively. Correlation with AUC, using different estimation algorithms, was better for C2 (r(2) = 0.79-0.99) than for C0 (r(2)= 0.11-0.52). The mean +/- SD values for C0 (microg/L) and C2 (microg/L) for rejectors (n = 3) were 215 +/- 68 and 949 +/- 204 versus 242 +/- 62 and 1359 +/- 474 for the nonrejectors (P = 0.66 and 0.12, respectively). Fisher exact test P values using the median as threshold value for C0 and C2 (234 microg/L and 1251 microg/L, respectively) were 0.6 and 0.1. Analysis of the data revealed that C0 values in rejectors have wider variability than C2. There were no rejectors among the 16 patients exceeding the C2 median value; for C0, however, there was not an easily identifiable threshold value. There is a trend for a significant relationship between C2 and the incidence of rejection, but the number of rejectors was too small to reach statistical significance. A prospective concentration-control de novo study design is recommended as the most appropriate way to fully evaluate the potential utility of C2 monitoring in heart transplant patients.     

MDR1 C1236T、G2677T/A、C3435T的基因多态性对中国汉族肾移植患者环孢素药动学的影响(英文)

目的探讨中国汉族人中肾移植患者的多药耐药基因(MDR1)外显子exon12 C1236T、exon21 G2677T/A、exon26 C3435T的单核苷酸多态性对免疫抑制剂环孢素(CsA)药动学的影响。方法采用聚合酶联反应和限制性内切片段长度多态性(PCR-RFLP)的方法对89例肾移植术后的患者进行MDR1基因分型。单克隆抗体荧光免疫偏振法测定患者术后CsA的谷浓度(c0)及服药后2 h浓度(c2)。比较不同基因型之间CsA浓度剂量比值的差异。结果在89例肾移植患者中,等位基因1236T、2677T、2677A、3435T突变频率分别为66%、43%、18%和37%。肾移植术后1 mo内,G2677T/A基因多态性与CsA的药动学有相关性,2个等位基因都发生突变的患者,其剂量校正c0,在术后1~7 d、8~15 d和16~30 d比野生型分别提高51%(P=0.005)、32%(P=0.002)和63%(P<0.001)。在术后16~30 d,无论携带有1个或2个突变等位基因的患者,剂量校正c2都要比野生型患者高26%(P=0.007)和19%(P=0.041)。C1236T的剂量校正c0在术后8~15...     

The effects of calcium channel blockers on cyclosporine and its metabolites in renal transplant recipients

Although calcium channel blockers have been reported to increase trough cyclosporine (CsA) blood levels, few studies have systematically examined the effects of calcium channel blockers on CsA pharmacokinetics. In the present investigation, complete pharmacokinetic profiles of CsA and its major metabolites (M1, M17, and M21) were determined in 11 verapamil-treated patients, 7 nifedipine-treated patients, and in 78 controls. Whole blood and urine levels were analyzed using high-performance liquid chromatography. Verapamil caused a 45% increase in CsA area under the curve, maximum concentration, steady-state concentration, and trough level. Metabolite 17 levels were increased in a parallel fashion, suggesting that altered CsA bioavailability rather than decreased metabolism may have caused the higher CsA levels in verapamil-treated patients. However, verapamil-induced reductions in CsA metabolism by other routes could not be ruled out. No changes in CsA or its metabolites were observed in nifedipine-treated patients. Unlike previous reports in patients treated with higher CsA doses, verapamil and nifedipine did not improve renal function in the present study. Nevertheless, the increase in CsA blood levels seen with verapamil may enhance the therapeutic cost-effectiveness of this agent in hypertensive renal transplant recipients.     

Area-under-the-curve monitoring of prednisolone for dose optimization in a stable renal transplant population

BACKGROUND: Renal transplant recipients were noted to appear cushingoid while on low doses of steroid as part of a triple therapy immunosuppression of cyclosporin A (CsA), prednisolone, and azathioprine. METHODS: The study group comprised adult renal transplant recipients with stable graft function who had received their renal allograft a minimum of 1 year previously (43 studies undertaken in 22 men and 20 women) with median daily prednisone dose of 7 mg (range 3-10). The control group was healthy nontransplant subjects [median dose 10 mg (10-30)]. Prednisolone bioavailability was measured using a limited 6-hour area under the curve (AUC), with prednisolone measured using specific HPLC assay. RESULTS: The median prednisolone AUC/mg dose for all transplant recipients was significantly greater than the control group by approximately 50% (316 nmol x h/L/mg prednisolone versus 218). AUC was significantly higher in female recipients (median 415 versus 297 for men) and in recipients receiving cyclosporin (348 versus 285). The highest AUC was in women on estrogen supplements who were receiving cyclosporin (median 595). A significantly higher proportion of patients on triple therapy had steroid side effects compared with those on steroid and azathioprine (17/27 versus 4/15), more women than men had side effects (14/16 versus 7/22), and the AUC/mg prednisone was greater in those with side effects than without (median 377 versus 288 nmol x h/L/mg). DISCUSSION: The results are consistent with the hypothesis that CsA increases the bioavailability of prednisolone, most likely through inhibition of P-glycoprotein. The increased exposure to steroid increased the side-effect profile of steroids in the majority of patients. Because the major contributor to AUC is the maximum postdose concentration, it may be possible to use single-point monitoring (2 hours postdose) for routine clinical studies.     

抗结核治疗对肾移植患者钙调酶抑制剂血药浓度的影响

目的:探讨抗结核治疗对肾移植患者钙调酶抑制剂血药浓度的影响。方法:对2例肾移植前、后并发结核感染的患者在抗结核治疗过程中钙调酶抑制剂血药浓度的变化进行分析。患者术后常规进行环孢素A(CsA)或他克莫司(FK506)+吗替麦考酚酯(MMF)+泼尼松(Pred)三联免疫抑制治疗,单克隆抗体荧光免疫偏振法测定服抗结核药前、后各个时期全血中CsA(或FK506)浓度的变化。结果:利福平可明显降低CsA的血药浓度。该患者的CsA日剂量需增加为原来的3倍以上才可维持较理想的血药浓度;利福喷汀可降低FK506的浓度,但降幅不大。结论:对肾移植前、后并发结核感染的患者应严密监测钙调酶抑制剂浓度,同时注意抗结核药不良反应的发生。     

The disposition of alfentanil in neonates with respiratory distress

The disposition of continuous infusion alfentanil was evaluated in 13 mechanically ventilated neonates (gestational age 37.6 +/- 2.4 wks) with hyaline membrane disease (n = 7) or persistent pulmonary hypertension of the newborn (n = 6). Alfentanil was administered as a loading dose 8 micrograms/kg, followed by a variable-rate continuous infusion (maximum 10 micrograms/kg/hr; minimum 2.5 micrograms/kg/hr) for 27 hours. Serial plasma samples were obtained for pharmacokinetic analysis. Noncompartmental pharmacokinetic analysis of the data revealed the following estimates (mean +/- SD): total-body clearance 3.24 +/- 2.23 ml/kg/minute, volume of distribution 0.54 +/- 0.21 L/kg, and elimination half-life 4.14 +/- 2.58 hours. A significant effect of alfentanil plasma concentration on total-body clearance was found (r = -0.75; p = 0.02), suggesting nonlinear pharmacokinetics. No correlation was seen between total-body clearance and alfentanil dose (r = -0.37; p = 0.32). The results suggest that a larger dose-proportionality study is required to determine the linearity or nonlinearity of alfentanil pharmacokinetics in neonates.     

肾移植受者环孢素A治疗窗浓度研究

目的 :寻找环孢素A(CsA )在肾移植受者三联免疫抑制用药方案中的理想治疗窗浓度。方法 :用特异性荧光偏振免疫法测定268例患者全血CsA谷值浓度 ,并按术后时间及临床诊断分组比较。结果 :CsA理想治疗窗浓度为 :术后1mo内300～400μg/L ,2mo～3mo内250～350μg/L ,4mo～6mo内150～250μg/L ,7mo～12mo内100～200μg/L ,12mo以后100～150μg/L。结论 :CsA在理想治疗窗浓度内 ,既能达到满意的免疫抑制效果 ,又能减少CsA毒性反应和排斥反应     

Clinical application of population pharmacokinetic methods developed for immunosuppressive drugs

After a brief overview of the relevant exposure indices for cyclosporine (CsA) and mycophenolate mofetil (MMF), as well as of the different steps necessary to develop maximum a posteriori Bayesian estimators (MAP-BE), this paper presents applications of MAP-BE for CsA or MMF to clinical cases and clinical trials. Ina renal transplant patient under CsA, grade I chronic allograft nephropathy was found at the sixth month posttransplantation, with CsA CO slightly above the target range and C2 markedly below; the AUCO0-12 h Bayesian estimate was quite high, at 5.6 mg h/L, as compared with a mean value of 4.3+0.9 mg.h/L in stable renal transplants at this period; the inconsistent C2 level found could be explained by delayed absorption of CsA in this patient, in which case C2 no longer represents the major part of the AUC. The patient was switched to sirolimus, which resulted in a slow and significant improvement of graft function with no acute rejection. In a 50-year-old female renal transplant recipient administered MMF and CsA and with a very favorable outcome otherwise, progressive anemia appeared 8 months posttransplantation. Clinical investigations were negative,but Bayesian estimation showed a rather high MPA AUCO0-12 h (69.8 mg h/L). After MMF dose reduction, hemoglobin level progressively returned to normal, without erythropoietin injection or blood transfusion. Finally, the feasibility of accurate dose adjustment using these MAP-BE is shown through preliminary results from 2 ongoing multicenter clinical trials, 1 evaluating an AUC-controlled cyclosporine-sparing strategy in stable renal transplants, the second evaluating the benefit of MMF therapeutic drug monitoring based on MPA AUCO0-12 h in de novo renal transplant recipients.     

Pharmacokinetic characterization of a pig model of ciclosporin A nephrotoxicity following intravenous administration.

BACKGROUND: Recently, we investigated pharmacokinetics and acute nephrotoxicity of oral ciclosporin A (CsA) in pigs. We found that pigs require higher oral CsA doses to obtain comparable area under the concentration versus time curve (AUC) levels to renal transplant patients. The purpose of this study was to examine pharmacokinetics and possible acute renal effects of intravenous CsA in order to further characterize the pig as a model of CsA nephrotoxicity. METHODS: Twenty-eight pigs were randomized into four groups: control and three groups subjected to a single CsA infusion at 3, 6, or 9 mg kg(-1). Blood samples for determination of whole blood CsA concentrations were collected over 7 h under general anaesthesia. At 0, 2, and 5 h, we measured blood pressure, serum creatinine, and haemoglobin, as well as renal blood flow (RBF), relative glomerular filtration rate (rGFR), and kidney volume using magnetic resonance imaging. RESULTS: CsA distribution exhibited two-compartmental behaviour. Compared to renal transplant patients, pigs had approximately the same total clearance of CsA (mean 0.31-0.34lh(-1)kg(-1)), which yields comparable AUC after equivalent dosage in both species. However, the volume of distribution at steady state (mean 1.9-3.0lkg(-1)) was lower in pigs. RBF remained stable in all groups, whereas rGFR decreased in all groups reaching statistical significance in the controls. CONCLUSIONS: Pigs require approximately the same intravenous CsA doses to obtain comparable total AUC to renal transplant patients. Single CsA infusion up to 9 mg kg(-1) for 1h has no deteriorating effect on renal haemodynamics and function.     

Pharmacokinetics of bisoprolol during repeated oral administration to healthy volunteers and patients with kidney or liver disease

The pharmacokinetics of bisoprolol were investigated following oral administration of 10mg once daily for 7 days in 8 healthy subjects, in 14 patients with different degrees of renal impairment and in 18 patients with liver disease. In healthy subjects peak and trough steady-state concentrations of 52 micrograms/L and 11 micrograms/L, respectively, an elimination half-life of 10.0 hours and total body clearance of 14.2 L/h were observed. 5.21 mg/24 hours of unchanged bisoprolol were recovered following urinary excretion during the dosage interval. In 11 patients with renal impairment (mean CLCR = 28 +/- 5 ml/min/1.72m2) half-life was prolonged to 18.5 hours, and peak and trough concentrations were 74 and 32 micrograms/L, respectively. Correspondingly, urinary excretion decreased to 3.35 mg/24 hours and total body clearance to 7.8 L/h. In uraemic patients (CLCR less than 5 ml/min/1.73m2) the total clearance of bisoprolol was 5.0 L/h and the elimination half-life was 24.2 hours. In patients with liver cirrhosis half-life increased to 13.5 hours, steady-state peak and trough concentrations increased to 62 and 22 micrograms/L, respectively, and total body clearance decreased to 10.8 L/h. The present study indicates that in patients with impairment of kidney or liver function accumulation of bisoprolol above a factor of 2 did not occur. However, in the terminal stages of insufficiency of kidney or liver function bisoprolol dosage should not exceed 10mg.     

Pharmacokinetics and protein binding of mycophenolic acid in stable lung transplant recipients

Mycophenolate mofetil (MMF) use is increasing in solid organ transplantation. Mycophenolic acid (MPA), the active metabolite of MMF, is highly protein bound and only free MPA is pharmacologically active. The average MPA free fraction in healthy adult individuals, stable renal transplant recipients, and heart transplant recipients is approximately 2 to 3%. However, no data are currently available on MPA protein binding in stable lung transplant recipients and little is known regarding MPA's pharmacokinetic characteristics after lung transplantation. The purpose of this study was to characterize the pharmacokinetic profile and protein binding of MPA in this patient population. Seven patients were entered into the study. On administration of a steady-state morning MMF dose, blood samples were collected at 0, 1, 2, 3, 4, 5, 6, 8, 9, 10, and 12 hours post-dose. Total MPA concentrations were measured by a validated HPLC method with UV detection and followed by ultrafiltration of pooled samples for free MPA concentrations. Area under the curve (AUC), peak concentration (Cmax), time to peak concentration (Tmax), trough concentration (Cmin), free fraction (f), and free MPA AUC were calculated by traditional pharmacokinetic methods. Patient characteristics included; 3 males and 4 females, an average of 4.4 years post-lung transplant (range, 0.3-11.5 yr), mean (+/- SD) age of 50 +/- 10 years and weight 69 +/- 20 kg. Mean albumin concentration was 37 +/- 3 g/L and serum creatinine was 142 +/- 49 micromol/L. All patients were on cyclosporine and prednisone. MMF dosage ranged from 1 to 3 g daily (35.5 +/- 14.1 mg/kg/d; range, 15.2-60.0 mg/kg/d). Mean (+/- SD) AUC was 45.78 +/- 18.35 microg.h/mL (range, 16.56-74.22 microg.h/mL), Cmax was 17.37 +/- 7.69 microg/mL (range, 4.92-26.63 microg/mL), Tmax was 1.2 +/- 0.4 hours (range, 1.0-2.0 h), Cmin was 3.12 +/- 1.41 microg/mL (range, 1.47-4.82 microg/mL), f was 2.90 +/- 0.56% (range, 2.00-3.40%), and free MPA AUC was 1.29 +/- 0.50 microg.h/mL (range, 0.54-1.88 microg.h/mL). This is the first study to determine these pharmacokinetic characteristics of MPA in the lung transplant population. Further studies should focus on identification of MMF dosing strategies that optimize immunosuppressive efficacy and minimize toxicity in lung allograft recipients.