Effect of chronic renal failure on the expression and function of rat intestinal P-glycoprotein in drug excretion

Comparative pharmacokinetics of six bioactive components of Shen-Wu-Yi-Shen tablets in normal and chronic renal failure rats based on UPLC-TSQ-MS/MS

ETHNOPHARMACOLOGICAL RELEVANCE

Shen-Wu-Yi-Shen tablets (SWYST), a Chinese patent medicine consisting of 12 herbal medicines, was formulated by a famous TCM nephrologist, Zou Yunxiang. It is clinically used to improve the symptoms of nausea, vomiting, poor appetite, dry mouth and throat, and dry stool in patients with chronic renal failure (CRF) accompanied by qi and yin deficiency, dampness, and turbidity. SWYST can reduce urea nitrogen, blood creatinine, and urinary protein loss, and increase the endogenous creatinine clearance rate. However, little is known about its pharmacokinetics.

AIM OF STUDY

To compare the pharmacokinetics of six bioactive components after oral administration of SWYST in normal and adenine-induced CRF rats.

MATERIALS AND METHODS

A method based on ultra-performance liquid chromatography coupled with a triple-stage quadrupole mass spectrometer (UPLC-TSQ-MS/MS) was developed and validated to determine the six bioactive compounds (albiflorin, paeoniflorin, plantagoguanidinic acid, rhein, aloe-emodin, and emodin) in rat plasma. Rat plasma samples were prepared using protein precipitation. Chromatography was performed on an Agilent Eclipse Plus C18 column (3.0 × 50 mm, 1.8 μm) using gradient elution with a mobile phase composed of acetonitrile and water containing 0.1% (v/v) formic acid, while detection was achieved by electrospray ionization MS under the multiple selective reaction monitoring modes. After SWYST administration, rat plasma was collected at different time points, and the pharmacokinetic parameters of six analytes were calculated and analyzed based on the measured plasma concentrations.

RESULTS

The UPLC-TSQ-MS/MS method was fully validated for its satisfactory linearity (r ≥ 0.9913), good precisions (RSD <11.5%), and accuracy (RE: -13.4∼13.1%), as well as acceptable limits in the extraction recoveries, matrix effects, and stability (RSD <15%). In normal rats, the six analytes were rapidly absorbed (Tmax ≤ 2 h), and approximately 80% of their total exposure was eliminated within 10 h. Moreover, in normal rats, the AUC0-t and Cmax of albiflorin, plantagoguanidinic acid, and rhein exhibited linear pharmacokinetics within the dose ranges, while that of paeoniflorin is non-linear. However, in CRF rats, the six analytes exhibited reduced elimination and significantly different AUC or Cmax values. These changes may reflect a decreased renal clearance rate or inhibition of drug-metabolizing enzymes and transporters in the liver and gastrointestinal tract caused by CRF.

CONCLUSIONS

A sensitive UPLC-TSQ-MS/MS method was validated and used to investigate the pharmacokinetics of SWYST in normal and CRF rats. This is the first study to investigate the pharmacokinetics of SWYST, and our findings elucidate the causes of their different pharmacokinetic behaviors in CRF rats. Furthermore, the results provide useful information to guide further research on the pharmacokinetic-pharmacodynamic correlation and clinical application of SWYST.

Quantification of CYP3A and Drug Transporters Activity in Healthy Young, Healthy Elderly and Chronic Kidney Disease Elderly Patients by a Microdose Cocktail Approach

Background: Ageing and chronic kidney disease (CKD) affect pharmacokinetic (PK) parameters. Since mechanisms are related and remain unclear, cytochrome P450 (CYP) 3A and drug transporter activities were investigated in the elderly with or without CKD and compared to healthy adults using a microdose cocktail. Methods: Healthy young participants (n = 20), healthy elderly participants (n = 16) and elderly patients with CKD (n = 17) received, in study period 1, a single dose of microdose cocktail probe containing 30 µg midazolam, 750 µg dabigatran etexilate, 100 µg atorvastatin, 10 µg pitavastatin, and 50 µg rosuvastatin. After a 14-day wash-out period, healthy young participants continued to study period 2 with the microdose cocktail plus rifampicin. PK parameters including area under the plasma concentration-time curve (AUC), maximum plasma drug concentration (C_max), and half-life were estimated before making pairwise comparisons of geometric mean ratios (GMR) between groups. Results: AUC and C_max GMR (95% confidence interval; CI) of midazolam, a CYP3A probe substrate, were increased 2.30 (1.70-3.09) and 2.90 (2.16-3.88) fold in healthy elderly and elderly patients with CKD, respectively, together with a prolonged half-life. AUC and C_max GMR (95%CI) of atorvastatin, another CYP3A substrate, was increased 2.14 (1.52-3.02) fold in healthy elderly and 4.15 (2.98-5.79) fold in elderly patients with CKD, indicating decreased CYP3A activity related to ageing. Associated AUC changes in the probe drug whose activity could be modified by intestinal P-glycoprotein (P-gp) activity, dabigatran etexilate, were observed in patients with CKD. However, whether the activity of pitavastatin and rosuvastatin is modified by organic anion transporting polypeptide 1B (OATP1B) and of breast cancer resistance protein (BCRP), respectively, in elderly participants with or without CKD was inconclusive. Conclusions: CYP3A activity is reduced in ageing. Intestinal P-gp function might be affected by CKD, but further confirmation appears warranted. Clinical Trial Registration:http://www.thaiclinicaltrials.org/ (TCTR 20180312002 registered on March 07, 2018).

Impact of kidney dysfunction on hepatic and intestinal drug transporters

Emerging information suggests that pathology of the kidney may not only affect expression and function of membrane transporters in the organ, but also in the gastrointestinal tract and the liver. Transporter dysfunction may cause effects on handling of drug as well as endogenous compounds with subsequent clinical consequences. A literature search was conducted on Ovid and PubMed databases to select relevant in vitro, animal and human studies that have reported expression, protein abundance and function of the gastrointestinal and liver localized ABC transporters and SLC carriers in kidney dysfunction or uremia states. The altered function of drug transporters in the liver and intestines in kidney failure subjects may provide compensatory activity in handling endogenous compounds (e.g. uremic toxins), which is expected to affect drug pharmacokinetics and local drug actions.

Renal and non-renal response of ABC and SLC transporters in chronic kidney disease

INTRODUCTION

The solute carrier (SLC) and the ATP-binding cassette (ABC) transporter superfamilies play essential roles in the disposition of small molecules (endogenous metabolites, uremic toxins, drugs) in the blood, kidney, liver, intestine, and other organs. In chronic kidney disease (CKD), the loss of renal function is associated with altered function of remote organs. As renal function declines, many molecules accumulate in the plasma. Many studies now support the view that ABC and SLC transporters as well as drug metabolizing enzymes (DMEs) in renal and non-renal tissues are directly or indirectly affected by the presence of various types of uremic toxins, including those derived from the gut microbiome; this can lead to aberrant inter-organ communication.

AREAS COVERED

Here, the expression, localization and/or function of various SLC and ABC transporters as well as DMEs in the kidney and other organs are discussed in the context of CKD and systemic pathophysiology.

EXPERT OPINION

According to the Remote Sensing and Signaling Theory (RSST), a transporter and DME-centric network that optimizes local and systemic metabolism maintains homeostasis in the steady state and resets homeostasis following perturbations due to renal dysfunction. The implications of this view for pharmacotherapy of CKD are also discussed.

Pharmacokinetics in children with chronic kidney disease

In children, the main causes of chronic kidney disease (CKD) are congenital diseases and glomerular disorders. CKD is associated with multiple physiological changes and may therefore influence various pharmacokinetic (PK) parameters. A well-known consequence of CKD on pharmacokinetics is a reduction in renal clearance due to a decrease in the glomerular filtration rate. The impact of renal impairment on pharmacokinetics is, however, not limited to a decreased elimination of drugs excreted by the kidney. In fact, renal dysfunction may lead to modifications in absorption, distribution, transport, and metabolism as well. Currently, insufficient evidence is available to guide dosing decisions on many commonly used drugs. Moreover, the impact of maturation on drug disposition and action should be taken into account when selecting and dosing drugs in the pediatric population. Clinicians should take PK changes into consideration when selecting and dosing drugs in pediatric CKD patients in order to avoid toxicity and increase efficiency of drugs in this population. The aim of this review is to summarize known PK changes in relation to CKD and to extrapolate available knowledge to the pediatric CKD population to provide guidance for clinical practice.

The prominent impairment of liver/intestinal cytochrome P450 and intestinal drug transporters in sepsis-induced acute kidney injury over acute and chronic renal ischemia, a mouse model comparison

Drug dosing adjustment in sepsis-induced acute kidney injury (sepsis-AKI) is currently adjusted based on renal function. Sepsis is a multiorgan injury, and thus, drug metabolism in sepsis-AKI might be interfered by non-renal factors such as changes in functions of drug-metabolizing enzymes in the liver and functions of intestinal drug transporters. We compared the defect on mouse CYP3A11 (human CYP3A4 representative) in liver and intestine along with several intestinal drug transporters (MDR1a, MRP2, and OATP3) in three mouse models; chronic ischemic reperfusion injury (Chr I/R; 4-week), acute ischemic reperfusion injury (Acute I/R; 24-h), and cecal ligation and puncture (CLP; 24-h) as representative of sepsis-AKI. Decreased expression of CYP3A11 and drug transporters was demonstrated in all models. Among these models, sepsis-AKI had the least severe renal injury (increased BUN and Scr) with the most severe liver injury (increased ALT and changes in liver histopathology), the most severe intestinal leakage (increased serum (1→3)-β-D-glucan) and the highest increase in serum IL-6. A reduced expression and activity of liver and intestinal CYP3A11 along with intestinal efflux-drug transporter expressions (MDR1a and MRP2), but not drug uptake transporter (OATP3), was predominant in sepsis-AKI compared with acute I/R. Additionally, a reduction of CYP3A4 expression with IL-6 was demonstrated on HepG2 cells implying a direct injury of IL-6 on human liver cells. Differences in drug metabolism were reported between sepsis-AKI and ischemic-AKI confirming that drug dosing adjustment in sepsis-AKI depends not just only on renal function but also on several non-renal factors. Further studies are warranted.

Case series on the association between blood levels and side effects of afatinib maleate

PURPOSE

Afatinib maleate (AFA) is a second-generation, tyrosine kinase inhibitor (TKI) treatment for specific variants of non-small cell lung cancer exhibiting epidermal growth factor receptor (EGFR) mutations. In this study, we measured the blood AFA levels in six patients with lung cancer and investigated the association between blood levels and side effects of this drug.

METHODS

The study subjects were patients who were administered AFA for non-small cell lung cancer. Of these subjects, six patients agreed to participate in the study. The starting dose of AFA was 40 mg/day. We measured trough blood AFA levels on day 1 and 3 after AFA administration, on day 8-12, and every month until AFA administration was discontinued. Side effects were evaluated according to the adverse event codialect standard (CTCAE v.4.0).

RESULTS

A temporary discontinuation and/or reduction in AFA dose (within 2 months) because of diarrhea and stomatitis was needed in four patients. Mean blood AFA levels on day 8-12 in these four patients were significantly higher than in other patients (47.0 ± 9.5 vs. 24.4 ± 0.1 ng/mL, P = 0.017). In addition, mean renal function prior to AFA administration in these four patients was significantly lower than that in the other patients (49.0 ± 9.6 mL/min/1.73 m² vs. 77.2 ± 9.0, P = 0.026).

CONCLUSIONS

High blood AFA levels were associated with the early discontinuation and/or dose reduction of AFA because of untoward side effects, which may also be associated with decreased renal function.

Pharmacokinetics and Safety of Tenofovir Alafenamide in HIV-Uninfected Subjects with Severe Renal Impairment

Tenofovir alafenamide (TAF) is an oral prodrug of tenofovir (TFV) that has greater stability in plasma than TFV disoproxil fumarate (TDF) and circulates as intact TAF, resulting in the direct and higher lymphatic loading of and exposure to TFV diphosphate, the active moiety. Unlike TFV, TAF is minimally eliminated in urine. The pharmacokinetics (PK) of TAF and TFV in HIV-uninfected subjects with severe renal impairment and matched healthy controls were evaluated. Subjects with severe renal impairment (RI; estimated glomerular filtration rate [eGFR], 15 to 29 ml/min) and controls (eGFR, ≥90 ml/min) matched for age, gender, and body mass index received a single dose of TAF at 25 mg. Blood and urine samples for TAF and TFV PK determinations were collected over 7 days postdosing, and subjects were followed up at 14 days. A total of 14 renally impaired subjects and 13 control subjects enrolled and completed the study. The TAF maximum observed concentration in plasma (Cmax) and the area under the concentration-versus-time curve (AUC) extrapolated to infinite time (AUCinf) were 79% and 92% higher, respectively, in subjects with severe RI than the controls, primarily due to higher absorption. The TFV Cmax and AUCinf were 2.8-fold and 5.7-fold higher, respectively, in subjects with severe RI than the controls. In subjects with severe RI, TAF at 25 mg provided a TFV AUC 10 to 40% lower than that from historical TDF-based TFV exposures in subjects with normal renal function. There were no discontinuations due to adverse events. In subjects with severe RI receiving TAF at 25 mg, TAF exposures were higher than those for the controls; these differences are unlikely to be clinically meaningful. TFV exposures were higher than those for the controls but lower than the exposures in nonrenally impaired subjects on TDF-based regimens.

Drug Transporters and Na+/H+ Exchange Regulatory Factor PSD-95/Drosophila Discs Large/ZO-1 Proteins

Drug transporters govern the absorption, distribution, and elimination of pharmacologically active compounds. Members of the solute carrier and ATP binding-cassette drug transporter family mediate cellular drug uptake and efflux processes, thereby coordinating the vectorial movement of drugs across epithelial barriers. To exert their physiologic and pharmacological function in polarized epithelia, drug transporters must be targeted and stabilized to appropriate regions of the cell membrane (i.e., apical versus basolateral). Despite the critical importance of drug transporter membrane targeting, the mechanisms that underlie these processes are largely unknown. Several clinically significant drug transporters possess a recognition sequence that binds to PSD-95/Drosophila discs large/ZO-1 (PDZ) proteins. PDZ proteins, such as the Na(+)/H(+) exchanger regulatory factor (NHERF) family, act to stabilize and organize membrane targeting of multiple transmembrane proteins, including many clinically relevant drug transporters. These PDZ proteins are normally abundant at apical membranes, where they tether membrane-delimited transporters. NHERF expression is particularly high at the apical membrane in polarized tissue such as intestinal, hepatic, and renal epithelia, tissues important to drug disposition. Several recent studies have highlighted NHERF proteins as determinants of drug transporter function secondary to their role in controlling membrane abundance and localization. Mounting evidence strongly suggests that NHERF proteins may have clinically significant roles in pharmacokinetics and pharmacodynamics of several pharmacologically active compounds and may affect drug action in cancer and chronic kidney disease. For these reasons, NHERF proteins represent a novel class of post-translational mediators of drug transport and novel targets for new drug development.

Conjugated metabolites represent the major circulating forms of Abelmoschus manihot in vivo and show an altered pharmacokinetic profile in renal pathology

CONTEXT

The nephron-protective efficacy of Abelmoschus manihot (Linn.) Medicus (Malvaceae) has been proved by randomized controlled clinical trial.

OBJECTIVE

Flavonoids are main active components of A. manihot, which can be transformed into glucuronide/sulfate conjugates in vivo. Exploring the pharmacokinetic profile of these conjugates is necessary to further elucidate the mechanism of action.

MATERIAL AND METHOD

Flavonoid fraction of A. manihot (FFA) was extracted from A. manihot flower with ethanol. FFA (400 mg/kg) was orally given to normal rats and chronic kidney disease (CKD) model rats. Blood samples were collected at 5, 15, 30, 45, 60, 90, 120, 240, 360, and 720 min after administration. The plasma concentrations of quercetin and isorhamnetin glucuronide/sulfate conjugates were analyzed by UPLC-MS/MS.

RESULTS

In normal rats, AUC of quercetin-glucuronide conjugates, isorhamnetin-glucuronide conjugates, quercetin-sulfate conjugates, and isorhamnetin-sulfate conjugates was 459.45 ± 192.70, 1153.01 ± 697.04, 417.81 ± 220.31, and 2475.19 ± 1085.22 μmol h/L, respectively. While AUC of quercetin and isorhamnetin was 5.47 ± 2.54 and 30.73 ± 25.95 μmol h/L. AUC of the glucuronide-sulfate conjugates of quercetin and isorhamnetin is 125-times higher than that of aglycone (quercetin and isorhamnetin), showing that glucuronide/sulfate conjugates represent the major circulating forms of A. manihot flavonoid in vivo. AUC of isorhamnetin-glucuronide conjugates and quercetin-sulfate conjugates was 719.65 ± 619.22 and 275.49 ± 1 60.95 μmol h/L, indicating that less conjugated metabolites were formed in CKD rats compared with normal rats. The ratio of AUCglucuronide/sulfate/AUCaglycone decreased from 125 to 104, which implied the impaired phase II metabolism ability in CKD rat.

DISCUSSION AND CONCLUSION

Glucuronide-sulfate conjugates provide an important clue for further elucidating the activity of conjugated metabolites and their relationship with the nephroprotective efficacy of A. manihot. It is necessary to take caution when extrapolating pharmacokinetics parameters from healthy animals in designing pharmacological studies.

Consequences of renal failure on non-renal clearance of drugs

Kidney disease not only alters the renal elimination but also the non-renal disposition of drugs that are metabolized by the liver. Indeed, modifications in the expression and activity of intestinal and hepatic drug metabolism enzymes and uptake and efflux transporters have been reported. Accumulated uremic toxins, inflammatory cytokines, and parathyroid hormones may modulate these proteins either directly or by inhibiting gene expression. This can lead to important unintended variations in exposure and response when drugs are administered without dose adjustment for reduced renal function. This review summarizes our current understanding of non-renal clearance in circumstances of chronic and acute renal failure with experimental but also clinical studies. It also evaluates the clinical impact on drug disposition. Predicting the extent of the drug disposition modification is difficult first because of the complex interplay between metabolic enzymes and transport proteins but also because of the differential effects in the different organs (liver, intestines). Recommendations of the US FDA are presented as they may be potentially helpful tools to predict these modifications when no specific pharmacokinetic studies are available.

Hemodialysis does not alter in vitro hepatic CYP3A4 and CYP2D6 metabolic activity in uremic serum

There is a paucity of studies evaluating the change in liver metabolism in subjects receiving hemodialysis. The purpose of this study was to compare the effect of uremic toxins on hepatic cytochrome P450 (CYP)3A4 and CYP2D6 metabolism before and after a 4-hour hemodialysis session. Midazolam and dextromethorphan were incubated with uremic serum collected from subjects before and after the 4-hour hemodialysis session. Analysis and quantification of the 1'-OH-midazolam and 4-OH-midazolam and dextrorphan metabolites were performed by high-pressure liquid chromatography/mass spectrometry. Statistical analysis using the Student's t-test (paired) was used to compare the amount of metabolite formed. The mean amount of 1'-OH-midazolam, 4-OH-midazolam, and dextrorphan metabolites formed before and after hemodialysis did not significantly differ. There was no significant difference in CYP3A4 and CYP2D6 metabolic activity in uremic serum before and after hemodialysis.

From gut to kidney: transporting and metabolizing calcineurin-inhibitors in solid organ transplantation

Since their introduction circa 35 years ago, calcineurin-inhibitors (CNI) have become the cornerstone of immunosuppressive therapy in solid organ transplantation. However, CNI's possess a narrow therapeutic index with potential severe consequences of drug under- or overexposure. This demands a meticulous policy of Therapeutic Drug Monitoring (TDM) to optimize outcome. In clinical practice optimal dosing is difficult to achieve due to important inter- and intraindividual variation in CNI pharmacokinetics. A complex and often interdependent set of factors appears relevant in determining drug exposure. These include recipient characteristics such as age, race, body composition, organ function, and food intake, but also graft-related characteristics such as: size, donor-age, and time after transplantation can be important. Fundamental (in vitro) and clinical studies have pointed out the intrinsic relation between the aforementioned variables and the functional capacity of enzymes and transporters involved in CNI metabolism, primarily located in intestine, liver and kidney. Commonly occurring polymorphisms in genes responsible for CNI metabolism (CYP3A4, CYP3A5, CYP3A7, PXR, POR, ABCB1 (P-gp) and possibly UGT) are able to explain an important part of interindividual variability. In particular, a highly prevalent SNP in CYP3A5 has proven to be an important determinant of CNI dose requirements and drug-dose-interactions. In addition, a discrepancy in genotype between graft and receptor has to be taken into account. Furthermore, common phenomena in solid organ transplantation such as inflammation, ischemia- reperfusion injury, graft function, co-medication, altered food intake and intestinal motility can have a differential effect on the expression enzymes and transporters involved in CNI metabolism. Notwithstanding the built-up knowledge, predicting individual CNI pharmacokinetics and dose requirements on the basis of current clinical and experimental data remains a challenge.

Current understanding of drug disposition in kidney disease

Patients with chronic kidney disease (CKD) represent 13% of the American population. CKD has been shown to significantly alter drug disposition of nonrenally eliminated drugs. Indeed, modifications in the expression and function of intestinal and hepatic drug metabolism enzymes and uptake and efflux transporters have been reported. Uremic toxins, inflammatory cytokines, and parathyroid hormone have been implicated as causes. These changes can have an important clinical impact on drug disposition and lead to unintended toxicity if they are administered without dose adjustment in patients with impaired kidney function. This review summarizes recent preclinical and clinical studies and presents the current understanding of the effect of CKD on drug absorption, distribution, metabolism, and excretion.

[Appropriate pharmacotherapy in patients with chronic kidney disease - new approach - ]

The kidney is the most important organ for the excretion of drugs. It was previously thought that appropriate dosages of these drugs could be easily estimated by evaluating the kidney function of patients and the excretion rate of the drug. However, the pharmacokinetic characteristics of patients with kidney disease are as follows: 1) Active metabolites with a higher polarity can accumulate, which can induce unpredictable adverse effects. For example, over sedation with morphine or the development of the fatal toxic syndrome in the case of allopulinol are due to the accumulation of active metabolites derived from these drugs. 2) Although the renal excretion rate of acetoaminophen is only less than 5%, the accumulation of its glucuronide conjugate during multiple dosing in patients with kidney failure may induce high serum acetoaminophen trough levels via the entero-hepatic circulation. 3) Although the renal excretion rate of the drugs are negligible, a remarkable increase in the serum levels of certain drugs were observed in patients with end stage kidney disease, suggesting a significant reduction in non-renal clearance probably by the accumulation of uremic toxins. For drugs that are likely to be administered to patients with kidney disease, even including drugs that are not excreted by the kidney, a full pharmacokinetic study should be conducted in patients and the results carefully assessed. Information on dosing adjustments for impaired kidney function based on estimated glomerular filtration rates should then be clearly stated in the package insert of the drugs.

Automation of cell-based drug absorption assays in 96-well format using permeable support systems

Cell-based drug absorption assays, such as Caco-2 and MDCK-MDR1, are an essential component of lead compound ADME/Tox testing. The permeability and transport data they provide can determine whether a compound continues in the drug discovery process. Current methods typically incorporate 24-well microplates and are performed manually. Yet the need to generate absorption data earlier in the drug discovery process, on an increasing number of compounds, is driving the use of higher density plates. A simple, more efficient process that incorporates 96-well permeable supports and proper instrumentation in an automated process provides more reproducible data compared to manual methods. Here we demonstrate the ability to perform drug permeability and transport assays using Caco-2 or MDCKII-MDR1 cells. The assay procedure was automated in a 96-well format, including cell seeding, media and buffer exchanges, compound dispense, and sample removal using simple robotic instrumentation. Cell monolayer integrity was confirmed via transepithelial electrical resistance and Lucifer yellow measurements. Proper cell function was validated by analyzing apical-to-basolateral and basolateral-to-apical movement of rhodamine 123, a known P-glycoprotein substrate. Apparent permeability and efflux data demonstrate how the automated procedure provides a less variable method than manual processing, and delivers a more accurate assessment of a compound's absorption characteristics.

Influences of Fructus evodiae pretreatment on the pharmacokinetics of Rhizoma coptidis alkaloids

ETHNOPHARMACOLOGICAL RELEVANCE

Rhizoma coptidis is a traditional Chinese medicine with pharmacological properties. It is usually prescribed with Fructus evodiae as traditional Chinese medicine (TCM) formulas. Here we report the influences of Fructus evodiae on the pharmacokinetics of the Rhizoma coptidis alkaloids and propose possible mechanisms.

MATERIALS AND METHODS

Pharmacokinetic experiments were performed in rats. In vitro absorption experiments were performed in everted rat gut sacs, while in vitro metabolism experiments and determination of hepatic UDP-glucuronosyltransferase (UGT) 1A1 mRNA expression were performed in rat liver microsomes.

RESULTS

Pretreatment with Fructus evodiae extract for two weeks decreased the systemic exposure of the Rhizoma coptidis alkaloids. This effect was not due to inhibition of absorption or enhanced hepatic phase I metabolism of the Rhizoma coptidis alkaloids. However, Fructus evodiae pretreatment enhanced both the activity and expression of hepatic UGT1A1.

CONCLUSIONS

The results showed that Fructus evodiae pretreatment decreased the systemic exposure of the Rhizoma coptidis alkaloids by inducing hepatic UGT1A1.

Factors that affect concentrations of cyclosporine during the induction period of kidney transplantation: multivariate analysis

OBJECTIVE

The pharmacokinetics of cyclosporine (CsA) depend on numerous factors over the transplantation course. The aim of this study was to evaluate the impact of several clinical variables on CsA concentrations during the induction period after kidney transplantation.

METHODS

Potential variables were contrasted with CsA concentrations at 2 hours postdose (C(2)) and with the area under the concentration curve of CsA (AUC) at days 3 and 10 after transplantation. Evaluated variables were: recipient age, gender, body mass index (BMI), type/duration of previous dialysis, pretransplant serum creatinine (sCr), donor type, CsA dose, cold ischemia time, reduction of sCr, and use of other immunosuppressive drugs.

RESULTS

This series included 112 patients who displayed an average age of 43 ± 13 years, including 62 men and 31 recipients of living donor organs. The induction dose of CsA was 8.36 ± 1.53 mg/kg. On day 3, the C(2) was related to the reduction of sCr (P = 0.034) and to the BMI (P = 0.033). There was an inverse correlation with pretransplant sCr (P = 0.012). The AUC correlated with BMI (P = 0.027) and living donor category (P = .002). Patients receiving rapamycin or a locally procured kidney showed a trend toward higher AUC values. On day 10, the CsA dose and use of rapamycin showed a trend to higher values of C(2); the AUC was related to the CsA dose (P = .034). None of the other variables showed significant effects. Analysis between variables showed that time on dialysis correlated with the pretransplant sCr (P = .002) and that the CsA dose was negatively associated with BMI (P = .009).

CONCLUSION

Pretransplant sCr, BMI, living donor kidney category, better functional recovery, and the dose of CsA were predictors of CsA concentrations of clinical interest during this induction period. The effect of BMI was not related to higher doses of CsA.

A prospective, open-label, observational clinical cohort study of the association between delayed renal allograft function, tacrolimus exposure, and CYP3A5 genotype in adult recipients

BACKGROUND

Tacrolimus, a calcineurin inhibitor with a macrolide lactone structure, is currently used as a cornerstone immunosuppressive drug in solid organ transplantation. It is metabolized by hepatic and intestinal cytochrome P450 (CYP) 3A4/3A5 enzymes and is a substrate for P-glycoprotein (ABCB1). The disposition of tacrolimus might be influenced by severe renal allograft dysfunction (eg, in cases of delayed graft function [DGF]). New-onset diabetes after transplantation (NODAT) is a known adverse effect of tacrolimus therapy and has been associated with DGF.

OBJECTIVES

The impact of DGF on tacrolimus C(min) and dose requirements was evaluated in renal transplant recipients in the first postoperative week. The effects of the CYP3A5*3 A6986G polymorphism on initial mean tacrolimus C(min) and dose requirements in the presence and absence of DGF were assessed. This study also tested the hypothesis that if DGF influences early tacrolimus exposure, this would lead to a higher risk for NODAT (defined as the need for glucose-lowering medication for an uninterrupted period of ≥ 26 weeks).

METHODS

This prospective, open-label, observational clinical cohort study enrolled renal allograft recipients aged ≥ 18 years. Tacrolimus was administered as an oral loading dose of 0.2 mg/kg/d and adjusted to achieve a target mean daily tacrolimus C(min) between 12 and 15 ng/mL. C(min) values and oral dose requirements in the first postoperative week were compared between patients with and without DGF. Patients were genotyped for the CYP3A4*1B -290A>G, CYP3A5*3 A6986G, ABCB1 Exon26 C3435T, ABCB1 Exon21 G2677T, and ABCB1 Exon21 G2677A single nucleotide polymorphisms. NODAT that occurred within the first 12 weeks after transplantation was confirmed using an oral glucose tolerance test.

RESULTS

A total of 304 patients were enrolled (184 men, 120 women; mean [SD] age, 52.9 [14.1] years). Through day 3 after transplantation, mean (SD) 12-hour tacrolimus C(min) values were significantly higher in recipients experiencing DGF despite identical loading doses of 0.2 mg/kg. Mean tacrolimus dose requirements were significantly lower in patients with DGF during the first week. After recovery of DGF, mean tacrolimus dose requirements were not significantly different between recipients with and without DGF. In homozygous CYP3A5*3 carriers (n = 252), mean (SD) tacrolimus dose requirements remained significantly lower during DGF, while in CYP3A5*1 carriers with DGF (n = 52), lower mean dose requirements were observed only after postoperative day 4. The proportion of patients in whom NODAT developed was significantly greater in patients with DGF and tacrolimus C(min) >15 ng/mL on the first day after transplantation (27.2%) compared with recipients who remained free of DGF and had C(min) ≤15 ng/mL on day 1 (6.5%) (P = 0.016). On logistic regression analysis, greater recipient age (odds ratio [OR] = 1.044; 95% CI, 1.009-1.080), higher tacrolimus C(min) on day 1 (OR = 1.048; 95% CI, 1.017-1.080), and DGF (OR = 2.968; 95% CI, 1.107-7.959) were associated with an increased risk for NODAT.

CONCLUSION

In this open-label, observational study, DGF was associated with higher initial mean tacrolimus C(min) values and lower daily dose requirements predominantly in CYP3A5 nonexpressers.

1α,25-dihydroxyvitamin D3 on intestinal transporter function: studies with the rat everted intestinal sac

Previous studies have shown that 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) treatment (2.56 nmol/kg i.p. daily×4) increased PepT1, Mrp2, Mrp4, Asbt, but not Mdr1/P-gp in the rat small intestine. In this study, the intestinal everted sac technique, together with various select probes: mannitol (paracellular transport), glycylsarcosine (PepT1), 5(and 6)-carboxy-2',7'-dichlorofluorescein (CDF) diacetate (precursor of CDF for Mrp2), adefovir dipivoxil (precursor of adefovir for Mrp4) and digoxin (P-gp) was used to examine the functional changes of these transporters. After establishing identical permeabilities (Papp) of mannitol for the apical-to-basolateral (A-to-B) and basolateral-to-apical (B-to-A) directions at 20 min in 1,25(OH)2D3-treated vs. vehicle-treated duodenal, jejunal and ileal everted sacs, a significant enhancement of net A-to-B transport of glycylsarcosine in the duodenum, increased B-to-A transport of CDF and A-to-B and B-to-A transport of adefovir in the jejunum were observed with 1,25(OH)2 D3 treatment. However, the A-to-B and B-to-A transport of digoxin in the ileum was unchanged. These changes in transporter function in the rat intestinal everted sac corresponded well to changes in proteins that were observed previously. This study confirms that the rat intestinal PepT1, Mrp2 and Mrp4, but not P-gp are functionally induced by 1,25(OH)2D3 treatment via the vitamin D receptor (VDR).

Hepatic clearance, but not gut availability, of erythromycin is altered in patients with end-stage renal disease

Nonrenal clearance of drugs can be significantly lower in patients with end-stage renal disease (ESRD) than in those with normal renal function. Using erythromycin (ER) as a probe compound, we investigated whether this decrease in nonrenal clearance is due to reduced hepatic clearance (CL(H)) and/or gut metabolism. We also examined the potential effects of the uremic toxins 3-carboxy-4-methyl-5-propyl-2-furan propanoic acid (CMPF) and indoxyl sulfate (Indox) on ER disposition. Route-randomized, two-way crossover pharmacokinetic studies of ER were conducted in 12 ESRD patients and 12 healthy controls after oral (250 mg) and intravenous (125 mg) dosing with ER. In patients with ESRD, CL(H) decreased 31% relative to baseline values (0.35 +/- 0.14 l/h/kg vs. 0.51 +/- 0.13 l/h/kg, P = 0.01), with no change in steady-state volume of distribution. With oral dosing, the bioavailability of ER increased 36% in patients with ESRD, and this increase was not related to changes in gut availability. As expected, plasma levels of CMPF and Indox were significantly higher in the patients than in the healthy controls. However, no correlation was observed between CL(H) of ER and the levels of uremic toxins.

The pharmacokinetics and pharmacogenomics of efavirenz and lopinavir/ritonavir in HIV-infected persons requiring hemodialysis

OBJECTIVE

To evaluate the pharmacokinetics and pharmacogenomics of efavirenz (EFV) and lopinavir/ritonavir (LPV/RTV) in HIV-infected persons requiring hemodialysis.

DESIGN

Prospective, observational study of HIV-infected hemodialysis patients receiving one 600 mg tablet daily of EFV (N = 13) or three 133.3/33.3 mg capsules twice daily of LPV/RTV (N = 13).

METHODS

Twenty-four-hour EFV and 12-h LPV/RTV pharmacokinetics were assessed. Geometric mean ratios were calculated using historical controls with normal renal function. The effects of several candidate gene polymorphisms were also explored.

RESULTS

The geometric mean [95% confidence interval (CI); percentage of coefficient of variation (% CV)] Cmin, Cmax, and area under the curve (AUC) for the EFV group were 1.81 microg/ml (0.93, 3.53; 103%), 5.04 microg/ml (3.48, 7.29; 72%), and 71.5 microg h/ml (43.2, 118.3; 93%), respectively. These parameters were 2.76 microg/ml (1.86, 4.11; 53%), 8.45 microg/ml (6.41, 11.15; 52%), and 69.6 microg h/ml (55.6, 87.2; 37%) for LPV and 0.08 microg/ml (0.05, 0.14; 63%), 0.58 microg/ml (0.44, 0.76; 41%), and 3.74 microg h/ml (2.91, 4.80; 37%) for RTV. The AUC geometric mean ratios (90% CI) for EFV, LPV, and RTV were 132% (89, 197), 81% (67, 97), and 92% (76, 111), respectively. LPV Cmin was lower than expected in the hemodialysis group. Higher EFV concentrations were associated with the CYP2B6 516G>T polymorphism.

CONCLUSION

The pharmacokinetics of EFV and LPV/RTV in hemodialysis suggests that no dosing adjustments are necessary in treatment-naive patients. As HIV-infected hemodialysis patients are disproportionately black, the increased frequency of the CYP2B6 516G>T polymorphism may lead to higher EFV levels. The potentially lower LPV trough levels in this population suggest that LPV/RTV should be used with caution in protease-inhibitor-experienced patients.

The effect of chronic renal failure on drug metabolism and transport

BACKGROUND

Chronic renal failure (CRF) has been shown to significantly reduce the nonrenal clearance and alter bioavailability of drugs predominantly metabolized by the liver and intestine.

OBJECTIVES

The purpose of this article is to review all significant animal and clinical studies dealing with the effect of CRF on drug metabolism and transport.

METHODS

A search of the National Library of Medicine PubMed was done with terms such as chronic renal failure, cytochrome P450 [CYP], liver metabolism, efflux drug transport and uptake transport, including relevant articles back to 1969.

RESULTS

Animal studies in CRF have shown a significant downregulation (40-85%) of hepatic and intestinal CYP metabolism. High levels of parathyroid hormone, cytokines and uremic toxins have been shown to reduce CYP activity. Phase II reactions and drug transporters such as P-glycoprotein and organic anion transporting polypeptide are also affected.

CONCLUSION

CRF alters intestinal, renal and hepatic drug metabolism and transport producing a clinically significant impact on drug disposition and increasing the risk for adverse drug reactions.

The unique character of cardiovascular disease in chronic kidney disease and its implications for treatment with lipid-lowering drugs

Although the risk for cardiovascular disease (CVD) is high in individuals with chronic kidney disease (CKD), there are very limited data to guide the use of lipid-lowering drugs (LLDs) in this population because the major trials of LLDs in the general population have included very few individuals with CKD. The pathophysiologic and epidemiologic differences of CVD in the CKD population suggest that the study findings derived in the general population may not be directly applicable to those with CKD, and the few trials that have been directed at patients with kidney disease have not shown clear clinical benefits of LLDs. The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) Work Group has provided consensus-based guidelines for managing dyslipidemias in individuals with CKD and after renal transplantation. Since the publication of these statements, further data have emerged and multiple studies are ongoing to define better the role of LLDs in patients with CKD. In this article, the data that are pertinent to the CKD population are reviewed, and updated recommendations for use of LLD in the CKD population are provided.

The impact of advancing age on P-glycoprotein expression and activity: current knowledge and future directions

With the progressive ageing of the population, an increasing number of elderly patients are being exposed to multiple drugs because of co-existing morbidity states requiring pharmacological management. However, the knowledge of the effects of ageing on the pharmacokinetics and pharmacodynamics of individual drugs is far from being optimal as very few elderly subjects are studied in Phase I and II premarketing trials. The efflux transporter P-glycoprotein has recently emerged as a major determinant of drug disposition in humans. This review discusses the current knowledge about the effects of advancing age on P-glycoprotein expression and activity. A critical appraisal of the published literature and an overview on future research directions are also provided.

Diuretics in pediatrics : current knowledge and future prospects

This review summarizes current knowledge on the pharmacology, pharmacokinetics, pharmacodynamics, and clinical application of the most commonly used diuretics in children. Diuretics are frequently prescribed drugs in children. Their main indication is to reduce fluid overload in acute and chronic disease states such as congestive heart failure and renal failure. As with most drugs used in children, optimal dosing schedules are largely unknown and empirical. This is undesirable as it can potentially result in either under- or over-treatment with the possibility of unwanted effects. The pharmacokinetics of diuretics vary in the different pediatric age groups as well as in different disease states. To exert their action, all diuretics, except spironolactone, have to reach the tubular lumen by glomerular filtration and/or proximal tubular secretion. Therefore, renal maturation and function influence drug delivery and consequently pharmacodynamics. Currently advised doses for diuretics are largely based on adult pharmacokinetic and pharmacodynamic studies. Therefore, additional pharmacokinetic and pharmacodynamic studies for the different pediatric age groups are necessary to develop dosing regimens based on pharmacokinetic and pharmacodynamic models for all routes of administration.

Down-Regulation of Intestinal Drug Transporters in Chronic Renal Failure in Rats

Chronic renal failure (CRF) is associated with an increased bioavailability of drugs by a poorly understood mechanism. One hypothesis is a reduction in the elimination of drugs by the intestine, i.e., drug elimination mediated by protein membrane transporters such as P-glycoprotein (Pgp) and multidrug-resistance-related protein (MRP) 2. The present study aimed to investigate the repercussions of CRF on intestinal transporters involved in drug absorption [organic anion-transportingpolypeptide (Oatp)] and those implicated in drug extrusion (Pgp and MRP2). Pgp, MRP2, MRP3, Oatp2, and Oatp3 protein expression and Pgp, MRP2, and Oatp3 mRNA expression were assessed in the intestine of CRF (induced by five-sixth nephrectomy) and control rats. Pgp and MRP2 activities were measured using the everted gut technique. Rat enterocytes and Caco-2 cells were incubated with sera from control and CRF rats to characterize the mechanism of transporters' down-regulation. Protein expression of Pgp, MRP2, and MRP3 were reduced by more than 40% (p < 0.01) in CRF rats, whereas Oatp2 and Oatp3 expression remained unchanged. There was no difference in the mRNA levels assessed by real-time polymerase chain reaction. Pgp and MRP2 activities were decreased by 30 and 25%, respectively, in CRF rats compared with control (p < 0.05). Uremic sera induced a reduction in protein expression and in activity of drug transporters compared with control sera. Our results demonstrate that CRF in rats is associated with a decrease in intestinal Pgp and MRP2 protein expression and function secondarily to serum uremic factors. This reduction could explain the increased bioavailability of drugs in CRF.

Prescription des statines en cas d’insuffisance rénale

BACKGROUND

Chronic kidney disease (CKD) is extremely common in adults, although often undiagnosed and thus untreated. Cardiovascular disease is the leading cause of death among patients with CKD and reducing its risk in this population is an important priority. Dyslipidemia is almost always present when proteinuria is above 3 gr/24 hours. Roughly two thirds of all patients with end-stage renal failure and kidney transplants suffer from dyslipidemia and should receive lipid-lowering therapy, as suggested by recent Afssaps (French drug agency) and NKF-K/DOQI (National Kidney Foundation-Kidney Disease Outcomes Quality Initiative) guidelines. We reviewed recent studies on efficacy, tolerability and prescription recommendations of statins in CKD and renal transplant patients.

METHODS

We searched Medline, the international medical database, to conduct a systematic review of the literature on the efficacy and tolerability of statins in CKD and renal transplant patients and on specific recommendations for dosage adjustments in this population.

RESULTS

The efficacy of statins in decreasing total cholesterol and LDL-cholesterol levels in dialysis and renal transplant patients is similar to that in the general population. On the other hand, large-scale randomized clinical trials among CKD (4D) and renal transplant (ALERT) patients do not demonstrate that statins significantly decrease rates of cardiovascular disease. They have a beneficial effect on proteinuria and lower the rate of kidney function deterioration in patients with dyslipidemia. Early introduction of a statin in transplant patients did not lead to improved kidney function or prevent loss of the graft. Although most statins are not excreted by the kidneys, the dosage of some must be adapted in CKD patients because of pharmacokinetic modifications induced by renal impairment.

CONCLUSION

Statins at appropriately adapted doses have the same efficacy in CKD patients as in subjects with normal kidney function, and tolerance is not a problem. Their effectiveness in cardiovascular prevention in this population has not been demonstrated to date. Results about statin-induced kidney protection are encouraging but further and more specific studies are needed.

Effects of renal failure on drug transport and metabolism

Renal failure not only alters the renal elimination, but also the non-renal disposition of drugs that are extensively metabolized by the liver. Although reduced metabolic enzyme activity in some cases can be responsible for the reduced drug clearance, alterations in the transporter systems may also be involved in the process. With the development of renal failure, the renal secretion of organic ions mediated by organic anion transporters (OATs) and organic cation transporters (OCTs) is decreased. 3-Carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) and other organic anionic uremic toxins may directly inhibit the renal excretion of various drugs and endogenous organic acids by competitively inhibiting OATs. In addition, the expression of OAT1 and OCT2 was reduced in chronic renal failure (CRF) rats. Renal failure also impairs the liver uptake of drugs and organic anions, such as bromosulphophthalein (BSP), indocyanine green (ICG), and thyroxine, where organic anion transport polypeptides (OATPs) are the major transporters. Most previous studies have been done in animals or cell culture, very often in rat models, but these are presumed to reflect the presentation of advanced renal disease in humans as well. Recent studies demonstrate that the uremic toxins CMPF and indoxyl sulfate (IS) can directly inhibit rOatp2 and hOATP-C in hepatocytes. The protein content of the liver uptake transporters Oatp1, 2, and 4 were significantly decreased in CRF rats. Decreased activity of the intestinal efflux transporter, P-glycoprotein (P-gp), was also observed in CRF rats, with no significant change of protein content, suggesting that uremic toxins may suppress P-gp function. However, increased protein levels of multidrug resistance-associated protein (MRP) 2 in the kidney and MRP3 in the liver were found in CRF rats, suggesting an adaptive response that may serve as a protective mechanism. Increases in drug areas under the curve (AUCs) in subjects with advanced renal disease for drugs that are not renally excreted are consistent with uremic toxin effects on either intestinal or hepatic cell transporters, metabolizing enzymes, or both. In conclusion, alterations of drug transporters, as well as metabolic enzymes, in patients with renal failure can be responsible for reduced drug clearance.

Drug dosing in chronic kidney disease

Patients with chronic kidney disease (CKD) are at high risk for adverse drug reactions and drug-drug interactions. Drug dosing in these patients often proves to be a difficult task. Renal dysfunction-induced changes in human pathophysiology regularly results may alter medication pharmacodynamics and handling. Several pharmacokinetic parameters are adversely affected by CKD, secondary to a reduced oral absorption and glomerular filtration; altered tubular secretion; and reabsorption and changes in intestinal, hepatic, and renal metabolism. In general, drug dosing can be accomplished by multiple methods; however, the most common recommendations are often to reduce the dose or expand the dosing interval, or use both methods simultaneously. Some medications need to be avoided all together in CKD either because of lack of efficacy or increased risk of toxicity. Nevertheless, specific recommendations are available for dosing of certain medications and are an important resource, because most are based on clinical or pharmacokinetic trials.

Limitations of C2 monitoring in renal transplant recipients

BACKGROUND

Recent developments have proposed the cyclosporin (CsA) concentration at 2 h post-dose (C(2)) as the best single time-point predictor of the extent of CsA exposure and as the optimal basis for monitoring immunosuppressive therapy in renal transplant patients. The present study sought to validate the cornerstones of the current concept of C(2) monitoring.

METHODS

We assessed the predictive value, dose proportionality and intrapatient variability of C(2) levels in 41 de novo renal transplant recipients treated with CsA microemulsion, steroids, mycophenolate sodium and basiliximab.

RESULTS

Patients with rejection and patients with CsA nephrotoxicity had lower C(2) (P = NS) and absorption (P<0.05 for toxicity), while C(0) did not show any significant difference. Receiver operating characteristic analysis did not detect discriminative C(2) values as a predictor of rejection or toxicity. In a substantial number of patients (29%) we observed poor and/or slow absorption, with C(0) >300 ng/ml and C(2) levels <800 ng/ml during the first month and a high rate of complications in these patients (18% rejection, 64% toxicity). Absorption increased over the first month post-transplant. Analysis of dose changes indicated that C(2) levels are not dose-proportional. Intrapatient variability of C(2) was as high as that of C(0).

CONCLUSIONS

C(2) levels do not predict rejection or toxicity. C(2) monitoring alone does not detect toxicity in poor and/or slow absorbers, who constitute a significant proportion of patients. Changes in absorption over time, high intrapatient variability and lack of dose proportionality constitute further limitations of the C(2) monitoring concept in the early post-transplant phase.

Increased protein level of PEPT1 intestinal H+-peptide cotransporter upregulates absorption of glycylsarcosine and ceftibuten in 5/6 nephrectomized rats

In chronic renal failure (CRF), dietary protein is one of the factors that deteriorates residual renal functions. Numerous studies have indicated that the products of protein digestion are mainly absorbed as small peptides. However, how small peptides are absorbed in CRF remains poorly understood. H(+)-coupled peptide transporter (PEPT1/SLC15A1) plays an important role in the absorption of small peptides and peptide-like drugs in the small intestine. Because dietary protein intake is one of the risk factors for renal failure, the alteration of intestinal PEPT1 might have implications in the progression of renal disease as well as the pharmacokinetics of peptide-like drugs. In this study, we examined the alteration of intestinal PEPT1 in 5/6 nephrectomized (5/6 NR) rats, extensively used as a model of chronic renal failure. Absorption of [(14)C]glycylsarcosine and ceftibuten was significantly increased in 5/6 NR rats compared with sham-operated rats, without a change in intestinal protease activity. Western blot analysis indicated that the amount of intestinal PEPT1 protein in 5/6 NR rats was increased mainly at the upper region. On the other hand, the amount of intestinal PEPT1 mRNA was not significantly different from that of sham-operated rats. These findings indicate that the increase in absorption of small peptides and peptide-like drugs, caused by the upregulation of intestinal PEPT1 protein, might contribute to the progression of renal failure as well as the alteration of drug pharmacokinetics.

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Alterations of CYP3A4 and P-glycoprotein activity in vivo with time in renal graft recipients

BACKGROUND

Catabolism by intestinal and hepatic cytochrome P450 3A4 (CYP3A4), and excretion by P-glycoprotein (PGP), has a major influence on oral bioavailability of calcineurin inhibitors. In this study, the activity of intestinal and hepatic CYP3A4 and PGP in vivo was assessed in renal transplant recipients during the first year after transplantation (Tx).

METHODS

Stable Caucasian renal transplant patients were tested at 1 week, 3 months, and 1 year after Tx, and compared with the results obtained in drug-free healthy volunteers. Intestinal and hepatic CYP3A4 and PGP activity were determined by measurement of (14)C-excretion dynamics in breath and urine after oral and intravenous administration of [N-methyl-(14)C]-erythromycin.

RESULTS

Compared with 1 week after Tx, intestinal and hepatic CYP3A4 activity significantly decreased at 3 months and 1 year after Tx (-33% and -45%; -7% and -33%, respectively). Compared with the healthy volunteers, intestinal and hepatic CYP3A4 activity of the patients was significantly increased at 1 week after Tx, but normalized at 1 year after Tx. A similar pattern, though not significant, was seen for intestinal PGP activity.

CONCLUSION

Phenotypic expression of hepatic and intestinal CYP3A4 was increased immediately after Tx, but gradually decreased to basal levels toward the end of the first year after Tx. The most plausible explanation for this evolution was the tapering of corticosteroid (CS) doses. These findings may also explain the increasing bioavailability of tacrolimus with time after Tx.

Cyclosporin A: a new drug in the field of canine dermatology

In the last few years, there has been growing interest in the use of cyclosporin to treat canine skin diseases. Cyclosporin exhibits potent immunomodulating properties that reflect its ability to block the transcription of cytokines genes in activated T lymphocytes. Cyclosporin also inhibits a number of immune allergic reactions that occur after activation of mast cells, Langerhans cells, eosinophils and keratinocytes. In randomized controlled trials, cyclosporin has proven to be as effective as glucocorticoids for treatment of canine atopic dermatitis at the inducing dosage of 5 mg kg(-1). The drug has also proven beneficial for the treatment of perianal fistulas in dogs. Other potential applications are suggested from small pilot open trials using dogs affected with various immune-mediated dermatological diseases. The pharmacokinetic properties of cyclosporin are very similar in dogs and man, but its safety margin is much wider in dogs. Therefore, routine cyclosporin blood level monitoring does not appear necessary. Although in man renal impairment and hypertension are often seen, even at low doses, these effects are not observed in dogs. Adverse reactions consist mainly of transient emesis and diarrhoea occurring during the first days of treatment. Other adverse reactions, such as gingival hyperplasia, verruciform lesions and hypertrichosis, appear to be dose-dependent, and occur rarely at therapeutic doses. An increased susceptibility to infections has not been reported in dogs receiving this drug.

Hepatic drug metabolism and transport in patients with kidney disease

The disposition of many drugs is altered in patients with acute (AKD) and chronic kidney disease (CKD). A decline in renal clearance of several drugs has been correlated significantly with residual renal function (ie, creatinine clearance) of subjects. Reductions in nonrenal clearance of some compounds also have been reported and associated with clearance of markers of oxidative and/or conjugative metabolism or P-glycoprotein-mediated transport. Although initial accounts of reduced hepatic microsomal cytochrome P-450 (CYP) content and activity in animal models of AKD and CKD were published almost 25 years ago, it is only in the last decade that technical advances in molecular biology and clinical pharmacology have enabled researchers to begin to characterize the phenotypic expression of individual enzymes and, importantly, distinguish the molecular and/or genetic basis for these changes. The selective modulation of hepatic CYP enzyme activity observed in kidney disease is caused, at least in part, by differentially altered expression of several CYP isoforms. This review summarizes data available through June 2003 regarding the effect of AKD and CKD on drug metabolism. Knowledge of the impact and nature of these alterations associated with kidney disease may facilitate the individualization of medication management in this patient population.

Pre- and postrenal transplantation pharmacokinetics of cyclosporine microemulsion

The availability of a microemulsion formulation (ME) of cyclosporin (CyA) displays improved bioavailability and reduced inter and intra-patient variability, resulting in improved long-term outcomes. Recent developments in therapeutic drug monitoring stress the need to optimize peak drug levels during the early posttransplant period to obtain long-term benefit.

METHODS

We studied early CyA-ME pharmacokinetics, comparing pre- versus immediate posttransplant values, to assess predictability of pre-transplant profiles in 22 patients including 3 diabetics. An 8 mg/kg per day amount in two divided doses was administered, for 5 days pretransplant and 10-14 days posttransplant before performing the pharmacokinetic studies. Drugs interacting with CyA metabolism/absorption were withdrawn and patients with liver disease were excluded the CyA level monitoring used a 5-point blood sampling (at 0 hours, 1 hours, 2 hours, 3 hours, and 4 hours post-dose). The study compared actual concentrations at each individual time and the limited 0-4 hour AUC.

RESULTS

The paired values at each point pre- and posttransplant were: C0 = 171 +/- 63 and 215 +/- 112, C1 = 723.86 +/- 345 and 1239.95 +/- 415, C2 = 972 +/- 185 and 1249.95 +/- 336, C3 = 822 +/- 242 and 942.7 +/- 286, and C4 = 601.54 +/- 190 and 670.5 +/- 208 ng/mL respectively. The C1 and C2 values were significantly higher posttransplant (P =.008 and 0.0045 respectively), suggesting a steeper absorption phase, a conclusion consistent with the higher 0-4 hour AUC posttransplant (P =.0089). However, linear regression analysis of pre- versus posttransplant values showed poor correlations.

CONCLUSIONS

CyA absorption is significantly lower among patients on maintenance hemodialysis and showed no predictive correlation with posttransplant levels. The possible role of uremia in retarding absorption which may have clinical significance for primary graft dysfunction, needs further evaluation.

Differential effect of acute hepatic failure on in vivo and in vitro P-glycoprotein functions in the intestine

PURPOSE

The expression and function of P-glycoprotein (P-gp) in the intestine in carbon tetrachloride-induced acute hepatic failure (AHF) were evaluated in rats.

METHODS

The expression of P-gp, in vivo absorption and exsorption of P-gp substrates (digoxin and rhodamine 123), and in vitro efflux transport of these P-gp substrates were studied in the absence and presence of a P-gp inhibitor (verapamil or cyclosporin A) using the distal region of small intestine of control and AHF rats.

RESULTS

Western blot analysis revealed that intestinal P-gp expression level remained unchanged, or rather increased, in AHF. The in vivo intestinal P-gp function was significantly lower in AHF, as evaluated by the absorption and exsorption of P-gp substrates. In contrast, in vitro P-gp function was significantly higher in AHF, as evaluated by the efflux transport of P-gp substrates across the everted intestine. Collectively, the intestinal P-gp function was differently affected by AHF between in vivo and in vitro conditions.

CONCLUSIONS

The in vivo intestinal P-gp function was suppressed in AHF, which could not be predicted from in vitro functional studies nor from P-gp expression level. The discrepancy between in vivo and in vitro results may be explained by the presence of endogenous P-gp inhibitors in the plasma of AHF rats.

Effect of interleukin-2 on intestinal P-glycoprotein expression and functionality in mice

P-glycoprotein (Pgp), an active drug transporter expressed in enterocytes, can reduce intestinal absorption of drugs. Until now, interleukin-2 (IL2) has been reported as a Pgp modulator only in vitro. The present study examines the effects in vivo of IL2 after chronic treatment on intestinal Pgp protein expression and activity. This work also describes the effects of IL2 on the oral bioavailability of a Pgp substrate (digoxin) and of a Pgp/CYP3A cosubstrate (saquinavir). Human recombinant interleukin-2 (rIL2), administered to mice at 9 million international units/kg by intraperitoneal route twice daily for 4 days, led to a decrease in intestinal Pgp protein expression evaluated by Western blot with C219 antibody. In an in vitro everted gut sac model, rIL2 pretreatment decreased the Pgp-mediated transport of rhodamine 123 across mouse intestine by 37%. Moreover, rIL2 pretreatment markedly raised the area under the curve of orally administered digoxin from 3.5 +/- 0.5 to 9.7 +/- 1.5 mg min l(-1) as a consequence of the reduction in intestinal Pgp activity. rIL2 treatment increased saquinavir bioavailability from 2.5 to 4.5%, showing that first-pass metabolism is not affected and that Pgp by itself has only a moderate effect on saquinavir oral bioavailability. In conclusion, rIL2 pretreatment reduces intestinal Pgp protein expression and activity in mice. However, the effect of such a treatment on drug bioavailability depends on the extent of their metabolism by CYP3A.