Effects of renal failure on drug transport and metabolism

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.

Pharmacokinetic considerations and dosing strategies of antibiotics in the critically ill patient

The treatment of sepsis remains a significant challenge and is the cause of high mortality and morbidity. The pathophysiological alterations that are associated with sepsis can complicate drug dosing. Critical care patients often have capillary leak, increased cardiac output and altered protein levels which can have profound effects on the volume of distribution (Vd) and clearance (Cl) of antibacterial agents, both of which may affect the pharmacokinetics (PK) / pharmacodynamics (PD) of the drug. Along with antibacterial factors such as the hydrophilicity and its kill characteristics and the susceptibility and site of action of the microorganism, different dosing and administration strategies may be needed for the different drug classes. In conclusion, developing dosing and administration regimes of antibacterials that adhere to PK/PD principles increase antibacterial exposure. Tailoring therapy to the individual patient combined with TDM may contribute to improved clinical efficacy and contain the spread of resistance.

Effect of impaired renal function on the maintenance dose of warfarin in Japanese patients

BACKGROUND

Chronic kidney disease (CKD) alters dose-effect relationship not only of drugs eliminated by the kidney but also of some drugs metabolized by the liver and not renally excreted. It is not known whether impaired renal function alters dose-effect relationship of warfarin in Asian patients. It is also unknown whether the maintenance dose of warfarin can be predicted more accurately by incorporating renal function in Asians.

METHODS

This was a cross-sectional study of patients receiving constant doses of warfarin who had PT-INR within 1.5-3.0 for 3 months or longer.

RESULTS

In a total of 137 participants, the estimated creatinine clearance (eCrCl) was 62.5±25.5 [ml/min] and the warfarin dose was 3.21±1.46 [mg/day] (both mean±standard deviation). There was a significant correlation between warfarin dose and eCrCl (p<0.0001, r(2)=0.23). In a stepwise linear regression with the maintenance dose of warfarin as the dependent variable, eCrCl as well as age, body weight, intra-individual average prothrombin time/international normalized ratio (PT-INR), and genotype of VKORC1 -1639 G>A polymorphism were chosen as independent variables. The coefficient of determination (r(2)) of this formula was 0.47. A regression equation with all the same explanatory variables except for eCrCl had an r(2) of 0.41.

CONCLUSIONS

The maintenance warfarin dose was positively correlated with kidney function as represented by eCrCl in Japanese patients. Incorporating eCrCl improved accuracy of predicting warfarin maintenance dose in this population.

Effects of chronic kidney disease on liver transport: quantitative intravital microscopy of fluorescein transport in the rat liver

Clinical studies indicate that hepatic drug transport may be altered in chronic kidney disease (CKD). Uremic solutes associated with CKD have been found to alter the expression and/or activity of hepatocyte transporters in experimental animals and in cultured cells. However, given the complexity and adaptability of hepatic transport, it is not clear whether these changes translate into significant alterations in hepatic transport in vivo. To directly measure the effect of CKD on hepatocyte transport in vivo, we conducted quantitative intravital microscopy of transport of the fluorescent organic anion fluorescein in the livers of rats following 5/6th nephrectomy, an established model of CKD. Our quantitative analysis of fluorescein transport showed that the rate of hepatocyte uptake was reduced by ∼20% in 5/6th nephrectomized rats, consistent with previous observations of Oatp downregulation. However, the overall rate of transport into bile canaliculi was unaffected, suggesting compensatory changes in Mrp2-mediated secretion. Our study suggests that uremia resulting from 5/6th nephrectomy does not significantly impact the overall hepatic clearance of an Oatp substrate.

Antibiotic Dosing in Patients With Acute Kidney Injury: "Enough But Not Too Much"

Increasing evidence suggests that antibiotic dosing in critically ill patients with acute kidney injury (AKI) often does not achieve pharmacodynamic goals, and the continued high mortality rate due to infectious causes appears to confirm these findings. Although there are compelling reasons why clinicians should use more aggressive antibiotic dosing, particularly in patients receiving aggressive renal replacement therapies, concerns for toxicity associated with higher doses are real. The presence of multisystem organ failure and polypharmacy predispose these patients to drug toxicity. This article examines the pharmacokinetic and pharmacodynamic consequences of critical illness, AKI, and renal replacement therapy and describes potential solutions to help clinicians give "enough but not too much" in these very complicated patients.

Pharmacokinetic of antiepileptic drugs in patients with hepatic or renal impairment

Many factors influence choice of antiepileptic drugs (AEDs), including efficacy of the drug for the indication (epilepsy, neuropathic pain, affective disorder, migraine), tolerability, and toxicity. The first-generation AEDs and some newer AEDs are predominately eliminated by hepatic metabolism. Other recent AEDs are eliminated by renal excretion of unchanged drug or a combination of hepatic metabolism and renal excretion. The effect of renal and hepatic disease on the dosing will depend on the fraction of the AED eliminated by hepatic and/or renal excretion, the metabolic isozymes involved, as well as the extent of protein binding, if therapeutic drug monitoring is used. For drugs that are eliminated by renal excretion, methods of estimating creatinine clearance can be used to determine dose adjustments. For drugs eliminated by hepatic metabolism, there are no specific markers of liver function that can be used to provide guidance in dosage adjustments. Based on studies with probe drugs, the hepatic metabolic enzymes are differentially affected depending on the cause and severity of hepatic disease, which can aid in predicting dose adjustment when clinical data are not available. Several AEDs are also associated with laboratory markers of mild hepatic dysfunction and, rarely, more severe hepatic injury. In contrast, the risk of renal injury from AEDs is generally low. In general, co-morbid hepatic or renal diseases influence the decision for the selection of an AED. For some patients dosing changes to their existing AEDs may be appropriate. For others, a change to another AED may be a better option.

Inhibition of human drug-metabolising cytochrome P450 and UDP-glucuronosyltransferase enzyme activities in vitro by uremic toxins

OBJECTIVE

To investigate the potential inhibitory effects of uremic toxins on the major human hepatic drug-metabolising cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes in vitro.

METHODS

Benzyl alcohol, p-cresol, indoxyl sulfate, hippuric acid and a combination of the four uremic toxins were co-incubated with human liver microsomes and selective probe substrates for the major human drug-metabolising CYP and UGT enzymes. The percentage of enzyme inhibition was calculated by measuring the rates of probe metabolite formation in the absence and presence of the uremic toxins. Kinetics studies were conducted to evaluate the K i values and mechanism(s) of the inhibition of CYP2E1, CYP3A4, UGT1A1 and UGT1A9 by p-cresol.

RESULTS

The individual uremic toxins inhibited CYP and UGT enzymes to a variable extent. p-Cresol was the most potent individual inhibitor, producing >50% inhibition of CYP2E1, CYP3A4, UGT1A1, UGT1A9 and UGT2B7 at a concentration of 100 μM. The greatest inhibition was observed with UGT1A9. p-Cresol was shown to be an uncompetitive inhibitor of UGT1A9, with unbound K i values of 9.1 and 2.5 μM in the absence and presence of bovine serum albumin (BSA), respectively. K i values for p-cresol inhibition of human liver microsomal CYP2E1, CYP3A4 and UGT1A1 ranged from 43 to 89 μM. A combination of the four uremic toxins produced >50% decreases in the activities of CYP1A2, CYP2C9, CYP2E1, CYP3A4, UGT1A1, UGT1A9 and UGT2B7.

CONCLUSIONS

Uremic toxins may contribute to decreases in drug hepatic clearance in individuals with kidney disease by inhibition of hepatic drug-metabolising enzymes.

Application of a physiologically based pharmacokinetic model informed by a top-down approach for the prediction of pharmacokinetics in chronic kidney disease patients

Quantitative prediction of the impact of chronic kidney disease (CKD) on drug disposition has become important for the optimal design of clinical studies in patients. In this study, clinical data of 151 compounds under CKD conditions were extensively surveyed, and alterations in pharmacokinetic parameters were evaluated. In CKD patients, the unbound hepatic intrinsic clearance decreased to a similar extent for drugs eliminated via hepatic metabolism by cytochrome P450, UDP-glucuronosyltransferase, and other mechanisms. Renal clearance showed a similar decrease to glomerular filtration rate, irrespective of the contribution of tubular secretion. The scaling factor (SF) obtained from the interquartile range of the relative change in each parameter was applied to the well-stirred model to predict clearance in patients. Hepatic and renal clearance could be successfully predicted for approximately half and two-thirds, respectively, of the applied compounds, showing the high utility of SFs. SFs were also introduced to a physiologically based pharmacokinetic (PBPK) model, and the plasma concentration profiles of 12 model compounds with different elimination pathways were predicted for CKD patients. The PBPK model combined with SFs provided good predictability for plasma concentration. The developed PBPK model with information on SFs would accelerate translational research in drug development by predicting pharmacokinetics in CKD patients.

Brain-kidney crosstalk

Encephalopathy and altered higher mental functions are common clinical complications of acute kidney injury. Although sepsis is a major triggering factor, acute kidney injury predisposes to confusion by causing generalised inflammation, leading to increased permeability of the blood–brain barrier, exacerbated by hyperosmolarity and metabolic acidosis due to the retention of products of nitrogen metabolism potentially resulting in increased brain water content. Downregulation of cell membrane transporters predisposes to alterations in neurotransmitter secretion and uptake, coupled with drug accumulation increasing the risk of encephalopathy. On the other hand, acute brain injury can induce a variety of changes in renal function ranging from altered function and electrolyte imbalances to inflammatory changes in brain death kidney donors.

Effects of renal impairment on the pharmacokinetics of morinidazole: uptake transporter-mediated renal clearance of the conjugated metabolites

Morinidazole is a novel 5-nitroimidazole antimicrobial drug that undergoes extensive metabolism in humans via N(+)-glucuronidation (N(+)-glucuronide of S-morinidazole [M8-1] and N(+)-glucuronide of R-morinidazole [M8-2]) and sulfation (sulfate conjugate of morinidazole [M7]). Our objectives were to assess the effects of renal impairment on the pharmacokinetics (PK) of morinidazole and to elucidate the potential mechanisms. In this parallel-group study, healthy subjects and patients with severe renal impairment received an intravenous infusion of 500 mg of morinidazole. Plasma and urine samples were collected and analyzed. The areas under the plasma concentration-time curves (AUC) for M7, M8-1, and M8-2 were 15.1, 20.4, and 17.4 times higher, respectively, in patients with severe renal impairment than in healthy subjects, while the AUC for morinidazole was 1.5 times higher. The urinary recovery of the major metabolites was not significantly different between the two groups over 0 to 48 h, but the renal clearances of M7, M8-1, and M8-2 in patients were 85.3%, 92.5%, and 92.2% lower, respectively. In vitro transporter studies revealed that M7 is a substrate for organic anion transporter 1 (OAT1) and OAT3 (Km = 28.6 and 54.0 μM, respectively). Only OAT3 transported M8-1 and M8-2. Morinidazole was not a substrate for the transporter-transfected cells examined. These results revealed that the function or activity of renal uptake transporters might be impaired in patients with severe renal impairment, which accounted for dramatically increased plasma exposure and reduced renal clearance of the conjugated metabolites of morinidazole, the substrates of renal transporters in patients. It will help clinicians to adjust the dose in patients with severe renal impairment and to predict possible transporter-based drug-drug interactions.

Effect of lycopene against cisplatin-induced acute renal injury in rats: organic anion and cation transporters evaluation

In the present study, we investigated the effects of lycopene on the expression of organic anion transporters (OATs), organic cation transporters (OCTs), and multidrug resistance-associated proteins (MRPs) of cisplatin-induced nephrotoxicity in rats. Twenty-eight 8-week-old Wistar rats were divided into four groups: control, lycopene-treated (6 mg/kg BW by oral gavage), cisplatin-treated (7 mg/kg BW, IP), and lycopene in combination with cisplatin-treated groups. In the presence of cisplatin, serum urea nitrogen (urea-N) (48.5 vs. 124.3 mg/dl) and creatinine (0.29 vs. 1.37 mg/dl) levels and the kidney efflux transporters MRP2 and MRP4 levels were significantly increased, whereas OAT1, OAT3, OCT1, and OCT2 levels in kidney were decreased in the treated rats compared with normal control rats. However, administration of lycopene in combination with cisplatin resulted in a reduction in the serum urea-N (124.3 vs. 62.4) and creatinine (1.37 vs. 0.40) levels and the kidney efflux transporters MRP2 and MRP4 proteins in the kidneys. Administration of lycopene to acute renal injury-induced rats largely upregulated the organic anion transporters (OAT1 and 3) and organic cation transporters (OCT1 and 2) to decrease the side effects of cisplatin. The present study suggests that lycopene synergizes with its nephroprotective effect against cisplatin-induced acute kidney injury in rats.

Factors affecting the development of adverse drug reactions (Review article)

OBJECTIVES

To discuss the effect of certain factors on the occurrence of Adverse Drug Reactions (ADRs).

DATA SOURCES

A systematic review of the literature in the period between 1991 and 2012 was made based on PubMed, the Cochrane database of systematic reviews, EMBASE and IDIS. Key words used were: medication error, adverse drug reaction, iatrogenic disease factors, ambulatory care, primary health care, side effects and treatment hazards.

SUMMARY

Many factors play a crucial role in the occurrence of ADRs, some of these are patient related, drug related or socially related factors. Age for instance has a very critical impact on the occurrence of ADRs, both very young and very old patients are more vulnerable to these reactions than other age groups. Alcohol intake also has a crucial impact on ADRs. Other factors are gender, race, pregnancy, breast feeding, kidney problems, liver function, drug dose and frequency and many other factors. The effect of these factors on ADRs is well documented in the medical literature. Taking these factors into consideration during medical evaluation enables medical practitioners to choose the best drug regimen.

CONCLUSION

Many factors affect the occurrence of ADRs. Some of these factors can be changed like smoking or alcohol intake others cannot be changed like age, presence of other diseases or genetic factors. Understanding the different effects of these factors on ADRs enables healthcare professionals to choose the most appropriate medication for that particular patient. It also helps the healthcare professionals to give the best advice to patients. Pharmacogenomics is the most recent science which emphasizes the genetic predisposition of ADRs. This innovative science provides a new perspective in dealing with the decision making process of drug selection.

Protein-bound molecules: a large family with a bad character

Many small solutes excreted by the kidney are bound to plasma proteins, chiefly albumin, in the circulation. The combination of protein binding and tubular secretion allows the kidney to reduce the free, unbound concentrations of such solutes to lower levels than could be obtained by tubular secretion alone. Protein-bound solutes accumulate in the plasma when the kidneys fail, and the free, unbound levels of these solutes increase more than their total plasma levels owing to competition for binding sites on plasma proteins. Given the efficiency by which the kidney can clear protein-bound solutes, it is tempting to speculate that some compounds in this class are important uremic toxins. Studies to date have focused largely on two specific protein-bound solutes: indoxyl sulfate and p-cresyl sulfate. The largest body of evidence suggests that both of these compounds contribute to cardiovascular disease, and that indoxyl sulfate contributes to the progression of chronic kidney disease. Other protein-bound solutes have been investigated to a much lesser extent, and could in the future prove to be even more important uremic toxins.

Xenobiotic metabolism: the effect of acute kidney injury on non-renal drug clearance and hepatic drug metabolism

Acute kidney injury (AKI) is a common complication of critical illness, and evidence is emerging that suggests AKI disrupts the function of other organs. It is a recognized phenomenon that patients with chronic kidney disease (CKD) have reduced hepatic metabolism of drugs, via the cytochrome P450 (CYP) enzyme group, and drug dosing guidelines in AKI are often extrapolated from data obtained from patients with CKD. This approach, however, is flawed because several confounding factors exist in AKI. The data from animal studies investigating the effects of AKI on CYP activity are conflicting, although the results of the majority do suggest that AKI impairs hepatic CYP activity. More recently, human study data have also demonstrated decreased CYP activity associated with AKI, in particular the CYP3A subtypes. Furthermore, preliminary data suggest that patients expressing the functional allele variant CYP3A5*1 may be protected from the deleterious effects of AKI when compared with patients homozygous for the variant CYP3A5*3, which codes for a non-functional protein. In conclusion, there is a need to individualize drug prescribing, particularly for the more sick and vulnerable patients, but this needs to be explored in greater depth.

Changes in the pharmacokinetic of sildenafil citrate in rats with Streptozotocin-induced diabetic nephropathy

Aim

The present investigates deals with the change in the pharmacokinetic of Sildenafil citrate (SIL) in disease condition like diabetic nephropathy (DN).

Method

Diabetes was induced in rats by administering Streptozotocin i.e. STZ (60 mg/kg, IP) saline solution. Assessment of diabetes was done by GOD-POD method and conformation of DN was done by assessing the level of Creatinine, Blood Urea Nitrogen (BUN) and Albuminurea. After the conformation of DN single dose of drug SIL (2.5 mg/kg, p.o.) were given orally and Pharmacokinetic Parameters like [AUC o-t (ug.h/ml), AUC 0-∞, C_max, T_max, Kel, Clast] were estimated in the plasma by the help of HPLC-UV.

Result

There was significant increase (p < 0.01) in the Pharmacokinetic parameters of SIL in DN rat (AUC_0-t, AUC_0-∞, C_max, T_max and T_1/2) compare to normal control rat and significant increase Kel in the DN rat compare to control rat.

Conclusion

The study concluded that there was significant (p < 0.01) increase in the bioavailability of SIL in DN.

Betaine reduces serum uric acid levels and improves kidney function in hyperuricemic mice

Betaine as a dietary alkaloid has attracted the attention of patients with kidney diseases. This study aimed to investigate the effects of betaine on serum uric acid levels and kidney function, and explore their underlying mechanisms in potassium oxonate-induced hyperuricemic mice. Betaine at 5, 10, 20, and 40 mg/kg was orally administered to hyperuricemic mice for 7 days and found to significantly reduce serum uric acid levels and increase fractional excretion of uric acid in hyperuricemic mice in a dose-dependent manner. It effectively restored renal protein level alterations of urate transport-related molecular proteins urate transporter 1, glucose transporter 9, organic anion transporter 1, and ATP-binding cassette subfamily G member 2 in this model, possibly resulting in the enhancement of kidney urate excretion. Moreover, betaine reduced serum creatinine and blood urea nitrogen levels and affected urinary levels of beta-2-microglobulin and N-acetyl-beta-D-glucosaminidase as well as upregulated renal protein levels of organic cation/carnitine transporters OCT1, OCTN1, and OCTN2, resulting in kidney function improvement in hyperuricemic mice. The findings from this study provide evidence that betaine has anti-hyperuricemic and nephroprotective actions by regulating protein levels of these renal organic ion transporters in hyperuricemic mice.

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.

Effect of uremic serum and uremic toxins on drug metabolism in human microsomes

There is increasing evidence that renal impairment modifies nonrenal drug clearance through drug metabolizing cytochrome P450 (CYP) enzymes. In this study, the direct inhibitory effect of serum from chronic renal failure (CRF) patients receiving dialysis was evaluated in CYP3A4 (testosterone) and CYP2B6 (bupropion) metabolism assays. Human liver microsomes were incubated with ultrafiltered serum collected pre- and post-hemodialysis from ten CRF patients. Additionally, several uremic toxins were evaluated in the CYP3A4 assay. In only three patients was there a significant decrease or increase in testosterone or bupropion metabolism post-dialysis. Urea, mannitol, guanidine, homocysteine, uridine and creatinine had no effect on CYP3A4 metabolism. CMPF, hippuric acid and p-cresol had IC50 values that fell within CRF patient plasma concentrations. The IC50 values for indoxyl sulfate and indole-3-acetic acid were greater than CRF plasma concentrations. The lack of a consistent effect on CYP3A4 or CYP2B6 metabolism by uremic serum may be due in part to the frequency of hemodialysis in these patients which reduced the accumulation of uremic toxins. CMPF, hippuric acid and p-cresol have the ability to inhibit CYP3A4 metabolism at clinical concentrations which may correspond to reports of changes in hepatic metabolism in some CRF patients.

Evaluation of the pharmacokinetics and drug interactions of the two recently developed statins, rosuvastatin and pitavastatin

INTRODUCTION

Statins are the cornerstone of lipid-lowering therapy to reduce the risk of coronary heart disease. Rosuvastatin and pitavastatin are the two recently developed statins with less potential for drug interaction resulting in improved safety profiles.

AREAS COVERED

This review summarizes the pharmacokinetics and drug interactions of rosuvastatin and pitavastatin. The materials reviewed were identified by searching PubMed for publications using 'rosuvastatin', 'pitavastatin', 'statins', 'pharmacokinetics' and 'drug interaction' as the search terms.

EXPERT OPINION

Rosuvastatin and pitavastatin have favorable pharmacokinetic and safety profiles as their disposition does not depend on or is only marginally influenced by cytochrome P450 (CYP) enzymes, thus potentially reducing the risk of drug-drug interactions of these two statins with other drugs known to inhibit CYP enzymes. However, drug transporters play a significant role in the disposition of rosuvastatin and pitavastatin and drug interactions may occur through these. Genetic polymorphisms in drug transporters may also affect the pharmacokinetics, drug interactions and/or the lipid-lowering effect of these statins to a different extent.

Effects of chronic kidney disease and uremia on hepatic drug metabolism and transport

The pharmacokinetics of non-renally cleared drugs in patients with chronic kidney disease is often unpredictable. Some of this variability may be due to alterations in the expression and activity of extra-renal drug metabolizing enzymes and transporters, primarily localized in the liver and intestine. Studies conducted in rodent models of renal failure have shown decreased mRNA and protein expression of many members of the cytochrome P450 enzyme (CYP) gene family and the ATP-Binding Cassette (ABC) and Solute Carrier (SLC) gene families of drug transporters. Uremic toxins interfere with transcriptional activation, cause down-regulation of gene expression mediated by proinflammatory cytokines, and directly inhibit the activity of the cytochrome P450s and drug transporters. While much has been learned about the effects of kidney disease on non-renal drug disposition, important questions remain regarding the mechanisms of these effects, as well as the interplay between drug metabolizing enzymes and drug transporters in the uremic milieu. In this review, we have highlighted the existing gaps in our knowledge and understanding of the impact of chronic kidney disease on non-renal drug clearance, and identified areas of opportunity for future research.

Pharmacokinetics of dolutegravir in HIV-seronegative subjects with severe renal impairment

PURPOSE

Dolutegravir (DTG), an unboosted HIV integrase inhibitor (INI), is metabolized by UGT1A1 and to a minor extent by CYP3A. Renal elimination of unchanged DTG is very low (< 1 %). As renal impairment may affect pharmacokinetics (PK), even for drugs primarily metabolized or secreted in bile, this study investigated the effect of renal impairment on the PK of DTG.

METHODS

This was an open-label, single-dose study of oral DTG 50 mg administered to subjects with severe renal impairment (creatinine clearance [CLcr] <30 mL/min; not on dialysis) and to healthy controls (CLcr >90 mL/min) matched for gender, age and body mass index (8 subjects per group). Serial PK samples were collected up to 72 h post-dose for determination of DTG and DTG-glucuronide (DTG-Gluc) concentrations in plasma. DTG unbound fraction in plasma was determined at 3 and 24 h. PK parameters were determined by non-compartmental methods and compared between groups by analysis of covariance.

RESULTS

DTG was well tolerated with a low incidence of Grade 1 adverse events. DTG PK parameters showed significant overlap between groups. DTG mean exposure was lower in subjects with severe renal impairment compared to healthy, matched subjects: AUC(0-∞) and Cmax were 40 % and 23 % lower, while mean DTG-Gluc was increased. Renal impairment did not affect DTG fraction unbound in plasma.

CONCLUSIONS

The modest reductions in mean PK exposures for DTG and increases for DTG-Gluc in the severe renal impairment group are not considered clinically significant. DTG does not require dose adjustment in patients with renal impairment.

In vivo alterations in drug metabolism and transport pathways in patients with chronic kidney diseases

STUDY OBJECTIVE

This study was designed to prospectively evaluate the in vivo activities of drug transporters, metabolizing enzymes, and pharmacokinetics in patients with chronic kidney diseases (CKD) caused by glomerulonephritis and nonglomerular etiologies.

DESIGN

A prospective study design.

PARTICIPANTS

Eighteen adults with CKD.

SETTING

General Clinical Research Center at the University of North Carolina and University of Pittsburgh.

MEASUREMENT AND MAIN RESULTS

Blood and urine were collected and assayed for fexofenadine (transporter function) as well as flurbiprofen and 4-hydroxyflurbiprofen (CYP2C9 function). CYP3A4 activity was assessed by the erythromycin breath test. In patients with glomerulonephritis, the apparent oral clearance of fexofenadine (representing transporter activity) was 58.8 ± 34.4 L/hour, documenting a 40% reduction compared with previous data in healthy controls. The CYP2C9 pathway (4-hydroxyflurbiprofen formation clearance) was similar in all the patients with CKD and was concordant with previous reports of patients with end-stage renal disease (ESRD) and healthy controls. For flurbiprofen, patients with glomerulonephritis had higher oral clearance than those with nonglomerular CKD, suggesting higher unbound fraction and enhanced metabolism through other (non-CYP2C9) routes. No statistically significant differences in CYP3A4 activity were observed in either group of patients or when compared with results from previous studies of patients with ESRD or healthy controls.

CONCLUSIONS

The current study suggests no statistically significant differences in the in vivo activity of CYP2C9 and CYP3A4 in patients with either glomerulonephritis or nonglomerular CKD. However, there are clinical differences in transporter function as defined by at least a 25% reduction in activity in glomerulonephritis as opposed to healthy controls. A similarity in the in vivo function between patients with glomerulonephritis and ESRD, and between patients with glomerulonephritis and nonglomerular CKD was present despite significant differences in kidney function. Further in vivo and in vitro studies are necessary to fully understand the physiologic and disease-specific nuances that contribute to alterations in drug disposition in patients with kidney diseases.

The effect of hepatic or renal impairment on the pharmacokinetics of edivoxetine, a selective norepinephrine transporter reuptake inhibitor

Purpose

To assess the impact of hepatic or renal impairment on the pharmacokinetics (PK) of edivoxetine.

Methods

Two separate multi-center, open-label studies with males and females were conducted. Subjects were categorized according to their hepatic function, determined by the Child–Pugh classification, or renal function, determined by creatinine clearance using the Cockcroft–Gault equation. Subjects received a single dose of 18 mg in the hepatic impairment study or 6 mg in the renal impairment study. Noncompartmental PK parameters were computed from the edivoxetine plasma concentration–time data.

Results

In the hepatic study, the geometric least squares mean (GLSM) and 90 % confidence interval (CI) of the ratio [impaired : normal] of area under the concentration versus time curve from time zero to infinity (AUC0-∞; h × ng/mL) was 1.24 (0.93, 1.64) in the mild, 1.60 (1.21, 2.12) in the moderate, and 1.70 (1.28, 2.24) in the severe group. In the renal impairment study, the GLSM (90 % CI) of the ratio [impaired : normal] of AUC0-∞ was 1.13 (0.73, 1.73) in mild, 1.90 (1.28, 2.82) in moderate, 1.55 (0.94, 2.55) in severe, and 1.03 (0.66, 1.59) in ESRD groups. Overall, the GLSM of the ratio [impaired : normal] of C_max was slightly less than or approximately 1 across the hepatic and renal impairment groups. Across both studies, there were no clinically significant changes in vital signs and laboratory values, the adverse events were mild in severity and mostly related to nervous system and gastrointestinal disorder-related events.

Conclusions

PK changes in subjects with hepatic or renal impairment were of small magnitude and did not appear to impact overall subject tolerability. Daily dosing of edivoxetine in a larger population of impaired subjects, including those with dual impairment, would aid in establishing edivoxetine tolerability and PK in a clinical practice scenario.

Indoxyl sulfate down-regulates SLCO4C1 transporter through up-regulation of GATA3

The accumulated uremic toxins inhibit the expression of various renal transporters and this inhibition may further reduce renal function and subsequently cause the accumulation of uremic toxins. However, the precise mechanism of the nephrotoxicity of uremic toxins on renal transport has been poorly understood. Here we report that indoxyl sulfate, one of the potent uremic toxins, directly suppresses the renal-specific organic anion transporter SLCO4C1 expression through a transcription factor GATA3. The promoter region of SLCO4C1 gene has several GATA motifs, and indoxyl sulfate up-regulated GATA3 mRNA and subsequently down-regulated SLCO4C1 mRNA. Overexpression of GATA3 significantly reduced SLCO4C1 expression, and silencing of GATA3 increased SLCO4C1 expression vice versa. Administration of indoxyl sulfate in rats reduced renal expression of slco4c1 and under this condition, plasma level of guanidinosuccinate, one of the preferable substrates of slco4c1, was significantly increased without changing plasma creatinine. Furthermore, in 5/6 nephrectomized rats, treatment with oral adsorbent AST-120 significantly decreased plasma indoxyl sulfate level and conversely increased the expression of slco4c1, following the reduction of plasma level of guanidinosuccinate. These data suggest that the removal of indoxyl sulfate and blocking its signal pathway may help to restore the SLCO4C1-mediated renal excretion of uremic toxins in CKD.

Pharmacokinetics of single-dose primaquine in patients with chronic kidney dysfunction

AIM

The pharmacokinetics of primaquine has not been studied in special populations. Being a basic compound, preferential binding to alpha-1 acid glycoprotein and substrate for P-glycoprotein, may predispose the drug for an altered pharmacokinetics in states of renal dysfunction. This study attempts to evaluate the pharmacokinetics of a single oral dose (15 mg) of primaquine in severely impaired renal function and end stage renal dysfunction patients compared to healthy participants.

MATERIALS AND METHODS

Twelve patients each with chronic kidney disease classified as either Stage IV or V (not on dialysis) were recruited. Data from 12 healthy participants was used as concurrent controls. Serial blood collections were performed following a single dose 15 mg Primaquine orally. Primaquine concentrations were measured in the plasma using a validated HPLC method.

RESULTS

The Cmax [median (range) in ng/ml] was 29.3 (14.6-104.3), 40.3 (14.8 - 78.6), and 49.8 (15 - 169.6) and the tmax [median (range) in hours] was 3.0 (1.0- 6.0), 2.0 (1.5 - 8) and 2.0 (1.0 - 4.0) for healthy and stage IV, V (not on dialysis) CKD participants, respectively. No statistically significant difference was observed in any of the pharmacokinetic parameters between healthy, stage IV and V CKD participants.

CONCLUSION

Pharmacokinetics of single oral dose primaquine (15 mg) does not appear to be altered in patients with severely impaired renal function and end stage renal dysfunction. A change in dose or frequency of the drug administration perhaps may not be required in this population.

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.

Drug absorption, distribution, metabolism and excretion considerations in critically ill adults

INTRODUCTION

All critically ill patients require medication to treat organ dysfunction. However, the pharmacokinetics of drugs used to treat these patients is complex due to frequent alterations in drug absorption, distribution, metabolism, and excretion (ADME).

AREAS COVERED

This review examines pharmacokinetic aspects of drug administration for adult intensive care unit (ICU) patients. Specifically, the authors examine the ADME changes that occur and which should be considered by clinicians when delivering drug therapy to critically ill patients.

EXPERT OPINION

Dosage pharmacokinetics determined from single-dose or limited-duration administration studies in healthy volunteers may not apply to critically ill patients. Organ dysfunction among these patients may be due to pre-existing disease or the effects of a systemic or locoregional inflammatory response precipitated by their illness. Alterations in pharmacokinetics observed among the critically ill include altered bioavailability after enteral administration, increased volume of distribution and blood-brain barrier permeability and changes in P-glycoprotein and cytochrome P450 enzyme function. However, the effect of these changes on clinically important outcomes remains uncertain and poorly studied. Future investigations should examine not only pharmacokinetic changes among the critically ill, but also whether recognition of these changes and alterations in drug therapy directed as a consequence of their observation alters patient outcomes.

Kidney transplantation down-regulates expression of organic cation transporters, which translocate β-blockers and fluoroquinolones

Kidney transplanted patients are often treated with immunosuppressive, antihypertensive, and antibiotic drugs such as cyclosporine A (CsA), β-blockers, and fluoroquinolones, respectively. Organic cation transporters (OCT) expressed in the basolateral membrane of proximal tubules represent an important drug excretion route. In this work, the renal expression of OCT after syngeneic and allogeneic kidney transplantation in rats with or without CsA immunosuppression was studied. Moreover, the interactions of CsA, β-blockers (pindolol/atenolol), and fluoroquinolones (ofloxacin/norfloxacin) with rOCT1, rOCT2, hOCT1, and hOCT2 in stably transfected HEK293-cells were studied. Kidney transplantation was associated with reduced expression of rOCT1, while rOCT2 showed only reduced expression after allogeneic transplantation. All drugs interacted subtype- and species-dependently with OCT. However, only atenolol, pindolol, and ofloxacin were transported by hOCT2, the main OCT in human kidneys. While CsA is not an OCT substrate, it exerts a short-term effect on OCT activity, changing their affinity for some substrates. In conclusion, appropriate drug dosing in transplanted patients is difficult partly because OCT are down-regulated and because concomitant CsA treatment may influence the affinity of the transporters. Moreover, drug-drug competition at the transporter can also alter drug excretion rate.

Pharmacokinetics of aliskiren in patients with end-stage renal disease undergoing haemodialysis

BACKGROUND AND OBJECTIVES

Aliskiren represents a novel class of orally active renin inhibitors. This study analyses the pharmacokinetics, tolerability and safety of single-dose aliskiren inpatients with end-stage renal disease (ESRD) undergoing haemodialysis.

METHODS

Six ESRD patients and six matched healthy volunteers were enrolled in an open-label, parallel-group, single-sequence study. The ESRD patients underwent two treatment periods where 300 mg of aliskiren was administered 48 or 1 h before a standardized haemodialysis session (4 h, 1.4 m(2) high-flux filter, blood flow 300 mL/min, dialysate flow 500 mL/min). Washout was >10 days between both periods. Blood and dialysis samples were taken for up to 96 h postdose to determine aliskiren concentrations.

RESULTS

Compared with the healthy subjects (1681 ± 1034 ng·h/mL), the area under the plasma concentration-time curve (AUC) from time zero to infinity was 61% (haemodialysis at 48 h) and 41% (haemodialysis at 1 h) higher in ESRD patients receiving single-dose aliskiren 300 mg. The maximum (peak) plasma drug concentration (481 ± 497 ng/mL in healthy subjects) was 17% higher (haemodialysis at 48 h) and 16% lower (haemodialysis at 1 h). In both treatment periods, dialysis clearance was below 2% of oral clearance and the mean fraction eliminated from circulation was 10 and 12% in period 1 and 2, respectively. Drug AUCs were similar in ESRD patients receiving aliskiren 1 or 48 h before dialysis. No severe adverse events occurred.

CONCLUSION

The exposure of aliskiren is moderately higher in ESRD patients. Only a minor portion is removed by a typical haemodialysis session. Aliskiren exposure is not significantly affected by intermittent haemodialysis, suggesting that no dose adjustment is necessary in this population.

The role of BCS (biopharmaceutics classification system) and BDDCS (biopharmaceutics drug disposition classification system) in drug development

Biopharmaceutics Classification System and Biopharmaceutics Drug Distribution Classification System are complimentary, not competing, classification systems that aim to improve, simplify, and speed drug development. Although both systems are based on classifying drugs and new molecular entities into four categories using the same solubility criteria, they differ in the criterion for permeability and have different purposes. Here, the details and applications of both systems are reviewed with particular emphasis of their role in drug development.

Changes in expression of renal Oat1, Oat3 and Mrp2 in cisplatin-induced acute renal failure after treatment of JBP485 in rats

The purpose of this study is to investigate whether the effect of cyclo-trans-4-l-hydroxyprolyl-l-serine (JBP485) on acute renal failure (ARF) induced by cisplatin is related to change in expression of renal Oat1, Oat3 and Mrp2 in rats. JBP485 reduced creatinine, blood urea nitrogen (BUN) and indoxyl sulfate (IS) in plasma and malondialdehyde (MDA) in kidney, and recovered the glomerular filtration rate (GFR) and the activity of superoxide dismutase (SOD) in cisplatin-treated rats. The plasma concentration of PAH (para-aminohippurate) determined by LC-MS/MS was increased markedly after intravenous administration of cisplatin, whereas cumulative urinary excretion of PAH and the uptake of PAH in kidney slices were significantly decreased. qRT-PCR and Western-blot showed a decrease in mRNA and protein of Oat1 and Oat3, an increase in mRNA and protein of Mrp2 in cisplatin-treated rats, and an increase in IS (a uremic toxin) after co-treatment with JBP485. It indicated that JBP485 promoted urinary excretion of toxins by upregulating renal Mrp2. This therefore gives in part the explanation about the mechanism by which JBP485 improves ARF induced by cisplatin in rats.