Clinical pharmacokinetics in patients with liver disease

Drug-Induced Liver Injury in Patients With Chronic Liver Disease

OBJECTIVE

Drug-induced liver injury (DILI) is a global problem and can develop from exposure to prescription or over-the-counter medications as well as herbal and dietary supplements. The diagnosis of DILI is clinically challenging, and liver injury can be severe leading to liver failure, death, or liver transplantation. Patients with underlying chronic liver diseases (CLD) may be at increased risk for DILI, which is associated with factors related to drug or liver disease.

METHODS

This review summarises current knowledge on the risk and outcomes of DILI in patients with CLD.

RESULTS

Patients with CLD may be at an increased risk for DILI. Additionally patients with underlying CLD are at risk for more severe liver injury and worse outcomes after DILI.

DISCUSSION

The risk for and poor outcomes from DILI are accentuated in patients with CLD and potentially leading to the worst-case scenario of acute-on-chronic liver failure. We highlight the key observations on DILI with a broad range of underlying liver diseases and the high-DILI risk agents implicated in those populations.

In Vitro to In Vivo Scalars for Drug Clearance in Nonalcoholic Fatty Liver and Steatohepatitis

In vitro-in vivo extrapolation (IVIVE) allows prediction of clinical outcomes across populations from in vitro data using specific scalars tailored to the biologic characteristics of each population. This study experimentally determined scalars for patients with varying degrees of nonalcoholic fatty liver disease (NAFLD), ranging from fatty liver to nonalcoholic steatohepatitis (NASH) and cirrhosis. Microsomal, S9, and cytosol fractions were extracted from 36 histologically normal and 66 NAFLD livers (27 nonalcoholic fatty liver [NAFL], 13 NASH, and 26 NASH with cirrhosis). Corrected microsomal protein per gram liver (MPPGL) progressively decreased with disease severity (26.8, 27.4, and 24.3 mg/g in NAFL, NASH, and NASH/cirrhosis, respectively, compared with 35.6 mg/g in normal livers; ANOVA, P < 0.001). Homogenate, S9, and cytosolic protein showed a consistent trend of decline in NASH/cirrhosis relative to normal control (post-hoc t test, P < 0.05). No differences across the groups were observed in homogenate, S9, cytosolic, and microsomal protein content in matched kidney samples. MPPGL-based scalars that combine protein content with liver size revealed that the reduction in MPPGL in NAFL and NASH was compensated by the reported increase in liver size (relative scalar ratios of 0.96 and 0.99, respectively), which was not the case with NASH/cirrhosis (ratio of 0.63), compared with healthy control. Physiologically based pharmacokinetics-informed global sensitivity analysis of the relative contribution of IVIVE scalars (hepatic CYP3A4 abundance, MPPGL, and liver size) to variability in exposure (area under the curve) to three CYP3A substrates (alprazolam, midazolam, and ibrutinib) revealed enzyme abundance as the most significant parameter, followed by MPPGL, whereas liver volume was the least impactful factor. SIGNIFICANCE STATEMENT: Nonalcoholic fatty liver disease-specific scalars necessary for extrapolation from in vitro systems to liver tissue are lacking. These are required in clearance prediction and dose selection in nonalcoholic fatty liver and steatohepatitis populations. Previously reported disease-driven changes have focused on cirrhosis, with no data on the initial stages of liver disease. The authors obtained experimental values for microsomal, cytosolic, and S9 fractions and assessed the relative impact of microsomal scalars on predicted exposure to substrate drugs using physiologically based pharmacokinetics.

Impact of liver fibrosis and clinical characteristics on dose-adjusted serum methadone concentrations

BACKGROUND

There is limited knowledge on the causes of large variations in serum methadone concentrations and dose requirements.

OBJECTIVES

We investigated the impact of the degree of liver fibrosis on dose-adjusted steady-state serum methadone concentrations.

METHODS

We assessed the clinical and laboratory data of 155 Norwegian patients with opioid use disorder undergoing methadone maintenance treatment in outpatient clinics in the period 2016-2020. A possible association between the degree of liver fibrosis and dose-adjusted serum methadone concentration was explored using a linear mixed-model analysis.

RESULTS

When adjusted for age, gender, body mass index, and genotypes of CYP2B6 and CYP3A5, the concentration-to-dose ratio of methadone did not increase among the participants with liver fibrosis (Coefficient: 0.70; 95% CI: -2.16, 3.57; P: 0.631), even among those with advanced cirrhosis (-0.50; -4.59, 3.59; 0.810).

CONCLUSIONS

Although no correlation was found between the degree of liver stiffness and dose-adjusted serum methadone concentration, close clinical monitoring should be considered, especially among patients with advanced cirrhosis. Still, serum methadone measurements can be considered a supplement to clinical assessments, taking into account intra-individual variations.

Using physiologically-based pharmacokinetic modeling for predicting the effects of hepatic impairment on the pharmacokinetics of olanzapine and samidorphan given as a combination tablet

A combination of olanzapine and samidorphan (OLZ/SAM) was recently approved by the US Food and Drug Administration for treatment of patients with schizophrenia or bipolar I disorder. The effects of moderate hepatic impairment on the pharmacokinetics (PKs) of olanzapine and samidorphan after a single dose of OLZ/SAM were characterized in a clinical study. Physiologically-based pharmacokinetic (PBPK) modeling was used to extend the clinical findings to predict the effects of varying degrees of hepatic impairment on the PKs of olanzapine and samidorphan. A previously developed PBPK model for OLZ/SAM was refined to recover the observed pharmacokinetic differences between individuals with moderate hepatic impairment and healthy controls. The optimized model was applied to predict changes in olanzapine and samidorphan PKs after multiple once-daily doses of OLZ/SAM in subjects with mild, moderate, and severe hepatic impairment relative to healthy controls. Modifications to model parameters, including absorption rate constant and fraction unbound to plasma protein, were made to recover the observed change in the PKs of olanzapine and samidorphan in individuals with moderate hepatic impairment. In applying the optimized model, mild, moderate, and severe hepatic impairment were predicted to increase steady-state total systemic exposures by 1.1-, 1.5-, and 1.6-fold, respectively, for olanzapine, and by 1.2-, 1.9-, and 2.3-fold, respectively, for samidorphan. PBPK modeling allowed for prediction of untested clinical scenarios of varying degrees of hepatic impairment in lieu of additional clinical studies.

Treatment Barriers in Portopulmonary Hypertension

Portopulmonary hypertension (PoPH) is a form of pulmonary arterial hypertension (PAH) that can develop as a complication of portal hypertension. Treatment of PoPH includes PAH-specific therapies, and in certain cases, such therapies are necessary to facilitate a successful liver transplantation. A significant number of barriers may limit the adequate treatment of patients with PoPH and explain the poorer survival of these patients when compared to patients with other types of PAH. Until recently, only one randomized controlled trial has included PoPH patients, and the majority of treatment data have been derived from relatively small observational studies. In the present article, we review some of the barriers in the treatment of patients with PoPH and implications for liver transplantation.

The Cytochrome P450-Mediated Metabolism Alternation of Four Effective Lignans From Schisandra chinensis in Carbon Tetrachloride-Intoxicated Rats and Patients With Advanced Hepatocellular Carcinoma

It is highly valuable to study the pharmacokinetics of herbal components under the pathological condition of liver dysfunction for safe and rational use of herbal medicines. In this study, the pharmacokinetic profiles of four effective lignans from Schisandra chinensis (SC), schisandrin, schisantherin A, deoxyshisandrin and γ-schisandrin, were investigated in carbon tetrachloride (CCl₄)-intoxicated rats. The metabolism of the four lignans was also studied using microsomes from patients with advanced hepatocellular carcinoma. In situ intestinal and hepatic perfusions were conducted to clarify the contributions from impairments of gut and liver on the pharmacokinetics of the four schisandra lignans in CCl₄-intoxicated rats. The metabolism in rat and human liver microsomes and transport in Caco-2 monolayer cell model were studied to reveal the key factors for the in vivo disposition of the four lignans. When SC alcoholic extract was orally administrated to CCl₄-intoxicated rat for a short term (4 days), the pharmacokinetics of four active SC lignans was significantly changed while its hepatotherapeutic effect was not obviously observed. The plasma concentrations of the four schisandra lignans were dramatically elevated compared with the control. The Cmax, AUC and MRT were all increased or prolonged significantly while parameter CLz/F was obviously reduced in rat pretreated with CCl₄. In hepatic perfusion study and liver microsomes incubation, it was found that the hepatic metabolism of the four lignans was markedly decreased mainly due to the activity reduction of multiple CYP450 isoenzymes involved the metabolism, which, eventually, might lead to the alternation of their pharmacokinetic profiles in CCl₄-intoxicated rats or patients with advanced hepatocellular carcinoma. The pharmacokinetic studies of SC components in pathological situation of liver dysfunction are expected to provide useful data for rational and safe application of SC preparations in clinic or further pharmacological and toxicological research.

Increase in the systemic exposure of primary metabolites of Midazolam in rat arising from CYP inhibition or hepatic dysfunction

The main purpose of this study is to demonstrate the possibility of increase in the systemic exposure of drug metabolites by CYP-inhibition or acute hepatitis. Midazolam (MDZ) was used as a model substrate of CYP3A and 1-aminobenzotriazole (ABT) was used as a CYP-inhibitor. After oral pretreatment with ABT, MDZ was intravenously injected to rats and the plasma profiles of MDZ and its primary metabolites, 1'-hydroxy MDZ and 4-hydroxy MDZ, were observed. In the ABT-pretreatment rats, plasma AUCs of both metabolites were much larger than those in control rats, demonstrating a higher systemic exposure of metabolites under CYP-inhibited condition. Furthermore, kinetic analysis revealed that the amount of both metabolites entered into the systemic circulation increased significantly (about 5-times). Increases in the systemic exposure of the primary metabolites of MDZ were also observed in the acute hepatitis rats induced by CCl₄-pretreatment. As underlying mechanisms, it was speculated that ABT inhibited the subsequent metabolism of primary metabolites of MDZ in the hepatocytes and enhanced their release to the systemic circulation. In vitro study with rat liver microsomes supported this speculation. In conclusion, this study showed the complexity of PK profiles of drug metabolites, which might lead to new aspects on their safety issue.

Pharmacokinetics of the novel oral prostacyclin receptor agonist selexipag in subjects with hepatic or renal impairment

AIM

The aim of the present study was to explore the effect of hepatic or renal dysfunction on the pharmacokinetics (PK), tolerability and safety of selexipag, an orally active prostacyclin receptor agonist.

METHODS

Two prospective, open-label studies evaluated the PK of selexipag and its active metabolite ACT-333679 in healthy subjects and in subjects with mild, moderate and severe hepatic impairment or severe renal function impairment (SRFI). A single dose of 200 μg or 400 μg was administered. The PK parameters were derived from plasma concentration-time profiles.

RESULTS

Exposure increased with the severity of hepatic impairment. Geometric mean ratios and 90% confidence intervals of the area under the concentration-time curve from time zero to infinity (AUC0-∞ ) for selexipag and ACT-333679 increased 2.1-fold (1.7-2.6) and 1.2-fold (0.9-1.6) in subjects with mild hepatic impairment, and 4.5-fold (3.4-5.8) and 2.2-fold (1.7-2.8) in subjects with moderate hepatic impairment when compared with healthy subjects. The two subjects with severe hepatic impairment showed similar dose-normalized exposure to that of subjects with moderate hepatic impairment. A 1.7-fold increase in the AUC0-∞ of selexipag and ACT-333679 was observed with SRFI compared with healthy subjects. Although exposure to selexipag and/or ACT-333679 was higher in subjects with mild or moderate hepatic impairment or SRFI vs. healthy subjects, no safety concerns were raised in these groups.

CONCLUSIONS

Based on these observations, the PK data suggest that the clinically used starting dose needs no adjustments in patients with mild or moderate hepatic impairment or SRFI. However, doses should be up-titrated with caution in these patients. The small number of subjects limits the interpretation of selexipag PK in subjects with severe hepatic impairment.

Role of enterohepatic recirculation in drug disposition: cooperation and complications

Enterohepatic recirculation (EHC) concerns many physiological processes and notably affects pharmacokinetic parameters such as plasma half-life and AUC as well as estimates of bioavailability of drugs. Also, EHC plays a detrimental role as the compounds/drugs are allowed to recycle. An in-depth comprehension of this phenomenon and its consequences on the pharmacological effects of affected drugs is important and decisive in the design and development of new candidate drugs. EHC of a compound/drug occurs by biliary excretion and intestinal reabsorption, sometimes with hepatic conjugation and intestinal deconjugation. EHC leads to prolonged elimination half-life of the drugs, altered pharmacokinetics and pharmacodynamics. Study of the EHC of any drug is complicated due to unavailability of the apposite model, sophisticated procedures and ethical concerns. Different in vitro and in vivo methods for studies in experimental animals and humans have been devised, each having its own merits and demerits. Involvement of the different transporters in biliary excretion, intra- and inter-species, pathological and biochemical variabilities obscure the study of the phenomenon. Modeling of drugs undergoing EHC has always been intricate and exigent models have been exploited to interpret the pharmacokinetic profiles of drugs witnessing multiple peaks due to EHC. Here, we critically appraise the mechanisms of bile formation, factors affecting biliary drug elimination, methods to estimate biliary excretion of drugs, EHC, multiple peak phenomenon and its modeling.

Pharmacokinetics of the novel dual endothelin receptor antagonist macitentan in subjects with hepatic or renal impairment

Macitentan is under development for the treatment of pulmonary arterial hypertension (PAH). Patients with PAH may suffer from comorbidities such as renal or hepatic impairment. Two prospective, single-center, open-label studies evaluated the pharmacokinetics of macitentan and its metabolites (pharmacologically active ACT-132577 and inactive ACT-373898) in healthy subjects and in subjects with mild, moderate, and severe hepatic impairment or severe renal function impairment (SRFI). After administering a single oral dose of 10 mg macitentan the pharmacokinetic parameters including area under the curve from zero to infinity (AUC∞) were derived from plasma concentration-time profiles. Exposure to macitentan and ACT-132577 was lower in hepatically impaired versus healthy subjects, with no correlation with the degree of hepatic impairment. Exposure to ACT-373898 was lower in subjects with moderate hepatic impairment only. Plasma concentration-time profiles for macitentan and ACT-132577 (active) were similar in healthy subjects and subjects with SRFI. AUC∞ of ACT-373898 (inactive) was 7.3-fold higher in subjects with SRFI versus healthy subjects. No safety concerns were raised in either study. Based on these observations, pharmacokinetic alterations of macitentan due to hepatic or renal function impairment are not considered clinically relevant and no dose adjustment is necessary in these patients.

Influence of mild and moderate liver impairment on the pharmacokinetics and metabolism of almorexant, a dual orexin receptor antagonist

This single-dose study aimed at investigating the effect of different degrees of hepatic impairment on the pharmacokinetics (PK), metabolism, and tolerability of almorexant, a first-in-class dual orexin receptor antagonist. Subjects with mild (Child-Pugh A, Group A, n=8) and moderate (Child-Pugh B, Group B, n=9) liver impairment and subjects with normal liver function (Group DA and DB, both n=9) received a dose of 100mg almorexant. PK parameters of almorexant and its four primary metabolites were determined. Almorexant exposure increased with severity of hepatic impairment. Geometric mean ratios (90% confidence interval) of AUC0-∞ were 2.8 (1.5-5.4), 7.2 (3.7-14.1), and 3.3 (1.7-6.4) comparing A vs. DA, B vs. DB, and B vs. A, respectively. The four metabolic pathways involved in the formation of the primary metabolites were affected in a different fashion. Geometric mean AUC0-∞ ratios comparing A vs. DA were 6.9, 1.1, 1.4, and 3.6 for M3, M5, M6, and M8, respectively. Comparing B vs. DB the corresponding figures were 7.3, 2.0, 5.4, and 1.3, respectively. Significant effects of hepatic impairment on the PK of almorexant suggested the need for dose adjustment in subjects with mild hepatic impairment and did not support its use in subjects with moderate or severe hepatic impairment.

Hepatic veno-occlusive disease resulting in tacrolimus toxicity after allogeneic hematopoietic stem cell transplantation

Tacrolimus is a widely used immunosuppressive agent for the prophylaxis of graft-versus-host disease in allogeneic hematopoietic stem cell transplantation (HSCT). Since tacrolimus is primarily metabolized by the liver, hepatic dysfunction may affect its metabolism. Hepatic veno-occlusive disease (VOD) is an early complication of HSCT that results in hepatic dysfunction, suggesting that VOD may affect tacrolimus metabolism. We report a case of hepatic VOD accompanied by a sustained high blood trough level of tacrolimus despite its discontinuation. The findings of this case suggest that the elimination of tacrolimus can be markedly delayed in patients with hepatic VOD, and that the clinician should carefully modulate the drug dosage for these patients.

HDAC inhibitors in experimental liver and kidney fibrosis

Histone deacetylase (HDAC) inhibitors have been extensively studied in experimental models of cancer, where their inhibition of deacetylation has been proven to regulate cell survival, proliferation, differentiation and apoptosis. This in turn has led to the use of a variety of HDAC inhibitors in clinical trials. In recent years the applicability of HDAC inhibitors in other areas of disease has been explored, including the treatment of fibrotic disorders. Impaired wound healing involves the continuous deposition and cross-linking of extracellular matrix governed by myofibroblasts leading to diseases such as liver and kidney fibrosis; both diseases have high unmet medical needs which are a burden on health budgets worldwide. We provide an overview of the potential use of HDAC inhibitors against liver and kidney fibrosis using the current understanding of these inhibitors in experimental animal models and in vitro models of fibrosis.

Analgesics in patients with hepatic impairment: pharmacology and clinical implications

The physiological changes that accompany hepatic impairment alter drug disposition. Porto-systemic shunting might decrease the first-pass metabolism of a drug and lead to increased oral bioavailability of highly extracted drugs. Distribution can also be altered as a result of impaired production of drug-binding proteins or changes in body composition. Furthermore, the activity and capacity of hepatic drug metabolizing enzymes might be affected to various degrees in patients with chronic liver disease. These changes would result in increased concentrations and reduced plasma clearance of drugs, which is often difficult to predict. The pharmacology of analgesics is also altered in liver disease. Pain management in hepatically impaired patients is challenging owing to a lack of evidence-based guidelines for the use of analgesics in this population. Complications such as bleeding due to antiplatelet activity, gastrointestinal irritation, and renal failure are more likely to occur with nonsteroidal anti-inflammatory drugs in patients with severe hepatic impairment. Thus, this analgesic class should be avoided in this population. The pharmacokinetic parameters of paracetamol (acetaminophen) are altered in patients with severe liver disease, but the short-term use of this drug at reduced doses (2 grams daily) appears to be safe in patients with non-alcoholic liver disease. The disposition of a large number of opioid drugs is affected in the presence of hepatic impairment. Certain opioids such as codeine or tramadol, for instance, rely on hepatic biotransformation to active metabolites. A possible reduction of their analgesic effect would be the expected pharmacodynamic consequence of hepatic impairment. Some opioids, such as pethidine (meperidine), have toxic metabolites. The slower elimination of these metabolites can result in an increased risk of toxicity in patients with liver disease, and these drugs should be avoided in this population. The drug clearance of a number of opioids, such as morphine, oxycodone, tramadol and alfentanil, might be decreased in moderate or severe hepatic impairment. For the highly excreted morphine, hydromorphone and oxycodone, an important increase in bioavailability occurs after oral administration in patients with hepatic impairment. Lower doses and/or longer administration intervals should be used when these opioids are administered to patients with liver disease to avoid the risk of accumulation and the potential increase of adverse effects. Finally, the pharmacokinetics of phenylpiperidine opioids such as fentanyl, sufentanil and remifentanil appear to be unaffected in hepatic disease. All opioid drugs can precipitate or aggravate hepatic encephalopathy in patients with severe liver disease, thus requiring cautious use and careful monitoring.

Pharmacokinetics of the novel PAR-1 antagonist vorapaxar in patients with hepatic impairment

PURPOSE

To determine whether hepatic impairment has an effect on the pharmacokinetics (PK) of vorapaxar or M20, its main pharmacologically active metabolite.

METHODS

This was an open-label study in which a single 40-mg oral dose of vorapaxar was administered to patients with mild (n = 6), moderate (n = 6), and severe (n = 4) hepatic impairment and healthy controls (n = 16) matched for age, gender, weight, and height. Blood samples for vorapaxar and M20 assay were collected predose and at frequent intervals up to 8 weeks postdose.

RESULTS

Plasma vorapaxar and M20 PK profiles were similar between patients with impaired liver function and healthy controls. Group mean values for vorapaxar C(max) and AUC(tf) were 206-279 ng/mL and 14,200-18,200 ng·h/mL, respectively, with the lowest values observed in patients with severe impairment. Vorapaxar median T(max) and mean t(1/2) values were 1.00-1.75 h and 298-366 h, respectively. There was no apparent correlation between vorapaxar or M20 exposure or t(1/2) values and disease severity. Vorapaxar was generally well tolerated; one serious adverse event (gastrointestinal bleeding secondary to ruptured esophageal varices) was reported in a patient with severe hepatic impairment.

CONCLUSIONS

Hepatic impairment had no clinically relevant effect on the PK of vorapaxar and M20. No dose or dosage adjustment of vorapaxar will be required in patients with mild to moderate hepatic impairment. Although systemic exposure to vorapaxar does not appear to increase in patients with severe hepatic impairment, administration of vorapaxar to such patients is not recommended given their bleeding diathesis.

The effect of rectal ozone on the portal vein oxygenation and pharmacokinetics of propranolol in liver cirrhosis (a preliminary human study)

AIM

The aim of this study was to investigate the effect of rectal ozone on portal vein oxygenation and the pharmacokinetic changes of propranolol in patients with liver cirrhosis.

METHODS

Fifteen patients with liver cirrhosis were included They were given a fixed oral dose of propranolol 80mg on the morning of day 1 after overnight fasting. Blood samples were collected at fixed time intervals for 24h. Patients were given 12 sessions of rectal ozone of 300ml of 40% ozone/oxygen mixture. On day 14 another oral dose of 80mg propranolol was given and blood samples were collected as on day 1. Plasma concentrations of propranolol were measured by HPLC. Portal vein oxygen tension and saturation were measured before and after rectal ozone.

RESULTS

Plasma concentrations of propranolol were reduced after ozone therapy with pronounced decreases in the maximum plasma concentration and the area under the plasma concentration-time curve. The changes were consistent with a decrease in propranolol bioavailability. There was a decrease in the elimination half-life and mean residence time. Portal vein oxygenation significantly increased after rectal ozone.

CONCLUSIONS

The changes in the pharmacokinetics of propranolol probably reflect an increase in the rate and extent of its metabolism resulting from improved portal vein oxygenation attributable to the ozone therapy. The present work highlights that ozone can be an alternative medical measure to improve portal vein oxygenation in liver cirrhosis.

Effect of blood decrease on micafungin disposition in rats

Micafungin (MCFG) is a novel echinocandin-class antifungal agent that extensively undergoes metabolic removal in the liver. In the present study, the influence of decreased blood volume on pharmacokinetic disposition of MCFG was examined using a rat model prepared by phlebotomy. In phlebotomized rats, hematocrit level and plasma albumin concentration were decreased by 50 and 15%, respectively. Regarding the pharmacokinetic parameters of MCFG, there were no significant differences in the total body clearance (CL(tot)) and elimination rate constant (k (e)) between control and phlebotomized rat groups. A slight increase was observed in the apparent volume of distribution at steady-state (Vd(ss)), but the degree of change was minimal. These findings demonstrate that the elimination capacity for MCFG is only slightly affected by severe anemia and moderate hypoalbuminemia, and provide experimental evidence for the preceding clinical studies suggesting that neither hematocrit level nor serum albumin concentration is a contributory factor for the metabolic clearance of MCFG.

How to manage medications in the setting of liver disease with the application of six questions

OBJECTIVE

Reviewing the current literature to guide clinicians managing medications in the setting of liver disease.

LITERATURE SOURCES

Using the terms liver disease, medication management, and therapeutic monitoring, a literature review was conducted to identify peer-reviewed articles in MEDLINE (1966-April 2009). Reference citations were reviewed as an additional resource. Published English-language literatures, articles and trials were reviewed. Emphasis was placed on prospective, randomised, double-blind, placebo-controlled clinical trials.

QUESTION SYNTHESIS

An informed decision on how to manage medications in the setting of liver disease should account for changes that transpire in a medication's first-pass metabolism, protein binding, volume of distribution, clearance and pharmacodynamic interactions. To incorporate these issues within one's thought process, clinicians can utilise the following six questions to evaluate a medication use: (i) Is the patient experiencing acute or chronic liver failure? (ii) Does the drug have high hepatic first-pass metabolism? (iii) Is the medication highly protein-bound? (iv) Is there a change in the volume of distribution for the medication? (v) Is the clearance of the medication significantly altered? and (vi) Is there a pharmacodynamic interaction with the medication?

CONCLUSIONS

The introduction and use of six clinically relevant questions in the setting of liver disease can serve as a guide to clinicians who manage patients with liver disease.

A semi-mechanistic model to predict the effects of liver cirrhosis on drug clearance

BACKGROUND AND OBJECTIVE

Liver cirrhosis is characterized by a decrease in functional hepatocytes, lowered circulating levels of plasma proteins and alterations in blood flow due to the development of portacaval shunts. Depending on the interplay between these parameters and the characteristics of an administered drug, varying degrees of impaired systemic clearance and first-pass metabolism are anticipated. The Simcyp Population-based ADME Simulator has already been used successfully to incorporate genetic, physiological and demographic attributes of certain subgroups within healthy populations into in vitro-in vivo extrapolation (IVIVE) of xenobiotic clearance. The objective of this study was to extend population models to predict systemic and oral drug clearance in relation to the severity of liver cirrhosis.

METHODS

Information on demographics, changes in hepatic blood flow, cytochrome P450 enzymes, liver size, plasma protein binding and renal function was incorporated into three separate population libraries. The latter corresponded to Child-Pugh scores A (mild), B (moderate) and C (severe) liver cirrhosis. These libraries, together with mechanistic IVIVE within the Simcyp Simulator, were used to predict the clearance of intravenous and oral midazolam, oral caffeine, intravenous and oral theophylline, intravenous and oral metoprolol, oral nifedipine, oral quinidine, oral diclofenac, oral sildenafil, and intravenous and oral omeprazole. The simulated patients matched the clinical studies as closely as possible with regard to demographics and Child-Pugh scores. Predicted clearance values in both healthy control and liver cirrhosis populations were compared with observed values, as were the fold increases in clearance values between these populations.

RESULTS

There was good agreement (lack of statistically significant difference, two-tailed paired t-test) between observed and predicted clearance ratios, with the exception of those for two studies of intravenous omeprazole. Predicted clearance ratios were within 0.8- to 1.25-fold of observed ratios in 65% of cases (range 0.34- to 2.5-fold).

CONCLUSION

The various drugs that were studied showed different changes in clearance in relation to disease severity, and a 'one size fits all' solution does not exist without considering the multiple sources of the changes. Predictions of the effects of liver cirrhosis on drug clearance are of potential value in the design of clinical studies during drug development and, clinically, in the assessment of likely dosage adjustment.

Hypoalbuminaemia and impaired renal function are associated with increased anticholinergic drug prescribing

BACKGROUND

A higher anticholinergic risk score (ARS) is associated with an increased risk of anticholinergic adverse effects in elderly patients. It is unknown whether factors other than the use of anticholinergic drugs determine the ARS.

METHODS

A comprehensive medical record review was conducted in 155 consecutive hospitalised patients (median age 79.0 years, interquartile range 66.0-86.0). Information was collected on: demographics; clinical characteristics (including medications and their doses); history of anticholinergic-induced adverse effects; and biochemical markers of hepatic and renal function (serum albumin concentrations and estimated glomerular filtration rate, eGFR). The ARS was calculated for each patient using a standard scoring approach and Poisson regression was used for identifying variables associated with the ARS.

RESULTS

Patients with an ARS >or= 3 had a lower eGFR (p = 0.012) and were receiving more non-anticholinergic drugs (p < 0.001) than patients with an ARS < 3. In addition to being prescribed more anticholinergic drugs, patients with ARS >or= 3 were prescribed high doses of these drugs more often than patients with ARS < 3 (41.3% vs. 26.9%, p = 0.034). A higher number of non-anticholinergic drugs (p < 0.001), a lower serum albumin concentration (p = 0.014), and a lower eGFR (p = 0.012) were independently associated with a higher ARS.

CONCLUSIONS

Polypharmacy, hypoalbuminaemia and low eGFR are independently associated with the ARS. Patients with a higher ARS are also prescribed higher doses of anticholinergic medications than those with lower ARS.

Pharmacokinetics of bicyclol in rats with acute hepatic failure

The aim of present study is to evaluate the pharmacokinetics of bicyclol in carbon tetrachloride (CCl(4))-intoxicated rats. The plasma concentration of bicyclol was detected in rats after a single oral or intravenous administration by high-performance liquid chromatography (HPLC) analysis. Rat intestinal and hepatic perfusion models were employed to clarify the respective effect of gut and liver on the pharmacokinetics of bicyclol in acute hepatic failure (AHF) rats. Rat in vitro microsomal incubation was also conducted. The bioavailability of bicyclol was increased 3.1-fold after CCl(4) intoxication in rats. The area under the curve (AUC)((0-infinity)), C(max), and clearance (CL) of bicyclol after intravenous administration were 13.4 mg h l(-1), 18.8 mg l(-1), and 1.8 l h(-1) kg(-1) in control rats, and 130 mg h l(-1), 33.1 mg l(-1), and 0.15 l h(-1) kg(-1) in AHF rats, respectively. In the present study we investigated the pharmacokinetics of bicyclol in CCl(4)-intoxicated rats and differentiated the respective role of intestine and liver by using in situ intestinal and hepatic perfusion in rats, and in vitro rat microsomes incubation. The studies are expected to provide a better understanding related to the alteration of pharmacokinetics of bicyclol in pathological situation.

Antiarrhythmics: elimination and dosage considerations in hepatic impairment

Many drugs, including most antiarrhythmics (some of which are now of limited clinical use) are eliminated by the hepatic route. If liver function is impaired, it can be anticipated that hepatic clearance will be delayed, which can lead to more pronounced drug accumulation with multiple dosing. Consequently, the potential risks of adverse events could be increased, especially as antiarrhythmics have a narrow therapeutic index. The present review summarises the available pharmacokinetic data on the most popular antiarrhythmic drugs to identify the enzymes involved in the metabolism of the various agents and confirm whether liver disease affects their elimination. Despite long usage of some of these drugs (e.g. amiodarone, diltiazem, disopyramide, procainamide and quinidine), surprisingly few data are available in patients with liver disease, making it difficult to give recommendations for dosage adjustment. In contrast, for carvedilol, lidocaine (lignocaine), propafenone and verapamil, sufficient clinical studies have been performed. For these drugs, a marked decrease in systemic and/or oral clearance and significant prolongation of the elimination half-life have been documented, which should be counteracted by a 2- to 3-fold reduction of the dosage in patients with moderate to severe liver cirrhosis. For sotalol, disopyramide and procainamide, renal clearance contributes considerably to overall elimination, suggesting that dosage reductions are probably unnecessary in patients with liver disease as long as renal function is normal. The hepatically eliminated antiarrhythmics are metabolised mainly by different cytochrome P450 (CYP) isoenzymes (e.g. CYP3A4, CYP1A2, CYP2C9, CYP2D6) and partly also by conjugations. As the extent of impairment in clearance is in the same range for all of these agents, it could be assumed that they have a common vulnerability and that, consequently, hepatic dysfunction will affect CYP-mediated phase I pathways in a similar fashion. The severity of liver disease has been estimated clinically by the validated Pugh score, and functionally by calculation of the clearance of probe drugs (e.g. antipyrine). Both approaches can be helpful in estimating/predicting impairments in drug metabolism, including antiarrhythmics. In conclusion, hepatic impairment decreases the elimination of many antiarrhythmics to such an extent that dosage reductions are highly recommended in such populations, especially in patients with cirrhosis.

Pharmacokinetics of diclofenac in rats intoxicated with CCL4, and in the regenerating liver

The pharmacokinetics of an intravenous and oral diclofenac dose of 3.2 mg/kg was studied in male Wistar rats under control conditions, 1 and 3 days after liver damage and regeneration induced by an oral injection of CCl(4). One day after CCl(4) administration, indicators of necrosis (alanine aminotransferase), cholestasis (gamma-glutamyl transpeptidase) and regeneration (alpha-fetoprotein) were significantly increased; these effects were reversed after 3 days. In nonintoxicated rats, t(1/2) was 43.83 +/- 4.95 min, V(d) was 0.37 +/- 0.04 l/kg, Cl was 129.21 +/- 9.20 ml/min kg, AUC(i.v.) was 25.62 +/- 1.45 microg/min ml, and AUC(p.o.) was 20.21 +/- 1.03. One day after intoxication, when the liver was damaged and regenerating, the metabolism was decreased: diclofenac t(1/2) was increased to 258.21 +/- 30.80 min but V(d) did not change significantly, therefore Cl was reduced to 32.81 +/- 3.38 ml/min kg. By day 3 after intoxication, liver function, regeneration and pharmacokinetics returned to normal. The results show that liver damage and regeneration increases the bioavailability by decreasing elimination. The present observations suggest that reduction of the pharmacokinetic parameters may lead to drug accumulation in the regenerating-damaged liver with an attendant possible increase in toxic effects. The results in rats, also suggest that once hepatic injury is finished and regeneration is complete, diclofenac can be administered normally.

The effect of old age on liver oxygenation and the hepatic expression of VEGF and VEGFR2

In old age, the liver contains less ATP and hypoxia-responsive genes are upregulated. Age-related changes in hepatic perfusion and the liver sinusoidal endothelial cell (LSEC) could contribute to this altered hepatic oxygen-dependent metabolism by causing intrahepatocytic hypoxia. Furthermore, age-related changes in the LSEC ('pseudocapillarization') have been partially induced by ATP depletion. To investigate whether there is intracellular hypoxia in the old rat liver, pimonidazole immunohistochemistry in intact livers and ATP levels in isolated LSECs were studied from young and old rats. There were no age-related changes. To determine whether defenestration of the LSEC could impair oxygen diffusion, pimonidazole immunohistochemistry was performed in rats treated with poloxamer 407. Despite defenestration, there was no change in pimonidazole staining. Immunohistochemistry was then performed to determine whether there are age-related changes in VEGF and VEGFR2. VEGF staining was not associated with age. However, there was an increase in perisinusoidal VEGFR2 expression with increasing age. In conclusion, liver hypoxia does not occur in old age and LSEC pseudocapillarization does not constitute an oxygen-diffusion barrier. There are no age-related changes in VEGF expression but an increase in perisinusoidal VEGFR2 expression, which has implications for the effects of aging on the hepatic sinusoid.

Pharmacokinetic-Pharmacodynamic Crisis in the Elderly

Advances in medical technology have led to improved survival after catastrophic illnesses. Many of the survivors require ongoing care including tracheostomy, mechanical ventilation, tube feedings, and indwelling venous catheters. Repeated hospitalizations may be necessary to treat infectious complications resulting from resistant organisms requiring intravenous antibiotic therapy. Because prolonged intravenous access may be difficult or even impossible in these patients, alternative means of therapy are necessary. Linezolid is the first of a new class of antimicrobial agents known as the oxazolidinones with activity against gram-positive bacteria similar to that of vancomycin and yet its oral bioavailability allows for enteral administration. We present our retrospective experience with oral linezolid in a cohort of pediatric intensive care unit patients. Primary infectious disease issues included endocarditis, tracheitis, pneumonia, or central line sepsis resulting from Staphylococcus epidermidis, methicillin-resistant Staphylococcus aureus, and Enterococcus. Treatment was initiated with vancomycin and changed to enteral linezolid (10 mg/kg every 12 hours). The duration of therapy with linezolid varied from 7 days to 6 weeks. All of the patients were discharged home to complete their course of enteral linezolid. No complications related to linezolid therapy were noted, and all of the patients completed their prescribed course of therapy without the need for rehospitalization. Our preliminary experience suggests that oral linezolid offers an effective alternative to intravenous vancomycin for the treatment of infections resulting from gram-positive bacteria and avoids the need for prolonged vascular access.

The influence of hepatic impairment on the pharmacokinetics of the dipeptidyl peptidase IV (DPP-4) inhibitor vildagliptin

OBJECTIVE

Vildagliptin is a potent and selective dipeptidyl peptidase-IV (DPP-4) inhibitor that improves glycemic control in patients with type 2 diabetes mellitus by increasing alpha- and beta-cell responsiveness to glucose. This study investigated the pharmacokinetics of vildagliptin in patients with hepatic impairment compared with healthy subjects.

METHODS

This was an open-label, parallel-group study in patients with mild (n = 6), moderate (n = 6) or severe (n = 4) hepatic impairment and healthy subjects (n = 6). All subjects received a single 100-mg oral dose of vildagliptin, and plasma concentrations of vildagliptin and its main pharmacologically inactive metabolite LAY151 were measured up to 36 h post-dose.

RESULTS

Exposure to vildagliptin (AUC(0-infinity) and C(max)) decreased non-significantly by 20 and 30%, respectively, in patients with mild hepatic impairment [geometric mean ratio (90% CI): AUC(0-infinity), 0.80 (0.60, 1.06), p = 0.192; C(max), 0.70 (0.46, 1.05), p = 0.149]. Exposure to vildagliptin was also decreased non-significantly in patients with moderate hepatic impairment [-8% for AUC(0-infinity), geometric mean ratio (90% CI): 0.92 (0.69, 1.23), p = 0.630; -23% for C(max), geometric mean ratio (90% CI): 0.77 (0.51, 1.17), p = 0.293]. In patients with severe hepatic impairment, C(max) was 6% lower than that in healthy subjects [geometric mean ratio (90% CI): 0.94 (0.59, 1.49), p = 0.285], whereas AUC(0-infinity) was increased by 22% [geometric mean ratio (90% CI): 1.22 (0.89, 1.68), p = 0.816). Across the hepatic impairment groups, LAY151 AUC(0-infinity) and C(max) were increased by 29-84% and 24-63%, respectively, compared with healthy subjects. The single 100-mg oral dose of vildagliptin was well tolerated by patients with hepatic impairment.

CONCLUSIONS

There was no significant difference in exposure to vildagliptin in patients with mild, moderate or severe hepatic impairment; therefore, no dose adjustment of vildagliptin is necessary in patients with hepatic impairment.

Change of drug excretory pathway by CCl4-induced liver dysfunction in rat

Liver dysfunction affects the pharmacokinetics of drugs. The liver plays an important role in drug excretion as well as drug metabolism and pharmacokinetics. In the present study, the relationship between changes in the cefmetazole (CMZ) excretory pathway and the degree of liver dysfunction induced by CCl(4) treatment was investigated. CMZ is mainly excreted as an unchanged form in feces in control rats. Depending on the serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), urinary CMZ excretion was increased, whereas fecal CMZ excretion was decreased in rat with liver dysfunction. The AUC of CMZ in rats with severe liver dysfunction was approximately 2-fold higher than that in control rats. Since drug transporters could be involved in drug excretion, changes in the expression of representative hepatic drug transporters in liver dysfunction were investigated by rat DNA microarray. Basolateral solute carrier transporters such as Ntcp, Oct1, and Oatp2 were decreased and basolateral ATP-binding cassette transporters such as Mrp3 and Mrp4 were increased by the CCl(4) treatment. On the other hand, canalicular Mrp2 and Bsep were decreased, but Mdr1 was increased. However, the transporter system for CMZ has not been identified yet. In conclusion, we clarified that the fecal and urinary excretory profiles of CMZ were changed clearly depending on the serum AST and ALT levels in liver dysfunction. The changes in the CMZ excretory pathway might be responsible for the changes in the expression of drug transporters.

Pharmacokinetics of sirolimus (rapamycin) in subjects with mild to moderate hepatic impairment

Eighteen adult subjects with mild to moderate hepatic impairment and 18 healthy control subjects were given a single 15-mg dose of sirolimus by oral solution. Mean whole-blood sirolimus weight-normalized oral-dose clearances (CL/F) were significantly decreased (P = .02) in subjects with mild to moderate hepatic impairment by -31.8% and -36.0%, respectively, compared with controls. There were no significant differences in mean sirolimus C(max) and t(max) values among groups. The observed decreases in CL/F may be relevant in renal transplant patients with mild to moderate hepatic impairment, based on the close similarity of sirolimus CL/F in controls and previously studied stable renal transplant patients receiving multiple-dose administration of sirolimus and cyclosporine. There was considerable overlap in the CL/F values of hepatic-impaired subjects and controls, suggesting that whole-blood sirolimus trough concentrations in renal transplant patients exhibiting mild to moderate hepatic impairment be initially monitored to assess the need for dose adjustments.

Altered metabolism of tacrolimus in hepatic veno-occlusive disease

Tacrolimus is widely used for the prophylaxis and treatment of graft-versus-host disease after allogeneic hematopoietic stem cell transplantation (HSCT) and graft rejection in solid organ transplantation. The metabolism of tacrolimus has been reported to be impaired in association with liver dysfunction, mostly as documented in liver transplant recipients. Hepatic veno-occlusive disease (VOD) is one of the serious complications after allogeneic HSCT. It is characterized by jaundice, fluid retention, and painful hepatomegaly, caused by endothelial cell injury resulting from the toxicity of the conditioning regimen. The impaired metabolism of tacrolimus in hepatic VOD has not previously been reported in the literature. Here, we report the notable alteration in the metabolism of tacrolimus in two patients with hepatic VOD, in whom the half-lives of tacrolimus were markedly prolonged (288 and 146 h).

Treatment of Active Tuberculosis: Challenges and Prospects

This article reviews the basic principles of drug treatment of tuberculosis, individual pharmacologic agents, current treatment recommendations, and several special situations that clinicians are likely to encounter in medical practice.

The Hepatic Sinusoid in Aging and Cirrhosis

The fenestrated sinusoidal endothelium ('liver sieve') and space of Disse in the healthy liver do not impede the transfer of most substrates, including drugs and oxygen, from the sinusoidal lumen to the hepatocyte. Plasma components transfer freely in both directions through the endothelial fenestrations and into the space of Disse. The endothelium is attenuated, there is no basement membrane and there is minimum collagen in the space of Disse, thus minimising any barriers to substrate diffusion. Both cirrhosis and aging are associated with marked structural changes in the sinusoidal endothelium and space of Disse that are likely to influence bulk plasma transfer into the space of Disse, and diffusion through the endothelium and space of Disse. These changes, termed capillarisation and pseudocapillarisation in cirrhosis and aging, respectively, impede the transfer of various substrates. Capillarisation is associated with exclusion of albumin, protein-bound drugs and macromolecules from the space of Disse, and the progressive transformation of flow-limited to barrier-limited distribution of some substrates. There is evidence that the sinusoidal changes in cirrhosis and aging contribute to hepatocyte hypoxia, thus providing a mechanism for the apparent differential reduction of oxygen-dependent phase I metabolic pathways in these conditions. Structural change and subsequent dysfunction of the liver sieve warrant consideration as a significant factor in the impairment of overall substrate handling and hepatic drug metabolism in cirrhosis and aging.

Aging biology and geriatric clinical pharmacology

Population aging evokes doomsday economic and sociological prognostication, despite a minority of older people suffering significant dependency and the potential for advances in therapeutics of age-related disease and primary aging. Biological aging processes are linked mechanistically to altered drug handling, altered physiological reserve, and pharmacodynamic responses. Parenteral loading doses need only be adjusted for body weight as volumes of distribution are little changed, whereas oral loading doses in some cases may require reduction to account for age-related increases in bioavailability. Age-related reduction of hepatic blood flow and hepatocyte mass and primary aging changes in hepatic sinusoidal endothelium with effects on drug transfer and oxygen delivery reduce hepatic drug clearance. Primary renal aging is evident, although renal clearance reduction in older people is predominantly disease-related and is poorly estimated by standard methods. The geriatric dosing axiom, "start low and go slow" is based on pharmacokinetic considerations and concern for adverse drug reactions, not from clinical trial data. In the absence of generalizable dosage guidelines, individualization via effect titration is required. Altered pharmacodynamics are well documented in the cardiovascular system, with changes in the autonomic system, autacoid receptors, drug receptors, and endothelial function to modify baseline cardiovascular tone and responses to stimuli such as postural change and feeding. Adverse drug reactions and polypharmacy represent major linkages to avoidable morbidity and mortality. This, combined with a deficient therapeutic evidence base, suggests that extrapolation of risk-benefit ratios from younger adults to geriatric populations is not necessarily valid. Even so, therapeutic advances generally may convert healthy longevity from an asset of fortunate individuals into a general social benefit.

No influence of mild-to-moderate hepatic impairment on the pharmacokinetics and pharmacodynamics of ximelagatran, an oral direct thrombin inhibitor

BACKGROUND

The oral direct thrombin inhibitor ximelagatran is a new class of anticoagulant currently in clinical development for the prevention and treatment of thromboembolic disease. After oral administration, ximelagatran is rapidly absorbed and bioconverted to its active form melagatran.

OBJECTIVE

To investigate the influence of mild-to-moderate hepatic impairment on the pharmacokinetic and pharmacodynamic properties of ximelagatran.

STUDY DESIGN

Nonblinded, nonrandomised study.

PARTICIPANTS

Twelve volunteers with mild-to-moderate hepatic impairment (classified as Child-Pugh A or B) and 12 age-, weight-, and sex-matched control volunteers with normal hepatic function.

METHODS

Volunteers received a single oral dose of ximelagatran 24mg. Plasma and urine samples were collected for pharmacokinetic and pharmacodynamic analyses.

RESULTS

The absorption and bioconversion of ximelagatran to melagatran were rapid in both groups. The maximum plasma concentration of melagatran (Cmax) was achieved 2-3 hours after administration; the mean elimination half-life (t1/2z) was 3.6 hours for hepatically impaired volunteers and 3.1 hours for the control volunteers. The area under the plasma concentration-time curve (AUC) and Cmax of melagatran in volunteers with hepatic impairment were 11 and 25% lower than in control volunteers, respectively. However, after correcting for the higher renal function (i.e. higher calculated creatinine clearance) in the hepatically impaired volunteers, the ratio of melagatran AUC for hepatically impaired/control volunteers was 0.98 (90% CI 0.80, 1.22), suggesting that mild-to-moderate hepatic impairment had no influence on the pharmacokinetics of ximelagatran. Melagatran was the predominant compound in urine, accounting for 13-14% of the ximelagatran dose. Renal clearance of melagatran was 13% higher in hepatically impaired than in control volunteers. There were no significant differences between the two groups in the concentration-response relationship between plasma melagatran concentration and activated partial thromboplastin time (APTT). Baseline prothrombin time (PT) was slightly longer in the hepatically impaired patients than in the control volunteers, probably reflecting a slight decrease in the activity of coagulation factors. However, when concentrations of melagatran were at their peak, the increase in PT from baseline values was the same in both groups. Capillary bleeding time was measured in the hepatically impaired patients only, and was not increased by ximelagatran. Ximelagatran was well tolerated in both groups.

CONCLUSION

There were no differences in the pharmacokinetic or pharmacodynamic properties of melagatran following oral administration of ximelagatran between the hepatically impaired and control volunteers. These findings suggest that dose adjustment for patients with mild-to-moderate impairment of hepatic function is not necessary.

Effect of Experimental Acute Renal and Hepatic Failure on Absorption of Tacrolimus in Rat Small Intestine

The objective of this study is to evaluate the effect of acute renal or hepatic failure on the intestinal absorption of tacrolimus. Simultaneous perfusion study in rat small intestine revealed that the extent of absorption into blood vessels was decreased in the jejunum and the ileum of rat of acute renal failure due to the decrease in the uptake of tacrolimus into enterocytes. In contrast, there observed no significant changes in tacrolimus absorption in rat of acute hepatic failure. Since it has been reported that tacrolimus absorption is regulated mainly by Cytochrome P-450 (CYP) mediated metabolism in the jejunum, but by P-glycoprotein (P-gp) mediated efflux in the ileum, these factors might contribute to the changes in intestinal absorption of tacrolimus in rat of acute renal failure. Enzyme inhibitor, ketoconazole, was co-perfused with tacrolimus to specify the effect of CYP and P-gp. However, since ketoconazole failed to recover the permeability in the jejunum and ileum of rat of acute renal failure, it is considered that the changes in CYP or P-gp functions might not be involved in the decreased uptake of tacrolimus. This type of kinetic study in rats should be valuable to identify the precise mechanisms of drug absorption and the effects of various diseases on it, such as acute renal or hepatic failure.

Pharmacokinetics of Phenol Red in Rat Models of Liver Damage Prepared by Liver Targeting of Carbon Tetrachloride

Animal models prepared by treatment with carbon tetrachloride (CCl(4)) have been used to examine drug disposition in hepatic disorder. However, previous studies demonstrated that systemic administration of CCl(4) impaired not only hepatic but also renal function. We recently reported that application of CCl(4) to the rat liver surface produced hepatic damage without impairing renal function. In the present study, we examined the pharmacokinetics of phenol red in our developed rat model. The rats treated with CCl(4) by liver surface application exhibited decreases in the biliary clearance of phenol red in comparison with normal rats from 0.54+/-0.03 to 0.31+/-0.06 ml/min, suggesting hepatic damage. In these rats, the renal clearance of phenol red did not decrease (0.50+/-0.16 ml/min vs. 0.46+/-0.07 ml/min in normal rats). On the other hand, oral and intraperitoneal treatments with CCl(4) reduced not only the biliary clearance of phenol red (0.34+/-0.03 ml/min in p.o. treated rats, 0.18+/-0.01 ml/min in i.p. treated rats) but also the renal clearance (0.26+/-0.05 ml/min in p.o. treated rats, 0.18+/-0.06 ml/min in i.p. treated rats) as compared with normal rats. These findings indicate that the rat model of liver damage prepared by liver surface application of CCl(4) is useful to investigate the effects of hepatic disorder on the pharmacokinetics of drugs.

Pharmacokinetics and pharmacodynamic action of budesonide in early- and late-stage primary biliary cirrhosis

Budesonide has been discussed as a potential treatment option in primary biliary cirrhosis (PBC). Therefore, we studied the pharmacokinetics and pharmacodynamics of budesonide in patients with PBC stage I/II and stage IV. Twelve patients with early PBC stage I/II and 7 patients with PBC stage IV under continuous treatment with ursodeoxycholic acid (UDCA) were enrolled in an exploratory trial. Each patient received oral budesonide for 3 weeks at weekly increasing dosages of 3 mg once to thrice per day. Budesonide and cortisol plasma levels, urinary cortisol excretion, serum liver tests, and immunoglobulins were determined on days 1, 7, and 21 of the study. Patients with PBC stage IV showed significantly higher peak plasma concentrations (4.9 +/- 3.5 vs. 1.5 +/- 0.4 ng/mL; P <.05) and areas under the plasma concentration-time curves (AUC) (23.2 +/- 16.8 vs. 5.1 +/- 1.4 hours. ng/mL, P <.01, total AUC extrapolated to infinity [AUC(0- infinity )]) after a single dose of 3 mg budesonide when compared with patients with PBC stage I/II. Equally, AUC of budesonide were significantly increased under a multiple dose regimen on day 21 (14.0 +/- 11.6 vs. 5.0 +/- 1.9 hours. ng/mL, P <.01, AUC at steady state from dosing time to 8 hours [AUC(ss,0-8 h)]). Higher levels of budesonide were related to a significant decrease in plasma cortisol and reduction of urinary cortisol excretion in patients with stage IV disease. Two patients with stage IV disease developed portal vein thrombosis (PVT). In conclusion, administration of budesonide leads to markedly elevated plasma levels in cirrhotic patients with PBC associated with serious adverse drug reactions. Thus, further evaluation of combined treatment with UDCA may be considered in early-stage PBC but not in cirrhotic patients with PBC.

Age-related pseudocapillarization of the human liver

Age-related changes in liver function are important because they may promote susceptibility to adverse drug reactions, neurotoxicity, atherosclerosis, and other important diseases in older people. Age-related changes in the rat hepatic sinusoidal endothelium, termed pseudocapillarization, have been described recently and these may contribute to hepatic impairment. The present study has examined surgical and post-mortem specimens with immunohistochemistry and transmission electron microscopy to determine whether pseudocapillarization also occurs in older humans. The age of the subject, independent of systemic disease or hepatic pathology in surgical and post-mortem samples of human liver, was associated with increased peri-sinusoidal expression of von Willebrand's factor, collagen I, collagen IV, and staining with Masson's trichrome. Electron microscopy revealed significant age-related thickening of the sinusoidal endothelium (young 165 +/- 17 nm, middle age 222 +/- 11 nm, older 289 +/- 9 nm, p < 0.001) with loss of fenestrations (young 7.7 +/- 0.7 per 10 micro m, middle age 3.6 +/- 0.5 per 10 micro m, older 1.5 +/- 0.4 per 10 micro m, p < 0.001), and age-related deposition of basal lamina and collagen. In conclusion, ageing in humans is associated with morphological changes in the sinusoidal endothelium and space of Disse which are presumptively related to the ageing process and potentially represent an important link between the ageing process and disease susceptibility.

A novel method for determining hepatic sinusoidal oxygen permeability in the isolated perfused rat liver using [15O]O2

Measurement of hepatic sinusoidal permeability of oxygen and other substrates may help elucidate the mechanisms responsible for impaired liver function in cirrhosis. However studies of sinusoidal oxygen permeability in normal liver and various disease states have been limited due to the considerable technical difficulties involved in the use of standard techniques. We have developed a new method for measuring sinusoidal oxygen permeability in the isolated perfused rat liver that overcomes the difficulties of previous methods by using [(15)O]O(2) and an in-line fluid monitor. This method uses data obtained from impulse response curves of radiolabelled red cells, albumin and oxygen that are fitted mathematically using the axial dispersion model to yield rate constants that describe oxygen transit through the liver. We have demonstrated the utility and reproducibility of this method by comparing multiple injections and permeability determinations in the same preparation. This approach could be used in isolated perfused organs to study oxygen permeability in a range of disease states.

A novel method for preparation of animal models of liver damage: liver targeting of carbon tetrachloride in rats

Animal models prepared by treatment with toxic compounds such as a carbon tetrachloride have been used to examine drug disposition in hepatic diseases. However, it is possible that these compounds accumulate and cause damage to other organs as they are administered systemically. In this study, we used the liver surface application technique to deliver a toxic compound to the liver to prepare an appropriate animal model in which only the liver is significantly damaged. To restrict the absorption area in the liver, a cylindrical diffusion cell was attached to the liver surface of male Wistar rats. Twenty-four hours after direct addition of carbon tetrachloride to the diffusion cell, plasma levels of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT), and hepatic malondialdehyde (MDA) concentration were increased, while there were no changes in plasma creatinine or renal MDA level. On the other hand, not only GOT, GPT and hepatic MDA, but also creatinine and renal MDA levels were markedly increased by p.o. and i.p. administration of carbon tetrachloride, suggesting renal damage. These results indicated that the animal models of liver damage prepared by utilizing drug delivery techniques to accumulate toxic compounds in the liver would enable us to investigate the precise effects of hepatic disorder on drug disposition.