Drug disposition and liver disease

Pharmacokinetics of Asciminib in Individuals With Hepatic or Renal Impairment

Asciminib is an investigational, first-in-class, specifically targeting the ABL myristoyl pocket (STAMP) inhibitor of BCR-ABL1 with a new mechanism of action compared with approved ATP-competitive tyrosine kinase inhibitors. This report describes the findings from 2 phase 1 studies assessing the pharmacokinetic (PK) profile of a single dose of asciminib (40 mg) in individuals with impaired renal function (based on absolute glomerular filtration rate; NCT03605277) or impaired hepatic function (based on Child-Pugh classification; NCT02857868). Individuals with severe renal impairment exhibited 49%-56% higher exposure (area under the curve [AUC]), with similar maximum plasma concentration (C_max ), than matched healthy controls. Based on these findings, as per the protocol, the PK of asciminib in individuals with mild or moderate renal impairment was not assessed. In individuals with mild and severe hepatic impairment, asciminib AUC was 21%-22% and 55%-66% higher, respectively, and C_max was 26% and 29% higher, respectively, compared with individuals with normal hepatic function. Individuals with moderate hepatic impairment had similar asciminib AUC and C_max than matched healthy controls. The increase in asciminib AUC and C_max in the mild hepatic impairment cohort was mainly driven by 1 participant with particularly high exposure. Asciminib was generally well tolerated, and the safety data were consistent with its known safety profile. In summary, these findings indicate that renal or hepatic impairment has no clinically meaningful effect on the exposure or safety profile of asciminib, and support its use in patients with varying degrees of renal or hepatic dysfunction.

Deriving an explicit hepatic clearance equation accounting for plasma protein binding and hepatocellular uptake

High throughput in vitro biochemical and cell-based assays have the promise to provide more mechanism-based assessments of the adverse effects of large numbers of chemicals. One of the most challenging hurdles for interpreting in vitro toxicity findings is the need for reverse dosimetry tools that estimate the exposures that will give concentrations in vivo similar to the active concentrations in vitro. Recent experience using IVIVE approaches to estimate in vivo pharmacokinetics (Wetmore et al., 2012) identified the need to develop a hepatic clearance equation that explicitly accounted for a broader set of protein binding and membrane transport processes and did not depend on a well-mixed description of the liver compartment. Here we derive an explicit steady-state hepatic clearance equation that includes these factors. In addition to the derivation, we provide simple computer code to calculate steady-state extraction for any combination of blood flow, membrane transport processes and plasma protein-chemical binding rates. This expanded equation provides a tool to estimate hepatic clearance for a more diverse array of compounds.

Impaired irinotecan biotransformation in hepatic microsomal fractions from patients with chronic liver disease

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The anticancer agent irinotecan is a prodrug that is hydrolyzed by hepatic carboxylesterase to its active and toxic metabolite SN-38 and oxidized by CYP3A4 to its inactive metabolite APC. Irinotecan therapy is complicated by co-administered drugs that inhibit CYP3A4 and decrease APC formation and that indirectly increase SN-38 formation. Dose adjustment in cancer patients with liver disease has been recommended.

WHAT THIS STUDY ADDS

In microsomal fractions from patients with severe hepatic dysfunction both APC and SN-38 formation were decreased due to down-regulation of CYP3A4 and carboxylesterase enzymes. Thus relative SN-38 : APC formation was preserved. In some fractions the SN-38:APC ratio was increased, thus providing a possible explanation for clinical reports of increased SN-38 exposure in some patients with liver dysfunction. Close monitoring of SN-38 formation in patients with severe liver disease is warranted.

AIMS

Dose modification with the anticancer agent irinotecan is recommended in patients with severe liver dysfunction. This study evaluated the impact of liver disease on the relative formation of phase I products of irinotecan biotransformation in human microsomes in vitro.

METHODS

Microsomes from subjects with normal liver function and liver dysfunction (n=20) were assessed for irinotecan biotransformation and the expression of cytochrome P450 (CYP) 3A4 and carboxylesterase (CES) enzymes.

RESULTS

Liver disease down-regulated CYP3A4 expression (median 33% of control, range 0-126%, P<0.05) and impaired CYP3A4-dependent oxidation of irinotecan to the inactive 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin (APC) (median 0.2, range 0-1.21 pmol mg protein(-1) min(-1) compared with median 0.66, range 0-2.35 in control, P<0.01). CES-mediated hydrolysis of irinotecan to 7-ethyl-10-hydroxycamptothecin (SN-38) was also impaired in liver disease (median 8.38, range 0-20.7 pmol mg protein(-1) min(-1) compared with median 13.3, range 0-28.9 in control, P<0.05). In seven of 20 liver disease microsomes neither metabolite was detected but in three the SN-38:APC ratio was high (41-68) compared with the remaining 10 samples (ratio 11-36).

CONCLUSIONS

Down-regulation of CYP3A4 in liver disease decreased APC formation from irinotecan. SN-38 production was decreased and CES1 and 2 were down-regulated in most samples. However, in a subset of disease samples SN-38 production was relatively high because CYP3A4 activity was markedly impaired. This may account for clinical reports of increased SN-38 exposure in some patients with liver disease. Dose adjustments in cancer patients with liver disease who receive irinotecan are important and circulating SN-38 concentrations should be monitored closely.

14C-Lidocaine Disposition in Serum and Tissues of Normal and Liver Diseased Rats

PURPOSE

This study was designed to investigate the disposition of (14)C-lidocaine in serum and tissues in rats with liver dysfunction.

MATERIALS AND METHODS

Eighteen male rats were randomly divided into 2 groups. Group A was considered as control while group B underwent liver damage by administrating CCl(4) 0.4 mg/kg twice a week for 6 weeks. Both groups received 5 doses of 2.5 mg/kg lidocaine mixture (labeled (14)C-lidocaine and nonlabeled). The rats were killed 2 hours after the last dose. Total lidocaine levels ((14)C-lidocaine and (14)C-lidocaine metabolite concentrations) as well as the percent of total lidocaine-bound fractions in tissues were measured.

RESULTS

(14)C-lidocaine concentrations were significantly increased in the serum (9.4+/-0.4 microg/mL), heart (7.8+/-2 microg/gL), and mandible (0.97+/-0.01 microg/g) in diseased rats as compared with normal rats (serum, 5.3+/-1.7 microg/mL; heart, 4.2+/-0.9 microg/g; mandible, 0.68+/-0.02 microg/g, respectively). (14)C-lidocaine bound fractions in the mandible and heart did not show any significant differences between the 2 groups. Instead, (14)C-lidocaine bound fractions in serum were significantly reduced in diseased animals as opposed to normal ones.

CONCLUSION

We concluded that liver dysfunction can modify (14)C-lidocaine concentrations in the serum and tissues without altering the lidocaine binding properties in the mandible and heart.

H3 Propranolol serum levels following lidocaine administration in rats with CCL4 — induced liver damage

Liver disease alters the pharmacokinetic and pharmacodynamic properties of hepatically eliminated drugs. The main factors influenced are plasma albumin levels, enzyme balance (induction & inhibition) and drug binding to tissue proteins. The influence of lidocaine on serum, heart and liver propranolol levels in Wistar rats after liver injury induced by carbon tetrachloride CCl4 0.4 ml/kg x 2/wkl, was investigated. 40 male Wistar rats were divided into four groups (I, II, III, IV; n=10), Group I animals received only propranolol (labelled + cold substance) 40 mg/kg/12 h p.o., group II propranolol plus lidocaine in a single dose of 4mg/kg s.c., group III was treated with CCl4 for 6 weeks and received propranolol x2 at the same dosage as group I, while group VI was treated with CCl4 and the same drug dosage as group II. The simultaneous administration of H3-propranolol and lidocaine increased propranolol levels in the serum and tissues. The liver in damaged animals showed an increase of propranolol level under lidocaine co-administration, probably due to CCl4 induced liver enzyme activity, resulting in a rapid propranolol metabolism or to competition between both drug protein binding sites. The increased propranolol levels in the heart after lidocaine administration were probably due to attributed to its high affinity for heart tissue. Consequently, as regards the therapeutic approach for patients with liver disease receiving propranolol their propranolol dosage should be reduced when lidocaine is co-administered.

Effect of transdermally administered fentanyl on minimum alveolar concentration of isoflurane in normothermic and hypothermic dogs

OBJECTIVE

To determine whether the minimum alveolar concentration (MAC) of isoflurane was altered by transdermal administration of fentanyl in normothermic and hypothermic dogs.

DESIGN

Randomized complete block crossover design.

ANIMALS

6 mature healthy dogs.

PROCEDURE

Dogs received each of 4 treatments in random order. Following induction of anesthesia, normothermia was maintained in dogs that were treated with a fentanyl patch (F-NORM) or sham patch (C-NORM), or hypothermia was maintained in dogs that were treated with a fentanyl patch (F-HYPO) or sham patch (C-HYPO). The appropriate patch was applied 24 hours prior to induction of anesthesia. Anesthesia was induced with isoflurane in oxygen; the dogs were intubated and mechanically ventilated. Target esophageal temperatures were maintained within 1 degrees C of baseline values (normothermia) or at 34.5 degrees C (94.1 degrees F; hypothermia) for 1 hour prior to starting MAC determinations. Supramaximal stimulation was achieved with an electrical stimulator attached to needle electrodes placed in the buccal mucosa of the lower jaw of the dog.

RESULTS

Mean MAC +/- SEM of isoflurane during C-NORM, C-HYPO, F-NORM, and F-HYPO treatments were 1.20 +/- 0.17, 0.89 +/- 0.18, 0.76 +/- 0.10, and 0.81 +/- 0.17, respectively. The mean MAC during C-NORM was significantly higher than values for the other treatments. There was no significant difference in mean MAC among the C-HYPO, F-NORM, and F-HYPO treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Data suggest that transdermal administration of fentanyl significantly reduces isoflurane requirements in normothermic dogs. The isoflurane MAC-sparing effects of transdermal fentanyl are not apparent in hypothermic dogs.

The effect of inhalant anesthetic and body temperature on peri-anesthetic serum concentrations of transdermally administered fentanyl in dogs

OBJECTIVES

To determine whether moderate hypothermia during anesthesia significantly affects the serum concentration of transdermally delivered fentanyl and whether halothane or isoflurane affect these concentrations.

STUDY DESIGN

Randomized cross-over experimental trial.

ANIMALS

Six mature, healthy Beagles (three males, three females) weighing 10.6 +/- 0.43 kg.

METHODS

A 50-microg hour(-1) fentanyl patch was applied 36 hours prior to anesthesia. Anesthesia was induced at time 0 (t = 0). Each dog received four treatments: isoflurane + normothermia (ISO-NORM), isoflurane + hypothermia (ISO-HYPO), halothane + normothermia (HAL-NORM), and halothane + hypothermia (HAL-HYPO). Dogs were intubated and maintained at 1.5 times MAC. Animals in the hypothermia treatments were cooled to 35 degrees C during anesthesia. Serum fentanyl analysis was performed at -36, -24, -12, 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 18, and 26 hours. Direct arterial blood pressures and arterial blood gases were monitored.

RESULTS

The mean body temperatures (+/-SEM) during the anesthetic period for the four treatments were: ISO-NORM = 37.7 +/- 0.07 degrees C, ISO-HYPO = 35.8 +/- 0.1 degrees C, HAL-NORM = 37.7 +/- 0.06 degrees C, and HAL-HYPO = 35.8 +/- 0.13 degrees C. The mean (+/-SEM) serum fentanyl concentrations (SFC) for both hypothermia treatments were significantly lower than baseline concentrations at t = 1 hour and persisted for the duration of anesthesia for the ISO-HYPO treatment but only from t = 1 to 2 hours for the HAL-HYPO treatment. Serum fentanyl concentrations returned to baseline within one hour of the end of anesthesia, regardless of body temperature. There were no significant differences between treatments for systolic or diastolic blood pressure but mean blood pressures were higher during normothermia versus hypothermia during the last hour of anesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

Hypothermia during inhalation anesthesia produced a significant reduction in SFC using transdermal administration and was more protracted with isoflurane than halothane anesthesia. While significant reductions in SFC occurred, the SFC were still within the range believed to confer analgesia.

Trimethylamine and foetor hepaticus

BACKGROUND

In patients with various degrees of hepatocellular failure and portosystemic shunting of blood, the breath may acquire a sweet, musty, or even slightly faecal aroma, termed foetor hepaticus, which has been attributed mainly to volatile sulphur compounds with contributions from various nitrogenous substances. Not infrequently in such patients, unusual body odours are also encountered and, by analogy with the 'fish-odour syndrome' known to be caused by excessive trimethylamine, the availability of this latter graveolent amine to potentially contribute to odours associated with hepatic disease was investigated.

METHODS

Urine (0-24 h) was collected from 63 patients with various liver diseases previously confirmed in hospital by means of various biochemical, immunologic, pathologic, and radiologic investigations. Total trimethylamine and trimethylamine N-oxide levels in urine were measured with head-space gas chromatography.

RESULTS

In total, 50% (32 of 63) of the patients (primary liver disease, 25 of 47, or 53.2%; secondary liver disease, 7 of 16, or 43.8%) had urinary trimethylamine levels greater than the upper end of the range considered normal (0.08-1.84 microg/ml). Seventeen patients excreted large amounts of free trimethylamine (more than 10 microg/ml), above the threshold usually associated with the appearance of a 'fish-like' body odour and tainted breath.

CONCLUSIONS

Excessive amounts of trimethylamine may well contribute to the overall body odour problems encountered among patients with severe hepatic disease, precipitating in these individuals a secondary form of the 'fish-odour syndrome'.

Clinical importance of non-genetic and genetic cytochrome P450 function tests in liver disease

Liver disease is associated with reduced metabolic capacity for drugs that are metabolized by oxidative biotransformation. Three cytochrome P450 (P450 or CYP) gene families in liver microsomes (CYP 1, CYP2 and CYP3) appear to be responsible for much of the drug metabolism that takes place. The genetic polymorphism of the CYPs responsible for debrisoquine/ sparteine (CYP2D6) metabolism and S-mephenytoin (CYP2C19) metabolism has been well documented, but information on the impairment of each isoform in liver disease is still limited. There are two types of hepatic P450 function tests. One type consists of non-genetic P450 function tests (CYP1A2, 2A6, 2C9/10, 2E1 and 3A3/4), and probe drugs include caffeine, catalysed by CYP1A2, coumarin by CYP2A6, phenytoin by CYP2C6, chlorzoxazone by CYP2E1, and nifedipine, erythromycin and lidocaine by CYP3A3/4. The second type of genetic P450 function tests (CYP2C19 and CYP2D6) involves probe drugs such as S-mephenytoin, catalysed by CYP2C19, and debrisoquine and sparteine, catalysed by CYP2D6. The metabolism of the probe drugs used in non-genetic P450 function tests in patients with liver disease falls into two categories: reduced (CYP1A2, CYP2C, 2E1 and 3A) and unchanged (CYP2C). In genetic P450 function tests there seems to be a lesser degree of inhibition in poor metabolizers (PMs) than extensive metabolizers (EMs) among patients with liver disease. There have been very few reports on changes in metabolism of the probe drugs used in genetic P450 function tests in liver disease. In this paper the subject is reviewed.

The effect of inflammation on the disposition of phenylbutazone in thoroughbred horses

The effect of inflammation on the disposition of phenylbutazone (PBZ) was investigated in Thoroughbred horses. An initial study (n = 5) in which PBZ (8.8 mg/kg) was injected intravenously twice, 5 weeks apart, suggested that the administration of PBZ would not affect the plasma kinetics of a subsequent dose. Two other groups of horses were given PBZ at either 8.8 mg/kg (n = 5) or 4.4 mg/kg (n = 4). Soft tissue inflammation was then induced by the injection of Freud's adjuvant and the administration of PBZ was repeated at a dose level equivalent to, but five weeks later than, the initial dose. Inflammation did not appear to affect the plasma kinetics or the urinary excretion of PBZ and its metabolites, oxyphenbutazone (OPBZ) or hydroxyphenylbutazone (OHPBZ) when PBZ was administered at 8.8 mg/kg. However, small but significant increases (P < 0.05) in total body clearance (CLB; 29.2 +/- 3.9 vs. 43.8 +/- 8.1 mL/ h.kg) and the volume of distribution, calculated by area (Vd(area); 0.18+/- 0.05 vs. 0.25 +/- 0.03 L/kg) or at steady-state (Vd(SS); 0.17 +/- 0.04 vs. 0.25 +/- 0.03 L/ kg), were obtained in horses after adjuvant injection, compared to controls, when PBZ was administered at 4.4 mg/kg which corresponded to relatively higher tissues concentrations and lower plasma concentrations (calculated) at the time of maximum peripheral PBZ concentration. Soft tissue inflammation also induced a significantly (P < 0.05) higher amount of OPBZ in the urine 18 h after PBZ administration but the total urinary excretion of analytes over 48 h was unchanged. These results have possible implications regarding the administration of PBZ to the horse close to race-day.

Drug metabolism in liver disease: implications for therapeutic drug monitoring

Over the last decades, a bulk of evidence has accumulated on the effect of liver disease on drug metabolism. It has convincingly been demonstrated that liver disease is associated with a reduced metabolic capacity with respect to drugs undergoing oxidative biotransformation, whereas conjugation reactions, especially glucuronidation, seem less affected. Nevertheless, many data have been conflicting, and it has become increasingly clear that differences in patient selection and severity of disease can account for these. Further, more recent communications suggest that liver disease led to a differential alteration of the cytochrome P-450s with regard to protein content and activity. From a clinical point of view, these findings may have important implications. However, when treating liver patients, we still have no generally accepted model for dose predictions; the best approach should be empiric and based on the clinical response. In selected cases, monitoring of plasma drug concentrations and liver function is recommended.

The association between rifamycin-SV (R-SV) related hyperbilirubinaemia and antipyrine clearance as a new test of liver function in cirrhosis

Several clearance tests have been used to assess the residual hepatic efficiency in liver cirrhosis. However, the altered clearance values found in cirrhotic patients may reflect not only the impairment in liver function but also a derangement in the hepatic blood-flow. Therefore, this study was designed to explore the possibility that the competition between Rifamycin-SV and bilirubin at the hepatic uptake site might be used as an index for quantitative assessment of residual hepatic efficiency in 48 patients with chronic liver disease. In this test, the interference of hepatic blood flow would be negligible. Antipyrine clearance was also evaluated in the same subjects in order to explore the cytoplasmic microsomal efficiency. Rifamycin-SV intravenous load was followed by a sustained increase in bilirubinaemia which significantly related with the degree of liver function as assessed by the Child-Pugh criteria. Also, antipyrine clearance was significantly altered in cirrhotic patients compared to controls. Moreover, a positive correlation was found between the Rifamycin-SV test and Antipyrine clearance. We suggest that a combination of these tests might be of use in the quantitative assessment of liver function.

The effect of a nutritional model of chronic liver injury on the hepatic glucuronidation of morphine in rats

The effect of a choline-deficient diet on the hepatic glucuronidation of morphine was investigated using a rat perfused liver system. Rats fed a choline-deficient diet developed a fatty liver with minimal necrosis. Despite the morphological changes, neither hepatic extraction ratio (0.51 +/- 0.02 in control; 0.45 +/- 0.04 in the choline-deficient rats) nor intrinsic clearance (0.85 +/- 0.05 in control; 0.77 +/- 0.09 in choline-deficient rats) were affected by this injury model. This finding suggests that glucuronidation is relatively resistant to this chronic liver injury.

Clearance by the liver in cirrhosis. II. Characterization of propranolol uptake with the multiple-indicator dilution technique

We studied the steady-state hepatic extraction and single-pass hepatic uptake of propranolol in isolated perfused livers from normal rats and compared these values with those of rats with carbon tetrachloride-induced cirrhosis, rats treated with chlorpromazine (an inhibitor of propranolol metabolism) and rats with acute liver injury. The kinetics of propranolol transport in the liver were characterized by means of the multiple-indicator dilution technique, and estimates of cellular influx, efflux and sequestration rate constants were obtained with a computer fit to the model of Goresky. The outflow pattern of propranolol in the hepatic veins was then resolved into throughput material, which had swept past the hepatocytes along with albumin, and returning material, which had entered the cells but returned in the outflow after escaping metabolic sequestration. The steady-state extraction of propranolol was significantly decreased in the three experimental groups compared with that in controls, but the outflow profile differed within each group. In cirrhotic animals, influx was markedly decreased and the sequestration rate constant remained unchanged; most of the propranolol in the outflow consisted of throughput material. In rats treated with chlorpromazine, the sequestration rate constant was decreased, and propranolol in the outflow was mainly returning material. In rats with acute liver injury, both influx and sequestration rate constants were decreased. Indicator dilution curves for nonsequestered tracers showed a decreased transit time for red blood cells and abnormal diffusion of albumin and sucrose into the space of Disse in cirrhotic rats compared with the other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Antipyrine, erythromycin and oxytetracycline disposition in experimental fasciolosis

The effects of fasciolosis on drug disposition were studied by administration of antipyrine, erythromycin and oxytetracycline to sheep and cattle. Fasciolosis was produced by administration of 200 or 400 metacercariae (MC) of Fasciola hepatica to sheep and 500 MC to cattle. The disease was subsequently confirmed by determination of plasma glutamate dehydrogenase and gamma-glutamyl transferase and identification and quantitation of mature flukes in the liver at necropsy. Acute or subacute fasciolosis in sheep was accompanied by a significant decrease in the elimination rate constant (beta) and increase in the elimination half-time (t 1/2) for antipyrine and erythromycin when compared with controls or infected sheep which had been treated with the anthelmintic luxabendazole. An increase in apparent volume of distribution (Vd) was seen only for erythromycin in sheep given 400 MC. There were no changes in the disposition of oxytetracycline in sheep with either acute or subacute infection and no effects on disposition of the three test drugs in chronically infected sheep. With early chronic disease in calves, only the disposition of oxytetracycline was affected; not that of antipyrine or erythromycin.

P450 enzymes. Inhibition mechanisms, genetic regulation and effects of liver disease

Multiple hepatic P450 enzymes play an important role in the oxidative biotransformation of a vast number of structurally diverse drugs. As such, these enzymes are a major determinant of the pharmacokinetic behaviour of most therapeutic agents. There are several factors that influence P450 activity, either directly or at the level of enzyme regulation. Drug elimination is decreased and the incidence of drug interactions is increased when there is competition between 2 or more drugs for oxidation by the same P450 enzyme. The available knowledge concerning the relationship between the presence of certain functional groups within the drug structure and inhibition of P450 activity is increasing. In many instances, it is possible to associate inhibition with certain drug classes, e.g. antimycotic imidazoles and macrolide antibiotics. Disease states, especially those with hepatic involvement, and the genetic makeup of the individual are conditions in which some P450s may be downregulated (that is, the enzyme concentrations in liver are decreased), with associated slower rates of drug elimination. In these individuals, dosages of drugs that are substrates for downregulated P450s should be decreased. Exposure to environmental pollutants as well as a large number of lipophilic drugs can result in induction (upregulation) of P450 enzyme activity. This raises the issue of previous approaches to the study of P450 induction in vivo. The use of human hepatocyte preparations in culture is a promising new direction that could assist the determination of modifications to drug therapy necessitated by exposure to inducing agents. Until such information is obtained, however, the use of drugs known to increase the microsomal expression of particular P450s, and increase associated drug oxidation capacity in humans, should be used with caution.

Pharmacokinetics of encainide in patients with cirrhosis

The pharmacokinetics of encainide were investigated in 10 patients with cirrhosis and 10 matched controls following single intravenous (IV, 25 mg), single oral (so, 25 mg), and multiple oral (mo, 25 mg thrice daily over 5 days) dosing. The hepatic oxidative drug-metabolizing enzyme capacity and its inducibility were assessed by antipyrine elimination and 6-beta-hydroxycortisol excretion. Eight controls and nine patients were of the extensive metabolizer phenotype (EM), as assessed by the sparteine metabolic ratio. Statistics was performed in EM only. The antipyrine half-life was significantly longer and clearance was significantly lower in patients with cirrhosis. Following IV administration, no significant differences in encainide half-life clearance, volume of distribution, or the area under the plasma concentration time curve (AUC) were observed between patients and controls. Following so and mo, there was a fourfold reduction in the oral clearance in cirrhotics. Thus, encainide bioavailability was increased in cirrhosis. Whereas the AUC of encainide was significantly higher in patients, no differences were observed in its active metabolites, O-desmethyl-encainide (ODE) and 3-methoxy-O-desmethylencainide (MODE). Plasma concentrations of encainide and its metabolites after 3 and 5 days of mo suggested steady-state conditions after 3 days of oral dosing. No change in antipyrine elimination and 6-beta-hydroxycortisol excretion following mo occurred. There was no relationship between parameters of encainide and antipyrine elimination. In conclusion, even though the elimination of encainide was reduced in patients with cirrhosis, plasma levels of the pharmacologically active metabolites, ODE and MODE, were comparable.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of intravenous metoclopramide in patients with hepatic cirrhosis

The pharmacokinetics of metoclopramide has been studied after acute IV administration to 12 patients with hepatic cirrhosis (6 with and 6 without ascites) and 6 control subjects. The elimination half-life was significantly longer in patients (11.4 h and 9.9 h in those with and without ascites, respectively, vs 6.4 h in controls). Total plasma clearance was significantly lower in patients (0.29 and 0.36 l.kg-1.h-1 vs 0.52 l.kg-1.h-1 in controls). The differences between patients with and without ascites did not reach statistical significance. Reduction of functional hepatic blood flow in cirrhotic patients is the probable cause of the observed alteration in metoclopramide kinetics.

Pharmacokinetics of flunitrazepam following single dose oral administration in liver disease patients compared with healthy volunteers

The pharmacokinetic behaviour of flunitrazepam and its main active metabolite, N-desmethyl flunitrazepam, was investigated in 12 patients with liver disease (cirrhosis or hepatitis) compared to 6 healthy volunteers. A gas-liquid chromatographic method allowing for simultaneous determination of flunitrazepam and N-desmethyl flunitrazepam in plasma samples was developed. The accuracy and the precision near the quantification limit of ca. 1 ng/ml were better than 5%. Plasma levels of flunitrazepam were not significantly altered by hepatic failure, whereas plasma levels of N-desmethyl flunitrazepam were lower in patients than in healthy subjects. Pharmacokinetic parameters did not differ significantly between healthy subjects and liver disease patients: the oral clearance was 3.5 +/- 0.8, 3.5 +/- 1.9 and 4.0 +/- 1.2 ml/min/kg, respectively in healthy subjects, patients with hepatitis and patients with cirrhosis. The apparent elimination half-life was 22 +/- 5 h in healthy subjects, 25 +/- 10 h in patients with hepatitis and 20 +/- 6 h in patients with cirrhosis. However, the expected increase of the drug free fraction during liver disease could decrease the therapeutic and toxic ranges of flunitrazepam in these patients.

Effect of altered albumin concentrations on elimination of unbound prazosin in vivo in the rat and in the isolated perfused rat liver

Albumin is known to affect the intrinsic clearance of many compounds in the isolated perfused rat liver, but little is known of its effect in vivo. The influence of decreased albumin concentrations on clearance of unbound prazosin and intrinsic clearance of prazosin was therefore studied in vivo in rats that had undergone plasmapheresis. An approximate 30% reduction in the plasma albumin concentration was achieved in animals not given plasma expanders and an approximate 50% reduction was achieved in animals given Ficol 70 as a plasma expander. No differences were seen in the intrinsic clearances or in the clearances of unbound prazosin between control animals and plasmapheretic animals. The reason for this lack of effect is apparent from parallel studies in isolated perfused rat livers. An increase in the clearance of unbound prazosin of 27% was seen when the albumin concentration was increased from 0 to 30 microM, and of 49% when the concentration of albumin was increased to 90 microM, with no further increase at higher albumin concentration. These results, therefore, suggest that changes in the albumin plasma concentrations normally encountered clinically may have little effect on the intrinsic elimination of drugs.

Influences of diet and nutrition on clinical pharmacokinetics

The human diet represents a complex and variable mixture of nutrients, many of which have the potential for altering the disposition of drugs. This review highlights progress from a number of laboratories illustrating nutrient influences on drug dispositions and actions. Emphasis is placed on nutritional effects on hepatic drug metabolism studied in humans. Data from animals have sometimes been difficult to extrapolate to humans, as illustrated by reports on the influences of starvation, dietary lipids, and ascorbic acid. From studies in healthy subjects it is now clear that a number of specific dietary factors can influence drug metabolism by the mixed function oxidase system and conjugating enzymes. These include dietary protein, cruciferous vegetables, charcoal-broiled beef containing polycyclic aromatic hydrocarbons, and methylxanthines. The effects of such dietary components have been demonstrated for only a limited number of drug substrates for these enzyme systems. Effects of food on bioavailability have been more widely studied, and depend greatly upon the type of drug. Malnutrition can be associated with variable but potentially important effects on the bioavailability, binding, hepatic metabolism, and renal clearance of drugs. In malnourished patients it is generally difficult to recognise the roles of individual nutrient deficiencies on drug disposition, and clinical predictors of altered pharmacokinetics for various drugs in such patients are not well defined. It is likely that many important interrelationships between nutrition and new or already marketed drugs remain to be recognised, and therefore warrant further research. Nutritional effects on drug metabolising enzymes also have implications for endogenous substances such as hormones and environmental toxins and carcinogens which are metabolised by the same or related enzyme systems, and for diseases likely to be related to the actions of such chemicals.

Drug disposition in patients with HBsAg-positive chronic liver disease

Chronic infection with hepatitis B virus (HBV) results in a spectrum of hepatic abnormalities ranging from minimal liver dysfunction to severe liver failure. These patients provide an opportunity to examine the relationship between the evolution of the liver disease and the ability to metabolize drugs. We have examined hepatic drug disposition in patients with chronic persistent hepatitis, chronic active hepatitis, and cirrhosis due to HBV infection. Four model drugs were used: two low-extraction capacity-limited drugs (antipyrine and aminopyrine) and two high-extraction flow-limited drugs (ICG and lidocaine). The disposition of the four drugs tested was comparable to that of healthy controls in patients with chronic persistent hepatitis, chronic active hepatitis, and mild cirrhosis. In patients with severe cirrhosis (as defined by the presence of ascites, encephalopathy, or large esophageal varices), there was a significant impairment in the aminopyrine breath test (-31%) and in the clearance of antipyrine (-53%), lidocaine (-49%), and ICG (-54%). These results indicate that impairment of drug clearance occurs only late in the evolution of HBV-related chronic liver disease. This is in keeping with the known slow and insidious progression of the disease.

Pharmacokinetics of methylprednisolone succinate, methylprednisolone, and lidocaine in the normal dog and during hemorrhagic shock

Pharmacokinetics of methylprednisolone succinate and methylprednisolone following methylprednisolone sodium succinate administration were studied in five dogs under normal conditions and then during a severe hemorrhagic shock. In order to evaluate hepatic blood flow, lidocaine clearance was simultaneously measured. In the normal state, the clearance of methylprednisolone succinate was 1.64 +/- 0.499 L/h/kg and its half-life was 15.33 +/- 3.84 min. The systemic availability of methylprednisolone from methylprednisolone succinate was 59.9 +/- 8.3%, and the maximal methylprednisolone concentration was observed after a delay of 7.68 +/- 6.31 min. Using a reservoir technique in anesthetized dogs, severe hemorrhagic shock was obtained. Changes in lidocaine clearance indicated a subsequent reduction of hepatic blood flow. The clearance of methylprednisolone succinate decreased to 0.488 +/- 0.240 L/kg/h, and the half-life increased to 40.66 +/- 23.48 min. The exact availability of methylprednisolone from methylprednisolone succinate during shock was not calculable because methylprednisolone kinetics were time dependent. The plasma methylprednisolone concentration was relatively high and persistent during the shock. It was concluded that methylprednisolone sodium succinate is a prodrug which can be released in sufficient quantities as its active moiety (i.e., methylprednisolone) during severe hemorrhagic shock in the dog. In addition, after a single intravenous administration, the slow process of methylprednisolone elimination may give sustained methylprednisolone concentrations for several hours.

Chloramphenicol, lincomycin and oxytetracycline disposition in calves with experimental pneumonic pasteurellosis

The effects of pneumonia on the pharmacokinetics of chloramphenicol, lincomycin, and oxytetracycline were evaluated in two-month-old calves. Pneumonia was induced by injection of Pasteurella haemolytica cultures directly through the thoracic wall into each lung. Six days prior to induction of pneumonia, the antibiotics were administered in a single i.v. dose. The antibiotics were administered again 48 (i.v.), 60 and 72 h (i.m.) following injection of P. haemolytica. The pharmacokinetics of chloramphenicol (25 mg/kg) and lincomycin (10 mg/kg) were not significantly different in calves with pneumonia. The hybrid rate constant beta for oxytetracycline was increased in calves with pneumonia from 0.0034 +/- 0.0003/min to 0.0048 +/- 0.0007/min between 2 h and 8 h. Thus the elimination half-life in serum was shortened from 212.4 +/- 20.3 min to 149.3 +/- 19.5 min. In addition, there was an apparent but not statistically significant decrease in K12 with pneumonia. These findings accentuate the need for observance of 12-h dose intervals with oxytetracycline.

Contraceptive steroid concentrations in women with early active schistosomiasis: lack of effect of antischistosomal drugs

Plasma concentrations of the oral contraceptive steroids (OCS) ethinyloestradiol (EE2) and levonorgestrel (LNG) have been determined in women with early active schistosomiasis and compared to those obtained in healthy volunteers. Steroid concentrations following a single dose of Ovral (500 micrograms LNG, 50 micrograms EE2) or during a multiple dose regimen were unaffected by the disease. There was no significant effect of the antischistosomal drugs praziquantel (40 mg X kg-1) or metrifonate (10 mg X kg-1 X 3 at 2-week intervals) on plasma steroid concentrations. In regular users of OCS, significantly higher concentrations of LNG were observed than in women who received only a single dose. We conclude that there is no pharmacokinetic reason for withholding OCS from patients with early active schistosomiasis who are also receiving either praziquantel or metrifonate.

Biliary elimination of indomethacin in man

The biliary elimination of indomethacin 100 mg p.o. has been investigated in patients with a T-tube drain after cholecystectomy, who had normal or abnormal liver function (Group I n = 5, and Group II n = 4, respectively). In plasma, the concentration maximum (Group I 9.5 +/- 1.4 mumol X l-1; Group II 19.4 +/- 3.8 mumol X l-1) and the total clearance (Group I 1.56 +/- 0.28 ml X min-1 X kg-1, Group II 0.5 +/- 0.06 ml X min-1 X kg-1) were significant different in the two groups. The bile:plasma ratio (bpr) in Group I was 1.3 +/- 0.33 and 10.1 +/- 3.2, respectively, for indomethacin (In) and conjugated In. The conjugated fraction of In was 87.5 +/- 1.9% of the total concentration. In Group II the bpr was lower (0.65 +/- 0.1). In is eliminated in bile by diffusion and conjugated In by active secretion. In Group I 0.99 +/- 0.1 mg In and 6.1 +/- 0.7 mg conjugated In and in Group II 2.1 +/- 0.3 mg In (p less than 0.05) were eliminated in bile. No influence of In on the biliary lipids was observed or on the bile acid-independent fraction of bile flow. It is concluded that the total plasma clearance of In was dependent of liver function. Conjugated In undergoes enterohepatic circulation.

The pharmacokinetics of antipyrine in patients with graded severity of schistosomiasis

The pharmacokinetics of antipyrine have been studied in patients with schistosomiasis. In comparison to a control group of subjects (n = 6), patients with early (active) schistosomiasis (passing live ova in urine or stools without clinical and laboratory evidence of liver involvement; n = 6) exhibited similar pharmacokinetic parameters. Of seven patients with hepatosplenic schistosomiasis (exhibiting hepatic fibrosis, splenomegaly, at least one episode of haematemesis, ascites), five showed markedly enhanced antipyrine half-life and reduced clearance. Compared to controls, the mean half-life of this group was increased from 10.9 +/- 2.4 to 19.9 +/- 9.5 h (mean +/- s.d.; P less than or equal to 0.05) and clearance reduced from 3.81 +/- 0.74 to 2.18 +/- 0.80 l h-1 (P less than or equal to 0.01). There was no change in the apparent volume of distribution. Liver biopsy was performed on all patients diagnosed as having hepatosplenic schistosomiasis in the 2 weeks prior to the antipyrine study. The results of this study indicate that hepatic microsomal metabolism is impaired in patients with advanced hepatosplenic schistosomiasis.

Lack of effect of liver disease on the pharmacokinetics of acebutolol and diacetolol: a single dose study

The pharmacokinetics of acebutolol and its major metabolite, diacetolol, following a single 400 mg oral dose, were investigated in patients with liver disease. No significant differences were found in any of the parameters measured.

Treatment of liver cirrhosis with microsomal enzyme-inducing compound in the rat

The effect of therapy with a microsomal enzyme-inducing drug on the cirrhotic liver in male Wistar rats was investigated by morphological and biochemical means. The cirrhotic animals were treated with medroxyprogesterone acetate (MPA) 100 mg/kg body wt, i.p. daily for a week. In the cirrhotic rats liver weight was enhanced, liver protein content was increased while total liver DNA content remained unchanged upon MPA treatment. The hepatic regenerative nodule size increased, as determined by morphological means. Hepatic microsomal metabolic activity was improved, as seen by increases in NADPH-cytochrome P-450 reductase and aminopyrine N-demethylase activities and cytochrome P-450 content. Since the increases in liver protein content and metabolic activity were relatively greater in the cirrhotic than intact animals upon MPA treatment, it was suggested that the spontaneous regeneration associated with liver cirrhosis may affect the induction phenomenon. The results demonstrate that an enzyme inducer may have beneficial effects on the cirrhotic liver by elevating metabolic activity and parenchymal mass.

Bioavailability of hetacillin in rats after liver enzyme induction by various inducers with or without protein binding properties

The serum levels and the half life of ampicillin derived from Hetacillin after administration of the latter to a total of 61 rats classified in 7 groups were determined. Each of these groups was pre-treated for 15 days with the following inducers; phenobarbital, diphenylhydantoin, diazepam, chlorpromazine and phenylbutazone. The control group received saline. The d-glucaric acid concentration in the urine prior to and after the administration of inducers and the liver weight were taken as enzyme induction indices. Results showed a positive correlation between the indices of induction and the levels of ampicillin originating from hetacillin with a significant correlation coefficient between the serum levels of ampicillin and urine d-glucaric acid for all drugs studied. The different effect of the various drugs indicated that they could be classified into the following two groups: a) those that induced a significant increase of the levels and half life (t1/2) of ampicillin. The effect was significant in decreasing order for phenylbutazone (r = 0,990), diazepam (r = 0,990) and diphenylhydantoin (r = 0,753). b) those which initially resulted in a significant increase of the levels of ampicillin and thereafter in a decrease with a significant shortening of its t1/2 too. The effect was most significant for phenobarbital (r = 0,887) and less so for chlorpromazine (r = 0,800). Only for these two drugs was a significant and actually negative correlation observed between d-glucaric acid and t1/2 that is: phenobarbital (r = -0,967) chlorpromazine (r = -0,752). Results suggest an interaction of Hetacillin and the above inducers.

Antipyrine clearance and metabolite formation in patients with alcoholic cirrhosis

The effect of liver cirrhosis on plasma clearance and metabolite profile of i.v. administered antipyrine was studied in 23 patients with alcoholic liver cirrhosis (age 37-70 years) and 17 healthy subjects (age 28-55 years). Liver volume was also measured and was found to be larger in patients than in controls, mean values being 1.86 and 1.36 l respectively. The elimination half-life of antipyrine in patients with alcoholic liver cirrhosis was significantly longer than in the healthy subjects (P less than 0.001). Mean values were 39.9 and 10.1 h respectively. Alcoholic liver cirrhosis had no effect on the apparent volume of distribution of antipyrine, but antipyrine plasma clearance was substantially reduced in the patients. Mean clearance values (ranges) were 13.5 (9.3-22.8) ml/min in the patients and 49.3 (31.1-103) ml/min in healthy subjects. Normalization of antipyrine plasma clearance for liver volume resulted in an only slightly increased distinction between patients and healthy subjects, mean values (ranges) being 7.8 (3.3-13.0) ml min(-1) 1(-1) and 36.1 (21.9-35.9) ml min(-1) 1(-1) respectively. The cumulative renal excretion of 4-hydroxyantipyrine (OHA) and norantipyrine (NORA) was significantly lower in patients with alcoholic liver cirrhosis than in healthy subjects, as was the total recovery of antipyrine and major metabolites from urine. Mean values were 15.0, 8.4 and 41.2% of dose in the patients respectively and 24.3, 25.8 and 68.9% of dose in the control subjects. Excreted amounts of total and unconjugated 3-hydroxymethylantipyrine (HMA) and of unchanged antipyrine were the same in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Single-dose kinetics of primidone in acute viral hepatitis

The pharmacokinetics of primidone (PRM) after oral administration of a single 500 mg dose was studied in 7 patients with acute viral hepatitis and 7 healthy control subjects. The elimination half-life and the apparent clearance of unchanged PRM in the patients were 18.0 +/- 3.1 h and 42 +/- 14 ml X h-1 X kg-1, respectively (mean +/- SD) and did not differ significantly from the values in the controls (half-life 17.0 +/- 2.4 h; clearance 35 +/- 8 ml X h-1 X kg-1). The metabolite phenylethylmalonamide (PEMA) was detected in the serum of all normal subjects within 2-24 h. By contrast, serum levels of this metabolite were undetectable (less than 2 mumol/1) in all but one of the patients. Serum levels of phenobarbital (PB) remained below the limit of detection (less than 2 mumol/1) in all subjects. The findings indicate that accumulation of PRM with its attendant toxicity is unlikely to occur in epileptic patients who develop acute viral hepatitis, despite evidence that the metabolism of the drug is affected by this condition. The possibility of impaired conversion to PB and its implications are discussed.

Effects of hepatic function on vancomycin clinical pharmacology

Using a recently developed radioimmunoassay, we performed 15 vancomycin pharmacology studies in cancer patients with infections. Vancomycin (500 mg) was infused intravenously for 30 min every 6 h for up to 7 days. The plasma disappearance curve was biphasic, with an initial half-life of less than 30 min. The second half-life (t1/2 beta), not dose related, varied from 1.4 to 231 h among the patients. In six studies of patients with normal hepatic functions, the t1/2 beta was 2.6 h; the rate of total clearance was 162 ml/min. In contrast, nine studies of patients with impaired liver function had a much longer t1/2 beta (37 h) and a decrease in the rate of total clearance to 48 ml/min. These factors resulted in an increase in the value of area under the concentration-time curve from 59 to 3,434 micrograms X h/ml. These results have demonstrated the importance of the effects of liver function on vancomycin disposition. The vancomycin dose and schedule should be adjusted for patients with liver impairment.

Clinical pharmacology of bruceantin by radioimmunoassay

During the phase I clinical trial of a new antitumor agent, bruceantin, the pharmacology was studied in 18 cancer patients. The drug was infused intravenously (IV) for 3 h at doses ranging from 1 to 3.6 mg/m2 per day for 5 days. The plasma drug disappearance curves were biphasic, with a fast initial half-life of less than 15 min. The second half-life (t1/2 beta) varied from 0.7 to 38 h among different patients and was not dose-related. The difference between the t1/2 beta on day 1 and that on day 5 was not significant. In patients with normal liver function, the mean plasma concentration at the end of infusion was 22 ng/ml, and the value of the area under the concentration X time curve (AUC) was 111 (ng/ml)h. In contrast, in patients with abnormal liver function the corresponding values were 115 ng/ml and 830 (ng/ml)h, respectively. In addition, these patients had a slower elimination half-life of 10.9 h and a decreased total clearance of 157 ml/min/m2, as compared with 2.6 h and 671 ml/min/m2, respectively, for the normal group. All these differences were statistically significant. Patients with abnormal liver function developed more severe toxicity, including fever, severe nausea, vomiting, and hypotension. Two patients with severe hepatic dysfunction received a reduced dose and developed no toxicity. These results demonstrated the importance of the effects of liver dysfunction on drug disposition and showed that the dosage should be reduced in patients with hepatic dysfunction.

The determination of aminopyrin elimination for control of the metabolic capacity of the liver in man

The kinetics of plasma and breath elimination of aminopyrine after 14C-aminopyrine given orally were studied using an open one-compartment model and first order rates of elimination. The study comprised eight healthy volunteers and two groups with histologically verified chronic liver diseases (cirrhosis, n = 12, and chronic aggressive hepatitis, n = 12). Elimination rates from plasma and breath were significantly reduced in the group with cirrhosis, but only so in chronic aggressive hepatitis when they were expressed relative to each other. Monomethylaminopyrine was eliminated more rapidly compared to aminopyrine, and the rate of formaldehyde formation was positively correlated to the excretion rate of CO2 (r = 0.53, P less than 0.002). No correlation was found with clinical or other laboratory data in the groups of liver diseases studied. The test is a quantitative indicator of the drug metabolizing mixed function oxidases of the endoplasmatic reticulum of the liver, and may reflect the degree of damage to this system in chronic liver disease.

Pharmacokinetics of metoprolol in patients with hepatic cirrhosis

The selective beta 1-adrenoceptor antagonist metoprolol is eliminated primarily by hepatic metabolism and usually less than 5% of an oral dose is excreted unchanged in the urine. The effects of impaired liver function on the pharmacokinetics of metoprolol were studied in 10 patients with hepatic cirrhosis. All subjects were given single doses of 20mg intravenously and 50mg orally on separate days. The mean fraction of the drug available systematically was 84 +/- 10% in patients and 50 +/- 11% in a control group of 6 healthy subjects (p less than 0.05). The total body clearance of metoprolol in the cirrhotics was 0.61 +/- 0.13L/min and in the controls 0.80 +/- 0.11L/min. These values correspond to elimination half-lives of 7.2 +/- 1.2 and 4.2 +/- 1.1 hours, respectively. The differences were not statistically significant. Impaired liver function had no effect on the volume of distribution of metoprolol. Total clearance was weakly but linearly related to galactose clearance (r2 = 0.52; p less than 0.05), and the half-life was related to serum bilirubin (r2 = 0.74; p less than 0.01).

Influence of liver disease and environmental factors on hepatic monooxygenase activity in vitro

The effects of liver disease and environmental factors on hepatic microsomal cytochrome P-450 content, NADPH-cytochrome c reductase (reductase) activity and aryl hydrocarbon hydroxylase (AHH) activity have been simultaneously investigated in 70 patients undergoing diagnostic liver biopsy. The activity of reductase was not significantly affected by the presence of liver disease or any of the environmental factors studied. Cytochrome P-450 content decreased with increasing severity of liver disease whereas AHH activity was only significantly reduced in biopsies showing hepatocellular destruction. None of the parameters of monooxygenase activity varied significantly with the age or sex of the patients. Alcohol excess was associated with decreased cytochrome P-450 content and AHH activity and this effect was independent of the histological status of the biopsy. Both high caffeine intake and cigarette smoking increased AHH activity in the absence of any change in cytochrome P-450 content. There was a positive correlation between the number of meat meals eaten per week and cytochrome P-450 content. Chronic treatment with enzyme-inducing anticonvulsants appeared to increase both cytochrome P-450 content and AHH activity. Despite differential effects of liver disease and environmental influences on cytochrome P-450 content and AHH activity there was a highly significant correlation between the two parameters. The results of the present study correlate well with the known effects of disease and environment on drug metabolism in vivo.

Effects of liver disease on urinary excretion of methadone and metabolites in maintenance patients: quantitation by direct probe chemical ionization mass spectrometry

This study was performed to define the amounts of methadone and metabolites excreted in urine in otherwise healthy maintenance patients, and to determine whether the metabolism and elimination of methadone, as assessed by analyses of urines, is altered in patients with liver disease. A method was developed for the simultaneous quantitation of methadone and six of its major and minor metabolites using chemical ionization mass spectrometry with direct probe introduction to increase sensitivity for analyses of the minor metabolites. Analyses of urine from unmedicated volunteers showed that the interferences at the mass range of interest (264-326) were usually small and therefore would not introduce significant error into analysis. Nineteen patients well-stabilized in chronic long-term methadone treatment were studied, five otherwise healthy males and fourteen patients with chronic liver disease (nine males and four females). Twenty-four hour urine collections were made and analyzed following extraction procedures. The concentrations of methadone and the major pyrrolidine metabolite exceeded 1 microgram ml-1 in all cases; the concentration (listed in descending order) of pyrrolidone, pyrroline, hydroxymethadone, hydroxypyrroline, methadol and hydroxypyrrolidine were all less than 1 microgram ml-1. The total 24 hour urinary excretion of methadone and its metabolites was 48.3% (+/- 1.71 SEM) in otherwise healthy patients but was significantly lower, 32.6% (+/- 3.19 SEM) in patients with liver disease (p less than 0.05). The total 24 hour excretion of the pyrrolidone metabolite, the end product of two pathways of methadone metabolism, was also significantly reduced in patients with liver disease (p less than 0.05). Females with liver disease had significantly higher ratios of pyrrolidine to methadone than did males with liver disease (p less than 0.05).

Blood clearance tests for detecting 2,3,7,8-tetrachlorodibenzo-p-dioxin hepatotoxicity in rats and rabbits

The objective was to determine if a blood clearance test would detect liver dysfunction in rats and rabbits treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Guinea pigs were included as a negative control, because TCDD does not produce detectable hepatotoxicity in this species. TCDD was given as a single dose to male rats (25 microgram/kg, po), rabbits (25 microgram/kg, ip) and guinea pigs (2 microgram/kg, ip) and liver function was assessed 10 days later by determining blood clearance of indocyanine green (ICG) and ouabain. Activity in serum of sorbitol dehydrogenase (SDH), glutamic pyruvic transaminase (SGPT) and gamma glutamyl transpeptidase (gamma GTP) were also measured and light microscopy performed on the liver. The results showed that hepatotoxicity in the rabbit could be detected by a reduction in ICG blood clearance and an elevation in SDH activity. In the rat, ouabain blood clearance was reduced and SDH activity elevated. None of the liver function tests were altered in the guinea pig. These results underline the usefulness of blood clearance tests using ICG and ouabain in detecting TCDD hepatotoxicity in animals.