Protein binding and kinetics of drugs in liver diseases

Pharmacokinetics of quinine in chronic liver disease

The pharmacokinetics of quinine were investigated in a) six healthy male Thai subjects, and b) nine male Thai patients with a moderate degree of chronic liver disease, after a single oral dose of 600 mg quinine sulphate. tmax and t1/2.2 were significantly prolonged in patients (median [range] tmax 2 [1-5] vs 1.6 [0.8-2] h; t1/2,z 23.4 [17.4-41.7] vs 9.7 [7.8-17.2] h), and Vz/F was significantly larger (median [range] 4.21 [2.33-15.87] vs 2.78 [1.49-3.38] 1 kg-1). Median (range) concentration of the plasma unbound Qn fraction collected from the patients at 4 h after drug administration was 17 (8.4-17.8)% of total drug concentration.

Disposition and urinary excretion of phenylbutazone in normal and febrile greyhounds

Five days after the induction of acute systemic inflammation in greyhounds by intramuscular and subcutaneous injections of Freund's adjuvant, the hepatic concentrations of cytochromes P-450 and b5, the activities of the hepatic microsomal enzymes aniline p-hydroxylase and aminopyrine n-demethylase and the disposition and urinary excretion of phenylbutazone were determined. The mean plasma concentrations of phenylbutazone after intravenous administration were described by the bi-exponential equations: Cp = 144.2e-34.6t + 171.5e-0.104t for five normal greyhounds and Cp = 113.6e-16.13t + 163.1e-0.108t for five febrile greyhounds. The elimination half-lives, total body clearances and apparent volumes of distribution were 6.7 hours, 18.4 ml kg-1 hour-1 and 0.18 litre kg-1, for the normal greyhounds, and 6.4 hours, 19.5 ml kg-1 hour-1 and 0.18 litre kg-1, for the febrile greyhounds. There were no significant differences between the pharmacokinetic parameters describing the distribution and elimination of phenylbutazone, or between the quantities of phenylbutazone, oxyphenbutazone and hydroxyphenylbutazone excreted in the urine. In the febrile greyhounds, there were significant decreases in the hepatic microsomal concentrations of cytochromes P-450 and b5 and in the activities of aniline p-hydroxylase and aminopyrine n-demethylase.

Acute trauma alters morphine clearance

Trauma is accompanied by changes in liver perfusion and acute phase proteins. Such changes have the potential to alter drug metabolism. There are few studies describing drug disposition in acute trauma. We determined the pharmacokinetics of an intermediate extraction drug, morphine, in trauma patients. Nine patients with an Injury Severity Score (ISS) > or = 16 were studied within 48 hours of trauma. Morphine 5 mg was given intravenously and serial blood and urine samples were drawn to derive pharmacokinetic parameters. Alpha acid glycoprotein (AAG) levels were determined. Total morphine clearance (CL) and volume of distribution (Vss) were decreased compared to established literature values. Area under the curve (AUC) and terminal half-life (T 1/2 alpha) were increased. AAG levels were higher than reference range. Elimination half-life was increased. The decrease we observed in Vss may be attributed to increased binding of morphine by AAG, which is increased after trauma as in our patients. Decreased clearance and increased half-life of an intermediate extraction drug may be explained by increased protein binding, decreased liver blood flow, and reduced hepatocellular function. Decreased clearance of the magnitude observed in these patients could result in drug accumulation. Better understanding of the effects of trauma on the pharmacokinetics of low, high, and intermediate extraction drugs will prevent excessive or suboptimal drug dosing.

Anti-infective agents and hepatic disease

Numerous factors such as changes in plasma protein binding, tissue binding, hepatic blood flow, hepatic metabolism, and distribution may occur in hepatic disease. The impact of these physiologic changes on pharmacokinetic and pharmacodynamic parameters of anti-infective agents is likely to be clinically significant. Unfortunately, these issues have not been thoroughly investigated. Even within the same type of liver disease, there is considerable interpatient variability in pharmacokinetic variables, rendering it difficult to predict drug disposition accurately. Pharmacokinetics of selected anti-infective agents are altered in hepatic disease, necessitating careful monitoring and dosage titration to avoid enhanced drug concentrations and risk of toxicity.

Oxygen supplementation restores theophylline clearance to normal in cirrhotic rats

BACKGROUND/AIMS

Capillarization associated with hepatic fibrosis may present a functional barrier to oxygen diffusion into the hepatocyte, and restriction on cellular oxygen supply may represent the rate-limiting constraint on hepatic oxidative drug metabolism. The aim of this study was to test this hypothesis by examining the effect of oxygen supplementation on plasma theophylline clearance in 10 control and 10 cirrhotic rats.

METHODS

Theophylline (3 mg/kg) was administered intravenously on two separate occasions, 24 hours apart, during which time the rats breathed either room air or oxygen (95%) from 1 hour before dosing until the end of plasma sampling with a randomized order of gas exposure.

RESULTS

Theophylline clearance was significantly reduced by a mean of 37% (n = 10; P = 0.003) in cirrhotic rats compared with controls. Oxygen supplementation significantly improved plasma theophylline clearance in cirrhotic rats by a mean of 40% (n = 10; P = 0.007), whereas clearance remained unchanged in healthy rats. Clearance in oxygen-supplemented cirrhotic rats was not significantly different from that in controls (P > 0.05).

CONCLUSIONS

These novel findings indicate an important role for hepatic oxygenation in improving drug disposition in cirrhosis, which may have potentially important clinical implications for the management of this disease.

The pharmacokinetics and neuromuscular effects of rocuronium bromide in patients with liver disease

To determine the effect of liver disease on the pharmacokinetics of rocuronium, the authors administered 0.6 mg/kg (twice the ED95) to 10 patients with liver disease and compared these results to values in 10 healthy surgical patients. Anesthesia was induced with thiopental and maintained with isoflurane (0.9%-1.1% end-tidal concentration) and nitrous oxide (60%). Venous blood samples were obtained for 6 h after rocuronium injection and plasma concentrations were measured using gas chromatography. Pharmacokinetic differences between groups were determined using a population-based pharmacokinetic analysis (NONMEM). Hepatic impairment did not alter the plasma clearance of rocuronium (217 +/- 21.8 mL/min, mean +/- SE, for both groups), but did increase the volume of the central compartment (5.96 +/- 1.01 L for controls, 7.87 +/- 1.33 L for patients with liver disease) and volume of distribution at steady state (16.4 L for controls, 23.4 L for patients with liver disease). In turn, elimination half-life was longer in patients with liver disease (111 min) compared to controls (75.4 min). The authors conclude that liver disease alters the pharmacokinetics of rocuronium by increasing its volume of distribution. The longer elimination half-life might result in a longer duration of action of rocuronium in patients with liver disease, particularly after prolonged administration.

Pharmacokinetics of famciclovir in subjects with chronic hepatic disease

The pharmacokinetic profile of penciclovir was determined after a single 500-mg dose of its oral precursor, famciclovir, in 9 healthy volunteers and in 14 patients with chronic hepatic disease. Plasma and urine samples were analyzed for concentrations of penciclovir and 6-deoxy-penciclovir using a reverse-phase high-performance liquid chromatography (HPLC) method. Famciclovir was not quantifiable in patients with hepatic disease, and 6-deoxy-penciclovir was quantifiable in only a limited number of specimens. The extent of systemic availability of penciclovir, as measured by AUC0-infinity, was similar in patients with hepatic disease and in healthy subjects. In contrast, Cmax was significantly lower (average decrease of 43%) in subjects with hepatic disease relative to healthy normal subjects. Median Tmax for subjects with hepatic disease was significantly increased (by 0.75 hours) compared with subjects with normal liver function. These data suggest a decrease in the rate, but not the extent, of systemic availability of penciclovir in patients with hepatic disease. It should be unnecessary to modify the dose of famciclovir for subjects with compensated hepatic disease and normal renal function.

Long-term depot antipsychotics. A risk-benefit assessment

The main advantage of depot antipsychotic medication is that it overcomes the problem of covert noncompliance. Patients receiving depot treatment who refuse their injection or fail to receive it for any other reason can be immediately identified and appropriate action taken. In the context of a carefully monitored management programme, depot treatment can have a major impact on compliance and, consequently, the risk of relapse and hospitalisation can be reduced. Another major advantage is that the considerable individual variation in bioavailability and metabolism with oral antipsychotic drugs is markedly reduced with depot treatment. A better correlation between the dose administered and the concentration of medication found in blood or plasma is achieved with depot treatment, and thus, the clinician has greater control over the amount of drug being delivered to the site of activity. A further benefit of depot treatment is the achievement of stable plasma concentrations over long periods, allowing injections to be given every few weeks. However, this also represents a potential disadvantage in that there is a lack of flexibility of administration. Should adverse effects develop, the drug cannot be rapidly withdrawn. Furthermore, adjustment to the optimal dose becomes a long term strategy. The controlled studies of low dose maintenance therapy with depot treatment suggest that it can take months or years for the consequences of dose reduction, in terms of increased risk of relapse, to become manifest. When weighing up the risks and benefits of long term antipsychotic treatment for the individual patient with schizophrenia, the clinician must take into account the nature, severity and frequency of past relapses, and the degree of distress and disability related to any adverse effects. However, the clinical decision to prescribe either a depot or an oral antipsychotic for maintenance treatment will probably rest largely on an assessment of the risk of poor compliance in the particular patient. There is no convincing evidence that the range, nature or severity of adverse effects reported with depot treatment is significantly different from that seen with oral treatment, and depot treatment has been shown to be as good or better than oral medication in preventing or postponing relapse. Furthermore, when adjusting the dose or frequency of depot injection, to improve control of psychotic symptoms or reduce adverse effects, the clinician can be confident that the dose prescribed is the dose being received by the patient.

Use of etoposide in patients with organ dysfunction: pharmacokinetic and pharmacodynamic considerations

Etoposide is a podophyllotoxin deriverative with activity against a wide variety of malignancies. It is also used in many clinical conditions in which renal or hepatic function is impaired. To establish a basis for making initial dose adjustments in patients with renal or hepatic dysfunction, the clinical pharmacology (e.g., absorption, distribution, protein binding, metabolism, and elimination) of etoposide is presented. Studies of the use of etoposide in patients with renal or hepatic dysfunction are summarized. The importance of protein binding to etoposide disposition, especially in patients with hepatic dysfunction is discussed. Pharmacodynamics refers to the relationship between drug concentration at the site of action (receptor) and pharmacologic response (toxicity or efficacy). The pharmacodynamics of etoposide has been studied in only a few patients with renal and (or) hepatic dysfunction and must be studied in larger populations before definitive dosing guidelines can be recommended. However, some general initial dosing recommendations for the use of etoposide in patients with renal and hepatic dysfunction are presented.

Variables affecting nicotine metabolism

Nicotine metabolism is exceedingly sensitive to perturbation by numerous host factors. To reduce the large variations and discrepancies in the literature pertaining to nicotine metabolism, investigators in future studies need to recognize and better control these host factors. Recent advances in the understanding of nicotine metabolism have suggested new approaches to elucidating underlying mechanisms of certain toxic effects associated with cigarette smoking.

Factors and conditions affecting the glucuronidation of oxazepam

The aim of the present work was to investigate the impact of disease states and environmental and host factors on the glucuronidation of oxazepam. Glucuronidation represents quantitatively one of the most important metabolic conjugation pathways (phase II) in man for the inactivation and detoxication of xenobiotics and endogenous compounds and the liver is the major site for it to take place. Far less attention has been paid to the conjugation reactions in previous clinical research in this field compared to the immense interest in the oxidative biotransformation pathways (phase I). This fact is mainly due to the latter giving rise to active or reactive metabolites with a toxicological potential. The metabolism of oxazepam expresses exclusively the capacity for glucuronide formation. It was a prerequisite to establish the bioavailability of oxazepam prior to succeeding studies on the oral disposition of the drug. A preparation for intravenous administration was created. Clearance was chosen as measurement of the capacity to glucuronidate oxazepam. Severe decompensated liver disease was associated with a significant decrease in oxazepam clearance, that became even more obvious when corrected for by a diminished binding to plasma proteins. This increase in free fraction of oxazepam was substantial and could mainly be accounted for by low plasma albumin values. The results are in part a settlement with earlier studies on glucuronidation in liver disease and they may undoubtedly be ascribed to the severe degree of liver disease. For the first time it was shown that hypothyroidism led to a decline in the clearance and metabolism of oxazepam and paracetamol that is mainly biotransformed by glucuronidation. It was concluded that the enzymes responsible for glucuronidation in hypothyroidism are under the influence of thyroid hormones as is the case with oxidative enzymes. Further studies focused on the effect of host and environmental factors on glucuronidation. A commercially available very low calorie product for the treatment of obesity resulted in a decrease in oxazepam clearance and a lack of co-factors as a consequence of the low calorie intake was explanatorily proposed. Beta-adrenoceptor antagonists are often prescribed together with other drugs and close knowledge on interactions is mandatory but insufficient in regard of drugs being glucuronidated. Despite the mutual metabolic pathway labetalol exerted no dispositional alterations concerning oxazepam. It was moreover suggested that very elderly subjects between the age of 80 to 94 years had a reduced clearance of oxazepam.(ABSTRACT TRUNCATED AT 400 WORDS)

Theophylline disposition following parenteral feeding of malnourished patients

OBJECTIVE

To investigate the effect of parenteral nutrition on theophylline disposition in malnourished patients.

DESIGN

Before-after trial.

SETTING

Tertiary care center.

PATIENTS

Ten patients with historic, anthropometric, and laboratory evidence of malnutrition.

INTERVENTIONS

Patients received two 5-mg/kg intravenous infusions of theophylline separated by at least 48 hours of glucose-based parenteral nutrition providing the entire estimated nutritional requirements.

MAIN OUTCOME MEASURES

Following each theophylline administration, serum theophylline samples were collected over a 24-hour period for delineation of maximum plasma concentrations, volume of distribution, elimination rate constant, clearance, and area under the curve.

RESULTS

Peak plasma theophylline concentrations were significantly lower prior to feeding (5.3 mumol/L, 95 percent confidence interval [CI] 0.78-10.0 mumol/L, p = 0.028). Volume of distribution decreased after parenteral feeding (0.08 L/kg, 95 percent CI 0.006-0.15 L/kg, p = 0.037). The elimination rate of theophylline increased after parenteral feeding reflected by an increase in the elimination rate constant (0.06 h-1, 95 percent CI 0.01-0.10 h-1, p = 0.023).

CONCLUSIONS

This study suggests that parenteral nutrition using a glucose-based solution acutely influences theophylline disposition in malnourished patients.

Psychopharmacologic issues in organ transplantation. Part I: Pharmacokinetics in organ failure and psychiatric aspects of immunosuppressants and anti-infectious agents

This article discusses pharmacokinetics and pharmacodynamics during hepatic, renal, and cardiovascular insufficiencies. Hepatic metabolism of psychotropic drugs and of drugs commonly used in transplant patients that have neuropsychiatric side effects is discussed. Neuropsychiatric effects of immunosuppressant agents, including cyclosporine, corticosteroids, azathioprine, OKT3, and FK 506, are reviewed. Certain infections occur more often in immunosuppressed patients; their treatment with antiviral, antifungal, and antibiotic drugs may have neuropsychiatric consequences. Because of altered drug sensitivities and metabolism, drug interactions, and severe medical illness, most drugs are used in reduced doses.

Digitoxin and its metabolites in patients with liver cirrhosis

Pharmacokinetic profile and urinary excretion of digitoxin and 4 metabolites were investigated in 9 patients with biopsy confirmed liver cirrhosis (median antipyrine clearance 20.0 +/- 5.4 ml/min; X +/- SEM) and were compared with that of 8 healthy volunteers (antipyrine clearance 36.9 +/- 4.9 ml/min) following intravenous and p.o. administration of 1 mg digitoxin. The kinetic parameters derived from the digotoxin plasma concentration time curve and from urinary recovery including total clearance of unchanged digitoxin did not differ significantly between both groups investigated. Renal clearance of digitoxin was 0.017 +/- 0.005 ml/min/kg in the patient group and 0.011 +/- 0.002 ml/min/kg in the volunteers (NS); it was 0.00340 +/- 0.00047 ml/min/kg and 0.00223 +/- 0.00039 ml/min/kg, respectively for digitoxigenin-bis-digitoxoside (NS), 0.00006 +/- 0.00001 ml/min/kg and 0.00016 +/- 0.00005 ml/min/kg for digitoxigenin-mono-digitoxoside (P < 0.05), 0.00041 +/- 0.00013 ml/min/kg and 0.00088 +/- 0.00032 ml/min/kg for digitoxigenin (P < 0.05), 0.00135 +/- 0.00049 ml/min/kg and 0.00113 +/- 0.00042 ml/min/kg for digoxin (NS). In conclusion, hydrolysis of digitoxin is altered in liver cirrhosis, whereby a significant reduction in the renal clearance and urinary recovery of digitoxigenin-mono-digitoxoside and digitoxigenin was seen in the present study.

Methods of determining plasma and tissue binding of drugs. Pharmacokinetic consequences

The available techniques for the investigation of drug binding to plasma and tissues protein are reviewed and the advantages and disadvantages of the various techniques stated. A comparison of different plasma protein binding techniques is made which shows that the size of the unbound fraction of drug may be influenced by the method used. Protein binding may be assayed by methods including equilibrium dialysis, ultrafiltration, ultracentrifugation, gel filtration, binding to albumin microspheres and circular dichroism. Tissue binding techniques can involve testing binding to isolated organs, tissue slices, homogenates and isolated subcellular particles. Details of the available methods to compute pharmacokinetic constants are given. Stereoselective binding has been investigated for a limited number of drugs and the difference in the binding of 2 enantiomers is usually modest. The measurement of the binding constants is often required to characterise the drug-protein interaction. Mathematical and graphical methods to compute the pharmacokinetic parameters are discussed. The implications of binding on the volume of distribution and clearance of drugs are examined.

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.

Altered pharmacokinetics of lignocaine after epidural injection in type II diabetics

The pharmacokinetics of lignocaine has been compared after epidural anaesthesia in diabetics and non-diabetic patients. Epidural lignocaine 8 mg.kg-1 was given to 8 well controlled Type II diabetic and 8 non-diabetic patients and the plasma drug concentration in serial blood samples were measured by HPLC. The plasma level of lignocaine was lower in diabetics compared to non-diabetics. The peak level was attained at 20 min in both groups. The clearance of the drug was significantly higher, (39.9 vs 16.7 ml.min-1.kg-1) associated with a decreased elimination half-life and mean residence time. The study suggests that the rate of absorption of lignocaine is not altered after epidural administration and that its hepatic metabolism is increased in diabetics compared to non-diabetics.

Theophylline metabolism in patients with hepatosplenic mansoniasis and cirrhosis

The pharmacokinetics of theophylline were studied in 12 patients with hepatosplenic mansoniasis, 14 patients with cirrhosis and 16 normal controls. Following a single intravenous dose of aminophylline volumes of distribution, serum half-lives and body clearances were determined. Volumes of distribution of theophylline in patients with schistosomiasis (mean 0.624 l/kg) did not differ from cirrhotic patients (mean 0.616 l/kg) or normal controls (mean 0.593 l/kg). Cirrhotic patients had a prolonged half-life compared to normal subjects (mean 22.1 vs. 9.9 h), while patients with schistosomiasis did not substantially differ from normal controls (15.8 vs. 9.9 h). Body clearance in patients with schistosomiasis was similar to controls (34.02 vs. 49.20 ml/h per kg) but decreased (29.24 ml/h per kg) in patients with cirrhosis. Individual analysis of the group with schistosomiasis disclosed three patients with reduced theophylline elimination. No relationship was found between laboratory tests of liver function and the pharmacokinetics of theophylline in any group. The administration of theophylline to patients with hepatosplenic schistosomiasis, although less dangerous than in cirrhosis, must be closely followed.

Clinical pharmacokinetics in patients with liver disease

From considerations of hepatic physiology and pathology coupled with pharmacokinetic principles, it appears that altered drug elimination in liver disease may result from the following mechanisms: reduction in absolute cell mass, in cellular enzyme content and/or activity, in portal vein perfusion due to extrahepatic/intrahepatic shunting, or of portal perfusion of hepatocyte mass due to decreased portal flow or sinusoidal perfusion; increase in arterial perfusion relative to portal perfusion; preferential perfusion of the sinusoidal midzone and terminal zones by arterioles; potential for direct mixing of arterial blood within the space of Disse; reduced exchange across the endothelial lining; and impaired diffusion within the space of Disse. In general, oxidative drug metabolism is impaired in liver disease and the degree of impairment of oxidisation differs between drugs but correlates best with the degree of sinusoidal capillarisation, i.e. the degree of access of the drug from the sinusoid to the hepatocyte. Drug conjugation appears to be relatively unaffected by liver disease, whereas elimination by biliary excretion correlates best with the degree of intrahepatic shunting and not with sinusoidal capillarisation. As the latter should impair hepatocyte access of all compounds similarly, a potentially important mechanism could be impaired access of oxygen to hepatocytes as oxidative metabolism is much more sensitive to oxygen supply than are conjugation or biliary excretion. This suggests a potentially important therapeutic role for agents which increase the hepatic oxygen supply. Useful adjunctive strategies may also derive from the oxygen limitation hypothesis. Anaemia should be targeted as a critically important variable, as should oxygen-carrying capacity, i.e. modification of the smoking habit. Additionally, enzyme inducers such as barbiturates may be used if overriding hypoxic constraints are removed by oxygen supplementation. Agents likely to seriously compromise arterial perfusion of the hepatic vascular bed should be avoided, e.g. those causing postural hypotension or vasospasm. Vasodilators can be used to actively promote arterial perfusion. While the effect of liver disease on drug handling is highly variable and difficult to predict, there are well recognised principles for modifying dosage. These include halving the dose of drugs given systemically (or of low clearance drugs given orally) and a 50 to 90% reduction in the dose of drugs with a high hepatic clearance given orally. Changes in the pharmacodynamic effects of drugs (either alone or in addition to pharmacokinetic changes) can also be profound, and awareness of this possibility should be increased.

Quantifying hepatic function in the presence of liver disease with phenazone (antipyrine) and its metabolites

The disposition of phenazone (antipyrine), a low extraction compound with low protein binding, is known to be altered in the presence of various types of hepatic dysfunction. As such, its pharmacokinetics may be useful in the objective characterisation of altered liver function. Understanding the known effects of various liver disease states upon the disposition of this probe may provide insight into future applications. This article provides a review of background information about normal plasma phenazone pharmacokinetics, urinary metabolite disposition and tabulations of reported total body clearances of the drug in the presence of cirrhosis, fatty liver, hepatitis and cholestasis in humans. An estimate is made of the sensitivity and specificity of phenazone testing for the verification of the presence of cirrhosis based on this compiled literature.

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.

Pharmacokinetics in acute illness

Severe illness at any age is accompanied by organ dysfunction, the administration of numerous drugs and complex changes in drug absorption, disposition and action. The clinician faced with a seriously ill patient should be aware of the important principles of drug treatment in critical illness. With acute illness of all types, the premature infant and the octogenarian lie at opposite ends of an age spectrum which encompasses the gamut of human disease and changeable organ pathophysiology. The common requirement of this host of variables is a flexible management plan, and careful observation of the patient's response to a therapeutic regimen which has been based on a sound knowledge of drug pharmacokinetics.

Glucuronidation of oxazepam is not spared in patients with hepatic encephalopathy

The disposition of oral oxazepam was investigated in seven patients with decompensated cirrhosis and encephalopathy and in nine healthy individuals to further examine the hypothesis of preservation of glucuronidation in liver disease. The patients showed a severe reduction in the quantitative liver function as assessed by estimation of the clearance of antipyrine; the median value was 9 ml.min-1 and the range was 6 to 12 ml.min-1. Apparent clearance of oxazepam in cirrhotic patients was 0.55 ml.min-1.kg-1, with a range of 0.46 to 1.24 ml.min-1.kg-1, compared with 1.19 ml.min-1.kg-1 and a range of 0.80 to 1.66 ml.min-1.kg-1 in the controls (p less than 0.05). The unbound clearance of oxazepam in patients was 4.1 ml.min-1.kg-1, with a range of 3.4 to 5.5 ml.min-1.kg-1, compared with 25.4 ml.min-1.kg-1, and a range of 16.7 to 43.7 ml.min-1.kg-1, p less than 0.001, in the controls. In patients with liver disease, the unbound clearance of oxazepam correlated significantly with antipyrine clearance (r = 0.88; p less than 0.05). The results suggest a reduced capacity for glucuronidation in patients with decompensated liver disease and severe hepatic failure that corresponds to the general reduction in the quantitative liver function.

The effect of age on serum concentrations of albumin and alpha 1-acid glycoprotein

1. Human serum albumin (HSA) concentrations and alpha 1-acid glycoprotein (AAG) concentrations were measured in 68 subjects, 35 males and 33 females, aged 20-90 years without evidence of acute or chronic inflammatory disease or malignancy. Subjects were drug free for at least 1 month. HSA and AAG concentrations were measured using rate nephelometry. 2. Age had no effect on alpha 1-acid glycoprotein concentration, whereas plasma albumin levels decreased as a function of age in both sexes. We observed no differences between males and females in the plasma concentrations of HSA and AAG. 3. These data show that in healthy subjects the HSA concentration decreases with increasing age, whereas age, uncomplicated by disease does not influence AAG concentration.

Psychopharmacology in patients with hepatic and gastrointestinal disease

Psychotropic drugs often need to be prescribed to patients who also have pre-existing gastrointestinal (GI) and/or hepatic disease. This paper addresses the effect of GI and hepatic disease on the pharmacokinetics of psychotropic drugs, the effect of psychotropic drugs on pre-existing GI and hepatic diseases, the adverse GI and hepatic effects of psychotropic medications, the effects of GI medications on mental status, and the potential drug interactions between commonly prescribed GI medications and psychotropic drugs. Drug selection and dosage modification based on these considerations should allow safe and effective psychotropic treatment for patients with pre-existing GI and/or hepatic disease.

Effect of plasma protein binding on kinetics of PN 200-110 in the isolated perfused rat heart

The myocardial accumulation and elimination pharmacokinetics of PN 200-110 (PN) were investigated in the single pass isolated perfused rat heart by two methods. A direct method, radioactivity measurement in myocardial tissue after various perfusion times, and an indirect method, concentration determination in coronary effluent, by fractionary collection of samples, during infusion and elimination periods. Both methods showed that the myocardium could be considered as a one-compartment model with regard to PN pharmacokinetics. The perfusion with a modified Krebs-Ringer (MKR) solution containing 1 nM of (+/-)PN 200-110 and [3H]-(+)PN 200-110 as radioactive tracer, led to an accumulation of about 61.4 fmol.mg-1 myocardial tissue at steady-state. The effect of protein binding on the uptake and pharmacokinetic parameters of PN has been investigated in this isolated perfused heart (IPH) model. binding of PN decreased as a function of increasing bovine serum albumin (BSA) levels in the perfusion solution. As a matter of fact, the mean steady state myocardial concentration of PN was decreased by 42.9, 56.2, 76.5, 83.9 and 95.5% for respectively, 1, 2.5, 6, 10 and 40 g.l-1 of BSA. In the same way, the free fraction, the apparent volume of distribution (Vd) and the distribution and elimination half-lives were decreased. On the contrary, the elimination rate constant was increased.

Plasma protein binding of frusemide in liver disease: effect of hypoalbuminaemia and hyperbilirubinaemia

The binding of frusemide was studied in the plasma of 20 healthy subjects and 45 patients with liver disease. The unbound percentage (mean +/- s.d.) of frusemide was 1.64 +/- 0.21 healthy subjects) and 2.24 +/- 0.79 (patients) (P less than 0.01). By grouping the patients on the basis of plasma albuminaemia and bilirubinaemia four clusters namely: 'normal concentrations of albumin and bilirubin' (A), 'hyperbilirubinaemia and normal albumin concentration' (B), 'hypoalbuminaemia and normal bilirubin concentration' (C) and 'hypoalbuminaemia and hyperbilirubinaemia' (D) were defined. The unbound percentage of frusemide was 1.80 +/- 0.36 in (A); 2.44 +/- 1.05 in (B); 2.23 +/- 0.38 in (C); 2.76 +/- 0.77 in (D). The figure for healthy volunteers was not different from A, whereas it was significantly lower than those for B and D (P less than 0.01) and for C (P less than 0.05). A lowered binding of frusemide was associated with hypoalbuminaemia or hyperbilirubinaemia.

Effect of albumin distribution. A simulation analysis of the effect of altered albumin distribution on the apparent volume of distribution and apparent elimination rate constant of drugs

The effects of altered albumin distribution on the apparent volume of distribution (V) and the apparent elimination rate constant (kappa) of drugs were investigated by a simulation analysis. The Equations derived by Oie et al. were modified for this purpose. Within the range observed in normal healthy subjects and patients, the change in albumin distribution significantly affected V of drugs but, in general, not kappa. For drugs with more than 90% plasma-protein binding, V changed by more than 100%. The change in plasma-protein binding caused by an altered albumin distribution produced a greater effect on V than that caused by an altered albumin amount. These results suggest that albumin distribution is an important factor in controlling the kinetics of drugs which are highly bound to plasma protein. This is illustrated using midazolam as an example.

Tianeptine and its main metabolite pharmacokinetics in chronic alcoholism and cirrhosis

The effect of chronic alcoholism (with or without associated moderate cirrhosis) on the disposition of the antidepressant tianeptine, which is devoid of substantial first-pass metabolism, was examined in 21 patients and 11 age-matched controls. Pharmacokinetic parameters for tianeptine and its C5 acid analogue metabolite (MC5 metabolite) were estimated by non-compartmental analysis. The area under the curve (AUC) for tianeptine, following a 12.5mg single oral dose, was decreased by 31% in chronic alcoholics and increased by only 14% in cirrhotics, compared to controls. These changes did not attain statistical significance. The trend of changes in the AUC for the MC5 metabolite was similar to that observed for the parent drug. No statistical difference was found in the terminal half-life for both tianeptine and its MC5 metabolite between patients and controls. On the basis of this study, it appears unnecessary to modify the proposed dosage regimen used in clinical trials (tianeptine sodium salt 12.5mg 3 times daily) in chronic alcoholics with or without associated moderate cirrhosis.

Covalent and noncovalent protein binding of drugs: implications for hepatic clearance, storage, and cell-specific drug delivery

This review deals with the mechanisms by which the liver disposes of drugs that are covalently or noncovalently associated with proteins. Many drugs bind to plasma proteins such as albumin (mainly anionic compounds) and alpha 1-acid glycoprotein (cationic compounds). Nevertheless, the liver is able to clear such drugs efficiently from the circulation because of intrahepatic dissociation of the drug-protein complex. This clearance may involve spontaneous dissociation because of progressive removal of the unbound drug during liver passage, a process that can be rate limiting in hepatic uptake. Alternatively, the porous endothelial lining of the hepatic sinusoids may allow extensive surface interactions of the drug-protein complexes with hepatocytes, leading to facilitation of drug dissociation. Binding to plasma proteins and intracellular proteins in the cytoplasm or cell organelles is an important factor determining the hepatic storage and elimination rate of drugs. Drugs noncovalently associated with glycosylated proteins, which can be endocytosed by various liver cells, are not coendocytosed with such proteins. However, covalently bound drugs can be internalized by receptor-mediated endocytosis, which permits specific targeting to hepatocytes, endothelial cells, Kupffer cells, and lipocytes by coupling to different glycoproteins that are recognized on the basis of their terminal sugar. The endocytosed drug-carrier complex is routed into endosomes and lysosomes, where the active drug is liberated by cleavage of acid-sensitive linkages or proteolytic degradation of peptide linkers. This concept has been applied to antineoplastic, antiparasitic, and antiviral drugs.

Plasma protein binding of alpidem in healthy volunteers, in neonates and in liver or renal insufficiency

The binding of alpidem, a new anxiolytic drug, has been studied in plasma from 6 healthy subjects, 12 patients with renal failure, 12 patients with liver cirrhosis and 12 chronic uraemics maintained on haemodialysis, as well as in 12 serum samples from the placental cord, to represent the situation in the newborn. The unbound fraction was 0.61% (healthy volunteers), 1.31% (newborns), 0.86% (cirrhotic patients), 0.72 (patients with renal failure), 0.70% (before haemodialysis) and 0.79% (after haemodialysis). Binding in the volunteers was significantly different from that in neonates and cirrhotics only. Alpidem became bound to isolated albumin (45 g.l-1) and alpha 1-acid glycoprotein (0.75 g.l-1) to 97.2% and 97.1%, respectively. The bound fraction of the drug in a mixture of two proteins was 99.1%. For alpidem, it appears that alpha 1-acid glycoprotein may balance the effect of any decrease in the albumin concentration.

Oral pharmacokinetics and ascitic fluid penetration of ofloxacin in cirrhosis

Plasma and ascitic fluid concentrations of ofloxacin were determined in 12 cirrhotic patients after a single dose and repeated 200 mg oral doses. The single dose kinetics were compared to those obtained in 12 healthy volunteers. Mean plasma elimination half-life was 11.6 h in cirrhotics and 7.0 h in controls. Mean total clearance was 2.3 times lower in patients than in controls, due to a significant decrease of renal clearance of the drug, unrelated to creatinine clearance. Mean apparent volume of distribution was 1.2 l/kg in patients and 1.8 l/kg in controls. Estimated by the ratio of AUC in peritoneal fluid and plasma, ascitic fluid penetration was 80% after the first oral dose. Ascitic fluid concentrations equaled corresponding plasma concentrations after 10 h, without pronounced accumulation of ofloxacin in ascites. We may conclude that, in cirrhotic patients with normal serum creatinine, a significant impairment of renal tubular handling of ofloxacin could be observed and led to a delayed elimination half-life of the drug. Because of its broad spectrum of activity, low side-effect profile, and large ascitic fluid penetration after oral administration, ofloxacin appears to be a new therapeutic approach of severe infections in cirrhotic patients, in particular spontaneous bacterial peritonitis.

Hepatic drug disposition in multiple organ failure

In 15 patients with multiple organ failure of septic etiology, some principal partial hepatic functions of drug disposition were measured by the test substances galactose, indocyanine green, theophylline and 4-methylumbelliferon. Glucuronidation was not impaired in any case, whereas flow-limited and capacity-limited drug elimination can be influenced. Drug monitoring and intense clinical observation seem necessary to improve drug therapy and the outcome of patients with multiple organ failure.

The pharmacokinetics of bendazac-lysine and 5-hydroxybendazac, its main metabolite, in patients with hepatic cirrhosis

We have studied the pharmacokinetics of bendazac and its major metabolite, 5-hydroxybendazac, in 11 patients with hepatic cirrhosis after the oral administration of a single 500 mg tablet of bendazac-lysine, and compared them with those obtained from 10 healthy adults. The rate of absorption of bendazac, as assessed by tmax and Cmax, is similar in patients and in healthy subjects. The drug is eliminated mostly by metabolism in healthy adults, more than 60% of the dose being excreted in the urine as 5-hydroxybendazac and its glucuronide. Hepatic insufficiency impairs this metabolism, a two-fold decrease in apparent plasma clearance (CL/f) being observed in the patients. Although the plasma unbound fraction of bendazac is increased in patients (the drug is highly bound to plasma albumin), the apparent volume of distribution (V/f) is unchanged. In consequence, the half-life of bendazac is increased two-fold in the patients. Impairment of metabolism decreases the formation of 5-hydroxybendazac, but metabolism remains the main route of its elimination. Renal excretion of bendazac accounts for about 10% of the dose in both patients with cirrhosis and healthy subjects. We conclude that in patients with severe hepatic insufficiency the daily dose of bendazac-lysine should be halved.

Buspirone pharmacokinetics in patients with cirrhosis

The pharmacokinetics of a single oral dose of buspirone (20 mg) were determined in 12 patients with cirrhosis and 12 normal subjects. The mean AUC of buspirone was 55 +/- 38 s.d. ng ml-1 h in cirrhotics and 3.5 +/- 2.4 s.d. ng ml-1 h in normals. The time until maximum concentration (tmax) attained was similar in the two groups (0.6 vs 0.7 h), but mean maximum concentration Cmax was higher in patients (18.8 +/- 16.3 s.d. ng ml-1) than in normals (1.2 +/- 0.8 s.d. ng ml-1). Mean elimination half-life of buspirone was greater in cirrhotics, but this difference was marginally significant statistically (cirrhotics, 6.1 +/- 3.5 s.d. h, normals 3.2 +/- 1.5 s.d. h, P = 0.05). Eight of 12 patients and seven of 12 normal subjects had a second peak in the plasma concentrations of buspirone. In patients this occurred at 10.8 +/- 7.4 s.d. h after the dose, and its mean concentration was 3.1 +/- 6.6 ng ml-1. In normal subjects the second peak occurred at 4.3 +/- 2.1 h after the dose and its mean concentration was 0.5 +/- 0.3 ng ml-1. On the kinetic evidence buspirone should be used with caution in liver disease.

The influence of binding to albumin and alpha 1-acid glycoprotein on the clearance of drugs by the liver

The liver is a major site for synthesis and catabolism of plasma proteins. Albumin has various binding sites for anionic drugs, alpha 1-acid glycoprotein possesses a single binding site for cationic drugs. In spite of extensive protein binding, the liver can efficiently remove drugs from the circulation. Intrahepatic dissociation of the drug-protein complex may involve dissociation-limited debinding under non-equilibrium conditions or surface interaction-facilitated dissociation phenomena. During liver or renal disease and acute-phase conditions plasma protein binding of drugs may be affected. Changes in the unbound drug fraction do not always result in proportional changes in clearance or distribution volume. Potential changes in the unbound concentration in steady-state as well as the fluctuations in total plasma levels depend on the extent of protein binding of a drug, the relative change in the unbound drug fraction type of clearance, the size of the distribution volume, route of administration as well as concomitant changes in intrinsic (cellular) clearance function. Optimization of dosage regimens for certain drugs and interpretation of liver function tests with diagnostic dyes may largely benefit from determination of the unbound rather than the total concentration of the drugs involved.

[Tryptophan metabolism in liver diseases: a pharmacokinetic and enzymatic study]

Tryptophan is considered to be one of the agents involved in the pathogenesis of hepatic encephalopathy. In our study, we evaluated tryptophan metabolism in liver disease. A bolus of 1.5 g of L-tryptophan was administered intravenously to 14 patients with noncirrhotic liver disease, 40 patients with liver cirrhosis, and 8 healthy volunteers. As pharmacokinetic parameters, the half life, clearance, and volume of distribution of free and total tryptophan were determined using a biexponential formula. In addition, the activity of liver tryptophan pyrrolase, the key enzyme of tryptophan metabolism, was measured in liver biopsy specimens of 15 patients with noncirrhotic liver disease, 8 patients with cirrhosis of the liver, and 4 patients with histologically normal livers. Healthy subjects and patients with noncirrhotic liver disease both showed similar results in measured and calculated data. In contrast, patients with cirrhosis revealed significant alterations of the pharmacokinetic parameters of free and total tryptophan: the half-life was increased by 195% and 176%, the clearance was decreased by 73% and 34%, respectively, and the activity of tryptophan pyrrolase was decreased by 22%. The tryptophan transfer in cirrhosis amounted to only 0.75 +/- 0.03 g per 24 h compared with 2.6 +/- 0.34 g per 24 h in healthy individuals. The findings demonstrate that patients with cirrhosis show a marked reduction in their ability to metabolize tryptophan. This should be taken into account in the oral and parenteral nutrition of those patients.

Massive glibenclamide overdose without hypoglycaemia in a man with diabetes after partial pancreatectomy

A 49-year-old man with non-insulin-dependent diabetes mellitus (NIDDM) from alcoholic pancreatitis took 100 mg of glibenclamide without symptoms of hypoglycaemia even when glibenclamide concentrations were high (191 micrograms/l). There was no increase in serum C-peptide concentration. The observed half-life of glibenclamide was 6 h. It is concluded that high doses of glibenclamide will not provoke pancreatic insulin secretion in NIDDM caused by pancreatic destruction, there was no evidence for an acute extra-pancreatic effect of glibenclamide and the elimination of glibenclamide may be slower than supposed previously.

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.

Bioavailability and elimination of digitoxin in patients with hepatorenal insufficiency

Following administration of digitoxin, 1 mg intravenously, the pharmacokinetics of this glycoside were studied in eight healthy volunteers and in eight patients with hepatorenal insufficiency (mean creatinine clearance 19.6 +/- 2.9 ml/min; antipyrine clearance 25.6 +/- 3.2 ml/min; means +/- SEM). Liver cirrhosis of the patients was confirmed by liver biopsy. Plasma protein binding of digitoxin (means +/- SEM) was 95.1 +/- 0.7% in the patients and 95.6 +/- 1.2% in the volunteers (NS). Total body clearance of digitoxin was 0.0530 +/- 0.0040 ml/min/kg of body weight in the patients and 0.0547 +/- 0.0043 ml/min/kg of body weight in the healthy subjects (NS). When elimination half-lives of the patients and the volunteers were compared, there was also no significant difference (7.0 +/- 0.77 days in the patient group and 7.8 +/- 0.8 days in the volunteers). Our data concerning digitoxin kinetics in patients with hepatorenal insufficiency do not indicate an accumulation of the drug in these patients.