Assessment of lidocaine metabolite formation in comparison with other quantitative liver function tests

Lidocaine/monoethylglycinexylidide test, galactose elimination test, and sorbitol elimination test for metabolic assessment of liver cell bioreactors

Various metabolic tests were compared for the performance characterization of a liver cell bioreactor as a routine function assessment of cultures in a standby for patient application in clinical studies. Everyday quality assessment (QA) is essential to ensure a continuous level of cellular functional capacity in the development of hepatic progenitor cell expansion systems providing cells for regenerative medicine research; it is also of interest to meet safety requirements in bioartificial extracorporeal liver support systems under clinical evaluation. Quality criteria for the description of bioreactor cultures were developed using primary porcine liver cells as a model. Porcine liver cells isolated by collagenase perfusion with an average of 3 x 10(9) primary cells were used in 39 bioreactors for culture periods up to 33 days. Measurements of monoethylglycinexylidide synthesis and elimination of lidocaine, galactose elimination, and sorbitol elimination proved to be useful for routine QA of primary liver cell cultures. We demonstrate two methods for dispensing test substances, bolus administration and continuous, steady-state administration. Bolus test data were grouped in Standard, Therapy, Infection/Contamination, and Cell-free control groups. Statistical analyses show significant differences among all groups for every test substance. Post hoc comparisons indicated significant differences between Standard and Cell-free groups for all elimination parameters. For continuous tests, results were categorized according to number of culture days and time-dependent changes were analyzed. Continuous administration enables a better view of culture health and the time dependency of cellular function, whereas bolus administration is more flexible. Both procedures can be used to define cell function. Assessment of cellular function and bioreactor quality can contribute significantly to the quality of experimental or clinical studies in the field of hepatic bioreactor development.

Pharmacokinetics and dosage adjustment in patients with hepatic dysfunction

The liver plays a central role in the pharmacokinetics of the majority of drugs. Liver dysfunction may not only reduce the blood/plasma clearance of drugs eliminated by hepatic metabolism or biliary excretion, it can also affect plasma protein binding, which in turn could influence the processes of distribution and elimination. Portal-systemic shunting, which is common in advanced liver cirrhosis, may substantially decrease the presystemic elimination (i.e., first-pass effect) of high extraction drugs following their oral administration, thus leading to a significant increase in the extent of absorption. Chronic liver diseases are associated with variable and non-uniform reductions in drug-metabolizing activities. For example, the activity of the various CYP450 enzymes seems to be differentially affected in patients with cirrhosis. Glucuronidation is often considered to be affected to a lesser extent than CYP450-mediated reactions in mild to moderate cirrhosis but can also be substantially impaired in patients with advanced cirrhosis. Patients with advanced cirrhosis often have impaired renal function and dose adjustment may, therefore, also be necessary for drugs eliminated by renal exctretion. In addition, patients with liver cirrhosis are more sensitive to the central adverse effects of opioid analgesics and the renal adverse effects of NSAIDs. In contrast, a decreased therapeutic effect has been noted in cirrhotic patients with beta-adrenoceptor antagonists and certain diuretics. Unfortunately, there is no simple endogenous marker to predict hepatic function with respect to the elimination capacity of specific drugs. Several quantitative liver tests that measure the elimination of marker substrates such as galactose, sorbitol, antipyrine, caffeine, erythromycin, and midazolam, have been developed and evaluated, but no single test has gained widespread clinical use to adjust dosage regimens for drugs in patients with hepatic dysfunction. The semi-quantitative Child-Pugh score is frequently used to assess the severity of liver function impairment, but only offers the clinician rough guidance for dosage adjustment because it lacks the sensitivity to quantitate the specific ability of the liver to metabolize individual drugs. The recommendations of the Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA) to study the effect of liver disease on the pharmacokinetics of drugs under development is clearly aimed at generating, if possible, specific dosage recommendations for patients with hepatic dysfunction. However, the limitations of the Child-Pugh score are acknowledged, and further research is needed to develop more sensitive liver function tests to guide drug dosage adjustment in patients with hepatic dysfunction.

Pharmacokinetics and dosage adjustment in patients with hepatic dysfunction

The liver plays a central role in the pharmacokinetics of the majority of drugs. Liver dysfunction may not only reduce the blood/plasma clearance of drugs eliminated by hepatic metabolism or biliary excretion, it can also affect plasma protein binding, which in turn could influence the processes of distribution and elimination. Portal-systemic shunting, which is common in advanced liver cirrhosis, may substantially decrease the presystemic elimination (i.e., first-pass effect) of high extraction drugs following their oral administration, thus leading to a significant increase in the extent of absorption. Chronic liver diseases are associated with variable and non-uniform reductions in drug-metabolizing activities. For example, the activity of the various CYP450 enzymes seems to be differentially affected in patients with cirrhosis. Glucuronidation is often considered to be affected to a lesser extent than CYP450-mediated reactions in mild to moderate cirrhosis but can also be substantially impaired in patients with advanced cirrhosis. Patients with advanced cirrhosis often have impaired renal function and dose adjustment may, therefore, also be necessary for drugs eliminated by renal exctretion. In addition, patients with liver cirrhosis are more sensitive to the central adverse effects of opioid analgesics and the renal adverse effects of NSAIDs. In contrast, a decreased therapeutic effect has been noted in cirrhotic patients with beta-adrenoceptor antagonists and certain diuretics. Unfortunately, there is no simple endogenous marker to predict hepatic function with respect to the elimination capacity of specific drugs. Several quantitative liver tests that measure the elimination of marker substrates such as galactose, sorbitol, antipyrine, caffeine, erythromycin, and midazolam, have been developed and evaluated, but no single test has gained widespread clinical use to adjust dosage regimens for drugs in patients with hepatic dysfunction. The semi-quantitative Child-Pugh score is frequently used to assess the severity of liver function impairment, but only offers the clinician rough guidance for dosage adjustment because it lacks the sensitivity to quantitate the specific ability of the liver to metabolize individual drugs. The recommendations of the Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA) to study the effect of liver disease on the pharmacokinetics of drugs under development is clearly aimed at generating, if possible, specific dosage recommendations for patients with hepatic dysfunction. However, the limitations of the Child-Pugh score are acknowledged, and further research is needed to develop more sensitive liver function tests to guide drug dosage adjustment in patients with hepatic dysfunction.

Prognostic value of quantitative liver function tests in viral cirrhosis: a prospective study

BACKGROUND AND AIMS

Widespread application of quantitative liver function tests as a prognostic tool is controversial. In this study we assessed the predictivity of serial evaluations of galactose elimination capacity (GEC) and the monoethylglycinexylidide (MEGX) test on survival in viral cirrhosis, and secondarily we compared these tests with Child-Turcotte-Pugh (CTP) and Model for End Stage Liver Disease (MELD) scores.

METHODS

In a cohort of 35 patients with viral cirrhosis, GEC and MEGX were evaluated every 6 months for 24 months and compared with CTP and MELD scores at the same time intervals. The end points were patient death or liver transplantation.

RESULTS

Statistically significant differences between dead/transplanted patients and survivors were found for basal values of GEC, MEGX, CTP and MELD. Receiver-operating characteristics curves of CTP and MELD scores showed a higher prognostic accuracy than GEC and MEGX. On multivariate analysis, neither GEC nor MEGX were independent predictors of survival. Repeated-measures analysis of GEC and MEGX did not increase the prognostic accuracy of these tests and did not add useful prognostic information on patient outcome during the following 6 months.

CONCLUSIONS

Our data suggest that neither single nor repeated determinations of GEC and MEGX are superior to CTP and MELD scores in predicting prognosis of patients with viral cirrhosis.

Use of lidocaine metabolism to test liver function during the long-term follow-up of liver transplant recipients

BACKGROUND/AIMS

The aim of this study was to assess the usefulness of the monoethylglycinexylidide (MEGX) test to monitoring the long-term function of liver allografts.

METHODS

MEGX production was measured prospectively in 60 consecutive liver transplant recipients undergoing their annual review.

RESULTS

Median MEGX values in liver recipients (54 ng/mL; range 10-146) were lower than those found in healthy controls (78 ng/mL; range 44-118). MEGX values correlated negatively with alanine aminotransferase (ALT) activity (p = 0.004) and with the overall histological score (p = 0.01), and positively with sulfobromophthalein (BSP) and indocyanine green (ICG) clearances (p = 0.0002 and p = 0.002, respectively). A stepwise decline was observed with worsening liver fibrosis, from 71 +/- 5 microg/L in patients with no fibrosis to 27 +/- 9 microg/L in patients with bridging fibrosis (p = 0.002). BSP and ICG clearances correlated more closely than the MEGX test with the overall histological score (p = 0.001 and p = 0.001, respectively) and portal fibrosis (p = 0.002 and p = 0.001).

CONCLUSIONS

The measurement of MEGX formation is a simple and non-invasive method to monitor liver graft function. It may constitute a valuable tool for assessing the degree of fibrosis.

Experimental study of the evaluation of liver function on the opposite side during portacaval anastomosis and ligation of the left portal branch

BACKGROUND

Hepatocellular carcinoma is likely to accompany liver cirrhosis in which the portal pressure increases with portasystemic shunt. When portal tumor thrombus is present in the primary bifurcation, blood flow differs between the thrombolic lobe and the non-thrombolic lobe. In those cases, it is difficult to evaluate exactly residual liver function by conventional test. Therefore, the following studies were performed.

MATERIALS AND METHODS

Adult mongrel dogs are divided into a control group (C group), group undergoing ligation of the left portal branch (PL group), group undergoing portacaval anastomosis (PCS group) and group undergoing both ligation of the left portal branch and portacaval anastomosis (PL+PCSgroup)(n=5). ICG-R15 and MEGX15 in peripheral venous blood and right hepatic venous blood were determined. Mitochondrial metabolic capacity (adenosine triphosphate level, energy charge) was measured by high-performance liquid chromatography using liver biopsied specimens.

RESULTS

The MEGX ratio (right hepatic venous blood MEGX15/peripheral venous blood MEGX 15) positively correlated with energy charge in the right hepatic lobe.

CONCLUSIONS

In evaluating liver function of the right hepatic lobe during portacaval shunt and the left portal branch ligation, the MEGX ratio may sensitively reflect the mitochondrial function.

Utility of nonaqueous capillary electrophoresis for the determination of lidocaine and its metabolites in human plasma: a comparison of ultraviolet and mass spectrometric detection

A nonaqueous capillary electrophoresis/electrospray mass spectrometry method for the separation of lidocaine (LID) and two of its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), has been developed. The separation medium was: 70 mM ammonium formate and 2.0 M formic acid in acetonitrile/methanol (60:40 v/v). With a sheath liquid of methanol/water (80:20 v/v) containing 2% formic acid and positive ion detection, reproducible determinations (8-11% relative standard deviation (RSD)) of lidocaine and its metabolites were performed in spiked human plasma. The limits of detection (LODs) were between 69.1 and 337 nM. The influences of sheath liquid composition, nebulizing gas pressure and drying gas temperature on the separation were examined.

Correlation between daily cyclosporine dose and allograft injury in liver recipients with and without recurrent hepatitis C

BACKGROUND: After liver transplantation, the daily cyclosporine dose is adjusted to maintain the blood level in a chosen range. The aim of this study was to assess the influence of liver graft injury on cyclosporine dose. METHODS: The parameters of liver function were investigated in 145 patients. Ninety-two patients took part in a longitudinal study. RESULTS: The cyclosporine dose correlated with the MEGX test (r=0.38, P=0.01) and with the ICG (r=0.38, P=0.0001) and BSP (r=0.37, P=0.0002) clearances; it had an inverse correlation with transaminases (AST: r=0.38, P=0.0001) and histological lesions (r=-0.29, P=0.005). The cyclosporine dose was lower in patients with recurrent hepatitis C (179+/-9 mg/day) than in those without (241+/-10 mg/day), and was lower in patients with chronic hepatitis (154+/-9 mg/day) than in those without (207+/-16 mg/day). In the longitudinal study, the percent variation of AST correlated inversely with that of cyclosporine dose (r=-0.62, P=0.0002). CONCLUSION: Progressive graft injury leads to a reduction in the cyclosporine dose, particularly in patients with recurrent hepatitis C.

Inducibility of microsomal liver function may differentiate cirrhotic patients with maintained compared with severely compromised liver reserve

BACKGROUND AND AIM

Quantitative tests of liver function (QTLF) can be modulated by enzyme-inducing agents. The objective of the study was to examine changes in QTLF after treatment with Phenobarbital, a potent cytochrome P450-inducing agent.

METHODS

Forty-six consecutive patients with liver cirrhosis Child-Pugh score B and C (34 alcoholic, 12 hepatitis C) and a compromised aminopyrine breath test (ABT) were included. Thirty-six patients (group I) received phenobarbitone (150 mg) for 7 days. Ten patients (group II) received a placebo. The QTLF, which included ABT (microsomal liver function), galactose elimination capacity (GEC, cytosolic liver function), sorbitol clearance (SCl, liver plasma flow) and indocyanine green clearance (ICG, liver perfusion) was carried out before and after pharmacological induction.

RESULTS

Group I showed a basal ABT of 0.18 +/- 0.11% dose.kg/mmol CO2 (normal >0.6%), which increased significantly after induction (172%, P < 0.05), whereas in group II the ABT values did not change. In group IB, a subgroup of group I which exceeded the basal threshold value of 0.30% after stimulation (n = 22), the ABT values increased significantly to 0.44 +/- 0.17% (244%, P < 0.01). The GEC, SCl and ICG remained unchanged before and after induction.

CONCLUSIONS

After pharmacological induction, microsomal liver function increased significantly in a subgroup of patients with liver cirrhosis, whereas the GEC, SCl and ICG remained unchanged. Inducibility of the microsomal liver function could be used as a novel parameter of functional hepatic reserve and prognosis in cirrhosis.

Comparison of MEGX (monoethylglycinexylidide) and antipyrine tests in patients with liver cirrhosis

The aim of the study was to compare the feasibility of the MEGX (monoethylglycinexylidide) and antipyrine tests in reference to standard biochemical parameters used for liver assessment in cirrhotic patients. The study was carried out in 44 subjects: 14 healthy controls and 30 cirrhotic patients classified according to the Child-Pugh's score to subgroups A (n=11), B (n=12) and C (n=7). All subjects underwent two dynamic liver tests, i.e. MEGX (monoethylglycinexylidide) and antipyrine test in a crossover schedule with at least 5-day interval. For the MEGX, lidocaine was administrated intravenously, at a dose of 1 mg/kg, and blood samples for MEGX assay were collected after 15 minutes. MEGX concentrations were measured by fluorescence polarization immunoassay. The antipyrine concentrations were evaluated following a single oral administration of 1000 mg antipyrine. The blood was sampled for 24 hours after the drug administration, and antipyrine concentrations were measured spectrophotometrically. Standard biochemical parameters used for liver assessment were measured by means of routine laboratory methods. It was concluded that in patients liver with cirrhosis, liver dynamic tests were better predictors of hepatic function. The MEGX test was more feasible in clinical setting, but it was noted that antipyrine test was more sensitive in staging liver cirrhosis.

The influence of midazolam on plasma concentrations and pharmacokinetic parameters of lidocaine in rabbits

The object of this study was to investigate the influence of midazolam on the plasma concentrations and pharmacokinetic parameters of lidocaine in rabbits. Lidocaine levels were determined by the immunofluorescence polarization method, using Abbott reagents. After intravenous administration of a combined dose of midazolam (0.2 mg kg(-1)i.v.) with lidocaine (1 mg kg(-1)i.v.) a statistically perceivable decrease of lidocaine concentration, together with an increase of the constant rate of its elimination and reduction of the biological half-life with average time of lidocaine remaining in the system were observed. Midazolam administered intravenously together with lidocaine shortens the residence time of the drug.

Separation of lidocaine and its metabolites by capillary electrophoresis using volatile aqueous and nonaqueous electrolyte systems

The separation of the basic drug lidocaine and six of its metabolites has been investigated both by using volatile aqueous electrolyte system, at low pH and by employing non-aqueous electrolyte systems. In aqueous systems, the best separation of the compounds under the investigated conditions was achieved by using the electrolyte 60 mM trifluoroacetic acid (TFA)/triethylamine (TEA) at pH 2.5 containing 15% methanol. With this electrolyte, all seven compounds were well separated with high efficiency and migration time repeatability. The separations with bare fused-silica capillaries and polyacrylamide-coated capillaries were compared with higher separation efficiency with the latter. On the other hand, near baseline separation of all the seven compounds was also obtained by employing the non-aqueous electrolyte, 40 mM ammonium acetate in methanol and TFA (99:1, v/v), with comparable migration time repeatability but lower separation efficiency relative to the aqueous system.

13C breath tests: visions and realities

Breath tests have been used in research laboratories for over 25 y. Originally, the tests were based on the use of (14)C, rather than on the nonradioactive isotope, (13)C. When (13)C became widely available at a reasonable cost, research groups in the United States and Europe developed methodologies to measure (13)C abundance in samples of CO(2). The tests used a variety of substrates and measured pancreatic function, fat absorption, bacterial overgrowth and P(450) mixed-function oxidase. Thus far, the only test to be approved by the Food and Drug Administration is the (13)C-urea breath test. This manuscript describes the process by which approval is gained, and indicates the steps necessary for other tests to receive Food and Drug Administration approval.

The MEGX test: a tool for the real-time assessment of hepatic function

The dynamic liver function test based on the hepatic conversion of lidocaine to monoethylglycinexylidide (MEGX) can complement established static liver function tests if prognostic information is of particular interest. Because of its ease of use and rapid turnaround, the MEGX test has found widespread application for realtime assessment of hepatic function in transplantation, critical care medicine, and various experimental models. Lidocaine is metabolized primarily by the liver cytochrome P450 system through sequential oxidative N-dealkylation, the major initial metabolite in humans being MEGX. Because of the relatively high extraction ratio of lidocaine, this liver function test depends not only on hepatic metabolic capacity but also on hepatic blood flow. For the determination of MEGX in serum, an immunoassay based on the fluorescence polarization immunoassay technique high-performance liquid chromatography and gas liquid chromatography methods have been described. Whereas high-performance liquid chromatography and gas liquid chromatography are specific for MEGX, the fluorescence polarization immunoassay also cross-reacts with 3-OH-MEGX. Although this is not a problem in humans, some species, such as the rat, produce significant amounts of this metabolite. The findings of most studies published so far suggest that the MEGX test is a useful tool that can improve our decision-making process with respect to the selection of transplant candidates. Patients with a MEGX 15- or 30-minute test value <10 microg/L have a particularly poor 1-year survival rate. Serial monitoring of liver graft recipients early after transplantation with the MEGX test may initially alert the clinician to a major change in liver function; if used with other tests, such as serum hyaluronic acid concentrations, it may become more discriminatory. In critically ill patients, several studies have shown that an initially rapid decrease in MEGX test values is associated with an enhanced risk for the development of multiple organ dysfunction syndrome and a poor outcome. Further, this decrease appears to be associated with an enhanced systemic inflammatory response. The MEGX test has potential for investigating the pathogenesis of multiple organ dysfunction syndrome with regard to early hepatic functional impairment in critically ill patients after polytrauma or sepsis.

Quantitative testing of liver function in patients with cirrhosis due to chronic hepatitis C to assess disease severity

BACKGROUND/AIMS

Quantitative testing of liver function (QTLF) may allow a prognostic assessment of patients with various liver diseases. However, there are insufficient data about patients with liver cirrhosis due to hepatitis C.

PATIENTS/METHODS

86 consecutive patients (58 males, 28 females, age: 48.3 +/- 11.7 years) with chronic hepatitis C (HCV RNA pos.) underwent sonographically guided liver biopsy to confirm the diagnosis of cirrhosis. QTLF included aminopyrine breath test (microsomal liver function), galactose elimination capacity (cytosolic liver function), sorbitol clearance (liver plasma flow) and indocyanine green clearance (liver perfusion). Values were correlated with the Child-Pugh classification.

RESULTS

55% of the patients (n=47) had cirrhosis of Child-Pugh grade A, 28% of grade B (n=24) and 17% of grade C (n=15). QTLF showed a steady decrease from Child-Pugh grade A to grade B and to grade C. Contrary to markedly reduced tests of metabolic liver function in Child-Pugh grade patients, surrogate tests of hepatic perfusion were at the lower normal limit. All QTLF were significantly reduced in Child-Pugh grade B and C patients compared to healthy controls. Differences between the three Child grades were significant.

CONCLUSION

In patients with cirrhosis due to hepatitis C, QTLF correlated inversely with Child-Pugh grades. Since in cirrhosis of grade A, surrogate tests of hepatic perfusion remained at the lower normal limit, whereas those of metabolic function were decreased, QTLF may be a tool to predict prognosis or complications in early cirrhosis due to chronic hepatitis C.

The clinical importance of conventional and quantitative liver function tests in liver transplantation

The advantages and disadvantages of using monoethylglycinexylidide (MEGX), the major metabolite of lidocaine, as a probe of hepatic function in liver transplantation are reviewed. A 'real time' test of liver function should give a measure of current hepatocellular capacity rather than reflect past damage. The hepatic metabolism of lidocaine to MEGX is the basis of a flow-dependent dynamic test of liver function. In pre-transplantation patients, data from this MEGX test support its role in assessing the risk of morbidity and mortality. In assessing the liver transplant donor, there are differences concerning its apparent usefulness and these must be resolved. In the liver transplant recipient, this MEGX test is also useful for measuring real-time hepatic metabolizing activity, and low MEGX values reflect the clinical condition of the patient. At present, however, this test has several limitations. Therefore, a comprehensive evaluation, not only by the MEGX test but also by a combination of other conventional liver function tests (biochemical parameters, etc.), or with histological evaluation, is thought to be desirable for deciding whether a liver transplantation should be carried out or not.

Neuromuscular paralysis as a pharmacodynamic probe to assess organ function during liver transplantation

Potential for assessing liver function during liver transplantation surgery by monitoring muscle paralysis from nondepolarizing neuromuscular blockers that are hepatically cleared is critically assessed. Rocuronium is strongly favored as a promising pharmacodynamic probe for predicting allograft liver function because it is predominantly eliminated via the liver and its putative metabolites are not active. Prolongation of recovery from rocuronium paralysis is closely correlated with allograft liver function postoperatively. Vecuronium, pancuronium, and perhaps pipecuronium may also prove to be useful probes, but the two former blockers have active metabolites. Further prospective studies are necessary with more precise measurement of neuromuscular function to confirm the predictive value of this method. Alterations in neuromuscular blocker plasma concentrations that are correlated with changes in liver function and either the dose required or the intensity or duration of paralysis needs to be demonstrated for this technique to be clinically useful.

Histologic determinants of monoethylglycinexylidide formation in patients with chronic hepatitis C

Patients affected by chronic hepatitis C (CHC) display a peculiar histologic picture characterized by the presence of steatosis and bile duct damage in addition to evidence of inflammation, necrosis, and fibrosis. In the staging of these patients, functional evaluation may be considered a complementary tool. The monoethylglycinexylidide (MEGX) test has been used in diagnostic and prognostic assessment of chronic liver disease as a quantitative liver function test. In this study the authors evaluated whether different sampling times for the test could reflect different histologic patterns. The authors studied 82 patients with biopsy-proven CHC who underwent functional evaluation by means of MEGX test. The authors found that MEGX15 better reflected the histologic findings of necrosis and inflammation, and MEGX60 the presence of fibrosis. Neither steatosis nor bile duct damage showed a strong correlation with either sampling time. Moreover, MEGX levels showed a progressive decrease as histologic grading of chronic hepatitis progressively increased. Stepwise regression analysis identified necrosis and inflammation as histologic variables associated with both MEGX15 and MEGX30, and fibrosis as a variable associated with MEGX60. These results suggest that a decline in liver metabolic function corresponds to a progressive increase in liver damage, and that this circumstance should be taken into account when prescribing drugs to patients with CHC.

Potential use of pharmacological markers to quantitatively assess liver function during liver transplantation surgery

Early functioning of the transplanted liver is of crucial importance to the recipient. This function may be assessed by measuring the disposition of substances that are mainly eliminated via the liver. None of the agents currently used is ideal for this purpose. Measurement of mono-ethyleneglycinexylidide (MEGX) formation from lignocaine is useful and has been widely used in liver transplantation to assess liver graft function. MEGX formation can be affected by the use of drugs that influence liver perfusion or interfere with the CYP450 enzyme system. Indocyanine green clearance is a convenient method but both blood flow and hepatocellular function affect the test results. Tests of caffeine clearance, galactose elimination capacity and antipyrine clearance all require time-consuming, technically cumbersome and expensive serial blood sampling. The aminopyrine breath test is non-invasive, but gastric emptying and the patient's physical state affect results. The potential hazard of exposure to radioactive compounds limits the wide clinical use of both aminopyrine and erythromycin breath tests. Monitoring the rate of recovery from neuromuscular blockade induced by vecuronium and rocuronium can provide valuable information on liver function.

The monoethylglycinexylidide test for grading of liver cirrhosis

BACKGROUND

Monoethylglycinexylidide (MEGX) formation following lignocaine injection has recently been proposed as a simple dynamic liver function test based on a single measurement of its serum concentration.

AIM

To determine the optimal sampling time for MEGX determination.

METHODS

A modelling analysis of lignocaine and MEGX kinetics was performed in seven normals and in four patients with compensated liver cirrhosis; a similar study was performed in 74 cirrhotic patients, divided into two groups according to disease severity (Pugh score).

RESULTS

Only the MEGX fractional formation rate (kf) and formation delay (tau) were significantly altered in cirrhotic patients compared to normals: kf = 0.15 +/- 0.03 vs. 0.32 +/- 0.10 min-1 (mean +/- s.d.); tau = 7.7 +/- 2.0 vs. 3.9 +/- 2.9 min-1. A good correlation was found between kf and late (r = 0.82) but not early (r = 0.63) serum MEGX formation, suggesting that late measurements for the clinical MEGX test are preferred. In the second part of our investigation, by discriminant analysis of MEGX test data for 74 cirrhotic patients, the late MEGX concentrations gave the best discrimination between the two classes. In particular, the 60 min MEGX concentration showed the best diagnostic accuracy (81%), sensitivity (75%) and specificity (84%). The association of this with other MEGX parameters, either singly or derived from the whole curve measurements, did not improve the performance of the method.

CONCLUSION

The MEGX test, based on a single determination 60 min after lignocaine injection, may be regarded as a simple and sensitive quantitative liver function test.

Effect of hepatic insufficiency on pharmacokinetics and drug dosing

The liver plays a central role in the pharmacokinetics of many drugs. Liver dysfunction may not only reduce the plasma clearance of a number of drugs eliminated by biotransformation and/or biliary excretion, but it can also affect plasma protein binding which in turn could influence the processes of distribution and elimination. In addition, reduced liver blood flow in patients with chronic liver disease will decrease the systemic clearance of flow limited (high extraction) drugs and portal-systemic shunting may substantially reduce their presystemic elimination (first-pass effect) following oral administration. When selecting a drug and its dosage regimen for a patient with liver disease additional considerations such as altered pharmacodynamics and impaired renal excretion (hepatorenal syndrome) of drugs and metabolites should also be taken into account. Consequently, dosage reduction is necessary for many drugs administered to patients with chronic liver disease such as liver cirrhosis.

Prognostic value of generation of growth hormone-stimulated insulin-like growth factor-I (IGF-I) and its binding protein-3 in patients with compensated and decompensated liver cirrhosis

Our aim was to study the prognostic value of growth hormone (GH) -stimulated insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) generation in patients with compensated [group 1 (N = 8) with a Child-Pugh (CP) score of 5-8] and decompensated postnecrotic liver cirrhosis [group 2 (N = 7) with a CP score of 9-12]. Serum levels of IGF-I, GH-binding protein (GHBP), and IGFBP-3 were measured before and 24 hr after a single subcutaneous injection of recombinant human GH (rhGH, 0.14 units/kg). Patients (mean age 56 years) were followed prospectively for three years. Six patients (40%) died during the follow-up period, of whom half had a CP score <9. Mean serum IGF-I levels 24 hr after rhGH injection (group 1 vs group 2, 17.4 +/- 6.8 vs 7.4 +/- 0.7 nmol/liter) predicted survival with 93% accuracy. Levels <10 nmol/liter portended a poor prognosis, with 15% survival at one year, whereas levels >10 nmol/liter had a 100% survival rate at one and two years, respectively. Baseline IGF-I (9.98 +/- 2.0 vs 6.38 +/- 0.8 nmol/liter), GHBP (9.2 +/- 3 vs 5.7 +/- 0.8%/50 microl), and IGFBP-3 serum levels at baseline (1.7 +/- 0.3 vs 0.86 +/- 0.2 mg/liter) and at 24 hr (2.04 +/- 0.38 vs 0.99 +/- 0.3 mg/liter) did not add to the predictive value of stimulated IGF-I levels at 24 hr and were less accurate in predicting the outcome in comparison to CP score (80%). We conclude that stimulated IGF-1 <10 nmol/liter may be a true predictor of a negative prognosis in patients with liver cirrhosis.

Assessment of monoethylglycinexylidide as measure of liver function for patients with chronic viral hepatitis

The liver metabolizes lidocaine by oxidative deethylation to form monoethylglycinexylidide (MEGX), an analyte proposed as an index of liver function. We determined MEGX and lidocaine serum concentrations with the TDx (Abbott Laboratories) at baseline and 15, 30, 60, and 90 min after the intravenous administration of lidocaine (1 mg/kg), analyzing specimens from 12 apparently healthy volunteers and 40 patients with chronic viral hepatitis diagnosed by liver biopsy and serum tests. The patients were grouped on the basis of the histology activity index. The following laboratory tests were performed on serum specimens from all subjects: albumin (ALB), alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, total bilirubin, and prothrombin time. The results showed no significant difference among the four groups for the concentrations of MEGX, lidocaine, and lidocaine/MEGX at the four time points. However, the concentrations of ALB, ALT, AST, AST/ALT, and prothrombin time were substantially different among the four groups. Thus, we conclude that assay of MEGX in our patients with chronic viral hepatitis did not contribute to the assessment of liver function when compared with apparently healthy volunteers and traditional tests of liver function.

Xenobiotic-induced hepatotoxicity: mechanisms of liver injury and methods of monitoring hepatic function

Xenobiotic-induced liver injury is a clinically important etiology of hepatic disease that, if not recognized, can lead to hepatic failure. In this article we discuss the mechanisms of xenobiotic-induced liver injury, various factors that can alter the risk and severity of injury, the clinical and laboratory manifestations of injury, and the methods used to detect the presence of injury and (or) functioning liver mass.

An improved method for the measurement of lidocaine and its metabolites in rat plasma

An improved method is described for the quantitation of lidocaine and its dominant metabolites in rat plasma, 3-hydroxy-lidocaine glucuronide and 3-hydroxy-MEG-X glucuronide. Frozen plasma samples (100-200 microliters) were thawed and deproteinated by precipitation with acetonitrile, before the conversion of glucuronidates into their respective hydroxylated forms by acid hydrolysis. After extraction with solid-phase C18 cartridge chromatography, the metabolites and parent drug were analyzed by capillary gas chromatography-nitrogen phosphorus detection, without derivativization. A detection limit of 0.005 microgram/ml for lidocaine and nonglucuronidated metabolites and 0.01 microgram/ml for glucuronidated metabolites was achieved. The method offers significant improvements in sensitivity relative to existing techniques, which should be of specific benefit to studies in which sample volume is limited, such as those concerned with the pharmacokinetics of lidocaine metabolism in small-animal pain state models.

The use of lidocaine as a test of liver function in liver transplantation

The hepatic metabolism of lidocaine to monoethyl-glycinexylidide (MEGX) is the basis of a dynamic test of liver function. To understand its potential value in liver transplantation, the latter has been considered in the following three separate stages: pretransplantation assessment of potential candidates, potential liver donors, and the transplant recipient. In pretransplantation patients, data support its role in assessing risk of morbidity and mortality. In assessment of the liver transplant donor, there are differences concerning apparent usefulness, and these must be resolved. In the liver transplant recipient, serial measurements are useful to measure real-time hepatic metabolic activity. Low MEGX values reflect the clinical condition of the patient, and the importance of entirely assessing the patient, not just noting the test result, is paramount. This review has considered the role of the MEGX test in liver transplantation.

Lidocaine elimination and monoethylglycinexylidide formation in the dehydrated camel

The elimination kinetics and the formation of the monoethylglycinexylidide (MEGX), a major metabolite of lidocaine, were studied in camels deprived of water for 14 days. The study was conducted on four camels in a crossover design. Lidocaine was administered intravenously at a dose of 1 mg/kg to adult female camels when water was given ad libitum (stage 1) and to the same camels after 14 days of dehydration. Blood samples were taken up to 6 h after dosing. Serum lidocaine and MEGX levels were analysed by polarization fluorescence immunoassay. The elimination profiles of lidocaine and the formation of the metabolite MEGX in the two phases of the study were essentially identical. No difference in any pharmacokinetic parameter was noticed between normally hydrated and water-deprived camels. It is thus concluded that dehydration does not affect the cytochrome P450 isozymes involved in degradation of lidocaine to MEGX nor does it affect the hepatic blood flow, which is a major determinant in the clearance of lidocaine. The very low clearance of lidocaine in the camel in comparison with other ruminant or monogastric mammals may be associated with the camel's ability to survive drought in the desert.

Liver function tests

For optimal timing of liver transplantation and for the evaluation of new pharmacotherapeutic options, objective modalities for estimating the liver's functional reserve and prognosis in an individual patient are highly desirable. In the past a number of tests and several scoring systems have been proposed and validated to varying degrees for this purpose. The issues still to be clarified include: (1) any observed prognostic value of individual quantitative function tests and of scoring systems must be validated in independent, large enough and well defined patient populations; (2) it must be prospectively defined which (serially performed) quantitative test(s) add(s) prognostic information for the individual patient to the survival estimates defined by the more universally available scores and in which disease state(s); and (3) existing scoring systems must be validated, or new ones developed, that allow follow-up data to be used in order to adapt the original prognosis estimate to the evolution of the disease, e.g. during therapy.

Review article: quantitative tests of liver function

The search continues for a single reliable test of liver function that provides accurate prognostic information in chronic liver disease, in acute liver failure, and about graft function following orthotopic liver transplantation. Although transaminases, the commonly used markers of hepatocellular injury, have a high sensitivity in screening for liver disease, they do not provide any information about prognosis. Rational assessment of liver function using bilirubin, serum albumin and prothrombin-time is limited by the relative lack of sensitivity of these measurements and their inability to identify the functional reserve of the liver. Dynamic liver function tests are an improvement on the static tests but are generally cumbersome. The ideal liver function test would be cheap, easy to perform and analyse, safe, have a simple pharmacokinetic profile with minimal drug interactions, have a high predictive value and provide quick results. Numerous quantitative liver function tests have been developed and have shown promise in some studies. The aim of this review is to assess the place of these tests in the practical management of liver disease.

Pharmacokinetics of lidocaine and its major metabolite- monoethylglycinexylidide (MEGX) in rabbits with experimental common bile duct obstruction

The aim of this study was to evaluate, using an experimental model, the effect of obstructive cholestasis on the pharmacokinetics of lidocaine and the formation rate of its major metabolite- monoethylglycinexylidide (MEGX)-in rabbits. The investigation was carried out on 20 rabbits, randomly divided into two groups: a control one sham-operated and an experimental one-animals with biliary duct ligation. The measurements, i.e. laboratory and pharmacodynamic tests, as well as pharmacokinetic assays were performed prior to the operation as well as 10-12 days after the bile duct ligation. At the end stage of the study, livers were examined macro- and microscopically and biochemical analysis of the liver microsomes were performed. Lidocaine was given intravenously, as a bolus of 6 mg/kg. Blood for pharmacokinetic assay was sampled within 6 h following the drug administration, and MEGX concentration was evaluated 15 min after lidocaine had been administered. The immunofluorescence polarization method was employed for determination of lidocaine and MEGX concentrations. The one-compartment open model was used for calculations.