Prognostic value of the monoethylglycinexylidide test in pediatric liver transplant candidates

Liquid chromatographic method for the determination of lidocaine and monoethylglycine xylidide in human serum containing various concentrations of bilirubin for the assessment of liver function

A high-performance liquid chromatographic method is described for determination of lidocaine (2-(dietyloamino)-N-(2,6-dimetylofenylo) acetamid) and its metabolite, monoethylglycine xylidide (MEGX), in human serum containing various concentration of bilirubin. Lidocaine and its metabolite were extracted from human serum using dichloromethane. After separation of the layers and freezing at -32 degrees C, the organic layer was decanted and evaporated under a stream of nitrogen. The sample was dissolved in the mobile phase (12% acetonitrile in 15mM potassium dihydrogen orthophosphate, pH 3.0), and after separation on a Supelcosil LC-8-DB column, the analytes were measured by ultraviolet detection at 205nm. Trimethoprim (TMP) was used as the internal standard. The recovery of the examined analytes ranged from 95.7 to 97.9% for lidocaine and from 98.0 to 99.9% for MEGX. The lower limit of quantification (LLOQ) was established at 200microg/l for lidocaine and at 10microg/l for MEGX. The choice of suitable conditions for chromatographic separation of lidocaine and its metabolite MEGX allowed the elimination of the influence of endogenous bilirubin on the result of analysis.

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.

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.

Determination of monoethylglycinexylidide by fluorescence polarization immunoassay in highly icteric serum samples: modified precipitation procedure and HPLC compared

Hyperbilirubinemia, which frequently occurs in severe liver disease, interferes with the fluorescence polarization immunoassay (FPIA) monoethylglycinexylidide (MEGX) assay manufactured by Abbott Diagnostics. Because the MEGX test is particularly helpful in this clinical situation, strategies have been developed to overcome this problem. Precipitation of serum with the Abbott Digoxin II precipitation reagent eliminates bilirubin. Therefore, we compared FPIA results after precipitation of 81 icteric samples from 27 MEGX tests to results obtained using a validated HPLC method. The precipitation did not substantially alter the performance characteristics of FPIA: detection limit, 8 μg/L; between-days imprecision, 5.3–6.2%; recovery, 102–104% (50–200μg/L). This pretreatment of serum did not eliminate all interference, and only a poor correlation was observed between serum MEGX concentrations measured with HPLC or modified FPIA (r2 = 0.46; Sy‖x = 20.0 μg/L). In contrast, MEGX formation values calculated by subtraction of the prelidocaine MEGX concentration were in close agreement (r2 = 0.98; Sy‖x = 2.3 μg/L). Because only MEGX formation is clinically relevant, this modified FPIA procedure offers a simple and rapid alternative to HPLC.

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

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

Pediatric solid organ transplantation

Solid organ transplantation offers hope for long-term survival and more normal lifestyles for children. Many of the procedures used are scaled-down versions of those used in adults and are associated with distinct challenges in children. Recent studies have provided insights into how transplantation can best serve these patients.

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.