[15N]methacetin urine test to measure liver function: methodology for application in pediatrics

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.

Enzyme induction by drugs and toxins

Enzyme induction by drugs mostly concerns those enzymes involved in drug metabolism: cytochromes P-450, UDP-glucuronosyltransferases, glutathione S-transferases, gamma-glutamyltransferases and epoxide hydrolases. A large variety of molecular forms exists, but not all of them are inducible (e.g. the inducible cytochromes P-450 in man are members of family IA, IIA, IIC, IIE, IIIA). Induction is most common in the liver, but also occurs in other organs (lung, placenta, lymphocytes). Over the past 20 years a relatively small number of drugs and environmental chemicals have been identified as enzyme inducers, perhaps fewer than early studies suggested. Information on inducing properties must be obtained as early as possible during the development of a new drug and made available to clinicians and clinical chemists when the drug is marketed. The main consequences of enzyme induction are changes in pharmacokinetics of the drug itself or of an associated drug. Much progress has been made in methods to identify these inducers.

Assessment of lidocaine metabolite formation as a quantitative liver function test in children

Lidocaine, an aminoethylamide, undergoes deethylation in the liver after intravenous injection, resulting in the formation of monoethylglycinexylidide. Serum monoethylglycinexylidide concentration can be measured by a simple, rapid fluorescent polarization immunoassay. We sought to determine whether lidocaine metabolism, as indicated by monoethylglycinexylidide formation, could be used as a quantitative index of hepatic function. Therefore we measured monoethylglycinexylidide formation in 10 healthy children and in 28 children with chronic liver disease. Patients with chronic liver disease were divided by disease severity as being at low, moderate or high risk for deterioration based on a clinical scoring system for liver transplant candidates. In healthy controls, the peak monoethylglycinexylidide concentration 15 min after injection of lidocaine (1 mg/kg) was 97 +/- 12 micrograms/L (mean +/- S.E.). However, monoethylglycinexylidide concentration was decreased in 28 children with chronic liver disease (32 +/- 5 micrograms/L, p less than 0.001). Furthermore, this value was inversely proportional to the severity of liver disease. The mean difference in monoethylglycinexylidide concentration between the low-risk and high-risk groups was statistically significant (42 +/- 6 vs. 11 +/- 4 micrograms/L, respectively, p less than 0.01). We conclude that the rate of formation of the lidocaine metabolite monoethylglycinexylidide is decreased in patients with chronic liver disease and is inversely related to disease severity. Therefore measurement of monoethylglycinexylidide concentration after lidocaine injection may be used as a quantitative assessment of liver function in children. We speculate that monoethylglycinexylidide formation may be a useful prognostic index in children with liver disease.

[15N]methacetin urine test: a method to study the development of hepatic detoxification capacity

The [15N]methacetin urine test was used to study human O-demethylase activities to characterize the maturation of hepatic detoxification capacity. The study involved 43 healthy subjects aged 1 day-47 years. The urinary 15N elimination rates were measured following oral administrations of an aqueous [15N]methacetin solution. Age-dependent normal values of hepatic drug elimination capacity were established. Parameters were the 15N elimination half-life and cumulative elimination of the 15N dose as a percentage over a 9 h period. The maximum elimination rate (% dose/h) and peak time can give additional information. The 15N method is a simple, non-invasive and non-radioactive liver function test avoiding disadvantages of 14C and 13C breath tests. The [15N]methacetin test is suitable and useful in studying the hepatic development at birth and pathological changes of the microsomal detoxification capacity in early childhood.