Formation kinetics of the lidocaine metabolite (MEGX) in patients with chronic active hepatitis and cirrhosis

Objective: To evaluate the formation kinetics of monoethylglycinexylidide (MEGX), the principal lidocaine metabolite, in patients with chronic active hepatitis or cirrhosis. Design: The study was designed in order to identify the best timing of MEGX determination and to compare MEGX formation with indocyanine green (ICG), galactose and chenodeoxycholic acid clearances. Methods: Fifty subjects were studied: six healthy individuals, 22 patients with chronic active hepatitis and 22 patients with cirrhosis. Serum MEGX concentrations were evaluated 15 min after i.v. lidocaine administration (1 mg/kg) and every 30 min for 180min. MEGX formation was related to lidocaine kinetic and quantitative liver tests. MEGX determination was carried out by fluorescence polarization immunoassay on the TDX system. Results: Determination of MEGX concentrations could differentiate between chronic active hepatitis and cirrhosis (P <0.01). Blood samples taken at 30 min (MEGX₃₀) after lidocaine administration showed the higher relationships both with fractional formation half-life (r =0.508, P <0.001) and hourly area under the curve (r = 0.995, P <0.001) of this metabolite. In multivariate analysis, MEGX₃₀ showed significant correlation with lidocaine elimination rate half-life (P = 0.0097), chenodeoxycholic acid (P = 0.0001) and ICG (P = 0.039) clearances. Discriminant MEGX₃₀ cut-off values between chronic active hepatitis and cirrhosis, showed four functional levels normal (> 72 ng/ml), mild (72-50 ng/ml), moderate (49-18ng/ml) and severe (<18ng/ml) functional impairment, according to progressive degrees of liver damage. Conclusion. Determination of MEGX concentrations at 30 min after lidocaine infusion seems a suitable 'one-sample' dynamic liver function test. MEGX determination could be a useful test to check the evolution of the chronic active hepatitis in addition to cirrhosis.