Metabolism of amylobarbitone in patients with chronic liver disease

Abstract

1 A single dose of amylobarbitone (3·23 mg/kg) was given by intravenous injection to each of ten healthy controls and two groups of five patients with chronic liver disease. A curve of serum amylobarbitone concentration against time was prepared for each subject and the proportion of the serum amylobarbitone bound to protein determined. The urinary excretion of the metabolite hydroxyamylobarbitone, ethyl (3 hydroxyisoamyl) barbituric acid was measured. 2 The degree of protein binding of serum amylobarbitone was reduced in the five patients (group I) with abnormally low concentrations of albumin in serum (3·5 g/100 ml). 3 The equation for a double exponential decay was fitted to the concentration/time curves for amylobarbitone free in the serum water. The mean intercepts and rate constants were used to calculate the dimensions of mathematical models based on a two compartment open system. 4 The five patients (group I) who had abnormally low concentrations of albumin in serum showed impairment of amylobarbitone metabolism; the rate constant β(h⁻¹) for the second exponential decay of serum amylobarbitone concentration was reduced (PPC_e ml/min) representing amylobarbitone elimination by metabolism was reduced. 5 The five patients (group II) who had normal concentrations of albumin in serum showed no impairment of amylobarbitone metabolism. Within the total patient group there were strong and significant positive correlations between the serum albumin concentration and each of the indices of the rate of amylobarbitone metabolism. 6 Both patient groups showed an increase in the first dispositional rate constant α(h⁻¹) and in the clearance (C_t ml/min) representing transfer between central and peripheral compartments. The physiological basis for this observation is uncertain. 7 The clinical response to the single intravenous dose of amylobarbitone was not significantly greater (P=0·11) in the patient group (I) with slow amylobarbitone metabolism than in the patient group (II) with a normal rate of amylobarbitone metabolism.