Effect of thioridazine on the first-pass kinetics of [14C]imipramine in perfused rat liver: interaction at hepatic binding sites.

1. The effect of thioridazine on the first-pass removal and hepatic metabolism of [14C]imipramine was examined in a single-pass rat liver perfusion system using a perfusate free of drug-binding components. Drug exposure continued for 45 min, and bile was collected and analysed during the final 15 min when approx. steady-state conditions were attained. 2. Thioridazine decreased the hepatic extraction ratio for imipramine, lowered the hepatic concentration (P < 0.1) and increased the effluent perfusate-to-liver ratios of imipramine. It is suggested that the increased imipramine in the effluent perfusate was due to competition of thioridazine for non-metabolizing binding sites in the liver rather than to inhibition of drug metabolism. 3. Thioridazine markedly increased desipramine concentrations in both liver and effluent perfusate. This may have resulted from decreased hepatic binding of imipramine, which made more free drug available for demthylation. Competition with thioridazine for hepatic binding sites also explains the increased diffusion of desipramine into the effluent perfusate. 4. Lower concentrations of 2-hydroxylated metabolites, especially 2-hydroxyimipramine, were found in bile when thioridazine was administered with imipramine. There was no evidence of inhibition of imipramine 2-hydroxylation. From bile-to-liver ratios, it is suggested that thioridazine and/or its metabolites inhibits glucuronylation of 2-hydroxyimipramine but not of 2-hydroxydesipramine.

Plasma sorbitol dehydrogenase determination in experimental hepatotoxicity using the Abbott Bichromatic Analyzer.

An automated single reagent micro-assay for the determination of sorbitol dehydrogenase (EC 1.1.1.14) catalytic activity concentration in mouse plasma was developed for the Abbott Bichromatic Analyzer (ABA-100). The kinetic rate determination was linear up to 250 U/l, had a CV of 2.65%, and required only 25 microliters of sample. Experimentally induced hepatotoxicity in the mouse by acetaminophen produced a dose dependent increase in blood sorbitol dehydrogenase activity.

Determination of amikacin in microlitre quantities of biological fluids by high-performance liquid chromatography using 1-fluoro-2,4-dinitrobenzene derivatization.

Pre-column derivatization of amikacin with 1-fluoro-2,4-dinitrobenzene in 25 microliter of guinea pig plasma or human serum produced a stable chromophore which was measured by UV detection after rapid separation on normal-phase or reversed-phase high-performance liquid chromatography systems. The reversed-phase system, selected for routine analysis due to instability of the normal-phase column, consisted of an Ultrasphere-ODS C18 column preceded by a guard column, and used acetonitrile--water (68:32) as the mobile phase. A high degree of linearity was found in the range of 2-64 microgram/ml with a coefficient of variation averaging less than 5%.

Hepatic effects of ketoconazole in the male Swiss Webster mouse: temporal changes in drug metabolic parameters.

There have been conflicting observations regarding the effects of ketoconazole on hepatic metabolism. The objectives of these studies were to determine whether ketoconazole was an enzyme inducer or inhibitor in the mouse and then to establish the time frame of these ketoconazole-induced enzyme changes. Ketoconazole was administered (150 mg/kg p.o. X 4 days) to male Swiss Webster mice. Biochemical observations over a period of 6 days following treatment indicated that ketoconazole had a temporal biphasic effect on the liver. Although liver weight and microsomal protein were elevated, all other parameters monitored were lower at 2 h following ketoconazole treatment. At 24 h after the last dose of ketoconazole, hepatic biochemical parameters (liver wt., % liver wt./body wt., microsomal protein, and cytochrome P-450) were statistically elevated, while enzyme activities (benzphetamine N-demethylation, 6 beta- and 7 alpha-hydroxylation of testosterone, formation of androstenedione and UDP-glucuronyltransferase) were inhibited. At 72 h the ketoconazole-induced changes in the hepatic biochemical parameters were comparable to those observed at 24 h, and enzymatic parameters generally appeared to be induced by ketoconazole, with the exception of benzphetamine N-demethylase and UDP-glucuronyltransferase, which exhibited lower enzyme activities. Ethoxyresorufin O-deethylase, 7 alpha-hydroxylation of testosterone and glutathione S-transferase, on the other hand, were unaltered by ketoconazole treatment. The opposing effects of ketoconazole on benzphetamine N-demethylase and ethylmorphine N-demethylase at 72 h were further examined. Enzyme kinetics studies indicated that ketoconazole did not effect the Michaelis constants (Km) of the two substrates, but the maximum velocity (Vmax) of the reactions was altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Ketoconazole-induced hepatic lysosomal phospholipidosis: the effect of concurrent barbiturate treatment.

An unusual hepatic phospholipidosis produced by repeated high doses of ketoconazole in the mouse was investigated. This abnormal phospholipid accumulation was dose dependent after seven days of daily oral treatment over a 150-350 mg/kg ketoconazole dose range. The accumulation continued after 21 days at the 250 mg/kg dose level. Ultrastructural and biochemical studies revealed that ketoconazole produced a hepatic lysosomal accumulation of concentric lamellar bodies, as typically produced by many cationic amphiphilic drugs. Ketoconazole administered orally in mice at 250 mg/kg also induced total hepatic protein, microsomal protein, cytochrome p-450, and ethylmorphine N-demethylation. Concurrent phenobarbital and ketoconazole administration appeared to further increase hepatic drug metabolizing parameters and to reduce the extent of the hepatic phospholipid accumulation.