Studies on the toxic interaction between monensin and tiamulin in rats: effects on P450 activities.

Studies were carried out to investigate the effects of monensin and tiamulin, and the simultaneous administration of both compounds on microsomal enzymes in rats. In Phase I of the experiments the effects of monensin and tiamulin were studied separately (monensin 10, 30, and 50 mg/kg or tiamulin 40, 120, and 200 mg/kg body weight, respectively), while in Phase II the two compounds were administered simultaneously (monesin 10 mg/kg and tiamulin 40 mg/kg b.w., respectively). When monensin was administered by itself, it exerted no significant effect on microsomal liver enzymes. In a few cases, slight inhibition of certain enzyme activities was seen. Tiamulin provoked a dose-dependent hepatic enzyme induction. The combined administration of monensin and tiamulin at low doses (10 and 40 mg/kg, respectively) resulted in marked elevation of P450-related enzyme activities. The enzyme induction was more pronounced in females than in males. The results suggest that the simultaneous administration of tiamulin may influence the biotransformation of monensin, possibly increasing the amount of reactive metabolite(s) of the ionophore antibiotic.

Studies on the toxic interaction between monensin and tiamulin in rats: toxicity and pathology.

The characteristics of the toxic interaction between monensin and tiamulin were investigated in rats. A three-day comparative oral repeated-dose toxicity study was performed in Phase I, when the effects of monensin and tiamulin were studied separately (monensin 10, 30, and 50 mg/kg or tiamulin 40, 120, and 200 mg/kg body weight, respectively). In Phase II, the two compounds were administered simultaneously to study the toxic interaction (monensin 10 mg/kg and tiamulin 40 mg/kg b.w., respectively). Monensin proved to be toxic to rats at doses of 30 and 50 mg/kg. Tiamulin was well tolerated up to the dose of 200 mg/kg. After combined administration, signs of toxicity were seen (including lethality in females). Monensin caused a dose-dependent cardiotoxic effect and vacuolar degeneration of the skeletal muscles in the animals given 50 mg/kg. Both compounds exerted a toxic effect on the liver in high doses. After simultaneous administration of the two compounds, there was a mild effect on the liver (females only), hydropic degeneration of the myocardium and vacuolar degeneration of the skeletal muscles. The alteration seen in the skeletal muscles was more marked than that seen after the administration of 50 mg/kg monensin alone.

Possible involvement of the dopaminergic system in the mode of action of the potential antidepressant trazium esilate.

Trazium esilate (EGYT-3615) is structurally an as-triazino isoquinolinium salt which showed considerable activity in pharmacological tests characteristic for antidepressants (antagonism of tetrabenazine, potentiation of yohimbine, behavioral despair). The compound exhibited minimal sedative effect. Some findings suggest that it influences the central dopaminergic system. The drug potentiated actions of amphetamine such as stereotypy and hypermotility. It differentially blocked the hypothermic and the stereotypy inducing action of apomorphine. Trazium esilate also inhibited the cataleptic state provoked by bulbocapnine in mice. In higher dose it decreased the plasma prolactin level in rats. The compound potentiated the effect of norepinephrine on isolated vas deferens of the rat. Trazium esilate is a weak displacer on a1-, a2- and D2-receptors, however, it induced a2-receptor desenzitization after repeated treatment. It had no influence on rat brain cortical noradrenaline and striatal dopamine release evoked by high K+ concentration, but it increased the spontaneous dopamine outflow in rat striatum. The compound also elevated the striatal dopamine and DOPAC levels both after acute and chronic treatment.