[Show abstract][Hide abstract] ABSTRACT: To evaluate the pharmacokinetic interactions between theophylline and antofloxacin in vivo and in vitro.
A randomized, 5-day treatment and 3-way crossover design was documented in 12 healthy subjects. The subjects were orally administered with antofloxacin (400 mg on d 1 and 200 mg on d 2 to 5), theophylline (100 mg twice a day and morning dose 200 mg on d 1 and 5), or theophylline plus antofloxacin. The plasma and urinary pharmacokinetics of antofloxacin and theophylline were characterized after the first and last dose. The effect of antofloxacin on theophylline metabolism was also investigated in pooled human liver microsomes.
The 5-day treatment with antofloxacin significantly increased the area of the plasma concentration-time curve and peak plasma concentration of theophylline, accompanied by a decrease in the excretion of theophylline metabolites. On the contrary, theophylline did not affect the pharmacokinetics of antofloxacin. In vitro studies using pooled human hepatic microsomes demonstrated that antofloxacin was a weak reversible and mechanism-based inhibitor of CYP1A2. The clinical interaction between theophylline and antofloxacin was further validated by the in vitro results.
The results showed that antofloxacin increases the plasma theophylline concentration, partly by acting as a mechanism-based inhibitor of CYP1A2.
[Show abstract][Hide abstract] ABSTRACT: Overexpression of P-glycoprotein may be involved in multidrug resistance of epilepsy, but the mechanisms are not clear. The aim of the studies was to investigate whether chronic exposure of antiepileptic drugs (AEDs) increased P-glycoprotein (P-gp) function and expression in brain of rats. Three drugs phenobarbital (PB), phenytion (PHT) and carbamazepine (CBZ) were orally given to rats twice a day for successive 21 days, P-gp activity in brain was assessed using the brain-to-plasma concentration ratios of rhodamine 123 (Rho 123) at 1 h following intravenous administration of 0.2 mg/kg. Immunohistochemistry was also used to analyze P-gp localization in rat brain regions. P-gp levels in the brain regions were further evaluated using western blot. The results showed 21-day exposure of AEDs resulted in significant decrease of tissue-to-plasma concentration ratios of Rho 123 in cerebral cortex and hippocampus without affecting their concentrations in plasma. Immunohistochemistry result showed that up-regulation of the P-gp mainly occurred in capillary endothelial vessels. Western blot result suggested that the protein level of P-gp in cortex and hippocampus of rats exposed to drugs was significantly higher than that of control rats. The P-gp levels were associated with P-gp activity in corresponding rats. All the results verified the hypothesis that chronic exposure of AEDs may increase P-gp function and level in brain of rats.
Full-text · Article · Aug 2008 · Journal of the Neurological Sciences
[Show abstract][Hide abstract] ABSTRACT: To investigate whether long-term exposure to four typical antiepileptic drugs (AEDs): phenobarbital (PB), phenytoin (PHT), carbamazepine (CBZ) and valproic acid (VPA) can increase P-glycoprotein (P-gp) level and function in primary cultured rat brain microvascular endothelial cells (rBMECs) in vitro, the rBMECs were incubated in culture medium containing indicated drugs (PB, PHT, CBZ, VPA and rifampin) for 60 days in a gradient concentration manner. Age-matched cells were incubated in normal culture medium. After a 60-day exposure to the indicated drugs, P-gp function and level in cells were measured using rhodamine 123 (Rho123) accumulations and Western blot analysis, respectively. Lower Rho123 accumulation in drug-treated cells was found than that in age-matched cells. Cyclosporin A (CsA) and verapamil (Ver) increased Rho123 accumulation both in drug-treated cells and age-matched cells. The magnitude of increased Rho123 accumulation in drug-treated cells was larger than that in age-matched cells. Higher P-gp levels were found to be consistent with decrease of Rho123 accumulation in drug-treated cells. The results verified the hypothesis that long-term exposure to the four antiepileptic drugs can induce P-gp function and level in rBMECs.
Full-text · Article · May 2008 · Neuroscience Letters
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to investigate whether diabetes mellitus (DM) affected breast cancer resistance protein (Bcrp) function and expression in rat brain. 5-week and 8-week diabetic rats were induced by streptozocin (STZ). Bcrp expression and function in brain cortex were assessed by western blot and measuring the brain-to-plasma concentration ratios of two typical substrates prazosin and cimetidine, respectively. The diabetic rats were treated with three different agents insulin, aminoguanidine (AG) and metformin (MET). It was found that the brain-to-plasma ratios of prazosin and cimetidine in diabetic rats were significantly higher than those of control rats, which were dependent on duration of diabetes. Lower levels of Bcrp were found in brain cortex of diabetic rats, which were in parallel with increase of brain-to-plasma ratios. Insulin treatment may attenuate the impairment of Bcrp expression and function induced by diabetes. Aminoguanidine and metformin treatment did not prevent the impairment of Bcrp function and expression in brain cortex of diabetic rats. All results gave a conclusion that STZ-induced DM may induce the impairment of function and expression of Bcrp in brain cortex, and lower levels of insulin may mainly contribute to Bcrp dysfunction in brain.
Full-text · Article · Jan 2008 · Biochemical Pharmacology