In vivo and in vitro toxicodynamic analyses of new quinolone-and nonsteroidal anti-inflammatory drug-induced effects on the central nervous system

Effect of enoxacin, felbinac, and sparfloxacin on fatty acid metabolism and glucose concentrations in rat tissues

Multiple changes in metabolic levels could be useful for understanding physiological toxicity. To explore further risk factors for the convulsions induced by the interaction of nonsteroidal anti-inflammatory and new quinolone antimicrobial drugs, the effect of sparfloxacin, enoxacin, and felbinac on fatty acid metabolism and glucose concentrations in the liver, brain, and blood of rats was investigated. The levels of long-chain acyl-CoAs (C(18:1) and C(20:4)) in the liver and brain were decreased at the onset of convulsions induced by the coadministration of enoxacin with felbinac. Then, glucose concentrations in the liver and blood were decreased, whereas they were increased in a dose-dependant manner in the brain. However, the formation of acyl-CoAs and glucose levels in the liver, brain, and blood was not significantly influenced by enoxacin, felbinac, and sparfloxacin alone, respectively. The disturbance of both fatty acid metabolism and glucose levels might be associated with the increased susceptibility to convulsions, which may contribute to further understanding of the toxic effects associated with these drugs.

Quantitative comparison of the convulsive activity of combinations of twelve fluoroquinolones with five nonsteroidal antiinflammatory agents

Concomitant administration of certain fluoroquinolone antimicrobials and nonsteroidal antiinflammatory agents (NSAIDs) induces serious convulsion in humans. There are differences in convulsive activity among fluoroquinolones and in the potentiation of fluoroquinolone-induced convulsion among NSAIDs, but a comprehensive, quantitative comparison has not been carried out. This study evaluates the inhibitory effects of twelve fluoroquinolones (ciprofloxacin, enoxacin, fleroxacin, gatifloxacin, levofloxacin, lomefloxacin, norfloxacin, ofloxacin, pazufloxacin, prulifloxacin, sparfloxacin, and tosufloxacin) alone or in the presence of an NSAID (4-biphenylacetic acid, diclofenac sodium, loxoprofen, lornoxicam or zaltoprofen) on the GABA(A) receptor binding of [(3)H]muscimol in an in vitro study using mice synaptic plasma membrane. The rank order of inhibitory effects of the fluoroquinolones was prulifloxacin asymptotically equal to norfloxacin > ciprofloxacin > or = enoxacin > gatifloxacin > or = ofloxacin asymptotically equal to tosufloxacin asymptotically equal to lomefloxacin > levofloxacin > or = sparfloxacin > or = pazufloxacin asymptotically equal to fleroxacin. 4-Biphenylacetic acid most potently enhanced the inhibitory effects of the fluoroquinolones, while zaltoprofen, loxoprofen, lornoxicam and diclofenac had essentially no effect. The clinical risk of convulsion for each combination was estimated using a pharmacodynamic model based on receptor occupancy using the in vitro data set obtained and pharmacokinetic parameters in humans collected from the literature. The combinations of 4-biphenylacetic acid with prulifloxacin and enoxacin were concluded to be the most hazardous.

Effects of acute renal failure and ganciclovir on the pharmacodynamics of levofloxacin-induced seizures in rats

Seizures have been reported in patients receiving fluoroquinolones, including levofloxacin (LVFX). In the present study, we investigated the effects of experimental renal failure and the concomitant treatment with ganciclovir on the pharmacodynamics of LVFX-induced seizures to identify whether these factors can alter the pharmacokinetics or the pharmacodynamics of LVFX. Male Wistar rats received an intravenous infusion of LVFX at 250, 500, or 1000 mg/h/rat until the onset of seizures, and samples of serum, brain, and cerebrospinal fluid (CSF) were obtained. The concentration of LVFX in CSF at the onset of seizures was not affected by the infusion rate, whereas that in serum and brain increased with increasing infusion rate. This suggests that the concentration of LVFX in CSF is an appropriate index of the drug concentration at the site of action. The concentration of LVFX in CSF at the onset of seizures was significantly lower in rats with renal failure than in the control rats. Pretreatment with methylguanidine, an uremic toxin, at 600 mg/h/rat for 8 min reduced the concentration of LVFX in CSF at the onset of seizures and the total body clearance of LVFX after the intravenous injection. In rats pretreated with ganciclovir at 500 mg/h/rat for 1 h, the concentration of LVFX in CSF at the onset of seizures was significantly lower than the control rats. These results suggest that renal failure and ganciclovir can be the risk factors for LVFX-induced seizures, and that they increase the sensitivity of the central nervous system to LVFX-induced seizures.

Isobolographic analysis of the antinociceptive interactions between ketoprofen and paracetamol

The present study was undertaken to evaluate the antinociceptive interaction between paracetamol and ketoprofen. The antinociceptive effect of oral administration of the drugs alone or in combination was evaluated using the mouse abdominal constriction test. The data were interpreted by isobolographic analysis to establish the nature of the interaction. The effective dose that produced 50% antinociception (ED(50,mix)) was calculated from the log dose-response curve of fixed-ratio combinations of paracetamol with ketoprofen. This ED(50,mix) was compared to the theoretical additive ED(50,add) by isobolographic analysis. The experimental ED(50,mix) was found to be significantly smaller than the theoretically calculated ED(50,add), indicating a synergistic antinociceptive interaction between ketoprofen and paracetamol. Pharmacokinetic studies were carried out with mice treated with combined ketoprofen (12 mg/kg) and paracetamol (36 mg/kg). Plasma levels of ketoprofen were not changed by concurrent paracetamol treatment, and similarly no statistically significant difference was observed between paracetamol alone and the combination with ketoprofen. The pharmacokinetic analysis revealed that the combination of ketoprofen with paracetamol exerted a synergistic (supra-additive) interaction that was not associated with a pharmacokinetic interaction. The results of this study demonstrate significant synergism between ketoprofen and paracetamol.

Celecoxib does not induce convulsions nor does it affect GABAA receptor binding activity in the presence of new quinolones in mice

We sought to determine whether celecoxib would induce convulsions when coadministered with new quinolone antimicrobial agents in mice. The oral administration of celecoxib (500 mg/kg) alone or in combination with enoxacin (500 mg/kg), lomefloxacin (1000 mg/kg), ciprofloxacin (1000 mg/kg), or levofloxacin (1000 mg/kg) induced no convulsions in mice. In contrast, some nonsteroidal anti-inflammatory drugs (NSAIDs), fenbufen (200 mg/kg), indomethacin (500 mg/kg), and naproxen (500 mg/kg) induced convulsions in combination with the majority of the new quinolones tested. gamma-Aminobutyric acid (GABA)(A) receptor blockade-mediated neuronal excitation is assumed to be involved in these toxic convulsions. Enoxacin (100 microM) and lomefloxacin (100 microM) only slightly reduced [3H]muscimol binding to GABA(A) receptors in mouse whole brain membrane. However, these reductions were markedly enhanced by the addition of fenbufen (100 microM), indomethacin (100 microM), or naproxen (100 microM). Conversely, celecoxib (100 microM) had no apparent effect on [3H]muscimol binding when applied alone or in combination with enoxacin or lomefloxacin. These results suggest that celecoxib may be a more desirable anti-inflammatory agent with respect to drug interactions with new quinolones compared with some conventional NSAIDs.

Characterization of the interaction between a novel convulsant agent, norbiphen, and GABA(A) and other ligand-gated ion channels

A hybrid molecule composed of the antimicrobial, norfloxacin, linked to the non-steroidal anti-inflammatory drug (NSAID), biphenylacetic acid, which we have termed norbiphen, is a lethal convulsant in vivo and an antagonist of rodent GABA(A) receptors in vitro. In the present study, the selectivity, molecular site(s) and mechanism of action of this novel convulsant were investigated using electrophysiological techniques. Sub-maximal GABA-evoked currents recorded from rodent hippocampal neurons were reversibly inhibited by norbiphen (1 microM) to 5+/-2% of control whereas glutamate, NMDA and glycine activated responses were little or unaffected. Sub-maximal GABA-evoked currents recorded from oocytes expressing recombinant human alpha1beta2gamma2s or alpha1beta2 GABA(A) receptors were also reversibly inhibited by norbiphen (1-1000 nM) with an IC(50) (+/-s.e.m.) of 5.7+/-1 and 8.8+/-1 nM, respectively. Similarly, GABA currents recorded from alpha1beta1gamma2s, alpha1beta1 and beta2gamma2s receptors were inhibited with IC(50)s of 16.1+/-1, 18.8+/-1 and 4.2+/-1 nM, respectively. In contrast, norbiphen (100 nM) had little or no effect at rho1 GABA(C) homomers. At alpha1beta2gamma2s receptors, norbiphen had no affect on the GABA reversal potential, and inhibition was not voltage-dependent, suggesting that this compound does not act at the ion channel. The GABA concentration response curve was shifted in a competitive-like fashion by norbiphen (10-300 nM) and a Schild analysis of these data yielded a slope of 0.94+/-0.1 and a pA(2) of 7.77. Our data reveal a novel, selective and highly potent antagonist of GABA(A) receptors. Norbiphen should be a valuable agent in future studies of this receptor complex.

Behavioural effects of laparotomy and analgesic effects of ketoprofen and carprofen in rats

Rat behaviour was studied to develop a reliable method of determining the severity and duration of post-laparotomy pain, and to assess analgesic effects of ketoprofen or carprofen. Behaviour was studied in groups of ten animals 1 h following subcutaneous (s/c) saline (0.2 ml/100 g), ketoprofen or carprofen (5, 10 or 15 mg/kg) given either alone, or prior to surgery. The frequency of over 150 individual behavioural acts was calculated during the first post-treatment hour, the hour immediately prior to darkness, and the first 15 min of each of 5 subsequent hours. Discriminant analysis and analysis of variance isolated several easily recognizable behaviours which were markedly altered in frequency by surgery. These were unaffected by drug administration alone and were mainly transient, easily quantifiable activities; 'cat-like' back arching, horizontal stretching followed by abdominal writhing and twitching while inactive. Reductions in the frequency of these behaviours following surgery with analgesic treatment supported the hypothesis that they reflected post-operative pain. Ketoprofen and carprofen were equipotent and no dose related effects were apparent. Analgesic activity lasted between 4 and 5 h with the 5 mg/kg dosage, this being estimated from the duration of overall and specific behaviour differences between saline and drug treated animals. The data provided substantial evidence as to the usefulness of behavioural criteria for estimating pain severity, and for the first time, the basis of a system for routine pain assessment and management in rats subjected to abdominal surgery.