Pharmacodynamic and pharmacokinetic characterization of interactions between levetiracetam and numerous antiepileptic drugs in the mouse maximal electroshock seizure model: an isobolographic analysis.

PURPOSE: Approximately 30% of patients with epilepsy do not experience satisfactory seizure control with antiepileptic drug (AED) monotherapy and often require polytherapy. The potential usefulness of AED combinations, in terms of efficacy and adverse effects, is therefore of major importance. The present study sought to identify potentially useful AED combinations with levetiracetam (LEV) METHODS: With isobolographic analysis, the mouse maximal electroshock (MES)-induced seizure model was investigated with regard to the anticonvulsant effects of carbamazepine (CBZ), phenytoin, phenobarbital (PB), valproate, lamotrigine, topiramate (TPM), and oxcarbazepine (OXC), administered singly and in combination with LEV. Acute adverse effects were ascertained by use of the chimney test evaluating motor performance and the step-through passive-avoidance task assessing long-term memory. Brain AED concentrations were determined to ascertain any pharmacokinetic contribution to the observed antiseizure effect. RESULTS: LEV in combination with TPM, at the fixed ratios of 1:2, 1:1, 2:1, and 4:1, was supraadditive (synergistic) in the MES test. Likewise, the combination of LEV with CBZ (at the fixed ratio of 16:1) and LEV with OXC (8:1 and 16:1) were supraadditive. In contrast, all other LEV/AED combinations displayed additivity. Furthermore, none of the investigated LEV/AED combinations altered motor performance and long-term memory. LEV brain concentrations were unaffected by concomitant AED administration, and LEV had no significant effect on brain concentrations of concomitant AEDs. CONCLUSIONS: These preclinical data would suggest that LEV in combination with TPM is associated with beneficial anticonvulsant pharmacodynamic interactions. Similar, but less profound effects were seen with OXC and CBZ.

Levetiracetam selectively potentiates the acute neurotoxic effects of topiramate and carbamazepine in the rotarod test in mice.

The effect of levetiracetam (LEV) on the acute neurotoxic profiles of various antiepileptic drugs (carbamazepine [CBZ], phenytoin [PHT], phenobarbital [PB], valproate [VPA], lamotrigine [LTG], topiramate [TPM], oxcarbazepine [OXC], and felbamate [FBM]) was evaluated in the rotarod test, allowing the determination of median toxic doses (TD50 values) with respect to impairment of motor coordination in mice. The TD50 of LEV administered singly was 1601 mg/kg. Whilst LEV at 150 mg/kg, being its TID50 (a dose increasing the electroconvulsive threshold by 50%), was without effect with regards to motor coordination impairment associated with PHT, PB, VPA, LTG, OXC, and FBM, it significantly enhanced that associated with CBZ and TPM co-administration. Thus LEV (150 mg/kg) significantly decreased the TD50 of CBZ from 53.6 to 37.3 mg/kg (P<0.01) and that of TPM from 423 to 246 mg/kg (P<0.01). In addition LEV (75 mg/kg) significantly decreased the TD50 of TPM from 423 to 278 (P<0.01). That concurrent measurement of total brain LEV, CBZ, and TPM concentrations showed that concentrations were not significantly different when AEDs were administered singly compared to when they were administered in combination would suggest that there is no pharmacokinetic interaction between these AEDs. Thus, the observed potentialization of the acute neurotoxic effects of CBZ and TPM by LEV is the consequence of a pharmacodynamic interaction. These data support both experimental and clinical published data advocating that LEV may interact with some AEDs by pharmacodynamic mechanisms.

Synergistic interaction of gabapentin and oxcarbazepine in the mouse maximal electroshock seizure model--an isobolographic analysis.

The anticonvulsant effects produced by mixtures of oxcarbazepine and gabapentin (two second-generation antiepileptic drugs) in numerous fixed-ratio combinations of 1:1, 1:2, 1:5, 1:10, 1:15, and 1:20 were examined isobolographically in the mouse maximal electroshock seizure model. Results displayed that mixtures of both drugs at the fixed-ratios of 1:2, 1:5, 1:10, 1:15, and 1:20 exerted supra-additive (synergistic) interactions against electroconvulsions. Only a fixed-ratio of 1:1 was indifferent with isobolography, although the combination displayed the trend towards supra-additivity. Furthermore, the combinations of oxcarbazepine with gabapentin, administered at their median effective doses (ED(50 mix)s), did not alter motor performance of animals challenged with the chimney test. Additionally, neither gabapentin nor oxcarbazepine affected total brain concentrations of co-administered drug, indicating a pharmacodynamic nature of interaction between these antiepileptics. Finally, based on preclinical data presented here the combination of oxcarbazepine and gabapentin is of particular importance for further therapy in patients with refractory partial seizures.

Pharmacological and behavioral characteristics of interactions between vigabatrin and conventional antiepileptic drugs in pentylenetetrazole-induced seizures in mice: an isobolographic analysis.

To characterize the anticonvulsant effects and types of interactions exerted by mixtures of vigabatrin (VGB) and conventional antiepileptic drugs (valproate (VPA), ethosuximide (ESM), phenobarbital (PB), and clonazepam (CZP)) in pentylenetetrazole (PTZ)-induced seizures in mice, the isobolographic analysis for three fixed-ratio combinations of 1 : 3, 1 : 1, and 3 : 1 was used. The adverse-effect profile of the combinations tested, at the doses corresponding to their median effective doses (ED(50)) at the fixed-ratio of 1 : 1 against PTZ-induced seizures, was determined by the chimney (motor performance), step-through passive avoidance (long-term memory), pain threshold (pain sensitivity), and Y-maze (general explorative locomotor activity) tests in mice. Additionally, the observed isobolographic interactions were verified in terms of a pharmacokinetic interaction existence. VGB combined with PB or ESM exerted supra-additive (synergistic) interactions against the clonic phase of PTZ-induced seizures, which was associated with the increment of PB or ESM concentrations in the brains of examined animals. The remaining combinations tested (ie VGB+VPA and VGB+CZP) occurred additive in the PTZ test, which was associated with no significant changes in the brain concentrations of VPA and CZP. None of the examined combinations exerted motor impairment in the chimney test in mice. In the standard variant of passive avoidance task (current of 0.6 mA; 2 s of stimulus duration), the combinations of VGB+CZP and VGB+VPA significantly affected long-term memory in mice. Moreover, VGB in a dose-dependent manner lengthened the latency to the first pain reaction in the pain threshold test in mice. The modified variant of step-through passive avoidance task (current of 0.6 mA; stimulus duration based on the latency from the pain threshold test) revealed no significant changes in the long-term memory of animals for the combinations of VGB+VPA and VGB+CZP; so the observed effects in the standard variant of passive avoidance task were a result of the antinociceptive effects produced by VGB. In the Y-maze test, VGB also, in a dose-dependent manner, increased the general explorative locomotor activity of the animals tested. Similarly, the total number of arm entries in the Y-maze was significantly increased for the combinations of VGB+CZP and VGB+ESM, but not for VGB+PB and VGB+VPA. The application of VGB in combination with PB, ESM, CZP, and VPA suppressed the clonic phase of PTZ-induced seizures, having no harmful or deleterious effects on behavioral functioning of the animals tested, which might be advantageous in further clinical practice.

Effect of lamotrigine combined with felbamate on the horizontal (ambulatory) activity in mice.

Exploratory and spontaneous locomotor activities, after administration of some novel antiepileptic drugs (felbamate and lamotrigine alone or in combination), were evaluated in mice by means of the electronically monitored locomotor activity system (Digiscan analyzer). Felbamate (injected intraperitoneally, at the single dose of 25.7 mg/kg) significantly reduced behavioral activity in terms of horizontal (ambulatory) activity in mice. The combination of felbamate (25.7 mg/kg) with lamotrigine (2.3 mg/kg) drastically reduced this parameter during the first 15-min period (habituation to a novel environment--being the rate of exploratory locomotor activity) and the second 15-min interval (spontaneous locomotor activity). Moreover, neither the exploratory, nor spontaneous locomotor activity of the mice, were affected by lamotrigine (at the separate dose of 2.3 mg/kg) with respect to the ambulatory activity of the animals tested. Felbamate administered alone or combined with lamotrigine considerably impaired exploratory and spontaneous locomotor activities of the animals tested in terms of horizontal activity.

Modified western blot technique in fast detection of heme oxygenase (HO-1/HO-2) in various tissues and organs of experimental animals.

The present study was aimed at determining all indispensable conditions required to detect heme oxygenase (HO) with western blot technique. Our modified immunoblotting method allowed the detection of HO after 2 hours of electro-transferring onto nitrocellulose membranes that evidently shortened the time of research study without any loss of sensitivity and specificity to detect HO in various tissues and organs of experimental animals. HO was detected in the brain, heart, kidney, liver, lung, spleen, testis, and thymus of the examined mouse and rat, in a quantity for providing evidence that this modified immunoblotting technique is sensitive enough to elicit the existence of this enzyme in various animals' tissues and organs. In conclusion, our modified western blot method permits the fast detection of HO that may be useful in further more advanced quantitative studies.