Isobolographic analysis of interaction between drugs with nonparallel dose–response relationship curves: a practical application

The objective of this study was to characterize the anticonvulsant and acute adverse-effect potentials of topiramate (TPM) and gabapentin (GBP)—two second-generation antiepileptic drugs administered alone and in combination in the maximal electroshock (MES)-induced seizures and chimney test in mice. The anticonvulsant and acute adverse effects of the combination of TPM with GBP at the fixed ratio of 1:1 were determined using the type I isobolographic analysis for nonparallel dose–response relationship curves (DRRCs). To ascertain any pharmacokinetic contribution to the observed interaction between TPM and GBP, total brain concentrations of both drugs were determined. The isobolographic analysis of interaction for TPM and GBP, whose DRRCs were not parallel in both MES and chimney tests, was accompanied with a presentation of all required calculations allowing the determination of lower and upper lines of additivity. The isobolographic analysis revealed that TPM combined with GBP at the fixed-ratio combination of 1:1 interacted supraadditively (synergistically) in terms of suppression of MES-induced seizures, and simultaneously, the combination produced additive interaction with respect to motor coordination impairment (adverse effects) in the chimney test. The evaluation of pharmacokinetic characteristics of interaction for the combination of TPM with GBP revealed that neither TPM nor GBP affected their total brain concentrations in experimental animals, and thus, the observed interaction in the MES test was pharmacodynamic in nature. In conclusion, the combination of TPM with GBP, because of supraadditivity in the MES test and additivity in terms of motor coordination impairment in the chimney test as well as lack of pharmacokinetic interactions between drugs, fulfilled the criterion of a favorable combination, worthy of recommendation in further clinical practice.     

Isobolographic analysis of interactions between loreclezole and conventional antiepileptic drugs in the mouse maximal electroshock-induced seizure model

This study examined the interaction characteristics between loreclezole (LCZ) and various conventional antiepileptic drugs (phenytoin - PHT, carbamazepine - CBZ, valproate - VPA and phenobarbital - PB) in the mouse maximal electroshock (MES)-induced seizure model using isobolographic analysis. Drug-related adverse effects were ascertained by use of the chimney test (motor impairment) and the step-through passive avoidance task (learning and retrieval). It was observed that the combination of LCZ with VPA or PB, at the fixed ratio of 1:1, was supra-additive (synergistic) and the combination of LCZ with CBZ, at all fixed ratios tested (1:3, 1:1 and 3:1), was supra-additive against electroconvulsions. The remaining combinations evaluated, i.e., LCZ with PB or VPA at fixed ratios of 1:3 and 3:1, as well as all fixed-ratio combinations between LCZ and PHT, were additive in the MES test in mice. Pharmacokinetic characterization revealed that LCZ significantly increased both free plasma and brain concentrations of CBZ and PHT, but was without effect on PB. Moreover, a bi-directional pharmacokinetic interaction between LCZ and VPA was observed in that while LCZ increased free plasma, but not total brain VPA concentrations, VPA increased the total brain, but not free plasma LCZ concentrations. Adverse-effect testing revealed that for all antiepileptic drug combinations neither motor performance nor long-term memory was altered. Of the drug combinations investigated, only that of LCZ and PB at the fixed ratio of 1:1 was not associated with any pharmacokinetic interactions, and thus it may be concluded that the supra-additive (synergistic) isobolographic interaction was pharmacodynamic in nature. Furthermore, the fact that LCZ and PB have similar mechanisms of action would suggest that drugs with similar mechanisms of action may provide rational polytherapy regimens.The results of this study were presented in part at the 8th Congress of the European Federation of Neurological Societies, held in Paris, France, on 4--7 September 2004 [Abstract available in Eur J Neurol 11(Suppl 2): 227, 2004].     

Isobolographic analysis of interactions between losigamone and conventional antiepileptic drugs in the mouse maximal electroshock model.

The aim of this study was the isobolographic evaluation of interactions between losigamone (LSG), valproate (VPA), carbamazepine (CBZ), phenytoin (PHT), and phenobarbital (PB) in the maximal electroshock (MES) test in mice. Electroconvulsions were produced by means of an alternating current (ear-clip electrodes, 0.2-s stimulus duration, and tonic hindlimb extension taken as the endpoint). Adverse effects were evaluated in the chimney test (motor coordination) and the passive avoidance task (long-term memory). Brain concentrations of antiepileptic drugs (AEDs) were measured by immunofluorescence or high-performance liquid chromatography. Isobolographic analysis indicated synergistic interactions between LSG and VPA. For example, in the proportion of 1:1 the theoretically calculated 50% effective dose for additivity (ED(50add)) was 138 mg/kg, while the experimentally derived ED(50) for the mixture (ED(50mix)) was 85.2 mg/kg. The difference was significant at p<0.001. LSG combined with CBZ or PHT showed additivity, whereas the combinations of LSG with PB were either additive, for the fixed ratios of 1:3 and 1:1, or antagonistic for the ratio of 3:1 (ED(50add)=18.4 mg/kg versus ED(50mix)=26.7 mg/kg, p<0.05). Impairment of long-term memory was noted only in the case of VPA given at its ED(50), however this AED did not affect motor performance. LSG, CBZ, PHT and PB (applied at their ED(50) values) and co-administration of LSG with conventional AEDs (including VPA) impaired neither motor performance nor long-term memory. LSG did not affect the brain concentration of VPA or PB, but significantly elevated the brain concentrations of CBZ and PHT. In contrast, VPA, CBZ and PHT significantly increased the brain concentration of LSG, indicating a pharmacokinetic contribution to the observed pharmacodynamic interactions. Although LSG exhibited some favorable pharmacodynamic interactions with various AEDs, these were complicated by pharmacokinetic interactions and emphasize the importance of measuring AED concentrations in studies designed to identify desirable AED combinations.     

Interactions between zonisamide and conventional antiepileptic drugs in the mouse maximal electroshock test model.

Despite the major advances in antiepileptic drug (AED) therapeutics, about one third of patients with epilepsy still do not have adequate seizure control with currently available AEDs when prescribed as monotherapy. Typically, in this setting polytherapy with two or more AEDs is used. Zonisamide (ZNS) is a new AED effective in the treatment of refractory epilepsy and since it is only prescribed in polytherapy regimens, its interactions with other AEDs is of particular importance. The aim of this study was to isobolographically determine interactions between ZNS and four conventional AEDs: carbamazepine (CBZ), phenytoin (PHT), phenobarbital (PB), and valproate (VPA), in the mouse maximal electroshock (MES)-induced seizure model. The total brain concentrations of conventional AEDs and ZNS were measured with immunofluorescence and high-pressure liquid chromatography (HPLC), respectively, in order to determine any pharmacokinetic contribution in any observed interactions. With isobolography, synergistic interactions were observed for the combination of ZNS plus VPA and ZNS plus PHT at the fixed-ratio of 1:1, while additivity was observed for their combinations at the remaining dose ratios of 1:3 and 3:1. In contrast, the interactions between ZNS and PB and between ZNS and CBZ, applied at the fixed-ratios of 1:3, 1:1 and 3:1 proved to be additive. None of these AED combinations were associated with motor and long-term memory impairment. Furthermore, whilst brain AED concentrations were unaffected by ZNS, PHT significantly increased and PB reduced brain ZNS concentrations. Thus, the resultant interactions between ZNS and PHT and between ZNZ and PB were consequent to both pharmacodynamic and pharmacokinetic components. Finally, one can conclude that because of the synergistic pharmacodynamic interaction between ZNS and VPA, this combination might be useful in clinical practice.     

Interaction between lamotrigine and felbamate in the maximal electroshock-induced seizures in mice: an isobolographic analysis.

Isobolographic profile of interactions between lamotrigine (LTG) and felbamate (FBM), two second-generation antiepileptic drugs, against maximal electroshock (MES)-induced seizures, and neurotoxic adverse effects in the chimney test in mice were determined. LTG combined with FBM at the fixed ratios of 1:3, 1:1, and 3:1 exerted merely additive interactions against MES-induced seizures. In the chimney test, isobolography revealed that LTG coadministered with FBM at the fixed ratio of 1:1 displayed subadditivity (antagonism), whereas the remaining combinations tested (1:3 and 3:1) exerted additivity in terms of their neurotoxic side effects. LTG (at the dose of 2.3 mg/kg) coadministered with FBM (25.7 mg/kg) at the fixed ratio of 1:1 from the MES test did not impair long-term memory of mice challenged with the passive avoidance task. Furthermore, FBM (25.7 mg/kg) altered neither the free plasma nor brain concentration of LTG, hence pharmacokinetic events, which might affect the observed interactions in the MES test, are unlikely. Considering benefit indices for the respective fixed ratio combinations, it may be concluded that the combination of LTG with FBM at the fixed ratio of 1:1 is advantageous from a preclinical point of view, offering the highest benefit index reaching the value of 1.46. Likewise, the two-drug combination of 1:3 was also beneficial and is worth recommendation with benefit index amounting to 1.36. Only the combination of 3:1 was neutral with a benefit index of 1.08. Protection offered by LTG in combination with FBM against maximal electroconvulsions and its favorable neurotoxic side effect profile might provide the patients with intractable seizures with an efficacious treatment, as the rational polytherapy however, it requires to be clinically confirmed and verified.     

Three-dimensional isobolographic analysis of interactions between lamotrigine and clonazepam in maximal electroshock-induced seizures in mice

The anticonvulsant effects of lamotrigine (LTG) and clonazepam (CZP) and combinations thereof against maximal electroshock (MES)-induced seizures in mice were investigated using three-dimensional (3D) isobolographic analysis. With this method, the doses of fixed-ratio combinations of the drugs (1:3, 1:1 and 3:1) that elicited 16, 50 and 84% of the maximum anticonvulsant effect were determined. Additionally, to evaluate the characteristics of interactions observed with 3D isobolography, the brain concentrations of both drugs were verified pharmacokinetically. The 3D isobolographic analysis showed that LTG and CZP combined at the fixed ratios of 3:1 and 1:1 interacted synergistically in the MES test for all anticonvulsant effects between 16% and 84% of maximum. In contrast, the combination of LTG and CZP at the fixed ratio of 1:3 showed only pure additivity for all estimated effects in 3D isobolography. Moreover, none of the examined antiepileptic drugs altered the brain concentrations of the coadministered drug, so the observed interactions in the MES test are of a pharmacodynamic nature. The 3D isobolographic findings suggest that in epilepsy therapy, increased efficacy of seizure control (synergistic interaction) might be achieved by using LTG and CZP in combination. In this study, some important problems and assumptions related to statistical analysis of data in 3D isobolography are discussed.     

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.     

Interactions of tiagabine with some antiepileptics in the maximal electroshock in mice

Tiagabine (TGB), a new potent gamma-aminobutyric acid (GABA) uptake inhibitor, is widely applied in adjunctive treatment of partial seizures in humans. Although, polytherapy is not an initial method of epilepsy treatment, clinicians often combine TGB with other antiepileptics as add-on therapy for assuring the anticonvulsant protection in patients with refractory seizures. To evaluate the character of pharmacological interactions between TGB and some antiepileptics, the isobolographic analysis was used as a suitable method for determining the exact types of interactions. Determination of an influence of TGB on the protective effects of diphenylhydantoin (DPH), carbamazepine (CBZ), valproate (VPA), phenobarbital (PB), lamotrigine (LTG), topiramate (TPM), and felbamate (FBM) in maximal electroshock-induced seizures was essential for this study. To exclude or confirm a pharmacokinetic character of observed interactions, the free plasma and brain concentrations of antiepileptic drugs (AEDs) studied were evaluated by using the immunofluorescence or high-pressure liquid chromatography (HPLC).TGB (up to 2.5 mg/kg) remained ineffective upon the electroconvulsive threshold, whilst the drug in doses of 5 and 10 mg/kg significantly raised the electroconvulsive threshold in mice. According to the isobolography, TGB appears to act synergistically with VPA. The remaining combinations tested exerted additive interactions. A pharmacokinetic character of interaction between TGB and VPA was evidently corroborated either in plasma or brains. Moreover, TGB significantly reduced the plasma and brain concentrations of DPH; however, pharmacokinetic events were not accompanied by any changes in anticonvulsant activity of the latter. Finally, the isobolographic analysis revealed that combinations of TGB with VPA exerted synergistic (supra-additive) interaction resulting from a pharmacokinetic interaction.     

Influence of oxcarbazepine and methsuximide on lamotrigine concentrations in epileptic patients with and without valproic acid comedication: results of a retrospective study

The aim of this retrospective study was to investigate the influence of oxcarbazepine (OCBZ) and methsuximide (MSM) on lamotrigine (LTG) serum concentrations. The effect of OCBZ compared to carbamazepine (CBZ) and the effect of MSM on LTG serum concentrations were examined in patients with and without valproic acid (VPA) comedication. Altogether, 376 samples from 222 patients were analyzed in routine drug monitoring. Two or more serum samples from the same patient were considered only if the comedication had been changed. For statistical evaluation, regression analytical methods and an analysis of variance were performed. For the analysis of variance, the LTG serum concentration in relation to LTG dose/ body weight--level-to-dose ratio (LDR), in (microg/mL)/(mg/kg)--was calculated and compared for different drug combinations. The nonlinear regression analysis including the LTG dose per body weight, age, gender, and the different kinds of comedication revealed that these variables have a significant influence on LTG serum concentration (r2 = 0.724). The relationship between LTG dose/body weight and serum concentration deviates only slightly from linearity, the LTG concentration was about 18% lower in women than in men, and age had a significant influence. The data indicate that children have significantly lower LTG concentrations than adults on a comparable LTG dose per body weight and that children may be more prone to enzyme induction by comedicated drugs. Methsuximide has a strong inducing effect on the LTG metabolism and decreases the LTG concentrations markedly (about 70% compared to LTG monotherapy). Carbamazepine also reduces the LTG concentrations considerably (by 54%). The inducing effect of OCBZ (29%) was less pronounced but also significant. The inducing effect of MSM, CBZ, and OCBZ was also seen in combination with VPA: VPA alone increases the LTG concentration approximately 211%, whereas in addition to MSM (8%), CBZ (21%), or OCBZ (111%), the increase of LTG was significantly smaller. The analysis of variance confirmed the results of the regression analysis. The effect of MSM on the LTG concentration should be considered if MSM is added or withdrawn in patients treated with LTG. Oxcarbazepine had a less pronounced inducing effect on LTG metabolism compared to CBZ. If CBZ is replaced by OCBZ as comedication, an increase in LTG serum concentrations should be expected.     

Influence of concomitant antiepileptic drugs on plasma lamotrigine concentration in adult Japanese epilepsy patients

Lamotrigine (LTG) is an antiepileptic drug (AED) that was approved in Japan in 2008. We evaluated the influence of AEDs that induce hepatic enzymes (including phenytoin (PHT), phenobarbital (PB), carbamazepine (CBZ)), valproic acid (VPA), and various combinations of these drugs, on plasma LTG concentration in adult Japanese epilepsy patients. A total of 621 patients (mean age 34.4±11.8 years) were evaluated retrospectively. We calculated the concentration to dose ratio (CD ratio) for LTG with different AED regimens, and employed multiple regression analysis to determine factors influencing the LTG concentration. There was a linear correlation between the dose and concentration of LTG in patients treated with LTG (group I), LTG+VPA (group II), LTG+inducers (group III), or LTG+VPA+inducers (group IV). The mean CD ratio of patients on LTG monotherapy was 1.43±0.4 (μg/mL)/(mg/kg). When LTG was combined with VPA, the CD ratio increased about 2.2-fold, but there was no significant correlation between the CD ratio and VPA concentration. The mean CD ratios calculated in patients receiving LTG+PHT, LTG+PB, and LTG+CBZ were 0.56, 0.84, and 0.91, respectively. Addition of PHT significantly reduced the CD ratio in a concentration-dependent manner, in comparison with PB and CBZ (p<0.005 and p<0.001, respectively). Stepwise multiple regression analysis showed that the coefficient of determination of groups I, II, III, and IV were 0.94, 0.94, 0.90, and 0.91, respectively. In the clinical setting, these findings can help to estimate LTG concentrations and predict the inducing or inhibiting effects of concomitant AEDs.     

Population pharmacokinetics of lamotrigine with data from therapeutic drug monitoring in German and Spanish patients with epilepsy

This study develops a population pharmacokinetic model for lamotrigine (LTG) in Spanish and German patients diagnosed with epilepsy. LTG steady-state plasma concentration data from therapeutic drug monitoring were collected retrospectively from 600 patients, with a total of 1699 plasma drug concentrations. The data were analyzed according to a one-compartment model using the nonlinear mixed effect modelling program. The influences of origin (Germany or Spain), sex, age, total body weight, and comedication with valproic acid (VPA), levetiracetam, and enzyme-inducing antiepileptic drugs (phenobarbital [PB], phenytoin [PHT], primidone [PRM], and carbamazepine [CBZ]) were investigated using step-wise generalized additive modelling. The final regression model for LTG clearance (CL) was as follows: CL(L/h) = 0.028*total body weight*e(-0.713*VPA)*e0.663*PHT*e0.588*(PB or PRM)*e0.467*CBZ*e0.864*IND, where IND refers to two or more inducers added to LTG treatment; this factor as well as VPA, PHT, PB, PRM, and CBZ take a value of zero or one according to their absence or presence, respectively. The administration of inducers led to a significant increase in mean LTG CL (values of 0.045-0.070 L/h/kg vs. 0.028 L/h/kg being reached in monotherapy), whereas VPA led to a significant decrease in CL (0.014 L/h/kg). Thus, comedication with these analyzed drugs can partly explain the interindividual variability in population LTG CL, which decreased from the basic model by more than 40%. The proposed model may be very useful for clinicians in establishing initial LTG dosage guidelines. However, the interindividual variability remaining in the final model (clearance coefficient of variation close to 30%) make these a priori dosage predictions imprecise and justifies the need for LTG plasma level monitoring to optimize dosage regimens. Thus, this final model allows easy implementation in clinical pharmacokinetic software and its application in dosage individualization using the Bayesian approach.     

Influence of imperatorin on the anticonvulsant activity and acute adverse-effect profile of lamotrigine in maximal electroshock-induced seizures and chimney test in mice

The influence of imperatorin (IMP) on the anticonvulsant activity and acute adverse-effect potential of lamotrigine (LTG, a second generation antiepileptic drug) was studied in the maximal electroshock-induced seizure (MES) model and chimney test in mice. In order to assess the nature of interaction between IMP and LTG in the MES test, total brain LTG concentrations were evaluated with high-pressure liquid chromatography (HPLC). Results indicate that IMP administered ip, 30 min before the test, at a dose of 50 mg/kg significantly enhanced the anticonvulsant action of LTG in the MES test by reducing the median effective dose (ED(50)) of LTG from 6.11 to 2.47 mg/kg (p < 0.05). In contrast, IMP administered ip at doses of 30 and 40 mg/kg did not significantly potentiate the anticonvulsant activity of LTG against MES induced seizures, although a reduction of the ED(50) values for LTG from 6.11 to 5.77, and 4.28 mg/kg, respectively, was observed. On the other hand, IMP administered ip, at doses of 30, 40 and 50 mg/kg had no impact on the acute adverse effects of LTG, and the median toxic doses for LTG (TD(50)) were almost unchanged, ranging from 22.13 to 30.04 mg/kg in the chimney test. The protective index (TD(50) to ED(50) ratio) for LTG administered alone was 4.90 and increased to 5.21, 6.77, and 8.96 for LTG in combination with IMPat doses of 30, 40 and 50 mg/kg, respectively. Pharmacokinetic evaluation of total brain LTG concentration with HPLC revealed that IMP at the dose of 50 mg/kg did not affect total brain LTG concentration in experimental animals and thus, the observed interaction between IMP and LTG in the MES test was pharmacodynamic in nature. The present study demonstrates that IMP ameliorates the pharmacological profile of LTG, when considering both, the antiseizure and acute adverse effects of the drug in preclinical study on animals. The combination of LTG with IMPcan be of pivotal importance for epileptic patients as a potentially advantageous combination if it is proven that the results of this study can be extrapolated to clinical settings.     

Effects of combined lamotrigine and valproate on basal and stimulated extracellular amino acids and monoamines in the hippocampus of freely moving rats

The antiepileptic drugs sodium valproate (VPA) and lamotrigine (LTG) are increasingly used in combination in patients in whom monotherapy has failed to control seizures. Although these drugs are known to interact pharmacokinetically, several authors have proposed a pharmacodynamic interaction between the two. In order to investigate this we have studied the effects of combined treatment with LTG and VPA on basal and stimulated extracellular aspartate (ASP), glutamate (GLU), taurine (TAU), gamma amino butyric acid (GABA), 5-hydroxytryptamine (5-HT) and dopamine (DA) release in the hippocampus of freely moving rats using microdialysis. Additionally, we measured the possible effect of VPA on LTG in plasma, whole brain and dialysates. Neither LTG (10 mg/kg) nor VPA (300 mg/kg) given alone significantly altered basal levels of ASP, GLU or TAU. When given together, however, the two drugs significantly reduced extracellular ASP and GLU while increasing TAU levels. In the case of GABA, LTG was without effect on basal levels of the transmitter, but these increased following VPA and this persisted with both drugs. When transmitter release was stimulated by 50 M veratridine, marked increases in the release of all amino acids occurred and this was decreased by LTG in all cases. VPA alone only altered GABA release, increasing it by approximately the same extent as basal GABA. For all of the amino acids studied, however, VPA reversed the decreases in release seen after LTG. VPA and LTG increased and decreased respectively basal 5-HT and DA. When given together the increase in extracellular 5-HT was greatly prolonged, but no effect on DA release was seen. When 5-HT release was evoked by veratridine this was increased by VPA and no other treatment. With DA, however, neither drug alone altered evoked release, but the two combined led to a marked increase. Co-administration of VPA with LTG showed no significant effect of this combination on LTG in any of the three compartments studied indicating that in this case a significant pharmacokinetic contribution to our findings is unlikely, which suggests that there is a probable pharmacodynamic interaction of the two drugs.     

癫痫患者丙戊酸与拉莫三嗪药代动力学相互作用研究

目的 考察癫痫患者合用丙戊酸(VPA)与拉莫三嗪(LTG)的药代动力学相互作用.方法 将纳入的癫痫患者随机分为3组:VPA组276例、LTG组254例和合用组334例.VPA组患者每天口服VPA 500～1000 mg,LTG组每天口服LTG 100～200 mg,合用组用VPA+LTG.高效液相色谱-质谱联用法测定V...     

Effect of lamotrigine on the pharmacokinetics of carbamazepine and its active metabolite in dogs.

The effect of lamotrigine (LTG) on the pharmacokinetics of carbamazepine (CBZ) and its active metabolite; carbamazepine-epoxine (CBZ-E), was investigated in dogs. Five male dogs received CBZ (2 x 200 mg tab, p.o.) daily for a period of 1 week. After the end of this period, blood samples were collected serially for up to 24 hrs. After a wash-out period of I week, LTG (100 mg tab, p.o.) was coadministered with the CBZ dose (2 x 200 mg tab, p.o.) for 7 days. Blood samples were again serially collected and plasma levels of CBZ and CBZ-E were analysed by high performance liquid chromatography (HPLC). Concurrent administration of LTG with CBZ did not have any significant effect on the pharmacokinetic parameters of CBZ. There was also no significant difference between the plasma concentration ratio (CBZ-E to CBZ) vs time profiles in the two schedules of drug administration signifying the absence of pharmacokinetic interaction between LTG and CBZ or its active metabolite in this animal model.     

Pharmacokinetics of lamotrigine in paediatric and young adult epileptic patients—nonlinear mixed effects modelling approach

Purpose

The purpose of the study was to examine and describe adjunctive lamotrigine (LTG) pharmacokinetics in paediatric and young adult patients using a nonlinear mixed effects modelling (NONMEM) approach.

Methods

The study included 53 patients (age range 3–35 years) who were concomitantly treated with carbamazepine (CBZ) and/or valproic acid (VPA). A total of 70 blood samples corresponding to trough levels were available for analysis. Data were modelled, and the final model was evaluated using NONMEM and auxiliary software tools.

Results

The final LTG population model included the effects of concomitant drugs and patient’s weight (WT) which stratified the population into three groups: ≤25 kg, >25 to <60 kg and ≥60 kg. Based on the final model, the estimated LTG oral clearance (CL/F) for a typical patient weighing ≤25 kg, >25 to <60 kg or ≥60 kg who was concomitantly treated with CBZ was estimated to be 3.28, 4.23, or 7.15 l/h, respectively. If a patient was concomitantly treated with CBZ + VPA, the CL/F decreased on average by 69.5 % relative to LTG + CBZ co-therapy. VPA was found to decrease the LTG CL/F by 87.6 % compared to co-therapy with only CBZ.

Conclusion

The LTG population pharmacokinetic model developed in this study may be a reliable method for individualising the LTG dosing regimen in paediatric and young adult patients on combination therapy during therapeutic drug monitoring.     

Biphasic characteristic of interactions between stiripentol and carbamazepine in the mouse maximal electroshock-induced seizure model: a three-dimensional isobolographic analysis

The anticonvulsant effects produced by stiripentol (STP), carbamazepine (CBZ), and their combination in the maximal electroshock (MES)-induced seizures in mice were investigated using three-dimensional (3D) isobolographic analysis. With 3D isobolography, the combinations of both drugs at the fixed-ratios of 1:3, 1:1, and 3:1 for 16%, 50% and 84% antiseizure effects, respectively, were examined in order to evaluate the preclinical characteristics of the interactions between STP and CBZ. Additionally, to characterize precisely the types of interactions observed in the MES test, free plasma and total brain CBZ concentrations were estimated for all fixed-ratios tested. The 3D isobolographic analysis showed that STP and CBZ combined at the fixed-ratio of 1:3 produced supra-additive (synergistic) interactions in the MES test for the anticonvulsant effects ranging between 16% and 84%. In contrast, the combination of STP with CBZ at the fixed-ratio of 3:1 exerted sub-additive (antagonistic) interactions in 3D isobolography for all antiseizure effects examined in the MES test. Only the combination of STP and CBZ at the fixed-ratio of 1:1 was additive for the investigated effects (16%, 50% and 84%) in 3D isobolography. Pharmacokinetic evaluation of CBZ concentrations revealed that STP increased both free plasma and total brain CBZ concentrations for all fixed-ratio combinations tested (1:3, 1:1 and 3:1). In conclusion, the 3D isobolographic findings suggest that the combination of STP with CBZ exerted biphasic characteristics of interactions in the MES test, despite the pharmacokinetic increase in CBZ content in plasma and brains of experimental animals.     

Interactions between ACE inhibitors and classical antiepileptic drugs in the mouse maximal electroshock seizures

This study evaluated the effect of two angiotensin-converting enzyme (ACE) inhibitors, enalapril and cilazapril, commonly used antihypertensive drugs, on the protective efficacy of the classical antiepileptics — carbamazepine (CBZ), phenytoin (PHT), valproate (VPA) and phenobarbital (PB). For this purpose, we used the maximal electroshock seizure (MES) test in mice. Additionally, adverse effects of combined treatment with ACE inhibitors and antiepileptic drugs in the passive avoidance task and chimney test were assessed. All drugs were administered intraperitoneally. Neither enalapril (10, 20 and 30 mg/kg) nor cilazapril (5, 10 and 20 mg/kg) affected the threshold for electroconvulsions. Enalapril (30 mg/kg) but not cilazapril (20 mg/kg), enhanced the protective action of VPA, decreasing its ED₅₀ value from 249.5 to 164.9 mg/kg (p < 0.01). Free plasma (non-protein-bound) and total brain concentrations of VPA were not significantly influenced by enalapril. Therefore, the observed interaction could be pharmacodynamic in nature. The combinations of ACE inhibitors with other antiepileptics (CBZ, PHT, and PB) were ineffective in that their ED₅₀ values against MES were not significantly changed. Enalapril and cilazapril remained ineffective as regards memory retention in the passive avoidance task or motor performance in the chimney test. The current study suggests that there are no negative interactions between the studied ACE inhibitors and classical antiepileptic drugs. Enalapril was even documented to enhance the anticonvulsant activity of VPA.     

Evaluation of neurotoxic and neuroprotective pathways affected by antiepileptic drugs in cultured hippocampal neurons

In this study we evaluated the neurotoxicity of eslicarbazepine acetate (ESL), and of its in vivo metabolites eslicarbazepine (S-Lic) and R-licarbazepine (R-Lic), as compared to the structurally-related compounds carbamazepine (CBZ) and oxcarbazepine (OXC), in an in vitro model of cultured rat hippocampal neurons. The non-related antiepileptic drugs (AEDs) lamotrigine (LTG) and sodium valproate (VPA) were also studied. We assessed whether AEDs modulate pro-survival/pro-apoptotic pathways, such as extracellular-regulated kinase (ERK1/2), Akt and stress activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK).We found that neither ESL nor its metabolites, CBZ or LTG, up to 0.3 mM, for 24 h of exposure, decreased cell viability. OXC was the most toxic drug decreasing cell viability in a concentration-dependent manner, leading to activation of caspase-3 and PARP cleavage. VPA caused the appearance of the apoptotic markers, but did not alter cell viability. ESL, S-Lic and OXC decreased the levels of phospho-ERK1/2 and of phospho-Akt, when compared to basal levels, whereas CBZ decreased phospho-SAPK/JNK and phospho-Akt levels. LTG and VPA increased the phosphorylation levels of SAPK/JNK.These results suggest that ESL and its main metabolite S-Lic, as well as CBZ, LTG and VPA, are less toxic to hippocampal neurons than OXC, which was the most toxic agent.     

Isobolographic and behavioral characterizations of interactions between vigabatrin and gabapentin in two experimental models of epilepsy

The aim of this study was to characterize the pharmacodynamic, pharmacokinetic and adverse-effect profiles of vigabatrin and gabapentin. Isobolographic analysis was used in two mouse experimental models of epilepsy: the maximal electroshock seizure threshold test and pentylenetetrazole-induced seizures. In the maximal electroshock seizure threshold test, electroconvulsions were produced by a current with various intensities whilst in the pentylenetetrazole test a CD(97) dose (100 mg/kg) was used. Potential adverse-effect profiles of interactions of vigabatrin with gabapentin at three fixed-ratios of 1:3, 1:1 and 3:1 from both seizure tests were evaluated in the chimney (motor performance) and grip-strength (skeletal muscular strength) tests. Vigabatrin and gabapentin total brain concentrations were determined with high performance liquid chromatography. Vigabatrin and gabapentin administered singly increased the electroconvulsive threshold (TID(20) - 226.2 and 70.0 mg/kg, respectively). With isobolography, the combination of vigabatrin with gabapentin at the fixed-ratio of 1:3 exerted supra-additive (synergistic) interactions whilst at 1:1 and 3:1 additivity occurred. Similarly, vigabatrin and gabapentin administered singly suppressed the pentylenetetrazole-induced seizures (ED(50) values - 622.5 and 201.1 mg/kg, respectively). Isobolography revealed that vigabatrin with gabapentin in combination at the fixed-ratio of 1:1 produced supra-additive (synergistic) interaction whilst at 1:3 and 3:1 additivity occurred. In combination neither motor coordination nor skeletal muscular strength was affected. Total vigabatrin and gabapentin brain concentrations revealed that neither drug affected the pharmacokinetics of the other. Vigabatrin and gabapentin have a favorable pharmacodynamic interaction in animal seizure models in the absence of acute adverse effects or concurrent pharmacokinetic changes.