Felbamate demonstrates low propensity for interaction with methylxanthines and Ca2+ channel modulators against experimental seizures in mice

Caffeine impairs anticonvulsant effects of levetiracetam in the maximal electroshock seizure threshold test in mice

OBJECTIVES

Caffeine is the most widely used psychoactive substance in the world. Animal studies indicate that acute caffeine exposure at high doses may induce seizures and diminish the anticonvulsant activity of antiepileptic drugs (AEDs) at much lower doses. The aim of the current study was to assess the effect of caffeine on the anticonvulsant action of levetiracetam (LEV) and vigabatrin (VGB).

METHODS

The anticonvulsant activity of LEV and VGB was examined in the maximal electroshock seizure threshold test in mice (MEST test). All drugs were administered intraperitoneally by single injections, and caffeine was applied at doses capable of interfering with AEDs. Effects of caffeine exposure on AEDs were also investigated in tests of memory and motor performance.

RESULTS

Caffeine reduced the protective effect of LEV against electroconvulsions. Total brain concentration of LEV was unaffected by caffeine as well as inversely; LEV had no significant impact on the brain caffeine concentration, suggesting a pharmacodynamic nature of the interaction between LEV and caffeine in the MEST test. VGB at applied doses did not affect the convulsive threshold. Administration of VGB, but not LEV, alone or in combination with caffeine, impaired memory retention. In the chimney test, the combined treatment with AEDs and caffeine did not cause motor coordination impairment.

CONCLUSIONS

It is suggested that caffeine may negatively affect the anticonvulsant action of LEV in patients with epilepsy.

The Use of Caffeine by People with Epilepsy: the Myths and the Evidence

PURPOSE OF REVIEW

Caffeine is the most widely consumed central nervous stimulant. For people with epilepsy, it is often unclear whether drinking coffee carries a risk of triggering seizures.

RECENT FINDINGS

The relationship between caffeine, seizures, epilepsy, and anti-seizure drugs is not fully understood. Clinical studies are scarce. In animal models, caffeine can increase seizure susceptibility but can also protect from seizures. Effects seem dose-dependent and are influenced by the duration of intake and the developmental stage at which caffeine exposure started. Caffeine reduces the efficacy of several anti-seizure medications, especially topiramate. It is unclear how these findings, mainly from animal studies, can be translated to the clinical condition. At present, there is no evidence to advise people with epilepsy against the use or overuse of caffeine. Until clinical studies suggest otherwise, caffeine intake should be considered as a factor in achieving and maintaining seizure control in epilepsy.

Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption

Most individuals adjust their caffeine intake according to the objective and subjective effects induced by the methylxanthine. However, to reach the desired effects, the quantity of caffeine consumed varies largely among individuals. It has been known for decades that the metabolism, clearance, and pharmacokinetics of caffeine is affected by many factors such as age, sex and hormones, liver disease, obesity, smoking, and diet. Caffeine also interacts with many medications. All these factors will be reviewed in the present document and discussed in light of the most recent data concerning the genetic variability affecting caffeine levels and effects at the pharmacokinetic and pharmacodynamic levels that both critically drive the level of caffeine consumption. The pharmacokinetics of caffeine are highly variable among individuals due to a polymorphism at the level of the CYP1A2 isoform of cytochrome P450, which metabolizes 95% of the caffeine ingested. Moreover there is a polymorphism at the level of another critical enzyme, N-acetyltransferase 2. At the pharmacodynamic level, there are several polymorphisms at the main brain target of caffeine, the adenosine A2A receptor or ADORA2. Genetic studies, including genome-wide association studies, identified several loci critically involved in caffeine consumption and its consequences on sleep, anxiety, and potentially in neurodegenerative and psychiatric diseases. We start reaching a better picture on how a multiplicity of biologic mechanisms seems to drive the levels of caffeine consumption, although much more knowledge is still required to understand caffeine consumption and effects on body functions.

Caffeine and seizures: A systematic review and quantitative analysis

PURPOSE

Caffeine is the most commonly used central nervous system (CNS) stimulant. The relationship between caffeine, seizures, epilepsy, and antiepileptic drugs (AEDs) is complex and not fully understood. Case reports suggest that caffeine triggers seizures in susceptible people. Our systematic review reports on the relationship between caffeine, seizures, and drugs in animal and human studies. Quantitative analyses were also done on animal studies regarding the effects of caffeine on AEDs.

METHODS

PubMed was searched for studies assessing the effects of caffeine on seizure susceptibility, epilepsy, and drug interactions in people and in animal models. To quantify the interaction between AEDs and caffeine, the data of six animal studies were pooled and analyzed using a general linear model univariate analysis or One-way Analysis of Variance (ANOVA).

RESULTS

In total, 442 items were identified from which we included 105 studies. Caffeine can increase seizure susceptibility and protect from seizures, depending on the dose, administration type (chronic or acute), and the developmental stage at which caffeine exposure started. In animal studies, caffeine decreased the antiepileptic potency of some drugs; this effect was strongest in topiramate.

CONCLUSION

Preclinical studies suggest that caffeine increases seizure susceptibility. In some cases, chronic use of caffeine may protect against seizures. Caffeine lowers the efficacy of several drugs, especially topiramate. It is unclear how these findings in models can be translated to the clinical condition. Until clinical studies suggest otherwise, caffeine intake should be considered as a factor in achieving and maintaining seizure control in epilepsy.

Methylxanthines, seizures, and excitotoxicity

Clinical evidence, in particular the wide use of theophylline as a bronchodilator, suggests that methylxanthines can cause seizures in patients without known underlying epilepsy. Theophylline is also known to be an added risk factor for seizure exacerbation in patients with epilepsy. The proconvulsant activity of methylxanthines can best be explained by their antagonizing the brain's own anticonvulsant adenosine. Recent evidence suggests that adenosine dysfunction is a pathological hallmark of epilepsy contributing to seizure generation and seizure spread. Conversely, adenosine augmentation therapies are effective in seizure suppression and prevention, whereas adenosine receptor antagonists such as methylxanthines generally exacerbate seizures. The impact of the methylxanthines caffeine and theophylline on seizures and excitotoxicity depends on timing, dose, and acute versus chronic use. New findings suggest a role of free radicals in theophylline-induced seizures, and adenosine-independent mechanisms for seizure generation have been proposed.

Influence of aminophylline on the anticonvulsive action of gabapentin in the mouse maximal electroshock seizure threshold model

Accumulating evidence indicates that aminophylline [theophylline(2) x ethylenediamine] markedly attenuates the anticonvulsant action of conventional antiepileptic drugs in experimental animal models of epilepsy and evokes severe seizure activity in patients treated with this methylxanthine. The objective of this study was to determine the influence of acute (single) and chronic (twice daily for 14 consecutive days) treatments with aminophylline on the anticonvulsant potential of gabapentin (a second-generation antiepileptic drug) in the mouse maximal electroshock seizure threshold model. Additionally, the effects of acute and chronic administration of aminophylline on the adverse effect potential of gabapentin in terms of motor coordination impairment were assessed in the chimney test. To evaluate pharmacokinetic characteristics of interaction between drugs, total brain concentrations of gabapentin and theophylline were estimated with high-pressure liquid chromatography and fluorescence polarization immunoassay, respectively. Results indicated that gabapentin (at doses of 75 and 100 mg/kg, i.p.) increased the threshold for electroconvulsions in mice. Aminophylline in non-convulsive doses of 50 and 100 mg/kg (i.p.), both in acute and chronic experiments, did not attenuate the anticonvulsant potential of gabapentin in the maximal electroshock seizure threshold test in mice. Similarly, aminophylline at a dose of 100 mg/kg had no impact on the adverse effect potential of gabapentin in the chimney test. Pharmacokinetic evaluation of total brain concentrations of gabapentin and theophylline revealed no significant changes in total brain concentrations of the drugs after both, acute and chronic applications of aminophylline in combination with gabapentin. The data show that aminophylline did not alter the ability of gabapentin to protect mice against seizures induced by electroconvulsive shock. The observed interaction between gabapentin and aminophylline in both acute and chronic experiments was pharmacodynamic in nature.

Synergistic combinations of anticonvulsant agents: what is the evidence from animal experiments?

PURPOSE

Combination therapy is often used in the treatment of seizures refractory to monotherapy. At the same time, the pharmacodynamic mechanisms that determine the combined efficacy of antiepileptic drugs (AEDs) are unknown, and this prevents a rational use of these drug combinations. We critically evaluate the existing evidence for pharmacodynamic synergism between AEDs from preclinical studies in animal models of epilepsy to identify useful combinations of mechanisms and to determine whether study outcome depends on the various research methods that are in use.

METHODS

Published articles were included if the studies were placebo-controlled, in vivo, or ex vivo animal studies investigating marketed or experimental AEDs. The animal models that were used in these studies, the primary molecular targets of the tested drugs, and the methods of interpretation were recorded. The potential association of these factors with the study outcome (synergism: yes or no) was assessed through logistic regression analysis.

RESULTS

In total, 107 studies were identified, in which 536 interaction experiments were conducted. In 54% of these experiments, the possibility of a pharmacokinetic interaction was not investigated. The majority of studies were conducted in the maximal electroshock model, and other established models were the pentylenetetrazole model, amygdala kindling, and the DBA/2 model. By far the most widely used method for interpretation of the results was evaluation of the effect of a threshold dose of one agent on the median effective dose (ED50) of another agent. Experiments relying on this method found synergism significantly more often compared with experiments relying on other methods (p<0.001). Furthermore, experiments including antagonists of the AMPA receptor were more likely to find synergism in comparison with all other experiments (p<0.001).

CONCLUSIONS

Intensive preclinical research into the effects of AED combinations has not led to an understanding of the pharmacodynamic properties of AED combinations. Specifically, the majority of the preclinical studies are not adequately designed to distinguish between additive, synergistic, and antagonistic interactions. Quantitative pharmacokinetic-pharmacodynamic studies of selectively acting AEDs in a battery of animal models are necessary for the development of truly synergistic drug combinations.

Pharmacokinetic and pharmacodynamic interactions of aminophylline and topiramate in the mouse maximal electroshock-induced seizure model

The aim of this study was to determine the influence of acute (single) and chronic (twice daily for 14 consecutive days) treatments with aminophylline (theophylline(2).ethylenediamine) on the anticonvulsant potential of topiramate (a broad-spectrum antiepileptic drug) in the mouse maximal electroshock-induced seizure model. Additionally, the effects of acute and chronic administration of aminophylline on the adverse effect potential of topiramate were assessed in the chimney test (motor performance). To evaluate pharmacokinetic characteristics of interaction between topiramate and aminophylline, total brain concentrations of topiramate and theophylline were estimated with fluorescence polarization immunoassay technique. Results indicate that aminophylline in non-convulsive doses of 50 and 100 mg/kg (i.p.), both in acute and chronic experiments, markedly attenuated the anticonvulsant potential of topiramate by raising its ED(50) value against maximal electroconvulsions. Aminophylline at a lower dose of 25 mg/kg did not affect significantly the ED(50) value of topiramate in the acute experiment, but the drug markedly increased the ED(50) value of topiramate during the chronic treatment in mice. Only, aminophylline at 12.5 mg/kg, in both acute and chronic experiments, did not affect the antielectroshock action of topiramate in mice. Moreover, aminophylline at a dose of 100 mg/kg had no impact on the adverse effect potential of topiramate in the chimney test. Pharmacokinetic evaluation of total brain concentrations of topiramate and theophylline revealed that topiramate significantly increased total brain theophylline concentrations following both acute and chronic applications of aminophylline. Conversely, aminophylline did not alter total brain concentrations of topiramate in mice. Based on this preclinical study, one can conclude that aminophylline attenuated the antiseizure action of topiramate in the mouse maximal electroshock-induced seizure model and the observed interaction between drugs was both pharmacokinetic and pharmacodynamic in nature.