Effect of valproate sodium on generalized penicillin epilepsy in the cat

Acute treatment with dexketoprofen reduces penicillin induced epileptiform activity in wistar albino rats (dexketoprofen in penicillin induced seizure model)

AIM

Dexketoprofen trometamol is one of the most commonly used anti-inflammatory analgesic agents for pain control. This study aims to investigate the effect of dexketoprofen on penicillin-induced epileptiform activity in rats.

METHOD

In this study, 28 male Wistar rats weighing 220-240 g were used. Tripolar electrodes were implanted under urethane anesthesia. Epileptiform activity was induced by micro-injection of 500 units (IU) penicillin into the rats' left somatomotor cortex. Dexketoprofen (5, 25, and 50 mg/kg) was administrated intraperitoneally after 30 min of penicillin injection. Epileptiform activity was evaluated by electrocorticography (ECoG).

RESULTS

The low dose of dexketoprofen administration (5 mg/kg) reduced the mean spike frequency of epileptiform activity 60 min after its injection. However, 25 and 50 mg/kg dexketoprofen significantly reduced the mean spike frequency 30 min after the dexketoprofen injection compared to the control group (p < 0.05). The amplitudes of epileptiform discharges in all groups were unaffected (p > 0.05).

CONCLUSION

This study revealed that dexketoprofen had a significant anti-seizure effect when applied at 5 mg/kg, 25 mg/kg, and 50 mg/kg (especially at 25 and 50 mg/kg), in the penicillin-induced seizure model. The obtained data revealed that dexketoprofen might play an essential role against epileptic seizures.

Systematic review of antiepileptic drugs' safety and effectiveness in feline epilepsy

BACKGROUND

Understanding the efficacy and safety profile of antiepileptic drugs (AEDs) in feline epilepsy is a crucial consideration for managing this important brain disease. However, there is a lack of information about the treatment of feline epilepsy and therefore a systematic review was constructed to assess current evidence for the AEDs' efficacy and tolerability in cats. The methods and materials of our former systematic reviews in canine epilepsy were mostly mirrored for the current systematic review in cats. Databases of PubMed, CAB Direct and Google scholar were searched to detect peer-reviewed studies reporting efficacy and/or adverse effects of AEDs in cats. The studies were assessed with regards to their quality of evidence, i.e. study design, study population, diagnostic criteria and overall risk of bias and the outcome measures reported, i.e. prevalence and 95% confidence interval of the successful and affected population in each study and in total.

RESULTS

Forty studies describing clinical outcomes of AEDs' efficacy and safety were included. Only two studies were classified as "blinded randomised controlled trials". The majority of the studies offered high overall risk of bias and described low feline populations with unclear diagnostic criteria and short treatment or follow-up periods. Individual AED assessments of efficacy and safety profile showed that phenobarbital might currently be considered as the first choice AED followed by levetiracetam and imepitoin. Only imepitoin's safety profile was supported by strong level of evidence. Imepitoin's efficacy as well as remaining AEDs' efficacy and safety profile were supported by weak level of evidence.

CONCLUSIONS

This systematic review reflects an evidence-based assessment of the published data on the AEDs' efficacy and safety for feline epilepsy. Currently, phenobarbital is likely to be the first-line for feline epileptic patients followed by levetiracetam and imepitoin. It is essential that clinicians evaluate both AEDs' effectiveness and tolerability before tailoring AED to the individual patient. Further studies in feline epilepsy treatment are by far crucial in order to establish definite guidelines for AEDs' efficacy and safety.

Feline generalized penicillin epilepsy

Feline generalized penicillin epilepsy represents an experimental model of generalized spike-and-wave discharges occurring during clinical absence attacks. Spike-and-wave discharges of feline generalized penicillin epilepsy also have a pharmacological profile that is similar to that encountered in human absence attacks. Studies on the respective roles played by the thalamus and cortex in the generation of spike-and-wave discharges indicate that both structures are important in the elaboration of such generalized activity. Moreover, GABAA-mediated, intracortical inhibitory mechanisms are preserved and eventually enhanced at a time when generalized spike-and-wave discharges of feline generalized penicillin epilepsy are recorded. A preservation of GABA-mediated mechanisms in pure absence epilepsy might explain the differences in prognostic outlook that characterizes this type of epilepsy from seizures in which GABAergic mechanisms break down (e.g., generalized convulsive and partial epileptic attacks).

Pharmacokinetics and pharmacodynamics of valproate analogues in rats. IV. Anticonvulsant action and neurotoxicity of octanoic acid, cyclohexanecarboxylic acid, and 1-methyl-1-cyclohexanecarboxylic acid

We examined the pharmacodynamics of valproate (VPA) and three structural analogues, octanoic acid (OA), cyclohexanecarboxylic acid (CCA), and 1-methyl-1-cyclohexanecarboxylic acid (MCCA) in rats. A pentylenetetrazol (PTZ) infusion seizure model was used to determine threshold convulsive doses of PTZ; the increase in PTZ threshold dose after administration of test compound was taken as an index of anticonvulsant activity. Each of the compounds investigated antagonized PTZ-induced seizures, with MCCA evidencing the highest potency. Both CCA and MCCA appeared to have an approximate twofold advantage relative to VPA in protective index (i.e., the ratio of concentrations that produce toxicity to concentrations that produce anticonvulsant effect), based on a rotorod assay of neurotoxicity. Examination of the time course of PTZ antagonism indicated that there was significant dissociation between pharmacokinetics and pharmacodynamics of VPA, with a marked delay in production of maximal anticonvulsant activity. In contrast, only a slight delay in production of maximal protection against PTZ-induced seizures was observed for MCCA, and no delay was evident for CCA. The data indicate that the dynamics of anticonvulsant action differ between these low-molecular-weight carboxylic acids despite their similar chemical structures.

Chemical models of epilepsy with some reference to their applicability in the development of anticonvulsants

This paper reviews chemical models of epilepsy and their relevance in the identification and characterization of anticonvulsants. For each convulsant we discuss possible modes of administration, clinical type(s) of seizures induced, proposed mechanism(s) of epileptogenesis and, where available, responsiveness of the induced seizures to anticonvulsants. The following compounds are reviewed: pentylenetetrazol, bicuculline, penicillin, picrotoxin, beta-carbolines, 3-mercaptopropionic acid, hydrazides, allylglycine; the glycine antagonist strychnine; gamma-hydroxybutyrate; excitatory amino acids (glutamate, aspartate, N-methyl-D-aspartate, quisqualate, kainate, quinolinic acid); monosubstituted guanidino compounds, metals (alumina, cobalt, zinc, iron); neuropeptides (opioid peptides, corticotropin releasing factor, somatostatin, vasopressin); cholinergic agents (acetylcholine, acetylcholinesterase inhibitors, pilocarpine); tetanus toxin; flurothyl; folates; homocysteine and colchicine. Although there are a multitude of chemical models of epilepsy, only a limited number are applied in the routine screening of potential anticonvulsants. Some chemical models have a predictive value with regard to the clinical profile of efficacy of the tested anticonvulsants. Some chemical models may contribute to a better understanding of possible mechanisms of epileptogenesis.

Animal models of the epilepsies

The study of mechanisms of the epilepsies requires employment of animal models. Choice of a model system depends upon several factors, including the question to be studied, the type of epilepsy to be modelled, familiarity and convenience. Over 50 models are reviewed. Major categories of models are those for simple partial seizures: topical convulsants, acute electrical stimulation, cortically implanted metals, cryogenic injury; for complex partial seizures: kainic acid, tetanus toxin, injections into area tempesta, kindling, rodent hippocampal slice, isolated cell preparations, human neurosurgical tissue; for generalized tonic-clonic seizures: genetically seizure-prone strains of mouse, rat, gerbil, fruitfly and baboon, maximal electroshock seizures, systemic chemical convulsants, metabolic derangements; and for generalized absence seizures: thalamic stimulation, bilateral cortical foci, systemic penicillin, gamma-hydroxy-butyrate, intraventricular opiates, genetic rat models. The lithium-pilocarpine, homocysteine and rapid repetitive stimulation models are most useful in studies of status epilepticus. Key findings learned from each of the models, the model's strengths and weaknesses are detailed. Interpretation of findings from each of these models can be difficult. Do results pertain to the epilepsies or to the particular model under study? How important are species differences? Which clinical seizure type is really being modelled? In a model are behavior or EEG findings only similar superficially to epilepsy, or are the mechanisms comparable? The wealth of preparations available to model the epilepsies underscores the need for unifying themes, and for better understanding of basic mechanisms of the epilepsies.

Epilepsy: relationships between electrophysiology and intracellular mechanisms involving second messengers and gene expression

It is well known that pure absence epilepsy is a benign form of seizure disorder, while most others, particularly partial and convulsive seizures may have transient or permanent deleterious consequences and are more difficult to bring under therapeutic control by anticonvulsants. The hypothesis is proposed that the preservation of GABA-ergic inhibition in absence attacks and its breakdown in most other seizures may explain these differences. Breakdown of GABA-ergic inhibition allows NMDA receptors to become active. This opens the way for Ca2+ to enter the cell. Such Ca2+ entry is a long-lasting phenomenon. It is likely to be massive during most seizures except during absence attacks, and may therefore damage the neuron transiently or permanently. It may even destroy it. Ca2+ entry is also a crucial factor in the activation of the second messenger cascade which involves cytosolic as well as nuclear (genomic) components. Activation of this cascade converts short-lived electrophysiological processes occurring at the membrane into much longer-lasting intracellular processes. These may include plastic changes at the synaptic and receptor level and may account for kindling and the increasing therapy-resistance of long-standing seizure disorders. Changes resulting from massive Ca2+ entry into the neuron may explain why most seizures, except absence attacks, may have deleterious consequences of various kinds, some short-lived, some of longer duration, and some even permanent.

Accumulation and washout kinetics of valproic acid and its active metabolites

There is growing evidence that the metabolites of valproic acid (VPA) may be pharmacologically active and could contribute to both the therapeutic and toxic effects of the drug. The accumulation and washout kinetics of VPA and its oxidative metabolites were, therefore, examined in five healthy volunteers. Valproic acid (250-mg capsules) was administered bid for 15 days. Blood samples were obtained periodically during the 15 days of drug administration and for seven days following termination of treatment. Urine was also collected over the final dosing interval. Steady-state serum concentrations of VPA were achieved within three to four days of treatment. The accumulation of all metabolites in serum lagged behind that of the parent compound, with the mono-desaturated metabolites accumulating more slowly than the hydroxylated species. Furthermore, the apparent washout half-life of each metabolite was longer than the elimination half-life of VPA. In general, the unsaturated metabolites were eliminated more slowly than the hydroxylated metabolites. The serum and urinary metabolite profiles of VPA observed in the healthy volunteers were comparable with those reported for epileptic patients. The differences in the disposition kinetics of VPA and of its potentially active metabolites may explain the previously observed dissociation between the pharmacokinetics and pharmacodynamics of the drug in epileptic patients.

Valproate metabolite concentrations in brain increase with chronic administration of sodium valproate

Rats were treated chronically with sodium valproate for varying periods of time up to eight weeks. A statistically significant negative correlation between plasma concentrations of valproate-derived substances (VDS) and length of treatment was observed while a statistically significant positive correlation was found between brain VDS concentration and length of treatment. Liver VDS concentrations showed a tendency to decrease with time but this trend was not statistically significant. A new procedure was developed to measure the tissue levels of VDS.

Differential participation of some 'specific' and 'non-specific' thalamic nuclei in generalized spike and wave discharges of feline generalized penicillin epilepsy

Extracellular single unit and electroencephalographic (EEG) activity during generalized spike and wave discharges (SW) induced by i.m. penicillin was recorded simultaneously in the cortex, in a 'specific' thalamic nucleus (n. lateralis posterior, LP) and in some 'non-specific' thalamic nuclei (n. centralis medialis, NCM; n. centrum medianum, CM; n. centralis lateralis, CL) Computer-generated EEG averages and histograms of single unit activity were triggered by either peaks of EEG transients or action potentials. The time at which cortical neurons (66/66) were most likely to fire was during the 'spike' of the SW complex while absence of firing was the rule during the 'wave'. Most LP neurons (23/26) showed a similar pattern, 3 cells firing preferentially during the 'wave'. In NCM only 17 of 39 neurons fired during the 'spike', 8 of 39 neurons during the 'wave' while the others showed no change in their firing pattern during SWs. Twenty-six of 30 CM and 20 of 24 CL neurons fired during the 'spike' of SW; the other cells in these nuclei did not change their firing pattern during SWs. When present, rhythmic fluctuations in firing linked to SW discharge were less prominent in these 'non-specific' thalamic nuclei than in cortex and LP. Furthermore, participation of NCM, CM and CL neurons in the SW rhythm occurred only after neurons in cortex and LP had become involved in it. Thus, as is the case for cortical neurons, the main firing pattern of thalamic cells during SWs consists of an oscillation between 'excitation' during the 'spike' and 'inhibition' during the 'wave' of the SW complex. However, the coupling between cortical and thalamic neuronal firing is less intimate for cells of the 'non-specific' thalamic nuclei than for a 'specific' nucleus such as LP. Thus, at least some 'specific' thalamic nuclei are more intimately involved in the mechanism of SW discharge than the midline intralaminar nuclei.

Behavioral alterations associated with generalized spike and wave discharges in the EEG of the cat

Instrumental conditioning procedures demonstrated that in feline generalized penicillin epilepsy (FGPE) the cat's ability to respond to sensory (visual or auditory) stimuli was selectively impaired during penicillin-induced generalized spike and wave (SW) discharge. Responsiveness between SW bursts remained unimpaired. Most often the performance deficit consisted of a total absence of a learned response to stimuli presented during SW bursts or, if such a response occurred, reaction times were on the average significantly longer than to stimuli presented between SW bursts. Stimuli falling in the middle of a SW burst were associated with the highest likelihood of response failure. Spontaneous motor performance which was not contingent on any stimulus was also impaired during SW discharge. Response failure during SW bursts is either attributable to a cognitive defect or to motor impairment associated with temporary amnesia. Impairment of motor performance unassociated with amnesia or a cognitive defect was sometimes present during SW discharge, as evidenced by failure to carry out a motor response or to complete it until the SW burst was over. These deficits are similar to those seen in human absence attacks associated with generalized SW discharge. These observations thus support the validity of FGPE as an acceptable model of human primary generalized epilepsy.

In vivo uptake of valproic acid into brain

The pharmacokinetics of valproic acid (VPA) penetration into the central nervous system of cats were studied. VPA levels in cortical gray matter and plasma were measured at timed intervals after rapid intravenous drug infusion. Brain uptake of the drug was maximal at 1 min postinfusion and decayed rapidly with a mean elimination half-life of 41 min. After a rapid distribution phase, plasma VPA levels remained stable for 90 min. The brain:plasma ratio was maximal at 1 min and also declined rapidly. The volume of distribution was 0.125 1/kg. The small volume of distribution, low brain:plasma ratios and rapid clearance from brain indicate that VPA is not significantly bound in cerebral cortex after a single dose.

Anticonvulsant and antiaggressive properties of di-n-propyl acetate after repeated treatment

Swiss albino mice were treated twice daily with 200 mg/kg (i.p.) di-n-propylacetate (DPA), for 14 days and sacrificed 15 hr after the last injection, with or without an additional injection of 400 mg/kg at 45 min before death. Without the additional injection, the brain distribution of GABA followed closely that of control mice; with the additional injection, the pattern of regional increase of brain GABA was very similar to that following an acute injection of DPA. The anticonvulsant and antiaggressive properties of DPA were similar in rodents treated acutely or additionally after repeated DPA treatment. Neither the anticonvulsant nor the antiaggressive properties could be observed 15 hr after the last of the repeated injections of DPA. A residual effect of DPA against seizures induced by pentetrazole was shown, i.e. a potentiation of the anticonvulsant properties of the second of two successive injections of DPA, the latter being given after the decrease of the GABA levels in whole brain to control values.

The presynaptic effects of valproic acid in the isolated frog spinal cord

The effects of the anticonvulsant valproic acid (n-dipropylacetate, DPA) on frog primary afferent fibers was examined with sucrose gap recordings from the dorsal roots. Addition of DPA to the superfusate consistently reduced the amplitude and duration of the dorsal root potential. In contrast, DPA augmented the depolarization of dorsal roots produced by GABA, beta-alanine and taurine. It also decreased afferent fiber 'desensitization' to GABA. DPA depressed the ability of K+ and the excitatory amino acids glutamate and aspartate to depolarize afferent fibers. In addition, the compounds decreased the amount of K+ released by tetanic stimulation of the dorsal root. The K+-evoked release of tritiated GABA from cord slices was initially reduced by exposure to DPA, but was then unaffected after a longer application of the anticonvulsant. On the other hand, the high affinity uptake of tritiated GABA and glycine were almost totally blocked by the addition of DPA to the incubating medium. In sum, DPA has complex effects on neuronal membranes. Some of these effects may serve to explain the anticonvulsant actions of this drug.

Electroencephalographic and behavioural effects of sodium valproate in patients with photosensitive epilepsy. A single dose trial

A single oral dose of Sodium valproate (VPA) given as Epilim (10 mg/kg) inhibited photoconvulsive responses, especially to 15--30 Hz frequency flicker, in seven out of ten patients with photosensitive epilepsy. In addition, in all patients (with an exception of one) the amplitude of the secondary slow negative wave of the visual evoked potentials was reduced 4--5 h after drug administration. However, in five of these patients the normalization of electrocortical reactions to a single flash and flickering light was accompanied by somnolence and fatigue, moderate slowing of EEG background, development of 3 Hz spike-wave activity and (in three patients) augmented response to hyperventilation. In two patients the EEG photoconvulsive discharge was exaggerated by VPA. There VPA effects suggest that photosensitivity and the underlying epileptic condition have overlapping albeit different pathophysiology. The data offer no support for the conclusion that reduced photosensitivity produced by VPA is associated with the therapeutic potency of the drug.

A multivariable evoked potential measure applied to human epilepsy

Based upon a three-dimensional plot (response plane) representing a condensation of human sensory evoked potential data obtained from a paired stimulus protocol, a study was undertaken to investigate electrophysiological changes following sodium valproate administration in subjects with photosensitive epilepsy. Initial results in two patients and two normal subjects suggest that the measure is reproducible and sensitive to electrophysiological changes accompanying anticonvulsant administration.