Pregabalin: as adjunctive treatment of partial seizures

Pharmacotherapy for Focal Seizures in Children and Adolescents

Focal-onset seizures are among the most common forms of seizures in children and adolescents and can be caused by a wide diversity of acquired or genetic etiologies. Despite the increasing array of antiseizure drugs available, treatment of focal-onset seizures in this population remains problematic, with as many as one-third of children having seizures refractory to medications. This review discusses contemporary concepts in focal seizure classification and pathophysiology and describes the antiseizure medications most commonly chosen for this age group. As antiseizure drug efficacy is comparable in children and adults, here we focus on pharmacokinetic aspects, drug-drug interactions, and side effect profiles. Finally, we provide some suggestions for choosing the optimal medication for the appropriate patient.

Antiepileptic drugs in development pipeline: A recent update

Epilepsy is the most common neurological disorder which significantly affects the quality of life and poses a health as well as economic burden on society. Epilepsy affects approximately 70 million people in the world. The present article reviews the scientific rationale, brief pathophysiology of epilepsy and newer antiepileptic drugs which are presently under clinical development. We have searched the investigational drugs using the key words ‘antiepileptic drugs,’ ‘epilepsy,’ ‘Phase I,’ ‘Phase II’ and ‘Phase III’ in American clinical trial registers (clinicaltrials.gov), the relevant published articles using National Library of Medicine's PubMed database, company websites and supplemented results with a manual search of cross-references and conference abstracts. This review provides a brief description about the antiepileptic drugs which are targeting different mechanisms and the clinical development status of these drugs. Besides the presence of old as well as new AEDs, still there is a need of new drugs or the modified version of old drugs in order to make affected people free of seizures. An optimistic approach should be used to translate the success of preclinical testing to clinical practice. There is an urgent need to improve animal models and to explore new targets with better understanding in order to develop the novel drugs with more efficacy and safety.

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This review primarily focused on antiepileptic drugs under clinical development.

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The more realistic approach is needed to discover and develop the novel antiepileptic drugs.

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Modification of conventional drugs or search of newer targets can lead to development of promising antiepileptic drugs.

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To develop more efficacious and safe drugs for treatment of epilepsy and refractory seizures

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There are a number of novel antiepileptic compounds which are under various stages of drug development.

7-Nitroindazole, but not NG-nitro-L-arginine, enhances the anticonvulsant activity of pregabalin in the mouse maximal electroshock-induced seizure model

The objective of this study was to determine the effects of 7-nitroindazole (7NI--a preferential neuronal nitric oxide synthase (NOS) inhibitor) and NG-nitro-L-arginine (NNA--a non-selective NOS inhibitor) on the anticonvulsant action of pregabalin (PGB--a third-generation antiepileptic drug) in the maximal electroshock (MES)-induced seizure model in mice. Electroconvulsions were produced in mice by means of an alternating current (50 Hz, 500 V, 25 mA, ear-clip electrodes, 0.2 s stimulus duration, tonic hindlimb extension taken as the endpoint). The anticonvulsant action of PGB in the MES test was expressed as median effective doses (ED50 values) of the drug, protecting 50% of animals tested against MES-induced seizures. The acute adverse-effect potentials of PGB in combination with 7NI and NNA were evaluated in the chimney test (motor coordination), step-through passive avoidance task (long-term memory) and grip-strength test (skeletal muscular strength) in mice. 7NI (50 mg/kg, ip) significantly enhanced the anticonvulsant action of PGB by reducing the ED50 value of PGB from 145.0 mg/kg to 74.4 mg/kg (p<0.01). Similarly, 7NI at the lower dose of 25 mg/kg also potentiated the anticonvulsant action of PGB by lowering the ED50 value of PGB from 145.0 mg/kg to 117.9 mg/kg, although the results did not attain statistical significance. In contrast, NNA (40 mg/kg, ip) had no impact on the anticonvulsant effects of PGB. Moreover, none of the examined combinations of PGB with 7NI and NNA affected motor coordination, long-term memory and skeletal muscular strength in mice. Based on this preclinical study, one can conclude that 7NI significantly enhanced and NNA had no effect on the anticonvulsant activity of PGB against MES-induced seizures in mice.

Interaction of pregabalin with carbamazepine in the mouse maximal electroshock-induced seizure model: a type I isobolographic analysis for non-parallel dose-response relationship curves

PURPOSE

To characterize the anticonvulsant effects of pregabalin (PGB - a third-generation antiepileptic drug) in combination with carbamazepine (CBZ - a classical antiepileptic drug) in the mouse maximal electroshock (MES)-induced seizure model by using the type I isobolographic analysis for non-parallel dose-response relationship curves (DRRCs).

MATERIAL/METHODS

Tonic hind limb extension (seizure activity) was evoked in adult male albino Swiss mice by a current (sine-wave, 25mA, 500V, 50Hz, 0.2s stimulus duration) delivered via auricular electrodes. Potential adverse-effect profiles of interaction of PGB with CBZ at the fixed-ratio of 1:1 in the MES test with respect to motor performance, long-term memory, skeletal muscular strength and antinociceptive activity were measured along with total brain CBZ concentrations.

RESULTS

In the mouse MES model, PGB administered singly had its DRRC non-parallel to that for CBZ. With type I isobolographic analysis for non-parallel DRRCs, the combination of PGB with CBZ at the fixed-ratio of 1:1 exerted additive interaction. In the combination, neither motor coordination, long-term memory nor muscular strength were affected. PGB administered alone and in combination with CBZ exerted antinociceptive effects, whereas CBZ administered alone produced no antinociceptive activity in mice subjected to the acute thermal pain model. Pharmacokinetic estimation of total brain antiepileptic drug concentrations revealed that PGB had no impact on total brain concentrations of CBZ in experimental animals.

CONCLUSIONS

In conclusion, the additive interaction between PGB and CBZ is worthy of consideration while extrapolating the results from this study to clinical settings.

Pregabalin in the management of partial epilepsy

Pregabalin is a new antiepileptic medication that works by binding to alpha 2 delta subunit of the voltage-dependent calcium channels present in presynaptic neurons. Its pharmacokinetic advantages include rapid and almost complete absorption, lack of protein binding, linear kinetics, absence of enzyme induction, and absence of interactions with other drugs. Pregabalin was found effective as adjunctive therapy for refractory partial-onset seizures, with up to 51% responder at a dose of 600 mg/day. The lowest effective dose was 150 mg/day. Pregabalin is also approved for treatment of painful diabetic polyneuropathy, postherpetic neuralgia and pain with fibromyalgia. Studies also suggest a beneficial effect on sleep and generalized anxiety disorders. Its main adverse effects in randomized adjunctive trials in adults have been mild to moderate. Most common side effects were dizziness, ataxia, somnolence and diplopia. Weight gain was not prominent in pivotal pregabalin trials, but was more problematic in long-term postmarketing analyses in epilepsy patients. Pregabalin, with its potent antiseizure effect, favorable pharmacokinetic profile, and effectiveness in common co-morbidities is an important addition to the treatment of epilepsy.

Pregabalin for the management of partial epilepsy

Pregabalin is one of the latest antiepileptic drugs introduced for the treatment of partial epilepsy. Its efficacy and safety as adjunctive therapy in refractory partial epilepsy have been established in four double-blind placebo-controlled trials (n = 1396) and 4 long-term open-label studies (n = 1480). In 3 fixed-dose trials, the proportion of patients with a >/=50% reduction in seizure frequency across the effective dose-range (150-600 mg/day) ranged between 14% and 51%, with a clear dose-response relationship. Suppression of seizure activity could be demonstrated as early as day 2. The most frequently reported CNS-related adverse events included dizziness, somnolence, ataxia and fatigue, were usually mild or moderate, and tended to be dose related. In long-term studies, weight gain was reported as an adverse event by 24% of patients. When pregabalin dose was individualized to according to response within the 150 to 600 mg/day dose range, tolerability was considerably improved compared with use of a high-dose, fixed-dose regimen (600 mg/day) without titration. In long-term studies up to 4 years, no evidence of loss efficacy was identified. During the last year on pregabalin, 3.7% of patients were seizure-free. Pregabalin appears to be a useful addition to the therapeutic armamentariun for the management of refractory partial epilepsy.

Successful use of gabapentin in acute pain management following burn injury: a case series

Pain after burn injury has multiple qualities, including neuropathic and hyperalgesic elements. This element of the burn patients' pain experience is frequently difficult to manage and contributes significantly to their suffering. The onset may be either immediate or delayed. Gabapentin has established efficacy in the reduction of burn-induced hyperalgesia and allodynia in animal and human experimental burn models. This article reports a case series of six patients who, following admission to hospital with burn injury, described burning dysesthesia at either the injury or graft donor site. These patients were prescribed gabapentin in addition to standard analgesia. The use of gabapentin resulted in a rapid reduction in the severity of the neuropathic element of the pain. The medication was well tolerated, with no severe adverse reactions. Conclusions. This case series introduces the use of gabapentin as a potentially important therapy in the management of neuropathic pain following burn injury. Further research is required to define the use of gabapentin in this specific setting.

The opening effect of pregabalin on ATP-sensitive potassium channels in differentiated hippocampal neuron-derived H19-7 cells

PURPOSE

Adenosine triphosphate (ATP)-sensitive K+ (KATP) channels can couple an intracellular metabolic state to an electrical activity, which is important in the control of neuronal excitability and seizure propagation. We investigated whether the newer antiepileptic drug, pregabalin (PGB), could exert effects on KATP channels in differentiated hippocampal neuron-derived H19-7 cells.

METHODS

The inside-out configuration of the patch-clamp technique was used to investigate KATP channel activities in H19-7 cells in the presence of PGB. Effects of various compounds known to alter KATP channel activities were compared.

RESULTS

The activity of KATP channels in these cells was characterized. The single-channel conductance from a linear current-voltage relation was 78 +/- 2 pS (n = 8) with a reversal potential of 63 +/- 2 mV (n = 8), similar to that of KATP channels reported in pancreatic beta cells. 2,4-Dinitrophenol activated channel activity, but the further addition of glucose (20 mM) or glibenclamide (30 microM) could offset these increments. PGB significantly opened these KATP channel activities in a concentration-dependent fashion with a median effective concentration (EC50) value of 18 microM. A significant increase was noted in the mean open lifetime of KATP channels in the presence of PGB (1.71 +/- 0.04 to 5.62 +/- 0.04 ms).

CONCLUSIONS

This study suggests that in differentiated hippocampal neuron-derived H19-7 cells, the opening effect on KATP channels could be one of the underlying mechanisms of PGB in the reduction of neuronal excitability.

Pharmacokinetic Variability of Newer Antiepileptic Drugs

A new generation of antiepileptic drugs (AEDs) has reached the market in recent years with ten new compounds: felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, tiagabine, topiramate, vigabatrin and zonisamide. The newer AEDs in general have more predictable pharmacokinetics than older AEDs such as phenytoin, carbamazepine and valproic acid (valproate sodium), which have a pronounced inter-individual variability in their pharmacokinetics and a narrow therapeutic range. For these older drugs it has been common practice to adjust the dosage to achieve a serum drug concentration within a predefined 'therapeutic range', representing an interval where most patients are expected to show an optimal response. However, such ranges must be interpreted with caution, since many patients are optimally treated when they have serum concentrations below or above the suggested range. It is often said that there is less need for therapeutic drug monitoring (TDM) with the newer AEDs, although this is partially based on the lack of documented correlation between serum concentration and drug effects. Nevertheless, TDM may be useful despite the shortcomings of existing therapeutic ranges, by utilisation of the concept of 'individual reference concentrations' based on intra-individual comparisons of drug serum concentrations. With this concept, TDM may be indicated regardless of the existence or lack of a well-defined therapeutic range. The ten newer AEDs all have different pharmacological properties, and therefore, the usefulness of TDM for these drugs has to be assessed individually. For vigabatrin, a clear relationship between drug concentration and clinical effect cannot be expected because of its unique mode of action. Therefore, TDM of vigabatrin is mainly to check compliance. The mode of action of the other new AEDs would not preclude the applicability of TDM. For the prodrug oxcarbazepine, TDM is also useful, since the active metabolite licarbazepine is measured. For drugs that are eliminated renally completely unchanged (gabapentin, pregabalin and vigabatrin) or mainly unchanged (levetiracetam and topiramate), the pharmacokinetic variability is less pronounced and more predictable. However, the dose-dependent absorption of gabapentin increases its pharmacokinetic variability. Drug interactions can affect topiramate concentrations markedly, and individual factors such as age, pregnancy and renal function will contribute to the pharmacokinetic variability of all renally eliminated AEDs. For those of the newer AEDs that are metabolised (felbamate, lamotrigine, oxcarbazepine, tiagabine and zonisamide), pharmacokinetic variability is just as relevant as for many of the older AEDs. Therefore, TDM is likely to be useful in many clinical settings for the newer AEDs. The purpose of the present review is to discuss individually the potential value of TDM of these newer AEDs, with emphasis on pharmacokinetic variability.

Management of Focal-Onset Seizures

Focal-onset seizures are manifestations of abnormal epileptic firing of brain cells in a localised area or areas of the brain. The diagnosis of focal-onset seizures initially entails an EEG, a detailed history from the patient and eyewitnesses, as well as computer tomographic or, preferably, magnetic resonance imaging scans. Video EEG to record ictal events may be necessary to establish the correct diagnosis. Focal seizures are classified according to the International Classification of Epileptic Seizures and International Classification of Epilepsies and Epilepsy Syndromes. It is important to try to decide how the seizure event fits into this system in order to successfully evaluate and optimise treatment, as well as to give detailed information to the patient about their seizures and prognosis. Once the decision to treat the seizures has been made, the physician must choose which medication is the most appropriate to begin with. Carbamazepine, phenytoin or valproic acid (sodium valproate) are often rated as first-line drugs, but factors such as adverse-effect profiles, age, possibility of pregnancy, and concomitant diseases and medication also need to be considered. Most of the newer antiepileptic drugs (AEDs) appear to have good efficacy and better tolerability than the older agents, but evidence to support their superiority is scarce and has led to conflicting advice in several guidelines. Among the newer AEDs, lamotrigine, gabapentin, topiramate and oxcarbazepine have obtained monotherapy indication in many countries. The higher costs of the newer AEDs may inhibit their wider use, especially in poorer countries.

Can Pharmacokinetic Variability Be Controlled for the Patient??s Benefit?

The aim of this brief communication is to update our recent review on therapeutic drug monitoring (TDM) of the newer antiepileptic drugs (AEDs). The potential value of TDM is discussed in relation to their mode of action and their pharmacokinetic proper-ties. Data on the relationships between serum concentrations and clinical efficacy are limited, and few studies have been designed primarily to study these relationships. As yet there are no generally accepted target ranges for any of the new AEDs. For most drugs a wide range in serum concentration is associated with clinical efficacy,and there is a considerable overlap in serum concentrations related to toxicity and lack of clinical efficacy. Although the available documentation is clearly insufficient, the pharmacological properties of some of the drugs suggest that they may be suitable candidates for TDM. The primary role of TDM for both the newer and established AEDs is to identify an individual's optimum concentration and thus establish a reference value in that patient.