Conversion from thrice daily to twice daily administration of gabapentin (GBP) in partial epilepsy: analysis of clinical efficacy and plasma levels

Gabapentin has been administered in placebo-controlled studies with a thrice daily (T.I.D.) schedule, because of its short half-life. However, clinical efficacy does not seem strictly related to plasma levels: a twice daily (B.I.D.) schedule might therefore be possible. The aim of our study was to verify if the conversion from a T.I.D. to a B.I.D. regimen affected the efficacy and safety of gabapentin therapy. Out of 171 patients treated with add-on gabapentin, we selected 29 stable responders, who were followed for three months with a T.I.D. schedule and then switched to B.I.D. regimen for further three months. Seizure number, side-effects and trough plasma levels of gabapentin were collected during both periods. Gabapentin mean dose was 2117.2 mg/day. Mean number of seizures/months was: 4.2 at baseline, 1.0 during the T.I.D., and 0.9 during the B.I.D. period. Mean trough plasma level of gabapentin was 5.9 microgram/ml during the T.I.D. and 5.2 microgram/ml during the B.I.D. period. Twelve side-effects were reported by 11 patients during the T.I.D. and 6 by 5 patients during the B.I.D. period., sedation and vertigo were the most frequent in both. Results of our study suggest that gabapentin can be administered safely and effectively either with a T.I.D. and a B.I.D. regimen.

Refractory epilepsy: treatment with new antiepileptic drugs

Five antiepileptic drugs have been marketed in the last decade. We report here a retrospective study of patients attending our unit who were prescribed one of the new antiepileptic drugs. All these patients had refractory localization related epilepsy and had failed to respond to a first-line drug. The drugs had a different profile of side-effects but topiramate (42%) was the most common drug to be withdrawn due to side-effects as compared with tiagabine (26%), vigabatrin (16%), gabapentin (16%), and lamotrigine (15%). With regard to efficacy, 31% of the patients receiving gabapentin had a greater than 50% reduction in seizures compared with lamotrigine (25%), topiramate (20%), vigabatrin (19%) and tiagabine (11%). The number of patients remaining seizure free with gabapentin was 8% whilst for lamotrigine this was 5%, vigabatrin 5%, topiramate 1% and tiagabine 4%. In conclusion, all these five antiepileptic drugs are useful in treating refractory localization related epilepsy.

Asterixis induced by gabapentin

We report the case of a patient with postherpetic neuralgia who developed asterixis while being treated with gabapentin. We discuss the possible mechanism of asterixis in this patient.

The clinical pharmacokinetics of the new antiepileptic drugs

Because pharmacokinetics is a major determinant of the magnitude and duration of pharmacologic response, understanding the kinetic properties of the new antiepileptic drugs (AEDs) is essential for the correct use of these compounds in clinical practice. After oral administration, absorption is rapid and relatively efficient for the new AEDs, the most notable exception being gabapentin, whose bioavailability decreases with increasing dosage. None of the new AEDs is extensively bound to plasma proteins except for tiagabine, which is over 95% protein-bound. The route of elimination differs to an important extent from one compound to another, and elimination half-lives range from over 30 h for zonisamide to 5-7 h for gabapentin. For all drugs that are metabolized, half-life is shortened and clearance is increased when patients receive concomitant enzyme-inducing agents such as barbiturates, phenytoin, and carbamazepine. Lamotrigine metabolism is markedly inhibited by valproic acid, and felbamate may increase the serum levels of most other AEDs. Felbamate, topiramate, and oxcarbazepine may also reduce the efficacy of the contraceptive pill by stimulating its metabolism.

[The effect of gabapentin in bucco-facial allodynia. Experimental correlation of the trigeminal nerve]

INTRODUCTION

Trigeminal neuralgia is an unilateral alteration of the trigeminal nerve, characterized by recurrent paroxysms of pain in one or more of the nerve's branches. Trigger areas are described in points of the facial skin (allodynia).

OBJECTIVE

To evaluate the effects of gabapentin (monotherapy) and associated with carbamazepine in allodynia of trigeminal neuralgia.

PATIENTS AND METHODS

The effects of these drugs were studied in 14 patients with trigeminal allodynia and with 12 experimental cats, with microelectrodes of multiple connections in the central nervous system and in dental pulp to precipitate pain in injured zones, area of primary hyperalgesia, secondary hyperalgesia and allodynia zone. Unitary registrations and evoked potentials were evaluated in neuronal trigeminal organizations, encephalon, limic system and neocortex.

RESULTS

The pairing of innocuous stimulus (allodynia) plus painful stimulus precipitate classic conditioned reflex. Unitary alteration and evoked potentials correlated with learning and memory were evaluated, involving the hippocampus in the results. The allodynia treatment obtains better results with the combined treatment than with the monotherapy.

CONCLUSIONS

Allodynia can be the result of a neuronal sensitization due to the increment on intracellular calcium facilitating the exocytosis. Changes in the mechano-receptors of low threshold establish communication with nociceptive neurons by a presynaptic mechanism, considering new synaptic and morphologic contacts associated with learning and memory. The major effectiveness in the combined treatment is the base of an association of the gabaergic mechanism of gabapentin and the blockade of sodium and potassium ionic channels by the carbamazepine.

Gabapentin as an adjunct to standard mood stabilizers in outpatients with mixed bipolar symptomatology

Gabapentin is a new adjunctive medication to antiseizure therapies. Anecdotal evidence suggests that it may also help to alleviate mood symptoms in patients with bipolar illness. An open-label study examined the effects of adjunctive gabapentin in bipolar patients with mixed symptoms who had previously demonstrated only partial treatment responses. Mood ratings and side-effect profiles were followed weekly in 10 patients for 1 month. Decreases in Hamilton depression (P < 0.05) and Bech mania ratings (P < 0.01) were evident in the first week of treatment and were sustained. Potent early improvements were noted in early, middle, and late insomnia. The results suggest that gabapentin may be of benefit to bipolar patients who only partially respond to other mood stabilizers. A favorable side-effect profile and rapid action make this drug an attractive choice as an adjunctive therapy.

How can physicians and their patients with ALS decide to use the newly-available treatments to slow disease progression?

The 1990s decade has seen the testing of treatments to slow disease progression in patients with ALS. Two such treatments (riluzole and myotrophin) have shown minimal or modest efficacy. Of these, riluzole has been approved for marketing in the United States, in Europe and in other countries. Patients and physicians who are trying to decide whether to use these treatments require background information: (a) to place these treatments in the context of other treatments; (b) to understand the outcome measures used; and (c) to understand the significance of the efficacy these treatments have shown. For example, in some cases treatment efficacy has been shown by some measures, but not others. This paper attempts to assist in this process. In addition, we attempt to show how to integrate objective data with relative or subjective factors, such as patient values, economic considerations, and the role of hope.

A case of sustained massive gabapentin overdose without serious side effects

Gabapentin is an antiepileptic agent that is indicated for use as adjunctive therapy for partial seizures. It has a relatively benign side effect profile, but little data exists on massive overdoses with this agent. The authors present a case of a patient who received a massive overdose of this agent but suffered no clinically significant toxicity.

New treatments of bipolar disorder

This clinical trials review is derived from the presentations made at the Third International Conference on Bipolar Disorder, held June 17-19, 1999 in Pittsburgh, PA, published as abstracts in Bipolar Disorders: An International Journal of Psychiatry and Neurosciences, Edited by Jair C. Soares, and Samuel Gershon. In this review, abstracts reporting on the efficacy of "third generation" anti-epileptic agents, including topiramate, lamotrigine, diphenylhydantoin, gabapentin, and the new generation antipsychotic agent, olanzapine in treating bipolar disorders are reviewed.

Voltage-dependent Ca2+ channel alpha2delta auxiliary subunit: structure, function and regulation

Voltage-dependent Ca2+ channels are heteromultimeric proteins consisting minimally of a alpha1 main subunit and auxiliary alpha2delta, and beta subunits. The alpha1 subunit forms the ion-conducting pore and contains receptor sites for ligands that modify channel activity. The auxiliary subunits appear to be necessary for the expression of the native kinetic properties of the channel. In particular, the alpha2delta complex, with the transmembrane domain-containing delta subunit arising as a result of proteolysis from the C-terminal end of a alpha2delta precursor, has shown to modify the biophysical and pharmacological properties of the alpha1 subunit in different model systems. Structure-function studies have provided insight into the molecular mechanisms through which alpha2delta exerts its actions and revealed that both allosteric modulation and cellular localization of the Ca2+ channel complex are important mechanisms for alpha2delta regulation of ionic current. Recent studies have shown that the alpha2delta subunit can also support pharmacological interactions with therapeutic agents for the treatment of neurological disorders.

Gabapentin leads to remission of somatoform pain disorder with major depression

Gabapentin, a novel antiepileptic drug, is effective in the treatment of partial seizures with and without secondary generalization. Evidence suggests that it may have mood-stabilizing and possibly antidepressant properties in bipolar depression. We report on a 48-year-old woman who had recurrent major depressive disorder. Following inguinal herniorrhaphy, she developed severe stabbing pain in the lower abdomen and inguinal area that progressed to constant pain in her whole body. She was depressive, hopeless, and had given up her social activities. A diagnosis of major depressive disorder and somatoform pain disorder was made. Antidepressants and carbamazepine were ineffective, and she had attempted suicide. Gabapentin resulted in remission of both the pain and the depressive mood at a dose of 1.800 mg/day.

Anticonvulsant activity of PNU-151774E in the amygdala kindled model of complex partial seizures

PURPOSE

PNU-151774E [(S)-(+)-2-(4-(3-fluorobenzyloxy) benzylamino) propanamide, methanesulfonate] is a novel antiepileptic drug (AED) with a broad spectrum of activity in a variety of chemically and mechanically induced seizures. The objective of this study was to evaluate the activity of PNU-151774E in the amygdala fully kindled rat model of complex partial seizures, and to compare its effects with those of carbamazepine (CBZ), phenytoin (PHT), lamotrigine (LTG), and gabapentin (GBP), drugs used to treat this disease state.

METHODS

Male Wistar rats were stimulated daily through electrodes implanted in the amygdala with a threshold current until fully generalized seizures developed. The rats were then treated with various doses of a single compound. Control values for each rat and drug dose were determined after vehicle administration followed by electrical stimulation 1 day before drug treatment.

RESULTS

PNU-151774E (1, 10, 30 mg/kg; i.p.) reduced the duration of behavioral seizures significantly and dose-dependently at doses starting from 1 mg/kg. Higher doses significantly reduced seizure severity and afterdischarge duration. In contrast, no dose-related effects were noted after administration of PHT, whereas after CBZ treatment, a plateau of activity was noted from the intermediate to higher doses. The effects of PNU-151774E were comparable to those of LTG and GBP.

CONCLUSIONS

The activity shown by PNU-151774E at doses similar to those that are active in models of generalized seizures indicates that PNU-151774E would also have potential efficacy in the treatment of complex partial seizures.

Managing pediatric epilepsy syndromes with new antiepileptic drugs

The management of epilepsy in the pediatric patient requires careful evaluation, classification, and pharmacologic treatment. Despite best efforts on the part of clinicians, approximately 25% of children remain refractory to appropriate medical therapies. The development of an improved classification system and the emergence of several new antiepileptic drugs have enabled some progress in this area, specifically in children with disorders such as Lennox-Gastaut syndrome and infantile spasms, which are notoriously difficult to control. However, limited data are available that define the optimal use of new antiepileptic agents in pediatric patients. To most effectively treat children with epilepsy syndromes, further research must be completed to validate the positive effects described in case reports, open-label clinical trials, and early controlled clinical trials.

Monostars: an aid to choosing an antiepileptic drug as monotherapy

This article describes a flexible, dynamic system for comparing antiepileptic drugs (AEDs) as monotherapy, taking into account the needs of the patient and the characteristics of the treatment. Because differences in efficacy between AEDs cannot readily be demonstrated in regulatory clinical trials, safety is of paramount importance. Each drug has been judged across 11 criteria. These include knowledge of mechanism of action, suitable pharmacokinetics, drug interactions, delineated range of efficacy, ease of titration, idiosyncratic reactions, sedative burden, neuropsychiatric profile, teratogenic potential, and the likelihood of producing long-term side effects. The final consideration relates to how "comfortable" the doctor is with prescribing the drug as monotherapy. Scores of -1 (drawback), 0 (neutral/unknown), or +1 (advantage) have been allocated under each category, depending on current knowledge and clinical experience. The sum of the individual scores determines the awarding of "stars." In addition, the positive and negative features of each AED, when used as monotherapy, are highlighted. A range of established and new AEDs has been examined using the "monostars" method, including phenobarbital, phenytoin, carbamazepine, sodium valproate, lamotrigine, gabapentin, oxcarbazepine, and vigabatrin. Scores can be adjusted as new information comes to light. Other agents can be added when suitable monotherapy data become available. This analysis supports the contention that choice of treatment in newly diagnosed epilepsy should take into consideration the patient's age, sex, general health, coexisting disabilities, concomitant medication, and life style. Seizure type, syndrome, and the AED's pharmacology, efficacy, and safety profile should also be considered. Because dosing is often modest, cost should rarely be the overriding factor in choosing a drug for a patient with newly diagnosed epilepsy in the developed world. With these criteria, some of the newer AEDs have potentially more to offer the patient as monotherapy than do the established agents.

Options after the first antiepileptic drug has failed

Long-term antiepileptic drug (AED) treatment is the standard therapy for epilepsies. In about 60% of patients, the first AED tried usually leads to seizure control. After failure of the first AED, it is important to achieve seizure control rapidly and without side effects. Combining the first drug with an add-on drug appears to be more effective than a second monotherapy. However, no scientifically based data are available that favor any particular drug combination. Along with pharmacokinetic considerations, clinical experience is an important determinant in choosing a second AED for use as an add-on. The time needed to introduce a particular AED is a further consideration. The simultaneous introduction of two add-on drugs, one requiring slow titration and one permitting rapid introduction, may be a useful strategy. If the quickly introduced drug is effective as an add-on, introduction of a slowly titrated second add-on can be obviated. If the quickly introduced drug reduces seizure frequency, the patient's quality of life is improved during titration of the second add-on. If the second, slowly titrated drug is more effective than the quickly introduced one, the less-effective drug can be withdrawn. This strategy also allows a direct comparison between two add-on drugs at the same time.

Monotherapy trials with gabapentin for partial epilepsy

The efficacy and safety of gabapentin as monotherapy for treatment of partial onset seizures were evaluated in three large multicenter, double-blind, parallel-group, dose-controlled trials. In the first trial, 275 outpatients with refractory partial epilepsy maintained on stable doses of one or two antiepileptic drugs (AEDs) were switched to gabapentin (GBP) monotherapy at 600 mg, 1200 mg, or 2400 mg daily. Patients were required to exit the 26-week double-blind phase of the study if they experienced worsening of seizure frequency. With respect to time to exit, there was no statistically significant difference among the three groups; only 3% of patients withdrew from the trial because of adverse events. In the second study, 82 hospitalized patients with medically refractory epilepsy were tapered off baseline AEDs and randomly assigned to GBP monotherapy at 300 mg/day or 3600 mg/day. Patients remained in the trial for a maximum of 8 days but had to exit the trial if they experienced one or more exit events. Time to exit was significantly longer in patients in the 3600-mg group (151 h) compared with those in the 300-mg group (85 h) (p = 0.0001). None of the patients withdrew from the trial because of side effects. In the third study, 292 patients with newly diagnosed partial seizures were randomized to GBP 300, 900, or 1800 mg/day or to carbamazepine (CBZ) 600 mg/day. Patients remained in the trial for up to 6 months or until they experienced an exit event. Mean time to exit was significantly longer for patients who received GBP 900 mg/day (p = 0.02) or 1800 mg/day (p = 0.04) compared with those who received 300 mg/day. The completion rate for the CBZ group (37%) was similar to that of the GBP 900-mg (39%) and 1800-mg (38%) groups. Patients receiving CBZ had a higher withdrawal rate because of adverse events compared with the GBP 900-mg and 1800-mg groups. The results of these trials provide good evidence of the efficacy and safety of GBP as monotherapy for the treatment of partial-onset seizures.