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PubMed2005

Quantitative determination of vigabatrin and gabapentin in human serum by gas chromatography-mass spectrometry.

BACKGROUND: Published methods for routine clinical monitoring of vigabatrin and gabapentin are often very laborious. A simple GC-MS method was developed for the simultaneous quantitative determination of vigabatrin and gabapentin in human serum. METHODS: After protein precipitation, the compounds are derivatized by methylation and analysed on a polydimethylsiloxane column using splitless injection. Cyclobarbital is used as the internal standard. To attain maximal sensitivity, detection is performed in selected ion monitoring mode. RESULTS: The method was fully validated and linear calibration curves were obtained in the concentration ranges from 5 to 80 microg/mL for vigabatrin and from 5 to 30 microg/mL for gabapentin. The within-day and day-to-day relative standard deviations at three different concentration levels were <10% and <15%, respectively. The limit of quantitation was 2 mug/mL for both compounds. CONCLUSIONS: The presented method provides high chromatographic resolution, good sensitivity and unequivocal identification potential and can be used for simultaneous analysis of both antiepileptics.

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PubMed2006

Comparative effects of some hydrophilic excipients on the rate of gabapentin and baclofen lactamization in lyophilized formulations.

The aim of this study was to gain insights into the role played by some excipients on the stability of gabapentin 1 and baclofen 2 which can undergo degradation giving rise to the corresponding lactams 2-azaspiro[4.5]decan-3-one 3 and 4-(4-chlorophenyl)-2-pyrrolidone 4, respectively. A screening study was carried out on drug and drug-excipient freeze-dried mixtures at 50 degrees C and under three different humidity values by using a number of commonly available excipients. These include hydroxypropyl-beta-(HP-beta-CD), sulfobutyl-beta-cyclodextrin (SBE-beta-CD), lactose, raffinose, trehalose, PVP-K30 and mannitol. For most cases, it was found that the lactam formation can be satisfactory described by an apparent zero-order equation. Excipients shown to negatively impact gabapentin stability are HP-beta-CD, SBE-beta-CD, lactose and PVP K30 while only this last excipient had a significant effect on the degradation of baclofen. The results can be rationalized in terms of conformational factors favouring the intramolecular dehydration reaction. A positive effect of moisture on the lactamization process was observed under some circumstances. Water may provide a favourable environment for degradation. These findings, taken together, should be considered during the selection of excipients for a possible formulation of gabapentin and baclofen.

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PubMed2004

Add-on gabapentin in the treatment of opiate withdrawal.

Gabapentin is an antiepileptic drug shown to be effective in the treatment of pain disorders and appears to be useful as well for several psychiatric disorders, including bipolar disorder, anxiety disorders, alcohol withdrawal and cocaine dependence. Gabapentin, at a dose of 600 mg three times a day, was evaluated as an add-on medication to a standard detoxification regime in seven heroin dependent individuals undergoing outpatient opiate withdrawal treatment. All seven patients successfully completed opiate detoxification and commenced opiate antagonist treatment with naltrexone on day five of withdrawal treatment, as scheduled. No adverse event was noted. Gabapentin appeared to lead a reduction in symptomatic medication and an overall beneficial effect on symptoms of heroin withdrawal.

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PubMed2001

A placebo-controlled trial of gabapentin in spinal muscular atrophy.

OBJECTIVE: To evaluate the efficacy of gabapentin in increasing muscle strength of patients with spinal muscular atrophy (SMA). BACKGROUND: Preclinical data in experimental models of motor neuron disease suggest a neuroprotective effect of gabapentin. METHODS: Gabapentin (1200 mg), or placebo, was administered three times daily in a randomized, double-blind trial for 12 months. The primary outcome measure was the average percent change from baseline, based on the measurement of strength in four muscles (elbow flexion and hand grip bilaterally) for each patient. Drug efficacy was examined by comparing the percent change in strength for patients on drug vs. placebo. Secondary efficacy variables included: forced vital capacity (FVC), SMA functional rating scale (SMAFRS), and mini-Sickness Impact Profile (SIP). RESULTS: Eighty-four patients, with type II or III SMA, were enrolled at eight sites across the United States. There were no differences in baseline features. There was no difference between the placebo and drug groups in any outcome measure. CONCLUSIONS: This study demonstrates the feasibility of this trial design and provides data for the design of future clinical trials in SMA.

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PubMed2003

Gabapentin in antipsychotic-induced tardive dyskinesia: results of 1-year follow-up.

BACKGROUND: In a previous study, improvement of antipsychotic-induced blefarospasm and involuntary oral-mandibulo movements were observed with the use of the anticonvulsant drug gabapentin among affectively ill patients who had been exposed to maintenance neuroleptics. The results reported in the present paper represent the sequel to the previous study. METHODS: The purported efficacy of gabapentin in the treatment of tardive dyskinesia has been assessed in an open design 1-year follow-up study, in which 30 schizoaffective, bipolar I and schizophrenic patients from seven Italian centres were evaluated by means of AIMS. The results showed a statistically significant time-related decrease in AIMS scores. The mean percentage of improvement at AIMS was 47.5+/-18.2%. An improvement of more than 35% after 1 year in 76% of the subjects who completed the trial (n=25) and in 63.3% of the entire sample admitted to the study was revealed. LIMITATION: Open trial. CONCLUSION: The introduction of new antipsychotic drugs has probably already limited the problems related to tardive dyskinesia. However, this type of side-effect is also observed during the course of treatment with atypical neuroleptics albeit with a lesser frequency. The fact that gabapentin treatment may have further improved clinical conditions of patients in whom therapeutic protocols had already been modified, appears to suggest exertion of a possible synergic action by the new neuroleptics on tardive dyskinesia.

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PubMed1999

Gabapentin as an adjunctive treatment in bipolar disorder.

OBJECTIVE: To evaluate the efficacy of gabapentin as an adjunctive treatment for bipolar disorder in both depressed and manic phases. METHOD: Thirty seven patients with bipolar type I or II with or without a rapid cycling course were openly treated with gabapentin added to current treatment for up to six months. Mood symptoms were rated weekly for 12 weeks then monthly for 3 months utilizing the HamD and YMS. RESULTS: Participants experienced a significant reduction in both depressive and manic symptoms. CONCLUSIONS: These findings are consistent with others in establishing the efficacy of gabapentin in both phases of bipolar disorder. LIMITATIONS: Small sample size and the use of an open uncontrolled design limit interpretation of results.

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PubMed2003

Treatment of post-herpetic pain in myasthenia gravis: exacerbation of weakness due to gabapentin.

Here, we present a case of a 64-year-old female suffering from a severe form of antibody-positive myasthenia gravis. Under an immunosuppressive regimen with cyclosporine A, she experienced an episode of thoracic herpes zoster followed by intense post-herpetic neuralgia. In order to avoid drug interactions as well as adverse effects of carbamazepine in myasthenia gravis, gabapentin was chosen for the treatment of neuropathic pain. Within a few days she noticed increasing weakness, but continued medication for 8 weeks as gabapentin was not identified as the hazardous agent by her physician. Acetylcholine receptor antibody levels remained unchanged, but increased decrement was observed clinically and in repetitive nerve stimulation. After withdrawal of gabapentin, she recovered quickly to her previous condition.

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PubMed2003

Pregabalin and gabapentin reduce release of substance P and CGRP from rat spinal tissues only after inflammation or activation of protein kinase C.

Gabapentin and pregabalin are amino acid derivatives of gamma-amino butyric acid that have anticonvulsant, analgesic, and anxiolytic-like properties in animal models. The mechanisms of these effects, however, are not well understood. To ascertain whether these drugs have effects on sensory neurons, we studied their actions on capsaicin-evoked release of the sensory neuropeptides, substance P and calcitonin gene-related peptide from rat spinal cord slices in vitro. Although release of immunoreactive peptides from non-inflamed animals was not altered by either drug, prior in vivo treatment by intraplantar injection of complete Freund's adjuvant enhanced release from spinal tissues in vitro, which was attenuated by gabapentin and pregabalin. These drugs also reduced release of immunoreactive neuropeptides in spinal tissues pretreated in vitro with the protein kinase C activator, phorbol 12,13-dibutyrate. Our results suggest that gabapentin and pregabalin modulate the release of sensory neuropeptides, but only under conditions corresponding to significant inflammation-induced sensitization of the spinal cord.

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PubMed1997

Effects of felbamate, gabapentin and lamotrigine on seizure parameters and excitability in the rat hippocampus.

The effects of three new antiepileptic drugs (felbamate, lamotrigine and gabapentin) on the parameters of seizure initiation and termination in one model of reverberatory seizures in the hippocampal-parahippocampal loop in urethane-anesthetized rats were determined. All three of the drugs caused a dose-dependent decrease in the duration of the seizure discharge. Only very high doses of felbamate had a significant effect on seizure initiation. In addition to the seizure model, we tested the three new anti-epileptic drugs for an effect on excitability, on paired-pulse inhibition and on long-term potentiation (LTP) in the dentate gyrus of the urethane-anesthetized rat. None of the drugs altered LTP or excitability. However, gabapentin altered paired-pulse inhibition, causing a loss of inhibition. For felbamate and lamotrigine, the effects of seizure duration are consistent with their clinical effects as antiepileptic drugs. However, the effect of gabapentin on paired-pulse inhibition suggests a proconvulsant effect and the effect on seizure duration suggests an antiepileptic effect.

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PubMed2000

Gabapentin in childhood epilepsy: a prospective evaluation of efficacy and safety.

PURPOSE: To evaluate the efficacy and safety of gabapentin (GBP) in partial epilepsy in children. METHODS: We performed a prospective open label add-on study in 52 children and adolescents (age 1.8-17.5 years, mean 11.1 years) with refractory partial seizures. Gabapentin was added to one other baseline drug and the efficacy was rated according to seizure type and frequency. RESULTS: The GBP dose ranged from 26 to 78 mg/kg per day (mean 52 mg/kg per day) and was well tolerated in most patients. The seizure frequency remained unchanged in 34 patients (65%). We saw a provocation of seizures in three children (6%). Initially 15 patients (29%) benefited from GBP: five (10%) with a seizure reduction of 50-74%, seven (13%) with a reduction of 75-99% and three (6%) became seizure free. All but three experienced a development of tolerance within the next weeks to months. CONCLUSIONS: Although gabapentin seems also to be safe in children, the efficacy in refractory partial seizures was disappointing.

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PubMed1999

Synthesis and biological evaluation of conformationally restricted Gabapentin analogues.

A series of conformationally restricted Gabapentin analogues has been synthesised. The pyrrolidine analogue (R)-2-Aza-spiro[4.5]decane-4-carboxylic acid hydrochloride (3a) had an IC50 of 120 nM, similar to that of Gabapentin (IC50 = 140 nM), at the Gabapentin binding site on the alpha2delta subunit of a calcium channel. Compound (3a) also reversed carrageenan induced hyperalgesia in rats.

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PubMed1999

An in vitro investigation into conformational aspects of gabapentin.

Conformational analysis of constrained cyclohexane systems was pioneered fifty years ago by Barton and Hassel. We now report an investigation based on a conformational analysis of a number of novel cyclohexane based Gabapentin analogues coupled with their in vitro evaluation at the Gabapentin binding site. These data are used to propose a possible binding conformation for Gabapentin.

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PubMed1997

Gabapentin for treatment of epilepsy in children.

Gabapentin is a recently introduced antiepileptic drug for the treatment of partial seizures. Although studied extensively in adults, there have been few pediatric studies. It is a unique drug because it has no protein binding, is not metabolized, and is excreted through the kidneys. There are no significant drug interactions with other antiepileptic drugs nor do other antiepileptic drugs alter the pharmacokinetics of gabapentin. The drug is effective in partial seizures, although most studies have used the drug as add-on therapy. It is approved for use of partial seizures with or without secondary generalization in patients over the age of 12 years. The side effect profile of the drug is quite good. No significant idiosyncratic reactions have been reported. The most common side effects have included dizziness, fatigue, and headache. Rarely, children will have adverse behavioral effects, such as hyperactivity and agitated behavior. Usually these children have pre-existing behavioral disturbances. Although the spectrum of efficacy of gabapentin remains to be determined, it is likely to have a major beneficial impact on the treatment of childhood epilepsy.

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PubMed2002

High-performance liquid chromatographic method for the determination of gabapentin in human plasma.

A sensitive high-performance liquid chromatography (HPLC) method using UV detection for the determination of gabapentin in human plasma has been developed. In this method, gabapentin was extracted from human plasma with a reversed-phase solid-phase extraction (SPE) cartridge followed by derivatization with phenylisothiocyanate. Analysis was achieved by using a HPLC system that was equipped with a UV detector. The quantitation limit of gabapentin in human plasma was 0.03 microg/ml. The method is sensitive with excellent selectivity and reproducibility and it has been applied to a bioequivalence clinical study with great success.

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PubMed2001

Gabapentin as add-on therapy in children with refractory partial seizures: a 24-week, multicentre, open-label study.

The efficacy and safety of gabapentin as add-on therapy for refractory partial seizures in 237 children, aged 3 to 12 years were evaluated over a 6-month period. All children received gabapentin at 24 to 70 mg/kg/day. Efficacy variables included the percent change in seizure frequency and the responder rate (defined as those patients who showed >50% reduction in seizure frequency). For all partial seizures, the median percent change in seizure frequency was -34% and the overall responder rate was 34%. Simple partial seizures showed a median reduction of -53%; complex partial seizures, -38%; and secondarily generalized tonic-clonic seizures, -35%. Thirteen patients (5%) withdrew during the 6-month period because of adverse events. Concurrent antiepileptic medication remained unchanged in 185 patients (78%), was decreased in 27 (11%), and increased in 25 (11%) patients. This 6-month follow-up study has demonstrated that gabapentin was well tolerated and appeared to show a sustained efficacy in a large population of children with refractory partial and secondarily generalized tonic-clonic seizures.

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PubMed1992

Stability studies of gabapentin in aqueous solutions.

Gabapentin is a gamma-aminobutyric acid analogue, which has been shown to be an effective antiepileptic. The solution stability of gabapentin in buffered systems was studied in order to facilitate the formulation of a liquid product. The degradation of the drug was followed as a function of pH, buffer concentration, ionic strength, and temperature. The results indicated that the rate of degradation was proportional to the buffer concentration and temperature. The pH-rate profile of gabapentin degradation showed that the rate of degradation was minimum at an approximate pH of 6.0. Further, the data suggested a slower solvent-catalyzed degradation rate for the zwitterionic species compared to the cationic or anionic species in the pH range of 4.5 to 7.0. There was no influence of ionic strength on the rate of degradation. Arrhenius plots of the data indicated that a shelf life of 2 years or more at room temperature may be obtained in an aqueous solution at a pH value of 6.0.

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PubMed1999

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.

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PubMed2001

Gabapentin in the treatment of hemifacial spasm.

OBJECTIVES: To evaluate the efficacy of gabapentin in the treatment of hemifacial spasm. MATERIAL AND METHODS: Twenty-three patients with hemifacial spasm not suitable for surgery or therapy with botulinum toxin were treated with gabapentin. The main efficacy parameter was the percentage of spasm reduction. RESULTS: A clinically significant reduction of spasms was obtained by 16 patients. CONCLUSION: Gabapentin was effective and safe in reducing hemifacial spasm in 16 out 23 (69.6%) patients.

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