Analysis of gabapentin in serum and plasma by solid-phase extraction and gas chromatography-mass spectrometry for therapeutic drug monitoring.
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A simple method for the determination of gabapentin (Neurontin) is described. The method uses solid-phase extraction by disk column and derivatization followed by gas chromatographic-mass spectrometric analysis. The single-step derivatization with MTBSTFA produces a t-BDMS derivative of both the carboxylic and amine moieties of the molecule. Each step of the procedure was optimized to assure reliable performance of the method. The assay limit of detection was 0.1 microg/mL with a linear range from 1.0 to 35 microg/mL. Within-run (n = 3) and between-run (n = 40) coefficients of variation were less than 8.2 and 15.9%, respectively. The method has proven reliable in routine production for more than a year, producing clean chromatography with unique ion fragments, consistent ion mass ratios, and no interferences. Statistical analysis of the gabapentin concentrations measured in 1020 random specimens over a 2-month period showed a mean concentration of 6.07 microg/mL with a standard deviation of 5.28. (+info)
Gabapentin suppresses ectopic nerve discharges and reverses allodynia in neuropathic rats.
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Repetitive ectopic discharges from injured afferent nerves play an important role in initiation and maintenance of neuropathic pain. Gabapentin is effective for treatment of neuropathic pain but the sites and mechanisms of its antinociceptive actions remain uncertain. In the present study, we tested a hypothesis that therapeutic doses of gabapentin suppress ectopic afferent discharge activity generated from injured peripheral nerves. Mechanical allodynia, induced by partial ligation of the sciatic nerve in rats, was determined by application of von Frey filaments to the hindpaw. Single-unit afferent nerve activity was recorded proximal to the ligated sciatic nerve site. Intravenous gabapentin, in a range of 30 to 90 mg/kg, significantly attenuated allodynia in nerve-injured rats. Furthermore, gabapentin, in the same therapeutic dose range, dose-dependently inhibited the ectopic discharge activity of 15 injured sciatic afferent nerve fibers through an action on impulse generation. However, the conduction velocity and responses of 12 normal afferent fibers to mechanical stimulation were not affected by gabapentin. Therefore, this study provides electrophysiological evidence that gabapentin is capable of suppressing the ectopic discharge activity from injured peripheral nerves. This action may contribute, at least in part, to the antiallodynic effect of gabapentin on neuropathic pain. (+info)
Anti-ulcer effects of 4'-(2-carboxyetyl) phenyl trans-4-aminomethyl cyclohexanecarboxylate hydrochloride (cetraxate) on various experimental gastric ulcers in rats.
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Anti-ulcer effects of cetraxate, a new compound possessing anti-plasmin, anti-casein and anti-trypsin actions were investigated by using experimental gastric ulcer models in rats. Cetraxate, 300 mg/kg p.o. showed significant inhibitory effects of 65.3%, 70.0%, 30.2%, and 67.1% against aucte types of ulcers producing by aspirin, phenylbutazone, indomethacin, and pyloric ligature (Shay's ulcer), respectively. These effects were greater than those obtained by gefarnate and aluminum sucrose sulfate may be mainly attributed to the protecting action of this drug on gastric mucosa. Ctraxate further revealed remarkable inhibitory effects on chronic types of ulcers produced by acetic acid, clamping, and clamping-cortisone. In acetic acid ulcer in particular, cetraxate was found to have a dose-dependent inhibitory effect at doses over 50 mg/kg. Of test drugs including L-glutamine and methylmethionine sulfonium chloride, cetraxate showed the most remarkable inhibitory effect on beta-glucuronidase activity in ulcer tissue of these three types of ulcers. These findings suggest that cetraxate may prevent the connective tissue in the ulcer location from decomposition due to lysosomal enzymes such as beta-glucuronidase, thereby accelerating the recovery from ulcer. (+info)
An in vitro electrophysiological study on the effects of phenytoin, lamotrigine and gabapentin on striatal neurons.
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We performed intracellular recordings from a rat corticostriatal slice preparation in order to compare the electrophysiological effects of the classical antiepileptic drug (AED) phenytoin (PHT) and the new AEDs lamotrigine (LTG) and gabapentin (GBP) on striatal neurons. PHT, LTG and GBP affected neither the resting membrane potential nor the input resistance/membrane conductance of the recorded cells. In contrast, these agents depressed in a dose-dependent and reversible manner the current-evoked repetitive firing discharge. These AEDs also reduced the amplitude of glutamatergic excitatory postsynaptic potentials (EPSPs) evoked by cortical stimulation. However, substantial pharmacological differences between these drugs were found. PHT was the most effective and potent agent in reducing sustained repetitive firing of action potentials, whereas LTG and GBP preferentially inhibited corticostriatal excitatory transmission. Concentrations of LTG and GBP effective in reducing EPSPs, in fact, produced only a slight inhibition of the firing activity of these cells. LTG, but not PHT and GBP, depressed cortically-evoked EPSPs increasing paired-pulse facilitation (PPF) of synaptic transmission, suggesting that a presynaptic site of action was implicated in the effect of this drug. Accordingly, PHT and GBP, but not LTG reduced the membrane depolarizations induced by exogenously-applied glutamate, suggesting that these drugs preferentially reduce postsynaptic sensitivity to glutamate released from corticostriatal terminals. These data indicate that in the striatum PHT, LTG and GBP decrease neuronal excitability by modulating multiple sites of action. The preferential modulation of excitatory synaptic transmission may represent the cellular substrate for the therapeutic effects of new AEDs whose use may be potentially extended to the therapy of neurodegenerative diseases involving the basal ganglia. (+info)
Adenosylcobalamin-mediated methyl transfer by toluate cis-dihydrodiol dehydrogenase of the TOL plasmid pWW0.
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We identified and characterized a methyl transfer activity of the toluate cis-dihydrodiol (4-methyl-3,5-cyclohexadiene-cis-1, 2-diol-1-carboxylic acid) dehydrogenase of the TOL plasmid pWW0 towards toluene cis-dihydrodiol (3-methyl-4,5-cyclohexadiene-cis-1, 2-diol). When the purified enzyme from the recombinant Escherichia coli containing the xylL gene was incubated with toluene cis-dihydrodiol in the presence of NAD+, the end products differed depending on the presence of adenosylcobalamin (coenzyme B12). The enzyme yielded catechol in the presence of adenosylcobalamin, while it gave 3-methylcatechol in the absence of the cofactor. Adenosylcobalamin was transformed to methylcobalamin as a result of the enzyme reaction, which indicates that the methyl group of the substrate was transferred to adenosylcobalamin. Other derivatives of the cobalamin such as aquo (hydroxy)- and cyanocobalamin did not mediate the methyl transfer reaction. The dehydrogenation and methyl transfer reactions were assumed to occur concomitantly, and the methyl transfer reaction seemed to depend on the dehydrogenation. To our knowledge, the enzyme is the first dehydrogenase that shows a methyl transfer activity as well. (+info)
The management of epilepsy in a hospital for people with a learning disability.
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The study examined changes in the use of antiepileptic drugs (AEDs) in a large hospital for people with a learning disability over a 2 year period, the use of investigations, and the presence of medication side-effects. The surveys were carried out in 1993 and 1995/6. In 1993, 27% of patients were being treated for epilepsy and in 1995/6, 30.1%. Ninety percent and 82.4% of patients, respectively, were receiving one or two AEDs. In the second survey there were fewer prescriptions for phenobarbitone (5.8% vs. 12.5%) and an increase in the use of lamotrigine (21.6% vs. 5%), gabapentin (5.8% vs. 0) and vigabatrin (3.9% vs. 2.5% in 1993). Side-effects were recorded in 6 (11.8%) patients. Seven (21.2%) patients receiving carbamazepine were found to have hyponatraemia. Of the 54 electroencephalograms (EEGs) requested, 41 (76%) were reported as abnormal. Six CT brain scans had been conducted, of which five were abnormal. People receiving antipsychotic drugs had fewer seizures than average. (+info)
Successful treatment with gabapentin in the presence of hypersensitivity syndrome to phenytoin and carbamazepine: a report of three cases.
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We report three consecutive patients with hypersensitivity syndrome (HSS) due to phenytoin and carbamazepine and successful treatment with gabapentin. HSS is a rare but potentially fatal reaction to multiple drugs including several anticonvulsants. Cross-reactivity among drugs may occur. Immediate withdrawal of the offending drug is the most important step in treatment. Benzodiazepines acutely and, after resolution of the hepatitis, valproic acid have been successfully used for seizure control in patients with HSS. Our cases indicate that gabapentin is also a safe anticonvulsant in HSS. (+info)
Gabapentin attenuates nociceptive behaviors in an acute arthritis model in rats.
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In this study, we investigated the effectiveness of gabapentin (Neurontin), administered spinally with a microdialysis fiber, in reducing nociceptive behavioral responses induced by a knee joint inflammation model. This model is produced by injection of the knee joint with kaolin and carrageenan in rats. The resultant knee joint inflammation produces a secondary hyperalgesia to radiant heat applied to the hindpaw. Both pretreatment and post-treatment protocols were examined. Spinal administration of gabapentin (10 mg/ml) infused 1.5 h before induction of knee joint inflammation, although having no effect on the baseline, prevented the development of heat hyperalgesia. Gabapentin also prevented the development of other pain-related behaviors scored subjectively. Gabapentin had no effect, however, on the joint circumference increase typical in this model. In animals with fully developed knee joint inflammation, gabapentin produced a reversal of heat hyperalgesia. The paw withdrawal latency responses and subjective pain scores were no longer significantly different from baseline, but joint circumference increases remained. These data suggest that gabapentin is an effective antinociceptive agent when administered either before or after induction of knee joint inflammation acting through a central neurogenic mechanism. (+info)