BACKGROUND: Gabapentin is a safe and well-tolerated anticonvulsant with a wide therapeutic index, and it is used for neuropathic pain. The aim of this study was to compare previous dosing methods with the administration of four different doses of gabapentin while maintaining the same maximum daily dose for the safe administration of high doses of the medication. METHODS: The subjects were outpatients with various neuropathic pain syndromes, with at least two of the following symptoms: allodynia, burning pain, shooting pain, or hyperalgesia. The TID group received equal doses of gabapentin 3 times per day, while the QID group received 4 different doses of gabapentin per day. The pain score, frequency of breakthrough pain (BTP), severity and the duration of pain, sleep disturbance due to nocturnal pain, and adverse effects were recorded each day. RESULTS: The average daily pain score and sleep disturbance were significantly reduced in the QID group between days 3 and 10 of the experiment. The adverse effects of the medication were also reduced in the QID group. However, the frequency of BTP and severity and duration of pain were not significantly different between two groups. CONCLUSIONS: Administration of 4 different doses of gabapentin during the initial titration in outpatients with neuropathic pain resulted in a significant reduction in awakening from breakthrough pain and a reduction in the adverse effects of the medication.
Ambulatory Care ; Amines ; Breakthrough Pain ; Burns ; Cyclohexanecarboxylic Acids ; Drug Administration Schedule ; gamma-Aminobutyric Acid ; Humans ; Hyperalgesia ; Neuralgia ; Outpatients

Gabapentin decreases the level of glutamate and elevates that of garmma-amino-butyric acid in the central nervous system. Gabapentin was shown to have antinociceptive effects in several facilitated pain models. Intrathecal gabapentin was also known to be effective in reducing mechanical allodynia in animals with neuropathic pain. In this study, we investigated to see whether intrathecal gabapentin produces antihyperalgesic effects on thermal and mechanical hyperalgesia in neuropathic rats and whether its effects are associated with motor impairment. To induce neuropathic pain in Sprague-Dawley rats, left L5 and L6 spinal nerves were ligated. After a week, lumbar catheterization into subarachnoid space was performed. Then, paw withdrawal times to thermal stimuli and vocalization thresholds to paw pressure were determined before and up to 2 hr after intrathecal injection of gabapentin. Also, motor functions including performance times on rota-rod were determined. Intrathecal gabapentin attenuated significantly thermal and mechanical hyperalgesia in neuropathic rats, but did not block thermal and mechanical nociception in sham-operated rats. Intrathecal gabapentin of antihyperalgesic doses inhibited motor coordination performance without evident ambulatory dysfunction. This study demonstrates that intrathecal gabapentin is effective against thermal and mechanical hyperalgesia, in spite of moderate impairment of motor coordination.
Acetic Acids/administration & dosage/*pharmacology ; *Amines ; Analgesics/administration & dosage/*pharmacology ; Animals ; *Cyclohexanecarboxylic Acids ; Dose-Response Relationship, Drug ; Injections, Spinal ; Ligation ; Male ; Rats ; Rats, Sprague-Dawley ; Spinal Nerves/*injuries ; Time Factors ; *gamma-Aminobutyric Acid

BACKGROUND: Experimental studies have shown that gabapentin can reduce neuronal injury in the setting of cerebral ischemia, but the mechanisms have not yet been clearly determined. This study was conducted to determine whether gabapentin pretreatment altered expression levels of heat shock protein 70 and reduced acute phase neuronal injury in rats subjected to transient focal cerebral ischemia/reperfusion. METHODS: Forty male Sprague-Dawley rats (260-300 g) were randomly assigned to one of four groups (saline-treated, or 0.1, 0.5, or 5 mg/kg gabapentin group). In all animals, focal cerebral ischemia was induced by intraluminal middle cerebral artery occlusion for 1 hour. The animals of the gabapentin groups were pretreated with a single intravenous administration of gabapentin 20 minutes before ischemic insults. The infarct volume, brain edema and motor behavior deficits were analyzed 24 hours after ischemic insult. Caspase-3-reactive cells and cells showing Hsp70 activity were counted in the caudoputamen and fronto-parietal cortex. RESULTS: The infarction ratio was significantly decreased in the 5 mg/kg gabapentin group (P < 0.05) and brain edema ratios were significantly reduced in the 0.1 mg/kg, 0.5 mg/kg, and 5 mg/kg gabapentin groups 24 hours after ischemia/reperfusion injury (P < 0.05). There were more Hsp70-reactive cells in the 5 mg/kg gabapentin group than in the saline group in both the caudoputamen and fronto-parietal cortex (P < 0.05). CONCLUSIONS: These results indicate that gabapentin may have a neuroprotective effect and can reduce early neuronal injury caused by focal cerebral ischemia/reperfusion; this may be mediated by expression of Hsp70. However, gabapentin pretreatment did not prevent caspase-dependent apoptosis.
Administration, Intravenous ; Amines ; Animals ; Apoptosis ; Brain ; Brain Edema ; Brain Injuries ; Brain Ischemia ; Caspase 3 ; Cyclohexanecarboxylic Acids ; gamma-Aminobutyric Acid ; HSP70 Heat-Shock Proteins ; Humans ; Infarction ; Infarction, Middle Cerebral Artery ; Male ; Neurons ; Neuroprotective Agents ; Rats ; Rats, Sprague-Dawley

BACKGROUND: Experimental studies have shown that gabapentin can reduce neuronal injury in the setting of cerebral ischemia, but the mechanisms have not yet been clearly determined. This study was conducted to determine whether gabapentin pretreatment altered expression levels of heat shock protein 70 and reduced acute phase neuronal injury in rats subjected to transient focal cerebral ischemia/reperfusion. METHODS: Forty male Sprague-Dawley rats (260-300 g) were randomly assigned to one of four groups (saline-treated, or 0.1, 0.5, or 5 mg/kg gabapentin group). In all animals, focal cerebral ischemia was induced by intraluminal middle cerebral artery occlusion for 1 hour. The animals of the gabapentin groups were pretreated with a single intravenous administration of gabapentin 20 minutes before ischemic insults. The infarct volume, brain edema and motor behavior deficits were analyzed 24 hours after ischemic insult. Caspase-3-reactive cells and cells showing Hsp70 activity were counted in the caudoputamen and fronto-parietal cortex. RESULTS: The infarction ratio was significantly decreased in the 5 mg/kg gabapentin group (P < 0.05) and brain edema ratios were significantly reduced in the 0.1 mg/kg, 0.5 mg/kg, and 5 mg/kg gabapentin groups 24 hours after ischemia/reperfusion injury (P < 0.05). There were more Hsp70-reactive cells in the 5 mg/kg gabapentin group than in the saline group in both the caudoputamen and fronto-parietal cortex (P < 0.05). CONCLUSIONS: These results indicate that gabapentin may have a neuroprotective effect and can reduce early neuronal injury caused by focal cerebral ischemia/reperfusion; this may be mediated by expression of Hsp70. However, gabapentin pretreatment did not prevent caspase-dependent apoptosis.
Administration, Intravenous ; Amines ; Animals ; Apoptosis ; Brain ; Brain Edema ; Brain Injuries ; Brain Ischemia ; Caspase 3 ; Cyclohexanecarboxylic Acids ; gamma-Aminobutyric Acid ; HSP70 Heat-Shock Proteins ; Humans ; Infarction ; Infarction, Middle Cerebral Artery ; Male ; Neurons ; Neuroprotective Agents ; Rats ; Rats, Sprague-Dawley

Spinal gabapentin and adenosine have been known to display an antinociceptive effect. We evaluated the nature of the interaction between gabapentin and adenosine in formalin-induced nociception at the spinal level. Male Sprague-Dawley rats were prepared for intrathecal catheterization. Pain was evoked by injection of formalin solution (5%, 50 microliter) into the hindpaw. After examination of the effects of gabapentin and adenosine, the resulting interaction was investigated with isobolographic and fractional analyses. Neither gabapentin nor adenosine affected motor function. Gabapentin or adenosine decreased the sum of the number of flinches during phase 2, but not during phase 1 in the formalin test. Isobolographic analysis, in phase 2, revealed an additive interaction between gabapentin and adenosine. Taken together, intrathecal gabapentin and adenosine attenuated the facilitated state and interacted additively with each other.
*Adenosine/administration & dosage/metabolism/therapeutic use ; *Amines/administration & dosage/metabolism/therapeutic use ; *Analgesics/administration & dosage/metabolism/therapeutic use ; Animals ; *Cyclohexanecarboxylic Acids/administration & Dose-Response Relationship, Drug ; Formaldehyde/*toxicity ; Injections, Spinal ; Male ; Motor Activity/physiology ; Pain Measurement ; Rats ; Rats, Sprague-Dawley ; Research Support, Non-U.S. Gov't ; *gamma-Aminobutyric Acid/administration & dosage/metabolism/therapeutic

A sensitive, rapid and specific liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method for quantification of gabapentin in human plasma has been developed. After a single plasma protein precipitation with methanol, gabapentin and metformin (internal standard) were chromatographed on a Inertsil ODS-3 column (50 mm x 2.1 mm ID, 3 microm) with mobile phase consisting of methanol-0.2% formic acid aqueous solution (80:20, v/v) at a flow-rate of 0.2 mL x min(-1). Electrospray ionization (ESI) source was applied and operated in the positive ion mode. Multiple reaction monitoring (MRM) mode with the transitions of m/z 172 --> m/z 154 and m/z 130 --> m/z 71 were used to quantify gabapentin and metformin, respectively. The run time was 2.2 min. The linear calibration curve was obtained in the concentration range of 40.8-8.16x10(3) ng x mL(-1). The lower limit of quantification was 40.8 ng x mL(-1). The intra- and inter-day precision (RSD) was less than 12%, and the accuracy (RE) was within +/-6.4% calculated from quality control (QC) samples. The method was used to determine the concentration of gabapentin in human plasma after a single oral administration of 600 mg gabapentin capsule to 20 healthy male Chinese volunteers. The method was proved to be selective, sensitive, rapid and suitable for pharmacokinetic study of gabapentin in human plasma.
Administration, Oral ; Amines ; administration & dosage ; blood ; pharmacokinetics ; Anticonvulsants ; administration & dosage ; blood ; pharmacokinetics ; Area Under Curve ; Chromatography, High Pressure Liquid ; Cyclohexanecarboxylic Acids ; administration & dosage ; blood ; pharmacokinetics ; Humans ; Male ; Spectrometry, Mass, Electrospray Ionization ; Tandem Mass Spectrometry ; gamma-Aminobutyric Acid ; administration & dosage ; blood ; pharmacokinetics

OBJECTIVETo study the clinical effects of gabapentin on the treatment of pruritus of scar resulting from deep partial-thickness burn.

METHODSA total of fifty-eight patients suffering from pruritus of scar after deep partial-thickness burn were hospitalized from January 2013 to January 2014. Patients were divided into placebo group (n =18, treated with oral vitamin C in the dose of 100 mg for 4 weeks, twice per day) , cetirizine group (n = 20, treated with oral cetirizine in the dose of 10 mg for 4 weeks, twice per day) , and gabapentin group (n = 20, treated with oral gabapentin in the dose of 300 mg for 4 weeks, twice per day) . Before treatment and on post treatment day (PTD) 3 and 28, the Visual Analog Scale (VAS) was used to assess the itching degree, and the mean scores were recorded. The remission rates of pruritus on PTD 3 and 28 were calculated. The adverse effects were observed during treatment. Data were processed with analysis of variance, q test, and chi-square test.

RESULTSCompared with that before treatment, the itching degree of patients with light, moderate, and severe itching in placebo group was not relieved after treatment; the itching degree of patients with moderate or severe itching in cetirizine group was alleviated after treatment, but not in patients with light itching; itching degree of all patients in gabapentin group was significantly relieved after treatment. There were no obvious differences in VAS scores among the 3 groups before treatment (F = 2.78, P > 0.05). On PTD 3 and 28, the VAS scores of patients in both gabapentin group [(2.3 ± 0.8) and (0.6 ± 0.3) points] and cetirizine group [(4.2 ± 1.7) and (2.8 ± 1.2) points] were lower than those in placebo group [(5.7 ± 2.0) and (5.7 ± 1.9) points, with q values from 6.70 to 7.75, P values below 0.05]. The VAS scores of patients in gabapentin group on PTD 3 and 28 were lower than those in cetirizine group (with q values respectively 6.30 and 6.90, P values below 0.05). The remission rates of pruritus of patients in gabapentin group on PTD 3 and 28 were respectively (66 ± 20)% and (91 ± 17)%, and they were higher than those in cetirizine group [(33 ± 8)% and (56 ± 14)%, with q values respectively 4.70 and 3.82, P values below 0.05]. The remission rate of pruritus of patients in placebo group on PTD 3 and 28 was 0, which was lower than that of the other 2 groups each (with q values from 3.94 to 6.76, P values below 0.05). During the course of treatment, 5 patients in gabapentin group suffered from adverse effects including mild-to-moderate drowsiness and dizziness, but they disappeared one week later. No adverse effects were observed in patients of the other two groups.

CONCLUSIONSFor patients with deep partial-thickness burn, gabapentin can effectively alleviate scar itching after wound healing with safety.

Amines ; administration & dosage ; therapeutic use ; Analgesics ; therapeutic use ; Ascorbic Acid ; administration & dosage ; Burns ; complications ; Cetirizine ; administration & dosage ; Cicatrix ; Cyclohexanecarboxylic Acids ; administration & dosage ; therapeutic use ; Humans ; Pruritus ; drug therapy ; Skin Transplantation ; Treatment Outcome ; Visual Analog Scale ; Wound Healing ; gamma-Aminobutyric Acid ; administration & dosage ; therapeutic use

We examined the antiallodynic interaction between gabapentin and adenosine A1 receptor agonist, N(6)-(2-phenylisopropyl)-adenosine R-(-)isomer (R-PIA), in a rat model of nerve ligation injury. Rats were prepared with ligation of left L5-6 spinal nerves and intrathecal catheter implantation for drug administration. Mechanical allodynia was measured by applying von Frey filaments. Gabapentin and R-PIA were administered to obtain the dose-response curve and the 50% effective dose (ED50). Fractions of ED50s were administered concurrently to establish the ED50 of the drug combination. The drug interaction between gabapentin and R-PIA was analyzed using the isobolographic method. Adenosine A1 receptor antagonist was administered intrathecally to examine the reversal of the antiallodynic effect. Locomotor function changes were evaluated by rotarod testing. Intrathecal gabapentin and R-PIA and their combination produced a dose-dependent antagonism against mechanical allodynia without severe side effects. Intrathecal gabapentin synergistically enhanced the antiallodynic effect of R-PIA when coadministered. There were no significant changes in rotarod performance time, except gabapentin 300 microgram. In the combination group, the maximal antiallodynic effect was reversed by A1 adenosine receptor antagonist. These results suggest that activation of adenosine A1 receptors at the spinal level is required for the synergistic interaction on the mechanical allodynia.
Adenosine/administration & dosage/*analogs & derivatives ; Amines/*administration & dosage ; Animals ; Cyclohexanecarboxylic Acids/*administration & dosage ; Dose-Response Relationship, Drug ; Drug Synergism ; Drug Therapy, Combination ; Injections, Spinal ; Ligation ; Male ; Pain/*drug therapy ; Rats ; Rats, Sprague-Dawley ; Receptor, Adenosine A1/drug effects/physiology ; Spinal Nerves/*injuries ; Xanthines/pharmacology ; gamma-Aminobutyric Acid/*administration & dosage

This study was designed to determine whether early gabapentin treatment has a protective analgesic effect on neuropathic pain and compared its effect to the late treatment in a rat neuropathic model, and as the potential mechanism of protective action, the alpha2delta1-subunit of the voltage-dependent calcium channel (alpha2delta1-subunit) was evaluated in both sides of the L5 dorsal root ganglia (DRG). Neuropathic pain was induced in male Sprague-Dawley rats by a surgical ligation of left L5 nerve. For the early treatment group, rats were injected with gabapentin (100 mg/kg) intraperitoneally 15 min prior to surgery and then every 24 hr during postoperative day (POD) 1-4. For the late treatment group, the same dose of gabapentin was injected every 24 hr during POD 8-12. For the control group, L5 nerve was ligated but no gabapentin was administered. In the early treatment group, the development of allodynia was delayed up to POD 10, whereas allodynia was developed on POD 2 in the control and the late treatment group (p<0.05). The alpha2delta1-subunit was up-regulated in all groups, however, there was no difference in the level of the alpha2delta1-subunit among the three groups. These results suggest that early treatment with gabapentin offers some protection against neuropathic pain but it is unlikely that this action is mediated through modulation of the alpha2delta1-subunit in DRG.
Amines/administration & dosage/*therapeutic use ; Analgesics/administration & dosage/*therapeutic use ; Animals ; Calcium Channels/genetics/*metabolism ; Cyclohexanecarboxylic Acids/administration & dosage/*therapeutic use ; Disease Models, Animal ; Injections, Intraperitoneal ; Ligation ; Male ; Neuralgia/*drug therapy/metabolism ; Pain Measurement ; Protein Subunits/genetics/metabolism ; Rats ; Rats, Sprague-Dawley ; Spinal Nerves/surgery ; Up-Regulation ; gamma-Aminobutyric Acid/administration & dosage/*therapeutic use

Antagonists for spinal N-methyl-D-aspartate (NMDA) and amino-hydroxy-methtyl-isoxazolepropionate (AMPA) receptors are effective in attenuating acute nociception or injury-induced hyperalgesia. The antinociception of spinal gabapentin is developed in injury-induced hyperalgesia without affecting acute nociception. The authors evaluated the effects of intrathecal gabapentin, NMDA antagonist (MK801) and AMPA antagonist (NBQX) in the formalin test which shows injury-induced hyperalgesia as well as acute pain. We further assessed the interactions between gabapentin and either MK801 or NBQX. Male Sprague-Dawley rats were implanted with intrathecal catheters. To evoke pain, 50 microliter of 5% formalin solution was injected into the hindpaw. The interaction was investigated by a fixed dose analysis or an isobolographic analysis. MK801 and NBQX suppressed flinching responses during phase 1 of the formalin test, while gabapentin had little effect on phase 1. All three agents decreased the phase 2 flinching response. A fixed dose analysis in phase 1 showed that gabapentin potentiated the antinociceptive effect of MK801 and NBQX. Isobolographic analysis in phase 2 revealed a synergistic interaction after coadministration of gabapentin-MK801 or gabapentin-NBQX. Correspondingly, spinal gabapentin with NMDA or AMPA antagonist may be useful in managing acute pain and injury-induced hyperalgesia.
Amines/administration & dosage/*pharmacology ; Analgesics/*pharmacology ; Animals ; Cyclohexanecarboxylic Acids/administration & dosage/*pharmacology ; Dizocilpine Maleate/*pharmacology ; Drug Interactions ; Excitatory Amino Acid Antagonists/*pharmacology ; Hyperalgesia/drug therapy ; Injections, Spinal ; Male ; Quinoxalines/*pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, AMPA/drug effects/physiology ; Receptors, N-Methyl-D-Aspartate/drug effects/physiology ; Research Support, Non-U.S. Gov't ; gamma-Aminobutyric Acid/administration & dosage/*pharmacology