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      Comparison of the efficacy of carbamazepine, gabapentin and lamotrigine for neuropathic pain in rats

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          Abstract

          Background:

          Neuropathic pain in cancer patients remain a treatment challenge. Many of the anticancer drugs have to be abandoned because patients develop neuropathic pain. Several antiepileptic drugs like carbamazepine, phenytoin, lamotrigine, felbamate are effective in neuropathic pain and trigeminal neuralgia. However, their efficacy varies.

          Aim:

          The aim of this study is to compare the efficacy of antiepileptic drugs in neuropathic pain induced by anticancer drugs.

          Materials and Methods:

          Neuropathic pain was induced in rats by injecting 4 doses of paclitaxel. The rats were divided into four groups of six animals each. Group I was treated with oral carbamazepine (cbz) 100 mg/kg, group II received oral gabapentin (gbp) 60 mg/kg, and group III was treated with oral lamotrigine (lam) 40 mg/kg and group IV was the control group. Behavioural testing for thermal hyperalgesia and mechanical hyperalgesia was assessed from 26 th day of paclitaxel administration to next five days by hot plate method and Randall Siletto test, respectively, in all the four groups. One way analysis of variance followed by Scheffe's post hoc test was used for statistical analysis.

          Results:

          In thermal hyperalgesia lam treated group was found to be significantly ( P < 0.001) superior to cbz and gbp treated group. In mechanical hyperalgesia, lam group showed significant response ( P < 0.05) as compared to gbp group. However, the gbp treated group showed a significant ( P < 0.01) improvement after three days of treatment.

          Conclusions:

          In paclitaxel induced neuropathic pain, lamotrigine appears to be a promising drug. The difference in responses shown by different antiepileptics’ depends on the etiology of the underlying mechanisms in neuropathic pain.

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          Most cited references 21

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          A method for measurement of analgesic activity on inflamed tissue.

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            Injury type-specific calcium channel alpha 2 delta-1 subunit up-regulation in rat neuropathic pain models correlates with antiallodynic effects of gabapentin.

            The calcium channel alpha2delta-1 subunit is a structural subunit important for functional calcium channel assembly. In vitro studies have shown that this subunit is the binding site for gabapentin, an anticonvulsant that exerts antihyperalgesic effects by unknown mechanisms. Increased expression of this subunit in the spinal cord and dorsal root ganglia (DRG) has been suggested to play a role in enhanced nociceptive responses of spinal nerve-injured rats to innocuous mechanical stimulation (allodynia). To investigate whether a common mechanism underlies allodynic states derived from different etiologies, and if so, whether similar alpha2delta-1 subunit up-regulation correlates with these allodynic states, we compared DRG and spinal cord alpha2delta-1 subunit levels and gabapentin sensitivity in allodynic rats with mechanical nerve injuries (sciatic nerve chronic constriction injury, spinal nerve transection, or ligation), a metabolic disorder (diabetes), or chemical neuropathy (vincristine neurotoxicity). Our data indicated that even though allodynia occurred in all types of nerve injury investigated, DRG and/or spinal cord alpha2delta-1 subunit up-regulation and gabapentin sensitivity only coexisted in the mechanical and diabetic neuropathies. Thus, induction of the alpha2delta-1 subunit in the DRG and spinal cord is likely regulated by factors that are specific for individual neuropathies and may contribute to gabapentin-sensitive allodynia. However, the calcium channel alpha2delta-1 subunit is not the sole molecular change that uniformly characterizes the neuropathic pain states.
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              Gabapentin and pregabalin, but not morphine and amitriptyline, block both static and dynamic components of mechanical allodynia induced by streptozocin in the rat.

              A single injection of streptozocin (50 mg/kg, i.p.) led to the development of static and dynamic allodynia in the rat. The two responses were detected, respectively, by application of pressure using von Frey hairs or lightly stroking the hind paw with a cotton bud. Static allodynia was present in the majority of the animals within 10 days following streptozocin. In contrast, dynamic allodynia took almost twice as long to develop and was only present in approximately 60% of rats. Morphine (1-3 mg/kg, s.c.) and amitriptyline (0.25-2.0 mg/kg, p.o.) dose-dependently blocked static allodynia. However, neither of the compounds was effective against dynamic allodynia. In contrast, gabapentin (10-100 mg/kg, p.o.) and the related compound pregabalin (3-30 mg/kg, p.o.) dose-dependently blocked both types of allodynia. However, the corresponding R-enantiomer (10-100 mg/kg, p.o.) of pregabalin, was found to be inactive. The intrathecal administration of gabapentin dose-dependently (1-100 microg/animal) blocked both static and dynamic allodynia. In contrast, administration of similar doses of gabapentin into the hind paw failed to block these responses. It is suggested that in this model of neuropathic pain dynamic allodynia is mediated by A beta-fibres and the static type involves small diameter nociceptive fibres. These data suggest that gabapentin and pregabalin possess a superior antiallodynic profile than morphine and amitriptyline, and may represent a novel class of therapeutic agents for the treatment of neuropathic pain.
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                Author and article information

                Journal
                Indian J Pharmacol
                IJPharm
                Indian Journal of Pharmacology
                Medknow Publications (India )
                0253-7613
                1998-3751
                Sep-Oct 2011
                : 43
                : 5
                : 596-598
                Affiliations
                Department of Pharmacology, Kasturba Medical College, Manipal University, Manipal, Karnataka, India
                Author notes
                Correspondence to: Dr. Bharti Chogtu, E-mail: bhartimagazine@ 123456gmail.com
                Article
                IJPharm-43-596
                10.4103/0253-7613.84980
                3195135
                22022008
                Copyright: © Indian Journal of Pharmacology

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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