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

FeTMPyP a peroxynitrite decomposition catalyst ameliorated functional and behavioral deficits in chronic constriction injury induced neuropathic pain in rats

Neuropathic pain is a maladaptive pain phenotype that results from injury or damage to the somatosensory nervous system and is proposed to be linked to a cascade of events including excitotoxicity, oxidative stress, mitochondrial dysfunction, neuroinflammation and apoptosis. Oxidative/nitrosative stress is a critical link between neuroinflammation and neurodegeneration through poly (ADP) ribose polymerase (PARP) overactivation. Hence, the present study investigated the antioxidant and anti-inflammatory effects of peroxynitrite decomposition catalyst; FeTMPyP in chronic constriction injury (CCI) of sciatic nerve-induced neuropathy in rats. CCI of the sciatic nerve manifested significant deficits in behavioral, biochemical, functional parameters and was markedly reversed by administration of FeTMPyP. After 14 days of CCI induction, oxidative/nitrosative stress and inflammatory markers such as iNOS, NF-kB, TNF-α and IL-6 were elevated in sciatic nerves of CCI rats along with depleted levels of ATP and elevated levels of poly (ADP) ribose (PAR) in both sciatic nerves in ipsilateral (L4-L5) dorsal root ganglions (DRG's), suggesting over activation of PARP. Additionally, CCI resulted in aberrations in mitochondrial function as evident by decreased Mn-SOD levels and respiratory complex activities with increased mitochondrial fission protein DRP-1. These changes were reversed by treatment with FeTMPyP (1 & 3 mg/kg, p.o.). Findings of this study suggest that FeTMPyP, by virtue of its antioxidant properties, reduced both PARP over-activation and subsequent neuroinflammation resulted in protection against CCI-induced functional, behavioral and biochemical deficits.

Carbamazepine conquers spinal GAP43 deficiency and sciatic Nav1.5 upregulation in diabetic mice: novel mechanisms in alleviating allodynia and hyperalgesia

This work tested the role of carbamazepine in alleviating alloxan-induced diabetic neuropathy and the enhancement of spinal plasticity. Mice were randomized into four groups: normal, control, carbamazepine (25-mg/kg) and carbamazepine (50-mg/kg). Nine weeks after induction of diabetes, symptoms of neuropathy were confirmed and carbamazepine (or vehicle) was given every other day for five weeks. After completing the treatment period, mice were sacrificed and the pathologic features in the spinal cord and the sciatic nerves were determined. The spinal cords were evaluated for synaptic plasticity (growth associated protein-43, GAP43), microglia cell expression (by CD11b) and astrocyte expression (glial fibrillary acidic protein, GFAP). Further, sciatic nerve expression of Nav1.5 was measured. Results revealed that carbamazepine 50 mg/kg prolonged the withdrawal threshold of von-Frey filaments and increased the hot plate jumping time. Carbamazepine improved the histopathologic pictures of the sciatic nerves and spinal cords. Spinal cord of carbamazepine-treated groups had enhanced expression of GAP43 but lower content of CD11b and GFAP. Furthermore, specimens from the sciatic nerve indicated low expression of Nav1.5. In conclusion, this work provided evidence, for the first time, that the preventive effect of carbamazepine against diabetic neuropathy involves correction of spinal neuronal plasticity and glia cell expression.

LOW-DOSE NALTREXONE REVERSES FACIAL MECHANICAL ALLODYNIA IN A RAT MODEL OF TRIGEMINAL NEURALGIA

Trigeminal neuralgia (TN) is a type of neuropathic pain characterized by intense pain; although anticonvulsants are used as an option to relieve pain, adverse side effects can decrease patient adherence. In this context, a low dose of naltrexone is effective in relieving pain in other pain conditions. Thus, the objective of the present study was to evaluate the analgesic effect of low-dose naltrexone on facial mechanical allodynia in a rat model of TN, as well as its effect(s) on biomarkers in the central nervous system (tumor necrosis factor-alpha, brain-derived neurotrophic factor [BDNF], interleukin [IL]-10, and toll-like receptor-4). Fifty-nine adult male Wistar rats (CEUA-HCPA#2017-0575) were allocated to following groups: control; sham-pain + vehicle; sham-pain + carbamazepine (100 mg/kg); sham-pain + naltrexone (0.5 mg/kg); pain + vehicle; pain + carbamazepine; and pain + naltrexone. TN was induced using chronic constriction of the infraorbital nerve. Facial allodynia was assessed using von Frey test. Drugs were administered by gavage 14 days after surgery for 10 days. At baseline, the mechanical threshold was similar between groups (P > 0.05; generalized estimating equation). Seven days after surgery, facial allodynia was observed in sham-TN and pain-TN groups (P < 0.05). Fourteen days after surgery, only pain-TN groups exhibited facial allodynia. The first dose of low-dose naltrexone or carbamazepine partially reversed facial allodynia. After 10 days of treatment, both drugs completely reversed it. Spinal cord levels of BDNF and IL-10 were modulated by low-dose naltrexone. Thus, low-dose naltrexone may be suitable to relieve TN; however, the exact mechanisms need to be clarified.

Use of Flavored Tablets of Gabapentin and Carprofen to Attenuate Postoperative Hypersensitivity in an Incisional Pain Model in Rats (Rattus norvegicus)

Providing postoperative analgesia to rats by oral administration, compared with injections, reduces stress from frequent handling and is technically easier for investigators. The purpose of this study was to investigate whether bacon-flavored tablets containing gabapentin, carprofen or a combination of both drugs effectively attenuates postoperative mechanical and thermal hypersensitivity in a rat model of incisional pain. Forty-eight Sprague-Dawley rats were randomly assigned to 1 of 5 treatment groups: placebo tablet; a single, subcutaneous injection of buprenorphine sustained release at 1.2 mg/kg; gabapentin 90 mg/tablet; carprofen 5 mg/tablet; gabapentin 90 mg and carprofen 5 mg/tablet (gabapentin/carprofen). Tablets were given to rats on days -3, -2, -1, 0 (surgery), 1, and 2. Rats were anesthetized using isoflurane. A 1 cm skin incision was made aseptically on the plantar surface of the left hindpaw and closed by using suture. Mechanical (von Frey monofilament) and thermal (Hargreaves method) hypersensitivity were tested daily, and analyzed on days -1, 1, 2, and 3. The amount of tablet consumed was recorded daily; postoperatively rats consumed 101 to 133 mg/kg of gabapentin, 5.5 to 5.8 mg/kg of carprofen, and 86-137/1.9-3 mg/kg of gabapentin/carprofen, respectively. Both the gabapentin and carprofen groups displayed attenuated mechanical hypersensitivity on all 3 postsurgical days and decreased thermal hypersensitivity on Day 3. The gabapentin/ carprofen group showed attenuated mechanical hypersensitivity on Day 2 and 3, but no significant reduction of thermal hypersensitivity. These data suggest that both gabapentin and carprofen, given orally by flavored tablet, effectively attenuate postoperative mechanical hypersensitivity for 3 d after surgery in a rat model of incisional pain.

Psychotropic Drugs for the Management of Chronic Pain and Itch

Clinical observations have shown that patients with chronic neuropathic pain or itch exhibit symptoms of increased anxiety, depression and cognitive impairment. Such patients need corrective therapy with antidepressants, antipsychotics or anticonvulsants. It is known that some psychotropic drugs are also effective for the treatment of neuropathic pain and pruritus syndromes due to interaction with the secondary molecular targets. Our own clinical studies have identified antipruritic and/or analgesic efficacy of the following compounds: tianeptine (atypical tricyclic antidepressant), citalopram (selective serotonin reuptake inhibitor), mianserin (tetracyclic antidepressant), carbamazepine (anticonvulsant), trazodone (serotonin antagonist and reuptake inhibitor), and chlorprothixene (antipsychotic). Venlafaxine (serotonin-norepinephrine reuptake inhibitor) is known to have an analgesic effect too. The mechanism of such effect of these drugs is not fully understood. Herein we review and correlate the literature data on analgesic/antipruritic activity with pharmacological profile of these compounds.

Effect of Gabapentin and Pregabalin in Rat Model of Taxol Induced Neuropathic Pain

BACKGROUND

Chemotherapy induced neuropathy pain remains as a major dose limiting side effect of many commonly used chemotherapeutic drugs. Presently newer antiepileptic agents have been developed with improved safety and tolerability profiles in alleviating neuropathic pain.

OBJECTIVES

To evaluate the effect of Gabapentin and Pregabalin in Paclitaxel (Taxol) induced neuropathic pain and to compare the effect of these drugs in animal models.

MATERIALS AND METHODS

Rats were randomly divided into four groups of six animals each. Group 1- vehicle, Group 2 - Paclitaxel (2mg/kg), Group 3 - Gabapentin (60mg/kg) with Paclitaxel, Group 4 - Pregabalin (30mg/kg) with Paclitaxel. Pain was induced by intraperitoneal injection of Paclitaxel on four alternate days. After taking the baseline values, the drugs treated groups (group 3 and 4) were administered with respective drugs once a day orally for eight consecutive days along with paclitaxel. All the animals were tested for thermal hyperalgesia and cold allodynia on day 0, 7, 14, 21 and 28 with Radiant heat method and Tail immersion test, Acetone drop method respectively.

RESULTS

In Radiant heat method, gabapentin and pregabalin treated animals found to have significant increase in the tail latency period compared to control and paclitaxel treated groups in all periods of observation. Acetone drop test and tail immersion test also showed significant response similar to Radiant heat method. Pregabalin showed highly significant effect when compared to gabapentin group.

CONCLUSION

Both gabapentin and pregabalin produced significant anti-hyperalgesic and anti-allodynic effects in experimental animal models. Pregabalin treated group showed highly significant effect compared to gabapentin treated animals.

Lamotrigine-induced severe cutaneous adverse reaction: Update data from 1999-2014

We systematically reviewed and analyzed published patients with Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN) associated with lamotrigine therapy to identify characteristics of these reactions. We identified a total of 70 patients (42 SJS, five SJS/TEN, 23 TEN). The female to male ratio was 2.83:1 in the TEN group and 1.47:1 in the SJS group. Patients in the TEN group were younger than in the SJS group but this difference was not significant (28.35 versus 32.71 years, respectively; p=0.27). The median time to onset was 25.33 versus 18.42 days for SJS and TEN, respectively. The median dosage at onset was 36.46 versus 57.29mg, and final dosage 111.25 versus 97.92mg/day for SJS and TEN, respectively. The median final dosages did not significantly differ. Concomitant use of valproate acid was reported in 54.55% of the SJS patients and 50.00% of the TEN patients. Three fatal reactions were reported, of which two patients deteriorated rapidly and died within 12h of admission, indicating that this disease can develop rapidly before effective treatment. There was no significant difference between the SJS and TEN groups in any of the clinical factors examined which confirmed the opinion that SJS and TEN are part of a single disease spectrum.

The Efficacy of Gabapentin in Patients with Central Post-stroke Pain

Thalamic pain syndrome, a type of central post-stroke pain (CPSP), may develops after a hemorrhagic or ischemic stroke and results in impairment of the thalamus. There is limited experience about gabapentin in treatment of central pains like CPSP. In a prospective observational study, the intensity of pain was recorded using the Numeric Rating Scale (NRS) at the entrance to the study. Patients eligible for treating with gabapentin, received gabapentin 300 mg twice-daily. The pain intensity was measured at entrance to the study and after one month using NRS. Decrease of 3 points from the initial NRS considered being clinically significant. From a total of 180 primarily screened patients, 84 (44 men and 40 women) were recruited. There was a significant difference between pre-treatment and post-treatment NRS (5.9 ± 2.51 vs. 4.7 ± 3.01; 95% CI: 0.442-1.962, p = 0.002). Fisher's exact test showed no statistically significant effect of clinical and demographic characteristics of patients on their therapeutic response to gabapentin. Given the safety, efficacy, well tolerability and lack of interaction with other drugs we suggest gabapentin to be more considered as a first line therapy or as add-on therapy for reducing the pain severity in patients with thalamic syndrome.

Gabapentin reverses central pain sensitization following a collagenase-induced intrathalamic hemorrhage in rats

PURPOSE

The treatment of central neuropathic pain remains amongst the biggest challenges for pain specialists. The main objective of this study was to assess gabapentin (GBP), amitriptyline (AMI), and carbamazepine (CARBA) for the treatment of a rodent central neuropathic pain model.

METHODS

Male Sprague Dawley rats were trained on the rotarod, Hargreaves, Von Frey and acetone behavioral tests, and baseline values were obtained prior to surgery. A stereotaxic injection of either a collagenase solution or saline was made in the right ventral posterolateral thalamic nucleus. The rats were tested on days 2, 4, 8, and 11 postsurgery. They were retested at regular intervals from day 15 to day 25 postsurgery, after oral administration of either the vehicle (n=7 and n=8 rats with intracerebral injections of collagenase and saline, respectively) or the different drugs (GBP [60 mg/kg], AMI [10 mg/kg], CARBA [100 mg/kg]; n=8 rats/drug).

RESULTS

A significant decrease in the mechanical thresholds and no change in heat threshold were observed in both hind limbs in the collagenase group, as we had previously shown elsewhere. Reversal of the mechanical hypersensitivity was achieved only with GBP (P<0.05). AMI and CARBA, at the dosages used, failed to show any effect on mechanical thresholds. Transient cold allodynia was observed in some collagenase-injected rats but failed to be statistically significant.

CONCLUSION

Intrathalamic hemorrhaging in the ventrolateral thalamic nucleus induced a bilateral mechanical allodynia, which was reversed by GBP but not AMI or CARBA.

The influence of spatial pulsed magnetic field application on neuropathic pain after tibial nerve transection in rat

The purpose of the study was to examine the influence of the spatial variable magnetic field (induction: 150-300 µT, 80-150 µT, 20-80 µT; frequency 40 Hz) on neuropathic pain after tibial nerve transection. The experiments were carried out on 64 male Wistar C rats. The exposure of animals to magnetic field was performed 1 d/20 min., 5 d/week, for 28 d. Behavioural tests assessing the intensity of allodynia and sensitivity to mechanical and thermal stimuli were conducted 1 d prior to surgery and 3, 7, 14, 21 and 28 d after the surgery. The extent of autotomy was examined. Histological and immunohistochemical analysis was performed. The use of extremely low-frequency magnetic fields of minimal induction values (20-80 µT/40 Hz) decreased pain in rats after nerve transection. The nociceptive sensitivity of healthy rats was not changed following the exposition to the spatial magnetic field of the low frequency. The results of histological and immunohistochemical investigations confirm those findings. Our results indicate that extremely low-frequency magnetic field may be useful in the neuropathic pain therapy.