The effect of gabapentin on neuropathic pain

Peripheral nerves in the tibial subchondral bone : the role of pain and homeostasis in osteoarthritis

Osteoarthritis (OA) is a highly prevalent degenerative joint disorder characterized by joint pain and physical disability. Aberrant subchondral bone induces pathological changes and is a major source of pain in OA. In the subchondral bone, which is highly innervated, nerves have dual roles in pain sensation and bone homeostasis regulation. The interaction between peripheral nerves and target cells in the subchondral bone, and the interplay between the sensory and sympathetic nervous systems, allow peripheral nerves to regulate subchondral bone homeostasis. Alterations in peripheral innervation and local transmitters are closely related to changes in nociception and subchondral bone homeostasis, and affect the progression of OA. Recent literature has substantially expanded our understanding of the physiological and pathological distribution and function of specific subtypes of neurones in bone. This review summarizes the types and distribution of nerves detected in the tibial subchondral bone, their cellular and molecular interactions with bone cells that regulate subchondral bone homeostasis, and their role in OA pain. A comprehensive understanding and further investigation of the functions of peripheral innervation in the subchondral bone will help to develop novel therapeutic approaches to effectively prevent OA, and alleviate OA pain.

Cite this article: Bone Joint Res 2022;11(7):439–452.

Animal Venom Peptides Cause Antinociceptive Effects by Voltage-gated Calcium Channels Activity Blockage

Pain is a complex phenomenon that is usually unpleasant and aversive. It can range widely in intensity, quality, and duration and has diverse pathophysiologic mechanisms and meanings. Voltage-gated sodium and calcium channels are essential to transmitting painful stimuli from the periphery until the dorsal horn of the spinal cord. Thus, blocking voltage-gated calcium channels (VGCCs) can effectively control pain refractory to treatments currently used in the clinic, such as cancer and neuropathic pain. VGCCs blockers isolated of cobra Naja naja kaouthia (α-cobratoxin), spider Agelenopsis aperta (ω-Agatoxin IVA), spider Phoneutria nigriventer (PhTx3.3, PhTx3.4, PhTx3.5, PhTx3.6), spider Hysterocrates gigas (SNX-482), cone snails Conus geographus (GVIA), Conus magus (MVIIA or ziconotide), Conus catus (CVID, CVIE and CVIF), Conus striatus (SO- 3), Conus fulmen (FVIA), Conus moncuri (MoVIA and MoVIB), Conus regularis (RsXXIVA), Conus eburneus (Eu1.6), Conus victoriae (Vc1.1.), Conus regius (RgIA), and spider Ornithoctonus huwena (huwentoxin-I and huwentoxin-XVI) venoms caused antinociceptive effects in different acute and chronic pain models. Currently, ziconotide is the only clinical used N-type VGCCs blocker peptide for chronic intractable pain. However, ziconotide causes different adverse effects, and the intrathecal route of administration also impairs its use in a more significant number of patients. In this sense, peptides isolated from animal venoms or their synthetic forms that act by modulating or blocking VGCCs channels seem to be a relevant prototype for developing new analgesics efficacious and well tolerated by patients.

Comparison of Oral Clonidine and Gabapentin Premedication for Attenuation of Pressor Response to Laryngoscopy and Endotracheal Intubation

Background:

During the administration of general anesthesia, direct laryngoscopy and endotracheal intubation cause an increase in heart rate, arterial pressure, and dysrhythmias in upto 90% of patients. These changes can be particularly hazardous for patients with cerebral or coronary diseases. Both clonidine and gabapentin have been used for anesthetic effects, but a better drug for controlling hemodynamic parameters is being investigated.

Aims:

The study was done to evaluate and compare the efficacy of oral clonidine 0.3 mg and oral gabapentin 900 mg as a premedication for attenuation of pressor response to laryngoscopy and endotracheal intubation.

Materials and Methods:

After obtaining approval from the ethics committee, 75 patients, American Society of Anesthesiologists physical status classes I and II between the ages of 18 and 60 years scheduled to undergo elective noncardiac surgical procedure were enrolled in the study. Patients were randomized into three groups of 25 each who received 0.3 mg clonidine, 900 mg gabapentin, and placebo. The hemodynamic parameters were recorded at various time intervals along with any adverse effects.

Statistical Analysis:

Quantitative variables were compared using unpaired t-test between the two groups and ANOVA for three groups. Qualitative variables were compared using the Chi-square test/Fisher's exact test. P < 0.05 was considered statistically significant.

Results:

In our study, we found that both clonidine and gabapentin are effective premedicants by oral route 2 h before induction of anesthesia to blunt the hemodynamic response to laryngoscopy and intubation as compared to placebo. Between clonidine and gabapentin, clonidine was found to be more effective with respect to blunting of systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP), although found to be statistically significant only at 15 min with respect to SBP and DBP.

Conclusion:

Using clonidine or gabapentin, one can effectively provide stable hemodynamic conditions during laryngoscopy and endotracheal intubation, but more so with clonidine.

A novel gabapentin analogue assuages neuropathic pain response in chronic sciatic nerve constriction model in rats

Gabapentin (GBP) is an established drug that has been used in the management of symptoms of neuropathy but it is associated with unwanted side effects such as sedation and motor incoordination. The goal of the study was to find out a drug with greater efficacy and safety for the treatment of neuropathic pain. Our previously synthesized GABA analogue (Gabapentsal, GPS) was tested (25-100 mg/kg, i.p) in chronic constriction injury (CCI) induced nociceptive model of static allodynia, dynamic allodynia, thermal hyperalgesia, mechanical hyperalgesia and cold allodynia in rats (Sprague Dawley). Open field and rotarod tests were performed to assess the impact of GPS on the motor performance of the animals. GBP (100 mg/kg, i.p) was used as a standard for comparison. GPS dose dependently reduced static (P <0.001) and dynamic allodynia (P <0.001), thermal hyperalgesia (P <0.001), mechanical hyperalgesia (P < 0.001) and cold allodynia (P < 0.001). In comparison to GBP, GPS failed to alter any significantly the motor performance of rats in both the open field and rotarod assays. These results suggest that GPS is effective in alleviating nociception in CCI neuropathic pain model but free from the side effect of motor discoordination seen in the treatment with GBP. In conclusion, GPS may prove to be a prospectively more effective and safer option in the management of neuropathic syndromes.

Gabapentin for phantom limb pain after amputation in pediatric oncology: a systematic review protocol

BACKGROUND

Phantom limb pain (PLP) is a prevalent problem for children after amputation because of the chemotherapy treatment. Gabapentin is a potential option to manage PLP after amputation in pediatric oncology. However, no systematic review specifically investigated this topic. Thus, this study aims to appraise the efficacy and safety of gabapentin for post-amputation PLP in pediatric oncology.

METHODS

Electronic databases (Cochrane Library, MEDLINE, EMBASE, Web of Science, CINAHL, PsychINFO, Scopus, WANGFANG, and Chinese Biomedical Literature Database) will be systematically searched from the beginning to the present without limitations to publication status and language. Primary outcome is pain intensity. Secondary outcomes are analgesic drug consumption, sleep quality, depression, anxiety, health-related quality of life, and adverse events. The treatment effect of all dichotomous outcome data will be estimated as risk ratio and 95% confidence intervals (CIs) and that of continuous outcome data will be calculated as mean difference or standardized mean difference and 95% CIs. Methodological quality of randomized controlled trials (RCTs) will be assessed using Cochrane risk of bias tool and that of case-controlled studies (CCSs) will be appraised using Newcastle-Ottawa Tool. Statistical analysis will be conducted using RevMan 5.3 software.

DISCUSSION

This study will summarize up-to-date high-quality RCTs and CCSs to assess the efficacy and safety of gabapentin for PLP after amputation in pediatric oncology. The findings of this study will help to determine whether or not gabapentin is effective and safe for children with PLP after amputation.

SYSTEMATIC REVIEW REGISTRATION

INPLASY202060090.

Prolonged Analgesia by Spinal Cord Stimulation Following a Spinal Injury Associated With Activation of Adult Neural Progenitors

OBJECTIVES

Responses of spinal progenitors to spinal cord stimulation (SCS) following spinal cord injury (SCI) in rats were assessed to reveal their potential contribution to SCS-induced analgesia.

METHODS

Spinal epidural electrodes were implanted in rats at T12 rostral to a quadrant dorsal horn injury at T13. Further groups additionally received either a microlesion to the dorsolateral funiculus (DLF) or gabapentin (10 mg/kg). SCS was performed at 25 Hz for 10 minutes on day 4 (early SCS) and at 10 Hz for 10 minutes on day 8 (late SCS) after injury. Paw withdrawal threshold (PWT) was measured before injury, 30 minutes before or after SCS, and before cull on day 14, followed by immunostaining assessment.

RESULTS

Paw withdrawal thresholds in uninjured animals (51.0 ± 4.0 g) were markedly reduced after SCI (17.3 ± 2.2 g). This was significantly increased by early SCS (38.5 ± 5.2 g, P < 0.01) and further enhanced by late SCS (50.9 ± 1.9 g, P < 0.01) over 6 days. Numbers of neural progenitors expressing nestin, Sox2, and doublecortin (DCX) in the spinal dorsal horn were increased 6 days after SCS by 6-fold, 2-fold, and 2.5-fold, respectively (P < 0.05 to 0.01). The elevated PWT evoked by SCS was abolished by DLF microlesions (48.9 ± 2.6 g vs. 19.0 ± 3.9 g, P < 0.01) and the number of nestin-positive cells was reduced to the level without SCS (P < 0.05). Gabapentin enhanced late SCS-induced analgesia from 37.0 ± 3.9 g to 54.0 ± 0.8 g (P < 0.01) and increased gamma-aminobutyric acid (GABA)-ergic neuronal marker vesicular GABA transporter-positive newborn cells 2-fold (P < 0.01).

CONCLUSIONS

Spinal progenitor cells appear to be activated by SCS via descending pathways, which may be enhanced by gabapentin and potentially contributes to relief of SCI-induced neuropathic pain.

Direct, gabapentin-insensitive interaction of a soluble form of the calcium channel subunit α2δ-1 with thrombospondin-4

The α₂δ‐1 subunit of voltage-gated calcium channels binds to gabapentin and pregabalin, mediating the analgesic action of these drugs against neuropathic pain. Extracellular matrix proteins from the thrombospondin (TSP) family have been identified as ligands of α₂δ‐1 in the CNS. This interaction was found to be crucial for excitatory synaptogenesis and neuronal sensitisation which in turn can be inhibited by gabapentin, suggesting a potential role in the pathogenesis of neuropathic pain. Here, we provide information on the biochemical properties of the direct TSP/α₂δ-1 interaction using an ELISA-style ligand binding assay. Our data reveal that full-length pentameric TSP-4, but neither TSP-5/COMP of the pentamer-forming subgroup B nor TSP-2 of the trimer-forming subgroup A directly interact with a soluble variant of α₂δ-1 (α₂δ-1_S). Interestingly, this interaction is not inhibited by gabapentin on a molecular level and is not detectable on the surface of HEK293-EBNA cells over-expressing α₂δ‐1 protein. These results provide biochemical evidence that supports a specific role of TSP-4 among the TSPs in mediating the binding to neuronal α₂δ‐1 and suggest that gabapentin does not directly target TSP/α₂δ-1 interaction to alleviate neuropathic pain.

Polymelia in a chimeric Simmental calf: nociceptive withdrawal reflex, anaesthetic and analgesic management, anatomic and genetic analysis

BACKGROUND

Polymelia is a congenital defect characterized by one or more supernumerary legs. The genetics and aetiology of this condition in cattle have not yet been thoroughly investigated even though several case reports do exist. The model of the nociceptive withdrawal reflex (NWR) has been characterized in several species to study spinal nociceptive processing. It is a polysynaptic spinal reflex that can be elicited by noxious electrical stimulation and recorded by electromyography. Thorough nociceptive examination and preventive analgesic management has not yet been an aspect in the perioperative management of polymelia cases.

CASE PRESENTATION

A 4-month-old female Simmental calf was presented with notomelia. The animal was in good health and showed no neurologic deficiencies. Preoperatively, computed tomography was performed to gain more detailed anatomical information. To evaluate the sensitivity of the accessory limb, NWR testing was performed and revealed a connection of the afferent reflex pathway of the accessory limb to the efferent of the normal limb. The accessory limb was surgically removed under general anaesthesia. Intensive care included multimodal pain therapy adapted to the pain intensity scored during regular pain assessment. A gross anatomical dissection as well as a genetic analysis of the accessory limb were performed postoperatively. The calf was identified as a chimera.

CONCLUSION

This calf was successfully relieved of its accessory limb. Chimerism has not been described in the congenital defect polymelia. As the accessory limb was pain sensitive and a common nociceptive reflex pathway was identified, thorough perioperative pain management was performed with the intention to prevent chronic neuropathic pain development.

Treatment-resistant prurigo nodularis: challenges and solutions

Prurigo nodualris (PN) is a chronic condition with highly pruritic, hyperkeratotic papules or nodules arising in the setting of chronic pruritus. While PN may serve as a phenotypic presentation of several underlying conditions such as atopic dermatitis, chronic kidney disease-related pruritus, and neurological diseases, it represents a distinct clinical entity that may persist despite the removal of the underlying cause, if one is identified. Neuronal proliferation, eosinophils, mast cells, and small-fiber neuropathy play a role in the production of pruritus in PN, although the exact mechanism has not yet been established. Identifying an underlying cause, if present, is essential to prevent recurrence of PN. Due to often present comorbidities, treatment is typically multimodal with utilization of topical and systemic therapies. We performed a PubMed/MEDLINE search for PN and present a review of recent developments in the treatment of PN. Treatment typically relies on the use of topical or intralesional steroids, though more severe or recalcitrant cases often necessitate the use of phototherapy or systemic immunosuppressives. Thalidomide and lenalidomide can both be used in severe cases; however, their toxicity profile makes them less favorable. Opioid receptor antagonists and neurokinin-1 receptor antagonists represent two novel families of therapeutic agents which may effectively treat PN with a lower toxicity profile than thalidomide or lenalidomide.

Peripheral gabapentin regulates mosquito allergy-induced itch in mice

The antipruritic activity of gabapentin, an anticonvulsant, was studied in a mouse model of allergic itch. In mice sensitized by an extract of the salivary glands of the mosquito (ESGM), an intradermal injection of ESGM elicited scratching and increased peripheral nerve firing. Oral or intradermal administration of gabapentin at the ESGM injection site inhibited ESGM-induced scratching and peripheral nerve firing. However, gabapentin did not affect histamine-induced scratching. The distributions of immunoreactivity to the voltage-dependent calcium channel α₂δ-1 subunit, a site of gabapentin action, and the histamine H₁ receptor differed in the mouse dorsal root ganglia. The α₂δ-1 subunit was mainly found in neurons that were 15-20 µm in diameter, whereas the H₁ receptor was mainly in 20-30 µm neurons. In addition, α₂δ-1 subunit immunoreactivity co-localized with that of transient receptor potential vanilloid 1 (TRPV1). These results suggest that gabapentin regulates allergic itch by acting on the calcium channel α₂δ-1 subunit in peripheral TRPV1-positive neurons.

Reduction of Postherpetic Neuralgia in Herpes Zoster

Background:

Persons 50 years of age and older are not only at increased risk of developing herpes zoster, they are also more likely to suffer the long-term morbidity of postherpetic neuralgia (PHN). PHN is pain persisting after the rash of herpes zoster has healed. PHN affects at least 40% of all herpes zoster patients over age 50 and over 75% of herpes zoster patients over age 75; PHN is the single most common neurologic condition in elderly patients.

Objective:

The objective of this review is to evaluate interventions that may reduce or even eliminate PHN. No single therapy has been consistently effective for PHN. The most effective approach appears to be with the use of antiviral therapy early in the course of herpes zoster. The goals of ongoing studies in herpes zoster are to develop interventions that will further reduce the symptoms of PHN and/or to eliminate PHN by prophylaxis using the varicella vaccine.

Conclusions:

Reduction of PHN can best be achieved with the use of antiviral medication early in the course of herpes zoster; other classes of drugs are minimally effective in treating established PHN. Widespread use of the varicella vaccine may lead to secondary reductions in PHN in the distant future.

Gabapentin for the treatment of painful diabetic neuropathy: dosing to achieve optimal clinical response

Objective

To determine whether gabapentin titrated to achieve clinical effect (≥ 50% reduction in pain; 900—3,600 mg/day) provides superior efficacy to a commonly prescribed fixed-dose (900 mg/day) in subjects with PDN.

Methods

In Latin America, an open-label trial randomised 339 subjects with PDN to gabapentin, 900 mg/day, for seven weeks (n=170), or to 900—3,600 mg/day titrated over four weeks to achieve clinical effect, followed by three weeks at stable dose (n=169).

Results

Gabapentin produced a significantly greater reduction in final weekly mean pain scores from baseline when titrated to clinical effect than when administered as a fixed-dose regimen (53.6% vs. 43.3%; p=0.009). Responder rate was significantly increased (64.5% vs. 47.5%; p=0.002), mean VAS scores significantly decreased, final weekly sleep interference scores significantly decreased (57% C vs. 37.2%; p=0.013), and trends favouring improvement in global functioning and QOL were seen in the titration to clinical effect group (p<0.001). Both regimens were well-tolerated.

Conclusions

Titration to clinical effect offered superior efficacy in treating PDN compared to a low fixed-dose treatment. Br J Diabetes Vasc Dis 2004;4:173—8

Phantom Limb Pain—A Complication of Lower Extremity Wound Management

Amputation is one treatment option for patients with critical limb ischemia, diabetic foot wounds, and occasionally, even venous leg ulcers. Amputation of the whole limb or part of it or the digits can cause complications including pain. Post-amputation pain, and especially phantom limb pain (PLP), is a poorly understood phenomenon. Effective management of established pain is a major challenge. This reviewis for wound workers who are a multiprofessional group. Any amputated limb, appendage, or viscera can be affected by PLP, though the focus of this article will be the treatment of PLP following limb loss. The pathophysiology is still not fully understood. The size of the problem of PLP, possible underlying physiological mechanisms, and potential preventative measures are presented in this article.

Central Mechanisms Mediating Thrombospondin-4-induced Pain States

Peripheral nerve injury induces increased expression of thrombospondin-4 (TSP4) in spinal cord and dorsal root ganglia that contributes to neuropathic pain states through unknown mechanisms. Here, we test the hypothesis that TSP4 activates its receptor, the voltage-gated calcium channel Cavα2δ1 subunit (Cavα2δ1), on sensory afferent terminals in dorsal spinal cord to promote excitatory synaptogenesis and central sensitization that contribute to neuropathic pain states. We show that there is a direct molecular interaction between TSP4 and Cavα2δ1 in the spinal cord in vivo and that TSP4/Cavα2δ1-dependent processes lead to increased behavioral sensitivities to stimuli. In dorsal spinal cord, TSP4/Cavα2δ1-dependent processes lead to increased frequency of miniature and amplitude of evoked excitatory post-synaptic currents in second-order neurons as well as increased VGlut2- and PSD95-positive puncta, indicative of increased excitatory synapses. Blockade of TSP4/Cavα2δ1-dependent processes with Cavα2δ1 ligand gabapentin or genetic Cavα2δ1 knockdown blocks TSP4 induced nociception and its pathological correlates. Conversely, TSP4 antibodies or genetic ablation blocks nociception and changes in synaptic transmission in mice overexpressing Cavα2δ1 Importantly, TSP4/Cavα2δ1-dependent processes also lead to similar behavioral and pathological changes in a neuropathic pain model of peripheral nerve injury. Thus, a TSP4/Cavα2δ1-dependent pathway activated by TSP4 or peripheral nerve injury promotes exaggerated presynaptic excitatory input and evoked sensory neuron hyperexcitability and excitatory synaptogenesis, which together lead to central sensitization and pain state development.

Passiflora incarnata attenuation of neuropathic allodynia and vulvodynia apropos GABA-ergic and opioidergic antinociceptive and behavioural mechanisms

Background

Passiflora incarnata is widely used as an anxiolytic and sedative due to its putative GABAergic properties. Passiflora incarnata L. methanolic extract (PI-ME) was evaluated in an animal model of streptozotocin-induced diabetic neuropathic allodynia and vulvodynia in rats along with antinociceptive, anxiolytic and sedative activities in mice in order to examine possible underlying mechanisms.

Methods

PI-ME was tested preliminary for qualitative phytochemical analysis and then quantitatively by proximate and GC-MS analysis. The antinociceptive property was evaluated using the abdominal constriction assay and hot plate test. The anxiolytic activity was performed in a stair case model and sedative activity in an open field test. The antagonistic activities were evaluated using naloxone and/or pentylenetetrazole (PTZ). PI-ME was evaluated for prospective anti-allodynic and anti-vulvodynic properties in a rat model of streptozotocin induced neuropathic pain using the static and dynamic testing paradigms of mechanical allodynia and vulvodynia.

Results

GC-MS analysis revealed that PI-ME contained predominant quantities of oleamide (9-octadecenamide), palmitic acid (hexadecanoic acid) and 3-hydroxy-dodecanoic acid, among other active constituents. In the abdominal constriction assay and hot plate test, PI-ME produced dose dependant, naloxone and pentylenetetrazole reversible antinociception suggesting an involvement of opioidergic and GABAergic mechanisms. In the stair case test, PI-ME at 200 mg/kg increased the number of steps climbed while at 600 mg/kg a significant decrease was observed. The rearing incidence was diminished by PI-ME at all tested doses and in the open field test, PI-ME decreased locomotor activity to an extent that was analagous to diazepam. The effects of PI-ME were antagonized by PTZ in both the staircase and open field tests implicating GABAergic mechanisms in its anxiolytic and sedative activities. In the streptozotocin-induced neuropathic nociceptive model, PI-ME (200 and 300 mg/kg) exhibited static and dynamic anti-allodynic effects exemplified by an increase in paw withdrawal threshold and paw withdrawal latency. PI-ME relieved only the dynamic component of vulvodynia by increasing flinching response latency.

Conclusions

These findings suggest that Passiflora incarnata might be useful for treating neuropathic pain. The antinociceptive and behavioural findings inferring that its activity may stem from underlying opioidergic and GABAergic mechanisms though a potential oleamide-sourced cannabimimetic involvement is also discussed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1048-6) contains supplementary material, which is available to authorized users.

Gabapentin Effects on PKC-ERK1/2 Signaling in the Spinal Cord of Rats with Formalin-Induced Visceral Inflammatory Pain

Currently, the clinical management of visceral pain remains unsatisfactory for many patients suffering from this disease. While preliminary animal studies have suggested the effectiveness of gabapentin in successfully treating visceral pain, the mechanism underlying its analgesic effect remains unclear. Evidence from other studies has demonstrated the involvement of protein kinase C (PKC) and extracellular signal-regulated kinase1/2 (ERK1/2) in the pathogenesis of visceral inflammatory pain. In this study, we tested the hypothesis that gabapentin produces analgesia for visceral inflammatory pain through its inhibitory effect on the PKC-ERK1/2 signaling pathway. Intracolonic injections of formalin were performed in rats to produce colitis pain. Our results showed that visceral pain behaviors in these rats decreased after intraperitoneal injection of gabapentin. These behaviors were also reduced by intrathecal injections of the PKC inhibitor, H-7, and the ERK1/2 inhibitor, PD98059. Neuronal firing of wide dynamic range neurons in L6–S1 of the rat spinal cord dorsal horn were significantly increased after intracolonic injection of formalin. This increased firing rate was inhibited by intraperitoneal injection of gabapentin and both the individual and combined intrathecal application of H-7 and PD98059. Western blot analysis also revealed that PKC membrane translocation and ERK1/2 phosphorylation increased significantly following formalin injection, confirming the recruitment of PKC and ERK1/2 during visceral inflammatory pain. These effects were also significantly reduced by intraperitoneal injection of gabapentin. Therefore, we concluded that the analgesic effect of gabapentin on visceral inflammatory pain is mediated through suppression of PKC and ERK1/2 signaling pathways. Furthermore, we found that the PKC inhibitor, H-7, significantly diminished ERK1/2 phosphorylation levels, implicating the involvement of PKC and ERK1/2 in the same signaling pathway. Thus, our results suggest a novel mechanism of gabapentin-mediated analgesia for visceral inflammatory pain through a PKC-ERK1/2 signaling pathway that may be a future therapeutic target for the treatment of visceral inflammatory pain.

Pregabalin for chronic pain: does one medication fit all?

BACKGROUND

Pregabalin is frequently prescribed for chronic non-cancer pain. No previous study has examined its off-label use.

OBJECTIVES

Our primary aim was to assess the proportion of patients taking pregabalin for conditions approved by Health Canada ('on-label') and compare their perspectives on its use to those who use pregabalin for other conditions ('off-label').

METHODS

Patients who have used pregabalin within the past year were recruited from two registries of chronic non-cancer pain patients treated in tertiary care clinics: the Quebec Pain Registry and the Fibromyalgia Patients Registry. Data on the use of pregabalin and its perceived benefits were collected from the registries and from completed questionnaires.

RESULTS

Out of 4339 screened chronic non-cancer pain patients, 355 (8.18%) met the study selection criteria. Three-quarters of them (268/355) used pregabalin for pain conditions not approved by Health Canada and were therefore regarded as off-label users. The most prevalent condition for pregabalin use was lumbar back pain (103/357; 28.85%). There were no significant differences between on- and off-label users in their perceived satisfaction from pregabalin therapy and its effect on function and quality of life. Among former users, the most prevalent reason for discontinuation was adverse effects, mainly dry mouth and weight gain.

CONCLUSIONS

We conclude that despite specific indications for pregabalin prescription, it is mainly used off-label, notably for low back pain. Nevertheless, off-label users were equally satisfied with its clinical effects. Although formal exploration of the broader analgesic properties of pregabalin is warranted, treating heterogeneous chronic pain conditions with pregabalin may be legitimate.

LIMITATIONS

The main limitations of the study are patients' low response rate, the recruitment of participants solely from a tertiary pain center and not from the general patient population and a possible recall bias that may have arisen from the retrospective nature of the study.

An unusual conformation of gabapentin (Gpn) in Pyr-Gpn-NH-NH-Pyr stabilized by weak interactions

The crystal structure of N-[(1-{2-oxo-2-[2-(pyrazin-2-ylcarbonyl)hydrazin-1-yl]ethyl}cyclohexyl)methyl]pyrazine-2-carboxamide monohydrate (Pyr-Gpn-NN-NH-Pyr·H2O), C19H23N7O3·H2O, reveals an unusual trans-gauche (tg(-)) conformation for the gabapentin (Gpn) residue around the C(γ)-C(β) (θ1) and C(β)-C(α) (θ2) bonds. The molecular conformation is stabilized by intramolecular N-H...N hydrogen bonds and weak C-H...O interactions. The packing of the molecules in the crystal lattice shows a network of strong N-H...O and O-H...O hydrogen bonds together with weak C-H...O and π-π inteactions.

A comparative study of efficacy and safety of gabapentin versus amitriptyline as coanalgesics in patients receiving opioid analgesics for neuropathic pain in malignancy

OBJECTIVE

To assess the efficacy and safety of gabapentin and amitriptyline along with opioids in patients suffering from neuropathic pain in malignancy.

MATERIALS AND METHODS

Eighty-eight adult patients between 18 and 70 years of age with neuropathic pain in stage III malignant disease, matched for baseline charactistics, were randomly assigned to two groups. Group A received oral tramadol and gabapentin and group B received oral tramadol and amitriptyline. The treatment duration of each patient was 6 months. Visual analog scale (VAS) was the primary efficacy parameter. Verbal rating scale (VRS) score, percentage of pain relief (PPR), and global pain score (GPS) were the secondary efficacy parameters. Oral morphine tablets or fentanyl transdermal patch were used as rescue medication. Data analysis was carried out in Graph Pad instat.

RESULTS

There was decline in VAS pain score from baseline in both the groups in the early phase of the study though there was no statistically detectable difference between them at any study point. Similar changes were seen in the secondary efficacy parameters too. Thus both the drugs were effective in providing relief to cancer patients with neuropathic pain though there was no statistically detectable difference in efficacy between them. Six patients in group A and eight patients in group B required rescue medication. A total of 12 subjects in the gabapentin group and 15 subjects in the amitriptyline group experienced adverse events which were of mild to moderate grades.

CONCLUSIONS

Amitriptyline may be a suitable alternative for management of neuropathic pain in cancer patients although gabapentin is widely used for this purpose. The lower cost of amitriptyline may favor patient compliance with lesser number of drop-outs.

Calcium-permeable ion channels in pain signaling

The detection and processing of painful stimuli in afferent sensory neurons is critically dependent on a wide range of different types of voltage- and ligand-gated ion channels, including sodium, calcium, and TRP channels, to name a few. The functions of these channels include the detection of mechanical and chemical insults, the generation of action potentials and regulation of neuronal firing patterns, the initiation of neurotransmitter release at dorsal horn synapses, and the ensuing activation of spinal cord neurons that project to pain centers in the brain. Long-term changes in ion channel expression and function are thought to contribute to chronic pain states. Many of the channels involved in the afferent pain pathway are permeable to calcium ions, suggesting a role in cell signaling beyond the mere generation of electrical activity. In this article, we provide a broad overview of different calcium-permeable ion channels in the afferent pain pathway and their role in pain pathophysiology.

The neurobiology of skeletal pain

Disorders of the skeleton are one of the most common causes of chronic pain and long-term physical disability in the world. Chronic skeletal pain is caused by a remarkably diverse group of conditions including trauma-induced fracture, osteoarthritis, osteoporosis, low back pain, orthopedic procedures, celiac disease, sickle cell disease and bone cancer. While these disorders are diverse, what they share in common is that when chronic skeletal pain occurs in these disorders, there are currently few therapies that can fully control the pain without significant unwanted side effects. In this review we focus on recent advances in our knowledge concerning the unique population of primary afferent sensory nerve fibers that innervate the skeleton, the nociceptive and neuropathic mechanisms that are involved in driving skeletal pain, and the neurochemical and structural changes that can occur in sensory and sympathetic nerve fibers and the CNS in chronic skeletal pain. We also discuss therapies targeting nerve growth factor or sclerostin for treating skeletal pain. These therapies have provided unique insight into the factors that drive skeletal pain and the structural decline that occurs in the aging skeleton. We conclude by discussing how these advances have changed our understanding and potentially the therapeutic options for treating and/or preventing chronic pain in the injured, diseased and aged skeleton.

Spinal morphine but not ziconotide or gabapentin analgesia is affected by alternative splicing of voltage-gated calcium channel CaV2.2 pre-mRNA

Presynaptic voltage-gated calcium Ca_V2.2 channels play a privileged role in spinal level sensitization following peripheral nerve injury. Direct and indirect inhibitors of Ca_V2.2 channel activity in spinal dorsal horn are analgesic in chronic pain states. Ca_V2.2 channels represent a family of splice isoforms that are expressed in different combinations according to cell-type. A pair of mutually exclusive exons in the Ca_V2.2 encoding Cacna1b gene, e37a and e37b, differentially influence morphine analgesia. In mice that lack exon e37a, which is enriched in nociceptors, the analgesic efficacy of intrathecal morphine against noxious thermal stimuli is reduced. Here we ask if sequences unique to e37a influence: the development of abnormal thermal and mechanical sensitivity associated with peripheral nerve injury; and the actions of two other classes of analgesics that owe part or all of their efficacy to Ca_V2.2 channel inhibition. We find that: i) the analgesic efficacy of morphine, but not ziconotide or gabapentin, is reduced in mice lacking e37a, ii) the induction and maintenance of behaviors associated with sensitization that accompany peripheral nerve injury, do not require e37a-specific sequence, iii) intrathecal morphine, but not ziconotide or gabapentin analgesia to thermal stimuli is significantly lower in wild-type mice after peripheral nerve injury, iv) the analgesic efficacy of ziconotide and gabapentin to mechanical stimuli is reduced following nerve injury, and iv) intrathecal morphine analgesia to thermal stimuli in mice lacking e37a is not further reduced by peripheral nerve injury. Our findings show that the analgesic action of morphine, but not ziconotide or gabapentin, to thermal stimuli is linked to which Cacna1b exon, e37a or e37b, is selected during alternative pre-mRNA splicing.

C5andC7intramolecular hydrogen bonds stabilize the structure ofN-pyrazinoyl-gabapentin (Pyr-Gpn-OH)

2-{1-[(Pyrazin-2-ylformamido)methyl]cyclohexyl}acetic acid (Pyr-Gpn-OH), C14H19N3O3, is an N-protected derivative of gabapentin (Gpn). The compound crystallizes in the triclinic space groupP\overline{1} and the molecular conformation is stabilized by intramolecular five- (C5) and seven-membered (C7) hydrogen-bonded rings. The packing of the molecules reveals intermolecular O—H...O and C—H...N hydrogen bonds, together with π–π interactions.

Antiepileptic drugs for the treatment of neuropathic pain: a systematic review

Many therapies have been proposed for the management of neuropathic pain, and they include the use of different antiepileptic drugs. However, the lack of high quality studies indicates that results on the different neuropathic disorders under study do not recommend a particular drug treatment. This study makes a systematic review of the published literature on the use of several antiepileptic drugs to treat neuropathic pain, and has the objective of considering both its clinical characteristics and pharmacological use, which will depend on their level of scientific evidence and will follow the principles of evidence-based dentistry. The articles were stratified according to their scientific evidence using the SORT criteria (Strength of Recommendation Taxonomy), and it included those articles that only have level 1 or 2. Randomized clinical trials were stratified according to their level of quality using the JADAD scale, an instrument described by Jadad et al. (7). to assess the quality of clinical trials, while studies with a level below 3 were discarded. Recently, type A or B recommendations are given in favor or against the use of antiepileptic drugs to treat neuropathic pain on the basis of their scientific quality.

Key words:Neuropathic pain, antiepileptic drugs (AEDs), trigeminal neuralgia, glossopharyngeal neuralgia, post- herpetic neuralgia, burning mouth syndrome, persistent idiopathic facial pain.

Painful diabetic neuropathy: an update

Diabetes, a silent killer, is a leading cause of neuropathy. Around 50% of diabetic patients develop peripheral neuropathy in 25 years. Painful diabetic neuropathy manifests as burning, excruciating, stabbing or intractable type of pain or presents with tingling or numbness. The pathophysiology of this condition is due to primarily metabolic and vascular factors. There is increase in sorbitol and fructose, glycated endproducts, reactive oxygen species and activation of protein kinase C in the diabetic state. All these factors lead to direct damage to the nerves. The first step in the management of painful diabetic neuropathy is a tight glycaemic control. Currently there is no drug which can halt or reverse the progression of the disease. Most of the therapies prevalent aim at providing symptomatic relief. Antidepressants like tricyclic antidepressants (TCAs) and selective norepinephrine reuptake inhibitors (SNRIs) have good efficacy in controlling the symptoms. Selective serotonin reuptake inhibitors have not shown the same consistent results. Anticonvulsants including pregabalin, gabapentin and lamotrigine have shown good results in the control of symptoms whereas same was not found with carbamazepine, oxcarbazepine and topiramate. Topical agents (capsaicin, topical nitrates and topical TCAs) and local anaesthetics have also been used with good results. Use of opioids and non steroidal anti-inflammatory drugs although common but is not preferable. The newer therapies under studies are NMDA antagonists, aldose reductase inhibitors, neurotropic factors, vascular endothelial growth factor, Gamma linolenic acid, protein kinase C beta inhibitors, immune therapy, hyperbaric oxygen and alpha lipoic acid.

Gabapentin, A GABA analogue, enhances cognitive performance in mice

Gabapentin is one of the new antiepileptic drugs (AEDs) launched recently. The advantage of new AEDs includes newer mechanism of action, broad spectrum of antiseizure effects, lesser drug interactions and fewer side effects. Gabapentin (GBP) a GABA analogue, is efficacious in several neurological and psychiatric conditions and it is conventionally used in the treatment of partial epilepsies. In this study, we aimed to evaluate the effects of GBP on learning and memory processes of naive mice in Morris water maze (MWM), passive avoidance (PA) and modified elevated plus maze (mEPM) tests. GBP (5 and 10mg/kg, i.p.) was administered on the probe trial of MWM and on the acquisation session of PA and mEPM tests. In the MWM test, GBP (10mg/kg) significantly increased the time spent in target quadrant and GBP (5 and 10mg/kg) significantly decreased the distance to platform compared to control group. In the mEPM test, GBP (5 and 10mg/kg) significantly decreased the transfer latency compared to control group on the second day and in the PA test, GBP (5 and 10mg/kg) significantly prolonged retention latency compared to control group. Our results indicate that GBP has improving effects on spatial and emotional cognitive performance of naive mice in MWM, PA and mEPM tasks.

Bladder pain syndrome treated with triple therapy with gabapentin, amitriptyline, and a nonsteroidal anti-inflammatory drug

Purpose

Bladder pain syndrome is a chronic disease that manifests as bladder pain, frequency, nocturia, and urgency. Gabapentin, amitriptyline, and nonsteroidal anti-inflammatory drugs are efficacious treatments for bladder pain syndrome. Here, we assessed the effect of triple therapy with these drugs in women with bladder pain syndrome.

Methods

Between May 2007 and May 2010, we conducted a prospective nonrandomized study on 74 patients with bladder pain syndrome. Of these patients, 38 (11 men and 27 women; mean age, 55.9 years; range, 25 to 77 years; mean follow-up, 12.6 months) were administered the interstitial cystitis (IC) symptom scales (O'Leary-Sant Symptom Index) and visual analog scale (VAS) 1, 3, and 6 months after treatment to assess the efficacy of triple therapy.

Results

The pretreatment O'Leary-Sant IC symptom score was 11.7, and the post-treatment scores were 4.4, 3.8, and 4.0 at 1, 3, and 6 months, respectively; the pretreatment problem index score was 10.5, and the post-treatment scores were 3.7, 2.7, and 2.9 at 1, 3, and 6 months, respectively. The pretreatment VAS score was 6.7, and the post-treatment scores were 1.8, 1.5, and 1.7 at 1, 3, and 6 months, respectively. The O'Leary-Sant IC symptom index and problem index and VAS scores improved considerably 1 month after treatment (P<0.05). However, the results at 1, 3, and 6 months after treatment were not significantly different (P>0.05).

Conclusions

Triple therapy was sufficiently effective in patients with bladder pain syndrome and caused no significant adverse effects. However, large-scale studies should be performed to verify our findings.

Spinal astrocytic activation contributes to mechanical allodynia in a mouse model of type 2 diabetes

Diabetic neuropathic pain (DNP) plays a major role in decreased life quality of type 2 diabetes patients, however, the molecular mechanisms underlying DNP remain unclear. Emerging research implicates the participation of spinal glial cells in some neuropathic pain models. However, it remains unknown whether spinal glial cells are activated under type 2 diabetic conditions and whether they contribute to diabetes-induced neuropathic pain. In the present study, using a db/db type 2 diabetes mouse model that displayed obvious mechanical allodynia, we found that spinal astrocyte but not microglia was dramatically activated. The mechanical allodynia was significantly attenuated by intrathecally administrated l-α-aminoadipate (astrocytic specific inhibitor) whereas minocycline (microglial specific inhibitor) did not have any effect on mechanical allodynia, which indicated that spinal astrocytic activation contributed to allodynia in db/db mice. Further study aimed to identify the detailed mechanism of astrocyte-induced allodynia in db/db mice. Results showed that spinal activated astrocytes dramatically increased interleukin (IL)-1β expression which may induce N-methyl-D-aspartic acid receptor (NMDAR) phosphorylation in spinal dorsal horn neurons to enhance pain transmission. Together, these results suggest that spinal activated astrocytes may be a crucial component of mechanical allodynia in type 2 diabetes and "Astrocyte-IL-1β-NMDAR-Neuron" pathway may be the detailed mechanism of astrocyte-induced allodynia. Thus, inhibiting astrocytic activation in the spinal dorsal horn may represent a novel therapeutic strategy for treating DNP.

Analgesic efficacy of oral gabapentin added to standard epidural corticosteroids in patients with failed back surgery

Objective

Failed back surgery syndrome is characterized by the presence of intractable pain and varying degrees of functional incapacity after lumbar spine surgery. Because the mechanisms that cause pain are variable, treatment of this syndrome is quite difficult, and one of the most common methods that is used for treatment nowadays is epidural injection. This research evaluates the analgesic efficacy of addition of oral gabapentin treatment to epidural corticosteroid application in patients with failed back surgery syndromes.

Methods

Forty-two patients, including 23 females and 19 males, with failed back surgery syndrome who had been previously operated on at least twice due to lumbar disc herniation were randomly divided into two groups. Following epidural application of a single dose of methylprednisolone in the first group of patients (Group K), an oral medical treatment containing naproxen sodium, tizanidine, and vitamin B and C complex, was devised to be applied for one month. For the second group, oral gabapentin was added to the same treatment regime (Group G). Pain levels were evaluated by a visual analog scale for straight leg raise before, during, and after treatment, as well as in the first and third months.

Results

There was no demographically significant difference between the patients (P > 0.05). After the beginning of treatment, it was observed that the pain level in Group G patients regressed earlier and that it progressed at a significantly lower level (both in the first and third month controls).

Conclusion

It was concluded that addition of oral gabapentin to epidural corticosteroid application in patients with failed back surgery syndromes was effective in ameliorating pain at an early stage without significant side effects.

Targeting voltage-gated calcium channels for neuropathic pain management

Voltage-gated calcium channels (VGCC) play obligatory roles in diverse physiological functions. Pathological conditions leading to changes in their biophysical properties and expression levels may cause malfunctions of VGCC-mediated activities, resulting in disease states. It is believed that changes in VGCC properties under pain-inducing conditions may play a causal role in the development of chronic pain, including nerve injury-induced pain or neuropathic pain. For the past several decades, preclinical and clinical research in developing VGCC blockers or modulators for chronic pain management has been fruitful, leading to some U.S. Food and Drug Administration-approved drugs currently available for chronic pain management. However, their efficacy in pain relief is limited in some patients, and their long-term use is limited by their side-effect profiles. Certainly, there is room for improvement in developing more subtype-specific VGCC blockers or modulators for chronic pain conditions. In this review, we summarized the most recent preclinical and clinical studies related to chronic pain medications acting on the VGCC. We also included clinical trials aiming to expand the application of approved VGCC drugs to different pain states derived from various pathological conditions, as well as drug combination therapies trying to improve the efficacies and side-effect profiles of current pain medications.

Ramsay-Hunt syndrome complicating osteonecrosis of edentulous maxilla and mandible: report of a rare case

Review of literature revealed atleast 30 cases of post herpes zoster osteonecrosis of maxilla or mandible. To our knowledge this is a first reported case of Ramsay-Hunt syndrome with post herpetic neuralgia and post herpes zoster osteonecrosis of edentulous maxilla and mandible. We have briefly reviewed the pathophysiology and management of post herpes zoster osteonecrosis and post herpetic neuralgia.

Solid state and solution conformations of a hybrid alphagammaalphaalphagammaalpha hexapeptide. Characterization of a backbone expanded analog of the alpha-polypeptide 3(10)-helix

The stereochemically constrained gamma amino acid residue gabapentin (1-(aminomethyl)cyclohexaneacetic acid, Gpn) has been incorporated into a host alpha-peptide sequence. The structure of a hybrid alphagammaalphaalphagammaalpha peptide, Boc-Leu-Gpn-Aib-Leu-Gpn-Aib-OMe in crystals reveals a continuous helical conformation stabilized by three intramolecular 4 --> 1 C(12) hydrogen bonds across the alphagamma/alphagamma segments and one C(10) hydrogen bond across the central alphaalpha segment. This conformation corresponds to an expanded analog of the canonical all-alpha polypeptide 3(10)-helix, with insertion of two additional backbone atoms at each gamma residue. Solvent dependence of NH chemical shifts in CDCl(3) solution are consistent with conformation in which the NH groups of Aib (3), Leu (4), Gpn (5), and Aib (6) are hydrogen bonded, a feature observed in the solid state. The nonsequential NOEs between Gpn (2) NH <--> Leu (4) NH and Gpn (2) NH <--> Gpn (5) NH support the presence of additional conformations in solution. Temperature-dependent line broadening of NH resonances confirms the occurrence of rapid exchange between multiple conformations at room temperature. Two conformational models which rationalize the observed nonsequential NOEs are presented, both of which contain three hydrogen bonds and are consistent with the known stereochemical preferences of the Gpn residue.

Enhanced pre-synaptic glutamate release in deep-dorsal horn contributes to calcium channel alpha-2-delta-1 protein-mediated spinal sensitization and behavioral hypersensitivity

Nerve injury-induced expression of the spinal calcium channel alpha-2-delta-1 subunit (Ca_vα₂δ₁) has been shown to mediate behavioral hypersensitivity through a yet identified mechanism. We examined if this neuroplasticity modulates behavioral hypersensitivity by regulating spinal glutamatergic neurotransmission in injury-free transgenic mice overexpressing the Ca_vα₂δ₁ proteins in neuronal tissues. The transgenic mice exhibited hypersensitivity to mechanical stimulation (allodynia) similar to the spinal nerve ligation injury model. Intrathecally delivered antagonists for N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxyl-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors, but not for the metabotropic glutamate receptors, caused a dose-dependent allodynia reversal in the transgenic mice without changing the behavioral sensitivity in wild-type mice. This suggests that elevated spinal Ca_vα₂δ₁ mediates allodynia through a pathway involving activation of selective glutamate receptors. To determine if this is mediated by enhanced spinal neuronal excitability or pre-synaptic glutamate release in deep-dorsal horn, we examined wide-dynamic-range (WDR) neuron excitability with extracellular recording and glutamate-mediated excitatory postsynaptic currents with whole-cell patch recording in deep-dorsal horn of the Ca_vα₂δ₁ transgenic mice. Our data indicated that overexpression of Ca_vα₂δ₁ in neuronal tissues led to increased frequency, but not amplitude, of miniature excitatory post synaptic currents mediated mainly by AMPA/kainate receptors at physiological membrane potentials, and also by NMDA receptors upon depolarization, without changing the excitability of WDR neurons to high intensity stimulation. Together, these findings support a mechanism of Ca_vα₂δ₁-mediated spinal sensitization in which elevated Ca_vα₂δ₁ causes increased pre-synaptic glutamate release that leads to reduced excitation thresholds of post-synaptic dorsal horn neurons to innocuous stimuli. This spinal sensitization mechanism may mediate at least partially the neuropathic pain states derived from increased pre-synaptic Ca_vα₂δ₁ expression.

Pain therapy

Cancer-related pain is a major issue of healthcare systems worldwide. The reported incidence, considering all stages of the disease, is 51%, which can increase to 74% in the advanced and terminal stages. For advanced cancer, pain is moderate to severe in about 40-50% and very severe or excruciating in 25-30% of cases. Pain is both a sensation and an emotional experience. Pain is always subjective; and may be affected by emotional, social and spiritual components thus it has been defined as "total pain". From a pathophysiological point of view, pain can be classified as nociceptive (somatic and visceral), neuropathic (central, peripheral, sympathetic) idiopathic or psychogenic. A proper pain assessment is fundamental for an effective and individualised treatment. In 1986 the World Health Organisation (WHO) published analgesic guidelines for the treatment of cancer pain based on a three-step ladder and practical recommendations. These guidelines serve as an algorithm for a sequential pharmacological approach to treatment according to the intensity of pain as reported by the patient. The WHO analgesic ladder remains the clinical model for pain therapy. Its clinical application should be employed only after a complete and comprehensive assessment and evaluation based on the needs of each patient. When applying the WHO guidelines, up to 90% of patients can find relief regardless of the settings of care, social and/or cultural environment. This is the standard treatment on a type C basis. Only when such an approach is ineffective are interventions such as spinal administration of opioid analgesics or neuroinvasive procedures recommended.

Crystal structures of a new polymorphic form of gabapentin monohydrate and the e and z isomers of 4-tertiarybutylgabapentin

Gabapentin, a widely used antiepileptic drug, crystallizes in multiple polymorphic forms. A new crystal form of gabapentin monohydrate in the space group Pbca is reported and the packing arrangement compared with that of a previously reported polymorph in the space group P2(1)/c [Ibers, J.A. (2001) Acta Crystallogr; C57:641]. Gabapentin polymorphs can also occur from a selection of one of the two distinct chair forms of the 1,1-disubstituted cyclohexane. Crystal structures of the E and Z isomers of 4-tert-butylgabapentin provide models for analyzing anticipated packing modes in the conformational isomers of gabapentin. The E isomer crystallized in the space group Pca2(1), while the Z isomer crystallized in the space group P2(1)/c. The crystal structure of E-4-tert-butylgabapentin provides the only example of a structure in a non-centrosymmetric space group. Crystal structures of the hydrochloride and hydrobromide salts of 4-tert-butyl derivatives are reported. The results suggest that for gabapentin, a large 'polymorph-space' may be anticipated, in view of the multiple conformational states that are accessible to the molecule.