Gabapentin in pain management

Effect of Sufentanil Combined with Gabapentin on Acute Postoperative Pain in Patients Undergoing Intraspinal Tumor Resection: Study Protocol for a Randomized Controlled Trial

Purpose

Patients undergoing intraspinal tumor resection usually experience severe postoperative pain. Inadequate postoperative analgesia usually leads to severe postsurgical pain, which could cause patients to suffer from many other related complications. Recently, an increasing number of studies have found that gabapentin can relieve hyperalgesia, postoperative pain, and postoperative inflammation. However, there have been no reports on the use of gabapentin combined with sufentanil preoperatively for acute pain following intraspinal tumor resection.

Study Design and Methods

This is a protocol for a randomized, placebo-controlled, and double-blinded trial. One-hundred and sixty-eight participants with chronic pain related to the intraspinal tumor will be randomized into the gabapentin and placebo groups in a 1:1 ratio. In the gabapentin group, patients will be given 300 mg gabapentin orally 36 h, 24 h, and 12 h before surgery; the placebo group will receive a placebo orally at the same time points preoperatively. To estimate the efficacy and safety endpoints, all the researchers and patients will be blinded until the completion of this study. The primary outcome will be the consumption of sufentanil within 48 h postoperatively. The secondary outcomes include the visual analog scale pain score and Von Frey mechanical pain threshold 36 h and 24 h before and 24 h and 48 h after surgery, the incidence of postoperative nausea, vomiting, and drowsiness, the length of hospital stay and medical expenses.

Discussion

This trial is to evaluate the efficacy and safety of gabapentin combined with sufentanil for postoperative analgesia in patients who complain of pain before intraspinal tumor resection. The findings will provide a new strategy for multimode perioperative analgesia management in these patients.

Opioid Sparing Anesthesia and Enhanced Recovery After Surgery Protocol for Pancreaticoduodenectomy

Background

Opioid sparing anesthesia and enhanced recovery after surgery protocols are not innovative ideas. However, the utilization of pancreaticoduodenectomy is limited. With the rise in awareness of the opioid epidemic in the United States, we have created a multimodal approach to anesthesia and postoperative care to limit adverse effects of opioids and curb the use of opioids postoperatively.

Methods

We conducted a retrospective cohort study performed by chart review of an opioid-sparing anesthetic and enhanced recovery after surgery (ERAS) protocol initiated jointly by the anesthesiology departments and transplant surgery for pancreaticoduodenectomy from January 2017 to October 2019.

Results

Demographic data was found to be comparable between the control and protocol groups. Hospital length of stay, ICU length of stay, and opioid requirements significantly decreased in the protocol group. Hospital length of stay decreased from 8.92 to 5.72 days, ICU days decreased from 1.52 to 0.42 days, and narcotics for the first five hospital days were significantly decreased from 130.13 to 71.2 morphine milligram equivalents.

Conclusion

Proper postoperative pain management can improve patient satisfaction and decrease complication rates. Pancreaticoduodenectomy is a complicated procedure with relatively limited data regarding enhanced recovery after surgery protocols. Likewise, there is limited data regarding opioid-sparing anesthesia techniques. Our protocol produced promising hospital length of stay and reduced opioid administration during the first five hospital days without increasing 30-day readmission rates.

Examination of the sedative and analgesic effects of gabapentin and dexmedetomidine in patients undergoing laparoscopic cholecystectomy surgery: A randomized controlled trial

Introduction:

At present, laparoscopic surgery is a very common method, especially for the removal of the gallbladder, because pain and anxiety following surgery is a major problem in surgical operations. Various studies have demonstrated the effectiveness of gabapentin and dexmedetomidine in reducing pain intensity after surgery. The present study is aimed at examining the sedative and analgesic effects of gabapentin and dexmedetomidine in patients undergoing laparoscopic cholecystectomy.

Methods:

This was a double-blinded clinical trial involving 40 patients who were candidates for laparoscopic cholecystectomy. The patients were randomly allotted in two groups of dexmedetomidine (n = 20) and gabapentin (n = 20). Then, pain intensity based on the visual analog scale (VAS) and sedation level based on the Ramsay Sedation Scale (RSS) were measured at the curtained times. As the data were not normally distributed, the Mann–Whitney U test was used to analyze the data, and the significance level was set at 0.05.

Results:

Across the follow-up points, more reduction in pain intensity was observed in the dexmedetomidine group as compared with the gabapentin group. The available dissimilarities between these two groups in pain decrement at the recovery room and 3 h after being discharged from the recovery room were not significant (P ≥ 0.414). In addition, across all the time points, there was considerable growth in sedation in the dexmedetomidine group in comparison with the gabapentin group (P < 0.024). This finding indicated that dexmedetomidine was more effective than gabapentin in creating sedation.

Conclusion:

Compared with gabapentin, dexmedetomidine leads to more pain reduction after surgery and better sedation during and after surgery.

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.

Gabapentin as add-on to morphine for severe neuropathic or mixed pain in children from age 3 months to 18 years - evaluation of the safety, pharmacokinetics, and efficacy of a new gabapentin liquid formulation: study protocol for a randomized controlled trial

Background

Gabapentin has shown efficacy in the treatment of chronic neuropathic or mixed pain in adults. Although pediatric pain specialists have extensive experience with gabapentin for the treatment of neuropathic pain, its use is off-label. Its efficacy and safety in this context have never been shown. The aim of this trial is to compare gabapentin with placebo as add-on to morphine for the treatment of severe chronic mixed or neuropathic pain in children. This trial is part of the European Union Seventh Framework Programme project Gabapentin in Paediatric Pain (GAPP) to develop a pediatric use marketing authorization for a new gabapentin suspension.

Methods/design

The GAPP-2 study is a randomized, double-blind, placebo-controlled, multicenter superiority phase II study in children with severe chronic neuropathic or mixed pain. Its primary objective is to evaluate the efficacy of a gabapentin liquid formulation as adjunctive therapy to morphine. Sixty-six eligible children 3 months to 18 years of age with severe pain (pain scores ≥ 7), stratified in three age groups, will be randomized to receive gabapentin (to an accumulating dose of 45 to 63 mg/kg/day, dependent on age) or placebo, both in addition to morphine, for 12 weeks. Randomization will be preceded by a short washout period, and treatment will be initiated by a titration period of 3 weeks. After the treatment period, medication will be tapered during 4 weeks. The primary endpoint is the average pain scores in the two treatment groups (average of two measures each day for 3 days before the end-of-study visit [V10] assessed by age-appropriate pain scales (Face, Legs, Activity, Cry, Consolability scale; Faces Pain Scale–Revised; Numeric Rating Scale). Secondary outcomes include percentage responders to treatment (subjects with 30% reduction in pain scale), number of episodes of breakthrough pain, number of rescue interventions, number of pain-free days, participant dropouts, quality of life (Pediatric Quality of Life Inventory), and acceptability of treatment. Outcomes will be measured at the end-of-study visit after 12 weeks of treatment at the optimal gabapentin dose. Groups will be compared on an intention-to-treat basis.

Discussion

We hope to provide evidence that the combination of morphine and gabapentin will provide better analgesia than morphine alone and will be safe. We also aim to obtain confirmation of the recommended pediatric dose.

Trial registration

EudractCT, 2014-004897-40. Registered on 7 September 2017.

ClinicalTrials.gov, NCT03275012. Registered on 7 September 2017.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-3169-3) contains supplementary material, which is available to authorized users.

LC-MS/MS Quantification of Tramadol and Gabapentin Utilizing Solid Phase Extraction

An accurate, highly sensitive, and precise method for quantitative analysis of tramadol (TMD) and gabapentin (GBP) by high performance liquid chromatography and tandem mass spectrometry in human plasma was proposed and validated successfully using venlafaxine and pregabalin as internal standards (ISTDs), respectively. An aliquot of 200 μL of plasma was mixed with internal standard dilution and extraction was performed by using solid phase extraction (SPE) technique. Peak resolution was achieved on Phenomenex PFP column (50×4.6 mm, 2.6 μm). The total analytical run time was 3.8 min. Both analytes were monitored using multiple reaction monitoring (MRM) scan and the mass spectrometer was operated in positive polarity mode. The method was validated for specificity, sensitivity, precision, accuracy, and other analytical parameters. The results found were satisfactory over the linear calibration range of 1-500 ng/mL and 10-6000 ng/mL for TMD and GBP, respectively. The developed method can be ready to use by scientific community for quantification of analytes in plasma samples from various clinical studies of different dose strengths.

Gabapentin-related suicide: Myth or fact?

Background:

The opioid epidemic in America is real and is estimated to be the number one cause of death in adults under 50 years of age. Finding alternative analgesic medications is part of the effort to decrease the prescription of narcotics, with gabapentin being at the top of the list.

Case Description:

In the present case, we discuss the side-effects of gabapentin, used as part of the multimodal treatment approach of painful spinal degenerative disease. The patient stated that he had noticed personality changes after gabapentin was initiated, and that he had become more depressed, frustrated, and aggressive. His uncontrolled pain and acute mood changes led him to attempt suicide by hanging himself. Gabapentin was discontinued and the patient's suicidal ideation completely subsided.

Conclusion:

It is imperative to screen, identify, and appropriately manage patients with underlying psychiatric disorders prior to initiating pain management with gabapentin. Therefore, it is crucial to raise awareness of gabapentin as a potential cause of depression, aggressive behavior, and suicidal ideation.

Population pharmacokinetics of gabapentin in healthy Korean subjects with influence of genetic polymorphisms of ABCB1

The objective of this study was to perform population pharmacokinetic (PK) analysis of gabapentin in healthy Korean subjects and to investigate the possible effect of genetic polymorphisms (1236C > T, 2677G > T/A, and 3435C > T) of ABCB1 gene on PK parameters of gabapentin. Data were collected from bioequivalence studies, in which 173 subjects orally received three different doses of gabapentin (300, 400, and 800 mg). Only data from reference formulation were used. Population pharmacokinetics (PKs) of gabapentin was estimated using a nonlinear mixed-effects model (NONMEM). Gabapentin showed considerable inter-individual variability (from 5.2- to 8.7-fold) in PK parameters. Serum concentration of gabapentin was well fitted by a one-compartment model with first-order absorption and lag time. An inhibitory Emax model was applied to describe the effect of dose on bioavailability. The oral clearance was estimated to be 11.1 L/h. The volume of distribution was characterized as 81.0 L. The absorption rate constant was estimated at 0.860 h^-1, and the lag time was predicted at 0.311 h. Oral bioavailability was estimated to be 68.8% at dose of 300 mg, 62.7% at dose of 400 mg, and 47.1% at dose of 800 mg. The creatinine clearance significantly influenced on the oral clearance (P < 0.005) and ABCB1 2677G > T/A genotypes significantly influenced on the absorption rate constant (P < 0.05) of gabapentin. However, ABCB1 1236C > T and 3435C > T genotypes showed no significant effect on gabapentin PK parameters. The results of the present study indicate that the oral bioavailability of gabapentin is decreased when its dosage is increased. In addition, ABCB1 2677G > T/A polymorphism can explain the substantial inter-individual variability in the absorption of gabapentin.

Development and Evaluation of Topical Gabapentin Formulations

Topical delivery of gabapentin is desirable to treat peripheral neuropathic pain conditions whilst avoiding systemic side effects. To date, reports of topical gabapentin delivery in vitro have been variable and dependent on the skin model employed, primarily involving rodent and porcine models. In this study a variety of topical gabapentin formulations were investigated, including Carbopol® hydrogels containing various permeation enhancers, and a range of proprietary bases including a compounded Lipoderm® formulation; furthermore microneedle facilitated delivery was used as a positive control. Critically, permeation of gabapentin across a human epidermal membrane in vitro was assessed using Franz-type diffusion cells. Subsequently this data was contextualised within the wider scope of the literature. Although reports of topical gabapentin delivery have been shown to vary, largely dependent upon the skin model used, this study demonstrated that 6% (w/w) gabapentin 0.75% (w/w) Carbopol® hydrogels containing 5% (w/w) DMSO or 70% (w/w) ethanol and a compounded 10% (w/w) gabapentin Lipoderm® formulation were able to facilitate permeation of the molecule across human skin. Further pre-clinical and clinical studies are required to investigate the topical delivery performance and pharmacodynamic actions of prospective formulations.

The comparative preemptive analgesic efficacy of addition of vitamin B complex to gabapentin versus gabapentin alone in women undergoing cesarean section under spinal anesthesia: A prospective randomized double-blind study

BACKGROUND

Development of new multimodal analgesic regimens have led to substantial improvement in postoperative pain relief. We designed this study to compare the effect of combined vitamin B complex-gabapentin versus gabapentin alone on postoperative pain in women undergoing cesarean section under spinal anesthesia.

METHODS

One hundred twenty-eight women who underwent cesarean section under spinal anesthesia were randomized to receive orally 300 mg gabapentin (group G) or 300 mg of gabapentin plus 2 vitamin B complex (group GB) tablets 30 minutes before surgery. Postoperative pain intensity and total analgesic consumption during 12 hours after surgery, vomiting, and drowsiness during recovery were assessed.

RESULTS

The pain intensity in the gabapentin plus vitamin B complex group was lower than gabapentin group during 12 hours after surgery (95% CI: 1.4-2.2; P < .001). Meanwhile, the total analgesic consumption in this group was less than gabapentin alone (95% CI: 1.07-1.24; P = 0.034). The incidence of vomiting in patients who receive combined gabapentin-vitamin B complex group was similar to gabapentin alone (P = .206). The difference of the distribution of the relative frequency of sedation according to Ramsay sedation scores in patients between 2 groups were insignificant (P = .82). All newborns in our study were free of any adverse effects.

CONCLUSION

Addition of vitamin B complex to gabapentin reduced intensity of postoperative pain and also the total amount of analgesic consumption within the first 12 hours postoperative following cesarean section.

Use of preoperative gabapentin significantly reduces postoperative opioid consumption: a meta-analysis

OBJECTIVES

Effective postoperative pain management is crucial in the care of surgical patients. Opioids, which are commonly used in managing postoperative pain, have a potential for tolerance and addiction, along with sedating side effects. Gabapentin's use as a multimodal analgesic regimen to treat neuropathic pain has been documented as having favorable side effects. This meta-analysis examined the use of preoperative gabapentin and its impact on postoperative opioid consumption.

MATERIALS AND METHODS

A comprehensive literature search was conducted to identify randomized control trials that evaluated preoperative gabapentin on postoperative opioid consumption. The outcomes of interest were cumulative opioid consumption following the surgery and the incidence of vomiting, somnolence, and nausea.

RESULTS

A total of 1,793 patients involved in 17 randomized control trials formed the final analysis for this study. Postoperative opioid consumption was reduced when using gabapentin within the initial 24 hours following surgery (standard mean difference -1.35, 95% confidence interval [CI]: -1.96 to -0.73; P<0.001). There was a significant reduction in morphine, fentanyl, and tramadol consumption (P<0.05). While a significant increase in postoperative somnolence incidence was observed (relative risk 1.30, 95% CI: 1.10-1.54, P<0.05), there were no significant effects on postoperative vomiting and nausea.

CONCLUSION

The administration of preoperative gabapentin reduced the consumption of opioids during the initial 24 hours following surgery. The reduction in postoperative opioids with preoperative gabapentin increased postoperative somnolence, but no significant differences were observed in nausea and vomiting incidences. The results from this study demonstrate that gabapentin is more beneficial in mastectomy and spinal, abdominal, and thyroid surgeries. Gabapentin is an effective analgesic adjunct, and clinicians should consider its use in multimodal treatment plans among patients undergoing elective surgery.

Comparative study of preoperative use of oral gabapentin, intravenous dexamethasone and their combination in gynaecological procedure

BACKGROUND

We studied the effects of oral gabapentin and intravenous (I.V.) dexamethasone given together or separately 1 h before the start of surgery on intraoperative hemodynamics Postoperative analgesia and postoperative nausea vomiting (PONV) in patients undergoing gynaecological procedure.

MATERIALS AND METHODS

Patients were randomly divided into three groups: Group 1 (gabapentin, n = 46) received 400 mg gabapentin, Group 2 (dexamethasone, n = 46) received 8 mg dexamethasone and Group 3 (gabapentin plus dexamethasone, n = 46) received both 400 mg gabapentin and 8 mg dexamethasone I.V. 1 h before the start of surgery. Standard induction and maintenance of anesthesia were accomplished. Visual analog scale for pain was recorded for 12 h. Side effects were noted.

RESULTS

Hemodynamics at various time interval (0, 5, 10, 15, 20, 25 and 30 min) of laryngeal mask airway insertion and PONV were found significantly lower in Group 3 than in Group 1 and Group 2 (P < 0.05). The average time to first postoperative analgesic requirement at (visual analogue score >3) was significantly longer in Group 3 (510.00 ± 61.64 min) than in Group 1 (352.83 ± 80.61 min) and in Group 2 (294.78 ± 60.76 min), (P < 0.05).

CONCLUSION

The present study concludes that the combination of oral Gabapentin and I.V. dexamethasone has significantly less hemodynamic changes, better postoperative analgesia and less incidence of PONV than individual administration of each drug.

A streptozotocin-induced diabetic neuropathic pain model for static or dynamic mechanical allodynia and vulvodynia: validation using topical and systemic gabapentin

Neuropathic vulvodynia is a state of vulval discomfort characterized by a burning sensation, diffuse pain, pruritus or rawness with an acute or chronic onset. Diabetes mellitus may cause this type of vulvar pain in several ways, so this study was conducted to evaluate streptozotocin-induced diabetes as a neuropathic pain model for vulvodynia in female rats. The presence of streptozotocin (50 mg/kg i.p.)-induced diabetes was initially verified by disclosure of pancreatic tissue degeneration, blood glucose elevation and body weight loss 5-29 days after a single treatment. Dynamic (shortened paw withdrawal latency to light brushing) and static (diminished von Frey filament threshold pressure) mechanical allodynia was then confirmed on the plantar foot surface. Subsequently, both static and dynamic vulvodynia was detected by application of the paradigm to the vulval region. Systemic gabapentin (75 mg/kg, i.p.) and topical gabapentin (10 % gel) were finally tested against allodynia and vulvodynia. Topical gabapentin and the control gel vehicle significantly increased paw withdrawal threshold in the case of the static allodynia model and also paw withdrawal latency in the model for dynamic allodynia when compared with the streptozotocin-pretreated group. Likewise, in the case of static and dynamic vulvodynia, there was a significant antivulvodynia effect of systemic and topical gabapentin treatment. These outcomes substantiate the value of this model not only for allodynia but also for vulvodynia, and this was corroborated by the findings not only with systemic but also with topical gabapentin.

Effect of melatonin and gabapentin on anxiety and pain associated with retrobulbar eye block for cataract surgery: a randomized double-blind study

Objectives:

To compare the effect of melatonin and gabapentin on anxiety, pain, sedation scores, and satisfaction of surgeon in patients of cataract surgery.

Materials and Methods:

One hundred thirty patients aged between 35 and 85 years scheduled for cataract surgery were randomly allocated to three study groups to receive melatonin (6 mg), gabapentin (600 mg) or placebo 90 min before arrival in the operating room. Pain, anxiety, and sedation scores during block and surgery as well as the surgeon's satisfaction with the surgery were assessed.

Results:

Anxiety scores decreased significantly in melatonin and gabapentin groups compared to the placebo group after premedication and extended to early postoperative period. The level of anxiety showed no statistically significant difference between melatonin and gabapentin groups at any time of measurement. There were significant differences between the pain scores during retrobulbar placement in gabapentin versus placebo (95% CI 3 to 4; P = 0.001) and melatonin (95% CI 3 to 4; P = 0.040) groups. Also, there were significant differences between the sedation scores during retrobulbar placement in gabapentin and placebo groups (95% CI 2 to 2.5; P = 0.046). The difference in sedation scores during retrobulbar placement in melatonin versus gabapentin and placebo groups was not significant. Neither the intraoperative pain scores nor the postoperative pain scores were different between the three groups. The surgeon reported similar quality of operation conditions during surgery for the three study groups.

Conclusion:

The level of anxiety was significantly lower with both anxiolytic drugs compared to placebo. Furthermore, gabapentin decreased the pain and improved the sedation scores only during retrobulbar placement compared to the placebo.

Gabapentin in acute postoperative pain management

Gabapentin (1-aminomethyl-cyclohexaneacetic acid) is an amino acid that has the structure of the neurotransmitter γ-aminobutyric acid (GABA). It is a novel drug used for the treatment of postoperative pain with antihyperalgesic properties and a unique mechanism of action. Gabapentin and the related, more potent compound pregabalin have been shown to be beneficial in the treatment of neuropathic pain as well as postoperative pain following spinal surgery and hysterectomy. This study reviews five aspects of gabapentin: (1) chemical and structural characteristics; (2) pharmacokinetics and pharmacodynamics; (3) application in acute pain management; (4) adverse effects; and (5) drug safety. Overall, gabapentin has been reported to be a safe and efficacious drug for the treatment of postoperative pain.

Update on neuropathic pain treatment: ion channel blockers and gabapentinoids

Neuropathic pain is a debilitating chronic pain condition, which remains difficult to treat. The current mainstays of treatment include physical therapy, interventional procedures and medications. Among medications, ion channel blockers and gabapentinoids are the 2 classes of drugs commonly used to treat neuropathic pain. It has been suggested that these medications may be useful to treat a variety of neuropathic pain conditions. This article provides several updates on the utility of both ion channel blockers and gabapentinoids for the treatment of neuropathic pain.

Once-daily gastroretentive gabapentin for the management of postherpetic neuralgia: an update for clinicians

Gabapentin was originally developed as an add-on anticonvulsant drug, but has been widely used in the USA for the management of postherpetic neuralgia since its approval for this indication in 2002. Gabapentin has a short elimination half life and limited absorption due to a saturable L-amino acid transport system, which is expressed predominantly in the proximal small intestine. Hence, the original immediate-release gabapentin formulation (gabapentin TID) must usually be taken three times a day for optimal efficacy. Gabapentin TID is also associated with a high incidence of dizziness and somnolence and some patients are unable to tolerate the doses required for maximum pain relief. A once-daily, gastroretentive formulation of gabapentin was recently approved by the US Food and Drug Administration (FDA) for the management of postherpetic neuralgia. This formulation provides gradual release of gabapentin to the optimal site of absorption in the proximal small intestine and reduces the chance of saturating intestinal uptake, thus enabling once-daily dosing of gabapentin. This gradual release and absorption have been demonstrated in pharmacokinetic studies in healthy subjects. The efficacy of once-daily gastroretentive gabapentin for the management of postherpetic neuralgia has been demonstrated in placebo-controlled clinical studies. In addition, data from these studies suggest that the incidence of dizziness and somnolence may be reduced compared with similar studies using gabapentin TID. This article provides an overview of the pharmacokinetics, efficacy, and safety of once-daily gastroretentive gabapentin for the management of postherpetic neuralgia.

Post-herpetic neuralgia

Background

In spite of the large body of evidence available in the literature, definition and treatment of Post-Herpetic Neuralgia (PHN) are still lacking a consistent and universally recognized standardization. Furthermore, many issues concerning diagnosis, prediction and prevention of PHN need to be clarified in view of recent contributions.

Objectives

To assess whether PHN may be better defined, predicted, treated and prevented in light of recent data, and whether available alternative or adjunctive therapies may improve pain relief in treatment recalcitrant PHN.

Methods

Systematic reviews, meta-analyses, randomized controlled trials, cohort studies and protocols were searched; the search sources included PubMed, Cochrane Library, NICE, and DARE. More than 130 papers were selected and evaluated.

Results

Diagnosis of PHN is essentially clinical, but it can be improved by resorting to the many tools available, including some practical and accessible questionnaires. Prediction of PHN can be now much more accurate, taking into consideration a few well validated clinical and anamnestic variables. Treatment of PHN is presently based on a well characterized array of drugs and drug associations, including, among others, tricyclic antidepressants, gabapentinoids, opioids and many topical formulations. It is still unsatisfactory, however, in a substantial proportion of patients, especially those with many comorbidities and intense pain at herpes zoster (HZ) presentation, so that this frequent complication of HZ still strongly impacts on the quality of life of affected patients.

Conclusion

Further efforts are needed to improve the management of PHN. Potentially relevant interventions may include early antiviral therapy of acute HZ, prevention of HZ by adult vaccination, as well as new therapeutic approaches for patients experiencing PHN.

Effect of gabapentin on morphine consumption and pain after surgical debridement of burn wounds: a double-blind randomized clinical trial study

Background:

Burn pain is recognized as being maximal during therapeutic procedures, and wound debridement can be more painful than the burn injury itself. Uncontrolled acute burn pain increases the stress response and the incidence of chronic pain and associated depression. Although opiates are excellent analgesics, they do not effectively prevent central sensitization to pain. The anticonvulsant gabapentin has been proven effective for treating neuropathic pain in large placebo-controlled clinical trials. Experimental and clinical studies have demonstrated antihyperalgesic effects in models with central neuronal sensitization. It has been suggested that central neuronal sensitization may play an important role in postoperative pain.

Objectives:

The aim of this study was to investigate the effect of gabapentin on morphine consumption and postoperative pain in burn patients undergoing resection of burn wounds.

Patients and Methods:

In a randomized, double-blind, placebo-controlled study, 50 burn patients received a single oral dose of gabapentin (1200mg) or placebo 2h before surgery. Anesthesia was induced with propofol and fentanyl and maintained by infusingpropofol, remifentanil, and 50% N2O in O2. All patients received patient-controlled analgesia with morphine at doses of 2.5 mg bolus and a lock-out time of 10 min for 24h before the operation. Pain was assessed on a visual analog scale (VAS) at rest and during movement at 1,4,8,12,16,20, and 24 h before the operation. Heart rate, oxygen saturation, mean arterial blood pressure, respiratory rate, sedation score, and morphine consumption were studied.

Results:

All the enrolled patients were able to complete the study; therefore, data from 50 patients wereanalyzed. The VAS scores at rest andduring movement at 1,4,8,12,16,20, and 24 h after the operation were significantly lower in the gabapentin group than in the placebo group (P < 0.05). Morphine consumption was significantly lessr in the gabapentin group than in the placebo group (P < 0.05). Sedation scores were similar in the 2 groups at all measured times. There were no differences in adverse effects between the groups.

Conclusions:

A single oral dose of 1200mg gabapentin resulted in a substantial reduction in postoperative morphine consumption and pain scores after surgical debridement in burn patients.

Study of the effect of oral gabapentin used as preemptive analgesia to attenuate post-operative pain in patients undergoing abdominal surgery under general anesthesia

Aims:

To study the effect of oral gabapentin used as preemptive analgesia to attenuate post operative pain in patients undergoing abdominal surgery under general anesthesia.

Materials and Methods:

In a randomized double blind study, 60 patients were divided into two groups. Group A received 600mg gabapentin and group B oral received placebo 1 h prior to surgery. Anesthesia was induced with Propofol 2 mg/kg and Vecuronium 0.1mg/kg and maintained with 60% N₂O in O₂ and Vecuronium 0.02 mg/kg. All cases were given Fentanyl 2µg/kg as pre medication and a repeat dose 1µg/kg at the end of the first hour. Assessment of post-operative pain was made with the visual analog score (VAS) at extubation (0 h), 2, 4, 6, 12, and 24 h post-operatively. Post-operative analgesia was provided with intravenous Tramadol. The first dose was given in the Post Anesthesia Care Unit as 2mg/kg, and repeated at 8 and 16 h. Rescue analgesia was given with Diclofenac 1.5mg/kg, slow intravenous. The number of doses of rescue analgesia in both the groups was noted.

Results:

The VAS scores at 0, 2, 4, 6, 12, and 24 h were 1.9 vs. 2.4 (P=0.002), 2.3 vs. 3.0 (P=0.000), 3.2 vs. 3.7 (P=0.006), 2.9 vs. 4.4 (P=0.000), 3.6 vs. 4.6 (P=0.000), and 3.7 vs.4.6 (P=0.000), respectively. Numbers of patients requiring rescue analgesia with Diclofenac were 3 vs. 14 (P=0.004).

Conclusion:

A single oral dose of gabapentin given pre-operatively enhanced the analgesic effect of Tramadol as it also reduced the requirement of rescue analgesia with Diclofenac.

Single dose of preoperative analgesia with gabapentin (600 mg) is safe and effective in monitored anesthesia care for nasal surgery

This study was aimed to compare the intraoperative sedative and perioperative analgesic drug requirements and the incidences of postoperative side effects on the patients who received preoperative gabapentin or placebo. Sixty patients undergoing nasal septal or nasal sinus surgery were included. The patients received either 600 mg gabapentin (Group G) or placebo (Group P) orally, 1 h before surgery. The scores for sedation and pain were recorded at 5, 15, 30, 45 and 60 min, intraoperatively and at 30 min, 1, 2, 4, 6, 9, 12, 16, 20, 24 h, postoperatively. Sedation was achieved with an IV bolus of propofol and continuous infusion of remifentanil. There were significant differences between gabapentin and placebo groups with regard to total consumptions of remifentanil (171.42 + or - 68 vs. 219.17 + or - 95 microg, respectively; P = 0.033) and propofol (59.45 + or - 36.08 vs. 104.14 + or - 54.98 mg, respectively; P = 0.001). Group G patients had significantly lower intraoperative VAS scores at all time points (P < 0.05). The anxiety score of Group G was better at all times (P < 0.05). All postoperative pain scores were lower in the Group G (P < 0.05). Time to first request for analgesic was 12.7 + or - 2.3 h in Group G, and 7.8 2.1 h in Group P (P < 0.0001). Total consumption of lornoxicam was lower in Group G (P < 0.004). We concluded that monitored anesthesia care combined with preoperative analgesia with a low dose of (600 mg) oral gabapentin is an efficient option with tolerable side effects for patients undergoing ear, nose and throat ambulatory surgery.

Postherpetic neuralgia: from preclinical models to the clinic

Postherpetic neuralgia (PHN), a common complication of herpes zoster, which results from reactivation of varicella zoster virus, is a challenging neuropathic pain syndrome. The incidence and severity of herpes zoster and PHN increases with immune impairment or age and may become a greater burden both in terms of health economics and individual suffering. A clearer understanding of the underlying mechanisms of this disease and translation of preclinical outcomes to the clinic may lead to more efficacious treatment options. Here we give an overview of recent findings from preclinical models and clinical research on PHN.

Translational pain research: achievements and challenges

The achievements in both preclinical and clinical pain research over the past 4 decades have led to significant progress in clinical pain management. However, pain research still faces enormous challenges and there remain many obstacles in the treatment of clinical pain, particularly chronic pain. Translational pain research needs to involve a number of important areas including: 1) bridging the gap between pain research and clinical pain management; 2) developing objective pain-assessment tools; 3) analyzing current theories of pain mechanisms and their relevance to clinical pain; 4) exploring new tools for both preclinical and clinical pain research; and 5) coordinating research efforts among basic scientists, clinical investigators, and pain-medicine practitioners. These issues are discussed in this article in light of the achievements and challenges of translational pain research.

PERSPECTIVE

The subjective nature of clinical pain calls for innovative research approaches. As translational pain research emerges as an important field in pain medicine, it will play a unique role in improving clinical pain management through coordinated bidirectional research approaches between bedside and bench.

A combined effect of dextromethorphan and melatonin on neuropathic pain behavior in rats

Previous study has shown that administration of melatonin into the anterior cingulate cortex contralateral to peripheral nerve injury prevented exacerbation of mechanical allodynia with a concurrent improvement of depression-like behavior in Wistar-Kyoto (WKY) rats, a genetic variation of Wistar rats. In the present study, we examined the effect of the individual versus combined treatment of melatonin and/or dextromethorphan (DM), a clinically available N-methyl-d-aspartate (NMDA) receptor antagonist, on pain behaviors in WKY rats with chronic constriction sciatic nerve injury (CCI). Pain behaviors (thermal hyperalgesia and mechanical allodynia) were established at one week after CCI. WKY rats were then treated intraperitoneally with various doses of melatonin, DM or their combination once daily for the following week. At the end of this one-week treatment, behavioral tests were repeated in these same rats. While DM alone was effective in reducing thermal hyperalgesia at three tested doses (15, 30 or 60 mg/kg), it reduced mechanical allodynia only at high doses (30 or 60 mg/kg). By comparison, administration of melatonin alone was effective in reducing thermal hyperalgesia only at the highest dose (120 mg/kg, but not 30 or 60 mg/kg) tested in this experiment. Melatonin alone failed to reverse allodynia at all three tested doses (30, 60 and 120 mg/kg). However, the combined intraperitoneal administration of melatonin (30 mg/kg) and DM (15 mg/kg) effectively reversed both thermal hyperalgesia and mechanical allodynia although each individual dose alone did not reduce pain behaviors. These results suggest that a combination of melatonin with a clinically available NMDA receptor antagonist might be more effective than either drug alone for the treatment of neuropathic pain.

The combined analgesic effect of gabapentin and transdermal fentanyl patch on acute and chronic pain after maxillary cancer surgeries

Purpose of this study was to evaluate the combined analgesic effect of gabapentin and transdermal fentanyl patch, on acute and chronic pain after surgery for maxillary cancer.

STUDY DESIGN

The Study was double blind and prospective. 100 subjects belonging to ASA grade I and II, 30-50 years age group, scheduled for maxillary cancer surgery were randomized into two groups; treatment group (GT): to receive gabapentin, transdermal fentanyl patch or control group ©: two placebos. For acute postoperative pain (Visual Analogue Score) and analgesic requirements were assessed 2, 4, 8 hours and 7 days after surgery. Subjects were also assessed for chronic pain 2, 4, 6 months later.

RESULTS

Subjects in treatment group required lesser dose of analgesic, as compared to control group, in the post operative period. Visual Analogue Scores were also significantly lower in the treatment group throughout the post operative period. Occurrence of side effects was non significant between both groups. 2, 4 and 6 months after surgery, 40, 35 and 28 subjects respectively, out of total 45 subjects of the control group, reported chronic pain. In comparison, 25, 10 and 4 subjects out of 42 subjects in the treatment group reported chronic pain 2, 4, 6 months respectively after surgery. 15, 10 and 6 out of 45 of the control group required analgesics, whereas 2, 0 and 0 out of 42 in the treatment group, required analgesics respectively 2, 4 and 6 months after surgery

CONCLUSION

Acute and chronic pain after maxillary cancer surgery is significantly reduced by multimodal analgesia.

Effects of gabapentin on morphine consumption and pain in severely burned patients

OBJECTIVE

Nociception is the major cause of burn pain and leads to central hyperalgesia. Gabapentin (Gp) is an antihyperalgesic drug that selectively affects central sensitization. We studied the opioid-sparing and analgesic effects of Gp in severely burned patients.

METHODS

Ten patients (mean total burned body surface area (TBSA), 25%), received 2400 mg of oral Gp daily from after burn days 3-24 in addition to standard pain therapy. They were compared to a retrospective matching group. Outcomes were cumulative morphine consumption and mean daily pain scores. Outcomes were recorded during treatment (21 days) and 21 days after treatment.

RESULTS

During treatment and post-treatment phases, patients receiving Gp had cumulative morphine consumption and a mean daily pain score significantly lower than controls.

CONCLUSION

Gp use reduced opioid consumption and lowered pain scores that seemed to extend beyond its pharmacologic action probably result from the ability of Gp to prevent central hyperalgesia induced by burns.

Experience with gabapentin for neuropathic pain in adolescents: report of five cases

Summary Gabapentin is an antiepileptic drug indicated for the treatment of partial seizures in children. Many studies have proved its analgesic action in the treatment of neuropathic pain in adults and we have noticed an analgesic action of gabapentin in neuropathic pain in children. Five patients treated in the Children's Hospital Pain Control Service for intractable neuropathic pain were included in gabapentin treatment. Four were cancer patients and one suffered from neuropathic pain in the neck (C3). The visual analog scale (VAS) scores of pain were compared before and during treatment with gabapentin. We noticed a rapid improvement, in 1 week, of our patients' VAS scores (from 9 or 10 to 4 or 3) with minimal adverse effects. In the follow-up period of 6 months we gradually reduced the dose of gabapentin. Our findings are that gabapentin should be included earlier in the treatment of neuropathic pain in adolescents, because it rapidly improves analgesia and has minimal side effects.

Recent advances in the development of treatments for alcohol and cocaine dependence: focus on topiramate and other modulators of GABA or glutamate function

Neuroscientific developments have promulgated interest in developing efficacious medications for the treatment of substance dependence. Previous pharmacological strategies that involve the use of relatively specific medications to alter corticomesolimbic dopaminergic neuronal activity--the critical pathway for expression of the reinforcing effects of abused drugs--have yielded modest efficacy in the treatment of alcohol dependence, and no medication has been established as a treatment for cocaine dependence. Since corticomesolimbic dopaminergic neurons interact with other neurotransmitters that modulate the effects of dopamine in the nucleus accumbens, would it not be possible to control these dopaminergic effects more reliably with a medication that acts contemporaneously on more than one neuromodulator of dopaminergic function? Further, since the long-term use of either alcohol or cocaine results in neuronal adaptations as a result of sensitisation, would the chances of effective therapy not be bolstered by administering a medication that was also able to mitigate these chronic effects? Thus, a new conceptual approach is needed. My proposal is that a medication--in this case topiramate--that principally potentiates inhibitory GABA(A) receptor-mediated input and antagonises excitatory glutamatergic afferents to the corticomesolimbic dopaminergic system should have therapeutic potential in treating either alcohol or cocaine dependence or perhaps both. This is because the principal neurochemical effects of topiramate would not only serve to decrease the acute reinforcing effects of alcohol or cocaine, but might also facilitate cessation of their use following a period of long-term use by decreasing neuronal sensitisation. This overview highlights the scientific concepts and clinical evidence for the development of topiramate in the treatment of alcohol dependence and introduces preliminary evidence to indicate that it might also have utility in treating cocaine dependence. Finally, to place the material on topiramate in context, information has been included on the utility and development of other medications that modulate GABA- or glutamate-mediated neuronal systems for the treatment of alcohol or cocaine dependence.

Human pooled immunoglobulin in the treatment of chronic pain syndromes

OBJECTIVE

To examine the use of intravenous immunoglobulin (i.v.i.g.) in chronic pain.

DESIGN

A prospective multiple-dose, open-label cohort study in 130 consecutive patients who suffered from 12 chronic pain syndromes. The largest symptom groups were (number of patients): Fibromyalgia (48); Spinal pain (20); Complex regional pain syndrome (CRPS, 11); Peripheral neuropathic pain (12); and Atypical odontalgia or atypical facial pain (11). All patients had insufficient pain relief with established treatments. Pain relief was recorded using average pain intensity values as documented in standardized diaries. A specific treatment protocol was developed, and patients were enrolled over a 36-month period.

RESULTS

Overall, 20% of patients had>70% pain relief and 27.7% of patients reported relief between 25% and 70%. Six patients (4.6%) had moderately increased pain levels for a duration of up to 9 weeks. Good relief, of more than 70%, was found in all major symptom groups. Patients with pain of short duration (<2 years) reported high relief rates (33.8% of patients in this group reported relief of >70%). No serious adverse events were reported. conclusions: i.v.i.g. may be effective in patients suffering from chronic pain. Controlled studies are needed to evaluate the efficacy of i.v.i.g. in these patients. Patients with a good response to i.v.i.g. may be models for the study of neuroimmune interactions in chronic pain.

Gabapentin may inhibit synaptic transmission in the mouse spinal cord dorsal horn through a preferential block of P/Q-type Ca2+ channels

Gabapentin is a lipophilic analog of gamma-amino butyric acid (GABA) with therapeutic activity against certain forms of epilepsy and neuropathic pain. Despite its structural similarity to GABA, it does not bind GABAA or GABAB receptors and the mechanism, especially of its analgesic action, has remained elusive. Here, we have studied its effects on synaptic transmission mediated by the major spinal fast excitatory and inhibitory neurotransmitters, L-glutamate and glycine, in the superficial layers of the spinal cord dorsal horn, a CNS area, which is critically involved in nociception. Gabapentin reversibly reduced evoked excitatory postsynaptic currents mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA-EPSCs) and inhibitory postsynaptic currents mediated by glycine (gly-IPSCs). Inhibition of AMPA-EPSCs and gly-IPSCs occurred with similar potencies (approximately 10-50 nM) and by about the same degree (approximately 40% at 1 microM). Gabapentin did not affect membrane currents elicited by exogenously applied glutamate or glycine arguing against a postsynaptic site of action. Selective blockade of N-type Ca2+ channels with omega-conotoxin GVIA dramatically increased and blockade of P/Q-type channels with omega-agatoxin IVA strongly attenuated inhibition of evoked synaptic transmission by gabapentin. These results show that gabapentin affects both excitatory and inhibitory spinal neurotransmission via a presynaptic mechanism which preferentially involves P/Q-type Ca2+ channels.

Topical and peripherally acting analgesics

Acute nociceptive, inflammatory, and neuropathic pain all depend to some degree on the peripheral activation of primary sensory afferent neurons. The localized peripheral administration of drugs, such as by topical application, can potentially optimize drug concentrations at the site of origin of the pain, while leading to lower systemic levels and fewer adverse systemic effects, fewer drug interactions, and no need to titrate doses into a therapeutic range compared with systemic administration. Primary sensory afferent neurons can be activated by a range of inflammatory mediators such as prostanoids, bradykinin, ATP, histamine, and serotonin, and inhibiting their actions represents a strategy for the development of analgesics. Peripheral nerve endings also express a variety of inhibitory neuroreceptors such as opioid, alpha-adrenergic, cholinergic, adenosine and cannabinoid receptors, and agonists for these receptors also represent viable targets for drug development. At present, topical and other forms of peripheral administration of nonsteroidal anti-inflammatory drugs, opioids, capsaicin, local anesthetics, and alpha-adrenoceptor agonists are being used in a variety of clinical states. There also are some clinical data on the use of topical antidepressants and glutamate receptor antagonists. There are preclinical data supporting the potential for development of local formulations of adenosine agonists, cannabinoid agonists, cholinergic ligands, cytokine antagonists, bradykinin antagonists, ATP antagonists, biogenic amine antagonists, neuropeptide antagonists, and agents that alter the availability of nerve growth factor. Given that activation of sensory neurons involves multiple mediators, combinations of agents targeting different mechanisms may be particularly useful. Topical analgesics represent a promising area for future drug development.

The use of gabapentin for the treatment of postherpetic neuralgia

BACKGROUND

Varicella-zoster virus causes chickenpox and can reemerge later in life to cause herpes zoster or shingles. One of the most common and disabling complications of herpes zoster is postherpetic neuralgia (PHN).

OBJECTIVES

This article reviews the current primary literature about the efficacy and tolerability of gabapentin for the treatment of PHN. Gabapentin pharmacokinetics and drug interactions are also reviewed.

METHODS

A literature search in the English language was conducted using OVID Web, which contained the following databases: MEDLINE (1966-present), EMBASE (1980-2002), Current Contents/Clinical Medicine (1999-2002), Cochrane Controlled Trials Register (1898-present), Cochrane Database of Systemic Reviews (fourth quarter, 2002), and International Pharmaceutical Abstracts (1970-2002). Search terms used were postherpetic neuralgia; zoster; gabapentin; neuropathic pain; pain; pharmacoeconomic; cost; controlled clinical trial; randomized, controlled trial; postherpetic neuralgia and gabapentin; gabapentin and pain; treatment and postherpetic neuralgia; gabapentin and age; gabapentin and gender; gabapentin and ethnicity; and gabapentin and pharmacokinetics.

RESULTS

Gabapentin displays nonlinear absorption kinetics, is minimally protein bound (< 3%), has a high mean (SD) volume of distribution (50.4 [8.0] L), and is excreted via the kidneys as unchanged drug. Two randomized, placebo-controlled, parallel-group, multicenter clinical trials demonstrated the effectiveness of gabapentin at doses of up to 3600 mg/d to significantly reduce pain (P < 0.01 and P < 0.001), improve sleep (P < 0.01), and improve some parameters on the Short Form-McGill Pain Questionnaire (P < 0.05). Dizziness and somnolence were the most common side effects leading to withdrawal from the trials. The recommended dosage in adults is 300 mg at bedtime on day 1,300 mg BID on day 2, and 300 mg TID on day 3, titrating up as needed to 2400 to 3600 mg/d. To reduce adverse events in patients with renal impairment, the dose should be adjusted based on the patient's creatinine clearance.

CONCLUSIONS

Gabapentin appears to be effective and well tolerated for the short-term treatment of PHN. However, future controlled studies are needed to determine whether the effectiveness of gabapentin for PHN is maintained for > 2 months, to establish the optimal dose of gabapentin for PHN, and to compare the efficacy of gabapentin with that of other pharmacologic agents used for the treatment of PHN.

Treatments for chronic pain associated with spinal cord injuries: many are tried, few are helpful

OBJECTIVE

The objective was to investigate, in two community samples of people with spinal cord injuries, the frequency of use of different pain treatments and the perceived helpfulness of these treatments.

DESIGN AND SETTING

A postal survey was conducted in the community.

PARTICIPANTS

The participants were 471 persons aged 18 years or older who had spinal cord injuries and pain. There were 2 separate samples (n = 308 and n = 163).

OUTCOME MEASURES

The pain treatments used, the helpfulness of these treatments, and the Chronic Pain Grade questionnaire answers were assessed.

RESULTS

Respondents reported multiple pain treatments (range of 0-14 and median of 4 in sample 1; range of 0-16 and median of 4 in sample 2). The most commonly reported treatments were oral medications and physical therapy. Medication types most commonly reported were nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and opioids. The treatments rated as most helpful were opioid medications, physical therapy, and diazepam therapy, and those rated as least helpful were spinal cord stimulation, counseling or psychotherapy, administration of acetaminophen, and administration of amitriptyline. Alternative treatments reported as most helpful were massage therapy and use of marijuana. Acupuncture was tried by many but was rated as only moderately helpful.

CONCLUSIONS

This survey of two large samples of community-dwelling individuals with spinal cord injury-related chronic pain indicates that multiple pain treatments are tried but only a few are rated as more than somewhat helpful. Furthermore, the treatments that are most commonly reported are not always those that are rated as most helpful. The findings point to a number of potentially fruitful directions for future research.