Gabapentin: pharmacology and its use in pain management

Comparison of Gabapentin and Ketotifen in Treatment of Uremic Pruritus in Hemodialysis Patients

Objectives:

Uremic pruritus is a common problem in hemodialysis patients. Several treatments have been used for decreasing itching in these patients. Gabapentin and ketotifen are two drugs used for treating uremic patients. The aim of this study was to compare gabapentin and ketotifen in treatment of uremic pruritus in hemodialysis patients.

Methods:

In this double-blind randomized clinical trial, 52 hemodialysis patients with uremic pruritus referred to 5azarTeaching Hospital in Gorgan in 2013 were studied. Patients were randomly assigned to two groups of 26 subjects (groups G and K). In group G, patients treated with gabapentin capsules 100 mg daily for 2 weeks, and in Group K, patients treated with ketotifen 1 mg twice daily for 2 weeks. Before and at the end of study, pruritus severity was determined based on Shiratori’s severity scores. Collected data were analyzed by SPSS-21 statistical software.

Results:

There was no significant different between two groups in the age and sex. After two weeks of treatment, severity of pruritus was significantly reduced in both groups (88.4% in group G vs. 76.9% in group K). Gabapentin compared with ketotifen had a better effect on improving itching in the age group of 30-60 years and in males. 5 patients (19.2%) in both groups suffered from drowsiness and dizziness, but no serious side effects were observed.

Conclusions:

The results showed that gabapentin and ketotifen significantly improved pruritus in hemodialysis patients, and no significant difference was observed between two groups.

Gabapentin for uremic pruritus in hemodialysis patients: a qualitative systematic review

PURPOSE OF THE REVIEW

Uremic pruritus (UP) is a common discomfort of dialysis-dependent end-stage renal disease. Some studies suggest a neuropathic cause of UP. Gabapentin, an anticonvulsant, has shown promising results as an emerging drug to treat this condition.

OBJECTIVE

An updated qualitative systematic review was conducted to evaluate its efficacy and safety in hemodialysis patients.

SOURCE OF INFORMATION

Ovid MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Clinicaltrials.gov, and Google Scholar through June 2015 were used as sources of information.

PATIENTS

Patients are adult hemodialysis patients receiving gabapentin for UP.

METHODS

All randomized controlled trials (RCTs), quasi-RCTs, observational studies, open-label studies, and retrospective studies were included. Case series and case reports were excluded. All descriptions and data were extracted independently by two authors.

RESULTS

Seven studies evaluating gabapentin with a total of 179 patients were included. Most patients were refractory to antihistamines and topical emollients. Statistically significant favorable outcomes on pruritus scores were found in six studies. Five studies evaluated antipruritic efficacy based on a 10-point visual analog scale (VAS), and improvements in the range of an absolute decrease of 5.7 to 9.4 points from baseline were achieved on average by 3-8 weeks of treatment. Side effects are common with six studies reporting at least 26 incidences of side effects such as somnolence, dizziness, and fatigue. A total of four patients reportedly discontinued gabapentin due to intolerability.

LIMITATIONS

Our review is limited by the inclusion of generally small, lower quality studies that lacked comparator groups or were open-label studies. Since the first two randomized controlled trials were published, no further high-quality studies have been conducted.

IMPLICATIONS

Our review supports a trial of gabapentin for the management of UP in hemodialysis patients refractory to antihistamines and/or emollients. The results should be interpreted cautiously due to the lower quality of included studies. We recommend a starting dose of 100 mg orally after hemodialysis to minimize adverse events in this population.

Gabapentin can significantly improve dystonia severity and quality of life in children

INTRODUCTION

Gabapentin has been used in the management of neuropathic pain, epilepsy and occasionally movement disorders.

METHODS

A four-year retrospective, observational study analysed the use of gabapentin for severe dystonia in children at the Evelina London Children's Hospital. Motor severity was classified according to the Gross Motor Function Classification System (GMFCS), Dystonia Severity Assessment Plan (DSAP) and levels of impairment in activities of daily living were graded according to the WHO International Classification of Functioning, Disability and Health, Children & Youth version (ICF-CY) before and after gabapentin.

RESULTS

The majority of the 69 children reported were level 5 GMFCS (non-ambulant). The DSAP grade fell significantly from grade 3 before to grade 1 after gabapentin. Significant improvements in median ICF-CY grades were seen following gabapentin in sleep quality, sleep amount, mood & agreeableness, pain, general muscle tone, involuntary muscle contractions and seating tolerance (p < 0.01 in all areas). A significantly higher mean dose of 18.1 mg/kg/dose (SD: 13.3) for dystonia, compared to 7.61 mg/kg/dose (SD: 4.14) for pain relief without dystonia (z = -2.54, p = 0.011) was noted.

DISCUSSION & CONCLUSION

Gabapentin may significantly ameliorate dystonia severity and improve activities of daily living and quality of life in children with severe dystonia.

Pain management in head and neck cancer patients undergoing chemo-radiotherapy: Clinical practical recommendations

Pain in head and neck cancer represents a major issue, before, during and after the oncological treatments. The most frequent cause of pain is chemo/radiation related oral mucositis, which involves 80% of the patients and worsens their quality of life inhibiting speaking, eating, drinking or swallowing and sometimes reducing the treatment compliance, the maximum dose intensity and thus the potential efficacy of treatment. Nevertheless pain is still often under estimated and undertreated. An Italian multidisciplinary group of head and neck cancer specialists met with the aim of reaching a consensus on pain management in this setting. The Delphi Appropriateness method was used for the consensus. External expert reviewers evaluated the final statements. The paper contains 30 consensus-reached statements about pain management in HNC patients and offers a review of recent literature in these topics.

Comparative evaluation of oral gabapentin versus clonidine as premedication on preoperative sedation and laryngoscopic stress response attenuation for the patients undergoing general anesthesia

Background:

Laryngoscopy and endotracheal intubation (L and I) is associated with rise in blood pressure (BP), heart rate (HR), leading to adverse cardiological outcome especially in susceptible individuals. To compare the BP, HR during L and I as well as to evaluate the preoperative sedation status between oral clonidine (Group C) and oral gabapentine (Group G) as premedication for the patients undergoing major surgery under general anesthesia (GA).

Materials and Methods:

From April 2008 to December 2009; in a prospective, double-blinded, and randomized controlled study; 100 adult patients of either sex, aged 20-45, of American Society of Anesthesiologists status I and II scheduled to undergo major surgery of >1 hour duration, randomly allocated into groups C and G were pre treated with oral clonidine (200 µg) and gabapentin (800 mg) respectively 2 h prior to induction. Preoperative sedation was assessed 2 h after premedication administration. Hemodynamic parameters were noted just before induction, during L and I 1,3,5,7, and10 min after intubation. The results obtained were then analyzed with statistical unpaired “t” test and Chi-square test and compared.

Results and Analysis:

Preoperative sedation between two groups were similar but group C attenuated HR, systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean blood pressure (MBP) more significantly before induction, during L and I, 1, 3, and 5 min, following L and I, while comparing with group G. Again gabapentin-reduced HR, BP, (SBP, DBP, MBP) significantly more at 7 and 10 min after L and I on comparison clonidine.

Conclusion:

Oral clonidine is equally effective in producing preoperative sedation in comparison to oral gabapentin, while on the contrary oral clonidine is more efficacious in reducing laryngoscopic stress response than oral gabapentin.

Pain and the thermally injured patient-a review of current therapies

Thermally injured patients experience tremendous pain from the moment of injury to months or years after their discharge from the hospital. Pain is therefore a critical component of proper management of burns. Although the importance of pain is well recognized, it is often undertreated. Acute uncontrolled pain has been shown to increase the incidence of mental health disorders and increase the incidence of suicide after discharge. Long-term poor pain control leads to an increase in the incidence of persistent pain. Most burn centers have used opioids as the mainstay analgesic, but recently, the significant side effects of opioids have led to the implementation of new and combined therapeutics. Pharmacological agents such as gabapentin, clonidine, dexmedetomidine, and ketamine have all been suggested as adjuncts to opioids in the treatment of burn pain. Nonpharmacological therapies such as hypnosis, virtual reality devices, and behavioral therapy are also essential adjuncts to current medications. This review aims at identifying the currently available pharmacological and nonpharmacological options for optimal pain management in the adult burn population.

Co-administration of morphine and gabapentin leads to dose dependent synergistic effects in a rat model of postoperative pain

Despite much evidence that combination of morphine and gabapentin can be beneficial for managing postoperative pain, the nature of the pharmacological interaction of the two drugs remains unclear. The aim of this study was to assess the interaction of morphine and gabapentin in range of different dose combinations and investigate whether co-administration leads to synergistic effects in a preclinical model of postoperative pain. The pharmacodynamic effects of morphine (1, 3 and 7mg/kg), gabapentin (10, 30 and 100mg/kg) or their combination (9 combinations in total) were evaluated in the rat plantar incision model using an electronic von Frey device. The percentage of maximum possible effect (%MPE) and the area under the response curve (AUC) were used for evaluation of the antihyperalgesic effects of the drugs. Identification of synergistic interactions was based on Loewe additivity response surface analyses. The combination of morphine and gabapentin resulted in synergistic antihyperalgesic effects in a preclinical model of postoperative pain. The synergistic interactions were found to be dose dependent and the increase in observed response compared to the theoretical additive response ranged between 26 and 58% for the synergistic doses. The finding of dose-dependent synergistic effects highlights that choosing the right dose-dose combination is of importance in postoperative pain therapy. Our results indicate benefit of high doses of gabapentin as adjuvant to morphine. If these findings translate to humans, they might have important implications for the treatment of pain in postoperative patients.

Effect of gabapentin pretreatment on myoclonus after etomidate: a randomized, double-blind, placebo-controlled study

AIM

To evaluate the effects of three different doses of gabapentin pretreatment on the incidence and severity of myoclonic movements linked to etomidate injection.

METHOD

One hundered patients, between 18 and 60 years of age and risk category American Society of Anesthesiologists I-II, with planned elective surgery under general anesthetic were included in the study. The patients were randomly divided into four groups and 2h before the operation were given oral capsules of placebo (Group P, n=25), 400mg gabapentin (Group G400, n=25), 800mg gabapentin (Group G800, n=25) or 1200mg gabapentin (Group G1200, n=25). Side effects before the operation were recorded. After preoxygenation for anesthesia induction 0.3mgkg(-1) etomidate was administered for 10s. A single anesthetist with no knowledge of the study medication evaluated sedation and myoclonic movements on a scale between 0 and 3. Two minutes after induction, 2μgkg(-1) fentanyl and 0.8mgkg(-1) rocuronium were administered for tracheal intubation.

RESULTS

Demographic data were similar. Incidence and severity of myoclonus in Group G1200 and Group G800 were significantly lower than in Group P; sedation incidence and level were appreciably higher compared to Group P and Group G400. While there was no difference in the incidence of myoclonus between Group P and Group G400, the severity of myoclonus in Group G400 was lower than in the placebo group. In the two-hour period before induction other than sedation none of the side effects related to gabapentin were observed in any patient.

CONCLUSION

Pretreatment with 800mg and 1200mg gabapentin 2h before the operation increased the level of sedation and reduced the incidence and severity of myoclonic movements due to etomidate.

Insomnia disorder

Insomnia disorder affects a large proportion of the population on a situational, recurrent or chronic basis and is among the most common complaints in medical practice. The disorder is predominantly characterized by dissatisfaction with sleep duration or quality and difficulties initiating or maintaining sleep, along with substantial distress and impairments of daytime functioning. It can present as the chief complaint or, more often, co-occurs with other medical or psychiatric disorders, such as pain and depression. Persistent insomnia has been linked with adverse long-term health outcomes, including diminished quality of life and physical and psychological morbidity. Despite its high prevalence and burden, the aetiology and pathophysiology of insomnia is poorly understood. In the past decade, important changes in classification and diagnostic paradigms have instigated a move from a purely symptom-based conceptualization to the recognition of insomnia as a disorder in its own right. These changes have been paralleled by key advances in therapy, with generic pharmacological and psychological interventions being increasingly replaced by approaches that have sleep-specific and insomnia-specific therapeutic targets. Psychological and pharmacological therapies effectively reduce the time it takes to fall asleep and the time spent awake after sleep onset, and produce a modest increase in total sleep time; these are outcomes that correlate with improvements in daytime functioning. Despite this progress, several challenges remain, including the need to improve our knowledge of the mechanisms that underlie insomnia and to develop more cost-effective, efficient and accessible therapies.

Pharmacovigilance in hospice/palliative care: net effect of gabapentin for neuropathic pain

OBJECTIVE

Hospice/palliative care patients may differ from better studied populations, and data from other populations cannot necessarily be extrapolated into hospice/palliative care clinical practice. Pharmacovigilance studies provide opportunities to understand the harms and benefits of medications in routine practice. Gabapentin, a γ-amino butyric acid analogue antiepileptic drug, is commonly prescribed for neuropathic pain in hospice/palliative care. Most of the evidence however relates to non-malignant, chronic pain syndromes (diabetic neuropathy, postherpetic neuralgia, central pain syndromes, fibromyalgia). The aim of this study was to quantify the immediate and short-term clinical benefits and harms of gabapentin in routine hospice/palliative care practice.

DESIGN

Multisite, prospective, consecutive cohort.

POPULATION

127 patients, 114 of whom had cancer, who started gabapentin for neuropathic pain as part of routine clinical care.

SETTINGS

42 centres from seven countries. Data were collected at three time points-at baseline, at day 7 (and at any time; immediate and short-term harms) and at day 21 (clinical benefits).

RESULTS

At day 21, the average dose of gabapentin for those still using it (n=68) was 653 mg/24 h (range 0-1800 mg) and 54 (42%) reported benefits, of whom 7 (6%) experienced complete pain resolution. Harms were reported in 39/127 (30%) patients at day 7, the most frequent of which were cognitive disturbance, somnolence, nausea and dizziness. Ten patients had their medication ceased due to harms. The presence of significant comorbidities, higher dose and increasing age increased the likelihood of harm.

CONCLUSIONS

Overall, 42% of people experienced benefit at a level that resulted in continued use at 21 days.

Treating Diabetic Neuropathy: Present Strategies and Emerging Solutions

Diabetic peripheral neuropathies (DPN) are a heterogeneous group of disorders caused by neuronal dysfunction in patients with diabetes. They have differing clinical courses, distributions, fiber involvement (large or small), and pathophysiology. These complications are associated with increased morbidity, distress, and healthcare costs. Approximately 50% of patients with diabetes develop peripheral neuropathy, and the projected rise in the global burden of diabetes is spurring an increase in neuropathy. Distal symmetrical polyneuropathy (DSPN) with painful diabetic neuropathy, occurring in around 20% of diabetes patients, and diabetic autonomic neuropathy (DAN) are the most common manifestations of DPN. Optimal glucose control represents the only broadly accepted therapeutic option though evidence of its benefit in type 2 diabetes is unclear. A number of symptomatic treatments are recommended in clinical guidelines for the management of painful DPN, including antidepressants such as amitriptyline and duloxetine, the γ-aminobutyric acid analogues gabapentin and pregabalin, opioids, and topical agents such as capsaicin. However, monotherapy is frequently not effective in achieving complete resolution of pain in DPN. There is a growing need for head-to-head studies of different single-drug and combination pharmacotherapies. Due to the ubiquity of autonomic innervation in the body, DAN causes a plethora of symptoms and signs affecting cardiovascular, urogenital, gastrointestinal, pupillomotor, thermoregulatory, and sudomotor systems. The current treatment of DAN is largely symptomatic, and does not correct the underlying autonomic nerve deficit. A number of novel potential candidates, including erythropoietin analogues, angiotensin II receptor type 2 antagonists, and sodium channel blockers are currently being evaluated in phase II clinical trials.

Targeting Opioid-Induced Hyperalgesia in Clinical Treatment: Neurobiological Considerations

Opioid analgesics have become a cornerstone in the treatment of moderate to severe pain, resulting in a steady rise of opioid prescriptions. Subsequently, there has been a striking increase in the number of opioid-dependent individuals, opioid-related overdoses, and fatalities. Clinical use of opioids is further complicated by an increasingly deleterious profile of side effects beyond addiction, including tolerance and opioid-induced hyperalgesia (OIH), where OIH is defined as an increased sensitivity to already painful stimuli. This paradoxical state of increased nociception results from acute and long-term exposure to opioids, and appears to develop in a substantial subset of patients using opioids. Recently, there has been considerable interest in developing an efficacious treatment regimen for acute and chronic pain. However, there are currently no well-established treatments for OIH. Several substrates have emerged as potential modulators of OIH, including the N-methyl-D-aspartate and γ-aminobutyric acid receptors, and most notably, the innate neuroimmune system. This review summarizes the neurobiology of OIH in the context of clinical treatment; specifically, we review evidence for several pathways that show promise for the treatment of pain going forward, as prospective adjuvants to opioid analgesics. Overall, we suggest that this paradoxical state be considered an additional target of clinical treatment for chronic pain.

Chronic dry eye symptoms after LASIK: parallels and lessons to be learned from other persistent post-operative pain disorders

Laser in-situ keratomileusis (LASIK) is a commonly performed surgical procedure used to correct refractive error. LASIK surgery involves cutting a corneal flap and ablating the stroma underneath, with known damage to corneal nerves. Despite this, the epidemiology of persistent pain and other long-term outcomes after LASIK surgery are not well understood. Available data suggest that approximately 20-55% of patients report persistent eye symptoms (generally regarded as at least 6 months post-operation) after LASIK surgery. While it was initially believed that these symptoms were caused by ocular surface dryness, and referred to as “dry eye,” it is now increasingly understood that corneal nerve damage produced by LASIK surgery resembles the pathologic neuroplasticity associated with other forms of persistent post-operative pain. In susceptible patients, these neuropathological changes, including peripheral sensitization, central sensitization, and altered descending modulation, may underlie certain persistent dry eye symptoms after LASIK surgery. This review will focus on the known epidemiology of symptoms after LASIK and discuss mechanisms of persistent post-op pain due to nerve injury that may be relevant to these patients. Potential preventative and treatment options based on approaches used for other forms of persistent post-op pain and their application to LASIK patients are also discussed. Finally, the concept of genetic susceptibility to post-LASIK ocular surface pain is presented.

Challenging neurological symptoms in paediatric palliative care: An approach to symptom evaluation and management in children with neurological impairment

Neurological symptoms are very common in children with life-limiting conditions and are challenging in terms of burden of illness. Moreover, neurological symptoms can significantly impact the child's quality of life and contribute to distress among parents, families, caregivers and health care providers. Knowing how to manage and alleviated these symptoms is essential for providing good palliative care. In the present article, the more common neurological symptoms of agitation/irritability, spasticity and dystonia will be reviewed. The aim of the present brief review is to provide a basic approach to both the identification and treatment of these neurological symptoms. A medication table is provided for quick reference. A brief commentary and guidance for the management of pain are also incorporated, with reference to further literature sources.

Treatment of painful diabetic peripheral neuropathy

BACKGROUND

Painful diabetic peripheral neuropathy impairs quality of life and can be difficult to treat.

OBJECTIVE

To discuss current treatment recommendations for painful diabetic peripheral neuropathy.

STUDY DESIGN

Literature review.

METHODS

Systematic review of the literature discussing treatment of painful diabetic peripheral neuropathy. Existing treatment guidelines were studied and compared.

RESULTS

Painful diabetic peripheral neuropathy occurs in about one in six people with diabetes. This condition impairs quality of life and increases healthcare costs. Treatment recommendations exist, but individual patient therapy can require a trial-and-error approach. Many treatment options have adjuvant benefits or side effects which should be considered prior to initiating therapy. Often, a combination of treatment modalities with various mechanisms of action is required for adequate pain control. Adequate medication titration and a reasonable trial period should be allowed.

CONCLUSION

The treatment of painful diabetic peripheral neuropathy can be challenging, but effective management can improve patient's quality of life.

CLINICAL RELEVANCE

Painful diabetic peripheral neuropathy impairs quality of life and can be difficult to treat. Many treatment options have adjuvant benefits or side effects which should be considered prior to initiating therapy. Often, a combination of treatment modalities with various mechanisms of action is required for adequate pain control.

Post-operative brachial plexus neuropraxia: A less recognised complication of combined plastic and laparoscopic surgeries

This presentation is to increase awareness of the potential for brachial plexus injury during prolonged combined plastic surgery procedures. A case of brachial plexus neuropraxia in a 26-year-old obese patient following a prolonged combined plastic surgery procedure was encountered. Nerve palsy due to faulty positioning on the operating table is commonly seen over the elbow and popliteal fossa. However, injury to the brachial plexus has been a recently reported phenomenon due to the increasing number of laparoscopic and robotic procedures. Brachial plexus injury needs to be recognised as a potential complication of prolonged combined plastic surgery. Preventive measures are discussed.

Effect of temperature on the surface free energy and acid–base properties of Gabapentin and Pregabalin drugs − a comparative study

Temperature dependent surface energy variations observed in Gabapentin and Pregabalin drugs.

Efficacy of gabapentin in the improvement of pruritus and quality of life of patients with notalgia paresthetica

BACKGROUND

notalgia paresthetica is a subdiagnosed sensory neuropathy presenting as a condition of intense itching and hyperchromic macule on the back that interferes with daily habits.

OBJECTIVES

To determine the efficacy of treatment of notalgia paresthetica using oral gabapentin, assessing the degree of improvement in itching and influence on quality of life. Moreover, to evaluate the signs and symptoms associated with notalgia paresthetica.

METHODS

We conducted an experimental, non-randomized, parallel, non-blinded study including 20 patients with clinical and histopathological diagnosis of notalgia paresthetica. After application of the visual analogue scale of pain adapted for pruritus and of the questionnaire of dermatology life quality index (DLQI), ten patients with visual analogue scale > 5 were given treatment with gabapentin at the dose of 300 mg/day for four weeks. The other ten were treated with topical capsaicin 0.025% daily for four weeks. After the treatment period, patients answered again the scale of itching.

RESULTS

The use of gabapentin was responsible for a significant improvement in pruritus (p=0.0020). Besides itching and hyperchromic stain on the back, patients reported paresthesia and back pain. It was observed that the main factor in the worsening of the rash is heat.

CONCLUSION

Gabapentin is a good option for the treatment of severe itching caused by nostalgia paresthetica.

Thrombospondin-4 and excitatory synaptogenesis promote spinal sensitization after painful mechanical joint injury

Facet joint injury induces persistent pain that may be maintained by structural plasticity in the spinal cord. Astrocyte-derived thrombospondins, especially thrombospondin-4 (TSP4), have been implicated in synaptogenesis and spinal sensitization in neuropathic pain, but the TSP4 response and its relationship to synaptic changes in the spinal cord have not been investigated for painful joint injury. This study investigates the role of TSP4 in the development and maintenance of persistent pain following injurious facet joint distraction in rats and tests the hypothesis that excitatory synaptogenesis contributes to such pain. Painful facet joint loading induces dorsal horn excitatory synaptogenesis along with decreased TSP4 in the DRG and increased astrocytic release of TSP4 in the spinal cord, all of which parallel the time course of sustained tactile allodynia. Blocking injury-induced spinal TSP4 expression with antisense oligonucleotides or reducing TSP4 activity at its neuronal receptor in the spinal cord with gabapentin treatment both attenuate the allodynia and dorsal horn synaptogenesis that develop after painful facet joint loading. Increased spinal TSP4 also facilitates the development of allodynia and spinal hyperexcitability, even after non-painful physiological loading of the facet joint. These results suggest that spinal TSP4 plays an important role in the development and maintenance of persistent joint-mediated pain by inducing excitatory synaptogenesis and facilitating the transduction of mechanical loading of the facet joint that leads to spinal hyperexcitability.

Single dose pharmacokinetic equivalence study of two gabapentin preparations in healthy subjects

BACKGROUND

The current study was conducted to find out whether two oral preparations of 300 mg gabapentin (the test and reference capsules) were bioequivalent.

SUBJECTS AND METHODS

This was a randomized, single-blind, crossover study under fasting condition, with a 7-day washout period, which included 37 healthy adult male and female subjects. After an overnight fast, subjects were given, orally, one capsule of the test drug or of the reference drug. Blood samples were drawn immediately before taking the drug, then at 20 and 40 minutes, and 1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 15, and 24 hours after dosing, to evaluate pharmacokinetic parameters of the single dose administration, ie, the area under the plasma concentration-time curve (AUC) from time zero to 24 hours (AUCt), AUC from time zero to infinity (AUC(inf)), the peak plasma concentration of the drug (Cmax), time needed to achieve Cmax (tmax), and the elimination half-life (t1/2). The plasma concentrations of gabapentin were determined using validated high-performance liquid chromatography with ultraviolet detection.

RESULTS

The geometric mean ratios (90% confidence interval) of the test drug/reference drug for gabapentin were 103.15% (90.38%-117.72%) for AUCt, 103.53% (90.78%-118.07%) for AUC(inf), and 108.06% (96.32%-121.24%) for Cmax. The differences in tmax and t1/2 values between the test and reference drug products for gabapentin were not statistically significant. Light-headedness, nausea, and headache were encountered during the study, but they were all mild and well tolerated. The 90% confidence intervals of the test/reference AUC ratio and Cmax ratio of gabapentin were within the acceptance range for bioequivalence.

CONCLUSION

The two preparations of gabapentin 300 mg capsule were bioequivalent, thus both can be used interchangeably in the clinical setting.

Pharmacogenetics of chronic pain management

OBJECTIVE

The experience of chronic pain is one of the commonest reasons individuals seek medical attention, making the management of chronic pain a major issue in clinical practice. Drug metabolism and responses are affected by many factors, with genetic variations offering only a partial explanation of an individual's response. There is a paucity of evidence for the benefits of pharmacogenetic testing in the context of pain management.

DESIGN AND METHODS

We reviewed the literature between 2000 and 2013, and references cited therein, using various keywords related to pain management, pharmacology and pharmacogenetics.

RESULTS

Opioids continue to be the mainstay of chronic pain management. Several non-opioid based therapies, such as treatment with cannabinoids, gene therapy and epigenetic-based approaches are now available for these patients. Adjuvant therapies with antidepressants, benzodiazepines or anticonvulsants can also be useful in managing pain. Currently, laboratory monitoring of pain management patients, if performed, is largely through urine drug measurements.

CONCLUSIONS

Drug half-life calculations can be used as functional markers of the cumulative effect of pharmacogenetics and drug-drug interactions. Assessment of half-life and therapeutic effects may be more useful than genetic testing in preventing adverse drug reactions to pain medications, while ensuring effective analgesia. Definitive, mass spectrometry-based methods, capable of measuring parent drug and metabolite levels, are the most useful assays for this purpose. Urine drug measurements do not necessarily correlate with serum drug concentrations or therapeutic effects. Therefore, they are limited in their use in monitoring efficacy and toxicity.

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.

Postoperative pain and long-term functional outcome after administration of gabapentin and pregabalin in patients undergoing spinal surgery

STUDY DESIGN

Prospective, double-blind study, randomized control trial.

OBJECTIVE

To evaluate and compare the analgesic efficacy, adverse effects, and clinical utility of gabapentin and pregabalin in postoperative pain management, long-term functional outcome, and quality of life in patients undergoing spinal surgery.

SUMMARY OF BACKGROUND DATA

Patient outcome after lumbar discectomy for radicular low back pain is variable and the benefit is inconsistent. The most common persistent symptoms are pain, motor deficit, and decreased functional status.

METHODS

This study was conducted in 90 patients belonging to the 18 to 75 age group of either sex undergoing spinal surgery under general anesthesia. Group A received 300 mg of gabapentin, group B received 75 mg of pregabalin, whereas group C received placebo 1 dose 1 hour before surgery and 8 hourly for 7 days, thereafter. The outcome of postoperative static and dynamic pain and functional outcome was recorded using 3 questionnaires-visual analogue scale, Prolo functional and economic score, Oswestry Disability Index score from preoperative period to 3 months postoperatively.

RESULTS

Among the 3 groups, subjects receiving pregabalin showed consistently reduced static and dynamic pain intensity and also required lesser amount of rescue drug throughout the postoperative period. There was statistically significant difference (P < 0.05) in the Prolo score and Oswestry Disability Index score at all time intervals between group B and group C. Although, significant difference in the functional outcome between group A and group B was seen at 3 months.

CONCLUSION

Preoperative pregabalin administration is associated with less pain intensity and improved functional outcomes 3 months after lumbar discectomy followed by gabapentin and then placebo.

LEVEL OF EVIDENCE

2.

Pharmacokinetic considerations for therapies used to treat interstitial cystitis

INTRODUCTION

Interstitial cystitis (IC) or bladder pain syndrome (BPS) is defined as supra-pubic pain related to bladder filling. IC is characterized by a particular symptom complex with no identifiable causes; as with bladder hypersensitivity it is usually associated with urinary frequency and urgency with bladder pain. No current treatments have a significant impact on symptoms over time.

AREAS COVERED

This systematic review examines the pharmacokinetic aspects and adverse event of present IC therapy to highlight appropriate treatment to improve the symptoms of IC. This article reviews material obtained via Medline, PubMed, and EMBASE literature searches up to October 2013.

EXPERT OPINION

The correct approach to IC should consider a multidisciplinary team of specialists and a multimodal treatment package that include psychotherapy, behavior change, physical activation, and analgesic treatment. Unfortunately, a single therapeutic target for IC is not yet known. With regard to pathophysiology and therapy, there is more to discover. The first insult damages the bladder urothelium, hence vehicles that lead the drug to penetrate the wall of the bladder might be a novel strategic approach.

Special Considerations for Multiple Limb Amputation

It has been estimated that more than 1.6 million individuals in the United States have undergone at least one amputation. The literature abounds with research of the classifications of such injuries, their etiologies, epidemiologies, treatment regimens, average age of onset (average age of amputation), and much more. The subpopulation that is often overlooked in these evaluations, however, is comprised of individuals who have suffered multiple limb loss. The challenges faced by those with single-limb loss are amplified for those with multiple limb loss. Pain, lifestyle adjustment, and quality of life return are just a few key areas of concern in this population. Along with amputations resulting from trauma, many individuals with multiple amputations have endured them as a result of dysvascular disease. Over recent years, amputations as a result of dysvascular disease have risen to comprise more than 80 % of new amputations occurring in the United States every year. This compares to just 54 % of total current prevalence. Those with diabetes comorbid with dysvascular disease make up 74 % of those with dysvascular amputations, and these individuals with diabetes comorbid with dysvascular disease have a 55 % chance of enduring an amputation of their contralateral limb within 2-3 years of their initial amputation. With the well-documented aging of the nation's population and the similarly skyrocketing prevalence of dysvascular disease and diabetes, it can be expected that the number of individuals with multiple limb loss will continue to increase in the United States. This article outlines the recommended measures of care for this particular subpopulation, including pain management, behavioral health considerations, strategies for rehabilitation for various levels and variations of multiple limb loss, and the assistive technology and adaptive equipment that might be available for these individuals to best enable them to continue healthy, fulfilling lives following amputation.

Gabapentin and pregabalin in the management of postoperative pain after lumbar spinal surgery: a systematic review and meta-analysis

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVE

To review the literature systematically and make a comprehensive understanding of the efficacy of these 2 drugs in the management of postoperative pain after lumbar spinal surgery.

SUMMARY OF BACKGROUND DATA

Several trials that evaluated the efficacy of gabapentin and pregabalin in the management of postoperative pain after lumbar spinal surgery have been published.

METHODS

PubMed (1980 to present), adapted for EMBASE (1980 to present), and Cochrane databases were searched for randomized placebo-controlled trials. Random effect model was used in our meta-analysis, and standard mean difference (SMD) was chosen as the pooled estimate.

RESULTS

Seven trials were included in our study. All included studies could be considered to be of high quality in methodology. The pooled results from meta-analysis demonstrated that compared with placebo, both gabapentin and pregabalin could significantly reduce the postoperative narcotic consumption (SMD, -1.54, and -1.16, respectively). Oral gabapentin was efficacious in the management of postoperative pain at all time points during the first day after surgery (SMD, -1.91 at 0-6 hr, -1.30 at 6-12 hr, -1.05 at 12-24 hr, respectively). Pregabalin seemed to be also efficacious in the management of postoperative pain at 0 to 6 hours (SMD, -1.05), at 6 to 12 hours (SMD, -0.62), and at 12 to 24 hours (SMD, -0.43). Both drugs could be well tolerated in our included trials, compared with placebo.

CONCLUSION

This work suggested that both gabapentin and pregabalin were efficacious in reduction of postoperative pain and narcotic requirements after lumbar spinal surgery, whereas more trials were needed to further assess the efficacy of pregabalin in the management of postoperative pain after lumbar spinal surgery.

LEVEL OF EVIDENCE

1.

Gabapentin alleviates facet-mediated pain in the rat through reduced neuronal hyperexcitability and astrocytic activation in the spinal cord

Although joint pain is common, its mechanisms remain undefined, with little known about the spinal neuronal responses that contribute to this type of pain. Afferent activity and sustained spinal neuronal hyperexcitability correlate to facet joint loading and the extent of behavioral sensitivity induced after painful facet injury, suggesting that spinal neuronal plasticity is induced in association with facet-mediated pain. This study used a rat model of painful C6-C7 facet joint stretch, together with intrathecal administration of gabapentin, to investigate the effects of one aspect of spinal neuronal function on joint pain. Gabapentin or saline vehicle was given via lumbar puncture prior to and at 1 day after painful joint distraction. Mechanical hyperalgesia was measured in the forepaw for 7 days. Extracellular recordings of neuronal activity and astrocytic and microglial activation in the cervical spinal cord were evaluated at day 7. Gabapentin significantly (P = .0001) attenuated mechanical hyperalgesia, and the frequency of evoked neuronal firing also significantly decreased (P < .047) with gabapentin treatment. Gabapentin also decreased (P < .04) spinal glial fibrillary acidic protein expression. Although spinal Iba1 expression was doubled over sham, gabapentin did not reduce it. Facet joint-mediated pain appears to be sustained through spinal neuronal modifications that are also associated with astrocytic activation.

PERSPECTIVE

Intrathecal gabapentin treatment was used to investigate behavioral, neuronal, and glial response in a rat model of painful C6-C7 facet joint stretch. Gabapentin attenuated mechanical hyperalgesia, reduced evoked neuronal firing, and decreased spinal astrocytic activation. This study supports that facet joint pain is sustained through spinal neuronal and astrocytic activation.

Neuroprotectin/protectin D1 protects against neuropathic pain in mice after nerve trauma

Prevalence of neuropathic pain is high after major surgery. However, effective treatment for preventing neuropathic pain is lacking. Here we report that perisurgical treatment of neuroprotectin D1/protectin D1 (NPD1/PD1), derived from docosahexaenoic acid, prevents nerve injury-induced mechanical allodynia and ongoing pain in mice. Intrathecal post-treatment of NPD1/PD1 also effectively reduces established neuropathic pain and produces no apparent signs of analgesic tolerance. Mechanistically, NPD1/PD1 treatment blocks nerve injury-induced long-term potentiation, glial reaction, and inflammatory responses, and reverses synaptic plasticity in the spinal cord. Thus, NPD1/PD1 and related mimetics might serve as a new class of analgesics for preventing and treating neuropathic pain.

Optimizing the Pharmacologic Treatment of Insomnia: Current Status and Future Horizons

A number of medications are available for treating patients with insomnia. These medications include agents approved as insomnia therapies by the U.S. Food and Drug Administration (FDA), agents approved by the FDA for another condition that are used "off-label" to treat insomnia, and agents available "over-the-counter" that are taken by individuals with insomnia. These agents differ in their properties, their safety and efficacy when used for different insomnia patient subtypes, and the available data on their efficacy and safety in these subtypes. As a result, optimizing the medication treatment of insomnia for a given patient requires that the clinician select an agent for use which has characteristics that make it most likely to effectively and safely address the type of sleep difficulty experienced by that individual. This article is intended to assist clinicians and researchers in carrying out this optimization. It begins by reviewing the basic characteristics of the medications used to treat insomnia. This is followed by a review of the fundamental ways that individuals with insomnia may differ and affect the choice of medication therapy. This review includes discussions that illustrate how to best choose a medication based on the characteristics of the available medications, the key differences among insomnia patients, and the available research literature. Lastly, we discuss future directions for the optimizing pharmacologic management of insomnia. It is hoped that the treatment tailoring methods discussed herein serve as a means of improving the clinical management of insomnia and, thus, improve the lives of the many patients who suffer from this common and impairing condition.

Randomized, placebo-controlled pilot trial of gabapentin during an outpatient, buprenorphine-assisted detoxification procedure

This pilot study examined the efficacy of the N-type calcium channel blocker gabapentin to improve outcomes during a brief detoxification protocol with buprenorphine. Treatment-seeking opioid-dependent individuals were enrolled in a 5-week, double-blind, placebo-controlled trial examining the effects of gabapentin during a 10-day outpatient detoxification from buprenorphine. Participants were inducted onto buprenorphine sublingual tablets during Week 1, were randomized and inducted onto gabapentin or placebo during Week 2, underwent a 10-day buprenorphine taper during Weeks 3 and 4, and then were tapered off gabapentin/placebo during Week 5. Assessments included thrice-weekly opioid withdrawal scales, vitals, and urine drug screens. Twenty-four individuals (13 male; 17 Caucasian, 3 African American, 4 Latino; mean age 29.7 years) participated in the detoxification portion of the study (gabapentin, n = 11; placebo, n = 13). Baseline characteristics did not differ significantly between groups. Self-reported and observer-rated opioid withdrawal ratings were relatively low and did not differ between groups during the buprenorphine taper. Urine results showed a Drug × Time interaction, such that the probability of opioid-positive urines significantly decreased over time in the gabapentin versus placebo groups during Weeks 3 and 4 (OR = 0.73, p = .004). These results suggest that gabapentin reduces opioid use during a 10-day buprenorphine detoxification procedure.

Gabapentin Therapy of Hiccups

OBJECTIVE:

To determine whether gabapentin is effective in the treatment of persistent or intractable hiccups.

DATA SOURCES:

A search of MEDLINE (1966-March 2013) using the MeSH search terms gabapentin, hiccups, and hiccups/drug therapy was performed. Additional databases searched included Web of Science (1945-March 2013) and International Pharmaceutical Abstracts (1970-March 2013) using the text words gabapentin and hiccups. Bibliographies of relevant articles were reviewed for additional citations.

STUDY SELECTION AND DATA EXTRACTION:

All data sources were considered for inclusion. Preference was given for articles written in English, although one abstract in German was used.

DATA SYNTHESIS:

Because of the low incidence of persistent or intractable hiccups, few if any controlled clinical trials are conducted on the efficacy of drug treatment. Therefore, most of the data involve case reports or case series. We evaluated 17 case reports and 2 case series involving gabapentin therapy for persistent or intractable hiccups. Therapeutic outcomes with gabapentin were positive in all cases, with temporal evidence suggesting an effect, but outcomes often were obscured by combination therapy and comorbidities in some cases. Case reports suggest that gabapentin might be useful as a second-line agent in patients undergoing stroke rehabilitation or in the palliative care setting where chlorpromazine adverse effects are undesirable. Gabapentin was very well tolerated, with only a few minor adverse effects.

CONCLUSIONS:

Gabapentin has a similar body of evidence as other pharmacotherapeutic agents used to treat hiccups. Gabapentin is well tolerated and should be considered as a second-line agent in selected patients.

Effects of axonal ion channel dysfunction on quality of life in type 2 diabetes

OBJECTIVE

Pharmacological agents for diabetic peripheral neuropathy (DN) target a number of mechanisms, including sodium channel function and γ-aminobutyric acid-minergic processes. At present, prescription is undertaken on a trial-and-error basis, leading to prolonged medication trials and greater healthcare costs. Nerve-excitability techniques are a novel method of assessing axonal ion channel function in the clinical setting. The aim of this study was to determine the effects of axonal ion channel dysfunction on neuropathy-specific quality-of-life (QoL) measures in DN.

RESEARCH DESIGN AND METHODS

Fifty-four patients with type 2 diabetes mellitus underwent comprehensive neurologic assessment, nerve-conduction studies, and nerve-excitability assessment. Neuropathy severity was assessed using the Total Neuropathy Score. Neuropathy-specific QoL was assessed using a DN-specific QoL questionnaire (Neuropathy-Specific Quality of Life Questionnaire [NeuroQoL]). Glycosylated hemoglobin and BMI were recorded in all patients.

RESULTS

NeuroQoL scores indicated significant QoL impairment (mean 9.08 ± 5.93). Strength-duration time constant (SDTC), an excitability parameter reflecting sodium channel function, was strongly correlated with QoL scores (r = 0.545; P < 0.005). SDTC was prolonged in 48.6% of patients who experienced neuropathic symptoms. A significant correlation was also noted between SDTC and neuropathy severity (r = 0.29; P < 0.05). This relationship was strengthened when looking specifically at patients with clinically graded neuropathy (r = 0.366; P < 0.05).

CONCLUSIONS

The current study has demonstrated an association between markers of sodium channel function and QoL in DN. The study demonstrates that excitability techniques may identify patients in whom altered sodium channel function may be the dominant abnormality. The findings suggest that excitability techniques may have a role in clinical decision making regarding neuropathic treatment prescription.

Pharmacotherapy of amphetamine-type stimulant dependence: an update

ISSUES

Methamphetamine- or amphetamine-type stimulants are the second most frequently used illicit drug worldwide, second only to cannabis. Behavioural treatments are efficacious, but their impact is limited underscoring the need for other treatment options, notably, pharmacotherapy.

APPROACH

A review of randomised controlled trials of pharmacotherapies for methamphetamine- or amphetamine-type stimulants was performed using PubMed and Google Scholar databases. Evidence for efficacy of medications is reported.

KEY FINDINGS

Clinical trials have yielded no broadly effective pharmacotherapy. Promising signals have been observed for methylphenidate, naltrexone, bupropion and mirtazapine in subgroups of patients in reducing stimulant use (e.g. patients with less severe dependence at baseline and men who have sex with men), though none has produced an unambiguous, replicable signal of efficacy.

IMPLICATIONS

Problems in Phase II trials, including high dropout rates, missing data and a lack of agreement on outcomes, complicate efforts to find a broadly effective pharmacotherapy for amphetamine-type stimulant disorders. Efforts to address these problems include calls for better validation of pharmacological target exposure, receptor binding and functional modulation. As well, there is a need for agreement in using findings from preclinical and early phases of the medication development process for selecting better pharmacotherapy candidates.

CONCLUSION

After over 20 years of efforts worldwide to develop a broadly effective medication for dependence on methamphetamine- or amphetamine-type stimulants, no candidate has emerged. This highlights the need for new compounds, consistent and stringent research methods, better integration between preclinical and clinical stages of medication development, and improved collaboration between government, industry and researchers.