Gabapentin: pharmacology and its use in pain management

High intraocular pressure after carbamazepine and gabapentin intake in a pseudoexfoliative patient

INTRODUCTION

Psychotropic agents may frequently be associated with ocular adverse effects, which include angle-closure glaucoma. We report a case of pseudoexfoliation glaucoma in which intraocular pressure (IOP) increased within hours after carbamazepine and gabapentin intake, with no observable evidence of any angle closure.

CASE REPORT

A 67-year-old woman with pseudoexfoliation glaucoma presented with high IOP in her right eye after carbamazepine and gabapentin intake. To investigate which psychotropic medicine was the cause of this fluctuation, the patient was called for 2 subsequent visits and the order of the medicines she took was changed in each examination. Baseline IOP was recorded in each examination, and the IOP was monitored hourly after the intake of medicines. Baseline and hourly Pentacam measurements were also made to demonstrate changes in anterior segment parameters.

DISCUSSION

Gabapentin and carbamazepine resulted in deepening of the anterior chamber, widening of the iridocorneal angle, and mild pupillary dilation in 2 visits. Carbamazepine was associated with a significant increase in IOP independent of gabapentin use. The absence of angle closure and plateau iris configuration suggested other mechanisms that might be related to high IOP after carbamazepine intake.

CONCLUSION

This is the first reported case of a large increase in IOP within hours after carbamazepine and gabapentin intake in a pseudoexfoliative eye.

Gabapentin and (S)-pregabalin decrease intracellular D-serine concentrations in PC-12 cells

The effects of gabapentin (GBP) and (S)-pregabalin (PGB) on the intracellular concentrations of d-serine and the expression of serine racemase (SR) in PC-12 cells were determined. Intracellular d-serine concentrations were determined using an enantioselective capillary electrophoresis assay with laser-induced fluorescence detection. Increasing concentrations of GBP, 0.1-20μM, produced a significant decrease in d-serine concentration relative to control, 22.9±6.7% at 20μM (*p<0.05), with an IC(50) value of 3.40±0.29μM. Increasing concentrations of PGB, 0.1-10μM, produced a significant decrease in d-serine concentration relative to control, 25.3±7.6% at 10μM (*p<0.05), with an IC(50) value of 3.38±0.21μM. The compounds had no effect on the expression of monomeric-SR or dimeric-SR as determined by Western blotting. The results suggest that incubation of PC-12 cells with GBP and PGB reduced the basal activity of SR, which is most likely a result of the decreased Ca(2+) flux produced via interaction of the drugs with the α(2)-δ subunit of voltage-gated calcium channels. d-Serine is a co-agonist of the N-methyl d-aspartate receptor (NMDAR) and reduced d-serine concentrations have been associated with reduced NMDAR activity. Thus, GBP and PGB may act as indirect antagonists of NMDAR, a mechanism that may contribute to the clinical effects of the drugs in neuropathic pain.

Understanding the pharmacokinetics of anxiolytic drugs

INTRODUCTION

Anxiety disorders are considered the most common mental disorders and they can increase the risk for comorbid mood and substance use disorders, significantly contributing to the global burden of disease. For this reason, anxiolytics are the most prescribed psychoactive drugs, particularly in the Western world.

AREAS COVERED

This review aims to analyze pharmacokinetic profile, plasma level variations so as the metabolism, interactions and possible relation to clinical effect of several drugs which are used primarily as anxiolytics. The drugs analyzed include benzodiazepines, anticonvulsants (pregabalin, gabapentin), buspirone, β-blockers and antihistamines (hydroxyzine). Regarding the most frequently used anxiolytic benzodiazepines, data on alprazolam, bromazepam, chlordesmethyldiazepam, chlordiazepoxide, clotiazepam, diazepam, etizolam, lorazepam, oxazepam, prazepam and clonazepam have been detailed.

EXPERT OPINION

There is a need for a more balanced assessment of the benefits and risks associated with benzodiazepine use, particularly considering pharmacokinetic profile of the drugs to ensure that patients, who would truly benefit from these agents, are not denied appropriate treatment. An optimal pharmacological approach involving an integrative pharmacokinetic and pharmacodynamic optimization strategy would ensure better treatment and personalization of anxiety disorders. So it would be desirable for the development of new anxiolytic drug(s) that are more selective, fast acting and free from the unwanted effects associated with the traditional benzodiazepines as tolerance or dependence.

Preoperative pregabalin does not reduce propofol ED(50): a randomized controlled trial

BACKGROUND

In many studies, gabapentinoids, such as pregabalin, have been shown to reduce preoperative anxiety. This anxiolysis is often accompanied by sedation, one of the most frequent side effects of pregabalin. We hypothesized that pregabalin taken preoperatively could reduce propofol requirements for induction of general anesthesia.

METHODS

A randomized double-blind placebo-controlled trial was conducted after approval by the local ethics committee. Fifty women aged 18-40 yr, American Anesthesiologists Society physical status I and II, and scheduled to undergo elective laparoscopic gynecologic procedures were enrolled after written consent. Treatment group patients were given pregabalin 150 mg po one hour before surgery while patients in the control group received a placebo. The primary outcome was the propofol dose required to achieve a targeted anesthetic depth in 50% of the population, i.e., effective dose (ED)50. The ED50 was estimated using Dixon's up-and-down methodology. The targeted anesthetic depth was defined based on predetermined entropy monitoring values (State Entropy [SE] < 50 and Response Entropy [RE]-SE < 10). As a secondary outcome, we tested if pregabalin reduced pre-induction anxiety levels which were measured on a 0-100 scale.

RESULTS

The propofol ED50 was not statistically different between the pregabalin group (mean 1.33 mg·kg(-1); 95% confidence interval [CI] 1.23 to 1.43) vs the placebo group (mean 1.37 mg·kg(-1); 95% CI 1.28 to 1.46); P = 0.19. Also, pre-induction anxiety level was not different between groups (median 31; interquartile range [IQR] [10-52] vs median 42; IQR [4-71], respectively; P = 0.41).

CONCLUSIONS

Preoperative pregabalin does not reduce propofol requirements in a population of healthy young women undergoing laparoscopic gynecologic procedures. This study failed to show a pre-induction anxiolytic effect of pregabalin in such a population. This trial was registered at www.clinicaltrials.gov (NCT01158859).

Effects of Preoperative Gabapentin on Postoperative Pain after Radical Retropubic Prostatectomy

Objective:

The impact of preoperative gabapentin on tramadol consumption using patient-controlled analgesia (PCA) and postoperative pain was assessed in patients undergoing radical retropubic prostatectomy (RRP).

Methods:

In this prospective, randomized trial, 51 patients undergoing RRP were randomized into two groups: the gabapentin group received 900 mg gabapentin orally 2 h before surgery; the control group did not receive gabapentin. Postoperative analgesia was provided by tramadol PCA. Pain was assessed using a visual analogue scale for 24 h, postoperatively.

Results:

Mean cumulative tramadol consumption at 24 h was comparable in the two groups. Pain scores at 45 min, 60 min and 2 h postoperatively, and the number of patients who required rescue analgesia, were significantly lower in the gabapentin group than in the control group. Side-effects were similar in the two groups.

Conclusions:

Preoperative administration of 900 mg gabapentin did not decrease tramadol consumption, but was associated with lower pain scores in the early postoperative phase and a reduced need for rescue analgesia, compared with controls, in patients undergoing RRP.

Perioperative management of the child on long-term opioids

The strategies used to manage children exposed to long-term opioids are extrapolated from adult literature. Opioid consumption during the perioperative period is more than three times that observed in patients not taking chronic opioids. A sparing use of opioids in the perioperative period results in both poor pain management and withdrawal phenomena. The child's pre-existing opioid requirement should be maintained, and acute pain associated with operative procedures should be managed with additional analgesia. This usually comprises short-acting opioids, regional or local anesthesia, and adjuvant therapies. Long-acting opioids, transdermal opioid patches, and implantable pumps can be used to maintain the regular opioid requirement. Intravenous infusion, nurse controlled analgesia, patient-controlled analgesia, or oral formulations are invaluable for supplemental requirements postoperatively. Effective management requires more than simply increasing opioid dose during this time. Collaboration of the child, family, and all teams involved is necessary. While chronic pain or palliative care teams and other staff experienced with the care of children suffering chronic pain may have helpful input, many pediatric hospitals do not have chronic pain teams, and many patients receiving long-term opioids are not palliative. Acute pain services are appropriate to deal with those on long-term opioids in the perioperative setting and do so successfully in many centers. Staff caring for such children in the perioperative period should be aware of the challenges these children face and be educated before surgery about strategies for postoperative management and discharge planning.

Acute postoperative pain management in the older patient

Acute pain management in the older adult is both challenging and rewarding. This review addresses the difficulty with assessment of pain in the older adult, variations in the pain experience of older adults, physiological differences between the young and old, changes in pharmacokinetics and pharmacodynamics with age, and useful pharmacological treatments for acute pain in older adults. It then presents a few representative cases of pain management in older adults. The goal of this review is to provide relevant information that can be used to manage acute postoperative pain in the older adult.

A randomized controlled trial to compare pregabalin with gabapentin for postoperative pain in abdominal hysterectomy

Background:

Pregabalin is a potent ligand for alpha-2-delta subunit of voltage-gated calcium channels in the central nervous system, which exhibits potent anticonvulsant, analgesic and anxiolytic activity. The pharmacological activity of pregabalin is similar to that of gabapentin and shows possible advantages. Although it shows analgesic efficacy against neuropathic pain, very limited evidence supports its postoperative analgesic efficacy. We investigated its analgesic efficacy in patients experiencing acute pain after abdominal hysterectomy and compared it with gabapentin and placebo.

Methods:

A randomized, double-blind, placebo-controlled study was conducted in 90 women undergoing abdominal hysterectomy who were anaesthetized in a standardized fashion. Patients received 300 mg pregabalin, 900 mg gabapentin or placebo, 1–2 hours prior to surgery. Postoperative analgesia was administered at visual analogue scale (VAS) ≥3. The primary outcome was analgesic consumption over 24 hours and patients were followed for pain scores, time to rescue analgesia and side effects as secondary outcomes.

Results:

The diclofenac consumption was statistically significant between pregabalin and control groups, and gabapentin and control groups; however, pregabalin and gabapentin groups were comparable. Moreover, the consumption of tramadol was statistically significant among all the groups. Patients in pregabalin and gabapentin groups had lower pain scores in the initial hour of recovery. However, pain scores were subsequently similar in all the groups. Time to first request for analgesia was longer in pregabalin group followed by gabapentin and control groups.

Conclusion:

A single dose of 300 mg pregabalin given 1–2 hours prior to surgery is superior to 900 mg gabapentin and placebo after abdominal hysterectomy. Both the drugs are better than placebo.

Simultaneous quantification of levetiracetam and gabapentin in plasma by ultra-pressure liquid chromatography coupled with tandem mass spectrometry detection

INTRODUCTION

Gabapentin (Neurontin) and levetiracetam (Keppra) are anticonvulsants with novel structures and suggested therapeutic ranges of 2-10 mg/L and 6-20 mg/L, respectively. Gabapentin is also used extensively to manage neuropathic pain, and for this indication, wherein higher doses are prescribed, plasma concentrations of 15-30 mg/L are typical.

OBJECTIVE

Here, we describe a simple rapid assay to support therapeutic drug monitoring of gabapentin and levetiracetam in plasma by ultra-pressure liquid chromatography couples to tandem mass spectrometry (UPLC-MS/MS) detection.

METHODS

After the addition of internal standard and protein precipitation of patient plasma with methanol:acetonitrile in a 50:50 ratio, 1 μL of supernatant sample is injected onto an Acquity UPLC HSS T3, 1.8 μm, 2.1 × 50 mm (Waters) column. Elution occurs using a linear gradient of acetonitrile and water, each having 0.1% formic acid added. The column is eluted into a Waters Acquity UPLC TQD, operating in a positive mode to detect gabapentin at transition 172.18 > 154.11, levetiracetam at 171.11 > 126, and internal standard (3-amino-2-naphthoic acid) at 188.06 > 170. Secondary transitions for each analyte are also monitored for gabapentin at 172.18 > 137.06, levetiracetam at 171.11 > 154, and internal standard at 188.06 > 115. Runtime is 1.5 minutes per injection with baseline resolved chromatographic separation.

RESULTS

The analytical measurement ranges were 1-150 mg/L for gabapentin and for levetiracetam. Intra-assay imprecision by the coefficient of variance (CV) was less than 8% and interassay CV was less than 5% for both analytes, at 4 different concentrations. Results obtained from patient samples were compared with results generated by established high-performance liquid chromatography-UV methods with the following regression statistics: y = 1.12x - 0.77, r = 0.996, Sy, x = 0.89, and n = 29 for gabapentin and y = 0.991x + 0.70, r = 0.997, Sy, x = 2.24, and n = 30 for levetiracetam. No analytical interferences were identified.

CONCLUSION

: In summary, a simple reliable UPLC-MS/MS method was developed and validated for routine clinical monitoring of gabapentin and levetiracetam.

Chemical analgesia for velvet antler removal in deer

There is a legal requirement to provide analgesia for velvet antler removal in New Zealand. Currently, this is achieved using local anaesthetic blockade, with or without systemically administered sedative/analgesic agents, or by compression in 1-year-old stags. Lignocaine hydrochloride 2% is most commonly used and is most effective when administered as a high-dose ring block. Combinations of various amino-amide local anaesthetic agents can achieve rapid onset and prolonged duration of analgesia, though concerns about drug residues and carcinogenic potential of a lignocaine metabolite have led to consideration of the amino-ester family of local anaesthetics as alternatives. Systemically administered analgesics, including opioids, alpha-2-adrenergic agents and ketamine provide dose-dependent sedation and analgesia. However, none are sufficient, alone or in combination, to produce surgical analgesia at currently recommended dose rates and when reversal agents are given, analgesic effects are usually reversed as well as sedation. Thus, local anaesthetic blockade is still indicated, though the potential for drug or drug-metabolite residues in velvet antler remains a concern. The need for and effectiveness of non-steroidal anti-inflammatory drugs (NSAIDs) for post-operative analgesia requires investigation. Amitriptyline, locally administered opioid agonists, tramadol and other systemically administered agents may warrant future investigation for surgical and post-operative analgesia for velvet antler removal.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Pharmacological interventions for pain in patients with temporomandibular disorders

BACKGROUND

Temporomandibular disorders (TMD) are a group of disorders affecting the temporomandibular joints and the muscles of mastication. TMDs are treated with a wide range of drugs. The extent to which the use of these drugs is based upon evidence is unknown.

OBJECTIVES

To assess the effectiveness of pharmacological interventions both alone and in combination with non-pharmacological therapy in relieving pain in patients with chronic TMD.

SEARCH STRATEGY

Electronic searches of the Cochrane Oral Health Group's Trials Register (2 August 2010), CENTRAL (The Cochrane Library 2010, Issue 3), MEDLINE via OVID (1950 to 2 August 2010), EMBASE via OVID (1980 to 2 August 2010) and CINAHL via EBSCO (1981 to 2 August 2010) were conducted. Reference lists of articles and previous reviews were scanned for relevant articles and authors were contacted for further information where appropriate.

SELECTION CRITERIA

Randomised controlled trials (RCTs) in which a pharmacological agent was compared with placebo for the management of pain in patients with TMD. Parenteral routes of administration were excluded.

DATA COLLECTION AND ANALYSIS

Duplicate data extraction and assessment of risk of bias in included studies was performed.

MAIN RESULTS

Eleven studies were included with a total of 496 participants. The primary outcome of most of the studies was pain. The risk of bias in the included studies was variable. Whilst four studies showed significant pain relief for the active treatment, three were of poor quality. Most adverse effects were mild to moderate in severity. Four studies reported withdrawals due to severe adverse reactions, but insufficient information was provided regarding the trial groups from which the withdrawals occurred. No meta-analysis was conducted due to lack of similarities across the included studies.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support or not support the effectiveness of the reported drugs for the management of pain due to TMD. There is a need for high quality RCTs to derive evidence of the effectiveness of pharmacological interventions to treat pain associated with TMD.

Chronic neuropathic pain in veterinary patients

Neuropathic pain is pathophysiologically distinct from other types of chronic pain and is defined by the Neuropathic Pain Special Interest Group of the International Association for the Study of Pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system." At least in humans, and perhaps in animals, neuropathic pain causes a much greater impairment in the patient's quality of life than is caused by other pain syndromes. And, unfortunately, this type of pain is generally quite difficult to accurately diagnose and even harder to effectively treat. A brief review of neuropathic pain and its treatment in veterinary patients is presented here.

Therapeutic hotline: Treatment of prurigo nodularis and lichen simplex chronicus with gabapentin

Psychocutaneous conditions are frequently encountered in dermatology practice. Prurigo nodularis and lichen simplex chronicus are two frustrating conditions that are classified in this category. They are often refractory to classical treatment with topical corticosteroids and antihistamines. Severe, generalized exacerbations require systemic therapy. Phototherapy, erythromycine, retinoids, cyclosporine, azathiopurine, naltrexone, and psychopharmacologic agents (pimozide, selective serotonin reuptake inhibitor antidepressants) were tried with some success. Here five cases with lichen simplex chronicus and four cases with prurigo nodularis, who responded well to gabapentin, are presented.

Gabapentin improves cold-pressor pain responses in methadone-maintained patients

Individuals on methadone maintenance for the treatment of addiction (MM) are demonstrated to be hyperalgesic to cold-pressor pain in comparison to matched controls and ex-opioid addicts, a finding described as clinical evidence of opioid-induced hyperalgesia (OIH). Interestingly, opioids induce hyperalgesia via many of the same neuro-inflammatory and central sensitization processes that occur with the development of neuropathic pain. Evaluated in this study was the efficacy of a key pharmacotherapy for neuropathic pain, gabapentin (GPN), to reverse OIH in MM patients. Utilizing a clinical trial design and double blind conditions, changes in cold-pressor pain threshold and tolerance following a 5-week trial of GPN (titrated to 2400mg/day) were evaluated at peak and trough methadone plasma levels in a well-characterized MM sample. Drug abstinence was encouraged via an escalating payment schedule, and compliance monitored via pill counts and GPN plasma levels; entered into the analyses were only those subjects compliant and abstinent throughout the study (approximately 45%). Utilizing change scores from baseline, significant improvements in cold-pressor pain threshold and pain tolerance were observed at both peak and trough methadone levels (p<0.05). Notably, drop-out rates due to medication side effects were low (2%) and the medication was well-tolerated. These results support that GPN, as prescribed for the treatment of neuropathic pain, is effective in decreasing OIH in patients who are abstinent and stable in methadone treatment.

Gabapentin for the treatment of pain related to radiation-induced mucositis in patients with head and neck tumors treated with intensity-modulated radiation therapy

BACKGROUND

This retrospective study evaluates the efficacy of gabapentin for the treatment of pain syndrome related to radiation-induced mucositis in patients with head and neck tumors.

METHODS

Thirty cases of head and neck malignancies treated with radiotherapy were analyzed.

RESULTS

By using a median dose of 2700 mg/day of gabapentin, only 10% of patients required additional narcotic pain medications for adequate pain relief during the third and fourth week of treatment, despite grade 2 or higher mucositis present in 56% and 73% of the patients, respectively. Likewise, during the last weeks of intensity-modulated radiation therapy (IMRT), only 35% of patients required additional narcotics for pain control, despite the presence of grade 2 or higher mucositis in 80% of cases.

CONCLUSIONS

Gabapentin appears promising in reducing the need for narcotic pain medication for patients with head and neck malignancies treated with IMRT and should be further evaluated prospectively in controlled clinical trials.

Inhibitory mechanisms of gabapentin, an antiseizure drug, on platelet aggregation

Gabapentin (Neurontin) is an analogue of gamma-aminobutyric acid (GABA) that is effective against partial seizures. Gabapentin has been reported to modulate serotonin release from platelets, but the effects of gabapentin on platelet activation have not been explored. In this study, gabapentin concentration-dependently (60–240 μm) inhibited platelet aggregation in washed platelets stimulated by collagen (1 μg mL−1), ADP (20 μm) and arachidonic acid (60 μm). Gabapentin (120 and 240 μm) also concentration-dependently inhibited collagen (1 μg mL−1)-induced phospho-inositide breakdown, intracellular Ca2+ mobilization, thromboxane A2 formation, and p38 MAPK phosphorylation in human platelets. In conclusion, the most important findings of this study suggest that gabapentin inhibits platelet aggregation, at least in part, through the phospholipase C-inositol 1,4,5-trisphosphate-thromboxane A2-Ca2+ pathway. Thus, it is possible that gabapentin treatment, alone or in combination with other antiplatelet drugs, may induce or potentiate inhibition of platelet aggregation, which may affect haemostasis in-vivo.

New treatments for chronic prostatitis/chronic pelvic pain syndrome

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is a common condition among men of a wide age range, with detrimental effects on quality of life. The etiology, pathogenesis, and optimal treatment of CP/CPPS remain unknown, although progress has been made in these domains in recent years. A wide variety of pharmacologic and nonpharmacologic therapies have been studied in clinical trials, but most have shown limited efficacy in symptom alleviation. CP/CPPS is increasingly viewed as a condition that involves variable degrees of neuropathic pain. Medications such as gabapentin, pregabalin, memantine, and tricyclic antidepressants are often used in other neuropathic pain conditions and, therefore, are considered potential treatments for CP/CPPS. Few studies of these agents in patients with CP/CPPS have been reported, but future clinical trials should help to determine their utility and to characterize the pathogenetic mechanisms of pain in CP/CPPS. Combining treatment trials with biomarker, genomic, and imaging studies, in addition to epidemiologic and symptom-based assessments, will maximize the ability to probe disease etiology and pathogenesis, as well as identify effective treatment.

Gabapentin decreases morphine consumption and improves functional recovery following total knee arthroplasty

BACKGROUND

Moderate to severe pain after total knee arthroplasty often interferes with postoperative rehabilitation and delays discharge from hospital. The present study examined the effects of a four-day postoperative gabapentin (GBP) regimen versus placebo on opioid consumption, pain scores and knee flexion, as well as adverse effects, after total knee arthroplasty.

METHODS

After obtaining research ethics board approval and informed consent, 40 patients were enrolled in a randomized, single-blind, placebo-controlled, open-label study. Patients were assigned to one of five groups - preoperative placebo/postoperative placebo (G1), preoperative GBP 600 mg/postoperative placebo (G2), preoperative GBP 600 mg/postoperative GBP 100 mg three times per day (G3), preoperative GBP 600 mg/ postoperative GBP 200 mg three times per day (G4) and preoperative GBP 600 mg/postoperative GBP 300 mg three times per day (G5). Postoperative GBP or placebo was continued for four days after surgery. Two hours before surgery, all patients received celecoxib 400 mg. Based on the above groupings, patients in G1 received placebo medication, whereas patients in G2, G3, G4 and G5 received gabapentin 600 mg 2 h preoperatively. All patients received femoral and sciatic nerve blocks, followed by spinal anesthesia. Beginning in the postanesthetic care unit, all patients received a regimen of celecoxib 200 mg every 12 h for four days and a patient-controlled morphine analgesia pump for 48 h.

RESULTS

Thirty-six patients (G1, n=7; G2, n=7; G3, n=8; G4, n=7; G5, n=7) completed the study. Data were analyzed by one-way ANOVA followed by a contrast comparing patients who received postoperative GBP (G3, G4 and G5) (n=22) with patients who received placebo postoperatively (G1 and G2) (n=14). Patients who received GBP postoperatively used significantly less patient-controlled morphine analgesia at 24 h, 36 h and 48 h (P<0.05). The postoperative GBP patients had significantly better active assisted knee flexion on postoperative days 2 and 3, with a trend toward better flexion on postoperative day 4. Patients who received GBP postoperatively reported less pruritus than patients who received placebo. There were no differences in pain scores.

CONCLUSIONS

These results support the use of GBP in the acute postoperative period. Further trials are needed to delineate the optimal dose, timing and duration of GBP use following surgery.

Adding gabapentin to a multimodal regimen does not reduce acute pain, opioid consumption or chronic pain after total hip arthroplasty

BACKGROUND

Gabapentin (GPN) is effective in reducing post-operative pain and opioid consumption, but its effects with regional anesthesia for total hip arthroplasty (THA) are not known. We designed this study to determine whether (1) gabapentin administration reduces pain and opioid use after THA using a multimodal analgesic regimen including spinal anesthesia; (2) pre-operative administration of gabapentin is more effective than post-operative administration.

METHODS

After REB approval and informed consent, 126 patients were enrolled in a double-blinded, randomized-controlled study. Patients received acetaminophen 1 g per os (p.o.), celecoxib 400 mg p.o. and dexamethasone 8 mg intravenously, 1-2 h pre-operatively. Patients were randomly assigned to one of three treatment groups (G1: Placebo/Placebo; G2: GPN/Placebo; G3: Placebo/GPN). Patients received gabapentin 600 mg (G2) or placebo (G1 and G3) 2 h before surgery. All patients had spinal anesthesia [15 mg (3cc) of 0.5% hypobaric bupivacaine with 10 microg of fentanyl]. In the post-anesthetic care unit, patients received gabapentin 600 mg (G3) or placebo (G1 and G2). On the ward, patients received acetaminophen 1000 mg p.o. q6h, celecoxib 200 mg p.o. q12h and a morphine PCA device. Patients were interviewed 6 months post-surgery to determine the incidence and severity of chronic post-surgical pain.

RESULTS

Mean+/-SD cumulative morphine (mg) consumption (G1=49.4+/-24.8, G2=47.2+/-30.1 and G3=56.1+/-38.2) at 48 h and pain scores at 12, 24, 36 and 48 h post-surgery were not significantly different among the groups [G1 (n=38), G2 (n=38) and G3 (n=38)]. Side effect profiles were similar across groups. Six months after surgery, the number of patients who reported chronic post-surgical pain (G1=10, G2=12 and G3=9) and the severity of the pain (G1=4.2+/-2.9, G2=4.1+/-2.2 and G3=4.9+/-2.2) did not differ significantly among the groups (P>0.05).

CONCLUSIONS

A single 600 mg dose of gabapentin given pre-operatively or post-operatively does not reduce morphine consumption or pain scores in hospital or at 6 months after hip arthroplasty within the context of spinal anesthesia and a robust multimodal analgesia regimen.

Transitional polytherapy: tricks of the trade for monotherapy to monotherapy AED conversions

The goal of epilepsy therapy is to help patients achieve seizure freedom without adverse effects. While monotherapy is preferable in epilepsy treatment, many patients fail a first drug due to lack of efficacy or failure to tolerate an initial medication, necessitating an alteration in therapy. Sudden changes between monotherapies are rarely feasible and sometimes deleterious given potential hazards of acute seizure exacerbation or intolerable adverse effects. The preferred method for converting between monotherapies is transitional polytherapy, a process involving initiation of a new antiepileptic drug (AED) and adjusting it toward a target dose while maintaining or reducing the dose of the baseline medication. A fixed-dose titration strategy of maintaining the baseline drug dose while titrating the new medication is preferable when breakthrough seizures are occurring and no adverse effects are present. However, a flexible titration strategy involving reduction of the baseline drug dose to ensure adequate tolerability of the new adjunctive medication is preferred when patients are already experiencing adverse effects. This article reviews pharmacokinetic considerations pertinent for ensuring successful transitional polytherapy with the standard and newer antiepileptic drugs. Practical consensus recommendations "from an expect panel (SPECTRA, Study by a Panel of Experts Considerations for Therapy Replacement and Antiepileptics) for a successful monotherapy" AED conversions are then summarized. Transitional polytherapy is most successful when clinicians appropriately manage the titration strategy and consider pharmacokinetic factors germane to the baseline and new adjunctive medication.

Gabapentin and uremic pruritus in hemodialysis patients

BACKGROUND

Pruritus is a common and bothersome problem in 30-50% of hemodialysis patients. The aim of this study was to determine the effect of gabapentin, 100 mg/three times a week (after each hemodialysis session), on uremic pruritus.

STUDY DESIGN

Patients older than 18 years who had undergone hemodialysis for more than three months were enrolled in this double-blind clinical trial. They had experienced pruritus refractory to antihistamines for at least two weeks. The patients were assigned to receive gabapentin 100 mg following hemodialysis for a period of four weeks, and after a washout week, they received the placebo for another four weeks. They were asked to evaluate the severity of their pruritus using a visual analogue scale (VAS). The reduction of pruritus >or= 50% was accepted as the response.

RESULTS

The mean pruritus score reached 6.44 +/- 8.4 (p < 0.0001), 15 +/- 11.2 (p < 0.001), and 81.11 +/- 11.07 (p < 0.001) during gabapentin, washout, and placebo periods, respectively. No significant correlation was found between age, sex, duration of dialysis, underlying diseases, and systolic and diastolic blood pressures and the gabapentin effect.

CONCLUSION

Gabapentin is an effective agent in treating uremic pruritus.