Gabapentin Enhances the Analgesic Effect of Morphine in Healthy Volunteers

Chronic Gabapentinoid Use and Lumbar Fusion Outcomes: A Comparative Analysis of Gabapentinoids Alone and in Combination With Opioids

STUDY DESIGN

Retrospective comparative cohort study.

OBJECTIVES

To examine the effects of chronic use of gabapentinoids (GPs) (alone or with opioids) on the outcomes of lumbar fusions.

SUMMARY OF BACKGROUND DATA

Opioids have historically been the mainstay medications for pain management, but the ongoing opioid epidemic led physicians to look for alternatives. GPs are used for various indications, and chronic use for any indication may lead to a higher risk of adverse events, especially when combined with opioids.

MATERIALS AND METHODS

Patients aged 18 years and older who underwent posterior fusion of the lumbosacral spine and ≥1-year follow-up were included. Patients were grouped according to their preoperative chronic GP and opioid usage as GP and opioid nonuser (-/-), GP user opioid nonuser (+/-), GP nonuser and opioid user (-/+), and GP and opioid user (+/+).

RESULTS

A total of 563 patients (M/F%=41/59, mean age 61.1 y) were included. Two hundred eighty (49%) patients were in the group -/-, while 110 (19%) were in +/-, 78 (15%) were in -/+, and 95 (17%) were in +/+. For ODI, back pain and leg pain, +/+ had the worst outcomes at all time points, while -/- had the best. Chronic GP users (+/-) showed back pain improvement similar to the -/- group; however, the improvements in leg pain and ODI were considerably less. GP use resulted in increased postoperative opioid requirements, although not as much as chronic opioid use. Complication rates were similar.

CONCLUSIONS

Chronic preoperative use of GPs may lead to inferior outcomes when compared with GP-naive patients, and this is significantly accentuated when taken concurrently with opioids. Patients who are using both GPs and opioids had the worst results for almost every outcome measure. Given the significantly worse surgical outcomes documented in this study, concurrent use with opioids should be avoided.

Gabapentin and D-cycloserine alone and in combination with naloxone in methadone-maintained humans responding under a naloxone novel-response discrimination procedure

The present study examined the impact of the N-type calcium channel blocker gabapentin (GBP) and the partial glycine agonist D-cycloserine (CYC) to attenuate the behavioral effects of naloxone in opioid-dependent humans responding under a naloxone discrimination procedure. Methadone-maintained participants were trained to distinguish between a low dose of naloxone (0.15 mg/70 kg, i.m.; i.e., drug A) and placebo (i.e. drug B) under an instructed novel-response drug discrimination procedure, in which participants identify the drug condition as 'A', 'B', or 'N' (neither A nor B - 'novel'). Once the discrimination was acquired, doses of CYC (0, 500, and 625 mg) and GBP (0, 100, 200, and 400 mg) each alone and in combination with the training dose of naloxone were tested. GBP alone produced only placebo-appropriate responding and did not significantly alter naloxone discrimination when coadministered with naloxone, though it modestly reduced naloxone-induced visual analog scale ratings of drug 'strength'. CYC alone also produced predominantly placebo-appropriate responding and did not modulate naloxone-appropriate responding, but increased ratings of bad effects and decreased ratings of like placebo relative to naloxone alone at the 500 mg dose. These null findings regarding the modulation of naloxone discrimination highlight the limited efficacy of GBP and CYC in this context, contributing to the understanding of pharmacological interactions with opioid antagonists and their potential implications for opioid withdrawal treatment.

α2δ-1-Linked NMDA and AMPA Receptors in Neuropathic Pain and Gabapentinoid Action

Chronic neuropathic pain is a debilitating condition that presents a significant therapeutic challenge. Unlike nociceptive pain, neuropathic pain is predominantly driven by glutamate NMDA receptors (NMDARs) and/or Ca2+-permeable AMPA receptors (CP-AMPARs) at synapses between primary afferent nerves and excitatory neurons in the spinal dorsal horn. The α2δ-1 protein, encoded by Cacna2d1 and historically recognized as a subunit of voltage-activated Ca2+ channels, is the primary target of gabapentinoids, such as gabapentin and pregabalin, which are widely prescribed for neuropathic pain and epilepsy. However, gabapentinoids have minimal effects on Ca2+ channel activity. Recent studies reveal that α2δ-1 plays a pivotal role in amplifying nociceptive input to the spinal cord in neuropathic pain. This action is mediated through its dynamic physical interactions with phosphorylated NMDARs and GluA1/GluA2 subunits via its intrinsically disordered C-terminal region. α2δ-1 not only promotes synaptic trafficking of NMDARs but also disrupts heteromeric assembly of GluA1/GluA2 subunits in the spinal dorsal horn. The central function of α2δ-1 is to elevate intracellular Ca2+ concentrations at both presynaptic and postsynaptic sites, augmenting nociceptive transmission. Consequently, α2δ-1 serves as a dual regulator coordinating synaptic expression of NMDARs and GluA1 homomeric CP-AMPARs, a function that underlies the therapeutic actions of gabapentinoids. By inhibiting α2δ-1, gabapentinoids reduce the hyperactivity of synaptic α2δ-1-bound NMDARs and CP-AMPARs, thereby dampening the excessive excitatory synaptic transmission characteristic of neuropathic pain. These newly identified roles of α2δ-1 in orchestrating glutamatergic synaptic plasticity suggest that gabapentinoids could be repurposed for treating other neurological disorders involving dysregulated synaptic NMDARs and CP-AMPARs.

Susceptibility to Pentylenetetrazole-Induced Seizures in Mice with Distinct Activity of the Endogenous Opioid System

Currently, pharmacotherapy provides successful seizure control in around 70% of patients with epilepsy; however, around 30% of cases are still resistant to available treatment. Therefore, effective anti-epileptic therapy still remains a challenge. In our study, we utilized two mouse lines selected for low (LA) and high (HA) endogenous opioid system activity to investigate the relationship between down- or upregulation of the opioid system and susceptibility to seizures. Pentylenetetrazole (PTZ) is a compound commonly used for kindling of generalized tonic-clonic convulsions in animal models. Our experiments revealed that in the LA mice, PTZ produced seizures of greater intensity and shorter latency than in HA mice. This observation suggests that proper opioid system tone is crucial for preventing the onset of generalized tonic-clonic seizures. Moreover, a combination of an opioid receptor antagonist-naloxone-and a GABA receptor agonist-diazepam (DZP)-facilitates a significant DZP-sparing effect. This is particularly important for the pharmacotherapy of neurological patients, since benzodiazepines display high addiction risk. In conclusion, our study shows a meaningful, protective role of the endogenous opioid system in the prevention of epileptic seizures and that disturbances in that balance may facilitate seizure occurrence.

State-level policies and receipt of CDC-informed opioid thresholds among commercially insured new chronic opioid users

OBJECTIVES

To evaluate the association of state-level policies on receipt of opioid regimens informed by Centers for Disease Control and Prevention (CDC) morphine milligram equivalent (MME)/day recommendations.

DESIGN

A retrospective cohort study of new chronic opioid users (NCOUs).

SETTING

Commercially insured plans across the United States using IQVIA PharMetrics® Plus for Academics database with new chronic use between January 2014 and March 2015.

PARTICIPANTS

NCOUs with ≥60-day coverage of opioids within a 90-day period with ≥30-day opioid-free period prior to the date of the first qualifying opioid prescription.

INTERVENTIONS

State-level policies including Prescription Drug Monitoring Program (PDMP) robustness and cannabis policies involving the presence of medical dispensaries and state-wide decriminalization.

MAIN OUTCOME MEASURES

NCOUs were placed in three-tiered risk-based average MME/day thresholds: low (>0 to <50), medium (≥50 to <90), and high (≥90). Multinomial logistic regression was used to estimate the association of state-level policies with the thresholds while adjusting for relevant patient-specific factors.

RESULTS

NCOUs in states with medium or high PDMP robustness had lower odds of receiving medium (adjusted odds ratio [AOR] 0.74; 95 percent confidence interval [CI]: 0.62-0.69) and high (AOR 0.74; 95 percent CI: 0.59-0.92) thresholds. With respect to cannabis policies, NCOUs in states with medical cannabis dispensaries had lower odds of receiving high (AOR 0.75; 95 percent CI: 0.60-0.93) thresholds, while cannabis decriminalization had higher odds of receiving high (AOR 1.24; 95 percent CI: 1.04-1.49) thresholds.

CONCLUSION

States with highly robust PDMPs and medical cannabis dispensaries had lower odds of receiving higher opioid thresholds, while cannabis decriminalization correlated with higher odds of receiving high opioid thresholds.

Short-term healthcare resource utilization associated with receipt of CDC-informed opioid thresholds among commercially insured new chronic opioid users

OBJECTIVE

To evaluate the impact of recent changes to the Centers for Disease Control and Prevention (CDC) morphine milligram equivalent (MME)/day threshold recommendations on healthcare utilization.

DESIGN

A retrospective cohort study of new chronic opioid users (NCOUs).

SETTING

Commercially insured plans across the United States using IQVIA PharMetrics® Plus for Academics database with new use between January 2014 and March 2015.

PATIENTS

NCOUs with ≥60-day coverage of opioids within a 90-day period with ≥30-day opioid-free period prior to the date of the first qualifying opioid -prescription.

INTERVENTIONS

NCOU categorized by the CDC three-tiered risk-based average MME/day thresholds: low (>0 to <50), medium (≥50 to <90), and high (≥90).

MAIN OUTCOME MEASURES

Multivariable logistic regression was used to calculate adjusted odds of incurring an acute care encounter (ACE) (all-cause and opioid-related) between the thresholds (adjusted odds, 95 percent confidence interval).

RESULTS

In adjusted analyses, when compared to low threshold, there was no difference in the odds of all-cause ACE across the medium (1.01, 0.94-1.28) and high (1.01, 0.84-1.22) thresholds. When compared to low threshold, a statistically insignificant increase was observed when evaluating opioid-related ACE among medium (1.86, 0.86-4.02) and high (1.51, 0.65-3.52) thresholds.

CONCLUSIONS

There was no difference in odds of an all-cause or opioid-related ACE associated with the thresholds. Early-intervention programs and policies exploring reduction of MME/day among NCOUs may not result in short-term reduction in all-cause or opioid-related ACEs. Further assessment of potential long-term reduction in ACEs among this cohort may be insightful.

Functional Changes of White Matter Are Related to Human Pain Sensitivity during Sustained Nociception

Pain is considered an unpleasant perceptual experience associated with actual or potential somatic and visceral harm. Human subjects have different sensitivity to painful stimulation, which may be related to different painful response pattern. Excellent studies using functional magnetic resonance imaging (fMRI) have found the effect of the functional organization of white matter (WM) on the descending pain modulatory system, which suggests that WM function is feasible during pain modulation. In this study, 26 pain sensitive (PS) subjects and 27 pain insensitive (PIS) subjects were recruited based on cold pressor test. Then, all subjects underwent the cold bottle test (CBT) in normal (26 degrees temperature stimulating) and cold (8 degrees temperature stimulating) conditions during fMRI scan, respectively. WM functional networks were obtained using K-means clustering, and the functional connectivity (FC) was assessed among WM networks, as well as gray matter (GM)-WM networks. Through repeated measures ANOVA, decreased FC was observed between the GM-cerebellum network and the WM-superior temporal network, as well as the WM-sensorimotor network in the PS group under the cold condition, while this difference was not found in PIS group. Importantly, the changed FC was positively correlated with the state and trait anxiety scores, respectively. This study highlighted that the WM functional network might play an integral part in pain processing, and an altered FC may be related to the descending pain modulatory system.

Provider-directed analgesia for dental pain

INTRODUCTION

Extraction of impacted molar teeth is a common procedure performed by oral surgeons and general dentists, with postoperative pain being a significant adverse event post-surgery. If mismanaged, pain can lead to complications that impact oral and systemic health. The current scourge of the opioid epidemic has ushered in a new era of provider-directed analgesic (PDA) therapy in dentistry.

AREAS COVERED

This article provides an in-depth review on the major pharmacological and therapeutic properties of established and alternative analgesics used to manage dental pain.

EXPERT OPINION

Substantial evidence-based literature shows combination of a non-steroidal anti-inflammatory drug (NSAID; e.g. ibuprofen) and acetaminophen provides superior pain relief than single-agent or combination opioid regimens. However, there are clinical scenarios (e.g. severe pain) when short-course opioid prescription is appropriate in select patients, in which a 2-3-day treatment duration is typically sufficient. Alternative agents (e.g. caffeine, gabapentin, phytotherapies), typically in combination with established agents, can mitigate postoperative dental pain. Some evidence suggests preemptive therapies (e.g. corticosteroids, NSAIDs) reduce amounts of postsurgical analgesic consumption and might lessen opioid prescription burden. In summary, this comprehensive review provides an opportune update on the evolving landscape of pharmacotherapy for acute postsurgical dental pain, informing best practices for PDA in the dental setting.

Neural and Molecular Investigation into the Paraventricular Thalamic-Nucleus Accumbens Circuit for Pain Sensation and Non-opioid Analgesia

The paucity of medications with novel mechanisms for pain treatment combined with the severe adverse effects of opioid analgesics has led to an imperative pursuit of non-opioid analgesia and a better understanding of pain mechanisms. Here, we identify the putative glutamatergic inputs from the paraventricular thalamic nucleus to the nucleus accumbens (PVT^Glut→NAc) as a novel neural circuit for pain sensation and non-opioid analgesia. Our in vivo fiber photometry and in vitro electrophysiology experiments found that PVT^Glut→NAc neuronal activity increased in response to acute thermal/mechanical stimuli and persistent inflammatory pain. Direct optogenetic activation of these neurons in the PVT or their terminals in the NAc induced pain-like behaviors. Conversely, inhibition of PVT^Glut→NAc neurons or their NAc terminals exhibited a potent analgesic effect in both naïve and pathological pain mice, which could not be prevented by pretreatment of naloxone, an opioid receptor antagonist. Anterograde trans-synaptic optogenetic experiments consistently demonstrated that the PVT^Glut→NAc circuit bi-directionally modulates pain behaviors. Furthermore, circuit-specific molecular profiling and pharmacological studies revealed dopamine receptor 3 as a candidate target for pain modulation and non-opioid analgesic development. Taken together, these findings provide a previously unknown neural circuit for pain sensation and non-opioid analgesia and a valuable molecular target for developing future safer medication.

Trends and correlates of concurrent opioid and benzodiazepine and/or gabapentinoid use among Ontario nursing home residents

BACKGROUND

A concern with long-term opioid use is the increased risk arising when opioids are used concurrently with drugs that can potentiate their associated adverse effects. The drugs most often encountered are benzodiazepines (BZDs) and gabapentinoids. Our study objectives were to examine trends in the concurrent use of opioids and BZDs, or gabapentinoids, in a Canadian nursing home population over an 11-year period, and current resident-level correlates of this concurrent use.

METHODS

We conducted a population-based, repeated cross-sectional study among Ontario nursing home residents (>65 years) dispensed opioids between April 2009 and February 2020. For the last study year, we examined cross-sectional associations between resident characteristics and concurrent use of opioids with BZDs or gabapentinoids. Linked data on nursing home residents from clinical and health administrative databases was used. The yearly proportions of residents who were dispensed an opioid concurrently with a BZD or gabapentinoid were plotted with percent change derived from log-binomial regression models. Separate modified Poisson regression models estimated resident-level correlates of concurrent use of opioids with BZDs or gabapentinoids.

RESULTS

Over the study period, among residents dispensed an opioid there was a 53.2% relative decrease (30.7% to 14.4%) in concurrent BZD and a 505.4% relative increase (4.4% to 26.6%) in concurrent gabapentinoid use. In adjusted models, increasing age and worsening cognition were inversely associated with the concurrent use of both classes, but most other significantly related covariates were unique to each drug class (e.g., sex and anxiety disorders for BZD, pain severity and presence of pain-related conditions for gabapentinoids).

CONCLUSIONS

Co-administration of BZDs or gabapentinoids in Ontario nursing home residents dispensed opioids remains common, but the pattern of co-use has changed over time. Observed covariates of concurrent use in 2019/20 suggest distinct but overlapping resident populations requiring consideration of the relative risks versus benefits of this co-use and monitoring for potential harm.

Functional Impairment and Cognitive Symptoms Among People with HIV Infection on Chronic Opioid Therapy for Pain: The Impact of Gabapentin and Other Sedating Medications

Gabapentin is associated with dizziness, falls, and somnolence yet commonly prescribed to people with HIV (PWH) treated with chronic opioid therapy (COT). Physical function and cognition are understudied when prescribed together. Among PWH on COT, we evaluated whether co-prescribed gabapentin is associated with (a) functional impairment; (b) trouble thinking clearly; and (c) difficulty controlling drowsiness using logistic regression models adjusted for prescribed opioid dose, other (non-gabapentin) sedating medication, substance use disorder, and mental/physical health indicators in a cross-sectional study. Among 166 participants, 40% were prescribed gabapentin, 41% reported functional impairment, 41% trouble thinking clearly, and 38% difficulty controlling drowsiness. Gabapentin co-prescribed with COT was significantly associated with trouble thinking clearly but not with functional impairment or difficulty controlling drowsiness. Clinicians should be cognizant of potential problems with thinking clearly when co-prescribing gabapentin and opioid medication.

Efficacy of Combination Therapy with Pregabalin in Neuropathic Pain: A Preclinical Study in the Rat L5 Spinal Nerve Ligation Model

PURPOSE

Neuropathic pain is sometimes difficult to manage because of limited efficacy of analgesic monotherapy even at high doses. Combination therapy may help address this issue, but there is little evidence for its effectiveness. Therefore, we evaluated the efficacy of combination therapy with pregabalin, an anchor drug for treating neuropathic pain, using the rat L5 spinal nerve ligation model.

METHODS

Experiments were performed on four-week-old L5 spinal nerve ligated male Sprague-Dawley rats. Mechanical allodynia was assessed using the von Frey test, where the 50% withdrawal threshold was evaluated for five drugs: pregabalin, duloxetine, venlafaxine, tramadol, and celecoxib. The single-drug experiment included 112 rats, where each drug was tested independently. Median effective doses (ED₅₀s) were determined. Combinations of pregabalin with each of the other four drugs were tested (n=84). The 50% withdrawal threshold in the von Frey test was evaluated. The ED₅₀ of each combination was determined experimentally. Isobolographic analyses were conducted to assess the synergistic potential of the drug combinations, excluding pregabalin-celecoxib, since the ED₅₀ of celecoxib could not be determined.

RESULTS

In the single-drug experiment, all drugs except celecoxib resulted in a dose-dependent increase in the 50% withdrawal threshold 2 h after administration, with a maximum possible effect ranging from 4.4% to 79.6%. Similarly, all pregabalin combinations demonstrated a dose-dependent increase in the 50% withdrawal threshold, with pregabalin-tramadol showing the greatest increment. Isobolographic analysis of this combination revealed synergistic effects. Specifically, the combination index was γ=0.4 (<1). Combinations of pregabalin with duloxetine and venlafaxine demonstrated additive (γ=0.9) and antagonistic effects (γ=2.0), respectively.

CONCLUSION

This study demonstrated that combination of pregabalin with tramadol has synergistic antiallodynic effects, while that with duloxetine has additive effects. Moreover, pregabalin combined with venlafaxine was potentially antagonistic. Pregabalin combined with tramadol may serve as a promising drug combination for the effective management of neuropathic pain.

Prevalence of Gabapentinoids and Central Nervous System Depressant Drugs, and Their Association with Risk Factors for Respiratory Depression in Primary Care Patients

BACKGROUND AND OBJECTIVES

Warnings have been published regarding an increased risk of severe respiratory depression in patients receiving gabapentinoids either alone or in combination with opioids and/or anxiolytics/hypnotics, especially in individuals with a respiratory risk factor. The aim is to report the prevalence of the use of gabapentinoids alone and associated with central nervous system depressant drugs, and possible associated risk factors for respiratory depression, in order to identify the most fragile population and establish intervention strategies.

METHODS

We performed a cross-sectional study using computerized prescription records from the northern area of Barcelona at Catalan Institute of Health for 363,007 inhabitants registered during 2021. Patients aged ≥ 18 years with one or more gabapentinoid prescription were included. Age, gender, polypharmacy, adjusted morbidity groups, quantity of chronic diseases, and the number of consultations per year were independent variables. Four age categories were defined (18-64 years, then 64-74, 75-84, and those aged 85 years or older). Descriptive and inferential statistics were employed. Level of statistical significance was 5% (p ≤ 0.05). For the analysis, the SPSS program (version 22) was employed.

RESULTS

Of the study sample, 9218 were prescribed gabapentidoids. Overall prevalence of use was 3.0% (women 3.6%, men 2.4%). On the whole, women used more drugs than men. In contrast to their younger counterparts, consumption increased 2.6 times, 3.8 times, and 4.0 times in the 65-74 age group, 75-84 age group, and those aged ≥ 85 years, respectively. Mean age was 65.59 (±15.80) years. Polypharmacy (5-9 drugs) was present in 41.7% of the patients and extreme polypharmacy (≥ 10 drugs) was present in 39.3% of the patients. Regarding renal function, 2396 patients (25.9%) had glomerular filtration that required dose adjustment (76.1% with gabapentin and 23.8% with pregabalin). In 141 patients (5.9%), a total daily dose higher than that authorized (109 with gabapentin, 29 with pregabalin) had been prescribed. The prescription of gabapentinoids combined with opioids and/or anxiolytics/hypnotics was significantly associated with (i) polypharmacy (5-9 drugs, OR: 3.42 [95% CI 3.00-3.88]; ≥ 10 drugs, OR 8.72 [95% CI 7.42-10.25]); (ii) quantity of chronic diseases, OR: 1.14 (95% CI 1.11-1.17); (iii) augmented number of consultations/year, OR: 1.01 (95% CI 1.00-1.01); (iv) female gender, OR: <  1 for men, OR: 0.66 (95% CI 0.60-0.73); (v) being elderly: 65-74 years, OR: 0.71 (95% CI 0.62-0.81); 75-84 years, OR: 0.62 (95% CI 0.54-0.71); ≥85 years, OR: 0.68 (95% CI 0.58-0.81); and (vi) adjusted morbidity groups, OR: 0.90 (95% CI 0.88-0.92), (p <  0.0001).

CONCLUSION

Exposure to gabapentinoids occurs in a non-negligible percentage of the population. Greater numbers of combinations of gabapentinoids and opioids and/or anxiolytics/hypnotics were associated with polypharmacy, quantity of chronic diseases, and augmented number of consultations, but not with male gender, older age, and adjusted morbidity groups.

Pharmacokinetic Drug-Drug Interactions among Antiepileptic Drugs, Including CBD, Drugs Used to Treat COVID-19 and Nutrients

Anti-epileptic drugs (AEDs) are an important group of drugs of several generations, ranging from the oldest phenobarbital (1912) to the most recent cenobamate (2019). Cannabidiol (CBD) is increasingly used to treat epilepsy. The outbreak of the SARS-CoV-2 pandemic in 2019 created new challenges in the effective treatment of epilepsy in COVID-19 patients. The purpose of this review is to present data from the last few years on drug–drug interactions among of AEDs, as well as AEDs with other drugs, nutrients and food. Literature data was collected mainly in PubMed, as well as google base. The most important pharmacokinetic parameters of the chosen 29 AEDs, mechanism of action and clinical application, as well as their biotransformation, are presented. We pay a special attention to the new potential interactions of the applied first-generation AEDs (carbamazepine, oxcarbazepine, phenytoin, phenobarbital and primidone), on decreased concentration of some medications (atazanavir and remdesivir), or their compositions (darunavir/cobicistat and lopinavir/ritonavir) used in the treatment of COVID-19 patients. CBD interactions with AEDs are clearly defined. In addition, nutrients, as well as diet, cause changes in pharmacokinetics of some AEDs. The understanding of the pharmacokinetic interactions of the AEDs seems to be important in effective management of epilepsy.

Development and validation of a rapid liquid chromatography/tandem mass spectrometry method to quantitate gabapentin and buprenorphine in human serum

RATIONALE

Gabapentin has shown initial promise as an opioid-sparing medication in pain patients as well as a treatment for opioid withdrawal and liquid chriomatography/tandem mass spectrometry (LC/MS/MS) is often used for clinical monitoring. Despite reports of validated tandem mass spectrometric methods for the determination of gabapentin and buprenorphine, mechanisms for the collision-induced fragmentation have not been adequetely described.

METHODS

A rapid analytical method has been developed to determine gabapentinoid, gabapentin, and the partial opioid agonist, buprenorphine, in 20 μL of human serum using LC/MS/MS with a chromatographic run time of 2 min. A simplified sample cleanup procedure using methanol precipitation of serum proteins/lipids followed by evaporation and reconstitution in mobile phase was demonstrated. Gabapentin and buprenorphine were detected following positive ion electrospray ionization using multiple-reaction monitoring. The internal standard approach was used for quantitation with labeled gabapentin-D10 and buprenorphine-D4 serving as internal standards. Using organic reaction principals and stable isotope labels, collision-induced fragmentation mechanisms for both gabapentin and buprenorphine are proposed. The method was validated according to the FDA Guidance for Industry - Bioanalytical Method Validation.

RESULTS

Accuracy was demonstrated by error values ≤15% for buprenorphine and ≤6% for gabapentin. The inter-day precision was ≤4.88% and 15.59% for gabapentin and buprenorphine and the intra-day precision was ≤5.20% and 11.65% for gabapentin and buprenorphine. The lower limit of quantitation corresponded to 10 ng/mL for gabapentin and 1 ng/mL for buprenorphine in serum. Recoveries were 104 ± 2.55% and 85 ± 2.03% for gabapentin and buprenorphine, respectively.

CONCLUSIONS

Concentrations of gabapentin and buprenorphine were determined for five authentic human serum samples to further validate the utility of the method and applicable to therapeutic drug monitoring beyond its use as a drug screening assay. Furthermore, new mechanisms for the collision-induced dissociation of gabapentin and buprenorphine have been proposed.

α2δ-1-Bound N-Methyl-D-aspartate Receptors Mediate Morphine-induced Hyperalgesia and Analgesic Tolerance by Potentiating Glutamatergic Input in Rodents

BACKGROUND

Chronic use of μ-opioid receptor agonists paradoxically causes both hyperalgesia and the loss of analgesic efficacy. Opioid treatment increases presynaptic N-methyl-D-aspartate receptor activity to potentiate nociceptive input to spinal dorsal horn neurons. However, the mechanism responsible for this opioid-induced activation of presynaptic N-methyl-D-aspartate receptors remains unclear. α2δ-1, formerly known as a calcium channel subunit, interacts with N-methyl-D-aspartate receptors and is primarily expressed at presynaptic terminals. This study tested the hypothesis that α2δ-1-bound N-methyl-D-aspartate receptors contribute to presynaptic N-methyl-D-aspartate receptor hyperactivity associated with opioid-induced hyperalgesia and analgesic tolerance.

METHODS

Rats (5 mg/kg) and wild-type and α2δ-1-knockout mice (10 mg/kg) were treated intraperitoneally with morphine twice/day for 8 consecutive days, and nociceptive thresholds were examined. Presynaptic N-methyl-D-aspartate receptor activity was recorded in spinal cord slices. Coimmunoprecipitation was performed to examine protein-protein interactions.

RESULTS

Chronic morphine treatment in rats increased α2δ-1 protein amounts in the dorsal root ganglion and spinal cord. Chronic morphine exposure also increased the physical interaction between α2δ-1 and N-methyl-D-aspartate receptors by 1.5 ± 0.3 fold (means ± SD, P = 0.009, n = 6) and the prevalence of α2δ-1-bound N-methyl-D-aspartate receptors at spinal cord synapses. Inhibiting α2δ-1 with gabapentin or genetic knockout of α2δ-1 abolished the increase in presynaptic N-methyl-D-aspartate receptor activity in the spinal dorsal horn induced by morphine treatment. Furthermore, uncoupling the α2δ-1-N-methyl-D-aspartate receptor interaction with an α2δ-1 C terminus-interfering peptide fully reversed morphine-induced tonic activation of N-methyl-D-aspartate receptors at the central terminal of primary afferents. Finally, intraperitoneal injection of gabapentin or intrathecal injection of an α2δ-1 C terminus-interfering peptide or α2δ-1 genetic knockout abolished the mechanical and thermal hyperalgesia induced by chronic morphine exposure and largely preserved morphine's analgesic effect during 8 days of morphine treatment.

CONCLUSIONS

α2δ-1-Bound N-methyl-D-aspartate receptors contribute to opioid-induced hyperalgesia and tolerance by augmenting presynaptic N-methyl-D-aspartate receptor expression and activity at the spinal cord level.

Pain management after total knee arthroplasty: A prospective randomized study

INTRODUCTION

Total knee arthroplasty (TKA) is a common procedure for improving mobility and quality of life in patients with osteoarthritis. Postoperative pain control management after TKA is still a concern as it relates to patients satisfaction and functional recovery.Many anesthetic regimens and techniques have been explored to decrease postoperative pain and enhance the fast recovery after TKA. The aim of this study was to evaluate the best anesthetic treatment in pain control after TKA.

METHODS

51 patients were included in a randomized prospective study and distributed in three groups. The first group (CG) in which no analgesic protocol was implemented (control group). The second group (LIA group) received an intraoperative local infiltration anesthesia (LIA) (60 ml mixture of two ropivacaine 75mg/10 mL + adrenaline 100μg/10 mL + physiological solution). The third group (FNB group) had only a femoral nerve block (FNB). Continuous outcomes including visual analogue scale (VAS) at 5,24,48 h and at 1 week, morphine consumption and range of motion (ROM) at 1,2,7 days.

RESULTS

There was significant difference between all groups (p < 0,001) in terms of the VAS score: at 5h after surgery (4.55,2.15,1.82); at 24h (4.15,2.65,3.36); at 48h (3.85,2.45,2.73); at 1 week (2.95,1.80, 1.64), respectively for groups CG, LIA, FNB.ROM was better in LIA and FNB groups than CG: at 1 die after surgery (44°,50°,54°); at 3 dies (69°,70°,71°); at 7 dies (91°,98°,98°), respectively for groups CG, LIA, FNB (p < 0,001).

DISCUSSION

LIA and FNB groups both showed a significant reduction at VAS score, better range of motion and less morphine consumption than CG (control group). LIA group has obtained a constant pain control in the postoperative days; FNB group had a good pain control in the hours after surgery, with a decrease in efficacy in the following days.

CONCLUSION

Further studies are still needed in order to define LIA as the reference pain management in TKA.

Misuse and Mortality Related to Gabapentin and Pregabalin are Being Under-Estimated: A Two-Year Post-Mortem Population Study

Due to the rise in their misuse and associated mortality, the UK government is reclassifying gabapentin (GBP) and pregabalin (PGL) to Class C controlled drugs from April 2019. However, it is impossible to gauge the extent of their use with current post-mortem toxicological screening, where GBP and PGL are only screened for if they are mentioned in the case documents. This study determines the prevalence of GBP and PGL, the potential extent of their under-reporting and poly-drug use in a post-mortem population. Between 1 January 2016 and 31 December 2017, 3,750 deceased from Coroners’ cases in London and South East England underwent a routine drugs screen and a specific screen for GBP and PGL. The prevalence of both drugs was determined in the cohort and the subcategories of heroin users and non-heroin-users. The prevalence of both drugs was compared to tramadol (Class C drug). Case documents were reviewed to investigate the under-reporting of GBP and PGL and poly-drug use. Of 3,750 samples analyzed, 118 (3.1%) were positive for GBP, 229 (6.1%) for PGL and 120 (3.2%) were positive for tramadol. If routine analysis without additional screening of GBP and PGL had been performed in this cohort, GBP would have been under-reported by 57.6% (P < 0.0001) and PGL by 53.7% (P < 0.0001) in deaths. The most common drug group observed with GBP and PGL was non-heroin-related opioids at 60.2% and 64.6%, respectively. In total 354 deceased (9.4%) were heroin users. GBP was positive in 23 (6.5%) of these cases and PGL was positive in 69 (19.5%). The prevalence of PGL in heroin users (19.5%) was 4.1 times greater than in non-heroin users (4.7%) (P < 0.0001). GBP and PGL are being significantly under reported in fatalities. Both drugs are extensively used with opioids. The prevalence of PGL in heroin users is highly significant.

Cancer-Related Neuropathic Pain: Review and Selective Topics

Neuropathic pain is the result of neuroplastic and neuroinflammatory changes from trauma or diseases that damage the somatosensory system. Cancer-related neuropathic pain is caused by treatment, cancer, or paraneoplastic reactions to cancer. Approximately 30% of patients with cancer have neuropathic pain, mostly mixed nociceptive and neuropathic pain. History, physical examination, quantitative sensory testing, skin punch biopsies, and functional MRIs help to divide pain into phenotypes that may facilitate analgesic choices. Guidelines for treating cancer-related neuropathic pain are not consistent and are highly dependent on trials in patients without cancer. Combinations of analgesics are promising, whereas evidence for cannabinoids is meager.

The effect of pre-emptive gabapentin on anaesthetic and analgesic requirements in patients undergoing rhinoplasty: A prospective randomised study

Background and Aims:

Hypotensive anaesthesia is necessary in rhinoplasty for better visualisation of surgical field and reduction of surgery time. Gabapentin is a new generation anticonvulsant with anti-hyperalgesic and anti-nociceptive properties. We aimed to investigate the effect of pre-operative administration of oral gabapentin (1200 mg) on anaesthetic requirements and post-operative analgesic consumption and its role in hypotensive anaesthesia for rhinoplasty.

Methods:

Seventy adult patients undergoing rhinoplasty, were randomly allocated to two groups. Group I (G I) (n = 35) received gabapentin 1.2 g and Group II (G II) (n = 35) received oral placebo capsules 2 h before surgery. General anaesthesia was maintained with sevoflurane in oxygen-nitrous oxide to maintain bispectral index value between 40 and 60, and remifentanil infusion to keep mean arterial pressure (MAP) at 55–60 mmHg. End-tidal sevoflurane concentration, intra-operative remifentanil consumption and time to intended MAP were recorded. Visual analogue scale (VAS) scores, post-operative analgesic requirements and side effects for the first 24 h were recorded.

Results:

G I required significantly lower intra-operative remifentanil (G I = 0.8 ± 0.26 mg and G II = 1.7 ± 0.42 mg; P = 0.001) and end-tidal sevoflurane concentration, with reduced doses of post-operative tramadol and diclofenac sodium. Time to the intended MAP was significantly less in G I than G II (59.1 ± 12.3 vs. 73.6 ± 16.4, respectively, with P = 0.001).

Conclusion:

Pre-operative oral gabapentin significantly reduced intra-operative remifentanil and sevoflurane requirements during hypotensive anaesthesia along with decreased post-operative analgesic requirement.

The efficacy of combination treatment of gabapentin and electro-acupuncture on paclitaxel-induced neuropathic pain

Paclitaxel, a chemotherapeutic drug, induces severe peripheral neuropathy. Gabapentin (GBT) is a first line agent used to treat neuropathic pain, and its effect is mediated by spinal noradrenergic and muscarinic cholinergic receptors. Electro-acupuncture (EA) is used for treating various types of pain via its action through spinal opioidergic and noradrenergic receptors. Here, we investigated whether combined treatment of these two agents could exert a synergistic effect on paclitaxel-induced cold and mechanical allodynia, which were assessed by the acetone drop test and von Frey filament assay, respectively. Significant signs of allodynia were observed after four paclitaxel injections (a cumulative dose of 8 mg/kg, i.p.). GBT (3, 30, and 100 mg/kg, i.p.) or EA (ST36, Zusanli) alone produced dose-dependent anti-allodynic effects. The medium and highest doses of GBT (30 and 100 mg/kg) provided a strong analgesic effect, but they induced motor dysfunction in Rota-rod tests. On the contrary, the lowest dose of GBT (3 mg/kg) did not induce motor weakness, but it provided a brief analgesic effect. The combination of the lowest dose of GBT and EA resulted in a greater and longer effect, without inducing motor dysfunction. This effect on mechanical allodynia was blocked by spinal opioidergic (naloxone, 20 μg), or noradrenergic (idazoxan, 10 μg) receptor antagonist, whereas on cold allodynia, only opioidergic receptor antagonist blocked the effect. In conclusion, the combination of the lowest dose of GBT and EA has a robust and enduring analgesic action against paclitaxel-induced neuropathic pain, and it should be considered as an alternative treatment method.

Gabapentin, opioids, and the risk of opioid-related death: A population-based nested case-control study

BACKGROUND

Prescription opioid use is highly associated with risk of opioid-related death, with 1 of every 550 chronic opioid users dying within approximately 2.5 years of their first opioid prescription. Although gabapentin is widely perceived as safe, drug-induced respiratory depression has been described when gabapentin is used alone or in combination with other medications. Because gabapentin and opioids are both commonly prescribed for pain, the likelihood of co-prescription is high. However, no published studies have examined whether concomitant gabapentin therapy is associated with an increased risk of accidental opioid-related death in patients receiving opioids. The objective of this study was to investigate whether co-prescription of opioids and gabapentin is associated with an increased risk of accidental opioid-related mortality.

METHODS AND FINDINGS

We conducted a population-based nested case-control study among opioid users who were residents of Ontario, Canada, between August 1, 1997, and December 31, 2013, using administrative databases. Cases, defined as opioid users who died of an opioid-related cause, were matched with up to 4 controls who also used opioids on age, sex, year of index date, history of chronic kidney disease, and a disease risk index. After matching, we included 1,256 cases and 4,619 controls. The primary exposure was concomitant gabapentin use in the 120 days preceding the index date. A secondary analysis characterized gabapentin dose as low (<900 mg daily), moderate (900 to 1,799 mg daily), or high (≥1,800 mg daily). A sensitivity analysis examined the effect of concomitant nonsteroidal anti-inflammatory drug (NSAID) use in the preceding 120 days. Overall, 12.3% of cases (155 of 1,256) and 6.8% of controls (313 of 4,619) were prescribed gabapentin in the prior 120 days. After multivariable adjustment, co-prescription of opioids and gabapentin was associated with a significantly increased odds of opioid-related death (odds ratio [OR] 1.99, 95% CI 1.61 to 2.47, p < 0.001; adjusted OR [aOR] 1.49, 95% CI 1.18 to 1.88, p < 0.001) compared to opioid prescription alone. In the dose-response analysis, moderate-dose (OR 2.05, 95% CI 1.46 to 2.87, p < 0.001; aOR 1.56, 95% CI 1.06 to 2.28, p = 0.024) and high-dose (OR 2.20, 95% CI 1.58 to 3.08, p < 0.001; aOR 1.58, 95% CI 1.09 to 2.27, p = 0.015) gabapentin use was associated with a nearly 60% increase in the odds of opioid-related death relative to no concomitant gabapentin use. As expected, we found no significant association between co-prescription of opioids and NSAIDs and opioid-related death (OR 1.11, 95% CI 0.98 to 1.27, p = 0.113; aOR 1.14, 95% CI 0.98 to 1.32, p = 0.083). In an exploratory analysis of patients at risk of combined opioid and gabapentin use, we found that 46.0% (45,173 of 98,288) of gabapentin users in calendar year 2013 received at least 1 concomitant prescription for an opioid. This study was limited to individuals eligible for public drug coverage in Ontario, we were only able to identify prescriptions reimbursed by the government and dispensed from retail pharmacies, and information on indication for gabapentin use was not available. Furthermore, as with all observational studies, confounding due to unmeasured variables is a potential source of bias.

CONCLUSIONS

In this study we found that among patients receiving prescription opioids, concomitant treatment with gabapentin was associated with a substantial increase in the risk of opioid-related death. Clinicians should consider carefully whether to continue prescribing this combination of products and, when the combination is deemed necessary, should closely monitor their patients and adjust opioid dose accordingly. Future research should investigate whether a similar interaction exists between pregabalin and opioids.

The research on long-term clinical effects and patients' satisfaction of gabapentin combined with oxycontin in treatment of severe cancer pain

Gabapentin has been used as an adjuvant for treatment of cancer pain. Previous studies showed that opioids combined with gabapentin for management of cancer pain reduced the dosage of opioids.The objective of this study was to explore the clinical effect and patients' satisfaction of oxycontin combined with gabapentin in treatment of severe cancer pain. After titration of morphine, 60 severe cancer patients with visual analog score (VAS) more than 7 were randomly divided into trial group (n = 30) and control group (n = 30). The control group was administered oxycontin and placebo, and the trial group was given oxycontin and gabapentin. VAS score was recorded pre- and post-treatment; while daily dose of oxycontin, daily cost of pain relief and life quality score were observed 1 week, 1 month, 2 months, 3 months, and 6 months post-treatment. We found that daily dose of oxycontin 1 month post was comparable between the 2 groups (P > 0.05). Three months post, compared with control group (58.0 ± 15.2 mg), average daily dose of oxycontin was significant lower in trial group (33.4 ± 11 mg) (P < 0.001). Average daily cost of pain relief in trail group (34.5 ± 10.2 RMB) was less than the control group (52.4 ± 13.7 RMB) (P < 0.001). Life quality score increased in all of the patients in both group post-treatment (P < 0.05); while life quality score in trail group was greater than in control group 3 months (46.8 ± 4.5 vs 43.5 ± 4.6, P = 0.007) and 6 months (46.5 ± 4.8 vs 41.4 ± 4.3, P < 0.001) post-treatment. The incidence of drowsiness and dizziness was comparable between the 2 groups (P > 0.05), while the incidence of nausea and vomiting (P = 0.038), and constipation (P < 0.001) was higher in the control group.We concluded that oxycontin combined with gabapentin used in severe cancer pain management can control pain effectively, decreased the dose of oxycontin and the cost of cancer pain relief, and reduced the incidence of nausea and vomiting, and constipation, increased the life quality.

Alpha2delta ligands, gabapentin, pregabalin and mirogabalin: a review of their clinical pharmacology and therapeutic use

INTRODUCTION

The first two alpha₂delta ligands - gabapentin (GBP) and pregabalin (PGB) - were initially synthesized as antiepileptics; however, they were later also found to be useful for the treatment of additional conditions. Areas covered: Relevant publications describing potential underlying mechanisms, clinical pharmacokinetics/pharmacokinetics, and clinical efficacy and safety of these drugs in various disease conditions were searched in PubMed and Scopus and included in this review. Expert commentary: GBP and PGB are effective for the treatment neuropathic pain, fibromyalgia and epilepsy; in addition, they may be useful for the reduction of postoperative pain. PGB is also effective for the treatment of generalized anxiety disorder and GBP for the treatment of restless legs syndrome. GBP may be considered a treatment option for pain associated with Guillain-Barré Syndrome and phantom limb and for the management of uremic pruritus. Mirogabalin (MGB), recently developed, is being investigated for the treatment of peripheral neuropathic pain and fibromyalgia, showing promising results in patients with diabetic peripheral neuropathy. Their most frequent adverse reactions are of neuropsychiatric nature and include fatigue, dizziness, sedation, somnolence, and ataxia; peripheral edema and weight gain are also frequently described. Pharmacokinetic interactions are scarce; however, pharmacodynamic interactions have been described in association with drugs with CNS-depressant effects.

Population Pharmacokinetic Modelling of Morphine, Gabapentin and their Combination in the Rat

PURPOSE

The combination of morphine and gabapentin seems promising for the treatment of postoperative and neuropathic pain. Despite the well characterised pharmacodynamic interaction, little is known about possible pharmacokinetic interactions. The aim of this study was to evaluate whether co-administration of the two drugs leads to modifications of their pharmacokinetic profiles.

METHODS

The pharmacokinetics of morphine, morphine-3-glucuronide and gabapentin were characterised in rats following subcutaneous injections of morphine, gabapentin or their combination. Non-linear mixed effects modelling was applied to describe the pharmacokinetics of the compounds and possible interactions.

RESULTS

The plasma-concentration-time profiles of morphine and gabapentin were best described using a three- and a one-compartment disposition model respectively. Dose dependencies were found for morphine absorption rate and gabapentin bioavailability. Enterohepatic circulation of morphine-3-glucuronide was modelled using an oscillatory model. The combination did not lead to pharmacokinetic interactions for morphine or gabapentin but resulted in an estimated ~33% diminished morphine-3-glucuronide formation.

CONCLUSIONS

The finding of a lack of pharmacokinetic interaction strengthens the notion that the combination of the two drugs leads to better efficacy in pain treatment due to interaction at the pharmacodynamic level. The interaction found between gabapentin and morphine-3-glucuronide, the latter being inactive, might not have any clinical relevance.

Comparison of Local Infiltration Analgesia With Femoral Nerve Block for Total Knee Arthroplasty: A Prospective, Randomized Clinical Trial

BACKGROUND

Total knee arthroplasty (TKA) is usually associated with severe postoperative pain, which can prevent rehabilitation of patients' knee function and influence the satisfaction of surgery. Local infiltration analgesia (LIA) as a new method to managing postoperative pain has been applied in clinical practice recently. However, the safety and efficacy of LIA compared with femoral nerve block (FNB) in postoperative pain management of TKA still remains controversial. Thus, we conducted an original clinical trial to compare LIA and FNB.

METHOD

One hundred fifty-seven patients undergoing TKA were enrolled in a randomized, double-blind, single-center study. The patients received either FNB (group A) or periarticular infiltration of local anesthetic (group B). The morphine consumption used in patient-controlled analgesia after surgery, postoperative Visual Analogue Scale (VAS), Knee Society Score, and range of motion before and after surgery in both groups were analyzed, as well as the adverse effects.

RESULTS

Group A consisted 78 patients, and group B contained 79 patients. The patients' characteristics including age and body mass index had no significant difference (P > .05). Morphine consumption, VAS at rest, range of motion, and Knee Society Score were similar between the 2 groups. Our study showed group B, the local anesthetic group had less VAS with movement on postoperative day 1 (P = .01) than that of group A, which means a better pain control. Because of the study design, the surgery time showed no significant difference. Eighteen patients in group A and 21 patients in group B experienced mild-to-medium nausea or vomiting. One patient in group B had dizziness and one patient in group A suffered a neuropraxic injury to the femoral nerve. No urinary retention case was seen during inpatient days. There were no significant differences between the 2 groups about side effects.

CONCLUSIONS

Our research showed that no significant differences were observed between the 2 treatment groups. LIA could provide a similar analgesic effect to FNBs with a low incidence of complications.

Randomized trial of standard pain control with or without gabapentin for pain related to radiation-induced mucositis in head and neck cancer

OBJECTIVE

Radiation-induced mucositis (RIM) in chemoradiotherapy (CRT) for head and neck cancer (HNC) causes severe pain and worsens CRT compliance, QOL and outcome. Following retrospective reports, we conducted a randomized trial of the safety and efficacy of gabapentin for RIM-associated pain during CRT.

METHODS

HNC patients (pts) receiving CRT were randomized to standard pain control (SPC) with acetaminophen and opioids, or SPC plus gabapentin (SPC+G). Gabapentin was maintained at 900mg/day for 4 weeks after CRT. Primary endpoint was maximum visual analogue scale (VAS) score during CRT, and secondary endpoints were total opioid dose, changes in QOL (EORTC QLQ-C30 and QLQ-HN 35) from baseline to 4 weeks after CRT, and adverse events.

RESULTS

Twenty-two eligible Stage III or IV pts were randomly assigned to SPC or SPC+G (n=11 each). Twelve were treated in a locally advanced setting and 10 in a postoperative setting. Median maximum VAS scores, median total dose of opioids at maximum VAS and total dose of opioids at 4 weeks after CRT tended to be higher in the SPC+G arm (47 in SPC vs. 74 in SPC+G, p=0.517; 215mg vs. 745.3mg, p=0.880; and 1260mg vs. 1537.5mg, p=0.9438, respectively), without significance. QOL analysis showed significantly worse scores in the SPC+G arm for weight gain (p=0.005). Adverse events related to gabapentin were manageable.

CONCLUSIONS

This pilot study is the first prospective randomized trial of gabapentin for RIM-related pain. Gabapentin had no apparent beneficial effect. Further research into agents for RIM-related pain is warranted.

Pregabalin Has Analgesic, Ventilatory, and Cognitive Effects in Combination with Remifentanil

Background

Pregabalin is widely used perioperatively. The authors explored the effects of pregabalin, remifentanil, and their combination on experimental pain, ventilatory, and cognitive function.

Methods

In a randomized, double-blinded crossover study, 12 volunteers received (1) pregabalin + placebo, (2) placebo + remifentanil, (3) pregabalin + remifentanil, and (4) placebo + placebo. Pregabalin 150 mg/placebo was administered twice orally. After baseline, remifentanil/placebo was given as effect-site target-controlled infusion (TCI): 0.6, 1.2, and 2.4 ng/ml. Pain during cold pressor test was scored on visual analog scale (0 to 100 mm). Ventilation was measured by spirometry and cognition tested with Color-Word Interference and Rapid Information Processing tests.

Results

Pain intensity after placebo was (mean) 72 mm (95% CI, 62 to 83). Pregabalin reduced pain score by −10 mm (−14 to −7, P &lt; 0.001). Remifentanil had dose-dependent analgesic effect, reducing pain score by −47 mm (−54 to −39, P &lt; 0.001) on highest TCI level, whereas pregabalin + remifentanil exerted additive effect, reducing pain score by −57 mm (−64 to −50, P &lt; 0.001). Respiratory depression was potentiated by adding pregabalin to remifentanil; end-tidal carbon dioxide was 39.3 mmHg (37.2 to 41.3) with placebo, increased 1.8 mmHg (−0.9 to 4.6, P = 0.4) with pregabalin, 10.1 mmHg (4.9 to 15.4, P &lt; 0.001) with remifentanil, and 16.4 mmHg (11.3 to 21.5, P &lt; 0.001) with pregabalin + remifentanil on highest TCI level. The combination pregabalin + remifentanil, but not either drug alone, adversely affected all cognitive tests.

Conclusions

The combination of pregabalin and remifentanil had additive analgesic effects, pregabalin potentiated remifentanil ventilatory depression, and the combination adversely affected cognition. These results question the clinical benefit of the combination compared with higher doses of opioids.

Opioid analgesics increase incidence of somnolence and dizziness as adverse effects of pregabalin: a retrospective study

BACKGROUND

Pregabalin, a gabapentinoid, is an adjuvant analgesic for treatment of neuropathic pain, but it has serious adverse effects such as somnolence and dizziness, particularly in elderly patients. Although decreased renal function is considered to the contributing factor for high frequency of these adverse effects in elder patients, only a few systematic clinical investigations, especially for hospitalized patients, have been performed on factors that might affect the incidence of its adverse effects. In this study, we performed a retrospective study on the effect of concomitant drugs on induction of somnolence and dizziness as adverse effects of pregabalin in hospitalized patients.

METHODS

The subjects were all pregabalin-administered patients in Shiga University of Medical Science Hospital from September 2010 to September 2012, and the subject number was 195. Multivariate logistic regression analysis was performed to determine predictors of the adverse effects, creatinine clearance, duration of pregabalin therapy, initial and maintenance doses of pregabalin, and concomitant drugs, including hypoglycemic drugs, anti-hypertensive ones, non-steroidal anti-inflammatory ones, opioids and central nervous system depressants, being used as independent variables.

RESULTS

The median initial doses of pregabalin in each renal function group were the same with the case of the defined dose. Although renal function is a well-known factor for prediction of development of adverse effects of pregabalin, we did not detect significant contribution of it. Alternatively, it was demonstrated that concomitant administration of opioids was the significant factor of the incidence of somnolence and dizziness. The first onset date of the adverse effects was frequently detected in the early days of the pregabalin therapy.

CONCLUSIONS

The fine tuning of pregabalin dosage schedule based on the renal function appeared to be critical for prevention of development of its adverse effects. Adverse effects tended to develop in the initial phase of pregabalin therapy. Concomitant administration of opioids with pregabalin has the potential to increase the incidence of adverse effects, and thus much more careful attention has to be paid especially in those situations.

A Survey on the Effect of Oral Gabapentin on Hemodynamic Changes During Direct Laryngoscopy and Tracheal Intubation and Intraoperative Bleeding in Patients Undergoing Septorhinoplasty

BACKGROUND

In patients undergoing septorhinoplasty, control of bleeding and hemodynamic variables is of great importance and laryngoscopy and tracheal intubation could be followed by a specific and transient increase in systemic blood pressure and heart rate.

OBJECTIVES

This study aimed to examine the effects of oral gabapentin on hemodynamic changes, during direct laryngoscopy, and the amount of bleeding in the patients undergoing septorhinoplasty.

PATIENTS AND METHODS

In a double-blind clinical trial, 103 patients (American society of anesthesiologists class I, II) aged 18 - 45 years old, who were septorhinoplasty candidates, were randomly assigned into two groups, a 900 mg gabapentin group and placebo, in Amir-Al-Momenin academic hospital. The drug was prescribed to the patients orally, 2 hours before the operation. Anesthetic technique was similar for all the patients. Heart rate (HR), systolic (SBP) and diastolic blood pressures (DBP), mean arterial blood pressure (MAP), oxygen saturation percentage of arterial blood (SaO2), before induction of anesthesia, 3, 5, 10, and 15 minutes after the intubation and tracheal extubation, and the amount of bleeding during operation were measured. Statistical analysis was performed with the SPSS (v. 16) software.

RESULTS

Variations in the HR, DBP and SaO2, in the specified time intervals, did not show any statistically significant difference, although variations in SBP were statistically significant (higher in gabapentin group). Regarding the average amount of bleeding volume, although there was a lower amount of bleeding in the gabapentin group, the difference was not statistically significant. Also, regarding the pain, there was no significant difference between the two groups in terms of visual analog scale (VAS) average and the received analgesic.

CONCLUSIONS

The present study showed that premedication with 900 mg gabapentin did not affect the hemodynamic changes induced by laryngoscopy and the amount of bleeding. However, the decreased amount of bleeding was observed in the gabapentin group.

A retrospective study to identify risk factors for somnolence and dizziness in patients treated with pregabalin

Background

Pregabalin is a therapeutic drug for neuropathic pain that is associated with somnolence and dizziness. These adverse events are often experienced shortly after initiating pregabalin, and may lead to treatment discontinuation. The purpose of this study was to explore factors that influence the incidence of somnolence and dizziness induced by pregabalin, and to identify patients at higher risk of adverse events.

Methods

A retrospective analysis was conducted of patient characteristics (age, gender, renal function, initial daily dose of pregabalin, co-administration of strong opioids and hypnotics) and the incidence of somnolence and dizziness during the first week of pregabalin treatment. An electronic chart was used to collect data from 204 inpatients prescribed pregabalin at Nagoya University Hospital from June 2011 to November 2012.

Results

Among 36 patients who regularly received strong opioids, 18 (50.0 %) reported somnolence or dizziness during the first week of pregabalin treatment. The remaining 168 patients did not regularly receive strong opioids, and 25 (14.9 %) had an adverse event. In multivariate analysis, age (≧65 years, adjusted odds ratio: 2.507, 95 % CI: 1.164-5.397, p = 0.019) and regular co-administration of strong opioids (adjusted odds ratio: 5.507, 95 % CI: 2.460-12.328, p < 0.001) correlated with somnolence or dizziness.

Conclusions

These data suggest that age (≧65 years) and co-administration of strong opioids are risk factors for somnolence or dizziness during pregabalin treatment for neuropathic pain. More careful dose titration is recommended for elderly patients and those receiving concomitant strong opioids.

Attenuation of the haemodynamic responses to tracheal intubation with gabapentin, fentanyl and a combination of both: A randomised controlled trial

BACKGROUND AND AIMS

We conducted a prospective, randomised, double-blind, controlled clinical trial to examine (1) whether a single preoperative dose of 800 mg gabapentin would be as effective as 2 μg/kg of intravenous (IV) fentanyl in blunting the haemodynamic response to tracheal intubation and (2) whether a combination of both would be more effective in this regard.

METHODS

Seventy-five patients (American Society of Anaesthesiologists physical status I), aged 20-50 years were allocated into one of three groups: 2 μg/kg IV fentanyl, 800 mg oral gabapentin or a combination of both. Gabapentin was administered 2 h and fentanyl 5 min before induction of anaesthesia, which was achieved with 5 mg/kg thiopentone, and tracheal intubation facilitated with 0.1 mg/kg vecuronium. Laryngoscopy lasting a maximum of 30 s was attempted 3 min after administration of the induction agents. Serial values of mean arterial pressure (MAP) and heart rate (HR) were compared among the three groups and with the respective preinduction measurements.

RESULTS

Patients receiving gabapentin 800 mg alone showed remarkable increases in HR and MAP in response to tracheal intubation (P < 0.05). The increases were similar for the other two regimens. These haemodynamic changes were lesser in patients receiving fentanyl and the combination of gabapentin and fentanyl.

CONCLUSION

Oral gabapentin does not produce significant reduction in laryngoscopy and tracheal intubation induced sympathetic responses as compared to IV fentanyl or the combination of gabapentin and fentanyl.

Gabapentin enacarbil and morphine administered in combination versus alone: a double-blind, randomized, pharmacokinetic, and tolerability comparison

PURPOSE

Coadministration of morphine with oral gabapentin has been shown to increase plasma gabapentin concentrations. This study evaluated whether there was any interaction between gabapentin enacarbil (GEn), which is a prodrug of gabapentin, and morphine in terms of pharmacokinetics, pharmacodynamics, safety, and tolerability.

METHODS

This randomized, double-blind, 3-treatment crossover study included nonelderly, healthy male subjects. The study subjects received (in random order and with a minimum 7-day washout between treatments) the following: morphine placebo + GEn 600 mg; morphine 60 mg + GEn 600 mg; and morphine 60 mg + GEn placebo. Morphine/morphine placebo was administered in fasted conditions, and GEn/GEn placebo was administered 2 hours later with food. The primary end points were AUC and C(max) for gabapentin, morphine, and morphine-6-glucuronide. Pharmacodynamic measures were limited to subject assessment of somnolence, dizziness, and nausea conducted by using a visual analog scale (VAS). Safety monitoring included adverse event reporting, clinical laboratory tests, vital signs, pulse oximetry, and 12-lead ECGs.

FINDINGS

Of the 18 enrolled subjects (mean age, 36 years), 15 (83%) completed the study. Sixteen received GEn, 15 received morphine, and 18 received the combination. Compared with the single treatments, the 90% CIs for the ratio of the geometric means for both AUC and C(max) were all within 0.8 to 1.25, the accepted range for bioequivalence. Ratios of geometric mean (90% CIs) values were as follows: gabapentin, AUC of 1.10 (1.035-1.162) and C(max) of 1.02 (0.920-1.126); morphine, AUC of 1.06 (1.014-1.098) and C(max) of 1.05 (0.967-1.134); and morphine-6-glucuronide, AUC of 0.992 (0.929-1.058) and C(max) of 0.953 (0.855-1.062). Mean changes from predose VAS scores were generally small and suggested a slight increase in dizziness after GEn and slight increases in dizziness, somnolence, and nausea after morphine. Trends were noted suggesting slightly greater score changes from predose with the combination treatment than with either drug given alone for somnolence and dizziness. Adverse events were generally mild; there were no serious adverse events or subject withdrawals due to adverse events. Headache and nausea were among the most commonly reported events for the combination and morphine treatments (headache, 27% and 28%; nausea, 13% and 11%, respectively). There were fewer adverse events with GEn alone than with either of the combination regimens.

IMPLICATIONS

No significant pharmacokinetic interaction between the 2 drugs was seen in this study. The VAS data suggest that the potential exists for increased adverse effects when GEn and morphine are coadministered. ClinicalTrials.gov identifier: NCT01476124.