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Neuropathic pain is caused by a lesion or disease of the somatosensory system, including peripheral fibres (Aβ, Aδ and C fibres) and central neurons, and affects 7–10% of the general population. Multiple causes of neuropathic pain have been described and its incidence is likely to increase owing to the ageing global population, increased incidence of diabetes mellitus and improved survival from cancer after chemotherapy. Indeed, imbalances between excitatory and inhibitory somatosensory signalling, alterations in ion channels and variability in the way that pain messages are modulated in the central nervous system all have been implicated in neuropathic pain. The burden of chronic neuropathic pain seems to be related to the complexity of neuropathic symptoms, poor outcomes and difficult treatment decisions. Importantly, quality of life is impaired in patients with neuropathic pain owing to increased drug prescriptions and visits to health care providers, as well as the morbidity from the pain itself and the inciting disease. Despite challenges, progress in the understanding of the pathophysiology of neuropathic pain is spurring the development of new diagnostic procedures and personalized interventions, which emphasize the need for a multidisciplinary approach to the management of neuropathic pain. Neuropathic pain is caused by a lesion or disease of the somatosensory system (including peripheral and central neurons). Here, the authors present the current descriptions of the presentation, causes, diagnosis and treatment of neuropathic pain with a focus on peripheral neuropathic pain, which has a greater knowledge base than central neuropathic pain.

Refractory chronic cough causes substantial symptoms and quality-of-life impairment. Similarities between central reflex sensitisation in refractory chronic cough and neuropathic pain suggest that neuromodulators such as gabapentin might be effective for refractory chronic cough. We established the efficacy of gabapentin in patients with refractory chronic cough. This randomised, double-blind, placebo-controlled trial was undertaken at an outpatient clinic in Australia. Adults with refractory chronic cough (>8 weeks' duration) without active respiratory disease or infection were randomly assigned to receive gabapentin (maximum tolerable daily dose of 1800 mg) or matching placebo for 10 weeks. Block randomisation was done with randomisation generator software, stratified by sex. Patients and investigators were masked to assigned treatment. The primary endpoint was change in cough-specific quality of life (Leicester cough questionnaire [LCQ] score) from baseline to 8 weeks of treatment, analysed by intention to treat. This study is registered with the Australian New Zealand Clinical Trials Registry, number ACTRN12608000248369. 62 patients were randomly assigned to gabepentin (n=32) or placebo (n=30) and ten patients withdrew before the study end. Gabapentin significantly improved cough-specific quality of life compared with placebo (between-group difference in LCQ score during treatment period 1·80, 95% CI 0·56–3·04; p=0·004; number needed to treat of 3·58). Side-effects occurred in ten patients (31%) given gabapentin (the most common being nausea and fatigue) and three (10%) given placebo. The treatment of refractory chronic cough with gabapentin is both effective and well tolerated. These positive effects suggest that central reflex sensitisation is a relevant mechanism in refractory chronic cough. National Health and Medical Research Council of Australia and Hunter Medical Research Institute, Newcastle, Australia.

Recent guidelines from the CDC recommend gabapentinoids as first-line agents for neuropathic pain. But some clinicians may be prescribing these medications excessively for various types of acute, subacute, and chronic noncancer pain in an attempt to avoid opioids.

Uremic pruritus or chronic kidney disease-associated pruritus (CKD-aP) remains a frequent and compromising symptom in patients with advanced or end-stage renal disease, strongly reducing the patient’s quality of life. More than 40% of patients undergoing hemodialysis suffer from chronic pruritus; half of them complain about generalized pruritus. The pathogenesis of CKD-aP remains obscure. Parathormone and histamine as well as calcium and magnesium salts have been suspected as pathogenetic factors. Newer hypotheses are focusing on opioid-receptor derangements and microinflammation as possible causes of CKD-aP, although until now this could not be proven. Pruritus may be extremely difficult to control, as therapeutic options are limited. The most consequential approaches to treatment are: topical treatment with or without anti-inflammatory compounds or systemic treatment with (a) gabapentin, (b) μ-opioid receptor antagonists and κ-agonists, (c) drugs with an anti-inflammatory action, (d) phototherapy, or (e) acupuncture. A stepwise approach is suggested starting with emollients and gabapentin or phototherapy as first-line treatments. In refractory cases, more experimental options as μ-opioid-receptor—antagonists (i.e., naltrexone) or κ-opioid-receptor agonist (nalfurafine) may be chosen. In desperate cases, patients suitable for transplantation might be set on ‘high urgency’-status, as successful kidney transplantation will relieve patients from CKD-aP.

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. 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. 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.

Gabapentinoids (e.g. pregabalin and gabapentin) are widely used in neurology, psychiatry and primary healthcare but are increasingly being reported as possessing a potential for misuse. In fact, increasing levels of both prescriptions and related fatalities, together with an anecdotally growing black market, have been reported from a range of countries. This article reviews the current evidence base of this potential, in an attempt to answer the question of whether there is cause for concern about these drugs. Potent binding of pregabalin/gabapentin at the calcium channel results in a reduction in the release of excitatory molecules. Furthermore, gabapentinoids are thought to possess GABA-mimetic properties whilst possibly presenting with direct/indirect effects on the dopaminergic ‘reward’ system. Overall, pregabalin is characterized by higher potency, quicker absorption rates and greater bioavailability levels than gabapentin. Although at therapeutic dosages gabapentinoids may present with low addictive liability levels, misusers’ perceptions for these molecules to constitute a valid substitute for most common illicit drugs may be a reason of concern. Gabapentinoid experimenters are profiled here as individuals with a history of recreational polydrug misuse, who self-administer with dosages clearly in excess (e.g. up to 3–20 times) of those that are clinically advisable. Physicians considering prescribing gabapentinoids for neurological/psychiatric disorders should carefully evaluate a possible previous history of drug abuse, whilst being able to promptly identify signs of pregabalin/gabapentin misuse and provide possible assistance in tapering off the medication.

The Neuropathic Pain Special Interest Group of the International Association for the Study of Pain recently sponsored the development of evidence-based guidelines for the pharmacological treatment of neuropathic pain. Tricyclic antidepressants, dual reuptake inhibitors of serotonin and norepinephrine, calcium channel α 2-δ ligands (ie, gabapentin and pregabalin), and topical lidocaine were recommended as first-line treatment options on the basis of the results of randomized clinical trials. Opioid analgesics and tramadol were recommended as second-line treatments that can be considered for first-line use in certain clinical circumstances. Results of several recent clinical trials have become available since the development of these guidelines. These studies have examined botulinum toxin, high-concentration capsaicin patch, lacosamide, selective serotonin reuptake inhibitors, and combination therapies in various neuropathic pain conditions. The increasing number of negative clinical trials of pharmacological treatments for neuropathic pain and ambiguities in the interpretation of these negative trials must also be considered in developing treatment guidelines. The objectives of the current article are to review the Neuropathic Pain Special Interest Group guidelines for the pharmacological management of neuropathic pain and to provide a brief overview of these recent studies.

EXECUTIVE SUMMARY This American Association of Clinical Endocrinologists (AACE)/American College of Endocrinology (ACE) Position Statement is designed to update the previous menopause clinical practice guidelines published in 2011 but does not replace them. The current document reviews new clinical trials published since then as well as new information regarding possible risks and benefits of therapies available for the treatment of menopausal symptoms. AACE reinforces the recommendations made in its previous guidelines and provides additional recommendations on the basis of new data. A summary regarding this position statement is listed below: New information available from randomized clinical trials and epidemiologic studies reported after 2011 was critically reviewed. No previous recommendations from the 2011 menopause clinical practice guidelines have been reversed or changed. Newer information enhances AACE's guidance for the use of hormone therapy in different subsets of women. Newer information helps to support the use of various types of estrogens, selective estrogen-receptor modulators (SERMs), and progesterone, as well as the route of delivery. Newer information supports the previous recommendation against the use of bioidentical hormones. The use of nonhormonal therapies for the symptomatic relief of menopausal symptoms is supported. Newer information enhances AACE's guidance for the use of hormone therapy in different subsets of women. Newer information helps to support the use of various types of estrogens, SERMs, and progesterone, as well as the route of delivery. Newer information supports the previous recommendation against the use of bioidentical hormones. The use of nonhormonal therapies for the symptomatic relief of menopausal symptoms is supported. New recommendations in this position statement include: 1. the use of menopausal hormone therapy in symptomatic postmenopausal women should be based on consideration of all risk factors for cardiovascular disease, age, and time from menopause. 2. the use of transdermal as compared with oral estrogen preparations may be considered less likely to produce thrombotic risk and perhaps the risk of stroke and coronary artery disease. 3. when the use of progesterone is necessary, micronized progesterone is considered the safer alternative. 4. in symptomatic menopausal women who are at significant risk from the use of hormone replacement therapy, the use of selective serotonin re-uptake inhibitors and possibly other nonhormonal agents may offer significant symptom relief. 5. AACE does not recommend use of bioidentical hormone therapy. 6. AACE fully supports the recommendations of the Comité de l'Évolution des Pratiques en Oncologie regarding the management of menopause in women with breast cancer. 7. HRT is not recommended for the prevention of diabetes. 8. In women with previously diagnosed diabetes, the use of HRT should be individualized, taking in to account age, metabolic, and cardiovascular risk factors. AACE = American Association of Clinical Endocrinologists; ACE = American College of Endocrinology; BMI = body mass index; CAC = coronary artery calcification; CEE = conjugated equine estrogen; CEPO = Comité de l'Évolution des Pratiques en Oncologie; CAD = coronary artery disease; CIMT = carotid intima media thickness; CVD = cardiovascular disease; FDA = Food and Drug Administration; HDL = high-density lipoprotein; HRT = hormone replacement therapy; HT = hypertension; KEEPS = Kronos Early Estrogen Prevention Study; LDL = low-density lipoprotein; MBS = metabolic syndrome; MPA = medroxyprogesterone acetate; RR = relative risk; SERM = selective estrogen-receptor modulator; SSRI = selective serotonin re-uptake inhibitor; VTE = venous thrombo-embolism; WHI = Women's Health Initiative.

Drugs for neuropathic pain have incomplete efficacy and dose-limiting side-effects when given as monotherapy. We assessed the efficacy and tolerability of combined nortriptyline and gabapentin compared with each drug given alone. In this double-blind, double-dummy, crossover trial, patients with diabetic polyneuropathy or postherpetic neuralgia, and who had a daily pain score of at least 4 (scale 0–10), were enrolled and treated at one study site in Canada between Nov 5, 2004, and Dec 13, 2007. 56 patients were randomised in a 1:1:1 ratio with a balanced Latin square design to receive one of three sequences of daily oral gabapentin, nortriptyline, and their combination. In sequence, a different drug was given to each randomised group in three treatment periods. During each 6-week treatment period, drug doses were titrated towards maximum tolerated dose. The primary outcome was mean daily pain at maximum tolerated dose. Analysis was by intention to treat. This trial is registered, number ISRCTN73178636. 45 patients completed all three treatment periods; 47 patients completed at least two treatment periods and were analysed for the primary outcome. Mean daily pain (0–10; numerical rating scale) was 5·4 (95% CI 5·0 to 5·8) at baseline, and at maximum tolerated dose, pain was 3·2 (2·5 to 3·8) for gabapentin, 2·9 (2·4 to 3·4) for nortriptyline, and 2·3 (1·8 to 2·8) for combination treatment. Pain with combination treatment was significantly lower than with gabapentin (−0·9, 95% CI −1·4 to −0·3, p=0·001) or nortriptyline alone (−0·6, 95% CI −1·1 to −0·1, p=0·02). At maximum tolerated dose, the most common adverse event was dry mouth, which was significantly less frequent in patients on gabapentin than on nortriptyline (p<0·0001) or combination treatment (p<0·0001). No serious adverse events were recorded for any patients during the trial. Combined gabapentin and nortriptyline seems to be more efficacious than either drug given alone for neuropathic pain, therefore we recommend use of this combination in patients who show a partial response to either drug given alone and seek additional pain relief. Future trials should compare other combinations to their respective monotherapies for treatment of such pain. Canadian Institutes of Health Research.

In responding to the opioid crisis, the FDA needs to recognize shifting trends in the addiction landscape. Taking a systematic approach to monitoring such trends should allow the agency to intervene promptly and appropriately to protect the public from associated risks.