Effect of prophylactic 5-HT3 receptor antagonists on pruritus induced by neuraxial opioids: a quantitative systematic review

Mechanisms and treatment of opioid-induced pruritus: Peripheral and central pathways

BACKGROUND AND OBJECTIVE

Pruritus (also known as itch) is defined as an unpleasant and irritating sensation of the skin that provokes an urge to scratch or rub. It is well known that opioid administration can cause pruritus, which is paradoxical as itch and pain share overlapping sensory pathways. Because opioids inhibit pain but can cause itching. Significant progress has been made to improve our understanding of the fundamental neurobiology of itch; however, much remains unknown about the mechanisms of opioid-induced pruritus. The prevention and treatment of opioid-induced pruritus remains a challenge in the field of pain management. The objective of this narrative review is to present and discuss the current body of literature and summarize the current understanding of the mechanisms underlying opioid-induced pruritus, and its relationship to analgesia, and possible treatment options.

RESULTS

The incidence of opioid-induced pruritus differs with different opioids and routes of administration, and the various mechanisms can be broadly divided into peripheral and central. Especially central mechanisms are intricate, even at the level of the spinal dorsal horn. There is evidence that opioid receptor antagonists and mixed agonist and antagonists, especially μ-opioid antagonists and κ-opioid agonists, are effective in relieving opioid-induced pruritus. Various treatments have been used for opioid-induced pruritus; however, most of them are controversial and have conflicting results.

CONCLUSION

The use of a multimodal analgesic treatment regimen combined with a mixed antagonist and κ agonists, especially μ-opioid antagonists, and κ-opioid agonists, seems to be the current best treatment modality for the management of opioid-induced pruritus and pain.

SIGNIFICANCE

Opioids remain the gold standard for the treatment of moderate to severe acute pain as well as cancer pain. It is well known that opioid-induced pruritus often does not respond to regular antipruritic treatment, thereby posing a challenge to clinicians in the field of pain management. We believe that our review makes a significant contribution to the literature, as studies on the mechanisms of opioid-induced pruritus and effective management strategies are crucial for the management of these patients.

Comparison of the ED50 of prophylactic butorphanol in preventing morphine-induced pruritus with or without palonosetron: a prospective, double-blinded, randomized dose-response trial using an up-down sequential allocation method

BACKGROUND

Butorphanol has been used to reduce the incidence and severity of neuraxial morphine-induced pruritus. Palonosetron is a commonly used antiemetic for the prevention of postoperative nausea and vomiting. The aim of our study was to compare the effective dose in 50% of subjects (ED50) of intravenous butorphanol infusion with or without a single intravenous bolus of palonosetron for preventing pruritus induced by epidural administration of morphine.

METHODS

A total of 120 parturients were randomly assigned to receive an intravenous bolus injection of palonosetron plus continuous infusion of butorphanol (Group P + B) or an intravenous bolus of saline plus continuous infusion of butorphanol (Group B) after epidural administration of morphine. The antipruritic effect was graded as satisfactory (numerical rating scale (NRS) of pruritus ≤3) or unsatisfactory (NRS >3) within 48 h after morphine treatment. The first patient in each group received butorphanol infusion at a rate of 4 µg/kg/h. The infusion dose for each subsequent patient in the corresponding group was increased by 0.2 µg/kg/h after an unsatisfactory response or decreased by 0.2 µg/kg/h after a satisfactory response. The ED50 was calculated for each group and compared using up-down sequential analysis.

RESULTS

The ED50 (mean [95% confidence interval (CI)]) of the dose of intravenous butorphanol infusion for preventing moderate to severe pruritus was lower in Group P + B (3.29 µg/kg/min [3.25-3.34 µg/kg/min]) than in Group B (3.57 µg/kg/min [3.47-3.67 µg/kg/min]) (p < 0.05).

CONCLUSIONS

Under the conditions of the present study, a prophylactic use of 0.25 mg palonosetron reduced the ED50 of prophylactic infusion of butorphanol by approximately 8% to achieve a satisfactory antipruritic effect after epidural morphine for post-caesarean analgesia.

Ondansetron for the Prevention of Pruritus in Women Undergoing Cesarean Delivery With Intrathecal Opioid: A Systematic Review and Meta-Analysis

BACKGROUND

Pruritus is a frequently reported and unpleasant side effect following intrathecal opioid use with frequency further increased among parturients. We have performed a systematic review to assess the overall efficacy of ondansetron for the prevention of pruritus in patients receiving intrathecal opioid as part of spinal anesthesia for cesarean delivery.

METHODS

A literature search of MEDLINE, Embase, Cochrane, and Web of Science databases was conducted from date of inception to September 2022. Studies that included patients undergoing cesarean delivery with spinal anesthesia using intrathecal opioid were included. The primary outcome was the presence of pruritus, and the secondary outcome was time to onset of pruritus. Data from included studies were pooled for analysis using an appropriately determined random-effects model. Outcomes were presented using forest plots and 95% confidence intervals. Additional sensitivity and subgroup analysis were performed. Trial sequential analysis was conducted for the primary outcome.

RESULTS

Twenty-three randomized controlled trials with a total of 2586 patients were included: 1219 received ondansetron, 1030 received a placebo, and a further 337 received a different study drug and were excluded from analysis. Opioids used in the included studies were morphine, fentanyl, and sufentanil. Patients who received ondansetron showed a significant reduction in the incidence of pruritus compared to the control group (RR, 0.81; 95% confidence interval [CI], 0.71-0.92; I 2 = 64%). There was no significant difference in pruritus onset between the groups (mean difference [MD], 17.54 minutes; 95% CI, -2.18 to 37.26; I 2 = 83%). The overall Grading of Recommendations Assessment, Development, and Evaluation (GRADE) assessment of quality of evidence was low.

CONCLUSIONS

This systematic review has demonstrated a significant reduction in the incidence of pruritus following the use of ondansetron. This is in contrast to previously published meta-analyses. Studies included were of varying quality and some at high risk of bias with a high degree of statistical heterogeneity. Furthermore, high-quality and well-powered studies are required to confirm these findings.

A novel anti-pruritic: Topical co-administration of high molecular weight hyaluronan (HMWH) with protamine, a transdermal transport enhancer

Pruritis, the sensation of itch, is produced by multiple substances, exogenous and endogenous, that sensitizes specialized sensory neurons (pruriceptors and pruri-nociceptors). Unfortunately, many patients with acute and chronic pruritis obtain only partial relief when treated with currently available treatment modalities. We recently demonstrated that the topical application of high molecular weight hyaluronan (HMWH), when combined with vehicles containing transdermal transport enhancers, produce potent long-lasting reversal of nociceptor sensitization associated with inflammatory and neuropathic pain. In the present experiments we tested the hypothesis that the topical formulation of HMWH with protamine, a transdermal transport enhancer, can also attenuate pruritis. We report that this topical formulation of HMWH markedly attenuates scratching behavior at the nape of the neck induced by serotonin (5-hydroxytryptamine, 5-HT), in male and female rats. Our results support the hypothesis that topical HMWH in a transdermal transport enhancer vehicle is a strong anti-pruritic.

Intravenous ondansetron reduced nausea but not pruritus following intrathecal morphine in children: Interim results of a randomized, double-blinded, placebo-control trial

STUDY OBJECTIVE

This study's purpose was to determine if ondansetron can prevent pruritus after administration of intrathecal morphine in children, as has been demonstrated in adults.

DESIGN

A double-blinded, randomized placebo-controlled trial.

SETTING

Operating room and first 24 h postoperative inpatient stay at an academic children's hospital.

PATIENTS

Forty-six children aged 3-17 years, who received 4-5 mcg/kg intrathecal morphine for urological or orthopedic procedures were included.

INTERVENTIONS

Children were randomized to receive intravenous ondansetron (treatment) or saline placebo (placebo), prior to intrathecal morphine administration, and q6H for 24 h thereafter. Intraoperative anti-emetics and postoperative rescue treatments for pruritus and nausea were standardized.

MEASUREMENTS

Patients were interviewed q6H for scored pruritus, nausea, and pain, using standardized scales.

MAIN RESULTS

The trial was terminated for futility after interim analysis. Forty-six children were recruited and 45 completed data collection. No significant difference was found between both groups for incidence of pruritus (requiring treatment) [relative risk (RR) 0.9, 95% CI: 0.7, 1.2], during the first postoperative 24 h. Notably, the incidence of pruritus was 84% overall, much higher than rates in previously published studies. Intravenous ondansetron significantly reduced the incidence of nausea, compared with the placebo group [RR 0.5, 95% CI: 0.3, 0.9].

CONCLUSIONS

This study found no evidence for intravenous ondansetron as an effective preventative for pruritus following intrathecal morphine in children. However, this RCT did find that the rate of pruritus following intrathecal morphine administration may be significantly higher than previously thought. Nausea and vomiting (a secondary outcome) were reduced significantly in the treatment group. The negative findings of this study reinforce the potential dangers of extrapolating the drug effects seen in adults onto pediatric patients.

Analgesic Effect of Ropivacaine Combined with Hydromorphone following Surgery for Mixed Hemorrhoids: A Pilot Study

Background

Postoperative pain is a major adverse effect of surgery for mixed hemorrhoids. We evaluated whether spinal anesthesia with ropivacaine and hydromorphone provided safe and effective analgesia after surgery for mixed hemorrhoids.

Methods

This single-center, double-blind pilot study included patients with mixed hemorrhoids who underwent a procedure for prolapse and hemorrhoids (PPH) and external hemorrhoidectomy under spinal anesthesia at Zhejiang Hospital, China (October 2020 to December 2020). Patients were randomized to a hydromorphone group (spinal anesthesia with 0.5% ropivacaine and 75 μg hydromorphone) or morphine group (spinal anesthesia with 0.5% ropivacaine and 150 μg morphine). Pain scores (numerical rating scale), incidences of vomiting and itching, and length of hospital stay (LoS) were recorded at 6, 12, 18, and 24 hours after surgery.

Results

The analysis included 40 patients in each group. Median (interquartile range) pain score in the hydromorphone group was higher than that in the morphine group at 12 hours (1 (0–2] vs. 0 (0–2), p=0.044) but not significantly different between groups at 6 hours (0 (0–1) vs. 0 (0-0) p=0.228), 18 hours (2 (2–3) vs. 2 (1–3) p=0.060) or 24 hours (2 (2–3) vs. 2 (1–3) p=0.081). The hydromorphone group had a lower incidence of pruritus than the morphine group (47.5% vs. 67.5%, p=0.018). There were no significant differences between groups in vomiting incidence or LoS.

Conclusion

In patients with mixed hemorrhoids, spinal anesthesia with ropivacaine/hydromorphone has a comparable analgesic effect and a lower incidence of pruritus during the first 24 hours after surgery than spinal anesthesia with ropivacaine/morphine.

Tapping into 5-HT3 Receptors to Modify Metabolic and Immune Responses

5-hydroxytryptamine type 3 (5-HT₃) receptors are ligand gated ion channels, which clearly distinguish their mode of action from the other G-protein coupled 5-HT or serotonin receptors. 5-HT₃ receptors are well established targets for emesis and gastrointestinal mobility and are used as adjunct targets in treating schizophrenia. However, the distribution of these receptors is wider than the nervous system and there is potential that these additional sites can be targeted to modulate inflammatory and/or metabolic conditions. Recent progress in structural biology and pharmacology of 5-HT₃ receptors have provided profound insights into mechanisms of their action. These advances, combined with insights into clinical relevance of mutations in genes encoding 5-HT₃ subunits and increasing understanding of their implications in patient's predisposition to diseases and response to the treatment, open new avenues for personalized precision medicine. In this review, we recap on the current status of 5-HT₃ receptor-based therapies using a biochemical and physiological perspective. We assess the potential for targeting 5-HT₃ receptors in conditions involving metabolic or inflammatory disorders based on recent findings, underscoring the challenges and limitations of this approach.

The Role of Intrathecal Morphine for Postoperative Analgesia in Primary Total Joint Arthroplasty under Spinal Anesthesia: A Systematic Review and Meta-Analysis

OBJECTIVE

To assess the efficacy and safety of intrathecal morphine (ITM) for postoperative analgesia in primary total joint arthroplasty (TJA) under spinal anesthesia and to explore the dose-response relationship for analgesic efficacy or risk of side effects.

METHODS

We searched MEDLINE, EMBASE, Web of Science, Cochrane Central Register of Controlled Trials and ClinicalTrials.gov for any studies meeting the inclusion criteria. All the data were summarized using the random effects model. Subgroup analyses were performed based on the surgical procedure and dose of ITM. Meta-regression was used to explore the dose-response relationship.

RESULTS

Eighteen randomized controlled trials were included. Compared with the placebo or blank control, ITM reduced the postoperative 24-h morphine consumption by 10.07 mg and prolonged the duration of analgesia. However, ITM significantly increased the risk of pruritus by 2.79 fold, with a tendency to increase the risk of postoperative nausea and/or vomiting (P = 0.08). No difference was observed regarding the length of stay (LOS) and incidence of respiratory depression or urinary retention. Furthermore, meta-regression showed a linear dose-response relationship for the postoperative 24-h morphine consumption but no linear dose-response relationship for the risk of side effects.

CONCLUSIONS

Adding morphine to intrathecal anesthetics provides a prolonged and robust analgesic effect without significantly increasing the risk of side effects other than pruritus. Although we found a linear dose-response relationship for the postoperative 24-h morphine consumption, the optimal dose of ITM remains to be further explored in high-quality RCTs with a large sample size.

Evaluation of Therapies for Peripheral and Neuraxial Opioid-induced Pruritus based on Molecular and Cellular Discoveries

Opioids are a mainstay of treatment for pain worldwide. Pruritus, a common side effect of opioids, is a patient dissatisfier that limits their use in many clinical settings. Both parenteral and neuraxial administration of opioids frequently evoke pruritus. The ability of opioids to suppress pain while causing itch continues to perplex clinicians and researchers alike. Several mechanisms have been proposed to explain how opioids can give rise to pruritus, but specific knowledge gaps perpetuate debate. This review summarizes the clinical burden of opioid-induced pruritus and emphasizes recent discoveries of peripheral and central mechanisms for opioid-induced pruritus, particularly with respect to scientific and conceptual advances in spinal cord circuitry and mast cell biology. The mechanisms and effectiveness of existing medications used for clinical management of pruritus will be evaluated, and we will highlight the emerging preclinical utility of selective κ-opioid receptor agonists, such as nalfurafine, for the management of opioid-induced pruritus.

Ondansetron versus ondansetron with dexamethasone to prevent intrathecal-morphine pruritus for caesarean patients: randomised double-blind trial

The objective of this randomised, double blinded clinical trial was to evaluate the efficacy of prophylactic administration of 4 mg ondansetron as monotherapy versus combination therapy of 4 mg ondansetron plus 8 mg dexamethasone for the prevention of intrathecal morphine-associated pruritus in caesarean section within 24 h. A total of 194 patients were included, 96 patients in the monotherapy group and 98 in the combination group. One hour after the operation, 11.5% of patients in ondansetron group had failure of prophylaxis for pruritus compared to 13.5% of patients in the combination group (p = .66). This decreased throughout the follow-up to reach 0.0% and 1.0% at 24 h in the ondansetron vs. the combination groups respectively. There was no superiority of combining ondansetron with dexamethasone over the use of ondansetron as prophylactic antipruritic in parturients receiving intrathecal morphine for caesarean section.IMPACT STATEMENTWhat is already known on this subject? The incidence of pruritus has been reported to be between 36% and 60% in patients undergoing caesarean section with intrathecal morphine. Ondansetron has been identified as possible antipruritic agent while the antipruritic effect of dexamethasone is inconclusive.What do the results of this study add? The study demonstrated that there was no superiority of combining ondansetron with dexamethasone over the use of ondansetron as prophylactic antipruritic in parturients receiving intrathecal morphine for caesarean section. Moreover, it seems that there is no effect of combining ondansetron with dexamethasone over ondansetron alone on antiemetic consequences.What are the implications of these findings for clinical practice and/or further research? Ondansetron could be an effective antipruritic if used solely for patients undergoing caesarean section.

Comparison of weight-adjusted dose versus fixed dose ondansetron in preventing shivering following spinal anaesthesia for caesarean deliveries

Background

Spinal anaesthesia is an effective regional anaesthesia technique, which is preferred in almost 86% of caesarean sections in the United States and United Kingdom. Eighty percent of caesarean sections done at the Aga Khan University hospital are under spinal anaesthesia. Shivering is a common complication of spinal anaesthesia, it occurs in 40%-64% of patients after neuraxial anaesthesia. Shivering may cause maternal and fetal hypoxemia, maternal discomfort and a problem to the anaesthesiologists when it comes to monitoring the patient during caesarean sections. Ondansetron a 5-HT3 receptor antagonist is effective in treatment and prevention of post-spinal anesthesia shivering. In published studies, use of a fixed dose in patients with different weights, masked the dose effect ondansetron in preventing shivering, such that not adjusting the dose according to the weight of patients' resulted in a higher occurrence of shivering. No study has compared different doses of ondansetron in preventing shivering in parturient women who have had spinal anaesthesia for caesarean section.

Objectives

To determine if a weight-adjusted dose is better than a fixed dose of ondansetron in preventing shivering following spinal anesthesia for caesarean delivery.

Method

This was a randomized, double-blinded controlled trial of 124 women scheduled for elective caesarean surgery. The women were randomized into two equal groups. The intervention group received intravenous ondansetron weight adjusted dosing at 0.1mg/kg and the control group received a fixed dose of 4mg before spinal anesthesia. The occurrence and severity of shivering and other outcomes, such as headache, pruritus were assessed and recorded during the surgery and post-operative period.

Results

A total of 124 patients were included in the study. Social demographic data and baseline vital signs did not differ significantly between the groups. Shivering was observed in 14 patients (22.6%) in the control group that received 4mg ondansetron and 7 patients (11.3%) in the intervention group that had 0.1mg/kg of ondansetron, but there was no statistical difference between the groups (p- value 0.090). The severity of shivering was greater in the control group compared to intervention group where patients who developed grade two shivering were 8.1% to 0% respectively. (P value 0.047). There was no difference in the occurrence of pruritus between the two groups. No patient required treatment for very severe shivering.

Conclusion

This study, found that ondansetron weight adjusted dose at 0.1mg/kg, reduced the severity of shivering when compared to a fixed dose ondansetron at 4mg.

Effects of an intrathecal TRPV1 antagonist, SB366791, on morphine-induced itch, body temperature, and antinociception in mice

Purpose

Transient receptor potential vanilloid 1 (TRPV1) not only is activated by multiple stimuli but also is involved with histamine-induced itch. The effects of TRPV1 on morphine-induced itch are unknown. We examined the effects of intrathecal administration of TRPV1 antagonist on morphine-induced itch, body temperature, and antinociception for mice.

Methods

Each C57/BL6j mouse was intrathecally administered with one of the following solutions: morphine, SB366791 (as the TRPV1 antagonist), morphine + SB366791, saline, or vehicle. For each mouse, each instance of observed scratching behavior was counted, the body temperature was measured, and the nociceptive threshold was determined using the tail-immersion test.

Results

SB366791 dose-dependently reduced the scratching behavior induced by the administration of morphine. SB366791 and the morphine + SB366791 groups did not manifest an increase in body temperature. Antinociceptive effects were observed to occur dose-dependently for morphine but not for SB366791. Compared with morphine alone, the administration of morphine + SB366791 did not reduce significant antinociceptive effects.

Conclusion

We propose that an intrathecal TRPV1 antagonist, SB366791, reduced morphine-induced itch without causing hyperthermia and did not suppress morphine-induced antinociception for mice.

Brain allopregnanolone induces marked scratching behaviour in diet-induced atopic dermatitis mouse model

Allopregnanolone (ALLO) is a neurosteroid produced in the brain, but so far, no study has explored its link with itching. Herein, we used a diet-induced atopic dermatitis mouse model to examine whether exogenously administered and endogenously produced ALLO contribute to inducing scratching. Systemic administration of ALLO elicited robust scratching in the atopic dermatitis model, while it did not affect spontaneous and pruritogen-induced scratching in normal mice. ALLO caused scratching when administered intracisternally, but not when administered intrathecally or intradermally, suggesting the involvement of supraspinal mechanisms. Pharmacological analyses suggested that both γ-aminobutyric acid type A receptor activation and serotonin type 3 receptor inhibition were involved in ALLO-induced scratching. We next examined whether endogenously produced ALLO is involved in ethanol-induced scratching in atopic dermatitis mice, because ethanol administration increases ALLO in rodent brain. Acute ethanol administration increased brain ALLO levels, which coincided with increased scratching. Pre-treatment with finasteride, a synthetic ALLO inhibitor, suppressed ethanol-induced scratching and ALLO production in the brain. Collectively, our results demonstrated for the first time that ALLO administration caused marked scratching in atopic dermatitis mice, and ethanol-induced scratching may be mediated through endogenously produced brain ALLO.

Postoperative pain management in patients undergoing posterior spinal fusion for adolescent idiopathic scoliosis: a narrative review

Posterior spinal fusion for adolescent idiopathic scoliosis is one of the most invasive surgical procedures performed in children and adolescents. Because of the extensive surgical incision and massive tissue trauma, posterior spinal fusion causes severe postoperative pain. Intravenous patient-controlled analgesia with opioids has been the mainstay of postoperative pain management in these patients. However, the use of systemic opioids is sometimes limited by opioid-related side effects, resulting in poor analgesia. To improve pain management while reducing opioid consumption and opioid-related complications, concurrent use of analgesics and analgesic modalities with different mechanisms of action seems to be rational. The efficacy of intrathecal opioids and nonsteroidal anti-inflammatory drugs as components of multimodal analgesia in scoliosis surgery has been well established. However, there is either controversy or insufficient evidence regarding the use of other analgesic methods, such as continuous ketamine infusion, perioperative oral gabapentin, acetaminophen, continuous wound infiltration of local anesthetics, a single dose of systemic dexamethasone, and lidocaine infusion in this patient population. Moreover, appropriate combinations of analgesics have not been established. The aim of this literature review is to provide detailed information of each analgesic technique so that clinicians can make appropriate choices regarding pain management in patients with adolescent idiopathic scoliosis undergoing posterior spinal fusion.

Acupuncture for reducing pruritus induced by intrathecal morphine at elective cesarean delivery: a placebo-controlled, randomized, double-blind trial

BACKGROUND

Intrathecal morphine is a standard postoperative analgesic administered after cesarean delivery, but frequently causes pruritus. Acupuncture reportedly resolves refractory pruritus in certain patients. The aim of the study was to investigate the effectiveness of acupuncture in preventing pruritus induced by intrathecal morphine.

METHODS

Thirty parturients received intrathecal hyperbaric bupivacaine (12 mg), fentanyl (10 µg), and morphine (150 µg) for spinal anesthesia at elective cesarean delivery at term. Patients were randomly divided into the acupuncture group (n=15) and the control group (n=15). In the acupuncture and control groups, certified acupuncturists inserted either indwelling press needles or sham needles, into Hegu (LI4), Neiguan (PC6), Quchi (LI11), and Zhigou (SJ6) on both arms the day before surgery. Needles were removed 48 hours postoperatively. The primary outcome was the incidence of postoperative pruritus. Adverse effects including nausea and vomiting were also investigated.

RESULTS

There were no significant differences between the acupuncture group and the control group in the incidence of pruritus (67% vs. 67%, P=1.000, RR 1.0 [95% CI 0.60 to 1.66]) or the requirement for antipruritic therapy (6.7% vs. 20.0%, P=0.283, RR 0.33 [95% CI 0.04 to 2.85]). The incidence of postoperative nausea in the acupuncture group versus control group was 40.0% vs. 13.3%, P=0.099, RR 3.0 [95% CI 0.72 to 12.6]). The postoperative analgesic effect was comparable.

CONCLUSION

Preoperatively administered acupuncture using press needles did not decrease intrathecal morphine-induced pruritus or the requirement for treatment.

Comparison of Palonosetron, Dexamethasone, and Palonosetron Plus Dexamethasone as Prophylactic Antiemetic and Antipruritic Drug in Patients Receiving Intrathecal Morphine for Lower Segment Cesarean Section

Background:

Intrathecal morphine is commonly used for postcesarean analgesia. Its use is frequently associated with opioid-induced nausea, vomiting, and pruritus. Palonosetron (0.075 mg) combined with dexamethasone (8 mg) is postulated to have an additive effect over each drug alone. The study, therefore, compared the effect of intravenous (i.v.) palonosetron, dexamethasone, and palonosetron with dexamethasone combination in preventing intrathecal morphine-induced postoperative vomiting and pruritus in lower segment cesarean section (LSCS) patients.

Settings and Design:

Randomized, prospective, double-blinded, observational clinical study.

Methods:

Ninety pregnant women, American Society of Anesthesiologists physical status class I undergoing LSCS were included in the study. They were randomly assigned to three groups – Group P received 0.075 mg palonosetron i.v., Group D received dexamethasone 8 mg i.v., and Group PD received palonosetron 0.075 mg along with dexamethasone 4 mg i.v., just after spinal anesthesia with bupivacaine 2.2 ml (12 mg) and 150 μg morphine. The incidence of pruritus, nausea, vomiting, and need for rescue drug were recorded for 24 h.

Statistical Analysis:

Statistical analysis was performed using Student's t-test for categorical variables and Chi-square test for noncategorical variables.

Results:

The incidence of nausea, vomiting was significantly more in Group D (40%) than Group P (27%) and Group PD (20%) in 24 h. The incidence of pruritus was significantly more in Group D (6%) than Group P and PD (3%). The need of rescue antiemetic was more in Group D (30%) than Group P (6%) and Group PD (3%). No difference in three groups requiring rescue antipruritic drug.

Conclusion:

Prevention of intrathecal morphine-induced vomiting and pruritus was more effective with palonosetron alone or with dexamethasone combination than dexamethasone alone. Combination of palonosetron and dexamethasone proved no better than palonosetron alone.

Is There a Role for 5-HT3 Receptor Antagonists in the Treatment of Opioid-Induced Pruritus?

Pruritus is an unpleasant irritation symptom that can be related to various systemic and dermatological conditions. Although underreported, pruritus is a common adverse event noted after use of opioid pain medications. This article reviews the current understanding of the mechanism of opioid-induced pruritus (OIP) and various pharmacological therapies. 5-Hydroxytryptamine 3 (5-HT₃) receptor antagonists are potentially effective for treating OIP and may be a valuable treatment option if further controlled studies are encouraging.

Ondansetron for neuraxial morphine-induced pruritus: A meta-analysis of randomized controlled trials

WHAT IS KNOWN AND OBJECTIVE

Pruritus is one of the most common adverse effects associated with neuraxial morphine. Ondansetron has been used to deal with the problem of neuraxial morphine-induced pruritus (NMIP). The aim of this meta-analysis was to evaluate the preventive efficacy of ondansetron on NMIP.

METHODS

Online databases such as PubMed, EMBASE and the Cochrane Central Register of Controlled Trials were searched for eligible randomized controlled trials (RCTs). The primary outcome was the incidence of NMIP. We calculated risk ratios (RR) with 95% confidence intervals (CI) for dichotomous data. Trial sequential analysis (TSA) was performed to avoid the risk of making a spurious claim of significant effect and to calculate the sample size necessary to make a robust claim of effect.

RESULTS AND DISCUSSION

Our traditional meta-analysis showed that prophylactic ondansetron could significantly reduce the incidence of NMIP in non-obstetric patients (three trials, RR=0.63, 95% CI 0.45-0.89, P=.008) with modest heterogeneity (I² =47%) while it did not show the preventive efficacy of NMIP in obstetric patients (seven trials, RR=0.84, 95% CI 0.69-1.03, P=.10) with obvious heterogeneity (I²  =82% ). However, TSA demonstrates that more high-quality RCTs are still needed to confirm the preventive efficacy of ondansetron on NMIP in non-obstetric populations and to study whether ondansetron prevents NMIP in obstetric patients.

WHAT IS NEW AND CONCLUSION

Prophylactic ondansetron can significantly reduce the incidence of NMIP in non-obstetric patients but not in obstetric patients. However, more well-designed trials are still required to test the reliability of the results in our traditional meta-analysis.

Optimal Pain Management After Cesarean Delivery

Cesarean delivery rates are increasing worldwide, and effective postoperative pain management is a key priority of women undergoing cesarean delivery. Inadequate pain management in the acute postoperative period is associated with persistent pain, greater opioid use, delayed functional recovery, and increased postpartum depression. In addition to pain relief, optimal management of patients after cesarean delivery should address the goals of unrestricted maternal mobility, minimal maternal and neonatal side effects, rapid recovery to baseline functionality, and early discharge home. Multimodal analgesia should include neuraxial morphine in conjunction with nonopioid adjuncts, with additional oral or intravenous opioids reserved for severe breakthrough pain.

Inadvertent spinal injection of ondansetron

Cesarean sections under spinal anesthesia are now a daily occurrence in most tertiary hospitals. We report the first published case of inadvertent spinal injection of ondansetron without any neurological sequelae in a patient undergoing elective Cesarean section under spinal anesthesia. She did not experience any permanent neurological sequelae, and also did not exhibit any central neuraxial opioid side effects-nausea, vomiting or pruritus. Vigilance is essential to reduce the risk of wrong route delivery of drugs, especially when presented in very similar-looking 2 mL ampules as in our institution.

A review of opioid-induced itching after cesarean birth

Currently, about one-third of all women giving birth have a cesarean surgical birth, and the majority are given an epidural or spinal anesthetic containing an opioid for surgery. An unpleasant side effect experienced by many of these women is itching. This article reviews the literature on itching after spinal and epidural administration of opioids and how nurses can best manage this side effect.

Effect of adding intrathecal morphine to a multimodal analgesic regimen for postoperative pain management after laparoscopic bariatric surgery: a prospective, double-blind, randomized controlled trial

BACKGROUND

Pain control after bariatric surgery is a major challenge. Our objective was to study the efficacy and safety of intrathecal (IT) morphine 0.3 mg added to bupivacaine 0.5% for postoperative pain after laparoscopic bariatric surgery.

METHODS

After local ethics committee approval, 100 morbidly obese patients scheduled for laparoscopic bariatric surgery were enrolled in this study. Patients were randomly assigned into two groups: Group I received IT 0.3 mg morphine (0.3 mL) added to 1.2 mL of bupivacaine 0.5%; Group II received IT 0.3 mL saline added to 1.2 mL of bupivacaine 0.5%, immediately before induction of general anaesthesia. For both groups, 60 mg ketorolac and 1000 mg paracetamol were infused 30 minutes before the end of surgery. After wound closure, 20 mL bupivacaine 0.25% was infiltrated at wound edges.

RESULTS

Visual Analogue Scale (VAS) score was significantly lower in group I immediately, 30 minutes and 1 hour postoperatively. Time to first ambulation, return of intestinal sounds and hospital stay were shorter in group I than group II (p < 0.05); total morphine consumption was significantly lower in group I than group II (p < 0.05). Sedation score was significantly higher in group I immediately postoperatively, while at 30 minutes, 1, 2 and 6 hours postoperatively sedation scores were significantly higher in group II. Itching was significantly higher in group I.

CONCLUSION

The addition of IT morphine to a multimodal analgesic regimen after laparoscopic bariatric surgery was an effective and safe method that markedly reduced postoperative pain, systemic opioid consumption and length of hospital stay.

Prophylactic Ondansetron for the Prevention of Intrathecal Fentanyl- or Sufentanil-Mediated Pruritus: A Meta-Analysis of Randomized Trials

BACKGROUND

Pruritus is a common side effect of intrathecal fentanyl or sufentanil that decreases patient satisfaction and may delay hospital discharge. There are conflicting reports about the efficacy of prophylactic ondansetron in reducing the incidence of pruritus. This meta-analysis aimed to assess the effect of prophylactic ondansetron on the incidence of intrathecal fentanyl- or sufentanil-mediated pruritus and the need for rescue treatment.

METHODS

A systematic search on PubMed, Medline, and the Cochrane Central Register of Controlled Trials from January 1, 1994, to January 1, 2014, was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Randomized controlled trials evaluating the efficacy of prophylactic ondansetron on pruritus associated with intrathecal fentanyl or sufentanil were included. The primary outcome was the incidence of pruritus, and the secondary outcome was patients' need for rescue therapy. Sensitivity analyses were conducted to assess the outcomes in obstetric and nonobstetric patients and in patients who received ondansetron before or after intrathecal opioid injection. Analyses used random-effect models.

RESULTS

Six randomized controlled trials involving 555 patients were included. In the overall analysis, prophylactic ondansetron did not significantly decrease the incidence of pruritus, but there was a trend toward reduced rescue medication use (risk ratio [RR], 0.57; 95% confidence interval [CI], 0.35-0.91; I = 0%; P = 0.02). Exploratory subgroups, including nonobstetric surgery patients and patients who received ondansetron before spinal opioid administration, also suggest a trend toward less rescue medication use (RR, 0.47; 95% CI, 0.26-0.85; P = 0.01; and RR, 0.62; 95% CI, 0.38-1.00; P = 0.05).

CONCLUSIONS

IV 8 mg prophylactic ondansetron does not decrease the incidence of fentanyl- or sufentanil-mediated pruritus but may decrease the need for pruritus rescue medication, particularly in specific subgroups. Randomized trials are needed to confirm these results.

Comparative study between nalbuphine and ondansetron in prevention of intrathecal morphine-induced pruritus in women undergoing cesarean section

BACKGROUND

Intrathecal morphine provides effective postoperative analgesia, but their use is associated with numerous side effects, including pruritus, nausea, vomiting, urinary retention, and respiratory depression. Pruritus is the most common side effect with a reported incidence of 58-85%.

OBJECTIVES

This prospective, randomized, and double-blinded study was performed for women scheduled for cesarean delivery using spinal anesthesia to compare nalbuphine and ondansetron in the prevention of intrathecal morphine-induced pruritus.

PATIENTS AND METHODS

Ninety women after spinal anesthesia with hyperbaric bupivacaine and intrathecal morphine patients randomly divided into three groups. Women in placebo group (P group) received 4 ml of normal saline intravenous (IV) injection, nalbuphine group (N group) received 4 ml of a 4 mg nalbuphine IV injection, and ondansetron 4 group (O group) received 4 ml of a 4 mg ondansetron IV injection, immediately after delivery of the baby. Studied women observed in postanesthesia care unit for 4 h. The primary outcome measures success of the treatment, defined as a pruritus score 1 (no pruritus) or 2 (mild pruritus - no treatment required) at 20 min after treatment.

RESULTS

Although, three was no significant difference between the three studied groups regarding; score 1 pruritus, while, score 2 pruritus (mild pruritus - no treatment requested) was significantly high in N and O groups compared to placebo group. Pruritus score 1 (no pruritus) plus pruritus score 2 were significantly high in N and O groups compared to placebo group (20 cases, 20 cases, 5 cases; respectively, P = 0.008). In addition; score 3 pruritus (moderate - treatment requested) was significantly less in N and O groups compared to placebo group.

CONCLUSION

Nalbuphine and ondansetron were found to be more effective than placebo for prevention of intrathecal morphine-induced pruritus in women undergoing cesarean delivery and nalbuphine is preferred than ondansetron because it is not excreted in the breast milk.

Neuraxial opioid-induced itch and its pharmacological antagonism

Given its profound analgesic nature, neuraxial opioids are frequently used for pain management. Unfortunately, the high incident rate of itch/pruritus after spinal administration of opioid analgesics reported in postoperative and obstetric patients greatly diminishes patient satisfaction and thus the value of the analgesics. Many endeavors to solve the mystery behind neuraxial opioid-induced itch had not been successful, as the pharmacological antagonism other than the blockade of mu opioid receptors remains elusive. Nevertheless, as the characteristics of all opioid receptor subtypes have become more understood, more studies have shed light on the potential effective treatments. This review discusses the mechanisms underlying neuraxial opioid-induced itch and compares pharmacological evidence in nonhuman primates with clinical findings across diverse drugs. Both nonhuman primate and human studies corroborate that mixed mu/kappa opioid partial agonists seem to be the most effective drugs in ameliorating neuraxial opioid-induced itch while retaining neuraxial opioid-induced analgesia.

HTR7 Mediates Serotonergic Acute and Chronic Itch

Chronic itch is a prevalent and debilitating condition for which few effective therapies are available. We harnessed the natural variation across genetically distinct mouse strains to identify transcripts co-regulated with itch behavior. This survey led to the discovery of the serotonin receptor HTR7 as a key mediator of serotonergic itch. Activation of HTR7 promoted opening of the ion channel TRPA1, which in turn triggered itch behaviors. In addition, acute itch triggered by serotonin or a selective serotonin reuptake inhibitor required both HTR7 and TRPA1. Aberrant serotonin signaling has long been linked to a variety of human chronic itch conditions, including atopic dermatitis. In a mouse model of atopic dermatitis, mice lacking HTR7 or TRPA1 displayed reduced scratching and skin lesion severity. These data highlight a role for HTR7 in acute and chronic itch and suggest that HTR7 antagonists may be useful for treating a variety of pathological itch conditions.

Prophylactic administration of ondansetron in prevention of intrathecal morphine-induced pruritus and post-operative nausea and vomiting in patients undergoing caesarean section

Background

Intrathecal morphine is commonly used for post caesarean analgesia. However, their use is frequently associated with the incidence of troublesome side effects such as nausea, vomiting and pruritus. Various mechanisms have been postulated for the opioid-induced pruritus, with a variety of medications with different mechanisms of actions formulated for the prevention and treatment. But, the results are inconsistent and hence the prevention and treatment of opioid-induced pruritus still remains a challenge. Ondansetron which is antiemetic, non-sedative and has no antianalgesic effect is an antagonist to 5-HT3 receptor, the receptor with which opioids interacts and imparts its effects. Ondansetron, thus, would be an attractive treatment strategy for both opioid-induced pruritus and post-operative nausea and vomiting.

Methods

After the approval from institutional review committee and written consent received from the patient, 50 healthy parturients of ASA I and II physical status undergoing caesarean section under spinal anaesthesia were enrolled for the study. They were randomly categorized into placebo group (2 ml normal saline) and treatment group (2 ml of 4 mg ondansetron), each group containing 25 patients. Pruritus and post-operative nausea and vomiting scores were recorded up to 24 hours after the administration of intrathecal morphine. Statistical analysis was performed using chi-square test.

Results

The incidence, severity and necessity of treatment for pruritus in the treatment group was significantly reduced compared to the placebo group (16% vs 88%). Similarly, the risk of post-operative nausea and vomiting in the treatment group was less compared to the placebo group (8% vs 56%).

Conclusion

Prophylactic administration of ondansetron to parturients receiving intrathecal morphine for post-operative analgesia provides a significant reduction of intrathecal morphine-induced pruritus and nausea and vomiting.

Trial registration

CTRI/2015/01/005362 registered on 07/01/2015 in Clinical Trials Registry – India (ctri.nic.in).

Anesthetic premedication: new horizons of an old practice

The practice of anesthetic premedication embarked upon soon after ether and chloroform were introduced as general anesthetics in the middle of the 19(th) century. By applying opioids and anticholinergics before surgery, the surgical patients could achieve a less anxious state, and more importantly, they would acquire a smoother course during the tedious and dangerous induction stage. Premedication with opioids and anticholinergics was not a routine practice in the 20(th) century when intravenous anesthetics were primarily used as induction agents that significantly shorten the induction time. The current practice of anesthetic premedication has evolved into a generalized scheme that incorporates several aspects of patient care: decreasing preoperative anxiety, dampening intraoperative noxious stimulus and its associated neuroendocrinological changes, and minimizing postoperative adverse effects of anesthesia and surgery. Rational use of premedication in modern anesthesia practice should be justified by individual needs, the types of surgery, and the anesthetic agents and techniques used. In this article, we will provide our readers with updated information about premedication of surgical patients with a focus on the recent application of second generation serotonin type 3 antagonist, antidepressants, and anticonvulsants.

Neuraxial opioid-induced pruritus: An update

Pruritus is a troublesome side-effect of neuraxial (epidural and intrathecal) opioids. Sometimes it may be more unpleasant than pain itself. The prevention and treatment still remains a challenge. A variety of medications with different mechanisms of action have been used for the prevention and treatment of opioid-induced pruritus, with mixed results. The aim of this article is to review the current body of literature and summarize the current understanding of the mechanisms and the pharmacological therapies available to manage opioid-induced pruritus. The literature source of this review was obtained via PubMed, Medline and Cochrane Database of Systematic Reviews until 2012. The search results were limited to the randomized controlled trials, systemic reviews and non-systemic reviews.

Strategies for preventing side effects of systemic opioid in postoperative pediatric patients

BACKGROUND AND OBJECTIVES

Opioid is the gold standard for treating moderate-to-severe pain in pediatric patients. However, its undesirable side effects lead to unsatisfied postoperative pain management outcome (Pediatr Anesth, 17, 2007, 756). The most commonly reported opioid-related side effects are vomiting (40%), pruritus (20-60%) (Anesthesiology, 77, 1992, 162; Drugs, 67, 2007, 2323), and constipation (15-90%) (Int J Clin Pract, 61, 2007, 1181). The potential life-threatening adverse event, respiratory depression, is less common (0.0013%) (Pediatr Anesth, 20, 2010, 119). The aim of this review was to evaluate prevention strategies that have been shown to decrease opioid side effects in pediatric patients during the postoperative period.

METHODS

Literature searches were conducted from 1984 to February 2013. Meta-analysis, systematic review, and randomized, placebo-controlled studies were obtained from PubMed and the Cochrane Library. The medical subject heading (MeSH) terms were opioid analgesics, adverse effects, pediatrics, children, side effects, and postoperative pain.

RESULTS AND CONCLUSION

Data from 62 studies were reviewed. The strategies that could effectively prevent and reduce opioid side effects in pediatric patients during the postoperative period included minimizing the amount of opioid consumption by a multimodal approach, opioid titration, using local anesthetic techniques and providing the specific prophylaxis for each side effect.

Butorphanol prevents morphine-induced pruritus without increasing pain and other side effects: a systematic review of randomized controlled trials

PURPOSE

Pruritus is a frequent adverse event after administration of morphine. Butorphanol has been used to prevent morphine-induced pruritus, but its efficacy is still controversial. The aim of this systematic review was to evaluate the efficacy of using butorphanol to prevent morphine-induced pruritus.

SOURCE

We searched PubMed, Cochrane Library, EMBASE, and China's BioMedical Disc for full reports of randomized controlled trials that compared the use of butorphanol with either placebo or no treatment for preventing morphine-induced pruritus. The number of patients experiencing pruritus or other side effects was analyzed using relative risk (RR) with 95% confidence intervals (CI).

PRINCIPAL FINDINGS

Sixteen trials (795 patients) were analyzed. Continuous intravenous and epidural butorphanol reduced pruritus with RR 0.22 (95% CI 0.10 to 0.45) and RR 0.24 (95% CI 0.16 to 0.36), respectively. Use of epidural butorphanol decreased the number of patients requesting rescue treatment for pruritus (RR 0.57; 95% CI 0.41 to 0.81). Butorphanol decreased postoperative pain intensity at four, eight, and 12 hr with standardized mean differences of -0.29 (95% CI -0.52 to -0.05), -0.30 (95% CI -0.56 to -0.04), and -0.23 (95% CI -0.46 to -0.01), respectively. Epidural but not intravenous butorphanol reduced postoperative nausea and vomiting (PONV) (RR 0.35; 95% CI 0.19 to 0.66). Butorphanol did not increase respiratory depression (RR 0.71; 95% CI 0.31 to 1.63), somnolence (RR 0.71; 95% CI 0.22 to 2.37), or dizziness (RR 2.45; 95% CI 0.35 to 17.14).

CONCLUSION

Butorphanol administered with morphine may be an effective strategy for preventing morphine-induced pruritus as it decreases pain intensity and PONV without increasing other side effects. Thus, it can be recommended for preventing morphine-induced pruritus during the perioperative period.

Intravenous butorphanol administration reduces intrathecal morphine-induced pruritus after cesarean delivery: a randomized, double-blind, placebo-controlled study

PURPOSE

Pruritus associated with intrathecal opioid administration is a common side effect. There is evidence that κ-opioid receptor agonists have antipruritic activity. Butorphanol has agonist actions at both κ-opioid and μ-opioid receptors. This study was designed to evaluate the antipruritic efficacy of butorphanol after intrathecal morphine administration in the setting of a randomized, double-blind study of parturients undergoing cesarean section.

METHODS

Ninety-one women who received combined spinal-epidural anesthesia with 1.2 ml 0.5 % isobaric bupivacaine and 0.1 mg preservative-free morphine were included in this study. After delivery of the baby, the parturients were randomly allocated to two groups: butorphanol group (n = 46) and physiological saline group (n = 45). In the butorphanol group, parturients received an intravenous loading dose of 1 mg butorphanol followed by infusion of 0.2 mg/h butorphanol. The physiological saline group received an infusion of the same volume of physiological saline. The presence of pruritus, visual analog scores for pain, sedation scores, and adverse effects were recorded 1, 2, 4, 6, 8, 10, 12, and 24 h after intrathecal morphine administration.

RESULTS

The incidence of pruritus at 24 h was significantly more frequent in the physiological saline group than in the butorphanol group (48.9 vs. 13.0 %, P < 0.001). The severity of pruritus was significantly greater in the saline group than in the butorphanol group 2, 4, 6, 8 and 10 h after intrathecal morphine injection (P = 0.004, 0.001, 0.002, and 0.003, respectively). The visual analog scale scores at 24 h were significantly lower in the butorphanol group than in physiological saline group (P < 0.001). The Ramsay sedation score in the butorphanol group was significantly higher than that in the physiological saline group after 1, 2, 4, 6, 8, 10, 12, and 24 h (P < 0.05). There were no significant differences between the two groups in nausea/vomiting and other adverse effects.

CONCLUSION

Administration of intravenous butorphanol after delivery of the baby can reduce pruritus that has been induced by intrathecal morphine administration in cesarean delivery with combined spinal-epidural anesthesia.

From QUOROM to PRISMA: a survey of high-impact medical journals' instructions to authors and a review of systematic reviews in anesthesia literature

BACKGROUND

The PRISMA (Preferred Reporting Items of Systematic reviews and Meta-Analyses) Statement was published to help authors improve how they report systematic reviews. It is unknown how many journals mention PRISMA in their instructions to authors, or whether stronger journal language regarding use of PRISMA improves author compliance.

METHODOLOGY/PRINCIPAL FINDINGS

An Internet-based investigation examined the extent to which 146 leading medical journals have incorporated the PRISMA Statement into their instructions to authors. Results were analyzed using descriptive statistics. Also, systematic reviews published in the leading anesthesiology journals and the QUOROM (QUality Of Reporting Of Meta-analyses) Statement were used to explore the hypothesis that indicating compliance with the QUOROM Statement in the manuscript is associated with improved compliance with the reporting guideline. In a sample of 146 journals publishing systematic reviews, the PRISMA Statement was referred to in the instructions to authors for 27% (40/146) of journals; more often in general and internal medicine journals (7/14; 50%) than in specialty medicine journals (33/132; 25%). In the second part of the study, 13 systematic reviews published in the leading anesthesiology journals in 2008 were included for appraisal. Mention of the QUOROM Statement in the manuscript was associated with higher compliance with the QUOROM checklist (P = 0.022).

CONCLUSIONS/SIGNIFICANCE

Most of the leading medical journals used ambiguous language regarding what was expected of authors. Further improvement on quality of reporting of systematic reviews may entail journals clearly informing authors of their requirements. Stronger directions, such as requiring an indication of adherence to a research quality of reporting statement in the manuscript, may improve reporting and utility of systematic reviews.

Pruritus: an overview of current concepts

Pruritus is an integral part of the patient's symptoms in numerous dermatological and systemic diseases in humans and animals. Comparable to chronic pain, pruritus can have a dramatic impact on the quality of life of the patient. In recent years, pruritus has been defined as an autonomous, pain-independent sensation, and itch-specific neurons, mediators, spinal neurons and cortical areas have been identified. These observations have not only improved our understanding of the neurobiology of itch but will also lead to improved diagnosis and to the development of new and more efficient therapeutic options. This article reviews the role of itch fibres and their response to various mediators of pruritus including histamine, vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), and substance P (SP), and opioids. Substances that may be involved in the induction or modulation of itch may be termed pruritogenic mediators and examples discussed include proteases, lipid mediators, neuropeptides, opioids and various cytokines. There is no single, generally accepted clinical classification of chronic pruritus. In the past pruritus has been classified on the basis of the neuroanatomical origin and on the potential underlying disease. Therapeutic options for the management of pruritus are discussed including topical and systemic therapies, assuming that trigger factors have been eliminated where possible. Topical agents may include capsaicin, the calcineurin inhibitors tacrolimus and pimecrolimus, and cannabinoid agonists such as N-palmitoyl ethanolamine. Systemic therapies may include antihistamines, anticonvulsants, opiate receptor antagonist or agonists, antidepressants, ciclosporin, and UV light.

Chronic pruritus in the absence of specific skin disease: an update on pathophysiology, diagnosis, and therapy

Chronic pruritus is a major and distressing symptom of many cutaneous and systemic diseases and can significantly impair the patient's quality of life. Pruritus perception is the final result of a complex network involving dedicated nerve pathways and brain areas, and an increasing number of peripheral and central mediators are thought to be involved. Itch is associated with most cutaneous disorders and, in these circumstances, its management overlaps with that of the skin disease. Itch can also occur without associated skin diseases or primary skin lesions, but only with nonspecific lesions secondary to rubbing or scratching. Chronic itch with no or minimal skin changes can be secondary to important diseases, such as neurologic disorders, chronic renal failure, cholestasis, systemic infections, malignancies, and endocrine disorders, and may also result from exposure to some drugs. The search for the cause of pruritus usually requires a meticulous step-by-step assessment involving careful history taking as well as clinical examination and laboratory investigations. Few evidence-based treatments for pruritus are available. Topical therapy, oral histamine H(1) receptor antagonists, and phototherapy with UV radiation can target pruritus elicitation in the skin, whereas antiepileptic drugs, opioid receptor antagonists, and antidepressants can block signal processing in the CNS.

Role of spinal neurotransmitter receptors in itch: new insights into therapies and drug development

Targets for antipruritic therapies are now expanding from the skin to the central nervous system. Recent studies demonstrate that various neuronal receptors in the spinal cord are involved in pruritus. The spinal opioid receptor is one of the best-known examples. Spinal administration of morphine is frequently accompanied by segmental pruritus. In addition to μ-opioid receptor antagonists, κ-opioid receptor agonists have recently come into usage as novel antipruritic drugs, and are expected to suppress certain subtypes of itch such as hemodialysis- and cholestasis-associated itch that are difficult to treat with antihistamines. The gastrin-releasing peptide receptor in the superficial dorsal horn of the spinal cord has also received recent attention as a novel pathway of itch-selective neural transmission. The NMDA glutamate receptor appears to be another potential target for the treatment of itch, especially in terms of central sensitization. The development of NMDA receptor antagonists with less undesirable side effects on the central nervous system might be beneficial for antipruritic therapies. Drugs suppressing presynaptic glutamate-release such as gabapentin and pregabalin also reportedly inhibit certain subtypes of itch such as brachioradial pruritus. Spinal receptors of other neuromediators such as bradykinin, substance P, serotonin, and histamine may also be potential targets for antipruritic therapies, given that most of these molecules interfere not only with pain, but also with itch transmission or regulation. Thus, the identification of itch-specific receptors and understanding itch-related circuits in the spinal cord may be innovative strategies for the development of novel antipruritic drugs.