Pruritus--itching for a cause and relief?

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.

Dimethylglycine, a methionine metabolite, participates in the suppressive effect of methionine on 1-fluoro-2,4-dinitrobenzene-induced dermatitis

Allergic contact dermatitis (ACD) is a common skin disorder caused by contact with allergens. The optimal treatment for ACD is to avoid contact with allergens. However, in some cases, avoiding exposure is not possible when the allergens are unknown. Therefore, establishing treatment methods other than allergen avoidance is important. We previously reported that the continuous administration of methionine, an essential amino acid, in a mouse model of atopic dermatitis alleviated its symptoms. In the present study, we investigated the effect of methionine on a mouse model of ACD caused by 1-fluoro-2,4-dinitrobenzene (DNFB). Differences in the effect of methionine were observed in DNFB-induced ACD model mice based on the mouse strain used. This difference was attributed to the suppression of hepatic dimethylglycine (DMG) production, which is associated with the suppression of hepatic betaine-homocysteine methyltransferase (Bhmt) expression by ACD. Although we did not reveal the mechanism underlying DMG suppression, our study suggests the presence of interactions between the liver and skin in dermatitis, such as the regulation of hepatic metabolic enzyme expression in dermatitis and the alleviation of dermatitis symptoms by the hepatic metabolism status of DMG.

Complementary and integrative remedies in the treatment of chronic pruritus: A review of clinical trials

BACKGROUND

Chronic pruritus is one of the most common conditions in dermatology and a common manifestation in many systemic diseases. Since the etiology of chronic pruritus remains somewhat unknown, hence, conventional medications may not always show a good therapeutic response. This finding has led both investigators and patients to use herbal and complementary remedies for its treatment. The aim of this study was to review clinical trials in which herbal and complementary medicine was used in the control and treatment of chronic pruritus.

MATERIALS AND METHODS

In this study, we reviewed related articles in this domain, from 2000 to 2020. The search involved electronic databases including PubMed, Scopus, Web of Science, Cochrane, Google Scholar, and SID databases using the keywords "pruritus," "itch," "herb," "complementary medicine," "traditional medicine," "integrative medicine," and their related MeSH terms. Finally, we extracted the pertinent information from these articles and summarized the results.

RESULTS

The findings of this study showed that 17 clinical trials have been conducted till date in order to evaluate the efficacy of herbal remedies and complementary medicines in the treatment of chronic pruritus. Herbal remedies including turmeric, Fumaria parviflora, Avena sativa, capsaicin, sweet almond oil, peppermint oil, violet oil, vinegar, as well as manual therapies including aromatherapy, auricular acupressure, and acupuncture, were significantly effective in the treatment of chronic pruritus.

CONCLUSION

There are only a few studies published on the therapeutic efficacy of herbal remedies and complementary medicine in the treatment of chronic pruritus. Some have shown promising results. Therefore, more evidence-based studies are needed in order to determine if herbal remedies and complementary medicine could be an effective alternative or adjuvant treatment modality in chronic pruritus.

Itch in Organs Beyond the Skin

PURPOSE OF REVIEW

The purpose of this review was to explore mechanisms, causes, and therapies of itchy conditions involving organs beyond the skin including the eyes, ears, nose, and genital region.

RECENT FINDINGS

Conditions which cause itch in these locations vary from skin diseases that extend to these areas (i.e., atopic dermatitis, seborrheic dermatitis, and psoriasis) to allergic conditions (i.e., allergic rhinitis and conjunctivitis) and to neuropathic conditions that relate to afferent nerve fiber damage (i.e., lumbosacral radiculopathies in genital disease) as well as some psychological components. Similar to the skin, itch in these locations involves a complex interaction between epithelial cells, unmyelinated C nerve fibers, and cytokines. There is also a significant component of neural sensitization phenomena. Mechanisms of itch beyond the skin are currently an understudied topic that affects millions of patients. Future research should be done in order to further understand the pathophysiology of itch in these body sites.

Gastrointestinal delivery of propofol from fospropofol: its bioavailability and activity in rodents and human volunteers

BACKGROUND

Propofol is a safe and widely used intravenous anesthetic agent, for which additional clinical uses including treatment of migraine, nausea, pain and anxiety have been proposed (Vasileiou et al. Eur J Pharmacol 605:1-8, 2009). However, propofol suffers from several disadvantages as a therapeutic outside anesthesia including its limited aqueous solubility and negligible oral bioavailability. The purpose of the studies described here was to evaluate, in both animals and human volunteers, whether fospropofol (a water soluble phosphate ester prodrug of propofol) would provide higher propofol bioavailability through non-intravenous routes.

METHODS

Fospropofol was administered via intravenous, oral and intraduodenal routes to rats. Pharmacokinetic and pharmacodynamic parameters were then evaluated. Based on the promising animal data we subsequently conducted an oral and intraduodenal pharmacokinetic/pharmacodynamic study in human volunteers.

RESULTS

In rats, bioavailability of propofol from fospropofol delivered orally was found to be appreciable, in the order of around 20-70%, depending on dose. Availability was especially marked following fospropofol administration via the intraduodenal route, where bioavailability approximated 100%. Fospropofol itself was not appreciably bioavailable when administered by any route except for intravenous. Pharmacologic effect following oral fospropofol was confirmed by observation of sedation and alleviation of thermal hyperalgesia in the rat chronic constrictive injury model of neuropathic pain. The human data also showed systemic availability of propofol from fospropofol administration via oral routes, a hereto novel finding. Assessment of sedation in human volunteers was correlated with pharmacokinetic measurements.

CONCLUSIONS

These data suggest potential utility of oral administration of fospropofol for various therapeutic indications previously considered for propofol.

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.

Sensory neurons and circuits mediating itch

Chemicals that are used experimentally to evoke itch elicit activity in diverse subpopulations of cutaneous pruriceptive neurons, all of which also respond to painful stimuli. However, itch is distinct from pain: it evokes different behaviours, such as scratching, and originates from the skin or certain mucosae but not from muscle, joints or viscera. New insights regarding the neurons that mediate the sensation of itch have been gained from experiments in which gene expression has been manipulated in different types of pruriceptive neurons as well as from comparisons between psychophysical measurements of itch and the neuronal discharges and other properties of peripheral and central pruriceptive neurons.

The effect of epidural administration of dexamethasone on postoperative pain: a randomized controlled study in radical subtotal gastrectomy

Background

Epidurally administered dexamethasone may reduce the incidence and severity of postoperative pain. We investigated whether postoperative pain could be alleviated by preoperative or postoperative epidural dexamethasone administration in patients undergoing major abdominal surgery.

Methods

Ninety patients (age 30-77 with American Society of Anesthesiologists physical status I and II) undergoing radical subtotal gastrectomy were randomly allocated to three groups using computer generated randomization. In all groups, 10 ml of 0.25% ropivacaine was injected epidurally before the start and at the end of the operation. In Group I, a bolus ropivacaine epidural without dexamethasone was administered. In Group II, dexamethasone (5 mg) was added to the ropivacaine bolus epidural before the start of operation. In Group III, the same amount of dexamethasone was given with the ropivacaine epidural at the end of operation. Effort and resting VAS, the use of rescue analgesics and any complications noted during the procedure were evaluated.

Results

VAS and requirements of rescue analgesics were significantly lower in Groups II and III when compared to Group I. There were no difference in the incidence of nausea and vomiting between groups, but an itching sensation was frequent in Group III.

Conclusions

The administration of 5 mg of dexamethasone epidurallly, before or after operation, could reduce the pain and analgesic requirement after radical subtotal gastrectomy.

Vertebrate melanophores as potential model for drug discovery and development: a review

Drug discovery in skin pharmacotherapy is an enormous, continually expanding field. Researchers are developing novel and sensitive pharmaceutical products and drugs that target specific receptors to elicit concerted and appropriate responses. The pigment-bearing cells called melanophores have a significant contribution to make in this field. Melanophores, which contain the dark brown or black pigment melanin, constitute an important class of chromatophores. They are highly specialized in the bidirectional and coordinated translocation of pigment granules when given an appropriate stimulus. The pigment granules can be stimulated to undergo rapid dispersion throughout the melanophores, making the cell appear dark, or to aggregate at the center, making the cell appear light. The major signals involved in pigment transport within the melanophores are dependent on a special class of cell surface receptors called G-protein-coupled receptors (GPCRs). Many of these receptors of adrenaline, acetylcholine, histamine, serotonin, endothelin and melatonin have been found on melanophores. They are believed to have clinical relevance to skin-related ailments and therefore have become targets for high throughput screening projects. The selective screening of these receptors requires the recognition of particular ligands, agonists and antagonists and the characterization of their effects on pigment motility within the cells. The mechanism of skin pigmentation is incredibly intricate, but it would be a considerable step forward to unravel its underlying physiological mechanism. This would provide an experimental basis for new pharmacotherapies for dermatological anomalies. The discernible stimuli that can trigger a variety of intracellular signals affecting pigment granule movement primarily include neurotransmitters and hormones. This review focuses on the role of the hormone and neurotransmitter signals involved in pigment movement in terms of the pharmacology of the specific receptors.

Histamine-induced itch and its relationship with pain

Itch is one of the major complications of skin diseases. Although there are various substances that induce itch or pruritus, it is evident that histamine is the best known endogenous agent that evokes itch. Even though histamine-induced itch has been studied for some time, the underlying mechanism of itch is just beginning to emerge. Although various downstream signaling pathways of histamine receptors have been revealed, more studies are required to determine the cause of histamine-induced itch. It appears that itch and pain involve different neuronal pathways. Pain generally inhibits itch, which indicates an inter-communication between the two. Complex interactions between itch and pain may be expected based on reports on disease states and opioids. In this review, we discuss the molecular mechanism and the pharmacological aspects of histamine-induced itch. Especially, the underlying mechanism of TRPV1 (an anti-pruritus target) has been determined to some extent.

Subcutaneous naloxone for the prevention of intrathecal morphine induced pruritus in elective Caesarean delivery

The aim of this study was to assess the antipruritic efficacy of subcutaneous naloxone following intrathecal morphine administration. Fifty women undergoing elective Caesarean section using spinal anaesthesia were randomly allocated, in a double-blind study design, to receive either naloxone 400 microg or placebo as a subcutaneous injection at the end of surgery. Spinal anaesthesia was performed using 0.5% hyperbaric bupivacaine, 25 microg fentanyl and 150 microg of preservative-free morphine sulphate. The primary outcome measures were: incidence of pruritus, nausea and vomiting, and quality of analgesia. The incidence of pruritus and nausea and vomiting was not significantly different between the two groups. There was also no significant difference in postoperative analgesia between the two groups. We conclude that pruritus, following intrathecal fentanyl 25 microg and preservative-free morphine sulphate 150 microg, is not reduced by the addition of naloxone 400 microg administered subcutaneously on the completion of surgery.

Intrathecal sufentanil (1.5 microg) added to hyperbaric bupivacaine (0.5%) for elective cesarean section provides adequate analgesia without need for pruritus therapy

PURPOSE

We compared the effects of different doses of intrathecal sufentanil when administered together with hyperbaric bupivacaine for elective caesarean section.

METHODS

This was a prospective, randomized, double-blind, controlled trial involving 100 pregnant women, American Society of Anesthesiologists (ASA) I-II, who were scheduled for elective caesarean section under spinal anesthesia. The patients were assigned to four groups according to the dose of sufentanil used: no sufentanil (group I; placebo) or 1.5, 2.5, or 5.0 microg sufentanil (groups 2-4, respectively). In every group, the local anesthetic used was hyperbaric bupivacaine 0.5% (12.5 mg), and the total volume of the solution was 3.5 ml. The duration of complete analgesia, maternal side effects, and maternal/fetal outcomes were recorded. The duration of complete analgesia was defined as the time from intrathecal injection to a vernal analogue score (VAS) of more than 0.

RESULTS

No patient experienced intraoperative pain. The duration of complete analgesia was prolonged in all groups receiving opioids. The duration of the analgesia and the 0- to 6-h intravenous analgesic requirements were similar in the sufentanil groups. Moreover, the sufentanil groups had longer durations of complete analgesia than the placebo group. Pruritus was more frequent in the 2.5- and 5-microg sufentanil groups than in the 1.5-microg sufentanil and placebo groups. There were no differences among the groups in umbilical cord blood gases on in neonatal Apgar scores.

CONCLUSION

The addition of sufentanil 1.5 and 2.5 microg to hyperbaric bupivacaine provided adequate anesthesia for caesarean delivery and good postoperative analgesia. In addition, the incidence of pruritus was significantly lower in the 1.5-microg sufentanil group when compared with that in the 2.5- and 5-microg groups.

Prevalence and predictors of psychosocial morbidity in patients with chronic pruritic skin diseases

BACKGROUND

Itch is a major symptom of many skin diseases and causes patients considerable distress, adversely affecting quality of life. Feelings of helplessness and lack of control can influence the perceived itch and psychosocial complaints.

OBJECTIVES

To determine the prevalence of psychosocial morbidity among patients with pruritic skin diseases, and the influence of itch-related variables, coping strategies, and demographic variables on psychosocial morbidity.

PATIENTS AND METHODS

One hundred and sixty-eight patients with pruritic skin diseases from five hospitals in the Netherlands participated in the study. Skin-related psychosocial morbidity was measured with the Adjustment to Chronic Skin Diseases questionnaire (ACS); general psychosocial morbidity was measured with the Symptom Checklist-90 (SCL-90). The frequency and intensity of itching and scratching was recorded in diaries. Itch-related coping was measured with the Itching Cognitions Questionnaire (ICQ). Multiple regression analyses were used.

RESULTS

Patients with pruritic skin diseases had higher SCL-90 scores than a healthy Dutch population. All patients had psychosocial complaints as measured with the ACS. Thirty-nine per cent of the variance in skin-related psychosocial morbidity was explained by 'catastrophizing and helpless coping'; another 11% was explained by itching and scratching. Age and sex together explained another 10%. The frequency of itching and scratching (11%), 'catastrophizing and helpless coping' (19%) and skin-related psychosocial morbidity (10%) explained the variance in general psychosocial morbidity.

CONCLUSIONS

Patients with a pruritic skin disease have a high level of psychosocial morbidity. Catastrophizing and helpless coping are the most important predictors of psychosocial morbidity, with itching, scratching and demographic variables having a limited influence.

The cutaneous serotoninergic/melatoninergic system: securing a place under the sun

It was recently discovered that mammalian skin can produce serotonin and transform it into melatonin. Pathways for the biosynthesis and biodegradation of serotonin and melatonin have been characterized in human and rodent skin and in their major cellular populations. Moreover, receptors for serotonin and melatonin receptors are expressed in keratinocytes, melanocytes, and fibroblasts and these mediate phenotypic actions on cellular proliferation and differentiation. Melatonin exerts receptor-independent effects, including activation of pathways protective of oxidative stress and the modification of cellular metabolism. While serotonin is known to have several roles in skin-e.g., pro-edema, vasodilatory, proinflammatory, and pruritogenic-melatonin has been experimentally implicated in hair growth cycling, pigmentation physiology, and melanoma control. Thus, the widespread expression of a cutaneous seorotoninergic/melatoninergic syste,m(s) indicates considerable selectivity of action to facilitate intra-, auto-, or paracrine mechanisms that define and influence skin function in a highly compartmentalized manner. Notably, the cutaneous melatoninergic system is organized to respond to continuous stimulation in contrast to the pineal gland, which (being insulated from the external environment) responds to discontinuous activation by the circadian clock. Overall, the cutaneous serotoninergic/melatoninergic system could counteract or buffer external (environmental) or internal stresses to preserve the biological integrity of the organ and to maintain its homeostasis.-Slominski, A. J., Wortsman, J., Tobin, D. J. The cutaneous serotoninergic/melatoninergic system: securing a place under the sun.

Prophylactic ondansetron does not reduce the incidence of itching induced by intrathecal sufentanil

PURPOSE

Postoperative itching after intrathecal (IT) narcotics may be a difficult and important problem for both the anesthesiologist and the patient in the postanesthetic care unit. Since some studies have reported success in preventing itching with ondansetron, we designed a prospective, randomized, double-blinded, and controlled study to test whether prophylactic iv ondansetron effectively reduces the incidence of IT sufentanil-induced pruritus.

METHODS

Thirty-four patients (ASA I-III, age 18-74 yr) underwent ambulatory surgery after spinal anesthesia with IT lidocaine (15-100 mg) and IT sufentanil (10 microg). The patients were randomized into two groups to receive iv either 4 mL saline (n = 13) or 8 mg ondansetron (n = 21) before the IT injection. The incidence of pruritus and other variables was recorded. Pruritus scores were obtained with a verbal analogue score with 0 meaning none and 10 the worst itching that the patient could imagine. Statistical difference was assumed if P < 0.05.

RESULTS

Ondansetron did not reduce the incidence of pruritus (77 vs 81%) compared to placebo (P = 1.000). The pruritus scores (4.4 vs 3.6) of the two groups were not significantly different (P = 0.670).

CONCLUSIONS

There are contradictory findings in the literature regarding the effectiveness of ondansetron in preventing narcotic-induced itching. Although some studies have indicated that ondansetron could prevent this side effect of IT narcotics, a recent report suggested that ondansetron is not effective in preventing narcotic-induced itching (sufentanil-morphine) after a Cesarean section. In the present study we obtained similar, negative results.

The effect of celecoxib on intrathecal morphine-induced pruritus in patients undergoing Caesarean section

Pruritus associated with intrathecal opioid administration is particularly common in pregnancy. Nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce the severity of this pruritus but have undesirable side effects. The recent development of drugs that can specifically inhibit the cyclooxygenase 2 isoenzyme have become an attractive alternative. This study was designed to evaluate the efficacy of such a drug (celecoxib) in reducing intrathecal opioid-induced pruritus in a randomised double-blinded study of 60 women undergoing Caesarean section. All of them received spinal anaesthesia with 3 ml of 0.5% hyperbaric bupivacaine and 0.3 mg preservative-free morphine. After delivery of the baby, they received either oral celecoxib 200 mg or placebo. Visual analogue scores for pain and pruritus were measured at 30 min, 2, 4, 8, and 24 h. There was no difference in the severity and onset of pain and pruritus between the two groups. Timing of administration, inadequate dosing and possible altered pharmacokinetics in pregnancy may explain the lack of efficacy.

Should epidural diamorphine be withheld after caesarean section from women who suffer severe pruritus following intrathecal fentanyl?

Pruritus following neuraxial opioids in 37 women undergoing caesarean section under combined epidural-spinal anaesthesia was investigated. All women received intrathecal fentanyl for intra-operative analgesia followed by epidural diamorphine for postoperative analgesia, when pain returned. Pruritus was assessed using a verbal rating scale at the end of surgery and again 24-36 h postoperatively. There was no relationship between pruritus experienced after intrathecal fentanyl and that experienced after epidural diamorphine. We conclude that there is no reason to withhold epidural diamorphine from women who have previously experienced severe itching after intrathecal fentanyl.

Characterization of scratching responses in rats following centrally administered morphine or bombesin

The aim of this study was to characterize scratching behavior elicited by central administration of morphine or bombesin in rats, and to determine the role of opioid receptors in scratching induced by both pruritogenic agents. Central administration included intracisternal (i.c.), intrathecal (i.t.), and intracerebroventricular (i.c.v.) routes. Scratching events made with hind paws were counted by observers blinded to treatment conditions. Intracisternal morphine (0.01-0.1 microg) produced dose-dependent increases in scratching; the maximum response to i.c. morphine 0.1 microg was approximately 500 scratches within a 1-hour period. Neither i.t. nor i.c.v. morphine significantly increased scratching. Bombesin (0.01-0.32 microg) elicited robust scratching following i.c. administration. The maximum response to i.c. bombesin 0.32 microg was approximately 4000 scratches within a 1-hour period. Both i.t. and i.c.v. bombesin produced profound scratching at similar doses. Antagonist studies confirmed that mu-opioid receptors selectively mediate i.c. morphine-induced scratching. However, selective mu-, kappa-, and delta-opioid antagonists did not attenuate i.c. bombesin-induced scratching. These results demonstrate that morphine and bombesin elicit scratching through different receptor mechanisms, at different central sites, and to different degrees.

Intrathecal lidocaine and sufentanil shorten postoperative recovery after outpatient rectal surgery

PURPOSE

A short recovery time for same day surgery is important to the patient and the hospital. A prospective, randomized, double-blinded study in the postanesthetic care unit was designed to compare the recovery time from spinal anesthesia with low-dose intrathecal (IT) lidocaine and sufentanil to that with IT lidocaine alone. The incidence of adverse effects was also assessed.

METHODS

Forty-nine patients (ASA I-III, age 20-69 yr) underwent spinal anesthesia for rectal surgery. The patients were randomized into two groups. One group (n = 28) received low-dose IT lidocaine (15 mg) and sufentanil (10 microg) and the other group (n = 21) received IT lidocaine (50 mg). The time to ambulation, the incidence of pruritus, and other variables were recorded. Statistical difference was assumed if P < 0.05.

RESULTS

Our results show a significantly shorter ambulation time (120 +/- 26 min) after IT low-dose lidocaine (15 mg) and 10 microg sufentanil vs 50 mg IT lidocaine (162 +/- 32 min, P < 0.0001). Patients who received IT lidocaine and sufentanil recovered faster. Fifty percent of the patients who received IT sufentanil suffered from pruritus.

CONCLUSION

IT lidocaine (15 mg) and sufentanil resulted in a shorter time to ambulation compared to IT lidocaine (50 mg) alone and provided excellent anesthesia despite its disadvantage of pruritus.

Intrathecal fentanyl-induced pruritus during labour: the effect of prophylactic ondansetron

Fentanyl is commonly used for spinal analgesia during labour but it is associated with a high incidence of pruritus. This randomised, double-blind, placebo-controlled study was performed to evaluate the effect of prophylactic ondansetron on the incidence and severity of pruritus among parturients receiving intrathecal fentanyl as part of combined spinal-epidural analgesia. Seventy-three women were randomised to receive either saline placebo (group P, n = 25), ondansetron 4 mg (group O4, n = 23) or ondansetron 8 mg (group O8, n = 25) intravenously before intrathecal fentanyl 25 micrograms and bupivacaine 2 mg. The incidence and severity of pruritus were measured using a verbal rating and a visual analogue scale, and by the requirement for rescue anti-pruritic medication (naloxone). The overall incidence of pruritus was 95% (group P 100%, group O4 95%, group O8 90%). There were no significant differences between groups for severity of pruritus or requirement for treatment (naloxone given to 45%, 28% and 35% of groups P, O4 and O8 respectively). Secondary outcomes such as the incidence of headache, pain and nausea were not significantly different between groups. We conclude that prophylactic ondansetron 4 or 8 mg intravenously was ineffective in reducing the incidence or severity of intrathecal fentanyl-induced pruritus during labour.

Paroxetine in the treatment of severe non-dermatological pruritus: a randomized, controlled trial

Severe pruritus may be an idiopathic phenomenon or associated with advanced systemic disease. It is one of the most distressing and difficult to treat symptoms. Uncontrolled studies have suggested that, in patients experiencing severe pruritus, paroxetine appeared to have a rapid anti-pruritic effect. This study was a prospective double-blind, randomized within patient comparison of paroxetine and placebo. The intensity of pruritus was measured subjectively with a numerical analogue scale. The primary endpoint of the trial was the mean pruritus score, measured for seven days after randomization and after cross-over. The secondary endpoint was individual global response to the treatment. Response was defined as at least 50% reduction of intensity of pruritus in the last three days of the treatment period vs. baseline. Adverse effects and patient satisfaction and preferences were also recorded. Twenty-six patients were included in the study; 17 of them had solid tumors, 4 had hematological malignancies and 5 had various nonmalignant or idiopathic conditions. Eight patients had drug-induced pruritus (none opioid-induced), 7 patients had paraneoplastic pruritus and 3 had cholestatic pruritus. After a run-in period, patients were randomly assigned to treatment with 20 mg paroxetine or placebo. The crossover took place after 7 days. Two patients discontinued treatment because of adverse effects of paroxetine. Twenty-four patients treated with paroxetine had lower pruritus intensity scores over the 7 treatment periods (mean+/-SE=5.2+/-0.32) as compared to placebo (mean+/-SE=6.0+/-0.32). Mean difference between placebo and paroxetine was 0.78 (95% CI=0.37-1.19). Nine of twenty-four patients (37.5%) fulfilled criteria of response. The onset of anti-pruritic action was observed usually after 2-3 days, irrespective of the order of treatment. The outcome of this study indicates that paroxetine is effective in the treatment of severe pruritus of non-dermatological origin.

Neuraxial opioid-induced pruritus: a review

When intrathecal and epidural opioids are administered, pruritus occurs as an unwanted and troublesome side effect. The reported incidence varies between 30% and 100%. The exact mechanisms of neuraxial opioid-induced pruritus remain unclear. Postulated mechanisms include the presence of an "itch center" in the central nervous system, medullary dorsal horn activation, and antagonism of inhibitory transmitters. The treatment of intrathecal opioid-induced pruritus remains a challenge. Many pharmacological therapies, including antihistamines, 5-HT(3)-receptor antagonists, opiate-antagonists, propofol, nonsteroid antiinflammatory drugs, and droperidol, have been studied. In this review, we will summarize pathophysiological and pharmacological advances that will improve understanding and ultimately the management of this troublesome problem.

Activation of kappa-opioid receptors inhibits pruritus evoked by subcutaneous or intrathecal administration of morphine in monkeys

Pruritus (itch sensation) is the most common side effect associated with spinal administration of morphine given to humans for analgesia. A variety of agents have been proposed as antipruritics with poorly understood mechanisms and they are effective with variable success. kappa-Opioid agonists possess several actions that are opposite to micro -opioid agonists. We proposed to investigate the role of kappa-opioid receptors (KORs) in morphine-induced scratching and antinociception in monkeys. Scratching responses were counted by observers blinded to treatment. Antinociception was measured by a warm water (50 degrees C) tail-withdrawal assay. Pretreatment with low doses of trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl]-cyclohexyl)-benzeneacetamide (U-50488H) (0.032-0.18 mg/kg s.c.), a selective KOR agonist, dose dependently suppressed the s.c. morphine dose-effect curve for scratching and potentiated s.c. morphine-induced antinociception. In addition, s.c. U-50488H attenuated i.t. morphine (10 and 32 micro g)-induced scratching while maintaining or enhancing i.t. morphine-induced antinociception. The combination of s.c. or i.t. morphine with low doses of U-50488H did not cause sedation. More importantly, pretreatment with 3.2 mg/kg nor-binaltorphimine, a selective KOR antagonist, blocked the effects of s.c. U-50488H on both s.c. and i.t. morphine-induced scratching. These results indicate that activation of KOR attenuates morphine-induced scratching without interfering with antinociception in monkeys. This mechanism-based finding provides functional evidence in support of the clinical potential of KOR agonists as antipruritics in the presence of MOR agonist-induced pruritus.

Extrahepatic manifestations of cholestasis

Pruritus, fatigue and metabolic bone disease represent three major extrahepatic manifestations of chronic cholestatic liver disease that considerably affect the patient's quality of life. The present article reviews pathogenetic aspects of and current therapeutic approaches to extrahepatic manifestations of cholestatic liver disease. Pathogenesis of pruritus of cholestasis remains poorly understood. The involvement of putative peripherally acting pruritogens, such as bile acids or endogenous opioids, is being discussed. More recently, central mechanisms, including an increased central opioidergic tone and pertubations in the serotonergic system have been proposed. Treatment of the underlying disease is beneficial also for the control of cholestasis-associated pruritus. Current therapeutic recommendations include ursodeoxycholic acid, cholestyramine, rifampicin and opioid antagonists. Liver transplantation may be indicated when severe pruritus is refractory to medical treatment. Fatigue is being recognized as the most frequent and one of the most disabling complaints in chronic cholestasis. Fatigue is presumably of central origin and its association with other neuropsychiatric disorders (e.g. depression, obsessive-compulsive disorders) is consistent with defective central neurotransmission. No specific therapies are currently available and a healthy lifestyle, regular sleep and avoidance of unnecessary stress and other precipiting factors are recommended. Antidepressant therapy may be warranted in selected patients. Osteopenia and osteoporosis are common in chronic cholestatic liver disease, whereas osteomalacia is rare. The pathophysiology of cholestasis-associated metabolic bone disease is regarded as multifactorial. Therapeutic recommendations include regular exercise, calcium and vitamin D supplementation in late stage disease, hormone replacement therapy in postmenopausal women and bisphosphonates.

Opioid antagonists: a review of their role in palliative care, focusing on use in opioid-related constipation

Opioid antagonists have well-established indications in the reversal of life-threatening opioid toxicity, but also hold considerable promise for other applications in palliative care practice, particularly management of opioid-related constipation. We briefly review current understanding of opioid receptors, focusing on their complex role in gastrointestinal physiology. We summarize the pharmacology, conventional indications, and clinical usage of three major groups of opioid antagonists, including a promising new peripherally acting agent, methylnaltrexone, which is not commercially available. We suggest an approach to administering opioid antagonists for reduction of life-threatening opioid toxicity in patients with pain. The literature on opioid-induced constipation and its treatment with opioid-antagonists is reviewed in detail. Finally, other potential uses of opioid antagonists in palliative care are described, especially strategies for reducing such opioid side effects as nausea and pruritus and for improving analgesia or reducing tolerance by concomitantly administrating both an opioid agonist and low dosages of an antagonist.

Patient-controlled analgesia: an appropriate method of pain control in children

Patient-controlled analgesia (PCA) is an analgesic technique originally used in adults but now with an established role in paediatric practice. It is well tolerated in children as young as 5 years and has uses in postoperative pain as well as burns, oncology and palliative care. The use of background infusions is more frequent in children and improves efficacy; however, it may increase the occurrence of adverse effects such as nausea and respiratory depression. Monitoring involves measurement of respiratory rate, level of sedation and oxygen saturation. Efficacy is assessed by self-reporting, visual analogue scales, faces pain scales and usage patterns. This is optimally performed both at rest and on movement. The selection of opioid used in PCA is perhaps less critical than the appropriate selection of parameters such as bolus dose, lockout and background infusion rate. Moreover, opioid choice may be based on adverse effect profile rather than efficacy. The concept of PCA continues to be developed in children, with patient-controlled epidural analgesia, subcutaneous PCA and intranasal PCA being recent extensions of the method. There may also be a role for patient-controlled sedation. PCA, when used with adequate monitoring, is a well tolerated technique with high patient and staff acceptance. It can now be regarded as a standard for the delivery of postoperative analgesia in children aged >5 years.

Understanding pruritus in systemic disease

Many pruritic conditions do not originate in the skin, but are the result of systemic abnormality. Among the diseases that can cause pruritus are renal insufficiency, cholestasis, Hodgkin's lymphoma, polycythemia vera, solid tumors, and many others. Other pruritic conditions appear to be iatrogenic; opioid-induced pruritus may be the most important in palliative medicine. Successful treatment of the underlying condition usually relieves itch. But, with time, many diseases progress and treatment of the cause will be impossible. Topical treatments may be of limited value. Strategies involving systemic treatments include use of antidepressants, oral opioid antagonists, or cholestyramine. There is no one cure for all pruritic symptoms. Better understanding of mechanisms of pruritus may help develop better treatments.

Itch-associated responses of afferent nerve innervating the murine skin: different effects of histamine and serotonin in ICR and ddY mice

To assess the itch-associated response of primary afferents innervating the murine skin in vivo, dose-response curves and time-courses for itch-scratching and cutaneous nerve firing responses to intradermal injections of pruritogens (histamine and serotonin) were compared in ICR and ddY mice. Serotonin increased the itch-scratch response and cutaneous nerve firing in either ICR or ddY mice. Histamine increased these two responses in ICR, but not ddY, mice. The dose-response curves and time-courses for serotonin- and histamine-induced nerve firing were similar to those for the itch-scratch response. The results suggest that cutaneous nerve firing evoked by peripherally given pruritogens includes the itch-associated response.

An experimental itch model in monkeys: characterization of intrathecal morphine-induced scratching and antinociception

BACKGROUND

The most common side effect of spinal opioid administration is pruritus, which has been treated with a variety of agents with variable success. Currently, there are few animal models developed to study this side effect. The aim of this study was to establish a nonhuman primate model to pharmacologically characterize the effects of intrathecal administration of morphine.

METHODS

Eight adult rhesus monkeys were used. Scratching responses were videotaped and counted by observers who were blinded to experimental conditions. Antinociception was measured by a warm-water (50 degrees C) tail-withdrawal assay. The dose-response of intrathecal morphine (1-320 microg) for both scratching and antinociception in all subjects was established. An opioid antagonist, nalmefene, was administered either intravenously or subcutaneously to assess its efficacy against intrathecal morphine.

RESULTS

Intrathecal morphine (1-32 microg) increased scratching in a dose-dependent manner. Higher doses of intrathecal morphine (10-100 microg) produced thermal antinociception in a dose-dependent manner. On the other hand, nalmefene (10-32 microg/kg intravenously) attenuated maximum scratching responses among subjects. Pretreatment with nalmefene (32 microg/kg subcutaneously) produced approximately 10-fold rightward shifts of intrathecal morphine dose-response curves for both behavioral effects.

CONCLUSIONS

These data indicate that intrathecal morphine-induced scratching and antinociception are mediated by opioid receptors. The magnitude of nalmefene antagonism of intrathecal morphine is consistent with microL opioid receptor mediation. This experimental itch model is useful for evaluating different agents that may suppress scratching without interfering with antinociception. It may also facilitate the clarification of mechanisms underlying these phenomena.

The effect of rectal diclofenac on pruritus in patients receiving intrathecal morphine

In this prospective randomised study, pruritus and pain were evaluated in patients undergoing abdominal surgery in which intrathecal morphine was administered. Each patient received intrathecal morphine 0.3 mg prior to induction, followed by a standard anaesthetic. The patients were randomly allocated to one of two groups. One group received 100 mg of rectal diclofenac immediately post-induction. Patients receiving diclofenac had significantly lower pruritus scores at 30 min (p = 0.0076), 2, 4, 8 and 24 h postoperatively, as well as significantly reduced pain scores at each time point (p < 0.0001 at each study interval). Morphine consumption in the first 24 h was also significantly lower in this group. In conclusion, rectal administration of diclofenac significantly reduces the incidence and severity of postoperative pruritus. It also significantly reduces pain and further analgesic requirements postoperatively.

The effect of intravenous ketoprofen on postoperative epidural sufentanil analgesia in children

We compared the effect of IV ketoprofen and placebo as an adjuvant to epidural sufentanil analgesia after major surgery. We used a prospective, randomized, double-blinded, placebo-controlled, parallel-group study design in 54 children aged 1-15 yr who received a standardized anesthetic. Either IV ketoprofen or saline was administered in addition to an epidural sufentanil infusion, which was adjusted as required clinically. The study drug infusions were discontinued when pain scores were <3 on 0-10 scale for 6 h at a sufentanil infusion rate of 0.03 microg x kg(-1) x h(-1). Children in the ketoprofen group had a better analgesic effect, as shown by decreased need for sufentanil (mean [10th-90th percentiles] 8.3 [3.1-15.1] microg/kg vs 12.5 [6.2-18.9] microg/kg; P = 0.002) and earlier possibility to discontinuation of the epidural sufentanil (11 [46%] vs 3 [13%]; P = 0.014) before the end of the 72-h study period. In the ketoprofen group, median (range) pain scores were lower during activity at 24 h (2 [0-5] vs 5 [0-7]; P = 0.01) and at 72 h (0 [0-3] vs 2 [0-6]; P = 0.033), and fewer children had inadequate pain relief during activity at 24 h (0 vs 5; P = 0.037). Children who received ketoprofen required fewer infusion rate adjustments (12 [4-20] vs 17 [6-42]; P = 0.016). In the ketoprofen group, the incidence of desaturation (1 [4%] vs 6 [26%]; P = 0.035) and fever (3 [12%] vs 11 [48%]; P = 0.008) was less than that in the placebo group. We conclude that ketoprofen improved postoperative pain in children.

IMPLICATIONS

We compared the effect of the IV nonsteroidal antiinflammatory drug ketoprofen versus placebo as adjuvants to epidural opioid analgesia with sufentanil. The continuous IV nonsteroidal antiinflammatory drug improved pain after major surgery in children receiving an epidural opioid. Although ketoprofen reduced epidural sufentanil requirements, the incidence of opioid-related adverse effects was not changed.

Antipruritic effect of millimeter waves in mice: evidence for opioid involvement

In our previous studies, exposure of mice to millimeter waves (MW) increased the duration of anesthesia caused by either ketamine or chloral hydrate, and this effect was blocked by naloxone. To further characterize the biological effects of MW, we have chosen a new animal model of experimental itch. Male Swiss albino mice were injected s.c. in the rostral part of the back with the pruritogenic agent, compound 48/80, with or without naloxone pretreatment. After a 15-min exposure of mice to MW (frequency, 61.22 GHz; incident power density, 15 mW/cm2), the number of scratches of the injected site was counted for 90 min post-injection. MW inhibited the scratching activity of mice by more than 2 times in comparison with the sham-exposed controls (p<0.005). Pretreatment of animals with (-)-naloxone (0.1-1.0 mg/kg, i.p.) suppressed the antipruritic effect of MW in a dose-dependent manner, while the inactive enantiomer (+)-naloxone at 1 mg/kg did not alter the effect. These results suggest that MW trigger the release of opioids in exposed subjects.

What's new with intrathecal narcotics for labor analgesia

The profound analgesic properties of intrathecal narcotics without motor blockade make them an excellent choice for pain relief during the first stage of labor. Recent studies have attempted to define more clearly the pharmacology of commonly used agents. In this review we shall outline some of these advances and discuss their impact on labor.

Pain Management

Postoperative pain management is essential and must be approached as an integral part of the perioperative care. It should be systematic and based on sound physiological and pharmacological principles. The intra operative management of pain is crucial, because there is perhaps an important role for preemptive analgesia. Because of its unique nature, pain is difficult to assess; for good results, adequate and repeated assessment are vital. The literature also points to the detrimental ef fects of inadequate pain control. There are a variety of methods available for pain management. In choosing a method, various factors need to be considered includ ing: (1) physician skill, (2) knowledge of analgesics and routes of administration, (3) patient and clinically re lated circumstances, (4) the availability of an environ ment supportive of effective pain management, and (5) the knowledge and skill of staff to assess and monitor patients. These need to be considered along with the risk-benefits and cost-benefit of the various drugs and techniques. The cornerstone of therapy is opioids, which can be administered by a variety of routes. The use of thoracic epidural analgesia (TEA) with opioids and local anesthetics is highly beneficial, especially in high-risk patients. The aim should be to provide all patients a balanced analgesic regimen based on the identification of multiple mechanisms involved in postoperative pain.