Antihistamines

Histaminergic regulation of food intake

Histamine is a biogenic amine that acts as a neuromodulator within the brain. In the hypothalamus, histaminergic signaling contributes to the regulation of numerous physiological and homeostatic processes, including the regulation of energy balance. Histaminergic neurons project extensively throughout the hypothalamus and two histamine receptors (H1R, H3R) are strongly expressed in key hypothalamic nuclei known to regulate energy homeostasis, including the paraventricular (PVH), ventromedial (VMH), dorsomedial (DMH), and arcuate (ARC) nuclei. The activation of different histamine receptors is associated with differential effects on neuronal activity, mediated by their different G protein-coupling. Consequently, activation of H1R has opposing effects on food intake to that of H3R: H1R activation suppresses food intake, while H3R activation mediates an orexigenic response. The central histaminergic system has been implicated in atypical antipsychotic-induced weight gain and has been proposed as a potential therapeutic target for the treatment of obesity. It has also been demonstrated to interact with other major regulators of energy homeostasis, including the central melanocortin system and the adipose-derived hormone leptin. However, the exact mechanisms by which the histaminergic system contributes to the modification of these satiety signals remain underexplored. The present review focuses on recent advances in our understanding of the central histaminergic system's role in regulating feeding and highlights unanswered questions remaining in our knowledge of the functionality of this system.

Use of cyproheptadine hydrochloride (HCl) to reduce neuromuscular hypertonicity in stroke survivors: A Randomized Trial: Reducing Hypertonicity in Stroke

OBJECTIVES

The goal of this study was to examine how the administration and dosing of the anti-serotonergic medication cyproheptadine hydrochloride (HCl) affects involuntary muscle hypertonicity of the spastic and paretic hands of stroke survivors.

MATERIALS AND METHODS

A randomized, double-blinded, placebo-controlled longitudinal intervention study was performed as a component of a larger clinical trial. 94 stroke survivors with chronic, severe hand impairment, rated as levels 2 or 3 on the Chedoke-McMaster Stroke Assessment Stage of Hand (CMSA-H), were block randomized to groups receiving doses of cyproheptadine HCl or matched doses of placebo. Doses were increased from 4 mg BID to 8 mg TID over 3 weeks. Outcomes were assessed at baseline and after each of the three weeks of intervention. Primary outcome measure was grip termination time; other measures included muscle strength, spasticity, coactivation of the long finger flexors, and recording of potential adverse effects such as sleepiness and depression.

RESULTS

89 participants (receiving cyproheptadine HCl: 44, receiving placebo: 45) completed the study. The Cyproheptadine group displayed significant reduction in grip termination time, in comparison with the Placebo group (p<0.05). Significant change in the Cyproheptadine group (45% time reduction) was observed after only one week at the 4mg BID dosage. The effect was pronounced for those participants in the Cyproheptadine group with more severe hand impairment (CMSA-H level 2) at baseline. Conversely, no significant effect of Group * Session interaction was observed for spasticity (p=0.6) or coactivation (p=0.53). There were no significant changes in strength (p=0.234) or depression (p=0.441) during the trial.

CONCLUSIONS

Use of cyproheptadine HCl was associated with a significant reduction in relaxation time of finger flexor muscles, without adversely affecting voluntary strength, although spasticity and coactivation were unchanged. Decreasing the duration of involuntary flexor activity can facilitate object release and repeated prehensile task performance.

REGISTRATION

Clinical Trial number: NCT02418949.

New Horizons: Is Obesity a Disorder of Neurotransmission?

Obesity is a disease of the nervous system. While some will view this statement as provocative, others will take it as obvious. Whatever our side is, the pharmacology tells us that targeting the nervous system works for promoting weight loss. It works, but at what cost? Is the nervous system a safe target for sustainable treatment of obesity? What have we learned-and unlearned-about the central control of energy balance in the last few years? Herein we provide a thought-provoking exploration of obesity as a disorder of neurotransmission. We discuss the state of knowledge on the brain pathways regulating energy homeostasis that are commonly targeted in anti-obesity therapy and explore how medications affecting neurotransmission such as atypical antipsychotics, antidepressants, and antihistamines relate to body weight. Our goal is to provide the endocrine community with a conceptual framework that will help expending our understanding of the pathophysiology of obesity, a disease of the nervous system.

[Antihistamines for treating pruritus : The end of an era?]

Antihistamines, mostly H1 antihistamines, administered both topically and systemically, are among the most widely used drugs. While systemically applicable antihistamines are usually taken orally or administered intravenously, while local therapy is used on the eye, nose or skin. Systemic antihistamines are most frequently used during the pollen season (hay fever, asthma) or are used all year round, e.g., for house dust and animal hair allergies. Furthermore, urticaria is a major indication for the use of H1 antihistamines, also as long-term treatment. Although H1 antihistamines are not licensed for pruritus and prurigo, they are frequently used in these diseases. However, since in many diseases with pruritus and prurigo the histamine receptor does not play a decisive role in the pathogenesis of pruritus, they show limited efficacy. Two Cochrane reviews have not shown any significant antipruritic effects of H1 antihistamine treatment in atopic eczema as single therapy or in combination, e.g., with topical glucocorticosteroid therapy. A retrospective case series with a so-called high-dose antihistamine therapy with non-sedating antihistamines was effective in treating chronic pruritus. This article summarizes the possibilities of systemic antihistamines in pruritus, especially with regard to limitations and future prospects.

Substance P and neurokinin 1 receptor are new targets for the treatment of chronic pruritus

BACKGROUND

Chronic pruritus is a distressing symptom associated with various dermatological conditions and systemic diseases. Current treatment options are often inadequate, resulting in impaired quality of life for many patients. An understanding of the underlying mechanisms of itch across pruritic conditions is important for development of effective, targeted treatments for chronic pruritus.

OBJECTIVES

To provide an overview of the pathogenesis of chronic pruritus, focusing on the role of substance P (SP) and neurokinin 1 receptor (NK₁ R) in itch signalling, and to describe data supporting NK₁ R antagonism as a potential strategy for the treatment of chronic pruritus.

METHODS

A PubMed search was conducted to determine what data were available that investigated the role of SP and NK₁ R in itch signalling.

RESULTS

SP is a neuropeptide that is a mediator of itch signalling. One of the target receptors for SP is NK₁ R, which is expressed in the central nervous system and on multiple cell types involved in the initiation and transmission of itch. Studies demonstrating that SP and NK₁ R are overexpressed across multiple chronic itch-inducing conditions and that NK₁ R antagonism disrupts itch signalling and reduces itch provide a rationale for targeting this pathway as a potential treatment of chronic pruritus across multiple diseases.

CONCLUSIONS

A large and growing body of evidence, including recent phase II clinical studies of NK₁ R antagonists, demonstrate that SP and NK₁ R play an important role in itch signalling. Additional studies are ongoing to further evaluate the use of NK₁ R antagonists for the treatment of chronic pruritus. What's already known about this topic? Chronic pruritus has a significant impact on quality of life. Current treatment options for chronic pruritus are inadequate. Substance P (SP) and neurokinin 1 receptor (NK₁ R) have been shown to play a role in itch signalling, and may be a rational target for addressing chronic pruritus. NK₁ R antagonists are being evaluated as potential treatment for chronic pruritus. What does this study add? This review provides a compilation of the most up-to-date data elucidating the role of SP and NK₁ R in itch signalling, which supports targeting this pathway as a potential treatment of chronic pruritus. NK₁ R antagonism disrupts itch signalling and reduces itch. A summary of the latest data on NK₁ R antagonists in the treatment of pruritus is provided.

Oral H1 antihistamines as monotherapy for eczema

BACKGROUND

Eczema is a common skin disease in many countries, and although the majority of cases of eczema occur before the age of five years and often resolve during childhood or adolescence, it can also persist into adulthood. Itch is the most important aspect of eczema, often impacting significantly on the quality of life of an affected individual.

OBJECTIVES

To assess the effects of oral antihistamines (H1 antagonists) as monotherapy in children and adults with eczema.

SEARCH METHODS

We searched the following databases up to March 2012: the Cochrane Skin Group Specialised Register, CENTRAL in The Cochrane Library (2012, Issue 3), MEDLINE (from 1946), EMBASE (from 1974), and LILACS (from 1982). We examined the reference lists of excluded studies in order to identify further references to relevant trials. We searched trials registers for ongoing and unpublished trials. We also handsearched the abstracts of the International Research Workshops on eczema, as well as the conference proceedings of the European Academy of Dermatology and Venereology (EADV) and the European Academy of Allergology and Clinical Immunology (EAACI), from 2000 to 2011.

SELECTION CRITERIA

We sought to include randomised controlled trials that assessed the effects and safety of oral H1 antihistamines as monotherapy in children and adults with eczema. We excluded studies that compared an antihistamine versus another antihistamine and had no placebo control arm. We also excluded topical antihistamines and oral H1 antihistamines as 'add-on' therapy and studies using any concomitant therapy other than emollients or moisturisers, principally because some of these forms of concomitant therapy may be considered treatment modifiers in assessments of the effects of antihistamines on eczema.

DATA COLLECTION AND ANALYSIS

Our search retrieved 409 references to studies. Based on assessments of their titles, abstracts, or both, we excluded all except 36 of these studies. After evaluation of the full text of each report, we excluded a further 35 studies, and 1 study is awaiting classification pending a response from the trial investigators.

MAIN RESULTS

No randomised controlled trials met our inclusion criteria.

AUTHORS' CONCLUSIONS

There is currently no high-level evidence to support or refute the efficacy or safety of oral H1 antihistamines used as monotherapy for eczema. Because most of the studies allowed the use of concomitant medications and involved multi-therapeutic approaches, meaningful assessments of the individual effects of oral H1 antihistamines on eczema were not feasible. Although well-designed randomised controlled trials excluding concomitant medications appear to be needed, consideration should be given to the potential ethical issues raised with the use of antihistamines as monotherapy for the management of eczema by withholding the use of rescue or additional therapies. A further systematic review of studies in which concomitant therapies were permitted might be of value in determining the potential benefits of oral H1 antihistamines as add-on therapy.

Oral H1 antihistamines as monotherapy for eczema

BACKGROUND

Eczema is a common skin disease in many countries, and although the majority of cases of eczema occur before the age of five years and often resolve during childhood or adolescence, it can also persist into adulthood. Itch is the most important aspect of eczema, often impacting significantly on the quality of life of an affected individual.

OBJECTIVES

To assess the effects of oral antihistamines (H1 antagonists) as monotherapy in children and adults with eczema.

SEARCH METHODS

We searched the following databases up to March 2012: the Cochrane Skin Group Specialised Register, CENTRAL in The Cochrane Library (2012, Issue 3), MEDLINE (from 1946), EMBASE (from 1974), and LILACS (from 1982). We examined the reference lists of excluded studies in order to identify further references to relevant trials. We searched trials registers for ongoing and unpublished trials. We also handsearched the abstracts of the International Research Workshops on eczema, as well as the conference proceedings of the European Academy of Dermatology and Venereology (EADV) and the European Academy of Allergology and Clinical Immunology (EAACI), from 2000 to 2011.

SELECTION CRITERIA

We sought to include randomised controlled trials that assessed the effects and safety of oral H1 antihistamines as monotherapy in children and adults with eczema. We excluded studies that compared an antihistamine versus another antihistamine and had no placebo control arm. We also excluded topical antihistamines and oral H1 antihistamines as 'add-on' therapy and studies using any concomitant therapy other than emollients or moisturisers, principally because some of these forms of concomitant therapy may be considered treatment modifiers in assessments of the effects of antihistamines on eczema.

DATA COLLECTION AND ANALYSIS

Our search retrieved 409 references to studies. Based on assessments of their titles, abstracts, or both, we excluded all except 36 of these studies. After evaluation of the full text of each report, we excluded a further 35 studies, and 1 study is awaiting classification pending a response from the trial investigators.

MAIN RESULTS

No randomised controlled trials met our inclusion criteria.

AUTHORS' CONCLUSIONS

There is currently no high-level evidence to support or refute the efficacy or safety of oral H1 antihistamines used as monotherapy for eczema. Because most of the studies allowed the use of concomitant medications and involved multi-therapeutic approaches, meaningful assessments of the individual effects of oral H1 antihistamines on eczema were not feasible. Although well-designed randomised controlled trials excluding concomitant medications appear to be needed, consideration should be given to the potential ethical issues raised with the use of antihistamines as monotherapy for the management of eczema by withholding the use of rescue or additional therapies. A further systematic review of studies in which concomitant therapies were permitted might be of value in determining the potential benefits of oral H1 antihistamines as add-on therapy.

Separate peripheral pathways for pruritus in man

Recent findings suggest that itch produced by intradermal insertion of cowhage spicules in human is histamine independent. Neuronal mechanisms underlying nonhistaminergic itch are poorly understood. To investigate which nerve fibers mediate cowhage induced itch in man, action potentials were recorded from cutaneous C-fibers of the peroneal nerve in healthy volunteers using microneurography. Mechano-responsive and -insensitive C-nociceptors were tested for their responsiveness to cowhage spicules, histamine, and capsaicin. Cowhage spicules induced itching and activated all tested mechano-responsive C-units (24/24), but no mechano-insensitive C-fibers (0/17). Histamine also induced itch, but in contrast to cowhage, it caused lasting activation only in mechano-insensitive units (8/12). In mechano-responsive C-units, histamine caused no or only short and weak responses unrelated to the time course of itching. Capsaicin injections activated four of six mechano-responsive fibers and three of four mechano-insensitive C-fibers. Cowhage and histamine activate distinctly different nonoverlapping populations of C-fibers while inducing similar sensations of itch. We hypothesize that cowhage activates a pathway for itch that originates peripherally from superficial mechano-responsive (polymodal) C-fibers and perhaps other afferent units. It is distinct from the pathway for histamine-mediated pruritus and does not involve the histamine-sensitive mechano-insensitive fibers.

Desloratadine for chronic idiopathic urticaria: a review of clinical efficacy

Chronic idiopathic urticaria (CIU) is a disabling affliction that considerably limits patients' daily activities and interferes with sleep. Clinical studies have shown that histamine H1-receptor antagonists (antihistamines) are highly effective for inhibiting the hives/wheals and pruritus associated with CIU, as well as improving patients' quality of life. Desloratadine is a rapid-acting, once-daily, nonsedating selective H1-receptor antagonist/inverse receptor agonist with proven clinical efficacy in patients with CIU. It has 10-20 times the in vivo H1 receptor-binding affinity of loratadine, its parent compound, and 52-194 times the H1 receptor-binding affinity of cetirizine, ebastine, loratadine, and fexofenadine. Desloratadine displays linear pharmacokinetics after oral administration. Age and sex have no apparent effect on the drug's metabolism and elimination, and food does not affect its bioavailability or absorption. Desloratadine also exerts anti-inflammatory effects via mechanisms that are independent of H1-receptor antagonism. Results from randomized, double-blind, placebo-controlled studies of 6 weeks' duration in adults and adolescents with moderate-to-severe CIU indicate that desloratadine significantly minimizes the severity of pruritus, reduces the number and size of hives, and improves disease-impaired sleep and daily activities. Improvements were noted after a single dose of desloratadine and were maintained over 6 weeks of treatment. Desloratadine was safe and well tolerated in clinical trials of patients with CIU. The adverse effect profile of desloratadine in adults, as well as in children aged from 6 months to 11 years, is comparable to that of placebo. Evaluations of cognitive and psychomotor performance in adults indicate no impairment of function with dosages of desloratadine 5 mg/day. In conclusion, desloratadine is an important therapeutic option for prompt and enduring symptom relief in patients with moderate-to-severe CIU. In addition to efficacy and safety, desloratadine affords a convenient administration regimen, rapid onset of action, and an absence of drug-drug or drug-food interactions. Other important prescribing considerations are that, unlike all first-generation and some second-generation antihistamines, desloratadine is nonsedating at its clinically approved dosage and does not impair psychomotor function.

Effective treatment of pruritus in atopic dermatitis using H1 antihistamines (second-generation antihistamines): changes in blood histamine and tryptase levels

BACKGROUND

Atopic dermatitis (AD) is a common chronic inflammatory and allergic skin disease that almost always begins in childhood and follows a course of remittance and flare-up. AD is characterized by intense pruritus and itchiness that can be triggered by an interplay of genetic, immunologic and environmental factors. Of the mediators, histamine is one of the most potent inducers of pruritus. Serum tryptase, which is also a mediator, may be used to examine allergic disease as well. The development of minimal sedation H1 antihistamines (second-generation antihistamines) has revolutionized treatment of allergic diseases.

OBJECTIVE

The present study examines the efficacy of second-generation antihistamines in relieving pruritus due to AD. In addition, the relationship between AD pruritus and antihistamine therapy was analyzed by measuring the blood histamine and tryptase levels.

METHODS

Thirty-two AD patients were recruited and underwent second-generation antihistamine therapy for 2 weeks. Seventeen received combined topical corticosteroid treatment (Group 1) and the other 15 did not receive steroid treatment (Group 2). The Severity Index and Pruritus Score were assessed as an AD clinical activity index and compared with baseline data.

RESULTS

Both the Severity Index and Pruritus Score improved significantly in Group 1 (P<0.001, P<0.05). Group 2 demonstrated a significant improvement in Pruritus Score (P<0.05), but not in the Severity Index. Plasma histamine levels were significantly higher in AD at baseline compared with healthy controls.

CONCLUSION

Following antihistamine therapy, these levels decreased significantly in both AD groups (P<0.05). There was a significant correlation between baseline blood histamine and typtase levels. However, this correlation was not evident following treatment. This may reflect insufficient detection capabilities of the measuring assay. The present results suggest that second-generation antihistamine therapy provides an effective clinical treatment for AD, with a notable improvement in pruritus. Furthermore, antihistamine therapy reduced plasma histamine levels in AD patients. These findings further suggest that high blood histamine and tryptase levels in AD patients contribute to the pathogenesis of this disorder, including the onset of pruritus.