Terfenadine, a potent histamine H1-receptor antagonist in the treatment of grass pollen sensitive asthma

Efficacy of levocetirizine in isolated rat tracheal smooth muscle

Histamine receptor-1 (H1) antagonists like levocetirizine are frequently used nowadays to treat rhinitis patients who experience rhinorrhea and sneezing. The trachea may be affected by the H1 antagonist when it is used to treat nasal symptoms, either orally or through inhalation. The purpose of this study was to ascertain in vitro effects of levocetirizine on isolated tracheal smooth muscle. As a parasympathetic mimetic, methacholine (10-6 M) causes contractions in tracheal smooth muscle, which is how we tested effectiveness of levocetirizine on isolated rat tracheal smooth muscle. We also tested the drug's impact on electrically induced tracheal smooth muscle contractions. The impact of menthol (either before or after) on the contraction brought on by 10-6 M methacholine was also investigated. According to the results, the addition of levocetirizine at concentrations of 10-5 M or more caused a slight relaxation in response to methacholine's 10-6 M contraction. Levocetirizine could prevent spike contraction brought on by electrical field stimulation (EFS). As the concentration rose, it alone had a neglect effect on the trachea's basal tension. Before menthol was applied, levocetirizine might have also inhibited the function of the cold receptor. According to this study, levocetirizine might potentially impede the parasympathetic function of the trachea. If levocetirizine was used prior to menthol addition, it also reduced the function of cold receptors.

Managing Chronic Cough Due to Asthma and NAEB in Adults and Adolescents: CHEST Guideline and Expert Panel Report

BACKGROUND

Asthma and non-asthmatic eosinophilic bronchitis (NAEB) are among the commonest causes of chronic cough in adults. We sought to determine the role of non-invasive measurements of airway inflammation, including induced sputum and fractional exhaled nitric oxide, in the evaluation of cough associated with asthma, and what the best treatment is for cough due to asthma or NAEB.

METHODS

We undertook three systematic reviews of randomized controlled trials and observational trials of adults and adolescents > 12 years of age with a chronic cough due to asthma or NAEB. Eligible studies were identified in MEDLINE, CENTRAL, and SCOPUS and assessed for relevance and quality. Guidelines were developed and voted upon using CHEST guideline methodology.

RESULTS

Of the citations reviewed, 3/1,175, 53/656, and 6/134 were identified as being eligible for inclusion in the three systematic reviews, respectively. In contrast to established guidelines for asthma therapies in general and the inclusion in some guidelines for a role of biomarkers of airway inflammation to guide treatment in severe disease, the evidence of specific benefit related to the use of non-invasive biomarkers in patients with chronic cough due to asthma was weak. The best therapeutic option for cough in asthma or NAEB is inhaled corticosteroids followed by leukotriene receptor antagonism.

CONCLUSIONS

This guideline offers recommendations on the role of non-invasive measurements of airway inflammation and treatment for cough due to asthma or NAEB based on the available literature, and identifies gaps in knowledge and areas for future research.

Small Molecules as Drugs to Upregulate Metastasis Suppressors in Cancer Cells

It is well-recognized that the majority of cancer-related deaths is attributed to metastasis, which can arise from virtually any type of tumor. Metastasis is a complex multistep process wherein cancer cells must break away from the primary tumor, intravasate into the circulatory or lymphatic systems, extravasate, proliferate and eventually colonize secondary sites. Since these molecular processes involve the coordinated actions of numerous proteins, targeted disruptions of key players along these pathways represent possible therapeutic interventions to impede metastasis formation and reduce cancer mortality. A diverse group of proteins with demonstrated ability to inhibit metastatic colonization have been identified and they are collectively known as metastasis suppressors. Given that the metastasis suppressors are often downregulated in tumors, drug-induced re-expression or upregulation of these proteins represents a promising approach to limit metastasis. Indeed, over 40 compounds are known to exhibit efficacy in upregulating the expression of metastasis suppressors via transcriptional or post-transcriptional mechanisms, and the most promising ones are being evaluated for their translational potentials. These small molecules range from natural products to drugs in clinical use and they apparently target different molecular pathways, reflecting the diverse nature of the metastasis suppressors. In this review, we provide an overview of the different classes of compounds known to possess the ability to upregulate one or more metastasis suppressors, with an emphasis on their mechanisms of action and therapeutic potentials.

Antihistamine from Tragia involucrata L. leaves

BACKGROUND

Synthetic antihistamine drugs cause various adverse effects to overcome these problems with natural phytomedicine or phytoconstituents.

METHODS

Tragia involucrata leaves were extracted with soxhlet apparatus and fractionated with column chromatography the homogenized fractions were monitored with thin layer chromatography (TLC) and characterized by using UV-visible, FT-IR, 1H NMR, 13C NMR and MS spectral studies. Isolated compounds were screened their antihistamine activity on ileum preparation, bronchoconstriction and triple response on histamine-induced guinea pig.

RESULTS

Antihistamine 5-hydroxy-1-methylpiperidin-2-one has been isolated and characterized from the leaves of Tragia involucrata L. A promising muscle relaxant, bronchorelaxant and anti-allergic effect of 5-hydroxy-1-methylpiperidin-2-one was observed in histamine-induced guinea pig and found to be 55.54±2.78% protection at the dose level of 12.5 mg/kg in bronchoconstriction effect and 49.05±2.45% protection in triple response. These findings were confirmed by in silico molecular docking also against histamine H1 receptor compared with chlorpheniramine maleate and mepyramine. This shows that the 5-hydroxy-1-methylpiperidine-2-one possess good inhibitory effect on histamine-induced guinea pig. The muscle relaxant, bronchodilating and anti-allergic potency of 5-hydroxy-1-methylpiperidin-2-one has been discussed in context with its probable profile as an anti-asthmatic agent from T. involucrata L. leaves.

CONCLUSIONS

We can conclude that isolated 5-hydroxy-1-methylpiperidin-2-one from T. involucrata L. has potent antihistamine agent on histamine-induced guinea pig.

The role of antihistamines in asthma management

Histamine is an important mediator in airway inflammation. It is elevated in the airways of asthmatic patients and is responsible for many of the pathophysiological features in asthma. Antihistamines block the actions of histamine and also have effects on inflammation which is independent of histamine-H(1)-receptor antagonism. Antihistamines have been shown to have bronchodilatory effects, effects on allergen-, exercise-, and adenosine-monophosphate-challenge testing, and also to prevent allergen-induced nonspecific airways hyperresponsiveness. Clinical studies have shown mixed results, and some studies have reported beneficial effects of azelastine, cetirizine, desloratadine, and fexofenadine on asthma symptoms or physiological measures in patients with asthma. The combination of an antihistamine and a leukotriene receptor antagonist has been shown to have additive effects in certain studies. Antihistamines have also been shown to delay or prevent the development of asthma in a subgroup of atopic children. These data suggest that antihistamines may have beneficial effects in the management of asthma.

The role of histamine in asthma

Histamine is a ubiquitous inflammatory mediator intimately associated with the pathology of allergy. Traditional antihistamines, targeting the histamine H1 receptor, have failed to demonstrate a significant role for histamine in asthma. Novel immunomodulatory roles for histamine and the discovery of a novel histamine receptor, the histamine H4 receptor, have resulted in a reassessment of its importance in asthma.

Effects of cetirizine on isolated rat's tracheal smooth muscle

Cetirizine (Zytec) is often used as a histamine receptor-1 (H(1)) antagonist in rhinitis patients who are suffering from sneezing and rhinorrhea. This H(1) antagonist is used as an oral tablet or nasal spray solution. The effect of H(1) antagonist on nasal mucosa in vivo is well known; however, the effect of the drug on tracheal smooth muscle has been rarely explored. Therefore, during administration of the H(1) antagonist for nasal symptoms, it might also affect the trachea via oral intake or inhalation. We used our preparation to test the effectiveness of Zytec on isolated rat's tracheal smooth muscle. The following assessments of Zytec were performed: (1) effect on tracheal smooth muscle resting tension; (2) effect on contraction caused by 5 x 10(-6) M methacholine as a parasympathetic mimetic; (3) effect of the drug on electrically induced tracheal smooth muscle contractions. Results indicated that addition of a parasympathetic mimetic to the incubation medium caused the trachea to contract in a dose-dependent manner. Addition of Zytec at doses of 10(-5) M or above elicited a relaxation response to 5 x 10(-6) M methacholine-induced contraction. Zytec could inhibit electrical field stimulation induced spike contraction, and basal tension was increased at the same time. However, it alone had a minimal effect on the basal tension of trachea as the concentration increased. This study indicated that high concentrations of Zytec might actually inhibit parasympathetic function of the trachea.

Plasticity of peripheral mechanisms of cough

The cough reflex pathway is characterized by a remarkable plasticity often resulting in a persistent and uncontrollable urge to cough during airway inflammation. In many instances cough becomes up regulated to the extent that ceases to fulfill its defensive role in protecting the airways. The exact mechanisms underlying this plasticity are unknown and likely involves a variety of factors influencing the function of the peripheral and central nervous system. This review outlines the evidence of increased cough sensitivity during airway disease. This is followed by a discussion of the peripheral mechanisms involved including the potential role of inflammatory mediators, neutrophins and changes in the airway mucosal structure. A greater understanding of the mechanisms leading to enhanced cough should lead to the development of more effective therapeutic strategies.

Efficacy of montelukast during the allergy season in patients with chronic asthma and seasonal aeroallergen sensitivity

BACKGROUND

Montelukast has proven efficacy in the treatment of chronic asthma and seasonal allergic rhinitis, but it has not been evaluated in the subpopulation of asthmatic patients with seasonal asthma symptoms.

OBJECTIVE

To determine the effectiveness of montelukast treatment in improving the control of asthma symptoms during the allergy season in patients with active asthma and seasonal aeroallergen sensitivity.

METHODS

Adults with a history of chronic asthma who are also symptomatic during the allergy season and with skin test sensitivity to seasonal aeroallergens were enrolled in a randomized, parallel-group, multicenter study with a 1-week, single-blind, placebo run-in period followed by 3 weeks of double-blind treatment during the spring of 2004. After the run-in period, eligible patients were randomly assigned to receive either oral montelukast (10 mg) or placebo. Daytime and nighttime asthma symptom scores, beta-agonist use, and morning and evening peak expiratory flow rates were recorded daily using an electronic diary. The primary end point was mean change from baseline to week 3 in the daytime asthma symptom score.

RESULTS

Of 455 randomized patients, 433 completed the study. Compared with placebo, treatment with montelukast resulted in a significant improvement from baseline in the daytime asthma symptom score (-0.54 vs -0.34; P = .002) and in beta-agonist use, nighttime symptoms, and peak expiratory flow rates. Few patients in the montelukast and placebo groups discontinued study participation because of asthma (1.3% and 3.0%, respectively).

CONCLUSION

In patients with chronic asthma and seasonal aeroallergen sensitivity, montelukast treatment provided significant asthma control during the allergy season compared with placebo.

Pharmacological management of allergic rhinitis in the elderly: safety issues with oral antihistamines

An increasing number of elderly persons in our society experience allergic rhinoconjunctivitis. Different agents are used in the pharmacological treatment of allergic rhinitis, with histamine H1 receptor antagonists (antihistamines) being the most frequently prescribed class. However, drug therapy of aged persons differs to a degree from that in other age groups primarily because of quantitative pharmacotherapeutic problems. The main problems are co-morbidities and polymedication, which may lead to drug-drug interactions. H1 receptor antagonists block the action of histamine at specific receptors and are available for both topical and systemic administration. First-generation H1 receptor antagonists are lipophilic and therefore may cross the blood-brain barrier; they also lack specificity for the H1 receptor. Second-generation H1 receptor antagonists have reduced capacity to cross the blood-brain barrier and greater specificity for the H1 receptor. Use of first-generation H1 receptor antagonists in the elderly should be considered carefully because of the large number of adverse effects and potential for interactions with these agents. Second-generation H1 receptor antagonists such as desloratadine, levocetirizine and ebastine provide good selective H1 receptor blockade without anticholinergic or alpha-adrenoceptor antagonist activity. Furthermore, they inhibit proinflammatory cytokines and are safe. Second-generation H1 receptor antagonists also offer therapeutic possibilities in patients with severe liver and/or renal dysfunction.

Effect of combined montelukast and desloratadine on the early asthmatic response to inhaled allergen

BACKGROUND

The early asthmatic response (EAR) to inhaled allergen results from IgE-mediated release of multiple mast-cell mediators, including leukotrienes and histamine, both of which cause bronchoconstriction. Combination therapy directed at blocking the effects of both mediators might protect against the EAR better than either therapy alone.

OBJECTIVE

We sought to evaluate the effect of desloratadine and montelukast, administered alone and in combination, on the EAR to inhaled allergen.

METHODS

Ten adults with mild-to-moderate atopic asthma participated in a randomized, 4-way crossover study design comparing placebo, 5 mg of desloratadine, 10 mg of montelukast, and the combination administered at 26 hours and 2 hours before each allergen challenge conducted at least 7 days apart. The primary end point was the concentration of allergen that resulted in a 20% decrease in FEV1 (PC20).

RESULTS

The geometric mean allergen PC20 (mean log +/- SEM) for combination therapy, montelukast, desloratadine, and placebo was 697 U/mL (2.8433 +/- 0.3253), 338 U/mL (2.5295 +/- 0.2979), 123 U/mL (2.0883 +/- 0.2102), and 104 U/mL (2.0166 +/- 0.2553), respectively (n = 9; P < .00001, ANOVA). Montelukast increased the allergen PC20 4.8-fold, and combination therapy increased the allergen PC20 8.9-fold. The effect of the combination was greater than that with montelukast alone (P < .02). Desloratadine treatment was no different than placebo.

CONCLUSIONS

The early response to inhaled allergen was unchanged after desloratadine therapy and partially inhibited with montelukast therapy. The combination of desloratadine and montelukast provided superior efficacy to either blocker administered alone. Investigations into the possible mechanisms of the enhanced inhibition are necessary.

Second-generation antihistamines in asthma therapy: is there a protective effect?

Second-generation histamine H(1) receptor antagonists are recognized as being highly effective treatments for allergic-based disease and are among the most frequently prescribed drugs in the world. The newer antihistamines represent a heterogeneous group of compounds with markedly different chemical structures, a spectrum of antihistaminic properties, adverse effects, half-life, tissue distribution, metabolism and varying degrees of anti-inflammatory effects. Histamine is an important mast cell- and basophil-derived mediator that has been implicated in the pathogenesis of asthma, resulting in smooth muscle contraction, mucus hypersecretion, and increased vascular permeability leading to mucosal edema. Antihistamines should never be used as monotherapy for asthma but there is evidence that these drugs give a measure of protection in histamine-induced bronchoconstriction. Furthermore, several studies have demonstrated that the use of second-generation antihistamines, as adjunct therapy, may benefit those patients whose allergic asthma co-exists with allergic rhinitis. Indeed, many patients present with both allergic rhinitis and asthma. The link between the upper and lower respiratory airways is now well established and there is increasing evidence that allergic rhinitis is a risk factor for the development of asthma. More recently, a number of novel antihistamines have been developed which are either metabolites of active drugs or enantiomers and there is emerging evidence that at least one of these drugs, desloratadine, may give significant symptomatic benefit in some types of asthma. It is of interest to note that cetirizine provides a primary pharmacological intervention strategy to prevent the development of asthma in specifically-sensitized high risk groups of infants. Moreover, the documented anti-inflammatory activities of antihistamines may provide a novel mechanism of action for the therapeutic control of virus-induced asthma exacerbations by inhibiting the expression of intercellular adhesion molecule-1 (ICAM-1) by airway epithelial cells. Finally, several well-conducted studies suggest that combination therapy with antihistamines and antileukotrienes may be as effective as corticosteroid use in patients with allergic asthma and seasonal allergic rhinitis.

Cough and asthma

Cough variant asthma and the closely related corticosteroid responsive cough syndromes eosinophilic bronchitis and atopic cough are common causes of chronic cough. The diagnosis is often not overt but detailed investigation of airway responsiveness and airway inflammation can be helpful. Cough variant asthma, eosinophilic bronchitis and atopic cough are all associated with eosinophilic airway inflammation, which is similar to that seen in non-cough predominant asthma. However, evidence of activated mast cells and increased concentrations of mast cell products appears to be confined to the conditions associated with cough, suggesting a role for mast cell degranulation in the superficial airway structures in the pathogenesis of cough. Cough variant asthma is typically corticosteroid responsive; leukotriene antagonists and antihistamines also help. Further study of this interesting asthma variant may increase our understanding of the relationship between airway inflammation and airway dysfunction.

Prospects for antihistamines in the treatment of asthma

Antihistamines have been evaluated as potential therapies for asthma for more than 50 years. With first-generation compounds, side effects prevented effective dosing. By reviewing published studies of the effectiveness of terfenadine, cetirizine, and loratadine in clinical asthma, evidence for the relevant effect of the second-generation antihistamines on bronchial asthma can be found. Terfenadine, at doses of 120 or 180 mg twice a day, reduced symptoms and improved pulmonary function in mild and moderate allergic asthma but was ineffective in severe perennial asthma. Fexofenadine at doses used for allergic rhinitis had little effect on seasonal allergic asthma. Research is ongoing to determine the effects of higher doses of fexofenadine. In 5 studies, cetirizine at doses of 10 to 20 mg, once or twice daily, consistently improved asthma symptoms compared with placebo or terfenadine 60 mg twice a day in 2 cases, whereas in 2 studies, loratadine at doses of 10 to 20 mg daily has not produced significant improvement in asthma. However, loratadine 5 mg combined with 60 mg of pseudo-ephedrine twice a day significantly improved both asthma symptoms and peak expiratory flow. Similarly, the combination of loratadine 20 mg and the leukotriene-receptor antagonist montelukast improved asthma symptoms, peak expiratory flow, and beta-agonist use over montelukast alone. Therefore, there might be a role for second- and third-generation antihistamines in treating mild and moderate asthma, which might require administering doses greater than those commonly used to treat allergic rhinitis. If higher doses are sedative, the addition of decongestants or leukotriene-receptor antagonists might enhance the effects of lower doses of the antihistamines.

Induced sputum inflammatory mediator concentrations in chronic cough

Previous studies have shown evidence of airway inflammation in patients with chronic cough and have suggested that the cough may be due to release of tussive mediators and activation of afferent sensory nerve endings. We measured the concentration of various proinflammatory and tussive mediators in induced sputum supernatants from 20 patients with cough variant asthma or eosinophilic bronchitis, 20 patients with nonasthmatic chronic cough, 22 patients with idiopathic chronic cough, and 18 healthy control subjects. We measured histamine, cysteinyl-leukotrienes, prostanoids (prostaglandin D2 and prostaglandin E2), and interleukin-8 by enzyme immunoassay. The median sputum histamine concentrations were significantly higher in patients with idiopathic chronic cough (8.0 ng/ml) and cough variant asthma/eosinophilic bronchitis (10.2 ng/ml) than in normal subjects (2.6 ng/ml; 95% confidence interval of difference from idiopathic chronic cough, 0.8 to 25.8 [p = 0.009] and 95% confidence interval of difference from cough variant asthma/eosinophilic bronchitis, 1.1 to 20.1 [p = 0.01]). Median sputum prostaglandin D2 and prostaglandin E2 concentrations were significantly higher in all categories of chronic cough. Our findings support the view that there is release of inflammatory and tussive mediators in patients with chronic cough and suggest that there might be similarities in the mechanism of cough in a diverse range of conditions.

Role of histamine in the pathophysiology of asthma: immunomodulatory and anti-inflammatory activities of H1-receptor antagonists

Cumulative clinical and laboratory evidence on histamine and its actions suggests that it has a pathophysiologic role in asthma. These findings have renewed interest in the potential therapeutic role of H1 antihistamines in this disease. A murine model of allergen-induced airway inflammation and methacholine-induced airway hyperresponsiveness has been used to clarify mechanisms of airway function, to identify potential therapeutic targets, and to investigate the effects of the H1-receptor antagonist fexofenadine. Findings suggest that there may be a role for second-generation antihistamines in treating asthma, with patient selection as well as dosing both important therapeutic considerations. Because high-dose therapy may be required to achieve a clinical response, agents with the widest therapeutic window and the lowest potential for sedation would offer the greatest therapeutic potential.

Fexofenadine modulates T-cell function, preventing allergen-induced airway inflammation and hyperresponsiveness

BACKGROUND

Antihistamines have been evaluated for usefulness in the treatment of asthma for more than 50 years. Interest was limited until the introduction of newer compounds that were free of much of the dose-limiting sedation associated with the earlier drugs.

OBJECTIVE

In a murine model of allergen-induced airway inflammation and hyperresponsiveness, the efficacy of an H1 receptor antagonist to prevent allergic inflammation and altered airway function was evaluated.

METHODS

Mice were sensitized and challenged to an allergen, ovalbumin, which elicited marked airway and tissue eosino-philia and airway hyperresponsiveness. Fexofenadine was administered before challenge, and airway responsiveness to inhaled methacholine, airway and tissue eosinophilia, bronchoalveolar lavage fluid cytokine levels, and serum IgE levels were assayed. In a second group of experiments, sensitized and challenged mice were treated or not treated with fexofenadine before challenge. T cells were isolated from the lungs and adoptively transferred into naive recipients before exposure to limited airway allergen challenge, and lung function and inflammation were evaluated.

RESULTS

Fexofenadine treatment of sensitized mice prevented the development of airway hyperresponsiveness in both the primary sensitization and challenge, as well as in the adoptive transfer experiments. These changes were accompanied by decreases in bronchoalveolar lavage and tissue eosinophilia, lymphocyte numbers, and T(H)2 cytokine production.

CONCLUSION

The results demonstrate the efficacy of an H1 receptor antagonist in preventing allergen-induced alterations in pulmonary inflammation and airway function. The data support the evaluation of drugs such as fexofenadine in the treatment of allergic asthma.

New insights into the second generation antihistamines

Second generation antihistamines are recognised as being highly effective treatments for allergy-based disease and are among the most frequently prescribed and safest drugs in the world. However, consideration of the therapeutic index or the benefit/risk ratio of the H1 receptor antagonists is of paramount importance when prescribing this class of compounds as they are used to treat non-life threatening conditions. There are many second generation antihistamines available and at first examination these appear to be comparable in terms of safety and efficacy. However, the newer antihistamines in fact represent a heterogeneous group of compounds, having markedly differing chemical structures, adverse effects, half-life, tissue distribution and metabolism, spectrum of antihistaminic properties, and varying degrees of anti-inflammatory effects. With regard to the latter, there is growing awareness that some of these compounds might represent useful adjunct medications in asthma therapy. In terms of safety issues, the current second generation grouping includes compounds with proven cardiotoxic effects and others with the potential for adverse drug interactions. Moreover, some of the second generation H1 antagonists have given cause for concern regarding their potential to cause a degree of somnolence in some individuals. It can be argued, therefore, that the present second generation grouping is too large and indistinct since this was based primarily on the concept of separating the first generation sedating compounds from nonsedating H1 antagonists. Although it is too early to talk about a third generation grouping of antihistamines, future membership of such a classification could be based on a low volume of distribution coupled with a lack of sedating effects, drug interactions and cardiotoxicity.

Assessment of antihistamine efficacy and potency

H1 antihistamines are widely used in the treatment of conditions such as seasonal and perennial allergic rhinitis, urticaria and angioedema, as well as being an adjunct therapy for anaphylaxis. The development of new compounds within this class of pharmacological agents is based on preclinical and clinical assessments prior to registration. Preclinical assessment of novel compounds has been advanced both by the definition of the molecular structure of the H1 receptor and by high throughput screening, which allows the definition of potent and selective candidate compounds. The elimination, in subsequent evaluations, of those compounds with potential for central nervous system and cardiotoxic effects and those with inappropriate pharmacokinetics restricts the subsequent toxicological and clinical evaluation of novel H1 antihistamines. Clinical evaluation is based initially on human volunteer studies to define pharmacodynamic, pharmacokinetic and safety parameters. Local challenge models such as in the skin or nose for oral therapy or nose and conjunctiva for topical drug development allow definition of potential dose for administration, speed of onset of activity and duration of effect, both in comparison to placebo and to reference compounds. While a range of laboratory allergen challenge models, pollen chamber challenge studies and acute 'day in the park' study designs have been used in the early clinical evaluation of H1 antihistaminic activity, ultimately it is the efficacy of novel compounds in naturally occurring disease that is of importance. The assessment of the magnitude and profile of clinical disease improvement in specific disease areas is thus the crucial evaluation. The appropriate selection and characterization of patients, the optimization of the trial design, dependent upon the nature of the disease, and the appropriate selection of endpoints for analysis are thus critical considerations, as well as evaluation of appropriate safety criteria.

Is antihistamine (H1-receptor antagonist) therapy useful in clinical asthma?

Airway hyperresponsiveness to histamine is a hallmark of asthma, and histamine inhalation reproduces asthma symptoms. Plasma histamine concentrations are elevated during the early and late responses to inhaled allergens, and may also increase during spontaneous acute asthma episodes. Ordinary doses of currently available antihistamines (H1-receptor antagonists) have minimal bronchodilator and bronchoprotective activity. In severe persistent asthma, H1 antagonists have no significant clinical effect. In moderate persistent asthma, clinical benefits of H1 antagonists are apparent, but may not be worth the potential risks of the higher-than-usual doses required. When mild seasonal asthma and allergic rhinitis coexist, however, relief of rhinitis symptoms with H1 antagonists administered in ordinary dose is associated with significant improvement in asthma symptoms.

The relationship between allergic rhinitis and bronchial asthma

Allergic rhinitis and bronchial asthma frequently coexist in the same patients. Many patients with rhinitis alone demonstrate nonspecific bronchial hyperresponsiveness, and prospective studies suggest that nasal allergy may be a predisposing risk factor for developing asthma. A growing body of literature has documented that the treatment of patients with allergic rhinitis may result in improvement of asthma symptoms, airway caliber, and bronchial hyperresponsiveness to methacholine and exercise. Finally, mechanistic studies of airway physiology have demonstrated that nasal disease may influence pulmonary function via both direct and indirect mechanisms. Nasal disease should be considered as a possible concomitant illness in all patients with asthma and treated appropriately when identified.

Diagnosis and management of rhinitis: complete guidelines of the Joint Task Force on Practice Parameters in Allergy, Asthma and Immunology. American Academy of Allergy, Asthma, and Immunology

This document contains complete guidelines for diagnosis and management of rhinitis developed by the Joint Task Force on Practice Parameters in Allergy, Asthma and Immunology, representing the American Academy of Allergy, Asthma and Immunology, the American College of Allergy, Asthma and Immunology and the Joint Council on Allergy, Asthma and Immunology. The guidelines are comprehensive and begin with statements on clinical characteristics and diagnosis of different forms of rhinitis (allergic, non-allergic, occupational rhinitis, hormonal rhinitis [pregnancy and hypothyroidism], drug-induced rhinitis, rhinitis from food ingestion), and other conditions that may be confused with rhinitis. Recommendations on patient evaluation discuss appropriate use of history, physical examination, and diagnostic testing, as well as unproven or inappropriate techniques that should not be used. Parameters on management include use of environmental control measures, pharmacologic therapy including recently introduced therapies and allergen immunotherapy. Because of the risks to patients and society from sedation and performance impairment caused by first generation antihistamines, second generation antihistamines that reduce or eliminate these side effects should usually be considered before first generation antihistamines for the treatment of allergic rhinitis. The document emphasizes the importance of rhinitis management for comorbid conditions (asthma, sinusitis, otitis media). Guidelines are also presented on special considerations in patients subsets (children, the elderly, pregnancy, athletes and patients with rhinitis medicamentosa); and when consultation with an allergist-immunologist should be considered.

Executive summary

Allergic rhinitis is now recognized as a major cause of morbidity that significantly impairs function and quality of life. Moreover, it is now widely held that the pathophysiologic mechanisms causing nasal allergy contribute, or predispose many individuals, to the development of other airway diseases, including asthma. Allergic rhinitis may well be a factor in 24% of children with otitis media with effusion (OME), and perhaps 28% of cases of chronic sinusitis. As many as 78% of persons with asthma aged 15 to 30 years have elevated serum IgE antibodies to five common aeroallergens. In many instances, nasal allergy signals the presence of more severe disease.

Considerable evidence now suggests that early and appropriate intervention can improve the quality of life and productivity of patients with allergic rhinitis, enhance the academic performance of children, and reduce the prevalence of airway complications. The goal of treatment has shifted from mere symptom alleviation to blocking the pathophysiologic mechanisms that cause chronic allergic inflammation and leave patients vulnerable to airway infections. The earlier in a patient's life that this can be accomplished, the better the anticipated consequences.

A panel of experts was convened in Amsterdam, The Netherlands, on 2 September 1996, to explore these issues and their impact on allergy prevention and treatment in primary care. Their undertaking was supported by an unrestricted educational grant from Schering‐Plough Pharmaceuticals.

Milestones in the biology and pharmacology of H1-receptor antagonists

Daniele Bovet's pioneering discovery that a series of compounds possessing anti-histamine activity reduced the symptoms of anaphylaxis provided the proof that histamine plays a pivotal role as a mediator of allergic reactions. Basophils and mast cells are the major sources of histamine in man and they are thus one of the primary effector cells of allergic inflammation. Some H1-receptor antagonists possess a variety of antiinflammatory activity to H1 antagonism in vitro and in vivo. This promising area should be explored further and much remains to be done in the evaluation of the immunomodulatory effects of anti-histamines.

A double-blind, placebo controlled study of the effect of the specific histamine H1-receptor antagonist, terfenadine, in chronic severe asthma

1. The characteristic changes seen in asthma are widely regarded as being caused by local mediator release in the airways, with histamine the first putative mediator in asthma to be identified. 2. We performed a double-blind, randomised, placebo-controlled crossover trial of the effect of 4 weeks treatment with terfenadine 120 mg twice daily in chronic severe asthma. 3. Forty-two subjects (20 male and 22 female) completed the 10 week study. 4. Terfenadine had no significant treatment effect on the primary efficacy variables measured. Mean (95% CI) measurements for terfenadine vs placebo treatment periods were 1.5 vs 1.5 (-0.3, 0.3) l for FEV1, 259 vs 260 (-42, 40) l min-1 for morning PEF and 0.8 vs 0.8 (-0.3, 0.3) for global symptom scores. 5. Bronchodilator use and sleep disturbance, the secondary efficacy variables studied, showed an improvement during terfenadine treatment but this only reached statistical significance for the number of times subjects awoke from sleep (P = 0.04). 6. There was a similar frequency of minor adverse effects reported during placebo (13.6%) and terfenadine (16.7%) treatments. 7. Addition of the potent and specific histamine H1-receptor antagonist terfenadine to maintenance asthma treatment had no significant therapeutic benefit in this group of chronic severe asthmatics.

Pharmacological studies of allergic cough in the guinea pig

The pharmacological mechanisms of allergic cough in the guinea pig were studied. Actively sensitized guinea pigs were exposed to aerosols of antigen to elicit coughing. In separate experiments, naive guinea pigs were exposed to aerosols of capsaicin to elicit coughing. Both allergic and capsaicin-induced cough were inhibited by loratadine (0.3-10 mg kg-1 p.o.) and chlorpheniramine (0.1-3.0 mg kg-1 p.o.). Neither cimetidine (10 mg kg-1 s.c.), nor thioperamide (3-10 mg kg-1 s.c.), inhibited allergic or capsaicin-induced cough. Codeine (3-30 mg kg-1 p.o.), salbutamol (0.003-3.0 mg kg-1 s.c.) and ipratropium (0.03-1.0 mg kg-1 s.c.) inhibited both allergic and capsaicin-induced cough. Hexamethonium (10 and 30 mg kg-1 s.c.) inhibited allergic, but not capsaicin-induced cough. Allergic and capsaicin-induced cough were unaffected by phenidone (5.0 and 10.0 mg kg-1 s.c.). Indomethacin (5.0 and 10.0 mg kg-1 s.c.) had no effect on allergic cough but slightly inhibited capsaicin-induced cough. We conclude that allergic and capsaicin-induced cough are modulated by histamine H1 receptor and cholinergic mechanisms. Histamine H2 or histamine H3 receptor mechanisms, and lipoxygenase and cyclooxygenase products of arachidonic acid metabolism do not influence allergic and capsaicin-induced cough. Ganglionic mechanisms play a minor role in the production of allergic cough and no role in capsaicin-induced cough.

The pharmacology and use of H1-receptor-antagonist drugs

The second-generation H1-antagonist drugs are supplanting their predecessors in the treatment of allergic rhinoconjunctivitis and chronic urticaria. Their use can be justified mainly on the basis of a more favorable risk-benefit ratio, because they are less toxic to the central nervous system. Future research into H1 antagonists should include additional dose-response studies in patients with allergic disorders, especially children and the elderly; objective studies of adverse effects; studies of topical mucosal application of H1 antagonists; and studies of H1-antagonist enantiomers and active metabolites. With the cloning of the gene encoding the H1 receptor and increased understanding of the precise structural requirements for H1-receptor activity, H1 antagonists with an even more favorable therapeutic index may be developed.

The effect of oral terfenadine on the sensitivity of the cough reflex in normal volunteers

Antihistamines have been reported to have antitussive actions in allergic rhinitis which may be due to an effect of the drug on the cough reflex. We have studied the effect on induced cough in normal volunteers. Ten volunteers inhaled capsaicin at concentrations between 0.78 and 200 microM, in increasing dose order, until they coughed more than five times. The challenge was performed three times before and three times each at 2 and 4 h after 120 mg terfenadine or matched placebo tablet in a double-blind, randomized, cross-over study. Neither affected the capsaicin cough challenge. Thus, any antitussive effect of terfenadine is more likely to be via an indirect mechanism such as inhibition of released histamine rather than on the cough reflex itself.

Pharmacokinetic optimisation of histamine H1-receptor antagonist therapy

Second-generation, relatively nonsedating histamine H1-receptor antagonists (H1-RA) are extensively used worldwide for the symptomatic treatment of allergic rhinoconjunctivitis and chronic urticaria. Information about the pharmacokinetics and pharmacodynamics of these medications, while still incomplete, is now sufficient to permit optimisation of therapy. Published pharmacokinetic and pharmacodynamic information on these H1-RA is summarised here, and areas where more data are required are delineated. Serum concentrations of most second-generation H1-RA are relatively low, and are usually measured by radioimmunoassay. After oral administration, peak concentrations are observed within 2 or 3 h. Bioavailability has not been well studied, due to the lack of intravenous formulations. Most H1-RA are metabolised in the hepatic cytochrome P450 system: terfenadine, astemizole, loratadine, azelastine, and ebastine have 1 or more active metabolites which are present in serum in higher concentrations than the respective parent compound, and therefore can be measured by high performance liquid chromatography. Cetirizine, an active metabolite of the first generation H1-receptor antagonist hydroxyzine, is not further metabolised to any great extent in vivo, and is eliminated via renal excretion. Levocabastine is also eliminated primarily by excretion. Serum elimination half-life values differ greatly from 1 H1-RA to another, and are 24 h or less for terfenadine, astemizole, loratadine, cetirizine, azelastine and ebastine, and the active metabolites of terfenadine, loratadine and ebastine. The active metabolite of azelastine (demethylazelastine) has a serum elimination half-life value of about 2 days, while that of astemizole (demethyl-astemizole) has a value of 9.5 days. From the few published studies in which the apparent volumes of distribution of the second-generation H1-RA have been calculated, it appears that tissue distribution is extensive. In children, the half-lives of H1-RA are generally shorter than are found in adults; there is no published information on the pharmacokinetics of astemizole, loratadine, azelastine, or ebastine in children. In some elderly adults, terfenadine, loratadine and cetirizine may have longer half-lives than in young healthy adults. There is little published data on the pharmacokinetics of the second-generation H1-RA in patients with impaired hepatic function. The half-life of cetirizine is prolonged in those with impaired renal function. There is a paucity of information on the pharmacokinetics of H1-RA in neonates, in pregnancy or during lactation.(ABSTRACT TRUNCATED AT 400 WORDS)