Histamine and tryptase in nasal lavage fluid after allergen challenge: effect of 1 week of pretreatment with intranasal azelastine or systemic cetirizine

KAAACI Allergic Rhinitis Guidelines: Part 1. Update in Pharmacotherapy

The prevalence of allergic rhinitis (AR) and the socioeconomic burden associated with the medical cost and quality of life (QOL) of AR have progressively increased. Therefore, practical guidelines for the appropriate management of AR need to be developed based on scientific evidence while considering the real-world environment, values, and preferences of patients and physicians. The Korean Academy of Asthma, Allergy and Clinical Immunology revised clinical guidelines of AR to address key clinical questions of the management of AR. Part 1 of the revised guideline covers the pharmacological management of patients with AR in Korea. Through a meta-analysis and systematic review, we made 4 recommendations for AR pharmacotherapy, including intranasal corticosteroid (INCS)/intranasal antihistamine (INAH) combination therapy, oral antihistamine/INCS combination therapy, leukotriene receptor antagonist treatment in AR patients with asthma, and prophylactic treatment for patients with pollen-induced AR. However, all recommendations are conditional because of the low or very low evidence of certainty. Well-designed and strictly executed randomized controlled trials are needed to measure and report appropriate outcomes.

Modulation of Allergic Inflammation in the Nasal Mucosa of Allergic Rhinitis Sufferers With Topical Pharmaceutical Agents

Allergic rhinitis (AR) is a chronic upper respiratory disease estimated to affect between 10 and 40% of the worldwide population. The mechanisms underlying AR are highly complex and involve multiple immune cells, mediators, and cytokines. As such, the development of a single drug to treat allergic inflammation and/or symptoms is confounded by the complexity of the disease pathophysiology. Complete avoidance of allergens that trigger AR symptoms is not possible and without a cure, the available therapeutic options are typically focused on achieving symptomatic relief. Topical therapies offer many advantages over oral therapies, such as delivering greater concentrations of drugs to the receptor sites at the source of the allergic inflammation and the reduced risk of systemic side effects. This review describes the complex pathophysiology of AR and identifies the mechanism(s) of action of topical treatments including antihistamines, steroids, anticholinergics, decongestants and chromones in relation to AR pathophysiology. Following the literature review a discussion on the future therapeutic strategies for AR treatment is provided.

MP29-02 reduces nasal hyperreactivity and nasal mediators in patients with house dust mite-allergic rhinitis

BACKGROUND

Nasal hyperreactivity (NHR) is an important clinical feature of allergic rhinitis (AR). The efficacy of MP29-02 (azelastine hydrochloride (AZE) and fluticasone propionate [FP]) nasal spray on local inflammatory mediators and NHR in AR is unknown. We tested if MP29-02 decreases inflammatory mediators and NHR in AR and if this effect is due to restoration of nasal epithelial barrier function.

METHODS

A 4-week double-blinded placebo-controlled trial with MP29-02 treatment was conducted in 28 patients with house dust mite (HDM) AR. The presence of NHR was evaluated by measuring reduction in nasal flow upon cold dry air exposure. The effects of AZE ± FP on barrier integrity and airway inflammation were studied in a murine model of HDM-induced NHR and on reduced activation of murine sensory neurons and human mast cells.

RESULTS

MP29-02 but not placebo reduced NHR (P < .0001 vs P = .21), levels of substance P (P = .026 vs P = .941), and β-hexosaminidase (P = .036 vs P = .632) in human nasal secretions. In wild-type C57BL6 mice, the reduction in β-hexosaminidase levels (P < .0001) by AZE + FP treatment upon HDM challenge was found in parallel with a decreased transmucosal passage (P = .0012) and completely reversed eosinophilic inflammation (P = .0013). In vitro, repeated applications of AZE + FP desensitized sensory neurons expressing the transient receptor potential channels TRPA1 and TRPV1. AZE + FP reduced MC degranulation to the same extent as AZE alone.

CONCLUSION

MP29-02 treatment reduces inflammatory mediators and NHR in AR. The effects of AZE + FP on MC degranulation, nasal epithelial barrier integrity, and TRP channels provide novel insights into the pathophysiology of allergic rhinitis.

Cleaved secretory leucocyte protease inhibitor as a biomarker of chymase activity in allergic airway disease

BACKGROUND

Secretory leucocyte protease inhibitor (SLPI), which is present in many physiological fluids including saliva, sputum and nasal discharge, is the most effective inhibitor of chymase. Previously, we demonstrated that chymase is able to cleave SLPI and that the cleaved portion, cSLPI, is a biomarker of chymase activity.

OBJECTIVE

We investigated the potential of cSLPI as a biomarker of chymase activity in subjects with allergic rhinitis (AR) and asthmatic airway disease.

METHODS

Baseline sputum samples were collected from atopic asthmatics and healthy controls (HC). Nasal lavages (NAL) were performed in subjects with AR both at baseline and following a nasal challenge with allergen or placebo. Levels of cSLPI and chymase were determined by Western analysis, and tryptase and alpha-2 macroglobulin were measured by immunoassay.

RESULTS

As compared with HC, asthmatics showed a significant increase in baseline cSLPI/total SLPI ratios and an increase in chymase levels. There was a high correlation of cSLPI/SLPI ratios to chymase levels in normal individuals and untreated asthmatics. In the NAL of patients with AR, as compared with placebo, allergen challenge increased inflammatory biomarkers, including cSLPI/SLPI ratios, chymase levels, tryptase levels and alpha2-macroglobulin levels. Correlations were observed between cSLPI/SLPI ratios and chymase levels and cSLPI/SLPI ratios and alpha2-macroglobulin levels; no correlation was seen between cSLPI/SLPI ratios and tryptase levels.

CONCLUSION

Our data indicate that cSLPI reflects chymase activity in AR and asthma. Hence, cSLPI may serve as a biomarker for disease activity and for monitoring the efficacy of novel anti-inflammatory treatments in chymase-mediated diseases.

Second-Generation Antihistamines

Antihistamines are useful medications for the treatment of a variety of allergic disorders. Second-generation antihistamines avidly and selectively bind to peripheral histamine H1 receptors and, consequently, provide gratifying relief of histamine-mediated symptoms in a majority of atopic patients. This tight receptor specificity additionally leads to few effects on other neuronal or hormonal systems, with the result that adverse effects associated with these medications, with the exception of noticeable sedation in about 10% of cetirizine-treated patients, resemble those of placebo overall. Similarly, serious adverse drug reactions and interactions are uncommon with these medicines. Therapeutic interchange to one of the available second-generation antihistamines is a reasonable approach to limiting an institutional formulary, and adoption of such a policy has proven capable of creating substantial cost savings. Differences in overall efficacy and safety between available second-generation antihistamines, when administered in equivalent dosages, are not large. However, among the antihistamines presently available, fexofenadine may offer the best overall balance of effectiveness and safety, and this agent is an appropriate selection for initial or switch therapy for most patients with mild or moderate allergic symptoms. Cetirizine is the most potent antihistamine available and has been subjected to more clinical study than any other. This agent is appropriate for patients proven unresponsive to other antihistamines and for those with the most severe symptoms who might benefit from antihistamine treatment of the highest potency that can be dose-titrated up to maximal intensity.

Cetirizine: a review of its use in allergic disorders

Cetirizine is a selective, second-generation histamine H1 receptor antagonist, with a rapid onset, a long duration of activity and low potential for interaction with drugs metabolised by the hepatic cytochrome P450 system. Cetirizine was generally more effective than other H1 receptor antagonists at inhibiting histamine-induced wheal and flare responses. Cetirizine is an effective and well tolerated agent for the treatment of symptoms of seasonal allergic rhinitis (SAR), perennial allergic rhinitis (PAR) and chronic idiopathic urticaria (CIU) in adult, adolescent and paediatric patients. In adults with these allergic disorders, cetirizine was as effective as conventional dosages of ebastine (SAR, PAR, CIU), fexofenadine (SAR), loratadine (SAR, CIU) or mizolastine (SAR). This agent was significantly more effective, and with a more rapid onset of action, than loratadine in 2-day studies in environmental exposure units (SAR). In paediatric patients, cetirizine was as at least as effective as chlorphenamine (chlorpheniramine) [SAR], loratadine (SAR, PAR) and oxatomide (CIU) in the short term, and more effective than oxatomide and ketotifen (PAR) in the long term. Cetirizine was effective in reducing symptoms of allergic asthma in adults and reduced the relative risk of developing asthma in infants with atopic dermatitis sensitised to grass pollen or house dust mite allergens. It had a corticosteroid-sparing effect in infants with severe atopic dermatitis and was effective in ameliorating reactions to mosquito bites in adults. Cetirizine was well tolerated in adults, adolescents and paediatric patients with allergic disorders. In adult, adolescent and paediatric patients aged 2-11 years, the incidence of somnolence with cetirizine was dose related and was generally similar to that with other second-generation H1 receptor antagonists. Although, its sedative effect was greater than that of fexofenadine in some clinical trials and that of loratadine or fexofenadine in a postmarketing surveillance study. In infants aged 6-24 months, the tolerability profile of cetirizine was similar to that of placebo. Cetirizine did not have any adverse effects on cognitive function in adults, or cognitive function, behaviour or achievement of psychomotor milestones in paediatric patients. Cetirizine was not associated with cardiotoxicity.

CONCLUSION

Cetirizine is well established in the treatment of symptoms of SAR, PAR or CIU. It demonstrated a corticosteroid-sparing effect and reduced the relative risk of developing asthma in sensitised infants with atopic dermatitis. Cetirizine was effective in the treatment of allergic cough and mosquito bites; however, its precise role in these indications has yet to be clearly established. On the basis of its favourable efficacy and tolerability profile and rapid onset of action, cetirizine provides an important option for the treatment of a wide range of allergic disorders.

Do tryptase, ECP and specific IgE measurement by nasal incubation increase the specific nasal provocation test sensitivity?

The specific Nasal Provocation Test (sNPT) is a third level diagnostic tool. Fitted to reproduce natural exposure condition to pick the responsible allergen for nasal symptoms out, it is applied when prick test and RAST responses are doubtful. SNPT results have been evaluated measuring nasal resistance (anterior rhinomanometry) and nasal symptoms (clinical score), reaching 50% of sensitivity. This study focused on the determination of allergic response markers, triggered by nasal challenge: tryptase levels in the nose, specific IgE and ECP (Eosinophil Cationic Protein). The aim was to increase sNPT sensitivity. Twenty patients suffering from allergic rhinitis and 16 age-matched-nonallergic subjects were enrolled in the study. Tryptase, specific IgE and ECP were determined in nasal mucosa applying a new method, based on in situ incubation, before and after sNPT. The latter was performed following a standardized method. Tryptase levels increased in 13 patients (65%), were unchanged in four patients (20%), and slightly decreased in three patients (15%). The increase recorded was significant in mite allergic patients (p=0.005), but not significant (p> 0.05) in pollen allergic patients. ECP values increased in 13 patients (65%), were unchanged in two patients (10%), and highly decreased in five patients (25%). ECP increase was not significant (p> 0.05). Specific IgE levels increased in seven patients (35%), were unchanged in 11 patients (55%) and decreased in two patients (10%). The IgE increase was significant in pollen-allergic patients (p<0.05), while it was not significant in mite-allergic patients (p>0.05). Tryptase, ECP, and specific IgE were not detected in the control group. The data obtained showed a positive sNPT response in 12 patients (60%). Comparing our results with those derived from classical-parameter employment, we gathered an improvement of 10%. On the basis of the usual parameters, in fact, we recorded 50% positivity, while the use of mediators provided an additional 10% improvement in sNPT sensitivity: taking together the usual parameters and nasal allergic mediators values, we reached an sNPT over-all sensitivity of 85%.

Treatment of nonallergic perennial rhinitis

Nonallergic perennial rhinitis (also commonly referred to as vasomotor rhinitis) is a chronic non-IgE-mediated condition that is characterized by symptoms which are similar to those seen in allergic rhinitis, but which persist for over nine months each year. Although treatment of vasomotor rhinitis involves the use of either intranasal corticosteroids or antihistamines, the corticosteroids are generally not effective in treatment of all the symptoms of vasomotor rhinitis and have generally been shown to be effective in patients with eosinophilia. With the exception of azelastine, the only topical antihistamine to be approved by the FDA for the treatment of nonallergic rhinitis, the antihistamines have also produced inconsistent results. While clinical studies of azelastine have demonstrated that this drug is highly efficacious in the treatment of all the symptoms of vasomotor rhinitis, mechanistic studies have demonstrated that azelastine has potent anti-inflammatory effects (in particular attenuation of the expression and synthesis of pro-inflammatory cytokines, leukotrienes, and cell adhesion molecules), which are likely to contribute to its clinical efficacy. Furthermore, pharamacokinetic studies have suggested that since azelastine has a more rapid onset of action, compared to most other antihistamines and intranasal corticosteroids, then azelastine nasal spray may be considered as primary therapy for patients with symptoms of both allergic and/or vasomotor (nonallergic perennial) rhinitis.

Levocetirizine better protects than desloratadine in a nasal provocation with allergen

BACKGROUND

Direct comparisons of antihistamines are rare but very much needed. Newly available antihistamine preparations, levocetirizine, the R-enantiomer of racemate cetirizine, and desloratadine, an active metabolite of loratadine, have been recently released for allergic rhinitis.

OBJECTIVE

We sought to compare levocetirizine and desloratadine in a nasal provocation test (NPT) with grass pollen.

METHODS

Twenty-four volunteers with grass pollen allergy and a history of rhinitis were enrolled in a double-blind, placebo-controlled, crossover study. Three NPTs were performed in a dose-escalating manner during the out-of-season period 4 hours after a single dose of levocetirizine (5 mg), desloratadine (5 mg), or placebo.

RESULTS

CONCLUSIONS

This study demonstrates a better overall protection of a single dose of levocetirizine compared with desloratadine in an NPT with grass pollen allergen. In contrast to late-phase inflammatory markers, which were unaffected, extravascular leakage of the early-phase marker albumin was significantly limited by levocetirizine.

Montelukast plus cetirizine in the prophylactic treatment of seasonal allergic rhinitis: influence on clinical symptoms and nasal allergic inflammation

BACKGROUND

The aim of our study was to investigate effects of 6-week pretreatment of seasonal allergic rhinitis (AR) with cetirizine, and montelukast, alone and in combination. Antihistamine/antileukotriene treatment is effective in AR. Antihistamines may prevent AR symptoms while prophylactic activity of antileukotrienes remains unclear.

METHODS

Sixty AR patients, aged 18-35 years, were randomized to receive placebo, montelukast only, cetirizine only, or montelukast plus cetirizine, 6 weeks prior and 6 weeks after the beginning of grass pollen season. Mean self-recorded in-season symptom scores and mean weekly all-symptom scores were analyzed. In 31 patients, nasal lavages were performed before treatment, and at the end of the study, i.e. 12 weeks after the treatment initiation. Eosinophil and basophil counts, eosinophil cationic protein (ECP), and mast cell tryptase (MCT) levels were evaluated in lavage samples.

RESULTS

Combined montelukast/cetirizine pretreatment significantly reduced in-season symptom score for sneezing, eye itching, nasal itching, rhinorrhea, and congestion. Montelukast plus cetirizine were more effective than cetirizine alone in preventing eye itching, rhinorrhea, and nasal itching. Moreover, combined pretreatment with montelukast and cetirizine delayed appearance of AR symptoms. Eosinophil nasal lavage fluid counts were significantly increased during pollen season in placebo and montelukast-only groups. No differences were observed in basophil counts. The in-season ECP level was significantly increased in all groups except montelukast-plus-cetirizine group. In-season MCT levels were not increased.

CONCLUSION

Combined antihistamine and antileukotriene treatment started 6 weeks before the pollen season is effective in preventing AR symptoms and reduces allergic inflammation in nasal mucosa during natural allergen exposure.

Comparison of intranasal corticosteroids and antihistamines in allergic rhinitis: a review of randomized, controlled trials

For several years there has been discussion of whether first-line pharmacological treatment of allergic rhinitis should be antihistamines or intranasal corticosteroids. No well documented, clinically relevant differences seem to exist for individual nonsedating antihistamines in the treatment of allergic rhinitis. Likewise, the current body of literature does not seem to favor any specific intranasal corticosteroid. When comparing efficacy of antihistamines and intranasal corticosteroids in allergic rhinitis, present data favor intranasal corticosteroids. Interestingly, data do not support antihistamines as superior in treating conjunctivitis associated with allergic rhinitis. Safety data from comparative studies in allergic rhinitis do not indicate differences between antihistamines and intranasal corticosteroids. Combining antihistamines and intranasal corticosteroids in the treatment of allergic rhinitis does not provide additional beneficial effects to intranasal corticosteroids alone. Considering present data, intranasal corticosteroids seem to offer superior relief in allergic rhinitis, when compared with antihistamines.

H1-receptors: localization and role in airway physiology and in immune functions

Histamine H(1)-receptors are involved in the pathologic processes of allergy. Clinical trials of H(1)-receptor antagonists have demonstrated the efficacy of these agents in reducing the sneezing, pruritus, and rhinorrhea associated with allergic rhinitis. In the lung, H(1)-receptors mediate the bronchoconstrictive effects of histamine and increase vascular permeability, which lead to plasma exudation. H(1)-receptors are present on T cells, B cells, monocytes, and lymphocytes, and stimulation of these receptors induces pro-inflammatory effects. It has been suggested that a signal from the H(1)-receptor contributes to the antigen receptor-mediated signaling pathways that induce proliferative responses and lead to the production of cytokines and antibodies by T cells and B cells, respectively. It would appear, therefore, that the H(1)-receptor has a wider role in inflammatory processes than simply mediating the actions of histamine.

Resident cardiac mast cells and ischemia-reperfusion injury

BACKGROUND

The intense inflammatory reaction following reperfusion of ischemic myocardium has been implicated as a factor in the extension of myocardial injury. One of the therapeutic goals of modern cardiology is to design strategies to limit the infarct size following myocardial infarction. A sound understanding of the inflammatory cascade that involves the release of various proinflammatory mediators from cardiac cells is necessary before a specific intervention is pursued.

OBSERVATION

Summarized is the role of resident cardiac mast cells, which are noted to release inflammatory mediators, in ischemia-reperfusion-induced myocardial injury. Various pharmacologic interventions, such as disodium cromoglycate and ketotifen, that stabilize cardiac mast cells, or agents such as chlorpheniramine and cetirizine that prevent their degranulation during ischemia and reperfusion, may prove to be potential therapeutic agents to limit or salvage ischemia-reperfusion-induced injury.

CONCLUSION

On the basis of the effects of histamine H1 antagonists, adrenoceptor blockers, cellular calcium and nitric oxide modulators, as well as inhibitors of phosphodiesterase and mitogen-activated protein kinase on mast cells, cardiac resident mast cells may represent a novel target for the development of cardioprotective agents.

Desloratadine: a nonsedating antihistamine

OBJECTIVE

To review information on desloratadine, a nonsedating antihistamine.

DATA SOURCES

An English-language MEDLINE search was conducted (1966-July 2002). References of identified articles were subsequently reviewed for additional data. Schering Corporation provided unpublished information.

STUDY SELECTION/DATA EXTRACTION

Articles and abstracts pertaining to desloratadine were considered for inclusion, with emphasis on randomized, placebo-controlled, double-blind trials.

DATA SYNTHESIS

Desloratadine is approved for the treatment of symptoms associated with seasonal allergic rhinitis (SAR), perennial allergic rhinitis (PAR), and chronic idiopathic urticaria (CIU) in patients aged > or =12 years. In placebo-controlled trials, desloratadine demonstrated superior efficacy as a once-daily treatment of SAR, PAR, and CIU. Data suggest that desloratadine has antiinflammatory and decongestant activity.

CONCLUSIONS

Desloratadine appears to be a "me-too" agent, with no major differences compared with other second-generation antihistamines.

Intranasal corticosteroids for allergic rhinitis: superior relief?

Whether first-line pharmacological treatment of allergic rhinitis should be antihistamines or intranasal corticosteroids has been discussed for several years. First-generation antihistamines are rarely used in the treatment of allergic rhinitis, mainly because of sedative and anticholinergic adverse effects. On the basis of clinical evidence of efficacy, no second-generation antihistamine seems preferable to another. Similarly, comparisons of topical and oral antihistamines have been unable to demonstrate superior efficacy for one method of administration over the other. Current data documents no striking differences in efficacy and safety parameters between intranasal corticosteroids. When the efficacy of antihistamines and intranasal corticosteroids are compared in patients with allergic rhinitis, present data favours intranasal corticosteroids. Interestingly, data do not show antihistamines as superior for the treatment of conjunctivitis. Safety data from comparative studies in patients with allergic rhinitis do not indicate differences between antihistamines and intranasal corticosteroids. Combining antihistamines and intranasal corticosteroids in the treatment of allergic rhinitis does not provide any additional effect to intranasal corticosteroids alone. On the basis of current data, intranasal corticosteroids seem to offer superior relief in allergic rhinitis than antihistamines.

Mast cell alpha-chymase reduces IgE recognition of birch pollen profilin by cleaving antibody-binding epitopes

In sensitized individuals birch pollen induces an allergic response characterized by IgE-dependent mast cell degranulation of mediators, such as alpha-chymase and other serine proteases. In birch and other plant pollens, a major allergen is profilin. In mammals, profilin homologues are found in an intracellular form bound to cytoskeletal or cytosolic proteins or in a secreted form that may initiate signal transduction. IgE specific to birch profilin also binds human profilin I. This cross-reactivity between airborne and endogenous proteins may help to sustain allergy symptoms. The current work demonstrates that cultured mast cells constitutively secrete profilin I, which is susceptible to degranulation-dependent proteolysis. Coincubation of chymase-rich BR mastocytoma cells with Ala-Ala-Pro-Phe-chloromethylketone (a chymase inhibitor) blocks profilin cleavage, which does not occur in degranulated HMC-1 mast cells, which are rich in tryptase, but chymase deficient. These data implicate chymase as the serine protease cleaving secreted mast cell profilin. Sequencing of chymase-cleaved profilins reveals hydrolysis at Tyr(6)-Val(7) and Trp(35)-Ala(36) in birch profilin and at Trp(32)-Ala(33) in human profilin, with all sites lying within IgE-reactive epitopes. IgE immunoblotting studies with sera from birch pollen-allergic individuals demonstrate that cleavage by chymase attenuates binding of birch profilin to IgE. Thus, destruction of IgE-binding epitopes by exocytosed chymase may limit further mast cell activation by this class of common plant allergens, thereby limiting the allergic responses in sensitized individuals.

Effects of intranasal azelastine on the response to nasal allergen challenge

OBJECTIVES/HYPOTHESIS

Azelastine, a second-generation H1-receptor antagonist, is available for topical administration. The aim of the study was to evaluate the effects of topical intranasal azelastine on the early-phase and the late-phase allergic responses and on nasal hyper-responsiveness to methacholine.

STUDY DESIGN

Double-blind, placebo-controlled, two-way crossover study in 20 subjects with seasonal allergic rhinitis, out of their allergy season.

METHODS

Subjects were randomly assigned to receive either placebo or two puffs of azelastine twice a day (548 microg/d) for 2 weeks followed by nasal challenge with allergen. Twenty-four hours later, while still receiving treatment, subjects underwent a nasal lavage and a nasal challenge with methacholine. End points included symptom scores, levels of mediators and number of eosinophils in nasal lavages, and the weight of secretions after methacholine challenge.

RESULTS

Compared with placebo, treatment with intranasal azelastine resulted in significant reductions in allergen-induced sneezing, rhinorrhea, itching, nasal congestion, and levels of albumin during the early-phase response (P <.05). Azelastine had no effect on levels of histamine or tryptase during the early-phase response. There was a significant eosinophil influx 24 hours after challenge, which was not inhibited by azelastine. Treatment with azelastine had no effect on the levels of albumin, interleukin-4, interleukin-5, intercellular adhesion molecule-1, tumor necrosis factor-alpha, and eosinophil cationic protein during the late-phase response. However, azelastine did show a significant inhibitory effect on the methacholine response 24 hours after nasal allergen challenge (P <.05).

CONCLUSIONS

The effects of intranasal azelastine are similar to those of oral second-generation antihistamines.

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.