Study of the effects of paf-acether on human nasal airways

In 6 normal subjects and 6 patients with allergic rhinitis, nasal response to insufflation of paf-acether (paf, platelet-activating factor), lyso-paf and histamine was evaluated. Nasal challenge with paf, at doses of 300 and 600 nM, induced nasal obstruction, associated with an increase in nasal airway resistances, measured by anterior passive rhinomanometry. Maximum increase in nasal airway resistance was observed at 30 min after challenge (mean percent change + 481 with 600 nM paf; P less than 0.05). Other symptoms induced by paf insufflation were rhinorrhea (6 out of 12 subjects), itching (8 out of 12), sneezing (4 out of 12) and a burning sensation (6 out of 12). No differences were observed between normal and rhinitic subjects, concerning nasal sensitivity to paf. Neither nasal symptoms nor changes in nasal airway resistance were observed after nasal challenge with lyso-paf (300 and 600 nM); by contrast, histamine (100 nM) induced sneezing, nasal obstruction, itching and rhinorrhea in all the studied subjects, associated with an increase in nasal airway resistance (maximum 5 min after challenge; percent change + 358; P less than 0.02). Nasal effects of paf were not mediated by histamine, since no increase in histamine levels was observed in nasal washings following paf insufflation. We conclude that paf may have pathogenetic relevance in allergic rhinitis.     

Mucosal blood flow in the human nose following local challenge with histamine

Nasal blood flow was measured using the 133Xe wash-out method in 10 non-allergic subjects and 13 asymptomatic hay fever patients. Determinations were made before and 15 min after challenge with diluent, 0.13 mg, 1.3 mg and 13 mg of histamine/nasal cavity. Nasal symptom scores were recorded. The nasal inspiratory peak flow was determined simultaneously in the hay fever patients. No differences in blood flow or symptom score recordings were found between the normal subjects and allergic patients under basal conditions or after histamine challenge. The nasal blood flow increased after challenge with the highest histamine dose. The increase was 34% (P less than 0.05) from baseline in normals and 47% (P less than 0.05) in allergics. There was a dose-dependent increase in nasal symptom scores following histamine challenge, again with no difference between normal and allergic subjects. The nasal peak flow decreased in a similar manner with a maximum decrease of 74% (P less than 0.001). The present study gives further support to the notion that histamine is not the only mediator involved in vascular reactions during allergic rhinitis.     

Activity of substance P on human skin and nasal airways

Nasal challenge and intradermal injection with substance P (SP) were performed in five normal subjects and in five patients suffering from allergic rhinitis. No clinical symptoms, local histamine release, or modifications of nasal airway resistance were observed when SP was insufflated in the nose. Conversely, intradermal injection with SP caused a wheal and flare reaction in all the studied subjects. The different response to SP is likely to be due to the heterogeneity of human skin and nasal mucosa mast cells as far as sensitivity to histamine-releasing agents is concerned. Our findings indicate that SP has no relevant effect on human nasal mucosa, even if a synergetic action of SP with other allergic mediators cannot be excluded. The role of SP in the pathogenesis of allergic diseases in humans remains to be defined and deserves further study.     

The role of leukotriene D4 in allergic rhinitis

We investigated the clinical significance of leukotriene D4 (LTD4) in nasal symptoms of allergy and compared this with antigen and histamine. Nasal provocations were carried out in patients with allergic rhinitis using serially increasing doses of LTD4, histamine, or antigen. The nasal responses induced were evaluated by counting the number of sneezes, the quantity of nasal secretion, and of nasal airway resistance. When the effects of topical provoking agents were compared at the threshold concentration, LTD4 produced no sneezing--unlike antigen and histamine--increased nasal secretion to a lesser degree than antigen and histamine (P less than .001), and increased nasal airway resistance similar to histamine but less than antigen (P less than .1) and longer than histamine, and similar to antigen in duration. LTD4 was approximately 5,000 times stronger than histamine in threshold concentration for nasal response. In conclusion, LTD4 plays an important role in nasal allergy presumably through long lasting and strong nasal blockage effects.     

Inflammatory cells and mediator release during ragweed challenge: correlation between histamine content in nasal secretions and appearance of inflammatory cells.

The early and late phase responses in the nasal tissues exhibit release of inflammatory mediators and a mixed cellular influx in separate nasal challenges. To explore this phenomenon further, histamine concentration was determined along with characterization of cell influx during dose-dependent ragweed challenges. Ten subjects with allergic rhinitis underwent two unilateral nasal lavages using incremental 3-fold concentrations of short ragweed. Low doses of ragweed (0.016 to 0.114 units Amb a I) rarely induced cell influx (1/18 challenges), whereas moderate doses (0.432 to 1.3 units Amb a I) caused cell influxes in 7/18 and high doses (3.39 to 11.7 units Amb a I) resulted in cell influxes in 8/17. The eluent contained greater than 50% neutrophils in seven challenges; greater than 50% eosinophils in three; and a mixed pattern in six. There was a significant association between the dose of antigen and the level of histamine. Challenges with an eosinophilic influx tended to be associated with higher concentrations of histamine than neutrophilic influxes. Similar to the immediate skin response, the early allergic response in the nose demonstrated a cell influx with release of histamine. Nasal cellular inflammation therefore can occur within minutes of allergen exposure.     

Histamine concentrations in nasal secretion and secretory activity in allergic rhinitis

The prerequisites for using the assayed histamine concentration in nasal secretion as an objective measure of disease activity in allergic rhinitis were investigated. It was demonstrated that in histamine determination procedures the presence of quenching substances in the nasal secretion could lead to underestimation of the histamine concentration. This bias was eliminated in a modified spectrofluorometric assay. Only an insignificant fraction of the histamine in samples collected by nasal spray washing was bound to unfiltrable particles or cells. The mean histamine concentration in nasal secretions from 15 healthy subjects was 11.2 micrograms/ml and in a group of nine patients with allergic rhinitis out of season 3.36 micrograms/ml. The histamine concentration in the latter group decreased during the pollen season and after positive allergen challenge. It is suggested that this decrease is caused by the increase in volume of the secretion during the allergic response. The use of lithium as an exogenous marker permitted quantitation of the increase in the relative amount of nasal secretion recovered by washing in the symptomatic subjects.     

Use of nasal peak flow to assess nasal patency

Nasal patency is usually assessed in the laboratory by measuring nasal airflow conductance ( Gnaw ); peak inspiratory and/or expiratory flow measurements via the nose (PIFna, PEFna) have been proposed as simple alternatives suitable for home monitoring of rhinitis. We have compared the scale of changes in PIFna and PEFna (measured with a pneumotachograph) with changes in Gnaw (measured by the forced-oscillation technique) when nasal patency was increased by a topical α-adrenergic agonist, xylometazoline (five control subjects, seven with seasonal rhinitis, studied when asymptomatic) or decreased by topical histamine (eight control subjects). In further experiments, we altered intrapulmonary airway calibre by having subjects inhale histamine or salbutamol aerosols and examined effects on the configuration of nasal flow-volume curves (six subjects with rhinitis and mild asthma). After topical xylometazoline, there was a mean 283% increase in Gnaw 80% increase in PEFna, and 63% increase in PIFna. After topical histamine, there was a mean 72% decrease in Gnaw, 38% decrease in PEFna, and 39% decrease in PIFna. Inducing intrapulmonary airway obstruction sometimes obscured changes in nasal patency by removing the effects of added nasal resistance on expiration and preventing development of flow limitation in the nose on inspiration. Thus, after topical drug treatment to the nose, changes in Gnaw were considerably larger than in PEFna or PIFna, which were proportionately similar. Because PIFna is usually restricted by nasal flow limitation, it is probably superior to PEFna for assessing nasal patency. When effort is submaximal, intrapulmonary dynamic resistance is increased, or nasal dynamic resistance is low, PEFna and PIFna can give a misleading impression of nasal patency. These errors can be avoided by comparisons with mouth PEF and/or PIF, suggesting that nasal and mouth peak flow should both be measured during home monitoring.     

Substance P induced histamine release from nasal mucosa of subjects with and without allergic rhinitis

OBJECTIVE AND DESIGN: There is evidence that substance P (SP) is involved in events related to allergic and nonallergic rhinitis. Furthermore, some effects of SP seem to be greater in subjects suffering from allergic rhinitis than in nonallergic subjects. To investigate if these effects may be partly mediated by histamine release (HR) we studied the influence of SP on HR from nasal mucosa of subjects with and without allergic rhinitis using an in vitro organ culture system. SUBJECTS: Nasal mucosa of the inferior turbinate was obtained from ten patients suffering from allergic rhinitis and eighteen non-allergic subjects receiving surgical therapy for nasal obstruction. METHODS: Tissue samples of nasal mucosa were stimulated with 10(-5) M SP or with 10(-5) M Ca-ionophore A23187 for 120 minutes, and the histamine content was determined in the culture supernatant. RESULTS: Both SP and Ca-ionophore A23187, caused a significantly higher HR from the samples of the non-allergic group (p < 0.01) compared to baseline controls (spontaneous release). The same effect was seen in the allergic group (p < 0.01 and p = 0.036). Comparing the increase in HR from allergic and non-allergic mucosa, in allergics the HR stimulated by SP was significantly higher (p = 0.031), whereas Ca-ionophore A23187 did not show this effect. CONCLUSION: These findings suggest a role of SP in inducing release of histamine from human nasal mucosa, thereby influencing physiologic and pathophysiologic nasal conditions, especially in allergic inflammatory processes.     

Variations in histamine concentration in nasal secretion in patients with allergic rhinitis

The histamine concentration and content in nasal secretion and the volume of nasal secretion in nasal washing samples were measured under different conditions in 28 patients with allergic rhinitis sensitive to birch pollen. The mean histamine concentration was significantly lower after intranasal birch pollen challenge (2.08 micrograms/ml) than in prechallenge samples (6.96 micrograms/ml), and was also significantly lower in untreated patients during the birch pollen season (2.30 micrograms/ml) than off-season (7.18 micrograms/ml). The same relationship was found between the histamine content of the secretion samples obtained on these occasions. The mean secretion volume was greater after than before challenge, but not significantly higher during the season than off-season. A partial reversion of the changes in histamine concentration and content that occurred during the season was observed during intranasal corticosteroid therapy. The concentration and content of histamine in nasal secretion from symptomatic patients after intranasal histamine challenge did not differ significantly from those in asymptomatic subjects before challenge. It was concluded that although the histamine level in nasal secretion can be used as a marker of changes in the severity of allergic rhinitis, it is not ideal for this purpose.     

Eustachian tube obstruction (ETO) after histamine nasal provocation--a double-blind dose-response study

Eustachian tube obstruction (ETO) has been reported to develop more frequently in subjects with allergic rhinitis (AR) than in subjects without AR after a single intranasal histamine challenge. The present double-blind crossover study was designed to confirm and extend this observation. In a pilot study, nebulization was demonstrated to be superior to insufflation in provoking ETO. Five subjects with AR and five subjects without AR were repeatedly challenged intranasally with nebulized normal saline or increasing doses of histamine (0.01, 0.1, 0.5, 1.0, 5, and 10 mg per nostril). Subjects with AR were selected on the basis of AR symptoms and IgE antibodies to allergens and were challenged in their nonallergy seasons. ETO was assessed by nine-step tympanometry and nasal airway resistance by anterior rhinomanometry before and after each challenge. Of nine ears in subjects with AR, ETO developed in five ears at 0.1 mg and in four ears at 0.5 mg. In contrast, in 10 ears of subjects without AR, ETO developed in two ears at 5 mg but did not develop in eight ears at doses as large as 10 mg. This test effectively discriminated subjects with AR from subjects without AR, groups that could not be similarly differentiated by nasal or skin responsiveness to histamine challenge. Saline challenges provoked ETO in three of nine ears of subjects with AR and in one of 10 ears of subjects without AR. These data suggest a hyperresponsiveness of the nasopharyngeal and/or tubal mucosa to histamine in subjects with AR that may predispose these patients to otitis media with effusion.     

A dose-ranging study of fluticasone propionate aqueous nasal spray for seasonal allergic rhinitis assessed by symptoms, rhinomanometry, and nasal cytology

Fluticasone propionate is a new glucocorticosteroid with potent topical activity. In a double-blind, randomized, parallel-group study, 423 adult patients with moderate to severe seasonal allergic rhinitis received placebo or fluticasone propionate aqueous nasal spray at doses of 25, 100, or 400 micrograms twice daily (b.i.d.) for 2 weeks. Efficacy was evaluated by nasal symptom scores, nasal airflow, nasal cytology, and global evaluation. All doses of fluticasone propionate were significantly better than placebo in reducing symptoms of seasonal allergic rhinitis. Patients receiving the largest dose of fluticasone propionate (400 micrograms b.i.d.) had a slightly greater reduction (not significant) in symptom scores than patients receiving the smallest dose (25 micrograms b.i.d.). Symptom improvement was evident within 3 days of treatment. Nasal airflow improved in the groups treated with fluticasone propionate, 100 and 400 micrograms b.i.d. Examination of nasal cytograms revealed a striking decrease in both eosinophils and basophils in all three groups receiving active treatment compared with placebo. There were few adverse events and no treatment-related abnormalities in laboratory assays or evaluations of hypothalamo-pituitary-adrenocortical axis function. Comparison of treatment groups indicated that fluticasone propionate aqueous nasal spray was as safe as placebo at the doses studied.     

Onset of action in the nasal antihistaminic effect of cetirizine and loratadine in patients with allergic rhinitis

Several studies have compared the cutaneous efficacy of cetirizine and loratadine and their onset of action. We assessed the nasal effect of these two antihistamines in a randomized, double-blind, crossover, placebo-controlled trial in order to compare objectively their efficacy and onset of action in the noses of patients with allergic rhinitis. Nasal challenge was performed by nebulization of increasing doubling doses of histamine (0, 0.04-1.28 mg/nostril) in 12 patients (eight men, four women, aged 22-39 years). Nasal airway resistance (NAR) was measured by posterior rhinomanometry either 1.5 h or 4 h after intake of cetirizine (10 mg), loratadine (10 mg), or placebo. Baseline NAR was identical between all study days (2.60-2.88 cmH₂O·1⁻¹·s). One and a half hours after intake, the increase in NAR induced by histamine was significantly reduced by both cetirizine and loratadine in contrast to placebo. However, with cetirizine the nasal obstruction was significantly lower than with loratadine ( P <0.05). Four hours after intake, a similar inhibition of the nasal obstruction caused by histamine was observed with both cetirizine and loratadine ( P <0.05). In conclusion, this study found cetirizine and loratadine to have similar nasal efficacy at therapeutic dosage 4 h after intake, whereas cetirizine was more effective than loratadine 1.5 h after intake. In agreement with the results observed in the skin, our study suggests a more rapid onset of action of cetirizine in the nose in allergic rhinitis.     

Atypical nasal challenges in patients with idiopathic rhinitis: more evidence for the existence of allergy in the absence of atopy?

BACKGROUND: The pathophysiology of idiopathic rhinitis is unknown although evidence is accumulating to suggest that many patients may have a localized form of allergic rhinitis in the absence of other atopic symptoms and markers. This study compares detailed nasal challenge results obtained from patients with idiopathic rhinitis to those of atopic and normal controls. METHODS: Patients with idiopathic rhinitis (n = 23), perennial allergic rhinitis (n = 8) and normal controls (n = 8) underwent a normal saline challenge to exclude hyper-reactivity and then bilateral nasal allergen challenges. Nasal patency was assessed by anterior active rhinomanometry. RESULTS: All of the patients with atopic rhinitis demonstrated positive bilateral allergen challenges. All normal control subjects had bilateral negative challenges. Two patients in the idiopathic group tested positively to saline and were excluded from further study with 62% of the remainder testing positive to allergens. Of the idiopathic patients testing positive, 85% were sensitive to house dust mite. CONCLUSION: A significant proportion of patients with idiopathic rhinitis have positive nasal challenges, the vast majority to house dust mite allergen. These findings add to the weight of evidence that suggests 'localized allergy' may exist in the absence of systemic atopic markers.     

Rhinomanometry study of patients with respiratory allergy

To examine the accuracy of nasal allergic disease, we examined the results of skin tests, measurement of serum specific IgE (RAST), and the nasal response to nasal challenge in 886 patients clinically suspected of having allergic respiratory disease. Nasal responses were assessed by measuring nasal airway resistance by both active anterior and posterior rhinomanometry. Nasal airway resistance was determined 25 min. after intranasal nebulization of saline solution and after administration of increasing doses of allergen (maximum dose = 280 micrograms). The dose of allergen causing a 100% increase over the value obtained after saline (Ri) at a flow rate of 0.15 l.s-1 was taken as the threshold dose (Dl). Our findings were that active anterior and posterior rhinomanometry yield comparable results; in subjects with a positive response to antigen challenge, the increase in nasal airway resistance correlated well with the dose of allergen administered and a significant inverse relationship was found between Ri and Dl; 3) a high level of serum specific IgE accurately predicted nasal responsiveness to a particular allergen, whereas skin tests were often positive to allergens that had no detectable effect on the nasal resistance. We conclude that nasal allergen provocation tests with rhinomanometric measurement of nasal resistance is a useful procedure for diagnosis of nasal allergic disease.     

Albumin, bradykinins, and eosinophil cationic protein on the nasal mucosal surface in patients with hay fever during natural allergen exposure

This study examined plasma- and eosinophil-derived products in nasal lavage fluids obtained from patients with hay fever during natural allergen exposure. Nine patients with strictly seasonal allergic rhinitis and five normal, nonallergic subjects (control group) were studied. Nasal lavages were performed twice weekly, starting 1 week before the expected birch-pollen season and continuing for 6 weeks, thereby covering the entire birch-pollen season. Nasal symptoms and pollen counts were recorded daily. The lavage fluid was analyzed for it content of albumin, bradykinins, and eosinophil cationic protein (ECP). During the pollen season, each of these solutes was significantly increased in the nasal lavage fluid from the allergic patients (p less than 0.05) but not from the control subjects. Albumin, bradykinins, and ECP generally correlated better between themselves than with symptoms and pollen counts. We conclude that natural exposure to allergens induces plasma exudation and increased levels of ECP on the human nasal mucosa.     

Effect of terfenadine on nasal, eustachian tube, and pulmonary function after provocative intranasal histamine challenge.

Previous studies have documented that intranasal histamine challenge results in nasal and eustachian tube obstruction (ETO) in human volunteers. The purpose of the present study was to assess the effect of pretreatment with terfenadine, a nonsedating antihistamine on the pathophysiologic consequences of intranasal histamine challenge. Fifteen subjects with allergic rhinitis were challenged intranasally with saline and increasing histamine doses (0.01, 0.1, 0.5, 1.0, 5.0, and 10.0 mg) before pretreatment (baseline) and after 1 week of pretreatment with terfenadine, 60 mg b.i.d., terfenadine, 120 mg b.i.d., and placebo. Nasal conductance as measured by posterior rhinomanometry showed a dose-dependent, monotonic decrease following sequential administration of the histamine solutions, but there were no apparent differences in the average responses among the four challenge sessions. The frequency of ETO after histamine challenge was decreased by pretreatment with both doses of terfenadine, although this was not significant. Histamine-induced sneezing and rhinorrhea, but not congestion, were significantly reduced by terfenadine pretreatment. There was no evidence of extension of the histamine effects to the lower airway. The results of the present study suggest that terfenadine, a nonsedating antihistamine, had a favorable effect on sneezing and rhinorrhea after provocative intranasal histamine challenge, but did not significantly attenuate the subjective or objective nasal and ET obstructive responses.     

Bradykinin increases the in vivo expression of the CXC chemokine receptors CXCR1 and CXCR2 in patients with allergic rhinitis

BACKGROUND: Increased levels of bradykinin and IL-8 have been detected within the airways of individuals with active symptoms of allergic rhinitis and asthma. OBJECTIVE: We sought to investigate the in vivo effect of bradykinin on the expression of the IL-8 receptors CXCR1 and CXCR2 in nasal cells. METHODS: Nasal samples were obtained from patients with active allergic rhinitis; patients with mild, quiescent allergic rhinitis; and healthy control subjects. CXCR1 and CXCR2 mRNA expression in the nasal cells was measured by means of quantitative real-time RT-PCR in baseline samples from all subjects, as well as in samples obtained after in vivo bradykinin challenge in healthy control subjects and patients with mild allergic rhinitis. CXCR1 and CXCR2 cell-surface expression was also assessed by means of flow cytometry in nasal epithelial cells at baseline and after ex vivo bradykinin challenge. RESULTS: No difference was seen in CXCR1 or CXCR2 mRNA expression between healthy control subjects and patients with quiescent allergic rhinitis at baseline; however, patients with active allergic rhinitis had increased baseline expression of both CXCR1 and CXCR2 mRNA. In vivo nasal bradykinin challenge significantly increased CXCR1 and CXCR2 mRNA expression in patients with quiescent allergic rhinitis but had no effect in healthy control subjects. Low levels of CXCR1 but not CXCR2 cell-surface expression was detected in nasal epithelial cells at baseline, and ex vivo bradykinin challenge induced CXCR2 cell-surface expression in nasal epithelial cells from patients with mild allergic rhinitis. CONCLUSION: This study demonstrates the in vivo regulation of chemokine receptors by means of bradykinin in human airway tissue in patients with allergic rhinitis.     

Epidermal growth factor receptor - but not histamine receptor - is upregulated in seasonal allergic rhinitis

BACKGROUND: We were interested in exploring the molecular mechanisms underlying the observed difference in histamine (H) responsiveness between seasonal allergic rhinitic (SAR) and nonrhinitic (NR) subjects. We hypothesized that SAR subjects express higher nasal mucosal histamine receptor 1 (H1R) and 2 (H2R) levels than do NR subjects. In addition, we examined expression of genes involved in regulating the glandular response, including epidermal growth factor (EGF), EGF receptor (EGFR), and mucins (Muc5Ac and Muc5B). METHODS: Fourteen subjects, seven SAR and seven NR, were provoked during pollen season with doubling doses of H (0.125-8.0 mg/ml). Nasal airway resistance (NAR) was measured by active posterior rhinomanometry. Provocation was halted when NAR exceeded 150% of baseline. Prior to provocation, nasal scrapings were obtained and mRNA quantified using two-step real-time PCR. RESULTS: The mean PD50 (concentration of H producing a 50% increase in NAR) was significantly lower in the SAR than NR group (0.36 vs 1.32 mg/ml; P < 0.05). The ratio of relative gene copy numbers between the SAR and NR groups were as follows: H1R, 0.85 (P = 0.52); H2R, 0.67 (P = 0.35); EGF, 1.02 (P = 0.93), and EGFR, 103.5 (P < 0.05). CONCLUSIONS: There were no significant differences in H1R or H2R mRNA levels between SAR and NR subjects in-season, despite observed differences in H reactivity. SAR subjects, however, did show a significant elevation in EGFR expression, consistent with the observation of mucus hypersecretion in allergic rhinitis.     

Tryptase in nasal lavage fluid after local allergen challenge: Relationship to histamine levels and TAME-esterase activity

The activation of mast cells is generally considered to be an important trigger mechanism in the immediate allergic response. This study focused on the determination of three markers of mast cell activation after an allergen challenge. Nasal allergen challenges were performed in 25 subjects with seasonal allergic rhinitis using three allergen doses increasing in 10-fold steps in a standardised nasal lavage model for the subsequent recovery of the markers of mast cell activation. The levels of histamine and tryptase in the nasal lavage fluid were determined using radioimmunoassays, while the TAME-esterase activity was determined using a radiochemical technique. The nasal symptoms obtained on challenge were assessed using a scoring technique. The allergen challenge resulted in significant increases in the levels of all three markers, tryptase, histamine and TAME-esterase. In the individual measurements after the challenges there was a highly significant correlation between the TAME-esterase levels and the tryptase levels (r = 0.71; P less than 0.001), while the generation of histamine and tryptase was not significantly correlated. When comparing the cumulative generation of the three markers, significant correlations were found between all three. Allergen challenges in six non-allergic controls using the same technique did not result in any increase in tryptase levels. The findings suggest that the determination of tryptase in nasal lavage fluid may be a valuable indicator of mast cell activation in the upper airways.     

The effect of intranasal azelastine, Rhinolast®, on nasal airways obstruction and sneezing following provocation testing with histamine and allergen

The effect of single dose topical nasal therapy with azelastine hydrochloride (azelastine) on the response of nasal airways resistance (NAR) to provocation testing was studied in 36 patients with seasonal allergic rhinitis. Nasal provocation testing (NPT) with histamine or grass pollen was performed after a single dose of azelastine, 0.28 mg to each nostril, or placebo. NAR was assessed by rhinomanometry for 10 hr following NPT. Compared to placebo the NAR response to histamine was inhibited at both 1 and 2 hr following azelastine administration, significant at 1 hr (P less than 0.02) and 2 hr (P less than 0.0001). No such effect was observed in relation to allergen-induced changes in NAR. Azelastine also inhibited numbers of sneezes for up to 10 hr following both histamine NPT (P less than 0.02) and allergen NPT (P less than 0.05), when compared to placebo. Forty-seven per cent of participants experienced bitter or unpleasant taste sensations after azelastine administration but no other unwanted effects were clearly related to azelastine therapy.