Astemizole and other H1-antihistaminic drug treatment of asthma

New H1-Receptor Antagonists: A Review

The new H1-receptor antagonists such as astemizole, cetirizine, loratadine, levocabastine, ketotifen, and azelastine have diverse pharmacokinetics, pharmacodynamics, and potency. Astemizole, for example, is the most long-acting of the new drugs and is not suitable for sporadic use. Cetirizine, the carboxylic acid metabolite of hydroxyzine, unlike other H1-receptor antagonists, is minimally metabolized in the body and is primarily excreted in unchanged form in the urine. Levocabastine is the most potent of the new drugs and can be applied topically to the conjunctivae or to the nasal mucosa for relief of allergic rhinoconjunctivitis. Ketotifen and azelastine have well-described antiallergic effects in addition of their antihistaminic effects. None of the new H1-receptor antagonists is any more effective in relieving nasal congestion than the first-generation H1-receptor antagonists are. Most, but not all, of the new H1-receptor antagonists lack anticholinergic effects and are relatively nonsedating.

A review of loratadine in the treatment of patients with allergic bronchial asthma

Patients with seasonal or allergic bronchial asthma experience an immediate allergic response caused by allergen-specific immunoglobulin E-mediated histamine release. The release of histamine and other chemical mediators may trigger airway hyperresponsiveness and exaggerated bronchoconstriction, characteristic features of allergic bronchial asthma. Traditional antihistamines have demonstrated only moderate activity of short duration against this disease. In contrast, loratadine, a potent, nonsedating, histamine-1-receptor antagonist with activity in seasonal and perennial allergic rhinitis, has demonstrated effective control of asthma symptoms, improved pulmonary function, and long duration of action in patients with allergic bronchial asthma. This review summarizes preclinical evidence for the antiallergic activity of loratadine and the results of clinical studies with oral loratadine in patients with allergic bronchial asthma.

The effect of cetirizine and loratadine on codeine-induced histamine release in human skin in vivo assessed by cutaneous microdialysis

OBJECTIVE AND DESIGN

To determine whether or not cetirizine and loratadine inhibit codeine- induced histamine release in human skin in vivo, we conducted a placebo-controlled double-blind trial in which histamine release was assessed by dermal microdialysis.

SUBJECTS

A group of ten normal volunteers were studied, each subject visiting the laboratory on three occasions with intervals of at least 2 weeks between visits.

TREATMENT

Cetirizine, loratadine (both 10 mg) or placebo was given orally 4 h before provocation of weal and flare responses in the skin by intradermal injection of 25 microliters of 3 or 10 mg/ml codeine 1 mm from the centre of individual 216 microns diameter microdialysis fibres inserted in the dermis.

METHODS

Dialysate was collected at 2 min intervals for 4 min before and 20 min after codeine injection and histamine assayed spectrofluorometrically. Weal and flare responses to codeine were assessed in the opposite arm.

RESULTS

Histamine concentrations in the microdialysis fibre outflow with 3 and 10 mg/ml codeine were maximal at 2-4 min when 910 +/- 156 and 1194 +/- 304 nM respectively were found in the placebo group. Cetirizine and loratadine did not modify either the kinetics or total histamine release while significantly (p < 0.01) inhibiting weal and flare responses.

CONCLUSIONS

Neither cetirizine nor loratadine inhibited codeine-induced histamine release or modified the time course of its release in human skin in vivo when given in clinically used doses which are sufficient to significantly reduce weal and flare responses.

Inhaled lysine acetylsalicylate (L-ASA) attenuates histamine-induced bronchoconstriction in asthma

When administered by inhalation, histamine provokes dose-related bronchoconstriction in asthmatic subjects mainly by a direct activation of histamine H1-receptors on airway smooth muscle. However, little is known of the change in airway responsiveness to histamine after cyclooxygenase blockade. The aim of the study was to investigate the effect of the potent cyclooxygenase inhibitor, lysine acetylsalicylate (L-ASA), administered by inhalation on histamine-induced bronchoconstriction in a group of 16 asthmatic subjects. The subjects studied attended the laboratory on four separate occasions to receive nebulized L-ASA (solution of 90 mg/ml) or matched placebo (glycine solution of 30 mg/ml) 15 min before bronchoprovocation tests with histamine and methacholine in a randomized, double-blind order. Changes in airway caliber were followed as forced expiratory volume in 1 s (FEV1), and agonist responsiveness was expressed as the provocative concentration causing a 20% fall in FEV1 from baseline (PC20). Administration of both L-ASA and glycine solution caused a small but significant acute fall in FEV1 from baseline, which returned to normal within 15 min. When compared to placebo, inhaled L-ASA reduced the airway responsiveness to histamine in 13 of the 16 subjects studied, the geometric mean (range) values fro PC20 histamine increasing significantly (P < 0.001) from 1.72 (0.13-5.49) mg/ml to 3.31 (0.36-12.00) mg/ml after placebo and L-ASA, respectively. No significant change in airway responsiveness to methacholine was recorded after L-ASA. Acute administration of L-ASA by inhalation protects the asthmatic airways against histamine-induced bronchoconstriction, thus suggesting that endogenous prostaglandins may play a contributory role in the airways response to histamine in human asthma.

Changing strategies in the management of asthma

Mortality from asthma is apparently on the rise and, in some cases, may be due to the type and amount of medication used by the patient. As a result, the role of some commonly prescribed agents has changed in recent years. In this article, the authors review modifications in the use of currently available drugs, discuss new applications of drugs not traditionally used for asthma, and examine the rationale behind the development of entirely new classes of drugs.

Role of histamine in allergen-induced asthmatic reactions, bronchial hyperreactivity and inflammation in unrestrained guinea pigs

In a new model using conscious, unrestrained and ovalbumin-sensitized guinea pigs, we investigated the effects of the selective histamine H1 receptor antagonist, mepyramine, on the development of allergen-induced early and late asthmatic reactions, bronchial hyperreactivity and airway inflammation, having each animal as its own control. In guinea pigs responding to a first allergen exposure with an early as well as a late asthmatic reaction (82% of the animals) a second, identical, allergen provocation was performed, in the absence (control) or presence of 1 mg/ml mepyramine aerosol, inhaled for 10 min, 1 h before provocation. The mepyramine treatment significantly reduced both early and late asthmatic reactions and prevented the development of bronchial hyperreactivity to histamine and methacholine after both reactions. Examination of the bronchoalveolar lavage fluid 24 h after the second allergen provocation revealed a general reduction of inflammatory cells after mepyramine treatment. The results indicate that histamine, released during the early asthmatic reaction, contributes to the development of the late asthmatic reaction as well as of early and late bronchial hyperreactivity, possibly via an effect on airway inflammation.

Immunoglobulin-G-dependent stimulation of guinea pig lung mast cells and macrophages

Alveolar macrophages and mast cells isolated from guinea pig lung were passively sensitized with IgG1, IgG2, or serum obtained from guinea pigs actively sensitized with ovalbumin. The release of histamine by mast cells and of thromboxane A2 by alveolar macrophages upon ovalbumin challenge indicated that both antibodies and serum were capable of sensitizing these cells with similar effectiveness. Heating the serum at 56 degrees C for 4 h to inactivate IgE did not modify the antigen-dependent response of lung cells. These results suggest a predominant role for IgG in the allergic response of the guinea pig through the activation of different cell types such as lung mast cells and alveolar macrophages.

Comparative efficacy of salbutamol and salmeterol in exercise-induced asthma

This study compared the protection provided by salbutamol and salmeterol against exercise-induced asthma. Asthmatic patients (n = 12) with exercise-induced asthma were exercised submaximally for 6 min on a treadmill 1, 6 and 12 h after inhalation of 200 micrograms salbutamol or 50 micrograms salmeterol. Each patient also took baseline exercise 1 h after two puffs of placebo. Two days later the drugs were administered in a double-blind trial of crossover design with an interval of 48 h between the two treatments. The main parameters measured were: air flow with a Wright flowmeter and mediator concentrations (histamine, leucotriene and prostaglandin D2 measured by radioimmunoassay) in venous blood, which was withdrawn before and 4 min after each exercise period. The maximum percentage bronchoconstriction recorded following placebo was 29 +/- 4% and following salbutamol inhalation it was 4 +/- 4%, 20 +/- 13%, 27 +/- 10%, respectively, for the exercise periods performed 1, 6 and 12 h after inhalation of the drug. Following salmeterol, the corresponding figures were 3 +/- 4%, 3 +/- 3% and 11 +/- 9%. The concentrations of mediator in plasma were significantly increased after exercise. Salbutamol and salmeterol intake reduced these concentrations both when the patients were at rest and following the exercise period. This effect of both drugs on the mediators corresponded with the protection they provided against exercise-induced asthma and was maintained for 12 h after salmeterol inhalation and for 6 h after salbutamol inhalation.

Duration of effect of loratadine and terfenadine administered once a day for one week on cutaneous and inhaled reactivity to histamine

STUDY OBJECTIVE

The duration of action of several new non-sedative antihistamine preparations as assessed by skin and bronchial reactivity to histamine has still not been well established. The aim of the study was to evaluate the duration of effect of loratadine (10 mg) and terfenadine (120 mg) administered once a day for one week on cutaneous and inhaled reactivity to histamine by comparison with a placebo.

SUBJECTS

Twenty-four adult asthmatic subjects were included in a parallel group study that compared the duration of effect of two antihistamines and a placebo on cutaneous and inhaled reactivity to histamine.

STUDY DESIGN

Baseline cutaneous and inhaled reactivity (concentration causing a fall of 20 percent in FEV1 [PC20]) to histamine was obtained on three consecutive days. Loratadine (10 mg), terfenadine (120 mg) and a placebo loratadine were administered daily for 1 week to 3 groups of subjects. The PC20 was measured at the end of the medication period, 3 days later, and weekly until PC20 returned to baseline value (upper limit of 2 SD from the mean baseline value).

RESULTS

The mean blocking duration on cutaneous reactivity for loratadine was 6.9 days and for terfenadine, 7.2 days. The mean duration of the blocking effect on PC20 histamine was 8.5 days for loratadine and 7.2 days for terfenadine. These figures were significantly longer than for the placebo.

CONCLUSION

These data suggest that terfenadine and loratadine have a comparable blocking effect on reactivity to cutaneous and inhaled histamine. A daily dose taken for one week will result in a mean blocking effect of one week.

Asthma pathogenesis and the implications for therapy in children

Gaining greater insight into the pathogenesis of asthma has redefined the approach to treatment of children with asthma. Clearly, the Expert Panel of the National Heart, Lung, and Blood Institute National Education Program has played a major role in taking the message to a wide audience of health care providers. Although only early trends are evident at this point in time, within several years therapeutic trends underway currently will be more commonplace, and we may observe how asthma continues to impact society and our health care system. The approach to therapy will continue to evolve and most likely be controversial for years to come.

Effects of anti-allergic drugs on human neutrophil superoxide-generating NADPH oxidase

The effects of anti-allergic drugs with or without H1-receptor antagonism on the NADPH oxidase (EC 1.6.99.6) from human neutrophils in both whole-cell and fully soluble (cell-free) systems were investigated. Three anti-allergic drugs with H1-receptor antagonism, azelastine, ketotifen and oxatomide, were found to inhibit the superoxide generation of human neutrophils exposed to phorbol myristate acetate in a whole-cell system and the activation of superoxide-generating NADPH oxidase by sodium dodecyl sulfate in a cell-free system. The concentrations of these drugs required for 50% inhibition of the oxidase (IC50) were: azelastine--0.7 microM in the whole-cell system and 0.5 microM in the cell-free system; ketotifen--60 microM in the whole-cell system and 6.8 microM in the cell-free system; and oxatomide--25 microM in the whole-cell system and 9.7 microM in the cell-free system. In addition, in the cell-free system, these drugs did not change the Km values for the NADPH of the oxidase. However, these drugs did not inhibit the superoxide generation of NADPH oxidase after its activation in whole-cell and cell-free systems, suggesting that these drugs do not have superoxide-scavenger actions. Concentrations of less than 200 microM of anti-allergic drugs without H1-receptor antagonism, tranilast, repirinast and ibudilast, did not inhibit neutrophil NADPH oxidase in whole-cell and cell-free systems. The IC50 of hydrocortisone in the cell-free system was 60 microM. These results suggest that anti-allergic drugs with H1-receptor antagonism inhibit activation of the solubilized membrane-bound enzyme by sodium dodecyl sulfate in cell-free systems and that they have much stronger anti-inflammatory action than hydrocortisone.

Effects of H1-receptor blockade with terfenadine in nocturnal asthma

1. In a single-blind placebo controlled study we have measured peak flow (PEFR) at 04.00 h and 16.00 h in eight asthmatics 6 h after placebo or terfenadine 120 mg, to determine if diurnal variation in histamine mediated effects contribute to nocturnal bronchoconstriction in asthma. 2. On placebo there was a significant diurnal variation in mean PEFR of 41 l min-1 (P less than 0.05). Terfenadine improved 04.00 h baseline mean PEFR from 242 to 278 l min-1 (P less than 0.05) but a 38 l min-1 diurnal variation in mean PEFR persisted (P less than 0.05). 3. We conclude that H1-receptor blockade with terfenadine may produce modest nocturnal bronchodilatation but does not influence the diurnal variation in PEFR in asthma suggesting that H1-receptor mediated effects are not important in the pathogenesis of nocturnal asthma.

Histamine H1-receptor-mediated cyclic GMP production in guinea-pig lung tissue is an L-arginine-dependent process

Histamine produces a rapid and massive increase of the c-GMP level of guinea-pig lung tissue. The EC50 value for this in vitro response is found to be 27 microM and the c-GMP level is maximally 9-fold elevated by 100 microM histamine. The response is stereoselectively inhibited by the enantiomers of chlorpheniramine, indicating H1-receptor involvement. Preincubation of lung tissue with 200 microM NCDC, a phospholipase C inhibitor, reduces the histamine (100 microM) responses to 16 +/- 3% (N = 6) of the control c-GMP production. Inhibition of protein kinase C by 50 microM H-7 does not significantly attenuate the H1-receptor response, whereas omittance of extracellular Ca2+ results in almost complete inhibition of the c-GMP production. The histamine-induced c-GMP response is inhibited by hemoglobin, methylene blue and the antioxidants butylated hydroxytoluene and nordihydroguaretic acid, indicating the involvement of a nitric oxide-dependent activation of soluble guanylate cyclase. This suggestion is supported by the concentration-dependent inhibition of the c-GMP production by NG-monomethyl-L-arginine (NMA). At a concentration of 20 microM NMA the histamine (100 microM) response is inhibited to 34 +/- 8% (N = 6) of the control response. This inhibition is reversed to 127 +/- 20% (N = 6) by the exogenous addition of 1 mM L-arginine. These findings show that after an initial H1-receptor-mediated, phospholipase C-dependent, Ca(2+)-mobilization the enzymatic conversion of L-arginine to nitric oxide is stimulated. This nitric oxide production is finally responsible for the activation of soluble guanylate cyclase, leading to the production of c-GMP.

The effect of cetirizine on the human isolated bronchus: interaction with salbutamol

The effects of cetirizine (C), a new generation, nonsedative, H1-antihistamine drug, were studied on human isolated bronchi. C is a potent antagonist of the bronchial muscle contraction induced by histamine, irrespective of whether C is administered by cumulative addition or prophylactically. In the former case, this effect of C was significant at a concentration of 3 X 10(-8) mol/L and was maximal at a concentration of 10(-5) mol/L. The -log of concentration of C causing 50% of the maximal effect induced was 7.30 +/- 0.05 (n = 6), and the effect produced was not significantly modified by bronchial epithelium removal. When C was administered prophylactically, the concentration-response curves to histamine were displaced to the right, but the reduction of maximum histamine response suggests a noncompetitive type of antagonism. C is devoid of notable anticholinergic effects. At concentrations of 10(-8) to 10(-7) mol/L, C proved capable of enhancing the relaxant effect produced by salbutamol (10(-7) to 3 X 10(-7) mol/L) on human isolated bronchi that had been contracted by either histamine or acetylcholine (ACh). The synergy appeared to be additive or potentiating, depending on salbutamol (SAL) concentrations. Under similar conditions, mepyramine does not potentiate the effects of SAL against histamine. Finally, at concentrations of 10(-8) to 10(-6) mol/L, C reduced the functional antagonism observed between SAL and ACh, as can be observed by the increase, in the presence of C, of the maximal relaxant effect of SAL on contractions produced by 10(-3) mol/L of ACh. We may, therefore, conclude that C appears to be a specific antihistamine on human isolated bronchi and that it appears to potentiate the bronchodilator effect of SAL on this preparation.

Asthma and chronic obstructive lung disease: a pharmacologic approach

Changing concepts are emerging that should improve our ability to adequately treat asthma. This volume of Disease-a-Month reviews the triggers and the role of inflammation in asthma, and outlines the treatment of acute asthma as well as the chronic management of reversible obstructive airways disease. There is general agreement that sympathomimetics are the treatment of choice for acute severe asthma. The role of theophylline for acute symptoms has been downplayed, and the role of corticosteroids continues to be debated. However, most authorities agree that patients with severe asthma will benefit from the addition of corticosteroids to the program. For the chronic management of asthma, appreciation that inflammation is a perpetuating feature suggests that treatment should generally be directed toward the inflammation. Corticosteroid aerosols have taken on greater prominence and have been advocated as the first line of approach. New concepts regarding the role of allergy in the perpetuation of asthma and the role of immunotherapy in its amelioration also have emerged. Medications not previously thought to be beneficial are being actively investigated. They include gold, methotrexate, and even intravenous gamma globulin.

Comparison of the effect of loratadine on the airway and skin responses to histamine, methacholine, and allergen in subjects with asthma

Loratadine is a highly selective, long-acting, H1-receptor antagonist. In a randomized, double-blind, crossover study, we evaluated the effects of loratadine, 10 and 20 mg, and placebo administered once daily for 3 days on the skin-wheal responses to histamine, the airway responses to inhaled histamine and methacholine, and the skin-wheal and airway responses to allergen in 12 subjects with asthma. There was no evidence of a bronchodilator action 3 hours after a third oral dose. In the airways, the geometric mean of the provocative concentration of histamine causing a 20% fall in FEV1 after placebo or loratadine, 10 and 20 mg, was 0.68 mg/ml, 2.71 mg/ml (p, not significant), and 5.96 mg/ml (p less than 0.05), respectively. The concentration ratios (value after active treatment/value after placebo) for loratadine, 10 and 20 mg, were 5.1 (p less than 0.05) and 13.4 (p less than 0.05). Neither dose of loratadine had any significant effect on the methacholine dose-response relationship. In the skin, loratadine also displaced the histamine log-concentration response curves to the right with concentration ratios of 4.7 and 6.7, respectively. Loratadine, 10 and 20 mg, had no protective effect on the early or late-phase bronchoconstrictor responses to inhaled allergen. In the skin, loratadine, 20 mg, significantly inhibited the mean wheal area to allergen. Thus, in the dose regimens studied, although loratadine is a moderately potent and selective H1 antagonist in the skin and airways, it failed to attenuate the early and late airway responses to inhaled allergen.

Prophylactic treatment of grass pollen-induced asthma with cetirizine

In a double-blind randomized parallel-group study, six investigators enrolled 43 subjects to study the prophylactic effect of 10 mg cetirizine b.i.d. on grass pollen-induced asthma. The control group received 60 mg b.i.d. terfenadine, given to avoid withdrawals from the trial because of hay fever symptoms. Subjects were included in the study between the appearance of the first symptoms of hay fever and those of pollen-induced asthma. The hay fever and asthma symptoms, visual analogue scores (VAS), FEV1 and self-assessment data on complaints, salvage treatment and peak-flow values were statistically analysed. Both treatments were well tolerated, with a low and similar incidence of side-effects. During the last 3 weeks of treatment, six (32%) of the 19 subjects on cetirizine who were evaluable for efficacy remained free of asthma complaints, and another two (10%) had only a single minor attack. None had a grade 3 (incapacitating) attack. Conversely, only one (5%) of the 20 evaluable subjects on terfenadine remained complaint free, and all others (95%) had multiple attacks, which incapacitated three (15%) of them. Nasal obstruction, dyspnoea, morning peak flow, consumption of beta 2-mimetics and an efficacy index on asthma, combining complaints and rescue drug consumption, were significantly better on cetirizine (P less than 0.05). It is concluded that cetirizine is able to prevent the exacerbation of asthma induced by grass pollen.

Duration of the effect of astemizole on histamine-inhalation tests

The aim of the study was to investigate if astemizole, a new, long-acting antihistamine preparation, has an effect on histamine-inhalation tests and to assess the duration of action of this medication. The study included a group of 15 adult subjects with asthma in a clinically stable state. The subjects all demonstrated mild to severe bronchial hyperresponsiveness (geometric mean provocative concentration causing a 20% fall in FEV1 (PC20) histamine, 0.57; range, 0.20 to 4.7 mg/ml). The first part of the study was a double-blind, 7-day trial of astemizole (10 mg/day) or placebo, assigned in random order for the first eight subjects. The seven subjects entering the trial subsequently were administered active medication only. PC20 histamine was assessed on the 3 consecutive days before starting the trial, on the last day of medication, 3 days later, and once a week thereafter until PC20 returned to baseline. PC20 methacholine was also assessed before the trial and regularly thereafter to ensure functional stability. No significant changes in PC20 histamine were documented in the placebo-treated group, but the four subjects receiving active medication demonstrated marked changes in PC20 histamine (from a tenfold to a greater than 100-fold difference) (p = 0.001). There were no significant differences in changes in PC20 methacholine between the two treatment groups (p = 0.27). The duration of recovery of bronchial response to histamine in all 15 subjects ranged from 12 to 102 days (mean, 42 days) and was in some subjects, longer than the duration of the blocking effect of histamine reactivity found with skin testing.(ABSTRACT TRUNCATED AT 250 WORDS)

CI-949: a new, potential antiallergy compound inhibits antigen-induced allergic reactions in guinea-pigs in vitro and in vivo

CI-949 (5-methoxy-3-(1-methyl-ethoxy)-1-phenyl-N-1H-tetrazol-5-yl-1H -indole-2-carboxamide) effectively inhibited the release of histamine and the synthesis or release of immunoreactive sulfidopeptide leukotrienes C4-D4 and thromboxane B2 from antigen-challenged lung fragments of of actively sensitized guinea-pigs. The IC50s were 26.7 +/- 2.8 microM for histamine, 2.7 +/- 2.4 microM for leukotriene, and 3.0 +/- 1.8 microM for thromboxane. Drugs including ketotifen, cromolyn and nedocromil did not inhibit histamine release or did so only at high concentrations, and only cromolyn inhibited the synthesis or releases of the 2 eicosanoids. A dose of 50 mg/kg i.p. of CI-949 protected conscious, aerosol-allergen challenged guinea-pigs for at least 1 h and 100 mg/kg i.p. or per os protected for at least 2 h. These results, the comparisons to standard antiallergic drugs, and other data from experiments with human lung fragments and isolated peripheral leukocytes 1,2,3,4 suggest that CI-949 should be evaluated for clinical activity against allergic and inflammatory conditions in which histamine, sulfidopeptide leukotrienes, and/or thromboxane mediate symptoms.

Effect of a non-sedative antihistaminic (loratadine) in moderate asthma. A double-blind controlled clinical crossover-trial

Seventeen patients with perennial asthma, stable on a moderate dose of inhaled steroid, participated in a crossover study comparing the clinical effect of a non-sedative, potent and highly selective H1 antagonist (loratadine 10 mg) with placebo. Each treatment period began with 2 weeks run-in followed by 8 weeks on either antihistamine or placebo. During the 8-week periods inhaled steroid was gradually tapered according to a fixed scheme. One patient was withdrawn from active treatment and three from placebo periods because of decreasing lung function (P greater than 0.1). Among the remaining 13 patients there was a threefold (1.8-4.8) decrease in the bronchial sensitivity to histamine during treatment with antihistamine compared to placebo (P less than 0.01). There was a trend in favour of active treatment with regard to changes in all symptom scores, lung function and use of escape medication, but these differences were not statistically significant. The increase in FEV1 was less than 5% of predicted normal (P less than 0.05). We concluded that the bronchial response to histamine can be attenuated by loratadine, an oral H1 receptor antagonist, but further studies are necessary to assess the clinical usefulness and place of loratadine in the therapy of asthma.

The effect of astemizole on bronchial hyperresponsiveness and exercise-induced asthma in children

The ability of the new generation H1-receptor antagonist, astemizole, to prevent histamine-induced airway obstruction and exercise-induced asthma (EIA) was studied in 20 children with asthma. The study was a randomised clinically controlled trial of oral astemizole versus placebo in a cross-over study. In each of the two treatment periods the children were tested at days 0, 6, 15 and 22 of therapy. The two treatment periods were separated by a washout period of 50 days, and at each visit a bronchial challenge with increasing concentrations of histamine followed by an exercise test was performed, and peak flow and asthmatic symptom score were recorded daily. The children tolerated significantly higher mean concentrations of histamine when treated with astemizole compared with placebo (P less than 0.001). Astemizole postponed the response to exercise, but no change in the maximal response was found. No differences between the treatment periods were found regarding frequency of asthmatic symptoms or the daily recording of peak flow.

Therapy of Childhood Asthma

The pathophysiology of asthma is briefly reviewed and the primary modalities of drug therapy are described. Symptoms of asthma are the result of bronchospasm, increased mucous secretion, and inflammation of the airways. An acute attack is a medical emergency that necessitates prompt treatment. Acute exacerbations are primarily treated with β-2 agonists by inhalation, with the addition of methylprednisolone and aminophylline as needed. The mainstay of therapy in chronic asthma is prophylaxis with theophylline, with cromolyn sodium as an alternative in certain patients. The addition of β-2 agonists, corticosteroids, or anticholinergics may be necessary, depending upon the severity and frequency of the attacks. The mechanisms of action of the standard therapeutic agents are reviewed, along with the dosages, side effects, and major drug interactions. Newer agents under investigation are also described, some of which represent totally new pharmacologic approaches to the therapy of asthma, such as H-1 receptor blockers, platelet activating factor (PAF) antagonists, and calcium channel blockers.

A study of the clinical efficacy of azelastine in patients with extrinsic asthma, and its effect on airway responsiveness

1. The effect of 4.4 mg azelastine administered orally on airway responsiveness, skin prick testing, daily peak expiratory flow rates and symptoms of asthma was compared with placebo in a 7 week double-blind, parallel group study of 24 patients with extrinsic asthma. The study was in two parts: a 2 week assessment period, during which all patients received placebo tablets but recorded daily peak flow rates (PEFRs) and symptoms, preceding the 7 week double-blind comparison. 2. Azelastine, 4.4 mg, significantly decreased airway responsiveness to histamine compared with placebo both after a single dose (P less than 0.001), and following 7 weeks continuous treatment (P less than 0.02). Airway responsiveness to methacholine was not altered by administration of azelastine compared with placebo. 3. Skin prick test weal diameters to both allergen and histamine were significantly reduced after both a single dose and following 7 weeks continuous therapy treatment with azelastine. 4. There was a significant improvement in both the mean of the morning and the evening peak flow rates recorded during the last week compared with the first week of the study in the group receiving 4.4 mg of azelastine twice daily compared with placebo. Scores for wheeze were significantly reduced during the final 3 weeks of the study in patients receiving azelastine compared both with those receiving placebo and with the first week of the study (P less than 0.05, P less than 0.01). Consumption of inhaled bronchodilators fell significantly during the study in the group receiving azelastine therapy (P less than 0.05); no such fall occurred in the placebo treated patients. 5. A bitter metallic taste was reported by 58% of patients who received azelastine therapy.

The effect of azelastine on exercise-induced asthma

In ten young asthmatic subjects, we studied the effect of a single oral dose of 4.4 mg of azelastine hydrochloride on exercise-induced bronchoconstriction during the breathing of cold air. Exercise challenges were performed on two different days before and four hours after azelastine and placebo given in a randomized double-blind crossover fashion. Placebo had no effect on baseline pulmonary function and postexertional obstruction of the airways, in contrast to azelastine, which exerted a small but significant (p less than 0.05) bronchodilation and a significant attenuation (p less than 0.01) of exercise-induced bronchoconstriction as compared to data from before treatment and after placebo.

Effect of azelastine on bronchoconstriction induced by histamine and leukotriene C4 in patients with extrinsic asthma

Azelastine, a new oral agent with antiallergic and antihistamine properties, has been shown to inhibit the effect of histamine and leukotriene (LT) in vitro, though not a specific leukotriene receptor antagonist. The effect of both a single dose (8.8 mg) and 14 days' treatment (8.8 mg twice daily) with azelastine on bronchoconstriction induced by LTC4 and histamine has been examined in 10 patients with mild asthma in a placebo controlled, double blind, crossover study. LTC4 and histamine were inhaled in doubling concentrations from a dosimeter and the results expressed as the cumulative dose (PD) producing a 20% fall in FEV1 (PD20FEV1) and 35% fall in specific airways conductance (PD35sGaw). The single dose of azelastine produced a significantly greater FEV1 and sGaw values than placebo at 3 hours, but this bronchodilator effect was not present after 14 days of treatment. Azelastine was an effective H1 antagonist; after a single dose and 14 days' treatment with placebo the geometric mean PD20FEV1 histamine values (mumol) were 0.52 (95% confidence interval 0.14-1.83) and 0.54 (0.12-2.38), compared with 22.9 (11.5-38.3) and 15.2 (6.47-35.6) after azelastine (p less than 0.01 for both). LTC4 was on average 1000 times more potent than histamine in inducing bronchoconstriction. Azelastine did not inhibit the effect of inhaled LTC4; the geometric mean PD20FEV1 LTC4 (nmol) after a single dose and 14 days' treatment was 0.60 and 0.59 with placebo compared with 0.65 and 0.75 with azelastine. The PD35sGaw LTC4 was also unchanged at 0.66 and 0.73 for placebo compared with 0.83 and 0.74 for azelastine. Thus prolonged blockade of H1 receptors did not attenuate the response to LTC4, suggesting that histamine and LTC4 act on bronchial smooth muscle through different receptors. Four patients complained of drowsiness while taking azelastine but only one who was taking placebo and three patients complained of a bitter, metallic taste while taking azelastine.

Astemizole: a long-acting, nonsedating antihistamine

Astemizole is a long-acting, highly selective histamine1-receptor antagonist with minimal central and anticholinergic effects. Comparison studies have shown astemizole to be equal or superior to currently available antihistamines, beclomethasone nasal spray, and cromolyn sodium in relieving allergic symptoms of seasonal and perennial allergic rhinitis. Other uses include treatment of allergic conjunctivitis and chronic urticaria. Astemizole is not as effective for treatment of acute allergic symptoms because of its delayed onset of action. Astemizole and its active metabolite, desmethylastemizole, have long elimination half-lives permitting once-daily dosing. The incidence of sedation is lower than with conventional antihistamines, but increased appetite and weight gain do occur. Astemizole should be useful for both maintenance and prophylactic therapy in patients with chronic allergic conditions who cannot tolerate the sedative or anticholinergic effects of conventional antihistamines.

Asthma: emerging concepts and potential therapies

Asthma is a disease of the airways that results in reversible airflow obstruction. Recent investigations have suggested that airway inflammation is associated with increased airway responsiveness and worsening of asthmatic symptoms. The role that mast cell mediators might play in the production of asthma has been investigated by use of newer analytical techniques and by use of fiberoptic bronchoscopy with lavage to obtain lower respiratory tract fluid and cells. In addition, new investigational compounds that interfere with the synthesis or action of inflammatory mediators have been tested. Developing lines of investigation suggest that chronic activation of inflammatory cells may be important in the pathogenesis of asthma.

Histamine release induced by bacteria. A new mechanism in asthma?

Bacteria release histamine from human basophil leukocytes and mast cells. The release can be caused by an immunological (IgE-dependent) mechanism, but mostly we found a non-immunological (lectin-mediated) mechanism which indicates that mediator release triggered by bacteria can occur without the person being sensitized to the micro-organism in question. Both bacteria and bacterial products such as endotoxins potentiate basophil histamine release caused by allergens in allergic patients or by bacteria in persons sensitized to the micro-organisms. It is therefore tempting to speculate that bacteria and their products might be of importance for asthma by their capacity to release histamine and to potentiate mediator release.