The comparative actions and adverse effect profile of single doses of H1-receptor antihistamines in the airways and skin of subjects with asthma

Methacholine challenge testing: comparative pharmacology

Standardization of the methacholine inhalation challenge, the most common direct bronchoprovocation test, is important. One aspect of standardization is the appropriate washout period for pharmacologic agents which affect the response. This review summarizes the available data on pharmacologic inhibition of the methacholine response. Specific (anti-muscarinic) agents demonstrate marked bronchoprotection (up to 7 days for the long-acting drugs) which lasts longer than the duration of bronchodilation. The functional antagonist (beta 2 agonist class of medications) shows marked, but less, bronchoprotection which is relatively short lived and is similar to the duration of bronchodilator efficacy. Tolerance develops quickly, especially to the long-acting agents. Single doses of controller medications, such as inhaled corticosteroids (ICS) and leukotriene receptor antagonists, have no effect on the methacholine test, while regular use, at least for ICS, has a modest protective effect whose duration is uncertain and likely variable. Theophylline has a small effect and H1 blockers (all generations) have a negligible effect.

The role of antihistamines in asthma management

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

Antihistaminic and antiallergic actions of extracts of Solanum nigrum berries: possible role in the treatment of asthma

ETHNOPHARMACOLOGICAL RELEVANCE

Berries of the plant Solanum nigrum Linn (Solanaceae) are used for the treatment of asthma in folk medicine and ancient books.

AIM OF STUDY

To evaluate potential of the plant berries in the treatment of asthma.

MATERIALS AND METHODS

Petroleum ether, ethanol and aqueous extracts of S. nigrum berries (50, 100 and 200mg/kg, i.p.) were screened for the treatment of asthma by the various methods viz. effect on clonidine and haloperidol induced catalepsy, milk-induced leucocytosis and eosinophilia, mast cell stabilizing activity in mice and studies on smooth muscle preparation of guinea pig ileum (in vitro). Active petroleum ether extract was standardized by HPTLC.

RESULTS

The petroleum ether extract of S. nigrum berries inhibited clonidine-induced catalepsy significantly but not haloperidol-induced catalepsy. Petroleum ether extract significantly inhibited increased leukocyte and eosinophil count due to milk allergen and showed maximum protection against mast cell degranulation by clonidine. Petroleum ether extract resisted contraction induced by histamine better than other extracts. All the results are dose dependant. Active petroleum ether extract showed presence of antiasthmatic compound, β-sitosterol.

CONCLUSION

The petroleum ether extract of S. nigrum berries can inhibits parameters linked to the asthma disease.

The role of histamine in asthma

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

Histamine: metabolism, physiology, and pathophysiology with applications in veterinary medicine

OBJECTIVE

To review the human and veterinary literature on histamine physiology and pathophysiology and potential applications for clinical use in veterinary critical care.

DATA SOURCES

Human and veterinary clinical studies, reviews, texts, and recent research in histamine receptor and antagonist therapy.

HUMAN DATA SYNTHESIS

Recent progress in molecular biology has led to a more complete understanding of the enzymes involved in histamine metabolism and histamine receptor physiology. The past decade of research has confirmed the role of histamine in the classical functions (contraction of smooth muscle, increase in vascular permeability, and stimulation of gastric acid secretion) and has also elucidated newer ones that are now under investigation. Data on the roles of histamine in angiogenesis, circadian rhythm, bone marrow regeneration, bacterial eradication, and cancer are emerging in the literature. Newer histamine antagonists are currently in drug trials and are expected to advance the clinical field in treatment of allergic, gastrointestinal, and cognitive disorders.

VETERINARY DATA SYNTHESIS

Veterinary histamine research is directed at identifying the effects of certain pharmacological agents on blood histamine concentrations and establishing the relevance in clinical disease states. Research demonstrates important species differences in regards to histamine receptor physiology and tissue response. Studies in the area of trauma, sepsis, anaphylaxis, allergy, and gastrointestinal disorders have direct applications to clinical veterinary medicine.

CONCLUSIONS

Histamine plays a key role in the morbidity and mortality associated with allergy, asthma, gastric ulcers, anaphylaxis, sepsis, hemorrhagic shock, anesthesia, surgery, cardiovascular disease, cancer, CNS disorders, and immune-mediated disease. Histamine antagonism has been in common use to block its adverse effects. With recent advances in the understanding of histamine receptor physiology, pharmaceutical agents targeting these receptors have increased the therapeutic options.

Adenosine receptors and asthma

The accumulation of evidence implicating a role for adenosine in the pathogenesis of asthma has led to investigations into all adenosine receptor subtypes as potential therapeutic targets for the treatment of asthma. Selective A(1) receptor antagonists are currently in preclinical development since adenosine has been shown experimentally to mediate various features of asthma through this receptor such as bronchoconstriction, mucus secretion and inflammation. The A(2A) receptor is expressed on most inflammatory cells implicated in asthma, and as A(2A) stimulation activates adenylate cyclase and consequently elevates cAMP, selective A(2A) receptor agonists have now reached clinical development. However, initial reports concerning their efficacy are inconclusive. A(2B) receptor antagonists are also under investigation based on the rationale that inhibiting the effects of adenosine on mast cells would be beneficial, in addition to other reported pro-inflammatory effects mediated by the A(2B) receptor on cells such as airway smooth muscle, epithelial cells and fibroblasts. Whilst the effects in pre-clinical models are promising, their efficacy in the clinical setting has also yet to be reported. Finally, adenosine A(3) receptor stimulation has been demonstrated to mediate inhibitory effects on eosinophils since it also elevates cAMP. However, some experimental reports suggest that A(3) antagonists mediate anti-inflammatory effects, thus the rationale for A(3) receptor ligands as therapeutic agents remains to be determined. In conclusion, establishing the precise role of adenosine in the pathogenesis of asthma and developing appropriate subtype selective agonists/antagonists represents an exciting opportunity for the development of novel therapeutics for the treatment of asthma.

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

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

Histamine in allergic inflammation and immune modulation

Histamine, originally considered as a mediator of acute inflammatory and immediate hypersensitivity responses has also been demonstrated to affect chronic inflammation and regulate several essential events in the immune response. On the other hand, various cytokines control histamine synthesis, release and expression of histamine receptors (HRs). The cells involved in the regulation of immune response and hematopoiesis express HRs and also secrete histamine, which can selectively recruit the major effector cells into tissue sites and affect their maturation, activation, polarization and effector functions leading to chronic inflammation. Histamine, acting through its receptor type 2, positively interferes with the peripheral antigen tolerance induced by T regulatory cells in several pathways. Histamine also regulates antigen-specific Th1 and Th2 cells, as well as related antibody isotype responses. The diverse effects of histamine on immune regulation are due to differential expression and regulation of four HRs and their distinct intracellular signals. In addition, differences in affinities of these receptors are highly decisive on the biological effects of histamine and agents that target HRs. This article highlights the findings leading to a change of perspective in histamine immunobiology.

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.

Prospects for antihistamines in the treatment of asthma

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

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.

Desloratadine inhibits allergen-induced airway inflammation and bronchial hyperresponsiveness and alters T-cell responses in murine models of asthma

BACKGROUND

Histamine elicits many features of immediate hypersensitivity reactions. Recent evidence indicates that H1 receptors modulate immune responses to antigens. Desloratadine (DL), a new, long-acting, H1 receptor antagonist, has both a potent antihistaminic function and anti-inflammatory properties.

OBJECTIVE

We sought to evaluate the effect of DL on allergic-airway responses in mice after inhalation of the naturally occurring aeroallergen Aspergillus fumigatus (Af ) and to examine the effects of DL on specific immune responses to a defined protein antigen with the use of an ovalbumin (OVA) model of asthma.

METHODS

Mice were subjected either to repeated, intranasal application of Af extract or to intraperitoneal immunization with OVA, followed by inhalation challenge. DL or a control fluid was given daily throughout the sensitization process. Immunoglobulin E (IgE) levels, bronchoalveolar lavage-fluid cytokines and cytology, lung histology, and physiologic responses to methacholine were assessed in the allergen-treated mice. Anti-OVA IgE responses and OVA-driven T-cell cytokine production were examined.

RESULTS

Treatment with DL did not impair IgE production but did inhibit bronchial inflammation and bronchial hyperresponsiveness in both Af- and OVA-treated mice. This inhibition required that DL be administered concurrently with allergen sensitization, indicating that the attenuation of bronchial hyperresponsiveness and inflammation was not caused by anticholinergic receptor effects. OVA-responsive T cells from DL-treated mice exhibited depressed production of IL-4, IL-5, and IL-13 and normal amounts of interferon-gamma. The amounts of IL-5 and IL-13 were also diminished in the bronchoalveolar lavage fluid.

CONCLUSION

DL, given at the time of exposure to the allergen, inhibits T(H)2 responses, the induction of allergic pulmonary inflammation, and bronchial hyperresponsiveness. These results suggest that DL or similar agents given during times of antigen exposure might alter disease progression in patients with respiratory allergy.

Relative potency of fexofenadine HCl 180 mg, loratadine 10 mg, and placebo using a skin test model of wheal-and-flare suppression

BACKGROUND

H1-receptor antagonists differ in their ability to produce peripheral H1-blockade. Suppression of histamine-induced flares and wheals is a useful objective test for measuring these differences.

OBJECTIVE

To evaluate the relative potency of fexofenadine HCI 180 mg, loratadine 10 mg, and placebo (PBO) in suppressing histamine-induced flares and wheals and compare the onset, duration, and maximum suppression of histamine achieved with each agent.

METHODS

Thirty healthy volunteers were enrolled in this randomized, double-blind, single-dose, crossover study. Flares and wheals induced by skin-prick testing with histamine 1.8 mg/mL were measured before treatment, every 20 minutes during the first hour after dosing, and thereafter hourly between 2 and 12 hours and between 23 and 25 hours postdose.

RESULTS

Fexofenadine was significantly more effective than loratadine in suppressing the histamine-induced flare response at hours 2 through 7 and 10 through 12 and produced greater flare suppression than did PBO at hours 2 through 25. Onset of flare suppression occurred 2 hours after dosing with fexofenadine and 4 hours after dosing with loratadine. Likewise, fexofenadine was superior to loratadine in suppressing the wheal response from hours 1 through 12 and was more effective than PBO at hours 1 through 12, 24, and 25. Throughout the 25-hour measurement interval, the magnitude of difference in both wheal and flare suppression consistently favored fexofenadine over loratadine.

CONCLUSIONS

In a skin test model of wheal-and-flare suppression, fexofenadine showed rapid distribution into the skin compartment with faster onset of action and greater potency vs loratadine.

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

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

Influence of zafirlukast and loratadine on exercise-induced bronchoconstriction

BACKGROUND

Airway obstruction induced by physical exercise is a common feature in asthma, and conventional treatments do not offer optimal protection. There is thus a need for additional therapies for optimal control of exercise-induced bronchoconstriction (EIB).

OBJECTIVE

The influence of treatment with the antihistamine loratadine and the antileukotriene zafirlukast alone and in combination on EIB was investigated. This combination has previously shown beneficial additive effects in allergen-induced bronchoconstriction.

METHODS

In a double-blind cross-over study loratadine (10 mg twice daily) and zafirlukast (80 mg twice daily) were evaluated alone and in combination in 16 nonsmoking patients with mild asthma, previously documented EIB, and airways hyperresponsiveness to histamine.

RESULTS

The mean +/- SE maximum decrease in FEV1 after a standardized exercise provocation was 21.6% +/- 3% after placebo, 22.8% +/- 3% after loratadine, 13.9% +/- 2% after zafirlukast (P <.05 vs placebo), and 10.3% +/- 2% after the combination of loratadine and zafirlukast (P <.05 vs placebo). Expressed as the area under the FEV1 percentage change versus time curve, the mean protection produced by zafirlukast and the combination of zafirlukast and loratadine was 57% and 65%, respectively, whereas loratadine alone had no significant protective effect. There was also no significant difference between the effect of zafirlukast alone or in combination with loratadine.

CONCLUSION

The study confirmed the beneficial effect of a leukotriene receptor antagonist in EIB but failed to obtain evidence that H1-receptor antagonism alone or together with the cysteinyl-leukotriene 1 receptor antagonist zafirlukast offers a protective effect.

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.

Impact of cetirizine on the burden of allergic rhinitis

OBJECTIVE

The goals of this article include the reporting of the epidemiology, economic and medical impact of allergic rhinitis. In addition, the pharmacology and clinical profile of the therapeutic agent cetirizine are reviewed.

DATA SOURCES

A detailed literature search was conducted. References are limited to the English language and human subjects and tissues. Studies considered relevant and important over the past 20 years are highlighted.

STUDY SELECTION

Prevalence and morbidity data were chosen from more recent assessments. Because cetirizine is a relatively new compound, studies from the past several years from peer-reviewed journals have been emphasized.

RESULTS

Allergic rhinitis affects between 15% and 25% of the US general population. It shares common pathophysiologic mechanisms with conjunctivitis and asthma and predisposes to nasal infections, otitis media, sinusitis, nasal polyposis, and orthodontic malocclusions. Direct medical care costs amount to up to 3 billion dollars every year. In addition, the quality of life of affected individuals is substantially compromised. Cetirizine is a potent H1-receptor antagonist and has anti-inflammatory properties. It does not interact with concomitantly administered medications, has no cardiac adverse effects, and does not appear to be associated with teratogenicity. Impairment of CNS function is comparable to other low-sedating antihistamines at the recommended dose of 10 mg daily for adults. Its clinical efficacy for allergic respiratory diseases has been established in numerous trials.

CONCLUSIONS

Allergic rhinitis causes considerable suffering. Cetirizine, with a fine risk-benefit ratio, can be a most valuable therapeutic option.

Assessment of antihistamine efficacy and potency

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

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

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

Peripheral H1-blockade effect of fexofenadine

BACKGROUND

Studies of the suppressive effect of H1-receptor antagonists on the histamine-induced wheal and flare are useful for assessing peripheral H1-blockade.

OBJECTIVE

To compare the peripheral H1-blockade produced by fexofenadine, 60 mg twice daily or 120 mg once daily; loratadine, 10 mg once daily; and placebo during 24 hours.

METHODS

In this randomized, double-blind, single-dose, crossover study in 20 subjects, the wheals and flares produced by epicutaneous tests with histamine phosphate 1 mg/mL were measured before and at intervals (20, 40, 60 minutes, hourly until 12 hours, and 24 hours) after the ingestion of fexofenadine, 60 mg twice daily; fexofenadine, 120 mg once daily; loratadine, 10 mg once daily; or placebo.

RESULTS

All active medications effectively suppressed the histamine-induced wheal and flare for 24 hours compared with placebo. Fexofenadine 60 mg twice daily and fexofenadine 120 mg once daily had a faster onset of action than loratadine in this experimental model.

CONCLUSIONS

Peripheral H1-blockade studies are useful for investigation of the differences among H1-receptor antagonists. They complement large clinical trials in which efficacy is subjectively assessed using symptom scores, and which are more likely to demonstrate similarities among the different medications in this class, and among different doses of the same H1-receptor antagonist.

Effects of inhaled histamine, methacholine and capsaicin on sputum levels of alpha 2-macroglobulin

BACKGROUND

Plasma exudation-derived proteins and peptides contribute significantly to inflammation in the airway mucosa in vivo. In the guinea pig trachea both histamine and the neurogenic stimulant capsaicin produce acute mucosal tissue distribution and luminal entry of bulk plasma, whereas cholinergic agonists fail to produce this effect. Of these agents, only histamine induces mucosal exudation of plasma in human nasal airways. The exudative effect of the above agents on human bronchi remains unknown.

METHODS

The bronchial exudative responses to inhalation of histamine, methacholine, and capsaicin were examined in two groups of healthy volunteers. Sputum was induced on three occasions in each study group by inhalation of hypertonic saline (4.5%) given as an aerosol for 40 minutes using an ultrasonic nebuliser. The second and third occasions were preceded by histamine and capsaicin challenges in the first study group, and by histamine and methacholine challenges in the second study group. Histamine and methacholine were given in cumulative doses (total doses 3160 micrograms, respectively) or until a 20% reduction in forced expiratory volume in one second (FEV1) was achieved. Cumulative doses of capsaicin were inhaled until coughing prevented the subjects from drawing a full breath. Sputum levels of alpha 2-macroglobulin (729 kDa) were measured as an index of mucosal exudation of bulk plasma.

RESULTS

Histamine increased mean (SE) sputum levels of alpha 2-macroglobulin from 2.72 (1.01) micrograms/ml (95% confidence interval (CI) 0.49 to 4.94) to 18.38 (8.03) micrograms/ml (95% CI 0.49 to 36.27) in the first group, and from 1.66 (0.84) micrograms/ml (95% CI -0.18 to 3.49) to 9.43 (3.63) micrograms/ml (95% CI 1.59 to 17.27) in the second group. In contrast, capsaicin evoked no exudation (sputum levels of alpha 2-macroglobulin 1.21 (0.28) micrograms/ml (95% CI 0.59 to 1.83)) and methacholine produced a minor increase in sputum levels of alpha 2-macroglobulin (2.90 (0.92) micrograms/ml (95% CI 0.90 to 4.89)).

CONCLUSIONS

These results indicate that histamine is a useful agent for studying bronchial exudative responsiveness in man and that exudative effects are only of marginal importance in the cough and bronchoconstriction produced by capsaicin and methacholine.

Low dose clemastine inhibits sneezing and rhinorrhea during the early nasal allergic reaction

BACKGROUND

Clemastine (1 mg) is currently available over-the-counter for the treatment of allergic rhinitis.

OBJECTIVE

To evaluate the efficacy of half the standard dose of clemastine (0.5 mg) in inhibiting the nasal response to allergen and the cutaneous response to histamine.

METHODS

Double-blind, placebo-controlled, crossover study of 20 allergic subjects out of season. The subjects received placebo or clemastine administered one, four, and six hours before the challenges. Filter paper discs were used both to challenge the nasal mucosa with diluent and allergen and collect generated secretions. Sneezes, secretion weights, nasal and ocular symptoms, and albumin levels in nasal secretions were monitored for the nasal challenge. Intradermal skin testing was performed with diluent followed by histamine and the wheal and flare reactions were measured.

RESULTS

There was a significant reduction in the number of sneezes after clemastine administered one, four, and six hours prior to challenge compared with placebo (P < .01). Clemastine administered four and six hours before challenge reduced sneezing significantly more than clemastine administered one hour before challenge (P < .05). Antigen-induced increases in secretion weights and symptoms of rhinorrhea were significantly reduced compared with placebo only when clemastine was administered four and six hours prior to challenge (P < .05). Pretreatment with clemastine had no significant inhibitory effects on other nasal symptoms or on albumin levels in nasal secretions, an objective index of increased vascular permeability. Pretreatment with clemastine did not inhibit the histamine-induced wheal skin reaction but showed a tendency, when administered six hours prior to the intradermal challenge, to reduce the flare reaction induced by the lowest dose of histamine (P = .05).

CONCLUSIONS

The data show that clemastine, given at half the usual dose four and six hours prior to allergen challenge, provides relief for sneezing and rhinorrhea and suggests that this dose might be useful in the treatment of allergic rhinitis.

Antihistamines in the treatment of asthma

Antihistamines were investigated for use in asthma shortly after discovery over fifty years ago. Earlier compounds proved ineffective because of side effects: this class of drugs was not thought useful for asthma, and were actually considered contraindicated. More recent drugs have greater potency, fewer side-effects, and no evidence of adverse effects in asthma. There are some studies showing second generation antihistamines, especially cetirizine, improve certain parameters of asthma.

Characterization of a primate model of asthma using anti-allergy/anti-asthma agents

The following study was performed to further characterize a primate model of asthma using classes of drugs that target allergy (pyrilamine, cetirizine), are bronchodilators for the treatment of asthma (salbutamol, salmeterol) or are anti-inflammatory (dexamethasone). These drugs were examined for their ability to inhibit acute, antigen-induced bronchoconstriction, the development of airway hyperresponsiveness (AHR) and the infiltration of leukocytes into the lungs of atopic cynomolgus monkeys (Macaca facsicularis) using a 10-day, multiple antigen (Ag) challenge protocol. All compounds except dexamethasone and cetirizine significantly (p < 0.05) reduced acute, Ag-induced bronchoconstriction (salbutamol: 74.2%, salmeterol: 52.6%%, pyrilamine: 62.4% inhibition) compared to vehicle control trials. Only dexamethasone and salmeterol prevented the development of AHR to methacholine challenge by 90.4 +/- 6.81% and 85.7 +/- 5.61% respectively. Dexamethasone significantly reduced the Ag-induced increase in BAL eosinophils by 85.9 +/- 8.53%. Cetirizine reduced the eosinophil response in 5 of 6 monkeys and salmeterol demonstrated a trend towards reduced eosinophil increases after multiple Ag challenge, but neither of these were statistically significant. These results further illustrate the utility of this model in predicting compound effects against several relevant functional endpoints that are consistent with the effects of similar classes of compounds in humans.

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

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