Adenosine monophosphate bronchial provocation and the actions of asthma therapy

Purinergic signaling in the airways

Evidence for a significant role and impact of purinergic signaling in normal and diseased airways is now beyond dispute. The present review intends to provide the current state of knowledge of the involvement of purinergic pathways in the upper and lower airways and lungs, thereby differentiating the involvement of different tissues, such as the epithelial lining, immune cells, airway smooth muscle, vasculature, peripheral and central innervation, and neuroendocrine system. In addition to the vast number of well illustrated functions for purinergic signaling in the healthy respiratory tract, increasing data pointing to enhanced levels of ATP and/or adenosine in airway secretions of patients with airway damage and respiratory diseases corroborates the emerging view that purines act as clinically important mediators resulting in either proinflammatory or protective responses. Purinergic signaling has been implicated in lung injury and in the pathogenesis of a wide range of respiratory disorders and diseases, including asthma, chronic obstructive pulmonary disease, inflammation, cystic fibrosis, lung cancer, and pulmonary hypertension. These ostensibly enigmatic actions are based on widely different mechanisms, which are influenced by the cellular microenvironment, but especially the subtypes of purine receptors involved and the activity of distinct members of the ectonucleotidase family, the latter being potential protein targets for therapeutic implementation.

The role of measuring airway hyperresponsiveness and inflammatory biomarkers in asthma

Asthma is characterized by inflammation and airway hyperresponsiveness, which results in episodic airflow obstruction. It is diagnosed once a compatible clinical history plus objective evidence of diurnal variability in peak expiratory flow or significant reversibility to inhaled bronchodilator is documented. In accordance with current guidelines, measures of airway calibre and symptoms allow patients and clinicians to assess the degree of asthma control and titrate pharmacotherapy. However, these parameters fail to reflect the extent of underlying endobronchial inflammation and airway hyperresponsiveness, which in turn suggests that additional measures of asthma control may be of benefit. This evidence-based review highlights ways by which inflammation and airway hyperresponsiveness can be assessed and how they may provide additional useful information in the diagnosis and management of asthmatic patients.

Effect of levocetirizine on nasal provocation testing with adenosine monophosphate compared with allergen challenge in allergic rhinitis

BACKGROUND

End-organ hyperreactivity is an important feature of the allergic airway. There are no data directly comparing the responsiveness to treatment of different nasal provocation tests (NPT).

OBJECTIVE

We compared the effect of levocetirizine on nasal adenosine 5'-monophosphate (AMP) with specific allergen challenge in patients with intermittent and persistent allergic rhinitis (AR).

METHODS

Patients with AR were randomized in double-blind cross-over fashion to receive single doses of levocetirizine 5 mg or identical placebo, with nasal challenge performed 12 h after dosing. Sixteen participants completed per protocol. Nasal AMP or allergen challenge was conducted on separate days with 1- and 2-week washout periods in between, respectively. Measurements of peak nasal inspiratory flow (PNIF) were made over 60 min after each challenge. The primary end-point was the provocative concentration of AMP or allergen causing a 20% drop in the PNIF (PC(20)).

RESULTS

The time-profile for PNIF recovery [area under the 60 min time-response curve as % PNIF change (min)] were significantly attenuated for AMP challenge, as mean difference [95% confidence interval (CI)]: 11.57 (3.87, 19.25), P=0.005 and for allergen challenge: 17.82 (0.11, 35.53), P=0.04. A highly significant correlation was shown between methods for the area under the curve: (R=0.86, P<0.001). A statistically significant correlation was also seen for the PC(20): (R=0.94, P<0.001). PC(20) improvement amounted to a 1.26 (95% CI 0.16, 2.35) and 0.16 (95% CI -0.41, 0.73) doubling-dilution shifts for allergen and AMP challenges, respectively. Bland-Altman plots confirmed good agreement between methods.

CONCLUSION

A high correlation and statistical agreement has been demonstrated between AMP and allergen challenge for all outcome measures. In particular, the recovery profile after NPT is a sensitive and discriminatory measure of anti-allergic treatment.

Side effect profile and tolerability of adenosine myocardial perfusion scintigraphy in patients with mild asthma or chronic obstructive pulmonary disease

BACKGROUND

Adenosine may cause bronchoconstriction in subjects with asthma or chronic obstructive pulmonary disease (COPD). Recent evidence suggests that this effect may be dependent on the severity of disease. This study investigates the tolerability of adenosine stress in patients with mild asthma or COPD undergoing myocardial perfusion scintigraphy.

METHODS AND RESULTS

In this case-control study patients with known or suspected mild asthma or COPD were pretreated with an inhaled beta(2)-adrenergic agonist and adenosine titrated up to the maximal dose of 140 microg x kg(-1) x min(-1) over a period of 6 minutes. The occurrence of side effects and test tolerability were compared between the airway disease group and 72 control subjects. Of 1261 patients, 124 had known or suspected airway disease; of these, 72 (58%) were suitable for adenosine stress. The proportion of tests completed as per protocol in the asthma/COPD group was similar to that of control subjects (93% vs 100%, P = .06). Dyspnea (n = 38 [53%] in asthma/COPD group vs n = 25 [35%] in control group, P = .03) and chest pain (n = 14 [19%] in asthma/COPD group vs n = 16 [22%] in control group, P = .7) were the most common side effects, and these were mostly mild and well tolerated. Bronchospasm occurred in 5 patients with asthma/COPD but reverted shortly after discontinuation of the adenosine infusion. Aminophylline was not required in any case.

CONCLUSIONS

A stepwise 6-minute adenosine infusion with prophylactic beta(2)-adrenergic agonist is safe and well tolerated in patients with mild asthma or COPD.

Regulation of mast cells by beta-agonists

The human lung mast cell is known to be a critical effector cell in the mediation of asthma. Activation of the mast cell by allergens and other stimuli leads to the release and generation of a wide variety of autacoids that cause bronchoconstriction, promote inflammation, and may influence airway remodeling. Therefore, the stabilization of mast cells has obvious value in the prevention of asthma. Among the drugs used to treat asthma, only beta-agonists are effective stabilizers of mast cells. Both short- and long-acting beta-agonists are effective against mast cells, but there are differences between agonists regarding the extent of inhibitory activity attained. Consequently, the type of beta-agonist prescribed influences the degree of mast cell stabilization possible. Despite the potential value of attenuating mast cell activity with beta-agonists, this benefit may diminish with time because of the development of tolerance. Both short- and long-acting beta-agonists can induce tolerance to mast cell stabilization, and generally, higher efficacy agonists tend to induce greater levels of tolerance; however, weaker agonists induce greater levels of tolerance than might be expected. Tolerance to the mast-cell-stabilizing effects of beta- agonists may be an issue clinically, because this occurs more readily than tolerance to smooth muscle relaxation. This could lead to a situation in which beta-agonists fail to prevent the release of mediators from mast cells but can still effectively relax airway smooth muscle. The continued ability to bronchodilate could mask the unfavorable consequences of unchecked mediator release from mast cells.

Pathophysiology and therapeutic potential of purinergic signaling

The concept of a purinergic signaling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of purines and pyrimidines as signaling molecules. These molecules mediate short-term (acute) signaling functions in neurotransmission, mechanosensory transduction, secretion and vasodilatation, and long-term (chronic) signaling functions in cell proliferation, differentiation, and death involved in development and regeneration. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of autonomic cotransmission. Recent advances in therapies using purinergic-related drugs in a wide range of pathological conditions will be addressed with speculation on future developments in the field.

Effects of aerosolized adenosine 5'-triphosphate vs adenosine 5'-monophosphate on dyspnea and airway caliber in healthy nonsmokers and patients with asthma

STUDY OBJECTIVES

Extracellular adenosine 5'-triphosphate (ATP) causes neurogenic bronchoconstriction, inflammation, and coughs, and may play a mechanistic role in obstructive airway diseases. The aims of this study were to determine the effects of inhaled ATP on airway function, and to compare these effects with those of adenosine 5'-monophosphate (AMP).

DESIGN

Prospective, randomized, double-blind study.

SETTING

Clinical research laboratory of a postgraduate teaching hospital.

METHODS

The effects of inhaled equimolar doses of ATP and AMP on airway caliber, perception of dyspnea quantified by the Borg score, and other symptoms were determined in 10 nonsmokers (age 41 +/- 3 years) and 10 patients with asthma (age 39 +/- 3 years) [+/- SEM].

RESULTS

None of the healthy nonsmokers responded to ATP or AMP. All the patients with asthma responded to ATP, and 90% responded to AMP. The geometric mean of the provocative dose causing a 20% fall in FEV1 (PD20) of ATP was 48.7 micromol/mL and that of PD20 AMP was 113.5 micromol/mL in responsive asthmatics (p < 0.05). In asthmatic patients, the percentage change in FEV1 caused by ATP was greater than that caused by AMP (deltaFEV1 ATP = 29% vs deltaFEV1 AMP = 22%, p < 0.05). Borg score increased significantly in asthmatics after ATP (from 0.1 to 3.3, p < 0.01) and after AMP (from 0.2 to 2.5, p < 0.01). This increase was also greater after ATP than AMP in asthma (deltaBorg ATP = 3.2 vs deltaBorg AMP = 2.3, p < 0.05). ATP induced cough in 16 subjects (80%), while AMP induced cough in 8 subjects (40%) [p < 0.05]; in addition, more subjects had throat irritation after inhalation of ATP than AMP (p < 0.05).

CONCLUSIONS

ATP is a more potent bronchoconstrictor and has greater effects on dyspnea and other symptoms than AMP in asthmatic patients. Therefore, ATP could potentially be used as a bronchoprovocator in the clinical setting.

Dose-response comparison of budesonide dry powder inhalers using adenosine monophosphate bronchial challenge

BACKGROUND

Bronchial hyperresponsiveness to adenosine monophosphate, an indirect measure of airway inflammation, is a sensitive marker of inhaled corticosteroid efficacy.

OBJECTIVE

To evaluate the relative therapeutic efficacy of budesonide delivered via Clickhaler and Turbuhaler dry powder inhalers in patients with mild-to-moderate persistent asthma.

METHODS

In a double-masked, dose-response crossover study, 27 patients received inhaled budesonide in cumulative sequential doubling dose increments, 2 weeks per dose, of 200, 400, and 800 microg/d. Each treatment block was preceded by 1- to 3-week placebo run-in and washout periods. End points were measured after each placebo (ie, baseline) and treatment period. Adenosine monophosphate bronchial challenge was the primary outcome, and exhaled nitric oxide, serum eosinophilic cationic protein, spirometry, domiciliary peak expiratory flow, symptoms, and rescue medication use were the secondary outcomes.

RESULTS

For the adenosine monophosphate provocation concentration that caused a decrease in forced expiratory volume in 1 second of 20% (PC20), a significant overall dose-response effect (P = .006) was found, and there was no significant difference between the devices (P = .8). The relative microgram dose potency ratio between Clickhaler and Turbuhaler was 1.11 (95% confidence interval [CI], 0.50-2.46). After administration of the highest dose of budesonide, the mean doubling dilution shift in adenosine monophosphate PC20 from placebo baseline was 3.46 (95% CI, 2.66-4.27) with the Clickhaler vs 3.41 (95% CI, 2.47-4.35) with the Turbuhaler. A significant overall dose-response effect was demonstrated for exhaled nitric oxide (P = .03) but not for any of the other secondary outcome measures. There were no significant differences between the devices for any of the outcome measures.

CONCLUSION

Inhaled budesonide exhibited overall dose-response effects on adenosine monophosphate PC20 delivered via Turbuhaler and Clickhaler, with no significant difference between the devices.

The Quintiles Prize Lecture 2004. The identification of the adenosine A2B receptor as a novel therapeutic target in asthma

Adenosine is a powerful bronchoconstrictor of asthmatic, but not normal, airways. In vitro studies on isolated human mast cells and basophils revealed that adenosine and selective analogues augmented inflammatory mediator release from mast cells by stimulating A(2) receptors. Pharmacological blockade of mast cell mediator release in vivo also attenuated adenosine-induced bronchoconstriction, as did theophylline, by adenosine A(2) receptor antagonism. Further in vitro studies revealed that the asthmatic response to adenosine is likely to be mediated via the A(2B) subtype which is selectively antagonised by enprofylline. Studies in animal models, especially mice, have shown a close synergistic interaction between adenosine, Th2 and airway remodelling responses. The recent description of A(2B) receptors on human airway smooth muscle cells that mediate cytokine and chemokine release and induce differentiation of fibroblasts into myofibroblasts strengthens the view that adenosine maybe more than an inflammatory mediator in asthma but also participates in airway wall remodelling in this disease. These data have provided a firm basis for developing adenosine A(2B) receptor antagonists as a new therapeutic approach to this disease.

Evaluation of an abbreviated adenosine monophosphate bronchial challenge

RATIONALE

Airway hyperresponsiveness to adenosine monophosphate (AMP) has been validated as a surrogate marker for airway inflammation. We wished to know whether an abbreviated challenge at the final threshold dose would produce the same fall in FEV1 as a full, conventional dose-response challenge.

METHODS

Seventeen patients with mild-to-moderate asthma (mean FEV1, 75.5% predicted) attended for a full dose-response protocol, where the highest concentration of AMP to produce > 20% fall in FEV1 was noted, along with the maximum percentage fall and recovery time. Patients returned within 2 days for a further challenge, when they received only the highest concentration (as a single bolus) reached on the previous visit.

RESULTS

The mean (+/- SEM) percentage fall in FEV1 after the full challenge was 25.5 +/- 1.3%, and after the abbreviated challenge was 9.4 +/- 2.4%. The mean recovery after the full challenge was 28.13 +/- 4.65 min, and after the abbreviated test was 10.81 +/- 4.27 min.

CONCLUSION

An abbreviated challenge using a single bolus dose of AMP grossly underestimates bronchial hyperresponsiveness. Although the pharmacologic half-life of AMP is short (90 s), the lesser response and shortened recovery with the abbreviated challenge suggest a more prolonged physiologic half-life, which in turn may have implications for abbreviated challenge protocols.

Effects of first and second generation antihistamines on muscarinic induced mucus gland cell ion transport

Background

The first generation antihistamines, such as diphenhydramine, are fairly potent muscarinic antagonists in addition to being H1 selective antihistamines. The antimuscarinic action is often not desirable since it is in part responsible for the drying of secretions in the airways and the sedative effect. We therefore examined a number of antihistamines for antimuscarinic effects on ion transport by mucus gland cells isolated from the airways of swine. Enzymatically isolated airway mucus gland cells were purified utilizing density gradients and grown in culture on porous inserts (Millicell HA™) at an air interface. Cells grown in this manner maintain phenotype and polarity. Transport of ions, as short-circuit current measured under voltage-clamp, was measured in response to acetylcholine (ACh) or histamine applied to the serosal side of the gland cell layers. Concentration-response relationships for ACh or histamine were generated in the presence and absence of various drugs. The potencies against muscarinic receptor activation were estimated using the dose-ratio method of Schild.

Results

Three known muscarinic antagonists were used to validate the system. Atropine had a pA₂ of 9.4 ± 0.1 (n = 9). 4-DAMP and methoctramine had pA₂ values of 8.6 ± 0.1 and 5.6 ± 0.1, respectively (n = 12, 11) all consistent with inhibition of an M3 subtype muscarinic receptor. The rank order of potency of the antihistamines against the inhibition of M3 receptors was desloratadine = diphenhydramine > hydroxyzine (pA₂; 6.4, 6.2, 4.8, respectively). pA₂ values for fexofenadine, loratadine and cetirizine were not determined since they had no effect on the cholinergic response at the highest drug concentrations tested (10, 10 and 100 μM, respectively). The pA₂ values for the antihistamines against the histamine response could not be calculated, but the estimates of the rank order of potency were estimated to be desloratadine> cetirizine ≈ hydroxyzine > fexofenadine > loratadine > diphenhydramine.

Conclusion

The rank order of selectivity for histamine receptors over muscarinic receptors was estimated to be cetirizine ≈ fexofenadine > loratadine > desloratadine ≥ hydroxyzine ≥ diphenhydramine.

Assessment of bronchial responsiveness following exposure to inhaled occupational and environmental agents

Inhalation of a range of agents can result in airway inflammation and/or irritation. This may result in occupational asthma or reactive airways dysfunction syndrome. Reactive airways dysfunction syndrome follows a single large exposure to a chemical agent but is now frequently embraced under the wider term of irritant-induced asthma, a term that also includes asthma due to persistent, lower dose irritant exposures. Bronchial hyperresponsiveness is a hallmark of both occupational asthma and reactive airways dysfunction syndrome, although some patients with occupational asthma may occasionally have typical clinical features without increased bronchial hyperresponsiveness. Following removal of the causal agent in occupational asthma, bronchial hyperresponsiveness generally returns towards normal over a 2-year period, although some individuals demonstrate increased bronchial hyperresponsiveness for longer. Measurement of specific bronchial hyperresponsiveness to the primary causal agent in occupational asthma is used diagnostically but not for assessing prognosis. Bronchial hyperresponsiveness to inhaled methacholine can be measured across individual workshifts to assess work-related change. It may also be measured at the end of a work period when exposure has occurred, and compared with values following a period away from work. There have been no direct, systematic comparisons of changes in methacholine responsiveness in the diagnosis of occupational asthma compared with the more frequently used serial peak flow measurements. Patients with reactive airways dysfunction syndrome classically exhibit non-specific bronchial hyperresponsiveness, which can be readily measured by evaluating responses to inhaled methacholine. Bronchial hyperresponsiveness in reactive airways dysfunction syndrome can persist for many years after initial exposure and serial changes can be used to assess recovery and subsequent disability over time.

Comparative cutoff points for adenosine monophosphate and methacholine challenge testing

BACKGROUND

Current use of the PC20 (provocation concentration that causes a decrease in forced expiratory volume in 1 second of 20%) cutoff point for bronchial challenge precludes its use in patients with more severe airflow obstruction.

OBJECTIVE

To evaluate the efficacy and safety of lower cutoff points for adenosine monophosphate (AMP) and methacholine (MCH) bronchial challenge tools to monitor response to treatment in chronic asthma.

METHODS

We retrospectively examined data from 5 previously published studies (2 using AMP, 2 using MCH, and 1 with MCH and AMP arms) and recalculated 10% and 15% cutoff points for AMP and MCH. Data were analyzed for correlation of single results and doubling dose shifts after anti-inflammatory treatment intervention.

RESULTS

A total of 175 individual MCH challenges and 152 AMP challenges were evaluated. Evaluating the doubling dose shift produced by the addition of anti-inflammatory treatment (inhaled corticosteroids or montelukast) produced the following Pearson correlation coefficients: MCH PD20 (provocation dose that causes a decrease in forced expiratory volume in 1 second of 20%) vs PD15, 0.80; MCH PD20 vs PD10, 0.65; AMP PC20 vs PC15, 0.96; and AMP PC20 vs PC10, 0.84 (P < .001 for all). Subgroup analysis of AMP for before and after inhaled corticosteroids only (n = 41) shows AMP PC20 vs PC15 of 0.92 and AMP PC20 vs PC10 of 0.84 (P < .001 for both).

CONCLUSIONS

The 10% and 15% cutoff points strongly predict the 20% cutoff value for AMP and MCH, as do the doubling dose shifts after anti-inflammatory treatment. The lower thresholds are suitable for monitoring response to therapy, and they expose patients to significantly less provocation agent.

Single and short-term dosing effects of levocetirizine on adenosine monophosphate bronchoprovocation in atopic asthma

AIMS

Adenosine monophosphate (AMP) acts indirectly via primed airway mast cells to induce bronchial hyper-responsiveness, which in turn correlates with eosinophilic asthmatic inflammation and atopic disease expression. We evaluated single and short-term dosing effects of a modern histamine H1-receptor antagonist, levocetirizine, given at the usual clinically recommended dose, on the primary outcome of AMP bronchoprovocation.

METHODS

Fifteen atopic asthmatics were randomized in double-blind, cross-over fashion to receive for 1 week either levocetirizine 5 mg or placebo. There was a 1-week washout period prior to each randomized treatment. The provocative concentration of AMP producing a 20% fall in FEV1 (PC20) was measured after each washout at baseline and at 4-6 h following the first and last doses of each randomized treatment.

RESULTS

Baseline mean +/- SEM values after washout prior to each randomized treatment comparing levocetirizine vs placebo were not significantly different for prechallenge FEV1 (% predicted) 83 +/- 4 vs 82 +/- 4, or AMP PC20 (mg ml(-1)) 45 +/- 24 vs 45 +/- 22, respectively. Airway calibre as prechallenge FEV1 for levocetirizine vs placebo was not significantly different following the first dose 86 +/- 4 vs 82 +/- 4, or the last dose 85 +/- 4 vs 83 +/- 4, respectively. There were significant improvements (P < 0.05) in AMP PC20 comparing levocetirizine vs placebo following the first dose 123 +/- 73 vs 48 +/- 24, a 1.4 doubling dilution difference (95% CI 0.8, 1.9), and the last dose 127 +/- 74 vs 53 +/- 29, a 1.2 doubling dilution difference (95% CI 0.5, 2.0). AMP PC20 was also improved (P < 0.05) by the first and last doses of levocetirizine but not placebo, vs respective baseline values, with there being no difference in the degree of protection between first and last doses.

CONCLUSIONS

Single and short-term dosing with levocetirizine conferred similar improvements in bronchial hyper-responsiveness to AMP challenge, which was unrelated to prechallenge airway calibre. Further studies are indicated to evaluate the longer-term effects of levocetirizine on asthma exacerbations.

Effects of single or combined histamine H1-receptor and leukotriene CysLT1-receptor antagonism on nasal adenosine monophosphate challenge in persistent allergic rhinitis

BACKGROUND

The effects of single or combined histamine H(1)-receptor and leukotriene CysLT(1)-receptor antagonism on nasal adenosine monophosphate (AMP) challenge in allergic rhinitis are unknown.

OBJECTIVE

We elected to study the effects of usual clinically recommended doses of fexofenadine (FEX), montelukast (ML) and FEX + ML combination, compared with placebo (PL), on nasal AMP challenge in patients with persistent allergic rhinitis.

METHODS

Twelve patients with persistent allergic rhinitis (all skin prick positive to house dust mite) were randomized in a double-blind cross-over fashion to receive for 1 week either FEX 180 mg, ML 10 mg, FEX 180 mg + ML 10 mg combination, or PL, with nasal AMP challenge performed 12 h after dosing. There was a 1-week washout period between each randomized treatment. The primary outcome measure was the maximum percentage peak nasal inspiratory flow (PNIF) fall from baseline over a 60-min period after nasal challenge with a single 400 mg ml(-1) dose of AMP. The area under the 60-min time-response curve (AUC) and nasal symptoms were measured as secondary outcomes.

RESULTS

There was significant attenuation (P < 0.05) of the mean maximum percentage PNIF fall from baseline after nasal AMP challenge vs. PL, 48; with FEX, 37; 95% confidence interval for difference 2, 20; ML, 35 (4, 22); and FEX + ML, 32 (7, 24). The AUC (%.min) was also significantly attenuated (P < 0.05) vs. PL, 1893; with FEX, 1306 (30, 1143); ML, 1246 (214, 1078); and FEX + ML, 1153 (251, 1227). There were no significant differences for FEX vs. ML vs. FEX + ML comparing either the maximum or AUC response. The total nasal symptom score (out of 12) was also significantly improved (P < 0.05) vs. PL, 3.3; with FEX, 2.1 (0.3, 2.0); ML, 2.0 (0.5, 1.9); and FEX + ML, 2.5 (0.1, 1.4).

CONCLUSION

FEX and ML as monotherapy significantly attenuated the response to nasal AMP challenge and improved nasal symptoms compared with PL, while combination therapy conferred no additional benefit.

A placebo-controlled evaluation of butterbur and fexofenadine on objective and subjective outcomes in perennial allergic rhinitis

BACKGROUND

There are presently no placebo-controlled data regarding the effects of butterbur (BB) on subjective and objective outcomes in patients with perennial allergic rhinitis.

OBJECTIVE

We performed a placebo-controlled evaluation of the effects of BB and fexofenadine (FEX) on subjective and objective outcomes in patients with perennial allergic rhinitis.

METHODS

Sixteen patients with perennial allergic rhinitis and house dust mite sensitization were randomized in double-blind cross-over fashion to receive for 1 week either BB 50 mg twice daily, FEX 180 mg once daily and placebo (PL) once daily, or PL twice daily. The peak nasal inspiratory flow (PNIF) response to adenosine monophosphate (AMP) challenge administered as a single 400 mg/mL dose was measured over a 60-min period after challenge, and domiciliary total nasal symptom score was recorded.

RESULTS

Pre-challenge values for mean+/-SEM PNIF (L/min) were not significantly different comparing all groups; BB (138+/-8), FEX (140+/-9), and PL (138+/-8). The maximum % PNIF fall from baseline after nasal AMP challenge was significantly attenuated (P<0.05) compared to PL (46+/-3), with BB (34+/-3) and FEX (39+/-3). The area under the 60-min time-response curve (%.min) was also significantly attenuated (P<0.05) compared to PL (1734+/-156), with BB (1052+/-258) and FEX (1194+/-161). There was also a significant reduction (P<0.05) in total nasal symptom score with BB (1.8+/-0.4) and FEX (1.8+/-0.4), compared to PL (2.8+/-0.5). There were no significant differences between BB and FEX for any outcomes.

CONCLUSION

BB and FEX, in comparison to PL, were equally effective in attenuating the nasal response to AMP and in improving nasal symptoms, highlighting a potential role for BB in the treatment of allergic rhinitis.

Comparative effects of desloratadine, fexofenadine, and levocetirizine on nasal adenosine monophosphate challenge in patients with perennial allergic rhinitis

Summary Background There are no data directly comparing the relative efficacy of modern H(1)-antihistamines in allergic rhinitis using nasal provocation challenge. Objective We elected to study the comparative effectiveness of usual clinically recommended doses of desloratadine (DES), fexofenadine (FEX), and levocetirizine (LEV), on nasal adenosine monophosphate (AMP) challenge in patients with perennial allergic rhinitis (PAR). Methods 16 patients with PAR were randomized in double-blind cross-over fashion to receive single doses of DES 5 mg, FEX 180 mg, LEV 5 mg, or placebo (PL), with nasal AMP challenge performed 12 h after dosing. Measurements of peak nasal inspiratory flow (PNIF) were made over 60 min after nasal AMP challenge. Results Pre-challenge values (mean+/-SEM) for PNIF (L/min) were not significantly different comparing all groups; DES (129+/-9), FEX (128+/-11), LEV (128+/-13), and PL (128+/-12). The maximum % PNIF fall from baseline over 60 min after nasal AMP challenge was significantly attenuated (P<0.05) compared to PL (50+/-4), with DES (32+/-5), FEX (36+/-4), and LEV (36+/-4). The area under the 60-min time-response curve (%.min) was also significantly attenuated (P<0.05) compared to PL (2110+/-268), with DES (1126+/-285), FEX (1225+/-255), and LEV (1261+/-194). There were no significant differences between the three H(1)-antihistamines for any outcomes. Conclusion DES, FEX, and LEV were equally effective in attenuating the response to nasal AMP challenge. However, further long-term studies will be required to study their comparative effects on nasal symptoms, quality of life, as well as on nasal inflammatory cells.

Repeated dosing effects of mediator antagonists in inhaled corticosteroid-treated atopic asthmatic patients

BACKGROUND

The anti-inflammatory effects of repeated dosing with mediator antagonists as add-on therapy to that with inhaled corticosteroids (ICSs) in patients with asthma remain to be fully established.

OBJECTIVE

We elected to evaluate the effects of repeated dosing with fexofenadine (FEX) and montelukast (ML) at clinically recommended doses in ICS-treated asthmatic patients using adenosine monophosphate (AMP) bronchial challenge as the primary outcome.

METHODS

Eighteen atopic asthmatic patients receiving a mean (+/- SEM) dose of 631 +/- 104 micro g daily of ICSs, which remained unchanged throughout the entire study, were randomized in double-blind, cross-over fashion to receive FEX, 180 mg, ML, 10 mg, or placebo (PL) for 1 week. There was a 1-week washout period prior to each randomized treatment. Measurements of the provocative concentration of a substance (ie, AMP) causing a 20% fall in FEV(1) (PC(20)) were made after each washout period and randomized treatment period.

RESULTS

The values for AMP PC(20) after the washout period prior to each randomized treatment were not significantly different (FEX, 74 +/- 15 mg/mL; ML, 73 +/- 18 mg/mL; PL, 71 +/- 19 mg/mL). There were significant improvements (p < 0.05) in AMP PC(20) with the use of FEX (127 +/- 38 mg/mL) and ML (121 +/- 27 mg/mL) compared to PL (78 +/- 23 mg/mL). Spontaneous recovery after AMP challenge, as determined by area under the 60-min time-response curve, was significantly enhanced (p < 0.05) with the use of ML (352 +/- 95%.min [corrected]) compared to FEX (758 +/- 140%.min) and PL (683 +/- 134%.min [corrected]). Both FEX and ML significantly suppressed (p < 0.05) the levels of exhaled nitric oxide, while only ML significantly reduced (p < 0.05) the peripheral blood eosinophil count compared to PL. Morning and evening peak expiratory flow were significantly higher (p < 0.05), and the frequency of salbutamol rescue was significantly reduced (p < 0.05) with FEX and ML compared to PL.

CONCLUSION

Repeated dosing with FEX and ML as add-on therapy improved AMP PC(20) and other surrogate inflammatory markers along with asthma diary outcomes in ICS-treated atopic asthmatic patients. Further studies are indicated to evaluate the long-term add-on effects of FEX on asthma exacerbations.

The effects of butterbur on the histamine and allergen cutaneous response

BACKGROUND

Butterbur or Petasites hybridus is an herbal remedy that exhibits antihistamine and antileukotriene activity and has been shown to attenuate the response to adenosine monophosphate challenge in patients with allergic rhinitis and asthma. However, no data are available regarding its effects on the histamine and allergen cutaneous response.

OBJECTIVE

To evaluate the effects of butterbur compared with fexofenadine and montelukast on the histamine and allergen wheal and flare cutaneous responses.

METHODS

Atopic patients were randomized into a double-blind, double-dummy, crossover study to receive for 1 week butterbur, 50 mg twice daily (8 AM and 10 PM); fexofenadine, 180 mg once daily (10 PM), and placebo once daily (8 AM); montelukast, 10 mg once daily (10 PM), and placebo once daily (8 AM); or placebo twice daily (8 AM and 10 PM). Patients attended the department at 10 AM and had measurements of the cutaneous wheal and flare responses to histamine, allergen, and saline control at 10-minute intervals for 60 minutes.

RESULTS

Twenty patients completed the study. The mean +/- SE histamine wheal and flare responses, respectively, were significantly attenuated (P < .05) by fexofenadine (9.4 +/- 1.8 mm2 and 13.5 +/- 3.2 mm2) compared with placebo (15.5 +/- 3.3 mm2 and 179.8 +/- 74.3 mm2) but not by butterbur (16.4 +/- 2.1 mm2 and 297.7 +/- 121.2 mm2) or montelukast (19 +/- 1.9 mm2 and 240.2 +/- 66.6 mm2). The allergen wheal and flare responses, respectively, were also significantly attenuated (P < .05) by fexofenadine (31.1 +/- 6.3 mm2 and 256.9 +/- 86.5 mm2) compared with placebo (65.4 +/- 15.2 mm2 and 1,014.5 +/- 250.0 mm2) but not by butterbur (50.4 +/- 9.2 mm2 and 1,110.3 +/- 256.1 mm2) or montelukast (58.8 +/- 9.1 mm2 and 1,463.6 +/- 295.6 mm2).

CONCLUSIONS

Butterbur did not produce any significant effects on the histamine and allergen cutaneous response compared with placebo, whereas mediator antagonism with fexofenadine but not montelukast produced significant attenuation. This finding would suggest that butterbur may not be effective in allergic skin disease.

Add-on therapy with montelukast or formoterol in patients with the glycine-16 beta2-receptor genotype

AIMS

We assessed whether montelukast or formoterol provides additive effects to asthmatics not controlled on inhaled corticosteroids, by studying patients who were considered to be genetically susceptible to beta2-receptor down regulation and subsensitivity, and who expressed the homozygous glycine-16 beta2-receptor genotype.

METHODS

Fifteen corticosteroid-treated, mild to moderate persistent asthmatics received montelukast 10 mg once daily or formoterol 9 micro g twice daily for 2 weeks, separated by a 2-week placebo run-in and washout, in a double-blind, double-dummy, randomized crossover design. Bronchoprotection against adenosine monophosphate (AMP) challenge (primary endpoint), spirometry and blood eosinophils were measured at trough after placebo, first and last doses.

RESULTS

For AMP PC20vs placebo, there were sustained significant (P < 0.05) doubling dilution improvements following first (1.1; 95% CI 0.4, 1.9) and last (1.0; 95% CI 0.3, 1.8) doses of montelukast, and following first (1.3; 95% CI 0.1, 2.6) but not last (0.3; 95% CI -0.9, 1.6) doses of formoterol. Blood eosinophils (x 10(6) l(-1)) were significantly (P < 0.05) suppressed after the last dose of montelukast (-71; 95% CI -3, -140) compared with placebo, while formoterol exhibited a nonsignificant rise (20; 95% CI -92, 132). Neither treatment significantly improved FEV1, FEF25-75 or PEF after 2 weeks.

CONCLUSIONS

In genetically susceptible patients with the homozygous glycine-16 genotype, montelukast, but not formoterol, conferred sustained anti-inflammatory properties in addition to inhaled corticosteroid, which were dissociated from changes in lung function after 2 weeks. Thus, assessing lung function may miss potentially beneficial anti-inflammatory effects of montelukast when used as add-on therapy.