Inhaled budesonide induced Cushing's syndrome in cystic fibrosis patients, due to drug inhibition of cytochrome P450

Two CF patients developed Cushing's syndrome during administration of inhaled budesonide (400 microg/d) with oral itraconazole in one and with clarithromycin in the other patient. Clinical features appeared respectively after 2 and 6 weeks of drug co-administration, with prolonged adrenal suppression, and a slow recovery after ceasing the drugs. Inhibitors of the cytochrome P450 interfere with the metabolism of corticosteroids. Combination of these drugs even with moderate doses of budesonide should be closely monitored.

Effects of inhaled fluticasone propionate in children less than 2 years old with recurrent wheezing

Our objective was to evaluate the efficacy and safety of two doses of fluticasone propionate (FP) in young children with recurrent wheezing and risk factors for asthma. Our study design was a randomized, double-blind, placebo-controlled comparison of inhaled FP 50 mcg twice daily (FP 100) and 125 mcg twice daily (FP 250), for 6 months. Outcome measures included number of wheezing episodes, days on albuterol, height standard deviation score (height SDS), osteocalcin (OC), bone alkaline phosphatase fraction (AKP), insulin-like growth factor-binding protein 3 (IGFBP-3), and serum levels of cortisol (SC). Our subjects were 30 patients, aged 7-24 months. Mean wheezing episodes were 6.0 +/- 1.9, 1.9 +/- 1.9, and 2.8 +/- 1.2; mean days of albuterol use were 24.3 +/- 1.3, 6.5 +/- 0.8, and 9.1 +/- 0.8, per patient for placebo, FP100, and FP250 groups, respectively. There was a significant reduction in clinical outcome in the two FP groups compared to placebo (P < 0.01). No significant correlations were found between FP dosage and height SDS, OC, AKP, IGFBP-3, and SC. In conclusion, in young children with asthmatic symptoms, FP at 50 and 125 mcg b.i.d. for 6 months significantly improved respiratory symptoms without causing significant side effects on growth and bone metabolism.

Budesonide fatty-acid esterification: a novel mechanism prolonging binding to airway tissue. Review of available data

AIMS

Evidence is accumulating that budesonide (BUD) forms intracellular esters in airways. which may affect both duration of action and therapeutic ratio of this drug. The aim of the present paper is to review the preclinical and human experimental evidence supporting the esterification of BUD, and to discuss the clinical implications this may have on asthma and rhinitis treatment.

RESULTS

After inhalation, intact BUD binds primarily to available steroid receptors, and mainly excess (unbound) BUD is esterified. Esterification of BUD is a rapid process: within 20 minutes of inhalation in the rat of radiolabeled BUD, approximately 80% of radioactivity within the trachea and main bronchi was associated with BUD esters, primarily BUD oleate. After 4 hours, the proportion of BUD esters/total cellular BUD was typically 40 to 50% for lung, 70 to 90% for trachea, and only 10 to 15% for peripheral muscle. Comparative in vitro and in vivo studies have shown that esterification prolongs BUD's anti-inflammatory activity longer than that of corticosteroids that can not form esters. Clinical studies have confirmed the prolonged presence of BUD esters, as well as intact BUD, in human airway tissues: 6 hours postdosing, nasal biopsy concentrations of intact BUD were >10-fold greater than those of fluticasone propionate and at 24 hours BUD was detectable in threefold more biopsies than fluticasone propionate. The impact of esterification on airway selectivity of BUD has also been demonstrated in vivo and using pharmacokinetic/pharmacodynamic models.

CONCLUSIONS

BUD is retained in airways as esters, a novel kinetic mechanism for synthetic glucocorticoids. In preclinical studies this esterification is correlated to a prolonged local tissue binding and efficacy, which is not found when the esterification is inhibited by an esterification blocker. Because less esters are formed in the systemic compartment than in airways/lung, the local benefit:systemic risk ratio may also be improved by this mechanism. BUD possesses favorable clinical properties, including its approved once-daily efficacy in asthma, which is probably in part attributable to esterification. However, a direct proof of the latter in patients requires effective and safe inhibitors of the esterification, which are not yet available. Therefore, evidence to support the therapeutic impact of esterification is still circumstantial.

Clinical pharmacokinetics of salmeterol

Salmeterol is an inhaled long-acting selective beta(2)-adrenoceptor agonist that is commercially available as the xinafoate (1-hydroxy-2-naphthoic acid) salt of the racemic mixture of the two optical isomers, (R)- and (S)-, of salmeterol. It acts locally in the lung through action on beta2 receptors. Limited data have been published on the pharmacokinetics of salmeterol. Moreover, there are no data on the extent to which inhaled salmeterol undergoes first-pass metabolism. This lack of information is most likely due to the very low plasma concentrations reached after inhalation of therapeutic doses of salmeterol and the problems in developing an analytical method that is sensitive enough to determine these concentrations. When salmeterol is inhaled, plasma concentrations of the drug often cannot be detected, even at 30 minutes after administration of therapeutic doses. Larger inhaled doses give approximately proportionally increased blood concentrations. Plasma salmeterol concentrations of 0.1 to 0.2 and 1 to 2 microg/L have been attained in healthy volunteers about 5 to 15 minutes after inhalation of a single dose of 50 and 400 microg, respectively. In patients who inhaled salmeterol 50microg twice daily for 10 months, a second peak concentration of 0.07 to 0.2 microg/L occurred 45 to 90 minutes after inhalation, probably because of the gastrointestinal absorption of the swallowed drug. Salmeterol xinafoate dissociates in solution to salmeterol and 1-hydroxy-2-naphthoic acid. These two compounds are then absorbed, distributed, metabolised and excreted independently. The xinafoate moiety has no apparent pharmacological activity, is highly protein bound (>99%), largely to albumin, and has a long elimination half-life of about 12 to 15 days in healthy individuals. For this reason, it accumulates in plasma during repeated administration, with steady-state concentrations reaching about 80 to 90 microg/L in patients treated with salmeterol 50microg twice daily for several months. The cytochrome P450 (CYP) isoform 3A4 is responsible for aliphatic oxidation of salmeterol base, which is extensively metabolised by hydroxylation with the major metabolite being alpha-hydroxysalmeterol, with subsequent elimination predominantly in the faeces. It has been demonstrated that 57.4% of administered radioactivity is recovered in the faeces and 23% in the urine; most is recovered between 24 and 72 hours after administration. Unchanged salmeterol accounts for <5% of the excreted dose in the urine. Since the therapeutic dose of salmeterol is very low, it is unlikely that any clinically relevant interactions will be observed as a consequence of the coadministration of salmeterol and other drugs, such as fluticasone propionate, that are metabolised by CYP3A. All the available data clearly show that at the recommended doses of salmeterol, systemic concentrations are low or even undetectable. This is an important point, because it has been demonstrated that the systemic effects of salmeterol are more likely to occur with higher doses, which lead to approximately proportionally increased blood concentrations.

Development status of second generation PDE4 inhibitors for asthma and COPD: the story so far

The beginning of the 1990s saw the synthesis and evaluation of orally-active, second generation phosphodiesterase (PDE) inhibitors that have high specificity for the PDE4 subtype. In vitro and in vivo studies established that this class of compounds suppresses the activity of many pro-inflammatory and immune cells indicating that they may be effective in the treatment of airway inflammatory diseases. In this article we review the development status of the most advanced and extensively studied PDE4 inhibitors for asthma and chronic obstructive pulmonary disease.

Differential adrenomedullin release and endothelin receptor expression in distinct subpopulations of human airway smooth-muscle cells

Although adrenomedullin (ADM) is implicated in the control of airway tone, regulation of ADM release from airway smooth-muscle cells (ASMCs) has not been explored. Preliminary experiments have indicated that human ASMC populations were heterogeneous in their rate of ADM release and expression of endothelin (ET)(A) and ET(B) receptors. We isolated these phenotypically distinct ASMCs from explants derived from the same airway segment. ASMCs possessing exclusively ET(A) receptors appeared smaller and proliferated faster than ET(A)/ET(B) isolates. Macroautoradiographic analysis confirmed the presence of both receptors in human bronchi. ADM release and messenger RNA expression was greater in ET(A)/ET(B) isolates compared with ET(A) isolates. No measurable ET release was detected from ASMCs. Exogenous ET-1 (1 to 100 nM) more potently stimulated the release of ADM from ET(A)/ET(B) compared with ET(A) isolates. In addition, ET-3 (1 to 100 nM) stimulated ADM release only from ET(A)/ET(B) isolates, implicating the ET(B) receptor in this response. Exogenous ET-1 potentiated platelet- derived growth factor-stimulated [3H]thymidine uptake in ET(A)/ ET(B) but not ET(A) isolates. ET-3 did not affect [3H]thymidine uptake in either cell type. Possession of ET(A)/ET(B) receptors is associated with higher rates of ADM release and slower proliferation, but a capacity for ET-1 stimulated DNA synthesis via ET(A) receptors. These results support a paracrine role for the regulation of ADM release predominantly via the ET(B) receptor in human ASMCs.

Cilomilast: a second generation phosphodiesterase 4 inhibitor for asthma and chronic obstructive pulmonary disease

Cilomilast (Ariflo, SB-207499) is an orally-active, second generation phosphodiesterase (PDE) inhibitor that may be effective in the treatment of asthma and chronic obstructive pulmonary disease (COPD). It has high selectivity for the cyclic AMP-specific, or PDE4, isoenzyme that predominates in pro-inflammatory and immune cells and is ten-fold more selective for PDE4D than for PDE4A, B and C. In vitro, cilomilast suppresses the activity of many pro-inflammatory and immune cells that have been implicated in the pathogenesis of asthma and COPD and is highly active in animal models of these diseases. Cilomilast demonstrates a markedly improved side effect profile over the archetypal PDE4 inhibitor, rolipram, which has been attributed to its inability to discriminate between the high affinity rolipram binding site and the catalytic domain of the enzyme, and the fact that it is negatively charged which at physiological pH should limit its penetration in to the CNS. In humans cilomilast is rapidly absorbed after oral administration, providing dose-proportional systemic exposure up to 4 mg, completely bioavailable, has a half-life of approximately 7 h and is subject to negligible first pass hepatic metabolism. Cilomilast is extensively metabolised with decyclopentylation, acyl glucuronidation and 3-hydroxylation of the cyclopentyl ring representing the principal routes. Most of the drug is excreted in the urine (approximately 90%) and faeces (6 - 7%) with unchanged cilomilast accounting for less than 1% of the administered dose. Cilomilast has been evaluated in Phase I, Phase II and Phase III trials and dose-response experiments have demonstrated a clinically significant increase in lung function and a perceived improvement in quality of life in patients with COPD. Trials of cilomilast in asthma have been less impressive although a trend towards improved lung function has been reported. Cilomilast is safe and well-tolerated at doses up to 15 mg in both short- and long-term dosing trials with a low incidence of adverse effects. No evidence for drug-drug interactions with commonly prescribed medications for COPD and asthma such as digoxin, corticosteroids, salbutamol, theophylline or warfarin has been found. Moreover, the pharmacokinetics of cilomilast are essentially the same in smokers and non-smokers, indicating that no dose adjustments of cilomilast will be required in patients with COPD. Thus, cilomilast displays a promising clinical profile in the treatment of inflammatory airway diseases, in particular COPD and the results of further Phase III trials are awaited with interest.

[Bioequivalence of bambuteral and its metabolites terbutaline after oral bambuteral tablet in healthy volunteers by HPLC/MS]

AIM

To study bioequivalence of bambuteral and its metablites terbutaline in 20 healthy male volunteers.

METHODS

A single oral dose of domestic or imported bambuteral tablet was given according to a randomized 2-way cross-over design. The plasma bambuteral and terbutaline concentrations were determined by HPLC/MS.

RESULTS

The pharmacokinetic parameters of domestic and imported bambuteral: AUC0-t were (52 +/- 21) microgram.h.L-1 and (51 +/- 20) microgram.h.L-1, Tmax were (2.9 +/- 0.9) h and (2.6 +/- 0.7) h, Cmax were (6.0 +/- 2.6) microgram.L-1 and (6.2 +/- 2.9) microgram.L-1, T1/2Ke were (11.2 +/- 2.3) h and (11.2 +/- 1.9) h, respectively; terbutaline: AUC0-t were (191 +/- 30) microgram.h.L-1 and (197 +/- 37) microgram.h.L-1; Tmax were (4.2 +/- 1.0) h and (4.2 +/- 1.0) h; Cmax were (10 +/- 5) microgram.L-1 and (10 +/- 4) microgram.L-1; T1/2Ke were (20 +/- 3) h and (21 +/- 4) h, respectively. The bioavaiability of the domestics was 102% +/- 8% (bambuteral) and 100% +/- 12% (terbutaline).

CONCLUSION

The results demonstrate that the two forms of bambuteral and terbutaline were bioequivalent by analysis of variance, two-one sided test and 90% confidential limit.

Tiotropium (Spiriva): mechanistical considerations and clinical profile in obstructive lung disease

Inhaled antimuscarinics, often called anticholinergics in clinical medicine, are established as first line bronchodilators in COPD. Tiotropium has been developed as a new generation antimuscarinic following ipratropium. Tiotropium is a specific, highly potent antimuscarinic, demonstrating very slow dissociation from muscarinic receptors. Dissociation from M2-receptors is faster than from M3 or M1, which in functional in vitro studies, appeared as kinetic receptor subtype selectivity of M3 and M1 over M2. The high potency and slow receptor dissociation found its clinical correlate in significant and long lasting bronchodilatation and bronchoprotection in patients with COPD and asthma. In asthma, protection against methacholine challenge exceeded the study period of 48 hours. In COPD, bronchodilatation of about 80% of the plateau was demonstrated after the first dose. Following chronic once daily inhalation for 28 days, the improvement in pulmonary function was sustained and there was a further increase in peak effects, but more importantly a rising baseline, achieving steady state within 2 weeks. Tiotropium achieves very stable long lasting effects with comparatively low variation of bronchodilatation between peak and trough (the level before the next administration). Stable 24 hour effectiveness profiles the compound as the first once daily bronchodilator. Clinical correlates of kinetic receptor subtype selective blockade remain to be shown. Plasma levels of tiotropium at trough are in the low pg/ml range and are unlikely to explain the sustained effectiveness in the airways. Slow dissociation from muscarinic receptors is likely to be responsible for the long duration of action.

A potent, long-acting, orally active (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamide: novel muscarinic M(3) receptor antagonist with high selectivity for M(3) over M(2) receptors

A novel series of (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamides was designed and synthesized based on the structure and biological profiles of an active metabolite 2 of our prototype muscarinic M(3) receptor selective antagonist 1, to develop a potent, long-acting, orally active M(3) antagonist for the treatment of urinary tract disorders, irritable bowel syndrome, and respiratory disorders. Investigation of (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamides containing a phenyl or heterocyclic ring as the piperidinyl side chain in place of the 4-methyl-3-pentenyl moiety of 15a revealed that this acid moiety was a versatile template for improving the selectivity for M(3) over M(2) receptors in comparison with the corresponding cyclopentylphenylacetic acid group. However, since the in vitro metabolic stability of these analogues was insufficient compared with that of 2, further derivatization was performed by introducing an appropriate hydrophilic group into the phenyl or 2-pyridyl ring. Thus, the 1-(6-aminopyridin-2-ylmethyl)piperidine analogue 15y exhibiting 190-fold selectivity for M(3) receptors (K(i) = 2.8 nM) over M(2) receptors (K(i) = 530 nM) in a human binding assay and good in vitro metabolic stability in dog and human hepatic microsomes was identified. This compound has excellent oral activity at 4 h after oral dosing (1 mg/kg), inhibiting methacholine-induced bronchoconstriction in dogs, and may be useful in clinical situations in which M(3) over M(2) selectivity is desirable.

Effect of dissolution fluid and presence of hog intestinal barrier on the dissolution of theophylline from bioadhesive granules

The effect of dissolution fluid and the presence of a natural barrier (hog intestine) on the release of theophylline from some bioadhesive granules is presented. A higher quantity of the drug was released in simulated intestinal fluid (SIF) than O. IN HCl. When a hog intestine was used as the diffusion barrier, the availability of the drug through the barrier into the sink solution was low, ranging from 20-35%.

Molecular interactions and metal binding in the theophylline-binding core of an RNA aptamer

An RNA aptamer containing a 15-nt binding site shows high affinity and specificity for the bronchodilator theophylline. A variety of base modifications or 2' deoxyribose substitutions in binding-site residues were tested for theophyllinebinding affinity and the results were compared with the previously determined three-dimensional structure of the RNA-theophylline complex. The RNA-theophylline complex contains a U6-A28-U23 base triple, and disruption of this A28-U23 Hoogsteen-pair by a 7-deaza, 2'-deoxy A28 mutant reduces theophylline binding >45-fold at 25 degrees C. U24 is part of a U-turn in the core of the RNA, and disruption of this U-turn motif by a 2'-deoxy substitution of U24 also reduces theophylline binding by >90-fold. Several mutations outside the "conserved core" of the RNA aptamer showed reduced binding affinity, and these effects could be rationalized by comparison with the three-dimensional structure of the complex. Divalent ions are absolutely required for high-affinity theophylline binding. High-affinity binding was observed with 5 mM Mg2+, Mn2+, or Co2+ ions, whereas little or no significant binding was observed for other divalent or lanthanide ions. A metal-binding site in the core of the complex was revealed by paramagnetic Mn2+-induced broadening of specific RNA resonances in the NMR spectra. When caffeine is added to the aptamer in tenfold excess, the NMR spectra show no evidence for binding in the conserved core and instead the drug stacks on the terminal helix. The lack of interaction between caffeine and the theophylline-binding site emphasizes the extreme molecular discrimination of this RNA aptamer.

Higher incidence of elevated body temperature or increased C-reactive protein level in asthmatic children showing transient reduction of theophylline metabolism

The authors investigated whether theophylline metabolism is decreased in asthmatic patients and what condition may be related to its reduction. Fifty-two children with asthma were given 15 mg/kg/day aminophylline intravenously at a constant rate. Blood and spot urine samples were collected at 24 hours, 48 hours, and 72 hours after beginning infusion. The ratio of plasma theophylline concentration at 72 hours to that at 24 hours (C72h/C24h) varied from 0.42 to 1.51 (average 0.894). Plasma theophylline concentration of patients with lower C72h/C24h than average reduced significantly, while the concentration of those with higher C72h/C24h remained unchanged. The urinary ratio of the sum of the metabolites to theophylline was significantly increased in the patients with the lower ratio. Among the demographic characteristics examined, significant difference was found only in the incidence of patients with C-reactive protein (CRP) of 0.5 mg/dl or greater or patients with a fever of 37.5 degrees C or greater when admitted. Acute febrile illness accompanied by increased CRP level may affect theophylline metabolism.

Prodrug to probe solution HFA pMDI formulation and pulmonary esterase activity

A novel salbutamol prodrug was synthesised. Solubility in HFA-134a and susceptibility to rat lung homogenate, blood and plasma esterase enzymes were investigated. Whereas salbutamol had a very low solubility in HFA-134a, the prodrug was found to be miscible in all proportions. In lung homogenate, the prodrug hydrolysed with a half-life of 45 min, re-generating approximately 17% of expected salbutamol after 8 h incubation. The use of a solution pMDI for pulmonary delivery of the salbutamol prodrug is predicted to result in liberation of salbutamol in the lungs following in vivo hydrolysis by lung esterases.

Enhanced theophylline metabolism in patients with bronchial asthma at age 4 and under

The plasma levels of theophylline (TP) and its metabolites were measured in patients with bronchial asthma who were treated with a slow-release preparation of TP. The ratios of the plasma levels of these metabolites to TP levels in the group aged 1-4 years were larger than those in the group aged 5 years and older, suggesting enhanced activity of drug-metabolizing enzymes during infancy.

J-104129, a novel muscarinic M3 receptor antagonist with high selectivity for M3 over M2 receptors

A new class of 4-acetamidopiperidine derivatives has been synthesized and investigated for human muscarinic receptor subtype selectivity. Introduction of a hydrocarbon chain of appropriate length into the piperidine nitrogen of the racemic N-(piperidin-4-yl)-2-cyclobutyl-2-hydroxy-2-phenylacetamide platform conferred up to 70-fold selectivity for human muscarinic M3 receptors over M2 receptors. Subsequent synthetic derivatizations resulted in highly potent M3 receptor antagonists with selectivity greater than two orders of magnitude for M3 over M2 receptors, from which the analogue 4r was selected. Preparation of both enantiomers of 4r led to the identification of (2R)-N-[1-(4-methyl-3-pentenyl)piperidin-4-yl]-2-cyclopentyl-2-hyd roxy-2-phenylacetamide (J-104129, (R)-4r), which exhibited 120-fold selectivity for M3 receptors (Ki = 4.2 nM) over M2 receptors (Ki = 490 nM). In isolated rat trachea, (R)-4r potently and specifically antagonized acetylcholine (ACh)-induced responses with a K(B) value of 3.3 nM. The highly subtype-selective profile was also seen in isolated rat tissue assays (50-fold) and in anesthetized rats (> 250-fold). Oral administration of J-104129 ((R)-4r) antagonized ACh-induced bronchoconstriction with an ED50 value of 0.58 mg/kg in rats. Thus, J-104129 ((R)-4r) may effectively facilitate bronchodilation in the treatment of obstructive airway disease.

Contrasting properties of albuterol stereoisomers

Racemic albuterol is composed of an equimolar mixture of stereoisomers. For asthma therapy, (R)-albuterol is the eutomer and (S)-albuterol is the distomer. By interacting with beta(2 )-adrenoceptors, (R)-albuterol has bronchodilator, bronchoprotective, anti-edematous properties and inhibits activation of mast cells and eosinophils. (S)-albuterol does not activate beta(2 )-adrenoceptors and does not modify activation of beta(2 )-adrenoceptors by (R)-albuterol so that for many years it was presumed to be biologically inert. Recently, it has been established that regular and excessive use of racemic albuterol induces paradoxical reactions in some subjects with asthma. Because such effects cannot be accounted for by activation of beta(2 )-adrenoceptors, the pharmacologic profile of (S)-albuterol has been more carefully defined. (S)-albuterol has distinctive pharmacologic properties that are unrelated to activation of beta(2 )-adrenoceptors. Thus, (S)-albuterol intensifies bronchoconstrictor responses of sensitized guinea pigs and induces hypersensitivity of asthmatic airways; it also promotes the activation of human eosinophils in vitro. These actions of (S)-albuterol may explain why racemic albuterol can intensify allergic bronchospasm and promote eosinophil activation in asthmatic airways. The capacity of (S)-albuterol to elevate intracellular Ca(2+) would account for the paradox because this action will oppose, or even nullify, the consequences of adenylyl cyclase activation by (R)-albuterol. Because (S)-albuterol is metabolized more slowly than (R)-albuterol and is retained preferentially within the airways, paradoxical effects become more prominent during regular and excessive use of racemic albuterol. Because (S)-albuterol has detrimental effects in asthmatic airways, levalbuterol [homochiral (R)-albuterol] should have advantages over racemic albuterol in therapy for asthma.

Tiotropium bromide (Ba 679 BR), a novel long-acting muscarinic antagonist for the treatment of obstructive airways disease

Tiotropium bromide (Ba 679 BR) is a novel potent and long-lasting muscarinic antagonist that has been developed for the treatment of chronic obstructive airways disease (COPD). Binding studies with [3H]tiotropium bromide in human lung have confirmed that this is a potent muscarinic antagonist with equal affinity for M1-, M2- and M3-receptors and is approximately 10-fold more potent than ipratropium bromide. Tiotropium bromide dissociates very slowly from lung muscarinic receptors compared with ipratropium bromide. In vitro tiotropium bromide has a potent inhibitory effect against cholinergic nerve-induced contraction of guinea-pig and human airways, that has a slower onset than atropine or ipratropium bromide. After washout, however, tiotropium bromide dissociates extremely slowly compared with the dissociation of atropine and ipratropium bromide. Measurement of acetylcholine (ACh) release from guinea-pig trachea shows that tiotropium bromide, ipratropium bromide and atropine all increase ACh release on neural stimulation and that this effect is washed out equally quickly for the three antagonists. This confirms binding studies to transfected human muscarinic receptors which suggested that tiotropium bromide dissociates slowly from M3-receptors (on airway smooth muscle) but rapidly from M2 autoreceptors (on cholinergic nerve terminals). Clinical studies with inhaled tiotropium bromide confirm that it is a potent and long-lasting bronchodilator in COPD and asthma. Furthermore, it protects against cholinergic bronchoconstriction for > 24 h. This suggests that tiotropium bromide will be a useful bronchodilator, particularly in patients with COPD, and may be suitable for daily dosing. The selectivity for M3- over M2-receptors may also confer a clinical advantage.

Nasal nitric oxide does not control basal nasal patency or acute congestion following allergen challenge in allergic rhinitis

Nasal nitric oxide (NO), a powerful vasodilator, could control the filling of nasal capacitance vessels, thus determining nasal patency and mediating the acute congestion accompanying allergen challenge. We examined the effect of topical N-nitro-L-arginine-methyl-ester (L-NAME; 100 to 200 mg), an NO synthase inhibitor, on nasal NO and on nasal patency assessed by acoustic rhinometry in 7 subjects with nasal allergy, and in 4 subjects we examined the effects of nasal allergen challenge on nasal NO before and after a short course of nasal steroid. After L-NAME, nasal NO fell to 42.1%+/-15.7% of baseline (p < .0001) with no significant change in minimal cross-sectional area. After allergen challenge, acute congestion was associated with a significant fall in nasal NO, which returned to baseline by 4 hours, when the congestion resolved. Repeat challenge after 2 weeks of nasal corticosteroid yielded similar findings. A role for NO in modulating vascular tone was not supported by the present study.

Nitrogen dioxide formation during inhaled nitric oxide therapy

BACKGROUND

Nitrogen dioxide (NO2) is a toxic by-product of inhalation therapy with nitric oxide (NO). The rate of NO2 formation during NO therapy is controversial.

METHODS

The formation of NO2 was studied under dynamic flows emulating a base case NO ventilator mixture containing 80 ppm NO in a 90% oxygen matrix. The difficulty in measuring NO2 concentrations below 2 ppm accurately was overcome by the use of tunable diode laser absorption spectroscopy.

RESULTS

Using a second-order model, the rate constant, k, for NO2 formation was determined to be (1.19 +/- 0.11) x 10(-11) ppm-2s-1, which is in basic agreement with evaluated data from atmospheric literature.

CONCLUSIONS

Inhaled NO can be delivered safely in a well-designed, continuous flow neonatal ventilatory circuit, and NO2 formation can be calculated reliably using the rate constant and circuit dwell time.

Airway synthesis of 20-hydroxyeicosatetraenoic acid: metabolism by cyclooxygenase to a bronchodilator

Rabbit airway tissue is a particularly rich source of cytochrome P-4504A protein, but very little information regarding the effect(s) of 20-hydroxyeicosatetraenoic acid (20-HETE) on bronchial tone is available. Our studies examined the response of rabbit bronchial rings to 20-HETE and the metabolism of arachidonic acid and 20-HETE from airway microsomes. 20-HETE (10(-8) to 10(-6) M) produced a concentration-dependent relaxation of bronchial rings precontracted with KCl or histamine but not with carbachol. Relaxation to 20-HETE was blocked by indomethacin or epithelium removal, consistent with the conversion of 20-HETE to a bronchial relaxant by epithelial cyclooxygenase. A cyclooxygenase product of 20-HETE also elicited relaxation of bronchial rings. [14C]arachidonic acid was converted by airway microsomes to products that comigrated with authentic 20-HETE (confirmed by gas chromatography-mass spectrometry as 19- and 20-HETE) and to unidentified polar metabolites. [3H]20-HETE was metabolized to indomethacin-inhibitable products. These data suggest that 20-HETE is an endogenous product of rabbit airway tissue and may modulate airway resistance in a cyclooxygenase-dependent manner.

Relationship between exhaled nitric oxide and childhood asthma

The purpose of the study was to determine if exhaled nitric oxide levels in children varied according to their asthmatic and atopic status. Exhaled nitric oxide was measured in a sample of 93 children attending the North West Lung Centre, Manchester, United Kingdom, for the clinical evaluation of a respiratory questionnaire being developed as a screening tool in general practice. The clinical assessment included full lung function, skin prick testing, and exercise challenge. Children were said to be asthmatic either by consensus decision of three independent consultant pediatricians, who reviewed all the clinical results except the nitric oxide measurements, or by positive exercise test. Atopic asthmatic children had higher geometric mean exhaled nitric oxide levels (consensus decision, 12.5 ppb [parts per billion] 95% CI, 8.3 to 18. 8; positive exercise test, 12.2 ppb 95% CI, 7.6 to 19.7) than did nonatopic asthmatic children (3.2 ppb 95% CI, 2.3 to 4.6; 3.2 ppb 95% CI, 2.0 to 5.0), atopic nonasthmatic children (3.8 ppb 95% CI, 2. 7 to 5.5; 5.7 ppb 95% CI, 4.1 to 8.0), or nonatopic nonasthmatic children (3.4 ppb 95% CI, 2.8 to 4.1; 3.5 ppb 95% CI, 3.0 to 4.1). Thus, exhaled nitric oxide was raised in atopic asthmatics but not in nonatopic asthmatics, and these nonatopic asthmatics had levels of exhaled nitric oxide similar to those of the nonasthmatics whether atopic or not.