Zafirlukast. A review of its pharmacology and therapeutic potential in the management of asthma

Zafirlukast ameliorates Docetaxel-induced activation of NOD-like receptor protein 3 (NLRP3) inflammasome, mediated by sirtuin1 (SIRT1) in hepatocytes

Docetaxel-associated liver injury has become a serious public health problem, resulting in therapy discontinuation, liver failure, and death. Zafirlukast is a typical leukotriene receptor antagonist used for prophylaxis and chronic treatment of asthma. In this study, we investigate whether treatment with Zafirlukast could alleviate Docetaxel-induced cytotoxicity in hepatocytes. Our results indicate that Zafirlukast mitigated Docetaxel-induced toxicity in LO-2 hepatocytes. Firstly, Zafirlukast reduced the production of 8-hydroxy-2p-deoxyguanosine (8-OHdG) and increased the levels of reduced glutathione (GSH) against Docetaxel. Secondly, Zafirlukast elevated the levels of mitochondrial membrane potential (ΔΨm) and adenosine triphosphate (ATP). Thirdly, Zafirlukast prevented Docetaxel-induced release of lactate dehydrogenase (LDH) and increased cell viability of LO-2 hepatocytes against Docetaxel. We also found that Zafirlukast ameliorated Docetaxel-induced apoptosis by reducing Caspase-3 and Caspase-9 activity. Mechanistically, our results demonstrate that Zafirlukast inhibited the activation of NOD-like receptor protein 3 (NLRP3), mediated by SIRT1. Based on these findings, we conclude that the administration of Zafirlukast might have a protective effect against Docetaxel-induced cytotoxicity in hepatocytes.

A large-scale computational screen identifies strong potential inhibitors for disrupting SARS-CoV-2 S-protein and human ACE2 interaction

SARS-CoV-2 has infected millions of individuals across the globe and has killed over 2.7 million people. Even though vaccines against this virus have recently been introduced, the antibody generated in the process has been reported to decline quickly. This can reduce the efficacy of vaccines over time and can result in re-infections. Thus, drugs that are effective against COVID-19 can provide a second line of defence and can prevent occurrence of the severe form of the disease. The interaction between SARS-CoV2 S-protein and human ACE2 (hACE2) is essential for the infection of the virus. Thus, drugs that block this interaction could potentially inhibit SARS-CoV-2 infection into the host cells. To identify such drugs, we first analyzed the recently published crystal structure of S-protein-hACE2 complex and identified essential residues of both S-protein and hACE2 for this interaction. We used this knowledge to virtually dock a drug library containing 4115 drug molecules against S-protein for repurposing drugs that could inhibit binding of S-protein to hACE2. We identified several potential inhibitors based on their docking scores, pharmacological effects and ability to block residues of S protein required for interaction with hACE2. The top inhibitors included drugs used for the treatment of hepatitis C (velpatasvir, pibrentasvir) as well as several vitamin D derivatives. Several molecules obtained from our screen already have good experimental support in published literature. Thus, we believe that our results will facilitate the discovery of an effective drug against COVID-19. Communicated by Ramaswamy H. Sarma.

An Innovative High-Throughput Screening Approach for Discovery of Small Molecules That Inhibit TNF Receptors

Tumor necrosis factor receptor 1 (TNFR1) is a transmembrane receptor that binds tumor necrosis factor or lymphotoxin-alpha and plays a critical role in regulating the inflammatory response. Upregulation of these ligands is associated with inflammatory and autoimmune diseases. Current treatments reduce symptoms by sequestering free ligands, but this can cause adverse side effects by unintentionally inhibiting ligand binding to off-target receptors. Hence, there is a need for new small molecules that specifically target the receptors, rather than the ligands. Here, we developed a TNFR1 FRET biosensor expressed in living cells to screen compounds from the NIH Clinical Collection. We used an innovative high-throughput fluorescence lifetime screening platform that has exquisite spatial and temporal resolution to identify two small-molecule compounds, zafirlukast and triclabendazole, that inhibit the TNFR1-induced IκBα degradation and NF-κB activation. Biochemical and computational docking methods were used to show that zafirlukast disrupts the interactions between TNFR1 pre-ligand assembly domain (PLAD), whereas triclabendazole acts allosterically. Importantly, neither compound inhibits ligand binding, proving for the first time that it is possible to inhibit receptor activation by targeting TNF receptor-receptor interactions. This strategy should be generally applicable to other members of the TNFR superfamily, as well as to oligomeric receptors in general.

PdCl2 catalyzed efficient assembly of organic azides, CO, and alcohols under mild conditions: a direct approach to synthesize carbamates

A simple and readily available PdCl2 catalyzed carbamate synthesis method via isocyanate generation and application in situ has been developed. This chemistry provides an efficient and practical approach to synthesize carbamates from simple organic azides, CO atmosphere and alcohols. The broad scope, mild and neutral conditions, and only N2 as the byproduct make this transformation very useful. Moreover, simple examples of modification of bioactive molecules and construction of macrocycles were achieved through this protocol.

Fluconazole but not the CYP3A4 inhibitor, itraconazole, increases zafirlukast plasma concentrations

PURPOSE

Zafirlukast is a substrate of cytochrome P450 2C9 (CYP2C9) and cytochrome P450 3A4 (CYP3A4) in vitro, but the role of these enzymes in its metabolism in vivo is unknown. To investigate the contribution of CYP2C9 and CYP3A4 to zafirlukast metabolism, we studied the effects of fluconazole and itraconazole on its pharmacokinetics (PK).

METHODS

In a randomized crossover study, 12 healthy volunteers ingested fluconazole 200 mg (first dose 400 mg) once daily, itraconazole 100 mg (first dose 200 mg) twice daily, or placebo twice daily for 5 days, and on day 3, 20 mg zafirlukast. Plasma concentrations of zafirlukast and the antimycotics were measured up to 72 h.

RESULTS

Fluconazole increased the total area under the plasma concentration-time curve (AUC) of zafirlukast 1.6-fold [95% confidence interval (CI) 1.3-2.0-fold, P < 0.001), and its peak plasma concentration 1.5-fold (95% CI 1.2-2.0-fold, P < 0.05). Fluconazole did not affect the time of peak plasma concentration or elimination half-life of zafirlukast. None of the zafirlukast PK variables differed significantly from the control in the itraconazole phase; e.g., the ratio to control of the total AUC of zafirlukast was 1.0 (95% CI 0.82-1.2) during the itraconazole phase.

CONCLUSIONS

Fluconazole, but not itraconazole, increases zafirlukast plasma concentrations, strongly suggesting that CYP2C9 but not CYP3A4 participates in zafirlukast metabolism in humans.

A High-Throughput, Homogeneous, Fluorescence Polarization Assay for Inhibitors of Hedgehog Protein Autoprocessing

Hedgehog (Hh) signaling plays an important role in embryonic patterning and adult stem cell renewal but has recently been found also to be involved in certain stem cell cancers. One of the first steps in Hh signaling is the autoprocessing of Hh protein, in which the C-terminal domain (Hh-C) catalyzes a cholesterol-dependent autocleavage reaction that leads to the production of the cholesterol ester of the N-terminal Hh domain (Hh-N), thereby yielding a signaling molecule that activates the Hh pathway by binding to the Patched receptor. This article describes an in vitro, homogeneous assay system that measures changes in fluorescence polarization that accompany the cholesterol-dependent autocleavage of Hh protein. The assay system makes use of a modified Hh protein in which Hh-N, which is not essential for autocleavage, is replaced by a 25-residue peptide containing a tetracysteine motif, complexed with a bisarsenical fluorophore. The assay is quite robust and easily adapted to high-throughput screening in 384-well plates with Z′ factors above 0.8. It has been used to screen the National Institutes of Health Clinical Collection, which has led to the identification of 2 compounds that inhibit the cholesterol-dependent autocleavage of Hh protein at micromolar concentrations.

Tolerance and rebound with zafirlukast in patients with persistent asthma

BACKGROUND

The potential for tolerance to develop to zafirlukast, a cysteinyl leukotriene (CysLT) receptor antagonist (LRA) in persistent asthma, has not been specifically examined.

OBJECTIVE

To look for any evidence of tolerance and potential for short-term clinical worsening on LRA withdrawal. Outcome measures included changes in; airway hyperresponsiveness to inhaled methacholine (PD20FEV1), daily symptoms and peak expiratory flows (PEF), sputum and blood cell profiles, sputum CysLT and prostaglandin (PG)E2 and exhaled nitric oxide (eNO) levels.

METHODS

A double blind, placebo-controlled study of zafirlukast, 20 mg twice daily over 12 weeks in 21 asthmatics taking beta2-agonists only (Group I), and 24 subjects treated with ICS (Group II).

RESULTS

In Group I, zafirlukast significantly improved morning PEF and FEV1compared to placebo (p < 0.01), and reduced morning waking with asthma from baseline after two weeks (p < 0.05). Similarly in Group II, FEV1 improved compared to placebo (p < 0.05), and there were early within-treatment group improvements in morning PEF, beta2-agonist use and asthma severity scores (p < 0.05). However, most improvements with zafirlukast in Group I and to a lesser extent in Group II deteriorated toward baseline values over 12 weeks. In both groups, one week following zafirlukast withdrawal there were significant deteriorations in morning and evening PEFs and FEV1 compared with placebo (p < or = 0.05) and increased nocturnal awakenings in Group II (p < 0.05). There were no changes in PD20FEV1, sputum CysLT concentrations or exhaled nitric oxide (eNO) levels. However, blood neutrophils significantly increased in both groups following zafirlukast withdrawal compared to placebo (p = 0.007).

CONCLUSION

Tolerance appears to develop to zafirlukast and there is rebound clinical deterioration on drug withdrawal, accompanied by a blood neutrophilia.

Tolerability profiles of leukotriene receptor antagonists and long-acting beta2-adrenoceptor agonists in combination with inhaled corticosteroids for treatment of asthma: a review

Inhaled corticosteroids, long-acting beta2-adrenoceptor agonists, and leukotriene receptor antagonists are widely used for treatment of asthma. Inhaled corticosteroids are recommended as first-line therapy, whereas long-acting beta2-adrenoceptor agonists and leukotriene receptor antagonists are indicated as add-on therapy in patients not adequately controlled with corticosteroids alone. A number of studies have investigated the efficacy of combinations of these drugs in asthma, but several issues concerning the safety of these treatments are highly debated. This review provides a critical appraisal of the tolerability profiles of long-acting beta2-agonists and leukotriene receptor antagonists used in combination with inhaled corticosteroids for the treatment of asthma.

Optimisation, validation and application of a capillary electrophoretic method for the determination of zafirlukast in pharmaceutical formulations

Zafirlukast is a selective and competitive orally administered inhibitor of the cysteinyl leukotrienes and currently indicated for the prophylaxis and treatment chronic asthma. A simple, rapid, reliable capillary zone electrophoresis method for the determination of ZAF in pharmaceutical formulations was developed and validated. The influence of buffer concentration, buffer pH, organic modifier, capillary temperature, applied voltage and injection time was systemically investigated in a fused silica capillary (i.d. 50 microm, total length 80.5 cm and effective length 72.0 cm). Optimum results were obtained with 50mM borate buffer at pH 8.50, capillary temperature 25 degrees C and applied voltage 30 kV. The samples were injected hydrodynamically for 3s at 50 mbar. Detection wavelength was set at 240 nm. Meloxicam was used as internal standard. The method was suitably validated with respect to linearity, limit of detection and quantification, accuracy, precision, selectivity, robustness and ruggedness. The linear calibration range was 2.00-80.00 microg mL(-1) and the limits of detection and quantification were 0.75 and 2.00 microg mL(-1) with R.S.D. of 3.88 and 2.75%, respectively. The proposed method was applied for the determination of ZAF in its pharmaceutical formulations. The results obtained from developed method were compared with a HPLC method reported in the literature and no significant difference was found statistically.

Safety of Zafirlukast

OBJECTIVES

A prescription event monitoring (PEM) postmarketing surveillance study was carried out to examine the safety of zafirlukast as used in general practice in England.

METHODS

Exposure data were obtained from the first National Health Service (NHS) prescription dispensed for patients whose prescription details were processed by the Prescription Pricing Authority between August 1998 and December 2000. Outcome data were obtained from 'green form' questionnaires sent to general practitioners (GPs) at least 6 months following the first prescription issued. Incidence densities (IDs) were calculated for events reported per 1000 months of patient exposure and ID differences between the first month of treatment and months 2-6 combined were analysed. Events of medical interest were followed up by postal questionnaire sent to GPs.

RESULTS

21 557 green forms were sent to 8051 doctors, of which 9124 (42.3%) were returned. Useful clinical data was obtained for 7976 patients of which 4664 (58.5%) were female and 3265 (40.9%) were male. The patient's sex was not specified in 47 (0.6%) forms. The median age of the cohort was 53 years (interquartile range 38-66 years). The most frequently reported primary indication was the licensed indication of asthma, but for a small proportion of the cohort it was prescribed 'off label'.A total of 152 events in 120 (1.5%) patients were reported as adverse drug reactions (ADRs) by GPs on the green forms. ADRs with the highest reported frequency were headache and nausea. There were 3514 reasons for stopping zafirlukast in 3148 (39.5%) patients, the most frequently reported of which was that the drug was 'ineffective' (2008 patients; 25.2%). The most frequently reported specified clinical reason for stopping was headache (82 patients; 1.0%). There were 28 pregnancies reported in this cohort, 20 of which were reported to have exposure to zafirlukast during the first trimester. Nine live births with no recorded congenital abnormalities were reported for pregnancies with exposure in the first trimester. There were 151 deaths reported during the study period (1.9%). The most frequently reported causes of death were related to the respiratory system (57; 37.7%), including chronic obstructive pulmonary disease, asthma and bronchopneumonia.

CONCLUSION

This study showed that zafirlukast, as used in general practice in England, is a generally well tolerated drug with few associated adverse events.

A Novel Dual Antagonist of Thromboxane A2 and Leukotriene D4 Receptors: Synthesis and Structure-Activity Relationships of Chloroquinolylvinyl Derivatives

To discover an orally active thromboxane A(2) (TXA(2)) and leukotriene D(4) (LTD(4)) dual antagonist, we designed and synthesized chloroquinolylvinyl derivatives based on the structures of the TXA(2) antagonist daltroban and the LTD(4) antagonist montelukast. Among these derivatives, 4-{[(2-(4-chlorophenylsulfonylamino)-1-{3-[(E)-2-(7-chloro-2-quinolyl)vinyl]phenyl}ethyl)thio]methyl}benzoic acid (18d) showed potent inhibitory activity against U46619-induced aggregation of guinea pig platelets and LTD(4)-induced contraction in the guinea pig ileum, with IC(50) values of 340 nm and 0.40 nm, respectively. Oral administration of 18 d also inhibited both the LTD(4)-induced acceleration of plasma leakage to skin in guinea pig and the U46619-induced increase in airway resistance in guinea pig with ED(50) values of 0.47 mg/kg and 3.3 mg/kg, respectively.

Cost effectiveness of leukotriene modifiers in adults with asthma

Asthma is the most common chronic disorder in industrialised nations, with over 100 million people worldwide affected. Leukotrienes are chemical mediators released from mast cells, eosinophils and basophils. They cause bronchoconstriction, an increase in mucous secretions and activation of inflammatory cells. Leukotriene modifiers are a long-term controller medication used to treat asthma. They function by selectively competing for the leukotriene receptor sites, thereby blocking their action, or by inhibiting 5-lipoxygenase and thus preventing leukotriene formation. Both current US and Global Initiative for Asthma treatment guidelines have clarified the role of leukotriene modifiers in the management of asthma in adults and children. Leukotriene modifiers have two distinct roles: to replace inhaled corticosteroids in milder asthma and as an add-on therapy to inhaled corticosteroids in more severe asthma. While efficacy is certainly an important issue, economic considerations are also important in a disease such as asthma where there are a variety of treatment options and the severity of the disease varies widely. This review examined published studies to better understand the cost effectiveness of leukotriene modifiers in adults with asthma. Fifteen articles were found that analysed the cost effectiveness of leukotriene modifiers, with almost all performed in the US. The vast majority of the studies were retrospective claims analyses, but three randomised controlled trials incorporating economic outcomes have been reported. The majority of the articles found that for both monotherapy in mild persistent asthma and add-on therapy in moderate persistent asthma, leukotriene modifiers were less cost effective than inhaled corticosteroids with or without a long-acting beta2-adrenoceptor agonist. However, these results must be viewed cautiously as in several studies there were methodological issues such as comparisons of unequal treatment groups or inappropriate use of leukotriene modifiers in stepwise treatment.

Pharmacokinetics of radiolabelled quinlukast in rats

Pharmacokinetics together with in vivo metabolism and elimination of quinlukast, a potential anti-asthmatic and anti-inflammatory drug, were designed in rats. For this purpose, bile duct cannulated rats and an in situ perfused rat liver preparation were employed. 3H-radiolabelled compound was administered i.v. or loaded to the perfusion medium, respectively. Quinlukast represented the main form of radioactivity determined in plasma; in comparison with the parent drug metabolites were present in lower levels in the systemic circulation. The pharmacokinetic parameters related to the whole animal were calculated from quinlukast rat plasma concentration-time course. The distribution of quinlukast in the body was relatively fast (distribution half-life was approx. 6 min), the elimination half-life exceeded 2h. Binding of quinlukast to rat plasma proteins was very high (approx. 99.7%) and this binding influenced distribution volumes of quinlukast. Both the volume of the central compartment and the volume at a steady state were approx. 115 and 430 ml, respectively. The experiments showed that the biliary clearance was the major route of elimination of this compound from the systemic circulation of rats. In agreement with the determined elimination half-life approx. 42% of the radioactivity was found in the bile, with <0.5% appearing in the urine. The majority of the eliminated radioactivity in the bile was in the form of polar metabolites; only a small part of the parent compound was determined. Two hours after intravenous administration, polar metabolites - but no parent drug - were detected in the urine.

Pranlukast: a review of its use in the management of asthma

Pranlukast (Onon, Azlaire), is an orally administered, selective, competitive antagonist of the cysteinyl leukotrienes (LT) C(4), LTD(4) and LTE(4). It is indicated for the prophylactic treatment of chronic bronchial asthma in paediatric and adult patients. The efficacy of pranlukast 225mg twice daily in adults with mild to moderate asthma was demonstrated in double-blind, placebo- or azelastine-controlled studies of 4 or 8 weeks' duration. The drug at this dosage was superior to both comparators in improving mean attack scores and morning and/or evening peak expiratory flow rates, and decreasing the use of rescue bronchodilators (p < 0.05). In limited clinical studies, pranlukast 225mg twice daily appeared to be as effective as montelukast 10mg once daily and zafirlukast 40mg twice daily in adults with mild to moderate asthma. Tachyphylaxis was absent when the drug was administered for up to 4 years. In patients requiring high-dose inhaled corticosteroid therapy, pranlukast 225 mg twice daily plus a halved dosage of inhaled corticosteroid was as effective as the original dosage of inhaled corticosteroid. Pranlukast was also effective in patients with mild to severe asthma in a clinical practice setting. In a double-blind trial, greater improvements in most outcome measures were observed with pranlukast than with oxatomide in children and adolescents with asthma. In clinical trials, pranlukast was well tolerated in adult and paediatric patients with asthma, with an adverse event profile similar to that of placebo. Gastrointestinal events and hepatic function abnormalities were the most commonly reported adverse events. No clinically significant differences in adverse event profiles between pranlukast, zafirlukast or montelukast were shown in limited comparisons. Although Churg-Strauss syndrome has been noted in pranlukast recipients, a direct causal relationship is unlikely.

CONCLUSIONS

Pranlukast is a well tolerated and effective preventative treatment in adult and paediatric patients with persistent asthma of all severities. In some patients, pranlukast may be beneficial when added to low-dose inhaled corticosteroids; it may also be a viable alternative to increasing inhaled corticosteroid dosages. The efficacy of pranlukast relative to placebo has been confirmed; its efficacy relative to other therapy awaits further investigation. Nonetheless, pranlukast is a useful therapeutic option (with as-required short-acting beta(2)-agonists), either as preventative monotherapy for the treatment of mild persistent asthma or in conjunction with inhaled corticosteroids in the management of moderate or severe persistent asthma.

Leukotriene antagonists

Hepatotoxicity is the most common cause of fulminant hepatic failure in the United States and the main indication for market withdrawal of drugs. This condition has been increasingly recognized as a problem of enormous medical, financial legal, and regulatory importance. It is in context of this heightened awareness of hepatotoxicity, particularly associated with new high profile drugs, that the authors reviews the published data regarding liver injury related to a novel group of asthma drugs.

Inflammatory cells in asthma: mechanisms and implications for therapy

Recent clinical studies have brought asthma's complex inflammatory processes into clearer focus, and understanding them can help to delineate therapeutic implications. Asthma is a chronic airway inflammatory disease characterized by the infiltration of airway T cells, CD(+) (T helper) cells, mast cells, basophils, macrophages, and eosinophils. The cysteinyl leukotrienes also are important mediators in asthma and modulators of cytokine function, and they have been implicated in the pathophysiology of asthma through multiple mechanisms. Although the role of eosinophils in asthma and their contribution to bronchial hyperresponsiveness are still debated, it is widely accepted that their numbers and activation status are increased. Eosinophils may be targets for various pharmacologic activities of leukotriene receptor antagonists through their ability to downregulate a number of events that may be key to the effector function of these cells.

Zafirlukast has no beneficial effects in the treatment of chronic urticaria

BACKGROUND

Leukotriene receptor antagonists have shown some efficacy in t he treatment of asthma. Injection of LTC4, LTD4 and LTE4 into the skin leads to a weal-and-flare reaction, suggesting an involvement of leukotrienes in the pathogenesis of urticaria. Indeed, various reports have indicated a beneficial effect for leukotriene receptor antagonists in patients with chronic urticaria.

OBJECTIVE

To determine the therapeutic effect of the leukotriene receptor antagonist zafirlukast in patients with chronic urticaria.

METHODS

The study was a double-blind, placebo-controlled, cross-over study lasting for 12 weeks. Fifty-two patients with chronic urticaria were investigated at a university hospital. The patients were randomized to receive 20 mg zafirlukast b.i.d. or placebo and cross-over was scheduled after 6 weeks. The efficacy of the treatment was evaluated by a daily symptom score, six physical examinations, the requirement of rescue antihistamines (acrivastine) and an overall assessment by the patient andthe investigating physician.

RESULTS

Forty-six patients completed the study: zafirlukast was well tolerated without alteration of the investigated laboratory parameters. In comparison with placebo, treatment with zafirlukast resulted in no significant positive effect for any of the efficacy measures. Moreover, we were unable to identify any subgroup of patients with chronic urticaria responding with a therapeutic benefit.

CONCLUSIONS

The leukotriene receptor antagonist zafirlukast does not provide a significant therapeutic benefit at a dose of 20 mg b.i.d. in patients with chronic urticaria.

The role of antileukotrienes in the treatment of asthma

Cysteinyl leukotrienes (Cys-LTs) are mediators released in asthma and are both direct bronchoconstrictors and proinflammatory substances that mediated several steps in the pathophysiology of chronic asthma, including inflammatory cells recruitment, vascular leakage, and possibly airway remodelling. Available evidence from clinical trials and real world experience derived from managing patients with asthma justifies a broader role for antiLTRAs in asthma management than that recommended in the National Asthma Education and Prevention Programm (NAEPP) and National Health Lung and Blood Institute (NHLBI) treatment guidelines. Leukotriene-receptor antagonist drugs (LTRAs) seem to be effective alternatives to inhaled corticosteroids (ICS) either as monotherapy or as adjunctive therapy that reduces the need for higher doses of ICS in patients with mild-to-moderate persistent asthma. LTRAs may be used as adjunctive therapy for al levels of disease severity because they are effective in combination with ICS during long-term maintenance therapy. The agents seem especially effective in preventing aspirin-induced asthma, exercise-induced asthma (EIA) and they may provide an additional advantage of reducing nasal congestion in patients with both asthma and rhinitis.

Gamma-glutamyl leukotrienase, a novel endothelial membrane protein, is specifically responsible for leukotriene D(4) formation in vivo

The metabolism of cysteinyl leukotrienes in vivo and the pathophysiological effects of individual cysteinyl leukotrienes are primarily unknown. Recently we identified an additional member of the gamma-glutamyl transpeptidase (GGT) family, gamma-glutamyl leukotrienase (GGL), and developed mice deficient in this enzyme. Here we show that in vivo GGL, and not GGT as previously believed, is primarily responsible for conversion of leukotriene C(4) to leukotriene D(4), the most potent of the cysteinyl leukotrienes and the immediate precursor of leukotriene E(4). GGL is a glycoprotein consisting of two polypeptide chains encoded by one gene and is attached at the amino terminus of the heavy chain to endothelial cell membranes. In mice it localizes to capillaries and sinusoids in most organs and in lung to larger vessels as well. In contrast to wild-type and GGT-deficient mice, GGL-deficient mice do not form leukotriene D(4) in vivo either in blood when exogenous leukotriene C(4) is administered intravenously or in bronchoalveolar lavage fluid of Aspergillus fumigatus extract-induced experimental asthma. Further, GGL-deficient mice show leukotriene C(4) accumulation and significantly more airway hyperreponsiveness than wild-type mice in the experimental asthma, and induction of asthma results in increased GGL protein levels and enzymatic activity. Thus GGL plays an important role in leukotriene D(4) synthesis in vivo and in inflammatory processes.

Pharmacokinetic profile of zafirlukast

Zafirlukast is a cysteinyl leukotriene type 1 receptor antagonist that causes bronchodilation and has anti-inflammatory properties. Clinical efficacy has been demonstrated when using oral doses of 20 to 40 mg twice daily. The pharmacokinetics of zafirlukast are best described by a two-compartment model. Maximum plasma concentrations (Cmax) were achieved 3 hours after a single oral dose of 20 or 40 mg to healthy volunteers. The absolute bioavailability of zafirlukast is unknown. However, coadministration of zafirlukast with food reduces bioavailability by approximately 40%. The drug binds to plasma proteins (>99%), predominantly to albumin, and has a mean terminal elimination half-life of approximately 10 hours in both healthy volunteers and patients with asthma. Zafirlukast undergoes extensive hepatic metabolism. Hydroxylation by cytochrome P450 (CYP) 2C9 is the major biotransformation pathway. The metabolites of zafirlukast contribute little to its overall activity. Zafirlukast is mainly eliminated in the faeces, while urinary excretion accounts for <10% of an orally administered dose. Because of its primarily hepatic metabolism, the clearance of zafirlukast is reduced in patients with hepatic impairment. In patients with stable alcoholic cirrhosis, Cmax and area under the plasma concentration-time curve for zafirlukast were increased by 50 to 60% compared with healthy volunteers. Asymptomatic elevations of serum liver enzymes have been reported with high dosages of zafirlukast (80 mg twice daily), returning to normal after cessation of the drug. Inhibition of the CYP2C9 and CYP3A isoenzymes by zafirlukast has been reported in vitro. Zafirlukast interacts with warfarin and produces a clinically significant increase in the prothrombin time, but it does not alter the pharmacokinetics of terfenadine carboxylate, the active metabolite of terfenadine. Plasma concentrations of zafirlukast decreased when the drug was administered concomitantly with erythromycin, terfenadine or theophylline, and increased when it was coadministered with aspirin (acetylsalicylic acid). Theophylline metabolism is unchanged in most cases by zafirlukast, but there is a report of one patient with increased theophylline plasma concentrations when zafirlukast was coadministered. Recently, cases of Churg-Strauss syndrome have been described in patients with asthma receiving zafirlukast treatment. This occurrence in patients being withdrawn from corticosteroid therapy while receiving zafirlukast has been attributed to a previously undiagnosed presence of this syndrome in these patients.

Leukotrienes in respiratory disease

Arachidonic acid metabolism via 5-lipoxygenase gives rise to a group of biologically active lipids known as leukotrienes: leukotriene B(4), which is a potent activator of leukocyte chemotaxis, and cysteinyl leukotrienes (leukotriene C(4), D(4)and E(4)) which account for the spasmogenic activity previously described as slow-reacting substance of anaphylaxis. The biological actions of leukotrienes and the observations that leukotrienes are synthesised in the lung following antigen provocation and are elevated in asthma, stimulated considerable activity in the pharmaceutical industry to find drugs that modulate the synthesis or actions of leukotrienes. Three cysteinyl leukotriene antagonists (zafirlukast [Accolate], montelukast [Singulair] and pranlukast) and one 5-lipoxygenase inhibitor (zileuton) have received regulatory approval for the treatment of asthma. The clinical data obtained from using these drugs are generally consistent and complimentary. As a class the leukotriene modulators produce a rapid improvement in lung function after the first oral dose. Lung function improvements are maintained on chronic administration and are associated with reductions in a variety of asthma symptom scores. All of the available data are consistent with the hypothesis that all the leukotriene modulators exert their clinical benefit primarily through interference with cysteinyl leukotrienes. There are no compelling clinical data for an additional contribution by leukotriene B(4)in human asthma. In other respiratory conditions such as COPD, which are characterised by pronounced neutrophil infiltration, it may be that the chemotactic properties of leukotriene B(4)are more important and therefore evaluation of 5-lipoxygenase inhibitors in this condition is warranted. The introduction of the leukotriene modulators into clinical practice is the culmination of over 60 years of research since the initial discovery of the slow-reacting substances. The leukotriene modulators, and in particular the cysteinyl leukotriene antagonists, provide respiratory physicians with an oral therapeutic option and have set an efficacy standard which new oral anti-inflammatory approaches will have to beat.

Efficacy and safety of long-term treatment of asthmatic patients with pranlukast, a cysteinyl-leukotriene-receptor antagonist: four-year followup study

BACKGROUND

There are few studies that have examined the long-term efficacy and safety of pranlukast, a leukotriene receptor antagonist, in asthmatic patients.

METHODS

Sixty-three asthmatic patients were entered in this 4-year study [group 1, mild or moderate (N = 22); group 2, severe without using oral prednisolone (N = 22); group 3, severe with using oral prednisolone (N = 19)]. Pranlukast was administered at 225 mg twice daily to 14 subjects in group 1 (group 1p), 14 in group 2 (group 2p), and 11 in group 3 (group 3p), chosen for pranlukast additional therapy at random. Another group of 24 asthmatic patients was assigned to conventional therapy group (groups 1c, 2c, and 3c). Efficacy was determined by improvement in symptom score, peak expiratory flow rate (PEFR) percentage predicted, reduced daily variability of PEFR (percentage), and reduced frequency of use of rescue beta2-agonist (times per week).

RESULTS

In groups 1p and 2p, PEFR percentage predicted began to improve from 2 weeks after commencement of treatment. The symptom score, daily variability of PEFR, and use of rescue beta2-agonist diminished significantly. In group 3p, pranlukast was ineffective in improving PEFR percentage predicted. All but two patients continued to receive pranlukast and no adverse effects were noted, at least during the 16-week therapy. Further, 22 patients continued to receive pranlukast for 4 years, and none experienced any adverse effects.

CONCLUSIONS

We showed in this study that long-term treatment with pranlukast is effective for asthmatic patients without any adverse effects.

The role of antileukotrienes in the treatment of asthma

OBJECTIVE

This article reviews the literature on the role of antileukotrienes (anti-LTs), specifically montelukast, zafirlukast, and zileuton, in the treatment of asthma.

DATA SOURCES

Relevant and appropriate controlled clinical studies were used. Only literature in the English language was reviewed.

STUDY SELECTION

Material was taken from academic/scholarly journals, appropriate reviews, and published abstracts.

RESULTS

In guidelines established by the National Asthma Education and Prevention Program and the National Heart, Lung, and Blood Institute, a stepwise approach to asthma management is recommended, with recommendations varying depending on degree of disease severity. The anti-LTs, the newest class of drugs for the treatment of asthma, play a circumscribed role in the guidelines as they were only recently available when the latest guidelines were published. Subsequently, however, extensive clinical experience with the anti-LTs has been amassed. Multiple clinical studies have demonstrated that the anti-LTs improve pulmonary function and quality of life, and reduce asthma symptoms, asthma exacerbations, and use of beta2-agonists and oral steroids. The anti-LTs may be particularly useful in asthma patients with aspirin sensitivity or concomitant allergic rhinitis, as well as in pediatric patients. These agents have additive effects with inhaled corticosteroids and may permit a reduction in inhaled corticosteroid dosages.

CONCLUSIONS

The anti-LTs have several features that are likey to promote adherence to treatment and are generally well tolerated. The available clinical data suggest that anti-LTs should be considered as a therapeutic option or as additive therapy in patients with mild to severe asthma.

Zafirlukast: an update of its pharmacology and therapeutic efficacy in asthma

Zafirlukast is a selective and competitive orally administered inhibitor of the cysteinyl leukotrienes LTC4, LTD4 and LTE4. The drug is indicated for the prophylaxis and treatment of chronic asthma, and has been developed in response to mounting evidence indicating the importance of the cysteinyl leukotrienes in the pathogenesis of this disorder. The efficacy of zafirlukast 20 mg twice daily has been shown in double-blind placebo-controlled studies of up to 13 weeks' duration in patients aged > or = 12 years. Zafirlukast was consistently superior to placebo in improving objective measures of lung function and subjective measures such as symptom scores and use of as-required bronchodilator therapy. This dosage is also as effective when added to low-dosage inhaled corticosteroid therapy as doubling of corticosteroid dosages. Recent studies indicate superior efficacy over zafirlukast of twice-daily inhaled fluticasone propionate 88 microg or salmeterol 42 microg, although zafirlukast was nevertheless associated with clinical improvement. Data also show zafirlukast 40 mg to be of similar efficacy to pranlukast 225 mg (both twice daily). Overall, preliminary pharmacoeconomic data suggest that healthcare costs are reduced by zafirlukast therapy, although superior cost effectiveness has been reported with inhaled fluticasone propionate. and further studies are needed. Data are available to show improvements in patient-rated quality of life, and preference for and high rates of compliance with zafirlukast. In clinical trials, zafirlukast has shown an adverse event profile similar to that of placebo. Isolated reports of hepatic dysfunction in a small number of individuals receiving the drug have been received, and recommendations for monitoring of patients are in place. Although no causal relationship has been established between zafirlukast and Churg-Strauss Syndrome, patients undergoing corticosteroid dosage reductions require careful surveillance.

CONCLUSIONS

zafirlukast is an effective and well tolerated agent for preventive monotherapy in mild to moderate persistent asthma. Emerging data indicate benefit of the drug when added to low-dosage inhaled corticosteroids and show that it may be a viable alternative to inhaled adjunctive treatments and increased corticosteroid dosages in some patients. Although inhaled fluticasone propionate and salmeterol have been associated with greater clinical improvement than zafirlukast in clinical studies, compliance considerations and the confirmed clinical efficacy relative to placebo of the drug denote zafirlukast as an effective alternative in treatment programmes based on individualised therapy. As experience with zafirlukast accumulates, it is expected that the drug will be positioned more definitively in national and international treatment guidelines.

Children with difficult asthma: a practical approach

Many open studies investigating the effects of innovative treatments for steroid-dependent asthma demonstrate some benefit. This is also true of the majority of placebo arms in placebo-controlled trials. This suggests that children with difficult asthma benefit from the high level of input that is typically provided in clinical trials, with or without additional medication. Such intensive management of patients, with the emphasis on establishing the diagnosis, improving adherence, and identifying provoking factors, is the key to optimizing asthma control for these children. For patients with genuinely severe asthma, despite high doses of conventional treatment, a greater understanding of the pathological basis of persistent symptoms is needed. Identification of different pathological subtypes of severe asthma should allow for more rational prescribing of asthma therapy, as well as the design of further trials of potential steroid-sparing treatments.

Inhibitors of the lipoxygenase pathway block development of Brugia malayi L3 in vitro

Brugia malayi L3 molt to the L4 stage in serum-free cultures supplemented with arachidonic, linoleic, or linolenic acids and the basidiomycetous yeast Rhodotorula minuta. These fatty acids are capable of entering the eicosanoid pathway of arachidonate metabolism, the pathway responsible for generating a number of biologically active mediators, including prostaglandins, leukotrienes, and lipoxins. To determine whether this pathway was required for L3 development, we added dual inhibitors of cyclooxygenase and lipoxygenase to in vitro cultures containing B. malayi L3. These compounds significantly inhibited L3 molting. To evaluate whether 1 or both of these pathways of arachidonate metabolism were involved in molting, we tested drugs inhibiting either cyclooxygenase or lipoxygenase. Lipoxygenase inhibitors blocked L3 molting, whereas cyclooxygenase inhibitors did not. To assess whether enzymes operating downstream of lipoxygenase were also involved in L3 molting, we added inhibitors of enzymes involved in leukotriene synthesis and found they were also capable of preventing development. We tested the same inhibitor panel on Dirofilaria immitis L3. A single lipoxygenase inhibitor and inhibitors of 2 different enzymes operating downstream of lipoxygenase disrupted D. immitis development. These results demonstrate that a lipoxygenase pathway product is required for molting of the infective stage larvae of filarial parasites.

Leukotriene modifiers in pediatric asthma management

Cysteinyl leukotrienes (Cys-LTs) are mediators released in asthma and virus-induced wheezing. Corticosteroids appear to have little or no effect on this release in vivo. Cys-LTs are both direct bronchoconstrictors and proinflammatory substances that mediate several steps in the pathophysiology of chronic asthma, including inflammatory cell recruitment, vascular leakage, and possibly airway remodeling. Blocking studies show that Cys-LTs are pivotal mediators in the pathophysiology of asthma. Cys-LTs are key components in the early and late allergic airway response and also contribute to bronchial obstruction after exercise and hyperventilation of cold, dry air in asthmatics. LT modifiers reduce airway eosinophil numbers and exhaled nitric oxide levels. Together these findings support an important role for the Cys-LTs in the asthma airway inflammation. Cys-LT receptor antagonists (Cys-LTRA) are generally well-tolerated. Phase III randomized, controlled clinical trials (RCT) show that LT modifiers are moderately effective, apparently with a particular between-patient variability in their clinical response. The clinical effects of LT modifiers are additive to those of beta-agonists and corticosteroids. The onset of action of LT modifiers is within 1 to several days, and not rapid enough to make them useful as rescue treatment. Although LT modifiers possess some antiinflammatory activity, they cannot substitute for corticosteroids for inflammation control. LT modifiers are alternatives to long-acting beta-agonists as complementary treatment to inhaled corticosteroids in pediatric asthma management because they provide bronchodilation and bronchoprotection without development of tolerance, and complement the antiinflammatory activity unchecked by steroids. In addition, the Cys-LTRA montelukast has been shown to ameliorate asthmatic symptoms and provide bronchoprotection in asthmatic preschool children from 2 years of age, which is of particular importance in this difficult-to-manage group of asthmatics. Given their efficacy, antiinflammatory activity, oral administration, and safety, LT modifiers will play an important role in the treatment of asthmatic children.

Clinical safety and tolerability of montelukast, a leukotriene receptor antagonist, in controlled clinical trials in patients aged > or = 6 years

OBJECTIVE

Montelukast is a leukotriene receptor antagonist administered orally once daily for treatment of chronic asthma in adults and children. A comprehensive analysis of safety data from double-blind, randomized, placebo-controlled trials with montelukast has not been previously reported.

PATIENTS AND METHODS

A pooled analysis of safety data from 11 multicentre, randomized, controlled montelukast Phase IIb and III trials and five long-term extension studies was performed. A total of 3386 adult patients (aged 15-85 years) and 336 paediatric patients (aged 6-14 years) were enrolled in the trials; 2031 adults received montelukast for up to 4.1 years, and 257 children received montelukast for up to 1.8 years. Summary statistics comparing incidences of adverse events among treatment groups were calculated.

RESULTS

The overall incidence of clinical and laboratory adverse events among montelukast-treated patients, both adult and paediatric, was similar to that among patients receiving placebo. There were no clinically relevant differences in individual adverse events, including infectious upper respiratory conditions and transaminase elevations, between montelukast and placebo groups. Discontinuations due to adverse events occurred with similar frequencies during placebo, montelukast and inhaled beclomethasone therapy. No dose-related adverse effects of montelukast were observed in adults treated with dosages as high as 200 mg per day (20 times the recommended dose) for 5 months. This tolerability profile montelukast observed in clinical trials has been generally reflected in the post-marketing safety experience seen to date.

CONCLUSIONS

These data indicate a tolerability profile for montelukast similar to placebo during both short-term and long-term administration, even at doses substantially higher than the recommended clinical dose of 10 mg once daily for adults and 5 mg once daily for children aged 6-14 years.

Late onset asthma: epidemiology, diagnosis and treatment

Asthma is common among older persons, affecting approximately 4 to 8% of those above the age of 65 years. Despite its prevalence, late onset asthma may be misdiagnosed and inadequately treated, with important negative consequences for the patient's health. The histopathology of late onset disease appears to be similar to that of asthma in general, with persistent airway inflammation a characteristic feature. It is less clear, however, that allergic exposure and sensitisation play the same role in the development of disease in adults as they do in children. Atopy is less common among those with late onset asthma, and the prevalence of elevated immunoglobulin E levels is lower among those aged over 55 years of age than younger patients. Occupational asthma is an aetiological consideration unique to adult onset disease, with important implications for treatment. The differential diagnosis for cough, wheeze, and dyspnoea in the elderly is broad, and includes chronic obstructive bronchitis, bronchiectasis, congestive heart failure, lung cancer with endobronchial lesion and vocal cord dysfunction. Keys to accurate diagnosis include a good history and physical examination, the demonstration of reversible airways obstruction on pulmonary function tests and a favorable response to treatment. Inhaled corticosteroid therapy is recommended for patients with persistent disease, and careful instruction in the use of metered-dose inhalers is particularly important for the elderly.

Effect of combined leukotriene D(4) and thromboxane A(2) receptor antagonist on mediator-controlled resistance in guinea pigs

The effects of YM158 (3-[(4-tert-butylthiazol-2-yl)methoxy]-5'-[3-(4-chlorobenzenesu lfonyl )propyl]-2'-(1H-tetrazol-5-ylmethoxy)benzanilide monosodium salt monohydrate), a new dual antagonist for leukotriene D(4) and thromboxane A(2) receptors, on antigen-induced increases in airway resistance were investigated in mediator-controlled novel asthmatic models using actively sensitized guinea pigs. While the predominant mediator was thromboxane A(2), complete inhibition of cyclooxygenase induced mediation by cysteinyl-leukotrienes. About 1-mg/kg indomethacin induced a state where both mediators participated equally. YM158 inhibited increases in resistance whether only one or both mediators were involved. When leukotriene D(4) and thromboxane A(2) equally participated, ED(50) values for 4-oxo-8-[4-(4-phenylbutoxy)benzoylamino]-2-(tetrazol-5-yl)-4 H-1-benzo pyran hemihydrate (pranlukast; 3.9 mg/kg) and 7-(3,5,6-trimethyl-1, 4-benzoquinon-2-yl)-7-phenylheptanoic acid (seratrodast; 2.1 mg/kg) were similar to that for YM158 (8.3 mg/kg), although those effects on the corresponding mediator-induced reaction were 10 times stronger than those of YM158. Additionally, the maximum inhibition of YM158 was stronger than those of either single receptor antagonist. In conclusion, YM158 has a potentially greater efficacy in wider types of experimental asthmatic models than single receptor antagonists.

Validation of a LC method for the analysis of zafirlukast in a pharmaceutical formulation

A reversed-phase high-performance liquid chromatographic (HPLC) method was developed and validated for estimation of zafirlukast in a pharmaceutical formulation. Assay samples were extracted utilizing acetonitrile. Drug and internal standard were chromatographed on reversed-phase C18 columns, using mixtures of acetonitrile/water and the eluents were monitored at different wavelengths. The method was validated statistically for its linearity, accuracy, robustness and precision. Experimental design was used during validation to evaluate method robustness and for the determination of intermediate precision. Factors examined for statistical approaches include laboratory, day, analyst, instrument, different percentage of organic modifier, temperature, wavelength and flow-rate. Due to its simplicity and accuracy, the method may be used for routine quality control analysis.

Role of leukotrienes in asthma pathophysiology

Inflammation is an essential component of asthma pathophysiology. While beta(2)-agonists are often used for short-term relief of acute bronchospasm, anti-inflammatory agents are required for the long-term management of chronic inflammation in this disease. Corticosteroids have emerged as the first-line anti-inflammatory therapy for asthma management. However, in some patients, especially children, the high doses of corticosteroids that may be required to control features of hyperresponsiveness, including exercise-induced asthma, raise safety concerns. Thus, there is a need for complementary anti-inflammatory, steroid-sparing agents in asthma therapy. Several inflammatory mediators have been targeted in an attempt to thwart this inflammatory process, but so far with little success. The cysteinyl leukotrienes (CysLT), LTC(4), LTD(4), and LTE(4), have been shown to be essential mediators in asthma, making them obvious targets for therapy. These cysteinyl leukotrienes, previously known as the slow-reacting substance of anaphylaxis (SRS-A), mediate many of the features of asthma, including bronchial constriction, bronchial hyperreactivity, edema, and eosinophilia. Data show that selective cysteinyl leukotriene receptor antagonists (CysLTRAs) effectively reverse these pathologic changes. Corticosteroids do not inhibit the production of CysLTs in vivo, suggesting that CysLTRAs and corticosteroids affect different targets. The bronchodilator properties of CysLTRAs seem to be additive to those of beta(2)-agonists and corticosteroids. These data suggest that CysLTs are important therapeutic targets in the management of inflammation in asthma.

Current treatment of asthma--focus on leukotrienes

Since their identification in 1979, the cysteinyl leukotrienes (cysLTs) have been shown to be prominent in many inflammatory conditions, including asthma, allergic rhinitis, rheumatoid arthritis, psoriasis, cystic fibrosis and inflammatory bowel disease. They are potent pro-inflammatory agents, as well as causing bronchoconstriction, and undoubtedly have a role in asthma. The cysLTs are products of arachidonic acid metabolism and have been shown to have effects via a cysteinyl leukotriene receptor (CysLTR1) on vascular permeability, mucus production, chemotaxis and bronchial smooth muscle. Their detection in certain body fluids in allergic, aspirin-sensitive and exercise-induced asthma is well documented and potential roles in pathogenesis, proposed. The development of agents affecting production or action offers an exciting new approach to the treatment of asthma. Two approaches to antileukotriene therapy have been developed: blocking their production by inhibiting the action of 5-lipoxygenase enzyme or blocking the CysLTR1. Both approaches have been tried in studies in asthma and overall the results are encouraging, with a decrease in both daytime and nocturnal symptoms, a decrease in additional beta 2 agonist usage and improvement in lung function. The changes, however, are small in some studies. This may be a reflection of disease severity in the study subjects, but of note is a heterogeneity of response to these treatments that may be genetically determined. Antileukotriene therapy has been shown to have an effect in specific types of asthma where the role of cysLTs seems well established--aspirin-sensitive/intolerant asthma and exercise-induced asthma. Longer term studies are needed in other areas such as severe asthma and chronic persistent asthma in both children and adults to provide evidence for the appropriate placement of antileukotriene treatment in current asthma guidelines, in comparison with other established treatments.

Guidelines update: where do the new therapies fit in the management of asthma? NHLBI and WHO Global Initiative for Asthma

The new leukotriene (LT) modifiers have been shown to be effective, safe and convenient 'controller' medications in patients with asthma. However, their use in asthma is recommended only in the most recent US guidelines, and then only as alternative long term controllers in patients with mild persistent asthma. In fact, as has now been shown in a number of studies, LT modifiers are effective in a variety of other asthma settings, and it is expected that expanded roles for these agents will be described in future asthma guidelines. Until then, clinicians aware of the advantages of individualising asthma therapy might consider LT modifiers for the diverse range of patients with asthma who are likely to benefit from the use of these agents.

Childhood asthma: causes, epidemiological factors and complications

Asthma is common in children and its prevalence in this age group is increasing. While the reasons for this reported increase, and indeed the true magnitude of the increase, remain unclear, there can be no doubt that asthma is now a major health problem in children worldwide. Fortunately, our knowledge of the pathophysiology of asthma is also increasing. It is now known that asthma is a chronic inflammatory disease regulated by a variety of mediators, of which perhaps the leukotrienes are among the most important. This new understanding of the pathophysiology of the disease has spurred the development of the antileukotriene agents, which can be expected to play an increasingly important role in the management of childhood asthma.

Anti-leukotrienes in asthma: yet to arrive

Inflammation plays a predominant role in the pathogenesis of asthma. The leukotrienes (LTs) exert their actions by binding to and activating various receptors. Leukotrienes B4, C4, D4, and E4 have been shown experimentally to play a role in inflammatory mechanisms, producing the pathologic changes seen in asthma. Antileukotrienes represent a new class of anti-asthma drugs with anti-inflammatory role. In asthma management, LT modifiers from the groups of 5 lipoxygenase inhibitor and Cys LT1 receptor antagonists are found useful. LAs are of main use in mild to moderate chronic asthma. Their usefulness is also observed in allergic rhinitis and even in severe chronic cases of asthma which are resistant to steroids. In chronic asthma they are required to be used for prolonged periods with other agents viz. inhaled steroids and beta 2 agonists. These agents are essentially safe. Except for Montelukast, which can be used in children above six years of age, the paediatric use of other agents is yet to be established. LAs are gradually becoming available in increasing number of countries. In India, we have to presumably wait for sometime before these drugs reach the market. The cost of LAs is reasonably high. Thus, India awaits arrival of LAs, may be for good, as more concrete information from various trials will permit us to practice more evidence based medicine.

Novel therapy for asthma

The health burden of asthma is increasing globally at an alarming rate, providing a strong impetus for the development of new therapeutics. Currently available inhaled bronchodilators and anti-inflammatory drugs are effective in most asthmatics, but this palliative therapy requires long-term daily administration. Despite considerable efforts by the pharmaceutical industry, it has been difficult to develop novel therapeutic agents; the leukotriene antagonists and synthesis inhibitors being the only new class of asthma treatments to have been licensed in the last 30 years. It is clearly important to understand more about the underlying mechanisms of asthma and about how current drugs work before rational improvements in therapy can be expected. There are numerous therapies in clinical development that combat the inflammation found in asthma, specifically targeting eosinophils, IgE, adhesion molecules, cytokines and chemokines, inflammatory mediators and cell signalling. In particular, there is the obvious need for new therapy for severe asthma that is poorly controlled by high doses of corticosteroids, as well as agents to counter acute emergency asthma. A long-term goal is to develop disease-modifying immunotherapy, that could be introduced in childhood to alter the natural history of asthma. Thanks to the extensive efforts of the pharmaceutical industry, in the near future we can expect the introduction of a range of novel therapies for asthma.

Leukotrienes, leukotriene receptor antagonists and leukotriene synthesis inhibitors in asthma: an update. Part II: clinical studies with leukotriene receptor antagonists and leukotriene synthesis inhibitors in asthma

The demonstration that leukotrienes, mainly cysteinyl leukotrienes, have biological properties relevant to the pathogenesis of asthma has stimulated the development of many therapeutic compounds to block these deleterious effects. Two main classes of leukotriene modulators have been developed: CysLT1 receptor antagonists and leukotriene synthesis inhibitors. This article reviews the pharmacodynamics, the effects on baseline airway function, the protective effects in airway challenges as well as the results in chronic asthma of the different leukotriene modulators. In addition, the complementary anti-inflammatory effect of leukotriene modulators to that of corticosteroids and H1-histamine receptor antagonists is reviewed. Finally, a concise overview of the clinical responsiveness to this new class of drug, the safety and the drug interactions as well as the place in the strategies of treatment for asthmatic patients of the leukotriene modulators is also provided.

New perspectives for asthma treatment: anti-leukotriene drugs

Leukotrienes are synthesized by different cells, including eosinophils, neutrophils, basophils, lymphocytes, macrophages, and mast cells. Cysteinyl leukotrienes (LTC4, LTD4, and LTE4) are the most important leukotrienes in the pathogenesis of asthma. Pharmacologically, there are two different ways of blocking the action of leukotrienes: inhibiting their production by blocking 5-lipoxygenase or its activating protein, 5-lipoxygenase-activating protein (FLAP), (inhibitors) or by blocking their receptors (antagonists). The available antagonists are, for the moment, directed against the one receptor demonstrated to play a role in asthma symptoms, CysLT1, and they act in a competitive way. The only marketed 5-lipoxygenase inhibitor is zileuton (Zyflo). CysLT1 antagonists, currently on the pharmaceutical market in some countries, are zafirlukast (Accolate), pranlukast (Ultair, Onon), and montelukast (Singulair). Undoubtedly, drugs acting on leukotrienes constitute a new pharmacologic class in the therapeutic armamentarium for the management of asthma. From the pediatric point of view, montelukast is currently the most interesting drug of the group to date because of published trials in patients as young as 6 yr of age. At present, zafirlukast is only approved for use in patients 12 yr of age and older, although we understand that applications are likely to extend the age range into childhood shortly. However, more experience is necessary to establish a definite place for both leukotrienes in the step-by-step asthma treatment. New comparative studies (with sodium cromoglycate and inhaled steroids), which will probably be published in the near future, as well as studies on the use of montelukast in the treatment of children under 6 yr of age will add crucial information to our knowledge, and help to identify an appropriate use in the therapeutic algorithm. Montelukast will not be a substitute for inhaled corticosteroids or beta-agonists, although it may act as a 'sparing drug' (which might help tapering of steroids in some instances). Its role in exercise-induced asthma seems promising. Although its more widespread use could highlight low-frequency adverse effects, its apparent excellent tolerability is an additional advantage for the drug. Patients' preference for a twice-daily dosage over the inhaled medication, resulting in a better compliance, is relatively well established, at least for zafirlukast in adults, and these findings can probably be extended to montelukast, which only requires once-daily dosing in children.