Pharmacokinetic profile of zafirlukast

Mechanism-based inactivation of cytochromes P450: implications in drug interactions and pharmacotherapy

Cytochrome P40 (CYP) enzymes dominate the metabolism of numerous endogenous and xenobiotic substances. While it is commonly believed that CYP-catalysed reactions result in the detoxication of foreign substances, these reactions can also yield reactive intermediates that can bind to cellular macromolecules to cause cytotoxicity or irreversibly inactivate CYPs that create them.Mechanism-based inactivation (MBI) produces either irreversible or quasi-irreversible inactivation and is commonly caused by CYP metabolic bioactivation to an electrophilic reactive intermediate. Many drugs that have been known to cause MBI in CYPs have been discovered as perpetrators in drug-drug interactions throughout the last 20-30 years.This review will highlight the key findings from the recent literature about the mechanisms of CYP enzyme inhibition, with a focus on the broad mechanistic elements of MBI for widely used drugs linked to the phenomenon. There will also be a brief discussion of the clinical or pharmacokinetic consequences of CYP inactivation with regard to drug interaction and toxicity risk.Gaining knowledge about the selective inactivation of CYPs by common therapeutic drugs helps with the assessment of factors that affect the systemic clearance of co-administered drugs and improves comprehension of anticipated interactions with other drugs or xenobiotics.

Zafirlukast induces DNA condensation and has bactericidal effect on replicating Mycobacterium abscessus

Mycobacterium abscessus infections are emerging in cystic fibrosis patients, and treatment success rate in these patients is only 33% due to extreme antibiotic resistance. Thus, new treatment options are essential. An interesting target could be Lsr2, a nucleoid-associated protein involved in mycobacterial virulence. Zafirlukast is a Food and Drug Administration (FDA)-approved drug against asthma that was shown to bind Lsr2. In this study, zafirlukast treatment is shown to reduce M. abscessus growth, with a minimal inhibitory concentration of 16 µM and a bactericidal concentration of 64 µM in replicating bacteria only. As an initial response, DNA condensation, a known stress response of mycobacteria, occurs after 1 h of treatment with zafirlukast. During continued zafirlukast treatment, the morphology of the bacteria alters and the structural integrity of the bacteria is lost. After 4 days of treatment, reduced viability is measured in different culture media, and growth of M. abscessus is reduced in a dose-dependent manner. Using transmission electron microscopy, we demonstrated that the hydrophobic multilayered cell wall and periplasm are disorganized and ribosomes are reduced in size and relocalized. In summary, our data demonstrate that zafirlukast alters the morphology of M. abscessus and is bactericidal at 64 µM. The bactericidal concentration of zafirlukast is relatively high, and it is only effective on replicating bacteria but as zafirlukast is an FDA-approved drug, and currently used as an anti-asthma treatment, it could be an interesting drug to further study in in vivo experiments to determine whether it could be used as an antibiotic for M. abscessus infections.

Bioisoteres for carboxylic acids: From ionized isosteres to novel unionized replacements

Carboxylic acids are key pharmacophoric elements in many molecules. They can be seen as a problem by some, due to perceived permeability challenges, potential for high plasma protein binding and the risk of forming reactive metabolites due to acyl-glucuronidation. By others they are viewed more favorably as they can decrease lipophilicity by adding an ionizable center which can be beneficial for solubility, and can add enthalpic interactions with the target protein. However, there are many instances where the replacement of a carboxylic acid with a bioisosteric group is required. This has led to the development of a number of ionizable groups which sufficiently mimic the carboxylic acid functionality whilst improving, for example, the metabolic profile of the molecule in question. An alternative strategy involves replacement of the carboxylate by neutral functional groups. This review initially details carefully selected examples whereby tetrazoles, acyl sulfonamides or isoxazolols have been beneficially utilized as carboxylic acid bioisosteres altering physicohemical properties, interactions with the target and metabolism and/or pharmacokinetics, before delving further into the binding mode of carboxylic acid derivatives with their target proteins. This analysis highlights new ways to consider the replacement of carboxylic acids by neutral bioisosteric groups which either rely on hydrogen bonds or cation-π interactions. It should serve as a useful guide for scientists working in drug discovery.

Searching for Novel Noncovalent Nuclear Export Inhibitors through a Drug Repurposing Approach

Chromosomal region maintenance protein 1 (CRM1) is a validated anticancer drug target, and its covalent inhibitor KPT-330 has been approved for marketing. However, the development of CRM1 inhibitors, especially the noncovalent ones, is still very limited. Drug repurposing is an effective strategy to develop drug leads for new targets. In this work, we virtually screened a library of marketed drugs and identified zafirlukast as a new CRM1 inhibitor. Biochemical and structural analysis revealed that zafirlukast was a noncovalent CRM1 inhibitor that bound to four subpockets in the nuclear-export-signal (NES) groove. Methylation of the sulfonamide group rendered zafirlukast completely inactive against CRM1. Zafirlukast inhibited the growth of a variety of cancer cells and worked synergistically with the drug doxorubicin. Taken together, these works laid a solid foundation for reshaping zafirlukast as a valuable lead compound for further design of noncovalent, specific, and potent CRM1 inhibitors toward the treatment of various cancers.

Novel tryptanthrin derivatives with benzenesulfonamide substituents: Design, synthesis, and anti-inflammatory evaluation

Herein, two series of tryptanthrin derivatives with benzenesulfonamide substituents were designed and synthesized to discover novel anti-inflammatory agents. The anti-inflammatory activities of all derivatives were screened by evaluating their inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 cells. Among them, compound 8j exhibited the best NO inhibitory activity (IC₅₀ = 1.25 ± 0.21 μM), with no obvious toxicity. Further evaluation showed that 8j could also significantly reduce the levels of pro-inflammatory cytokines interleukin-1β (IL-1β, IC₅₀ = 8.48 ± 0.23 μM) and tumor necrosis factor-α (TNF-α, IC₅₀ = 11.53 ± 0.35 μM) and downregulate the LPS-induced expression of iNOS and COX-2. Reverse docking of 8j suggested p38α as the molecular target, which is a well-known crucial player in the p38 MAPK signaling pathway that controls the transcription of pro-inflammatory mediators. Cellular thermal shift assay showed that 8j efficiently stabilized p38α in LPS-treated RAW264.7 cells. Western blot showed that inflammatory response was inhibited by 8j through inhibiting the phosphorylation of p38α and MK2 in the p38 MAPK signaling pathway. Finally, In vivo studies showed that 8j could significantly ameliorate the degree of foot swelling and knee joint pathology in adjuvant-induced arthritis (AIA) rats and reduce levels of TNF-α and IL-1β in serum, achieving the effect of protecting synovial tissue and ameliorating arthritis. These findings suggested that 8j may be a promising compound for further development of anti-inflammatory agents.

Structured solubility behaviour in bioequivalent fasted simulated intestinal fluids

Drug solubility in intestinal fluid is a key parameter controlling absorption after the administration of a solid oral dosage form. To measure solubility in vitro simulated intestinal fluids have been developed, but there are multiple recipes and the optimum is unknown. This situation creates difficulties during drug discovery and development research. A recent study characterised sampled fasted intestinal fluids using a multidimensional approach to derive nine bioequivalent fasted intestinal media that covered over 90% of the compositional variability. These media have been applied in this study to examine the equilibrium solubility of twenty one exemplar drugs (naproxen, indomethacin, phenytoin, zafirlukast, piroxicam, ibuprofen, mefenamic acid, furosemide, aprepitant, carvedilol, tadalafil, dipyridamole, posaconazole, atazanavir, fenofibrate, felodipine, griseofulvin, probucol, paracetamol, acyclovir and carbamazepine) to determine if consistent solubility behaviour was present. The bioequivalent media provide in the majority of cases structured solubility behaviour that is consistent with physicochemical properties and previous solubility studies. For the acidic drugs (pKa < 6.3) solubility is controlled by media pH, the profile is identical and consistent and the lowest and highest pH media identify the lowest and highest solubility in over 70% of cases. For weakly acidic (pKa > 8), basic and neutral drugs solubility is controlled by a combination of media pH and total amphiphile concentration (TAC), a consistent solubility behaviour is evident but with variation related to individual drug interactions within the media. The lowest and highest pH x TAC media identify the lowest and highest solubility in over 78% of cases. A subset of the latter category consisting of neutral and drugs non-ionised in the media pH range have been identified with a very narrow solubility range, indicating that the impact of the simulated intestinal media on their solubility is minimal. Two drugs probucol and atazanavir exhibit unusual behaviour. The study indicates that the use of two appropriate bioequivalent fasted intestinal media from the nine will identify in vitro the maximum and minimum solubility boundaries for drugs and due to the media derivation this is probably applicable in vivo. These media could be applied during discovery and development activities to provide a solubility range, which would assist placement of the drug within the BCS/DCS and rationalise drug and formulation decisions.

Identification of FDA approved drugs against SARS-CoV-2 RNA dependent RNA polymerase (RdRp) and 3-chymotrypsin-like protease (3CLpro), drug repurposing approach

The RNA-dependent RNA polymerase (RdRp) and 3C-like protease (3CLpro) from SARS-CoV-2 play crucial roles in the viral life cycle and are considered the most promising targets for drug discovery against SARS-CoV-2. In this study, FDA-approved drugs were screened to identify the probable anti-RdRp and 3CLpro inhibitors by molecular docking approach. The number of ligands selected from the PubChem database of NCBI for screening was 1760. Ligands were energy minimized using Open Babel. The RdRp and 3CLpro protein sequences were retrieved from the NCBI database. For Homology Modeling predictions, we used the Swiss model server. Their structure was then energetically minimized using SPDB viewer software and visualized in the CHIMERA UCSF software. Molecular dockings were performed using AutoDock Vina, and candidate drugs were selected based on binding affinity (∆G). Hydrogen bonding and hydrophobic interactions between ligands and proteins were visualized using Ligplot and the Discovery Studio Visualizer v3.0 software. Our results showed 58 drugs against RdRp, which had binding energy of - 8.5 or less, and 69 drugs to inhibit the 3CLpro enzyme with a binding energy of - 8.1 or less. Six drugs based on binding energy and number of hydrogen bonds were chosen for the next step of molecular dynamics (MD) simulations to investigate drug-protein interactions (including Nilotinib, Imatinib and dihydroergotamine for 3clpro and Lapatinib, Dexasone and Relategravir for RdRp). Except for Lapatinib, other drugs-complexes were stable during MD simulation. Raltegravir, an anti-HIV drug, was observed to be the best compound against RdRp based on docking binding energy (-9.5 kcal/mole) and MD results. According to the MD results and binding energy, dihydroergotamine is a suitable candidate for 3clpro inhibition (-9.6 kcal/mol). These drugs were classified into several categories, including antiviral, antibacterial, anti-inflammatory, anti-allergic, cardiovascular, anticoagulant, BPH and impotence, antipsychotic, antimigraine, anticancer, and so on. The common prescription-indications for some of these medication categories appeared somewhat in line with manifestations of COVID-19. We hope that they can be beneficial for patients with certain specific symptoms of SARS-CoV-2 infection, but they can also probably inhibit viral enzymes. We recommend further experimental evaluations in vitro and in vivo on these FDA-approved drugs to assess their potential antiviral effect on SARS-CoV-2.

Fasted and fed state human duodenal fluids: Characterization, drug solubility, and comparison to simulated fluids and with human bioavailability

Accurate in vivo predictions of intestinal absorption of low solubility drugs require knowing their solubility in physiologically relevant dissolution media. Aspirated human intestinal fluids (HIF) are the gold standard, followed by simulated intestinal HIF in the fasted and fed state (FaSSIF/FeSSIF). However, current HIF characterization data vary, and there is also some controversy regarding the accuracy of FaSSIF and FeSSIF for predicting drug solubility in HIF. This study aimed at characterizing fasted and fed state duodenal HIF from 16 human volunteers with respect to pH, buffer capacity, osmolarity, surface tension, as well as protein, phospholipid, and bile salt content. The fasted and fed state HIF samples were further used to investigate the equilibrium solubility of 17 representative low-solubility small-molecule drugs, six of which were confidential industry compounds and 11 were known and characterized regarding chemical diversity. These solubility values were then compared to reported solubility values in fasted and fed state HIF, FaSSIF and FeSSIF, as well as with their human bioavailability for both states. The HIF compositions corresponded well to previously reported values and current FaSSIF and FeSSIF compositions. The drug solubility values in HIF (both fasted and fed states) were also well in line with reported solubility data for HIF, as well as simulated FaSSIF and FeSSIF. This indicates that the in vivo conditions in the proximal small intestine are well represented by simulated intestinal fluids in both composition and drug equilibrium solubility. However, increased drug solubility in the fed vs. fasted states in HIF did not correlate with the human bioavailability changes of the same drugs following oral administration in either state.

Zafirlukast is a broad-spectrum thiol isomerase inhibitor that inhibits thrombosis without altering bleeding times

BACKGROUND AND PURPOSE

Multiple members of the thiol isomerase (TI) family of enzymes are present in and released by platelets. Inhibition of these enzymes results in diminished platelet responses, aggregation, adhesion and thrombus formation. Recently, the therapeutic potential of TI inhibition has been recognised and drug-development technologies were used to identify selective small molecule inhibitors. To date, few pan-TI inhibitors have been characterised and the most studied, bacitracin, is known to be nephrotoxic, which prohibits its systemic therapeutic usage.

EXPERIMENTAL APPROACH

We therefore sought to identify novel broad-spectrum inhibitors of these enzymes and test their effects in vivo. A total of 3,641 compounds were screened for inhibitory effects on the redox activity of ERp5, protein disulphide isomerase (PDI), ERp57, ERp72 and thioredoxin in an insulin turbidity assay. Of the lead compounds identified, zafirlukast was selected for further investigation.

KEY RESULTS

When applied to platelets, zafirlukast diminished platelet responses in vitro. Zafirlukast was antithrombotic in murine models of thrombosis but did not impair responses in a model of haemostasis. Since TIs are known to modulate adhesion receptor function, we explored the effects of zafirlukast on cell migration. This was inhibited independently of cysteinyl LT receptor expression and was associated with modulation of cell-surface free thiol levels consistent with alterations in redox activity on the cell surface.

CONCLUSION AND IMPLICATIONS

We identify zafirlukast to be a novel, potent, broad-spectrum TI inhibitor, with wide-ranging effects on platelet function, thrombosis and integrin-mediated cell migration. Zafirlukast is antithrombotic but does not cause bleeding.

CysLT1 receptor antagonists pranlukast and zafirlukast inhibit LRRC8-mediated volume regulated anion channels independently of the receptor

Volume-regulated anion channels (VRACs) encoded by the leucine-rich repeat containing 8 (LRRC8) gene family play critical roles in myriad cellular processes and might represent druggable targets. The dearth of pharmacological compounds available for studying VRAC physiology led us to perform a high-throughput screen of 1,184 of US Food and Drug Administration-approved drugs for novel VRAC modulators. We discovered the cysteinyl leukotriene receptor 1 (CysLT1R) antagonist, pranlukast, as a novel inhibitor of endogenous VRAC expressed in human embryonic kidney 293 (HEK293) cells. Pranlukast inhibits VRAC voltage-independently, reversibly, and dose-dependently with a maximal efficacy of only ~50%. The CysLT1R pathway has been implicated in activation of VRAC in other cell types, prompting us to test whether pranlukast requires the CysLT1R for inhibition of VRAC. Quantitative PCR analysis demonstrated that CYSLTR1 mRNA is virtually undetectable in HEK293 cells. Furthermore, the CysLT1R agonist leukotriene D4 had no effect on VRAC activity and failed to stimulate G_q-coupled receptor signaling. Heterologous expression of the CysLT1R reconstituted LTD4-CysLT1R- G_q-calcium signaling in HEK293 cells but had no effect on VRAC inhibition by pranlukast. Finally, we show the CysLT1R antagonist zafirlukast inhibits VRAC with an IC₅₀ of ~17 µM and does so with full efficacy. Our data suggest that both pranlukast and zafirlukast are likely direct channel inhibitors that work independently of the CysLT1R. This study provides clarifying insights into the putative role of leukotriene signaling in modulation of VRAC and identifies two new chemical scaffolds that can be used for development of more potent and specific VRAC inhibitors.

Type 2 NADH Dehydrogenase Is the Only Point of Entry for Electrons into the Streptococcus agalactiae Respiratory Chain and Is a Potential Drug Target

The opportunistic pathogen Streptococcus agalactiae is the major cause of meningitis and sepsis in a newborn’s first week, as well as a considerable cause of pneumonia, urinary tract infections, and sepsis in immunocompromised adults. This pathogen respires aerobically if heme and quinone are available in the environment, and a functional respiratory chain is required for full virulence. Remarkably, it is shown here that the entire respiratory chain of S. agalactiae consists of only two enzymes, a type 2 NADH dehydrogenase (NDH-2) and a cytochrome bd oxygen reductase. There are no respiratory dehydrogenases other than NDH-2 to feed electrons into the respiratory chain, and there is only one respiratory oxygen reductase to reduce oxygen to water. Although S. agalactiae grows well in vitro by fermentative metabolism, it is shown here that the absence of NDH-2 results in attenuated virulence, as observed by reduced colonization in heart and kidney in a mouse model of systemic infection. The lack of NDH-2 in mammalian mitochondria and its important role for virulence suggest this enzyme may be a potential drug target. For this reason, in this study, S. agalactiae NDH-2 was purified and biochemically characterized, and the isolated enzyme was used to screen for inhibitors from libraries of FDA-approved drugs. Zafirlukast was identified to successfully inhibit both NDH-2 activity and aerobic respiration in intact cells. This compound may be useful as a laboratory tool to inhibit respiration in S. agalactiae and, since it has few side effects, it might be considered a lead compound for therapeutics development.

S. agalactiae is part of the human intestinal microbiota and is present in the vagina of ~30% of healthy women. Although a commensal, it is also the leading cause of septicemia and meningitis in neonates and immunocompromised adults. This organism can aerobically respire, but only using external sources of heme and quinone, required to have a functional electron transport chain. Although bacteria usually have a branched respiratory chain with multiple dehydrogenases and terminal oxygen reductases, here we establish that S. agalactiae utilizes only one type 2 NADH dehydrogenase (NDH-2) and one cytochrome bd oxygen reductase to perform respiration. NADH-dependent respiration plays a critical role in the pathogen in maintaining NADH/NAD⁺ redox balance in the cell, optimizing ATP production, and tolerating oxygen. In summary, we demonstrate the essential role of NDH-2 in respiration and its contribution to S. agalactiae virulence and propose it as a potential drug target.

Cysteinyl leukotriene receptor antagonists induce apoptosis and inhibit proliferation of human glioblastoma cells by downregulating B-cell lymphoma 2 and inducing cell cycle arrest

Glioblastoma is the most aggressive type of brain cancer with the highest proliferation, invasion, and migration. Montelukast and zafirlukast, 2 widely used leukotriene receptor antagonists (LTRAs) for asthma treatment, inhibited invasion and migration of glioblastoma cell lines. Montelukast induces apoptosis and inhibits cell proliferation of various cancer cells. Herein, apoptotic and antiproliferative effects of montelukast and zafirlukast were investigated in 2 glioblastoma cell lines, A172 and U-87 MG. Both LTRAs induced apoptosis and inhibited cell proliferation of glioblastoma cells in a concentration-dependent manner. Montelukast was more cytotoxic and induced higher levels of apoptosis than zafirlukast in A172 cells, but not in U-87 MG cells. Both drugs decreased expression of B-cell lymphoma 2 (Bcl-2) protein without affecting Bcl-2-associated X (Bax) levels. LTRAs also reduced the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). In contrast, zafirlukast showed a greater antiproliferative effect than montelukast and induced G0/G1 cell cycle arrest by upregulating p53 and p21 expression. These results suggested the therapeutic potential of LTRAs in glioblastoma.

Leukotriene Receptor Antagonists Inhibit Mitogenic Activity in Triple Negative Breast Cancer Cells

Despite a discovery of hormonal pathways regulating breast cancer, a definitive cure for the disease requires further identification of alternative targets that provide a hormone-independent support. Apart from their role in inflammatory diseases, cysteinyl leukotriene (CysLT) receptor antagonists (LTRAs) decrease the risk of lung cancer in asthma patients and inhibit tumor progression in several malignancies. In the present study, we evaluate the effects of two chemically different, clinically relevant LTRAs (montelukast and zafirlukast) in a triple negative breast cancer cell line, MDAMB- 231. We found that these two LTRAs reduced breast cancer cell viability in a dose-dependent manner with the 50% inhibitory concentration (IC50) between 5-10 μM. Although both LTRAs have several pharmacological properties in common, we noticed that montelukast mainly induced apoptosis, while zafirlukast mainly exerted its action on cell cycle. However, the precise mechanisms responsible for such different effects remain unclear. In summary, our results suggest that CysLT plays a role in proliferation and survivability of breast cancer cells in the absence of hormonal stimuli.

Role of Cytochrome P450 2C8 in Drug Metabolism and Interactions

During the last 10-15 years, cytochrome P450 (CYP) 2C8 has emerged as an important drug-metabolizing enzyme. CYP2C8 is highly expressed in human liver and is known to metabolize more than 100 drugs. CYP2C8 substrate drugs include amodiaquine, cerivastatin, dasabuvir, enzalutamide, imatinib, loperamide, montelukast, paclitaxel, pioglitazone, repaglinide, and rosiglitazone, and the number is increasing. Similarly, many drugs have been identified as CYP2C8 inhibitors or inducers. In vivo, already a small dose of gemfibrozil, i.e., 10% of its therapeutic dose, is a strong, irreversible inhibitor of CYP2C8. Interestingly, recent findings indicate that the acyl-β-glucuronides of gemfibrozil and clopidogrel cause metabolism-dependent inactivation of CYP2C8, leading to a strong potential for drug interactions. Also several other glucuronide metabolites interact with CYP2C8 as substrates or inhibitors, suggesting that an interplay between CYP2C8 and glucuronides is common. Lack of fully selective and safe probe substrates, inhibitors, and inducers challenges execution and interpretation of drug-drug interaction studies in humans. Apart from drug-drug interactions, some CYP2C8 genetic variants are associated with altered CYP2C8 activity and exhibit significant interethnic frequency differences. Herein, we review the current knowledge on substrates, inhibitors, inducers, and pharmacogenetics of CYP2C8, as well as its role in clinically relevant drug interactions. In addition, implications for selection of CYP2C8 marker and perpetrator drugs to investigate CYP2C8-mediated drug metabolism and interactions in preclinical and clinical studies are discussed.

Quantitative Rationalization of Gemfibrozil Drug Interactions: Consideration of Transporters-Enzyme Interplay and the Role of Circulating Metabolite Gemfibrozil 1-O-β-Glucuronide

Gemfibrozil has been suggested as a sensitive cytochrome P450 2C8 (CYP2C8) inhibitor for clinical investigation by the U.S. Food and Drug Administration and the European Medicines Agency. However, gemfibrozil drug-drug interactions (DDIs) are complex; its major circulating metabolite, gemfibrozil 1-O-β-glucuronide (Gem-Glu), exhibits time-dependent inhibition of CYP2C8, and both parent and metabolite also behave as moderate inhibitors of organic anion transporting polypeptide 1B1 (OATP1B1) in vitro. Additionally, parent and metabolite also inhibit renal transport mediated by OAT3. Here, in vitro inhibition data for gemfibrozil and Gem-Glu were used to assess their impact on the pharmacokinetics of several victim drugs (including rosiglitazone, pioglitazone, cerivastatin, and repaglinide) by employing both static mechanistic and dynamic physiologically based pharmacokinetic (PBPK) models. Of the 48 cases evaluated using the static models, about 75% and 98% of the DDIs were predicted within 1.5- and 2-fold of the observed values, respectively, when incorporating the interaction potential of both gemfibrozil and its 1-O-β-glucuronide. Moreover, the PBPK model was able to recover the plasma profiles of rosiglitazone, pioglitazone, cerivastatin, and repaglinide under control and gemfibrozil treatment conditions. Analyses suggest that Gem-Glu is the major contributor to the DDIs, and its exposure needed to bring about complete inactivation of CYP2C8 is only a fraction of that achieved in the clinic after a therapeutic gemfibrozil dose. Overall, the complex interactions of gemfibrozil can be quantitatively rationalized, and the learnings from this analysis can be applied in support of future predictions of gemfibrozil DDIs.

Targeted screen for human UDP-glucuronosyltransferases inhibitors and the evaluation of potential drug-drug interactions with zafirlukast

Inhibition of drug metabolizing enzymes is a major mechanism in drug-drug interactions (DDIs). A number of cases of DDIs via inhibition of UDP-glucuronosyltranseferases (UGTs) have been reported, although the changes in pharmacokinetics are relatively small in comparison with drugs that are metabolized by cytochrome P450s. Most of the past studies have investigated hepatic UGTs, although recent studies have revealed a significant contribution of UGTs in the small intestine to drug clearance. To evaluate potential DDIs caused by inhibition of intestinal UGTs, we assessed inhibitory effects of 578 compounds, including drugs, xenobiotics, and endobiotics, on human UGT1A8 and UGT1A10, which are major contributors to intestinal glucuronidation. We identified 29 inhibitors by monitoring raloxifene glucuronidation with recombinant UGTs. All of the inhibitors potently inhibited UGT1A1 activity, as well. We found that zafirlukast is a potent general inhibitor of UGT1As and a moderate inhibitor of UGT2Bs because it monitors 4-methylumbelliferone glucuronidation by recombinant UGTs. However, zafirlukast did not potently inhibit diclofenac glucuronidation, suggesting that the inhibitory effects might be substrate specific. Inhibitory effects of zafirlukast on some UGT substrates were further investigated in human liver and human small intestine microsomes in order to evaluate potential DDIs. The R values (the ratios of intrinsic clearance with and without an inhibitor) revealed that zafirlukast has potential to cause clinical DDIs in the small intestine. Although we could not identify specific UGT1A8 and UGT1A10 inhibitors, zafirlukast was identified as a general inhibitor for UGTs in vitro. The present study suggests that the inhibition of UGT in the small intestine would be an underlying mechanism for DDIs.

Organic carbamates in drug design and medicinal chemistry

The carbamate group is a key structural motif in many approved drugs and prodrugs. There is an increasing use of carbamates in medicinal chemistry and many derivatives are specifically designed to make drug-target interactions through their carbamate moiety. In this Perspective, we present properties and stabilities of carbamates, reagents and chemical methodologies for the synthesis of carbamates, and recent applications of carbamates in drug design and medicinal chemistry.

Addition to inhaled corticosteroids of long-acting beta2-agonists versus anti-leukotrienes for chronic asthma

BACKGROUND

Asthma patients who continue to experience symptoms despite taking regular inhaled corticosteroids (ICS) represent a management challenge. Long-acting beta2-agonists (LABA) and anti-leukotrienes (LTRA) are two treatment options that could be considered as add-on therapy to ICS.

OBJECTIVES

To compare the safety and efficacy of adding LABA versus LTRA to the treatment regimen for children and adults with asthma who remain symptomatic in spite of regular treatment with ICS. We specifically wished to examine the relative impact of the two agents on asthma exacerbations, lung function, symptoms, quality of life, adverse health events and withdrawals.

SEARCH METHODS

We searched the Cochrane Airways Group Specialised Register until December 2012. We consulted reference lists of all included studies and contacted pharmaceutical manufacturers to ask about other published or unpublished studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) conducted in adults or children with recurrent asthma that was treated with ICS along with a fixed dose of a LABA or an LTRA for a minimum of four weeks.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the risk of bias of included studies and extracted data. We sought unpublished data and further details of study design when necessary.

MAIN RESULTS

We included 18 RCTs (7208 participants), of which 16 recruited adults and adolescents (6872) and two recruited children six to 17 years of age (336) with asthma and significant reversibility to bronchodilator at baseline. Fourteen (79%) trials were of high methodological quality.The risk of exacerbations requiring systemic corticosteroids (primary outcome of the review) was significantly lower with the combination of LABA + ICS compared with LTRA + ICS-from 13% to 11% (eight studies, 5923 adults and 334 children; risk ratio (RR) 0.87, 95% confidence interval (CI) 0.76 to 0.99; high-quality evidence). The number needed to treat for an additional beneficial outcome (NNTB) with LABA compared with LTRA to prevent one additional exacerbation over four to 102 weeks was 62 (95% CI 34 to 794). The choice of LTRA, the dose of ICS and the participants' age group did not significantly influence the magnitude of effect. Although results were inconclusive, the effect appeared stronger in trials that used a single device rather than two devices to administer ICS and LABA and in trials of less than 12 weeks' duration.The addition of LABA to ICS was associated with a statistically greater improvement from baseline in lung function, as well as in symptoms, rescue medication use and quality of life, although the latter effects were modest. LTRA was superior in the prevention of exercise-induced bronchospasm. More participants were satisfied with the combination of LABA + ICS than LTRA + ICS (three studies, 1625 adults; RR 1.12, 95% CI 1.04 to 1.20; moderate-quality evidence). The overall risk of withdrawal was significantly lower with LABA + ICS than with LTRA + ICS (13 studies, 6652 adults and 308 children; RR 0.84, 95% CI 0.74 to 0.96; moderate-quality evidence). Although the risk of overall adverse events was equivalent between the two groups, the risk of serious adverse events (SAE) approached statistical significance in disfavour of LABA compared with LTRA (nine studies, 5658 adults and 630 children; RR 1.33, 95% CI 0.99 to 1.79; P value 0.06; moderate-quality evidence), with no apparent impact of participants' age group.The following adverse events were reported, but no significant differences were demonstrated between groups: headache (11 studies, N = 6538); cardiovascular events (five studies, N = 5163), osteopenia and osteoporosis (two studies, N = 2963), adverse events (10 studies, N = 5977 adults and 300 children). A significant difference in the risk of oral moniliasis was noted, but this represents a low occurrence rate.

AUTHORS' CONCLUSIONS

In adults with asthma that is inadequately controlled by predominantly low-dose ICS with significant bronchodilator reversibility, the addition of LABA to ICS is modestly superior to the addition of LTRA in reducing oral corticosteroid-treated exacerbations, with an absolute reduction of two percentage points. Differences favouring LABA over LTRA as adjunct therapy were observed in lung function and, to a lesser extend, in rescue medication use, symptoms and quality of life. The lower overall withdrawal rate and the higher proportion of participants satisfied with their therapy indirectly favour the combination of LABA + ICS over LTRA + ICS. Evidence showed a slightly increased risk of SAE with LABA compared with LTRA, with an absolute increase of one percentage point. Our findings modestly support the use of a single inhaler for the delivery of both LABA and low- or medium-dose ICS. Because of the paucity of paediatric trials, we are unable to draw firm conclusions about the best adjunct therapy in children.

Zafirlukast inhibits complexation of Lsr2 with DNA and growth of Mycobacterium tuberculosis

The mycobacterial nucleoid-associated protein Lsr2 is a DNA-bridging protein that plays a role in condensation and structural organization of the genome and acts as a global repressor of gene transcription. Here we describe experiments demonstrating that zafirlukast inhibits the complexation between Lsr2 and DNA in vitro. Zafirlukast is shown to inhibit growth in two different species of mycobacteria tested but exhibits no growth inhibition of Escherichia coli. The Lsr2 inhibitory activity is reflected in vivo as determined by monitoring of transcription levels in Mycobacterium tuberculosis. These data suggest that zafirlukast inhibits Lsr2 function in vivo, promoting dysregulation of the expression of an array of genes typically bound by Lsr2 and hindering growth. Since zafirlukast likely operates by a mechanism distinct from current M. tuberculosis drugs and is currently used as a prophylactic treatment for asthma, it offers an intriguing lead for development of new treatments for tuberculosis.

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.

Addition to inhaled corticosteroids of long-acting beta2-agonists versus anti-leukotrienes for chronic asthma

BACKGROUND

Asthma patients who continue to experience symptoms despite being on regular inhaled corticosteroids (ICS) represent a management challenge. Long-acting beta(2)-agonists (LABA) or anti-leukotrienes (LTRA) are two treatment options that could be considered as add-on therapy to ICS.

OBJECTIVES

We compared the efficacy and safety profile of adding either daily LABA or LTRA in adults and children with asthma who remain symptomatic on ICS.

SEARCH STRATEGY

We searched the Cochrane Airways Group Specialised Register (up to and including March 2010). We consulted reference lists of all included studies and contacted authors and pharmaceutical manufacturers for other published or unpublished studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) conducted in adults or children with recurrent asthma that was treated with ICS and where a fixed dose of a long-acting beta(2)-agonist or leukotriene agent was added for a minimum of 28 days.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the risk of bias of included studies and extracted data. We sought unpublished data and further details of study design, where necessary.

MAIN RESULTS

We included 17 RCTs (7032 participants), of which 16 recruited adults and adolescents (6850) and one recruited children aged 6 to 17 years (182). Participants demonstrated substantial reversibility to short-acting beta-agonist at baseline. The studies were at a low risk of bias. The risk of exacerbations requiring systemic corticosteroids was lower with the combination of LABA and ICS compared with LTRA and ICS, from 11% to 9% (RR 0.83, 95% CI 0.71 to 0.97; six studies, 5571 adults). The number needed to treat (NNT) with LABA compared to LTRA to prevent one exacerbation over 48 weeks was 38 (95% CI 22 to 244). The choice of LTRA did not significantly affect the results. The effect appeared stronger in the trials using a single device to administer ICS and LABA compared to those using two devices. In the absence of data from the paediatric trial and the clinical homogeneity of studies, we could not perform subgroup analyses. The addition to ICS of LABA compared to LTRA was associated with a statistically greater improvement from baseline in several of the secondary outcomes, including lung function, functional status measures and quality of life. Serious adverse events were more common with LABA than LTRA, although the estimate was imprecise (RR 1.35, 95% CI 1.00 to 1.82), and the NNT to harm for one additional patient to suffer a serious adverse event on LABA over 48 weeks was 78 (95% CI 33 to infinity). The risk of withdrawal for any reason in adults was significantly lower with LABA and ICS compared to LTRA and ICS (RR 0.84, 95% CI 0.74 to 0.96).

AUTHORS' CONCLUSIONS

In adults with asthma that is inadequately controlled on low doses of inhaled steroids and showing significant reversibility with beta(2)-agonists, LABA is superior to LTRA in reducing oral steroid treated exacerbations. Differences favouring LABA in lung function, functional status and quality of life scores are generally modest. There is some evidence of increased risk of SAEs with LABA. The findings support the use of a single inhaler for the delivery of LABA and inhaled corticosteroids. We are unable to draw conclusions about which treatment is better as add-on therapy for children.

Cysteinyl-leukotriene receptor antagonism blunts the acute hypotensive response to endotoxin in cats

This study evaluated the effects of a cysteinyl-leukotriene-1 (cys-LT(1)) receptor antagonist, zarfirlukast, during feline endotoxemia. Six adult, sexually intact male cats received either placebo or zarfirlukast (10mg, PO) and endotoxin (2 μg/kg/h q 6h) in a cross-over design. Rectal temperature, heart rate, systolic arterial blood pressure, plasma tumor necrosis factor (TNF) activity, interleukin (IL)-6 concentration and urine cys-LT to creatinine ratio were evaluated. The rectal temperature, plasma TNF activity and IL-6 concentrations were significantly higher and systolic arterial blood pressure and heart rate significantly lower after endotoxin infusion. Cats treated with zafirlukast had a significantly higher blood pressure at 4h (P=0.002) compared to placebo. Urine cys-LT to creatinine ratio was significantly greater in the cats treated with zafirlukast compared to placebo (P=0.02). Zafirlukast administration ameliorated the acute hypotensive response to endotoxin in cats, but failed to significantly alter rectal temperature, heart rate or production of TNF and IL-6.

Characterization of enzymes responsible for biotransformation of the new antileukotrienic drug quinlukast in rat liver microsomes and in primary cultures of rat hepatocytes

The promising new drug quinlukast, 4-(4-(quinoline-2′-yl-methoxy)phenylsulphanyl)benzoic acid (VÚFB 19363), is under investigation for its anti-inflammatory and anti-asthmatic effects. The main metabolite of quinlukast identified in incubations of rat microsomal fraction, and in primary culture of rat hepatocytes, is quinlukast sulfoxide (M2). Also, several other metabolites of quinlukast were found: two dihydrodiol derivatives (M3, M5) and quinlukast sulfone (M4). This study was conducted to characterize the enzymes involved in quinlukast biotransformation in rat in-vitro. Primary cultures of rat hepatocytes were treated with inducers of different cytochrome P450s (CYPs) for 48 h. Quinlukast (100 μm) was incubated for 24 h in a primary culture of induced or control hepatocytes. The effects of CYP inhibitors, ketoconazole, methylpyrazole, metyrapone and α-naphthoflavone (2, 10, 50 μm), on quinlukast metabolism were tested in induced and control hepatocytes. Significant induction of M2 (6 times), M5 (twice) and M3 (by 50%) formation by dexamethasone and strong concentration-dependent inhibition by ketoconazole indicated that CYP3A participates in formation of these metabolites. CYP1A catalyses formation of metabolite M3 mainly, as β-naphthoflavone induced (10 times) production of M3 and a strong inhibitory effect of α-naphthoflavone on its formation was observed. A significant inhibitory effect of quinlukast (2, 10, 50 μm) on ethoxyresorufin, methoxyresorufin and benzyloxyresorufin O-dealkylase activity was observed as well.

Therapeutic management of allergic diseases

Allergic diseases are characterized by the activation of inflammatory cells and by a massive release of mediators. The aim of this chapter was to describe succinctly the modes of action, indications, and side effects of the major antiallergic and antiasthmatic drugs. When considering the ideal pharmacokinetic characteristics of a drug, a poorly metabolized drug may confer a lower variability in plasma concentrations and metabolism-based drug interactions, although poorly metabolized drugs may be prone to transporter-based disposition and interactions. The ideal pharmacological properties of a drug include high binding affinity, high selectivity, and appropriate association and dissociation rates. Finally, from a patient perspective, the frequency and route of administration are important considerations for ease of use.

Pharmacokinetics in special populations

Pharmacokinetics are typically dependent on a variety of physiological variables (e.g., age, ethnicity, or pregnancy) or pathological conditions (e.g., renal and hepatic insufficiency, cardiac dysfunction, obesity, etc.). The influence of some of these conditions has not always been thoroughly assessed in the clinical studies of antiallergic drugs. However, the knowledge of the physiological grounds of the pharmacokinetics can provide some insight for predicting the potential alterations and guiding the initial prescription strategies. It is important to recognize that both pharmacokinetic and pharmacodynamic differences between populations should be considered. The available information on drugs used for the therapy of allergic diseases is reviewed in this chapter.

Drug interactions

Drugs for allergy are often taken in combination with other drugs, either to treat allergy or other conditions. In common with many pharmaceuticals, most such drugs are subject to metabolism by P450 enzymes and to transmembrane transport. This gives rise to considerable potential for drug-drug interactions, to which must be added consideration of drug-diet interactions. The potential for metabolism-based drug interactions is increasingly being taken into account during drug development, using a variety of in silico and in vitro approaches. Prediction of transporter-based interactions is not as advanced. The clinical importance of a drug interaction will depend upon a number of factors, and it is important to address concerns quantitatively, taking into account the therapeutic index of the compound.

Drug metabolism and pharmacokinetics

In this article, aspects of absorption, distribution, metabolism, and excretion have been described bearing in mind the pathogenesis of allergic diseases and their possible therapeutic opportunities. The importance of the routes of administration of the different therapeutic groups has been emphasized. The classical aspects of drug metabolism and disposition related to oral administration have been reviewed, but special emphasis has been given to intranasal, cutaneous, transdermal, and ocular administration as well as to the absorption and the subsequent bioavailability of drugs. Drug-metabolizing enzymes and transporters present in extrahepatic tissues, such as nasal mucosa and the respiratory tract, have been particularly discussed. As marketed antiallergic drugs include both racemates and enantiomers, aspects of stereoselective absorption, distribution, metabolism, and excretion have been discussed. Finally, a new and promising methodology, microdosing, has been presented, although it has not yet been applied to drugs used in the treatment of allergic diseases.

Complexities of diagnosis and treatment of allergic respiratory disease in the elderly

Atopic diseases such as rhinitis and asthma are relatively common in children and young adults. However, many patients aged >65 years are also affected by these disorders. Indeed, the literature suggests that between 3-12% and 4-13% of individuals in this age range have allergic rhinitis and asthma, respectively. However, these numbers are most likely underestimates because atopic diseases are frequently not considered in older patients. The diagnosis of both allergic rhinitis and asthma in older patients is more difficult than in younger patients because of a wide differential diagnosis of other diseases that can produce similar symptoms and must be excluded. Furthermore, treatment of these disorders is complicated by the potential for drug interactions, concern about the adverse effects of medications, in particular corticosteroids, and the lack of drug trials specifically targeting treatment of older patients with allergic rhinitis and asthma.

Adenosine receptors and asthma

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

Treatment heterogeneity in asthma: genetics of response to leukotriene modifiers

Despite advances in treatment, asthma continues to be a significant health and economic burden. Although asthma cannot be cured, several drugs, including beta2 agonists, corticosteroids, and leukotriene (LT) modifiers, are well tolerated and effective in minimizing symptoms, improving lung function, and preventing exacerbations. However, inter-patient variability in response to asthma drugs limits their effectiveness. It has been estimated that 60-80% of this inter-patient variability may be attributable to genetic variation. LT modifiers, in particular, have been associated with heterogeneity in response. These drugs exert their action by inhibiting the activity of cysteinyl leukotrienes (CysLTs), which are potent bronchoconstrictors and pro-inflammatory agents. Two classes of LT modifiers are 5-lipoxygenase (ALOX5) inhibitors (zileuton) and leukotriene receptor antagonists (LTRAs) [montelukast, pranlukast, and zarfirlukast]. LT modifiers can be used as alternatives to low-dose inhaled corticosteroids (ICS) in mild persistent asthma, as add-on therapy to low- to medium-dose ICS in moderate persistent asthma, and as add-on to high-dose ICS and a long-acting ss2 agonist in severe persistent asthma. At least six genes encode key proteins in the LT pathway: arachidonate 5-lipoxygenase (ALOX5), ALOX5 activating protein (ALOX5AP [FLAP]), leukotriene A4 hydrolase (LTA4H), LTC4 synthase (LTC4S), the ATP-binding cassette family member ABCC1 (multidrug resistance protein 1 [MRP1]), and cysteinyl leukotriene receptor 1 (CYSLTR1). Studies have reported that genetic variation in ALOX5, LTA4H, LTC4S, and ABCC1 influences response to LT modifiers. Plasma concentrations of LTRAs vary considerably among patients. Physio-chemical characteristics make it likely that membrane efflux and uptake transporters mediate the absorption of LTRAs into the systemic circulation following oral administration. Genes that encode efflux and uptake transport proteins harbor many variants that could influence the pharmacokinetics, and particularly the bioavailability, of LTRAs, and could contribute to heterogeneity in response. In the future, large, well designed clinical trials studying the pharmacogenetics of LT modifiers in diverse populations are warranted to determine whether a genetic signature can be developed that will accurately predict which patients will respond.

Long-acting beta2-agonists versus anti-leukotrienes as add-on therapy to inhaled corticosteroids for chronic asthma

BACKGROUND

Patients who continue to experience asthma symptoms despite taking regular inhaled corticosteroids (ICS) represent a management challenge. Leukotriene receptor antagonists (LTRA) and long-acting beta(2)-agonists (LABA) agents may both be considered as add-on therapy to inhaled corticosteroids (ICS).

OBJECTIVES

We compared the efficacy and safety profile of adding either daily LABA or LTRA in asthmatic patients who remained symptomatic on ICS.

SEARCH STRATEGY

The Cochrane Airways Group Specialised Register was searched for randomised controlled trials up to and including March 2006. Reference lists of all included studies and reviews were screened to identify potentially relevant citations. Inquiries regarding other published or unpublished studies supported by the authors of the included studies or pharmaceutical companies who manufacture these agents were made. Conference proceedings of major respiratory meetings were also searched.

SELECTION CRITERIA

Only randomised controlled trials conducted in adults or children with recurrent asthma where a LABA (for example, salmeterol or formoterol) or LTRA (for example, montelukast, pranlukast, zafirlukast) was added to ICS for a minimum of 28 days were considered for inclusion. Inhaled short-acting beta(2)-agonists and short courses of oral steroids were permitted as rescue medications. Other daily asthma treatments were permitted, providing the dose remained constant during the intervention period. Two reviewers independently reviewed the literature searches.

DATA COLLECTION AND ANALYSIS

Data extraction and trial quality assessment were conducted independently by two reviewers. Whenever possible, primary study authors were requested to confirm methodology and data extraction and to provide additional information and clarification when needed. Where necessary, expansion of graphic reproductions and estimation from other data presented in the paper was performed.

MAIN RESULTS

Fifteen randomised controlled trials met the inclusion criteria; eleven trials including 6,030 participants provided data in sufficient detail to permit aggregation. All eleven trials pertained to adults with moderate airway obstruction (% predicted FEV(1) 66-76%) at baseline. Montelukast (n=9) or Zafirlukast (n=2) was compared to Salmeterol (n=9) or Formoterol (n=2) as add-on therapy to 400-565 mcg of beclomethasone or equivalent. Risk of exacerbations requiring systemic corticosteroids was significantly lower with LABA+ICS when compared to LTRA+ICS (RR= 0.83, 95% Confidence Interval (95%CI): 0.71, 0.97): the number needed to treat with LABA compared to LTRA, to prevent one exacerbation over 48 weeks, was 38 (95% CI: 23 to 247). The following outcomes also improved significantly with the addition of LABA compared to LTRA to inhaled steroids (Weighted Mean Difference; 95%CI): morning PEFR (16 L/min; 13 to 18), evening PEFR (12 L/min; 9 to 15), FEV(1) (80 mL; 60 to 100), rescue-free days (9%; 5% to 13%), symptom-free days (6%; 2 to 11), rescue beta(2)-agonists (-0.5 puffs/day; -0.2 to -1), quality of life (0.1; 0.05 to 0.2), symptom score (Standard Mean Difference -0.2; -0.1 to -0.3), night awakenings (-0.1/week; -0.06 to -0.2) and patient satisfaction (RR 1.12; 1.07 to 1.16). Risk of withdrawals due to any reason was significantly lower with LABA+ICS compared to LTRA+ICS (Risk Ratio 0.83, 95% CI 0.73 to 0.95). Withdrawals due to adverse events or due to poor asthma control, hospitalisation, osteopenia, serious adverse events, overall adverse events, headache or cardiovascular events were not significantly different between the two study groups.

AUTHORS' CONCLUSIONS

In asthmatic adults inadequately controlled on low doses of inhaled steroids, the addition of LABA is superior to LTRA for preventing exacerbations requiring systemic steroids, and for improving lung function, symptoms, and the use of rescue beta(2)-agonists.

Montelukast and zafirlukast do not affect the pharmacokinetics of the CYP2C8 substrate pioglitazone

OBJECTIVE

Pioglitazone, a thiazolidinedione antidiabetic drug, is metabolised mainly by the cytochrome P450 (CYP) 2C8 enzyme. The leukotriene receptor antagonists montelukast and zafirlukast have potently inhibited CYP2C8 activity and the metabolism of pioglitazone in vitro. Our objective was to determine whether montelukast and zafirlukast increase the plasma concentrations of pioglitazone in humans.

METHODS

In a randomised, double-blind crossover study with three phases and a washout period of 3 weeks, 12 healthy volunteers took either 10 mg montelukast once daily and placebo once daily, or 20 mg zafirlukast twice daily, or placebo twice daily, for 6 days. On day 3, they received a single oral dose of 15 mg pioglitazone. The plasma concentrations of pioglitazone and its metabolites M-IV, M-III, M-V and M-XI were measured for 96 h.

RESULTS

The total area under the plasma concentration-time curve of pioglitazone during the montelukast and zafirlukast phases was 101% (range 71-143%) and 103% (range 78-146%), respectively, of that during the placebo phase. Also, the peak plasma concentration and elimination half-life of pioglitazone remained unaffected by montelukast and zafirlukast. There were no statistically significant differences in the pharmacokinetics of any of the metabolites of pioglitazone between the phases.

CONCLUSIONS

Montelukast and zafirlukast do not increase the plasma concentrations of pioglitazone, indicating that their inhibitory effect on CYP2C8 is negligible in vivo, despite their strong inhibitory effect on CYP2C8 in vitro. The results highlight the importance of in vivo interaction studies and of the incorporation of relevant pharmacokinetic properties of drugs, including plasma protein binding data, to in vitro-in vivo interaction predictions.

Long-acting beta2-agonists versus anti-leukotrienes as add-on therapy to inhaled corticosteroids for chronic asthma

BACKGROUND

Patients who continue to experience asthma symptoms despite taking regular inhaled corticosteroids (ICS) represent a management challenge. Leukotriene receptor antagonists (LTRA) and long-acting beta2-agonists (LABA) agents may both be considered as add-on therapy to inhaled corticosteroids (ICS).

OBJECTIVES

We compare the efficacy and safety profile of adding either daily LABA or LTRA in asthmatic patients with asthma who remained symptomatic on ICS.

SEARCH STRATEGY

MEDLINE, EMBASE, CINAHL databases were searched for randomised controlled trials up to and including January 2004. Reference lists of all included studies and reviews were screened to identify potentially relevant citations. Inquiries regarding other published or unpublished studies supported by the authors of the included studies or pharmaceutical companies who manufacture these agents were made. Conference proceedings of major respiratory meetings were also searched.

SELECTION CRITERIA

Only randomised controlled trials conducted in adults or children with recurrent asthma where a LABA (for example, salmeterol or formoterol) or LTRA (for example, montelukast, pranlukast, zafirlukast) was added to ICS for a minimum of 28 days were considered for inclusion. Inhaled short-acting beta2-agonists and short courses of oral steroids were permitted as rescue medications. Other daily asthma treatments were permitted, providing the dose remained constant during the intervention period. Two reviewers independently reviewed the literature searches.

DATA COLLECTION AND ANALYSIS

Data extraction and trial quality assessment were conducted independently by two reviewers. Whenever possible, primary study authors were requested to confirm methodology and data extraction and to provide additional information and clarification when needed. Where necessary, expansion of graphic reproductions and estimation from other data presented in the paper was performed.

MAIN RESULTS

Twelve randomised controlled trials met the inclusion criteria; only eight trials including 5,895 patients, provided data in sufficient details to allow aggregation. All eight trials pertained to adults with moderate airway obstruction (% predicted FEV1 66-76%) at baseline. Montelukast (n=6) or Zafirlukast (n=2) was compared to Salmeterol (n=7) or Formoterol (n=1) as add-on therapy to 400-565 mcg of beclomethasone or equivalent. Risk of exacerbations requiring systemic corticosteroids was significantly lower with LABA+ICS when compared to LTRA+ICS (RR= 0.83, 95% Confidence Interval (95%CI): 0.71, 0.97): the number needed to treat with LABA compared to LTRA, to prevent one exacerbation over 48 weeks, was 38 (95% CI: 23 to 247). The following outcomes also improved significantly with the addition of LABA compared to LTRA to inhaled steroids (Weighted Mean Difference; 95%CI): morning PEFR (16 L/min; 13 to 18), evening PEFR (12 L/min; 9 to 15), FEV(1) (80 mL; 60 to 100), rescue-free days (9%; 4 to 14), symptom-free days (6%; 2 to 11), rescue beta2-agonists (-0.4 puffs/day; -0.2 to -0.5), quality of life (0.1; 0.05 to 0.2), symptom score (Standard Mean Difference -0.2; -0.1 to -0.3), night awakenings (-0.1/week; -0.06 to -0.2) and patient satisfaction (RR 1.12; 1.07 to 1.16). Risk of withdrawals due to any reason was significantly lower with LABA+ICS compared to LTRA+ICS (Relative Risk 0.84, 95% CI 0.74 to 0.96). Withdrawals due to adverse events or due to poor asthma control, hospitalisation, osteopenia, serious adverse events, overall adverse events, headache or cardiovascular events were not significantly different between the two study groups.

AUTHORS' CONCLUSIONS

In asthmatic adults inadequately controlled on low doses of inhaled steroids, the addition of LABA is superior to LTRA for preventing exacerbations requiring systemic steroids, and for improving lung function, symptoms, and use of rescue beta2-agonists.

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.