title: Tolerance and rebound with zafirlukast in patients with persistent asthma.
abstract: 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).
  
  
  CONCLUSIONS
  Tolerance appears to develop to zafirlukast and there is rebound clinical deterioration on drug withdrawal, accompanied by a blood neutrophilia.
authors.affiliation: Respiratory Research Group, Menzies Research Institute, University of Tasmania Hobart, Tasmania, Australia. d.e.c.reid@utas.edu.au
authors.forename: David W
authors.initials: DW
authors.lastname: Reid
authors.forename: Neil L
authors.initials: NL
authors.lastname: Misso
authors.forename: Shashi
authors.initials: S
authors.lastname: Aggarwal
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Thompson
authors.forename: David P
authors.initials: DP
authors.lastname: Johns
authors.forename: E Haydn
authors.initials: EH
authors.lastname: Walters
mesh_terms: D000328:Adult; D000368:Aged; D001249:Asthma / Q000188:drug therapy* / Q000473:pathology*; D015232:Dinoprostone / Q000378:metabolism; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007211:Indoles; D020024:Leukotriene Antagonists / Q000494:pharmacology; D008297:Male; D016210:Methacholine Chloride / Q000494:pharmacology; D008875:Middle Aged; D009569:Nitric Oxide / Q000378:metabolism; D010366:Peak Expiratory Flow Rate; D048448:Phenylcarbamates; D010919:Placebos; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism; D013449:Sulfonamides; D014105:Tosyl Compounds / Q000494:pharmacology*
chemical_list: D007211:Indoles; D020024:Leukotriene Antagonists; D048448:Phenylcarbamates; D010919:Placebos; D018343:Receptors, Adrenergic, beta-2; D013449:Sulfonamides; D014105:Tosyl Compounds; D016210:Methacholine Chloride; D009569:Nitric Oxide; D015232:Dinoprostone; C062735:zafirlukast