Pediatric Pulmonology 42:989–1001 (2007) State of the Art Pharmacotherapy of Impaired Mucociliary Clearance in Non-CF Pediatric Lung Disease. A Review of the Literature 1 1 1,2 Ruben Boogaard, MD, * Johan C. de Jongste, MD, PhD, and Peter J.F.M. Merkus, MD, PhD Summary. Mucoactive agents are used to treat a variety of lung diseases involving impaired mucociliary clearance or mucus hypersecretion. The mucoactive agents studied most frequently are N-acetylcysteine (NAC), recombinant human DNase (rhDNase), and hypertonic saline. Studies on the efficacy of these have been mainly conducted in adults, and in patients with cystic fibrosis (CF). The exact role of mucoactive agents in children with non-CF lung disease is not well established. We present an overview of the current literature reporting clinical outcome measures of treatment with NAC, rhDNase, and hypertonic saline in children. Pediatr Pulmonol. 2007; 42:989–1001. ß 2007 Wiley-Liss, Inc. Key words: mucolytic; sulfhydryl compounds; N-acetylcysteine; dornase alfa; hyper- tonic saline; respiratory tract disease. INTRODUCTION One possible means to evaluate a mucoactive agent is to assess its effect on mucociliary clearance (MCC) or cough Mucus clearance is an important primary innate airway clearance with the use of radiolabeled aerosol. Discussing defense mechanism, and our understanding of the key this subject is outside the scope of this review. Moreover, parameters underlying its function has grown rapidly in the studies on mucoactive agents in CF patients, and studies last decade.1,2 Impaired mucus clearance or mucus hyper- on physiotherapy or secretion clearance techniques in secretion are important clinical features in diseases such as (pediatric) lung disease patients have been reviewed by cystic fibrosis (CF), recurrent bronchitis, asthma, and others, and will therefore not be discussed in this review. primary ciliary dyskinesia (PCD). Moreover, viral respira- The interested reader is referred to existing reviews that tory tract infections—that occur frequently during child- cover: hood—may cause epithelial damage and loss of cilia,3 and thus impaired mucus clearance through secondary ciliary . basic and clinical aspects of mucociliary clearance;8 dysfunction. Impaired clearance causes mucus to accumu- . regulation of mucociliary clearance in health and late in the airways and to initiate cough and sputum disease;9 production. Accumulated mucus can lead to airways obstruction, bacterial colonization, and recurrent infec- 1Department of Pediatric Pulmonology, Erasmus MC-Sophia Children’s tions, negatively affecting quality of life. By completely Hospital, Rotterdam, The Netherlands. obstructing the peripheral airways it may lead to atelectasis and hypoxia, and may contribute to a fatal outcome, such as 2Department of Pediatric Pulmonology, Radboud University Nijmegen in an acute asthma exacerbation.4 Medical Centre, Nijmegen, The Netherlands. Mucoactive agents are drugs that are meant to change 5 *Correspondence to: Ruben Boogaard, MD, Department of Pediatric the properties of airway secretions. Many different Pulmonology, Erasmus MC-Sophia Children’s Hospital, Room Sb-2666, mucoactive agents have been evaluated for their ability PO Box 2060, 3000 CB Rotterdam, The Netherlands. to either change the properties of airway mucus, or to E-mail: [email protected] decrease mucus secretion.6,7 Classified by proposed mechanism of action, they encompass classical muco- Received 6 June 2007; Revised 9 July 2007; Accepted 10 July 2007. lytics, peptide mucolytics, nondestructive mucolytics, DOI 10.1002/ppul.20693 expectorants, mucokinetic agents, and mucoregulators Published online in Wiley InterScience (Table 1). (www.interscience.wiley.com). ß 2007 Wiley-Liss, Inc. 990 Boogaard et al. TABLE 1— Mucoactive Agents (Adapted From Rubin7) Mucoactive agent Possible mechanism of action Expectorants Hypertonic saline Increases secretion volume and increases hydration Mannitol Increases hydration and may increase ciliary beat frequency by stimulating release of mediators; break hydrogen bonds between mucins; increase secretion volume Classical mucolytics N-acetylcysteine Breaks disulfide bond linking of mucin oligomers Nacystelyn Breaks disulfide bond linking of mucin oligomers and increases hydration (by increased chloride secretion) Peptide mucolytics Dornase alfa Hydrolyzes DNA polymer with reduction in DNA fragment length Gelsolin or Thymosin b4 Depolymerizes F-actin Non-destructive mucolytics Dextran Breaks hydrogen bonds and increases hydration Low molecular weight heparin May break both hydrogen and ionic bonds Mucoregulatory agents Anticholinergic agents Decreases volume of stimulated secretions Glucocorticoids Decreases airway inflammation and mucin secretion Indomethacin Decreases airway inflammation Macrolide antibiotics Decreases airway inflammation and mucin secretion Cough clearance promotors Bronchodilators Improves cough clearance by increasing expiratory flow Surfactants Decreases sputum adhesivity . different methodologies to measure mucociliary clear- METHODS ance;10,11 We searched MEDLINE (1966 to June 2007) with . effects of drugs on physiological properties of mucus,12 the medical subject headings (MESH): ‘respiratory tract and on MCC;11,13 diseases,’ ‘acetylcysteine,’ ‘sulfhydryl compounds,’ ‘hyper- . pharmacological approach to discovery and develop- tonic saline solution,’ and ‘DNASE1 protein, human’— ment of new mucolytic agents;5 the latter is the MESH term for the drug ‘recombinant . efficacy of N-acetylcysteine (NAC) in CF patients;14 human DNase (rhDNase, dornase alfa)’. Randomized . efficacy of recombinant human DNase (rhDNase) in CF controlled trials (RCTs) as well as uncontrolled, observa- patients;15,16 tional studies retrieved by MEDLINE, published in . efficacy of hypertonic saline in CF patients;17 English and reporting clinical data on children aged 0– . physiotherapy and secretion clearance techniques in 18 years were looked up and their reference lists were (pediatric) lung disease.18–20 scanned for relevant unretrieved material. The Cochrane library was checked for any additional clinical trials. The aim of the present review is to summarize the published literature on the mucoactive agents most RESULTS OF LITERATURE SEARCH frequently used and studied in children with non-CF lung disease, that is, NAC and other sulfhydryl compounds, A total of 34 relevant articles were retrieved (Fig. 1). rhDNase, and hypertonic saline. We will focus on Twelve articles reported RCTs, while 22 articles reported literature reporting effects of mucoactive agents on uncontrolled clinical observations. clinical outcome measures, such as length of hospital stay, symptom severity, and chest radiographs. N-ACETYLCYSTEINE AND OTHER SULFHYDRYL COMPOUNDS ABBREVIATIONS Mode of Action BPD bronchopulmonary dysplasia N-acetylcysteine (NAC) and the other sulfhydryl CF cystic fibrosis compounds—that is, S-carboxymethylcysteine (carbo- NAC N-acetylcysteine MCC mucociliary clearance cysteine) and 2-mercaptoethane sulfonate (Mesna)— Mesna 2-mercaptoethane sulfonate depolimerize mucus in vitro by breaking disulfide bonds PCD primary ciliary dyskinesia of the glycoproteins, thereby lowering viscosity and RCT randomized controlled trial potentially improving expectoration.21 Besides potential RhDNase recombinant human DNase effects on MCC, sulfhydryl compounds have anti-oxidant RSV respiratory syncytial virus effects that could be useful in preventing lung damage in Pharmacotherapy of Impaired Mucociliary Clearance 991 Fig. 1. Results of the literature search in MEDLINE on mucoactive agents in non-CF pediatric lung disease, using the medical subject headings (MESH) ‘respiratory tract diseases,’ ‘acetylcysteine,’ ‘sulfhydryl compounds,’ ‘hypertonic saline solution,’ and ‘DNASE1 protein, human’—the latter is the MESH term for the drug ‘recombinant human DNase (rhDNase, dornase alfa).’ chronic lung disease. NAC is usually given orally, as Primary Ciliary Dyskinesia inhalation can cause bronchospasm in patients with Stafanger et al.26 conducted a double blind, randomized airway hyperresponsiveness,22,23 releases an unpleasant crossover trial in 13 out-clinic patients with PCD. Oral sulfurous smell and is time consuming. However, for NAC for 3 months had no effect on subjective clinical orally administered NAC to exert a clinical effect—that is, scores, lung function parameters and ciliary function. by changing the properties of mucus—it must pass into the mucus. There is no proof that orally administered Chronic Lung Disease of Infancy NAC results in therapeutic concentrations in airway secretions.24 In some studies in healthy adults or in Bibi et al.27 conducted a crossover trial in which they chronic bronchitis patients, sulfhydryl compounds improv- intratracheally administered NAC or placebo for 7 days to ed MCC, whereas in other such studies there was no premature infants ventilated for chronic lung disease. effect.13 Airway resistance at day 3 worsened twofold in the NAC group. Dynamic compliance, clinical signs, ventilatory Randomized Controlled Trials of NAC settings and chest X-ray scores did not change. Two in Non-CF Lung Diseases patients treated with NAC showed more cyanotic spells and bradycardia. A large RCT (n ¼ 391) aimed to assess Most studies indicating efficacy of oral NAC or possible anti-oxidant benefits of intravenous NAC in carbocysteine concern adults with chronic bronchitis or premature infants with extremely low birth weight.28,29 It chronic obstructive pulmonary disease