Preliminary Study of Dornase Alfa to Treat Chest Infections Post Lung Transplant.

According to the International Society for Heart and Lung Transplantation (ISHLT), the incidence of lung transplants per annum worldwide is rising annually, with over 3000 transplants completed according to the latest registry(1). The Alfred is a state-wide, internationally renowned lung transplant service, transplanting between 59 - 79 patients over the last two calendar years, with a wait-list of more than 40 potential recipients. This makes it one of only 7 centres worldwide completing this volume of transplants(1).

Patients who have undergone lung transplantation for end-stage lung disease are subject to life-long immunosuppression to prevent allograft rejection. These patients are at a heightened risk of acquiring opportunistic lower respiratory tract infections (LRTI)(2), often characterized by sputum retention and / or production, which can have a negative impact on both morbidity and mortality(3). Patients post lung transplant often find it difficult to clear secretions due to an alteration in normal physiology. Transplanted lung tissue is denervated upon resection from the donor, which has been shown to lead to slower cilial beat frequencies(4), impaired muco-ciliary clearance (MCC) rates(4-6) and an impaired cough reflex(7). Devascularisation to lung tissue post ischaemic surgical time in the acute period can lead to an alteration in mucosal properties and structural changes around anastomoses, which may further impair the ability to clear secretions(3).

Inhaled, nebulised mucolytic agents are commonly used in the management of other suppurative chronic lung diseases characterized by excessive production of secretions. Dornase alfa acts by digesting the extracellular deoxyribonucleic acid (DNA) released by inflammatory cells during infection(8). It has been shown to have positive long-term effects on lung function in cystic fibrosis (CF)(8) and short-term benefits treating atelectasis and mucous plugging in acute, non-CF adult and pediatric cases(9-11). Yet shown to be safe in normal subjects(8), it has been shown to have a detrimental effect on pulmonary function in non-CF bronchiectasis(12).

Inhaled saline acts by restoring the airway surface liquid layer of the mucosa, favorably altering mucous properties, accelerating MCC and stimulating cough(13-14). Positive evidence exists for hypertonic saline (6-7%) in CF(13-14) and both hypertonic and isotonic (0.9%) saline in non-CF bronchiectasis(15). There is discussion of clinical use of saline as a mucolytic in the post transplant patient(16) with no evidence by way of randomized controlled trial to demonstrate effect. There is no current evidence on the use of inhaled mucolytics post transplant.

Currently, both dornase alfa and saline (isotonic / hypertonic) are used in the inpatient and outpatient setting at this institution as a reactive treatment strategy for LRTI characterized by excessive sputum production and / or retention. The investigators believe this warrants a short-term, randomized trial to assess the efficacy of current practice, and to evaluate whether dornase alfa is more effective than 0.9% saline, a cheaper, more accessible alternative.

Aim

To evaluate the efficacy of inhaled dornase alfa compared to inhaled isotonic (0.9%) saline on:

• Quantitative and qualitative respiratory outcomes
• The need for antibiotics, length of stay and exacerbation / re-admission rates

Hypothesis Dornase alfa is more effective than isotonic saline in the post lung transplant population during LRTI.

Study design Phase 2, assessor blinded, prospective randomized controlled trial.

Intervention On admission to the ward as an inpatient, patients who give informed consent within 48 hours of initial presentation will be randomly assigned to one of two groups defined below. The randomization sequence will be concealed using opaque envelopes. Randomization will be stratified according to pre-transplant diagnosis (cystic fibrosis or not) as people with cystic fibrosis are expected to be younger and have a different underlying systemic disease process.

All participants will undertake treatment for one month according to their allocated group, with follow up to 3 months, (2 months off randomized intervention). Both groups will continue to do their regular prescribed physical exercise routine over the course of the study.

Timing of assessment All outcome measures will be performed at study baseline, 1 month and 3 months follow-up. Daily outcome measures used as a monitoring diary are an exception. There are no cough-specific quality of life questionnaires validated for use in the post lung transplant population.

Sample size and power calculation A total of 30 participants (15 in each group) will enter this study. The probability is 80 percent that the study will detect a treatment difference at a two-sided 0.05 significance level, if the true difference between treatments is 1.000 unit in lung clearance index (LCI).

This is a conservative estimate that is smaller than previous differences found in pediatric populations(17-18). This is based on the assumption that the standard deviation of the response variable is 0.94 units(17-18).

As a phase 2 study, this project is powered to detect differences in physiological outcomes, rather than quality of life or hospitalization. However, should the treatment prove to have physiological benefits, the secondary outcomes of this study will provide critical information for powering a future phase 3 trial.

Feasibility: Approximately 12 patients with pulmonary exacerbations are admitted under the lung transplant service each month (minimum estimate). Investigators estimate that 70% will meet the eligibility criteria for the study and 50% will consent to participate. It is therefore anticipated that it will be possible to recruit the numbers needed for this study in 8 months.

Statistical analysis An intention to treat analysis will be conducted, with inclusion of all randomized participants, regardless of study completion. Data for continuous outcomes including LCI will be analyzed using a linear mixed models analysis, which makes use of all available data at each time point and is less affected by incomplete data than analysis of variance. The likelihood of exacerbation or hospitalization during the follow-up period for the dornase alpha group will be expressed as a relative risk compared to the isotonic saline group.

Bias / Confounders There is potential for performance bias in this study due to the lack of ability to blind participants to their allocated treatment regimen. Investigators are unable to package medications in a way other than that currently produced. It is the aim to outline, as part of the participant information and consent form (PICF), that both inhaled medications have proven to be efficacious (and detrimental in certain circumstances) in disease processes other than post lung transplant LRTI. Detection bias will be controlled by the use of a blinded outcome assessor for all follow-up data collection points.

Potential confounders in this study include the diagnosis of bronchiolitis obliterans (BOS), or chronic lung rejection, during which LRTI occurs simultaneously. Patients with a diagnosis of BOS may in fact demonstrate differences in lung physiology and ease of sputum expectoration, which may have an effect on outcomes variables. We feel that excluding these patients may have a detrimental impact on the external validity of this study, therefore we will stratify patients according to a diagnosis of BOS on study inclusion.

Outcomes and Significance This will be the first randomized controlled trial to analyze inhaled dornase alfa and isotonic saline in the post lung transplant population.

The outcome of this trial will help to guide physiotherapy and pharmacological management of post lung transplant patients with LRTI in the future, both nationally and internationally.