We reviewed the evidence about the effect of inhaling mannitol to treat lung disease in people with cystic fibrosis.
Cystic fibrosis is a genetic disorder that affects the exocrine glands (sweat glands and others). Lung infections produce thick mucus (phlegm) which can block air passages and cause more infection and repeated inflammation. In turn, this progressively damages the lungs and can eventually cause respiratory failure. There are several drugs that are used to clear mucus from the airways of people with cystic fibrosis and inhaled dry powder mannitol is a new one that may improve their lung function. The dry powder formulation of mannitol may be more convenient and easier to use compared with established agents delivered by a nebuliser (e.g. hypertonic saline). Mannitol is available in Australia and some European countries. This is an updated version of the review.
The evidence is current to: 28 September 2017.
We included six studies (with a total of 784 adults and children) in this review. Five studies compared a standard dose of mannitol with control (a very low dose of mannitol or a version of mannitol which did not allow the active drug to reach the lungs) and the sixth study compared mannitol with nebulised recombinant human deoxyribonuclease (dornase alfa), both alone and taken together. Participants could continue using dornase alfa and other standard therapies, but were excluded from the five of the six studies if they were using hypertonic saline. Treatment in these studies lasted from 12 days to six months. Five studies provided the treatments to people as outpatients and in one study, the children treated were in hospital due to pulmonary exacerbations (flare ups of disease).
It was difficult to combine evidence from the studies in this review due to differences in the designs of the studies, treatments examined and the settings (hospital or outpatients). Some additional information was obtained from the drug manufacturer and one study author to aid the review.
The review found low- to very low-quality evidence that there is no difference between mannitol and control treatments or mannitol given either with or without additional dornase alfa in terms of quality of life. There was moderate-quality evidence of improvements in some measures of lung function across the larger studies comparing mannitol to control. Beneficial effects were also seen in the subgroup of adults and in both those who were using dornase alfa and those who were not. Cough (including coughing up blood), contraction of the airways, pain in the pharynx or larynx and post-treatment vomiting were the most commonly reported side effects on both treatments, but there was no evidence to suggest that these side effects occurred more on mannitol than on control treatments or on dornase alfa.
None of the studies compared mannitol to nebulised hypertonic saline and so we can not comment on which agent is better for airway clearance. More research is needed to answer this question.
Quality of the evidence
We judged the quality of the evidence from this review to be of very low to moderate quality, depending on the outcome measured. We do not think that the way the studies were designed affected the results. We judged that everyone taking part had equal chances of being in either of the treatment groups and would not have known in advance or during the study which treatment they were receiving. However, the numbers of people who dropped out of the studies might affect how the results are interpreted, as well as how many people were recruited into the studies and how they were selected from all people with cystic fibrosis who could have been included.
Although some of these issues were resolved when the drug’s manufacturer (who also sponsored the studies) provided some additional information. It is important to realise that before people started the study, they took a test to see if they could tolerate mannitol and only those who did could carry on. This means that the results of the studies only apply to those people with cystic fibrosis who can tolerate mannitol.