Biomedical Engineering Reference
In-Depth Information
Mucolytics
Decreasing the viscosity of, or 'thinning', viscous airway mucus with muco-
lytic drugs is one way of improving mucus clearance, both by cough and
mucociliary transport. However, although numerous mucolytic drugs are
available worldwide, their effectiveness in treatment of stable COPD has
not been established (95). In addition, there are safety issues with a number
of mucolytic preparations, for example iodinated glycerol. Consequently,
mucolytics are not generally recommended in current guidelines on clinical
management of COPD (3). Nevertheless, two rigorous meta-analyses found
that treatment for at least 2 months with certain mucolytic drugs, with a
heavy bias towards N-acetylcycsteine, reduces number of exacerbations
and days of illness (96,97). Cost effective treatment would be in severe
patients (98). However, it is not clear whether the beneficial effects of
N-acetylcysteine (or the other drugs) are due to its mucolytic or antioxidant
properties (or both).
Contraindications to Mucolytic Therapy
Severe airflow limitation reduces the effectiveness of cough to clear secre-
tions (49). Consequently, there is a theoretical risk that, in the presence of
reduced effectiveness of cough clearance, if secretions are thinned or loo-
sened the mucus could lodge deeper into the lung, thereby causing greater
obstruction. However, patients with moderately severe CF lung disease
(FVC
<
40% predicted) given human recombinant DNAse (Dornase alfa)
to thin their secretions did not demonstrate a worsening of pulmonary func-
tion (99). Nevertheless, any mucoactive therapy, except those that increase
airflow or do not require active expectoration on the part of the patient,
should be used with caution in patients with end-stage pulmonary disease
or neuromuscular weakness.
Patients with acute mucus retention, for example during exacerbations
of COPD, appear less responsive to mucoactive medications than stable
patients (97). This may be due to decreased airflow caused both by the
increase in infection and to muscular weakness in association with the pul-
monary exacerbation, further reducing airflow dependent clearance mechan-
isms. In some patients with COPD (especially those with hyperreactive
airways, sputum production, and small airways disease) lung function,
wheezing, and bronchoconstriction may follow the use of chest physical
therapy (100). In patients in whom mucus transport is increased by chest
physiotherapy and cough, mucociliary clearance may be slowed or absent
due to airway compression during the procedure. Patients with gastroeso-
phageal reflux coupled with reduced mucus clearance, for example by
impaired cough, are at risk from postural drainage. They may be at addi-
tional risk with mucus mobilizing or expectorant therapy, particularly when
the medication increases the volume of secretions produced (101).
