β-agonists in the treatment of asthma
The first line of treatment for relief of asthma is one of the
selective β2-agonists taken by inhalation. β2-agonists
are the most effective bronchodilators in asthma. They start to work
quickly – salbutamol and terbutaline take effect within 15 minutes
and last for 4 to 6 hours. There is no clear threshold for all patients,
but if there has been an exacerbation of asthma in the last 2 years,
inhaled β2-agonists are needed or symptoms present at least three
times a week or asthma disturbs sleep one night a week, then
additional treatment must be considered.
The dose response varies among patients as does the dose that will produce side effects, such as tremor. Patients should be taught to monitor their inhaler use and to understand that if they need it more, or if its effects lessen,these are danger signals. They indicate deterioration in asthmatic control and the need for further treatment.
Side effects of beta agonists:
Some patients worry that β2-agonists may become less effective
with time, particularly if the dose is high. There is little evidence
of clinically significant tachyphylaxis for the airway effects in asthmatics.
If it exists, it is a minor effect that is quickly reversed, either
by stopping the treatment temporarily or by taking corticosteroids.
Tremor, palpitations and muscle cramps may occur, but are rarely troublesome. Some studies found that regular use of β2-agonists was associated wth increased bronchial reactivity, worsening asthma control and accelerated decline of lung function. These have not been confirmed.
However, when the steps in standard guidelines are followed,
β2-agonists are not used regularly unless needed for control of
symptoms and in this way never without a regular preventer
therapy such as inhaled steroids.