Bronchodilator

A bronchodilator (sometimes called a broncholytic, though that term can also include substances that block secretions) is an agent that widens the bronchi and bronchioles. This reduces resistance in the airways and allows more air to flow into the lungs. These substances can occur naturally in the body or be given as medications, most often via inhalers, to treat breathing problems. They are most effective for obstructive lung diseases, especially asthma and chronic obstructive pulmonary disease (COPD).

Short-acting β2-adrenergic agonists

Their use in bronchiolitis and bronchiectasis is debated, and they are often prescribed for restrictive lung diseases despite a lack of proven benefit. Bronchodilators come in two main types: short-acting and long-acting. Short-acting ones provide quick, "rescue" relief from sudden airway narrowing, while long-acting ones are used regularly to control and prevent symptoms.

The three main classes of prescription bronchodilators are beta-2 adrenergic agonists (available in both short- and long-acting forms), anticholinergics (also short- and long-acting), and theophylline (which is long-acting only). Short-acting β2-adrenergic agonists are rescue medications that offer fast, temporary relief from asthma symptoms or flare-ups. They typically work within 20 minutes and last four to six hours. These inhaled drugs are best for sudden, severe, or new asthma symptoms.

Taken 15 to 20 minutes beforehand, they can also prevent symptoms triggered by exercise or cold air. Some, like salbutamol, are lung-specific (β2-selective) and relieve bronchospasms without the unwanted heart effects of non-selective β-agonists such as ephedrine or epinephrine. Patients who need these rescue medications often or regularly should see a doctor, as this suggests uncontrolled asthma and a possible need to adjust their daily maintenance medications. Long-acting β2-adrenergic agonists are taken routinely to control and prevent airway narrowing, not for fast relief.

Long-acting β2-adrenergic agonists

They take longer to start working but keep airways open for up to 12 hours. Usually taken twice daily alongside an anti-inflammatory medication, they maintain open airways and prevent asthma symptoms, especially at night. Examples include salmeterol and formoterol. Anticholinergics include tiotropium (Spiriva) and ipratropium bromide.

Anticholinergics

Tiotropium is a long-acting, 24-hour anticholinergic used for COPD. Ipratropium bromide, available only as an inhalant, is used for asthma and COPD. As a short-acting anticholinergic, it improves lung function and lowers the risk of exacerbations in symptomatic asthma, but it will not stop an asthma attack already in progress.

Because it has no effect on asthma symptoms when used alone, it is usually paired with a short-acting β2-agonist. Though considered a rescue medication, it can take a full hour to work, so it plays a secondary role in acute asthma treatment. Dry throat is the most common side effect; if it gets in the eyes, it can briefly blur vision. Combining anticholinergics with short-acting β2-agonists has been shown to reduce hospital admissions for acute asthma in both children and adults.

Other

Theophylline, available in oral and injectable forms, is a long-acting bronchodilator that prevents asthma episodes. It belongs to the methylxanthine chemical class (along with caffeine) and is prescribed for severe or hard-to-control asthma. It must be taken one to four times daily without missing doses, and blood tests are needed to monitor therapy and adjust dosage. Side effects can include nausea, vomiting, diarrhea, stomach or headache, rapid or irregular heartbeat, muscle cramps, nervousness, and hyperactivity, which may signal a need for dosage change.

It can also promote acid reflux (GERD) by relaxing the lower esophageal sphincter. Certain medications (like seizure and ulcer drugs, and antibiotics containing erythromycin) can interfere with theophylline. Coffee, tea, colas, cigarette smoking, and viral illnesses can also affect its action. A physician must monitor dosage to match each patient's needs.

Some psychostimulants with amphetamine-like action—such as amphetamine, methamphetamine, and cocaine—also have bronchodilating effects and were once used for asthma due to a lack of effective β2-agonists, but they are now rarely, if ever, used medically for this purpose. Gaseous carbon dioxide relaxes airway muscles as well: hypocapnia from deliberate hyperventilation increases airway resistance, while hypercapnia from inhaling carbon dioxide reduces it. However, this bronchodilating effect lasts only four to five minutes.

This observation led to the development of S-1226, a carbon dioxide-enriched air formulated with nebulized perflubron. Common bronchodilators are divided into short- and long-acting groups. Short-acting ones are used for relief of airway narrowing; long-acting ones are mainly for prevention. Short-acting bronchodilators include salbutamol/albuterol (Proventil or Ventolin) and levosalbutamol/levalbuterol (Xopenex).