Chapter 43: Respiratory Drugs

ORGANIZATION OF CLASS

Bronchoconstriction, inflammation, and loss of lung elasticity are the most common processes that result in respiratory compromise. Bronchoconstriction can be treated with adrenergic agonists, cholinergic antagonists, and some other compounds. Inflammation is treatable with corticosteroids. Obstruction of the airways can also occur with infection and increased secretions. The infection is treated with antibiotics. Because the antibiotics and steroids have been covered elsewhere, this chapter focuses on the bronchodilators. Much of this will be a review from autonomic pharmacology.

Most of these drugs are now administered by inhalation. This gets the drug to the site of action and limits the systemic effects.

BRONCHODILATORS

β-AGONISTS

Inhaled short-acting β₂-agonists are the most effective drugs available for treatment of acute bronchospasm and for prevention of exercise-induced asthma. β₂-Selective agents are preferred to avoid the cardiac effect of β₁-activation.

There are a number of β-agonists that are used in the treatment of asthma and chronic obstructive pulmonary disease (COPD).

In an emergency, such as the bronchoconstriction associated with anaphylaxis, epinephrine can be used. Use of a short-acting β-agonist more than two to three times a week means that the asthma is not well controlled and adjustments to baseline medication need to be made. Long-acting β-agonists can be used in combination with inhaled corticosteroids to control asthma symptoms.

CHOLINERGIC ANTAGONISTS

The cholinergic antagonists block the bronchoconstriction caused by activation of the parasympathetic nervous system.

The long-acting cholinergic antagonists, aclidinium, glycopyrrolate, revefenacin, tiotropium, and umeclidinium, have found use in the treatment of COPD. The anticholinergic drugs reduce air trapping and improve exercise tolerance in patients with COPD.

METHYLXANTHINES

Theophylline (or aminophylline) was once the treatment of choice for the management of asthma. Now, the combination of inhaled corticosteroids and β₂-agonists are first-line therapy. The methylxanthines increase cyclic adenosine monophosphate (cAMP) levels, but the exact mechanism by which they cause bronchodilation is not known. Theophylline is still listed as a treatment option for COPD. It is rare that students mistake these drugs for another class of compounds. The ending “-phylline” is a dead giveaway.

ANTI-INFLAMMATORY DRUGS

INHALED CORTICOSTEROIDS