Pharmacology

Pharmacology defines the interactions between the drug and the patient’s body. Pharmacodynamics is the study of how drugs affect the body, while pharmacokinetics is the study of how the body absorbs, distributes, metabolizes and excretes drugs. Pharmacodynamics includes an attempt to understand the drug’s mechanism of action, clinical effects and adverse effects. Pharmacokinetics studies systemic bioavailability, the portion of the drug dose that reaches the bloodstream. Increased systemic bioavailability may be undesirable with asthma drugs intended to work in the airways, due to increased unintended drug exposure to other body systems and an increased risk of adverse effects.

Asthma medications may fall into two categories: relievers and controllers. Relievers, such as short-acting beta2-agonists, anticholinergics and systemic corticosteroids (via injection or oral) can help with acute symptoms. The short-acting beta2-agonists are preferred. There are five types of controllers, which are taken daily over the long-term to achieve and maintain control when indicated. Controllers include long-acting beta2-agonists, corticosteroids (usually inhaled) and anticholinergics.

Long-acting beta2-agonists (LABAs) such as formoterol and salmeterol are indicated for the long-term prevention and reduction of asthma symptoms when added to an inhaled corticosteroid. Side effects include tachycardia. LABAs are not anti-inflammatory agents, nor are they indicated as monotherapy nor for treatment of acute asthma symptoms or exacerbations.28

There are three types of inhalation devices usually used for the control and treatment of asthma, the pressurized metered-dose inhaler (pMDI), the dry powder inhaler (DPI) and the nebulizer. pMDIs are the most popular, being small and portable, but can be challenging to coordinate. Spacers can be used as extensions to pMDIs to allow for delayed inhalation. DPIs require less coordination, but require effective ability to inhale. Nebulizers can be used by any age patient but are time consuming and may have varying output.