Systemic corticosteroids contain a chemical that activates cortisol receptors. Cortisol receptors are in many cells in the body, including the cells making the inflamed lining of the airways in patients with asthma and COPD. When the cortisol receptor is activated, the inflammatory response of the cells stops, and the lining of the airways returns to its original size. This allows better airflow and reduces the feelings of breathlessness in patients with COPD and asthma.
Systemic corticosteroids provide superior anti-inflammatory effects compared to inhaled corticosteroids, and are therefore used during severe asthma attacks and periods of COPD worsening. Commonly used systemic corticosteroids are prednisone, methylprednisolone (Solu-medrol), and dexamethasone (Decadron). However, there are downsides to systemic corticosteroids which prevents them from being used as a first line treatment of milder asthma and COPD. As opposed to inhaled corticosteroids, which only affect the lungs, systemic corticosteroids travel to every organ of the body, affecting most of them in some way. To understand the effects better, one must understand what cortisol normally does in the body.
Cortisol is produced in the adrenal glands, which sit above the kidneys. While there is a normal baseline, the production of cortisol ramps up when the body or mind is exposed to stress. This boost in cortisol results in a boost in blood sugar, the most commonly used fuel in the body. This extra fuel can then be burned in the muscles and nerves, allowing people to think faster and run longer, so that they can get away from the stressor. However, cortisol gets this sugar by turning off various maintenance functions of the body: parts of immune system including inflammation; skeletal calcium replacement; and wound healing. Normally, the natural cortisol response due to stress generally ends within hours to days, and the loss of maintenance has no effect.
To treat severe asthma attacks and COPD exacerbations, on the other hand, high doses of systemic corticosteroids are necessary. As stated above, physicians desire the reduction of inflammation. However, as a side effect, patients also suffers high blood sugars, a weakened immune system, skeletal calcium loss, and poor wound healing. While the high blood sugars can sometimes cause symptoms, the loss of the maintenance functions has no effect in the short term. If needed, patients can stay on corticosteroids for a few weeks without any fear. However, after a month of corticosteroid use, the high blood sugars and loss of maintenance functions add up, and result in worsening fat redistribution, muscle loss, increased susceptibility to infection, osteoporosis, and poor wound healing. Because of the time distribution of side effects, doctors are quick to prescribe systemic corticosteroids when they believe the drugs are necessary, but are cautious about using them for extended periods.
Another issue with systemic corticosteroids is that it suppresses the body's ability to produce its own cortisol. The human body needs cortisol to deal with stress; it can be life-threatening if the level of cortisol falls short. Therefore physicians prefer to wean patients off of systemic corticosteroids slowly, giving the body time to ramp up its natural production of cortisol.