What is the best marker for inhaled corticosteroid safety?

The development of modern corticosteroids has revolutionized the treatment and management of asthma. Importantly, to a great extent, it has reduced the incidence of systemic side effects. However, at high doses, inhaled corticosteroid therapy is not devoid of systemic side effects such as growth suppression, reduction in bone density, and cataracts. Hence, it becomes important to monitor these effects. The most commonly used parameters that are monitored for systemic steroid effects measure the endogenous cortisol secretion. Measured parameters allow a direct comparison of the degree of systemic activity, which is difficult, based on steroid drug levels, because of the difference in potency of the various compounds. Evaluation of endogenous cortisol concentrations is complicated because of the presence of a circadian rhythm with highest cortisol concentrations in the morning and trough concentrations around bedtime. However, methods are available that consider circadian cortisol secretion. Cortisol levels should be measured over 24 hours at steady state. The area between the serum cortisol concentrations in the control group and the suppressed group is recognized as a good cumulative marker of systemic steroid activity. Cortisol suppression is a more sensitive marker for inhaled corticosteroid safety than parameters that consider effects on bone or lymphocyte suppression. If an inhaled corticosteroid dosing regimen does not show any significant cortisol suppression based on 24-hour serum area under the curve values, it can be assumed that this treatment is safe and unlikely to present any clinically relevant safety with respect to systemic steroid activity.