Clinical efficacy of an inhalational drugs depends on proper inhalation technique and aerodynamic properties of aerosol including the respirable fraction. Investigations of systemic pharmacokinetics of inhalational drugs could not always estimate their pharmacological equivalence so as rela tionships between the inhaled dose, the systemic concentration and the topic activity of an inhalational drug are not fully investigated. Therefore, identical formulation and similar route of administration are not sufficient to estimate pharmacological interchangeability. Possibility to interchange inhalational agents has still been controversial. As such, equal efficacy and safety of inhalational drugs with the same active substance could be esti mated in real clinical practice according to results of postmarketing trials and pharmacological surveillance. Spontaneous messages are a tool for gathering information about unwanted reactions or drug inefficacy and possible risks of substitution of drugs within the same international nonpro prietary name. In summary, it is necessary to estimate pharmacological equivalence and interchangeability of inhalational drugs carefully. This approach could improve efficacy and safety of treatment of patients with asthma and COPD. © 2017 Medical Education. All rights reserved.