Do we really target the receptors? Deposition and co-deposition of ICS-LABA fixed combination drugs

Fixed dose combinations of aerosolized bronchodilators and steroids are routinely used in current asthma and COPD management. As spatial distribution of their receptors within the human airways is different, it is a challenging task to deliver the right drug component to the right receptor. The aim of this work was to apply numerical methods to analyse the airway deposition distribution of two inhalation corticosteroid (ICS) – long-acting beta-agonist (LABA) combination drugs in comparison with the distribution of the corresponding receptors. Our results revealed that different combination drugs exhibit different co-deposition patterns depending on the aerodynamic properties of their components. While ICS and LABA components of Symbicort® Turbuhaler® had similar deposition efficiencies in the same airway generation throughout the whole respiratory tract, the steroid component of Relvar® Ellipta® had up to 25% higher deposition than its bronchodilator component in the large bronchi and up to 40% lower deposition in the deeper airways. Present results highlight the need for extensive research to elucidate whether each drug component should deposit according to its receptor distribution or similar deposition distribution patterns of the components should be attained to benefit from the synergistic effects documented in the open literature. Once this aspect clarified, the next step will be to tailor the aerodynamic properties of each component of combination drugs to yield the desired deposition distribution in the lungs.