Beclomethasone dipropionate and formoterol fumarate synergistically interact in hyperresponsive medium bronchi and small airways

Background: Corticosteroids increase the expression of β2-adrenoceptors (β2-ARs) and protect them against down-regulation. Conversely, β2-AR agonists improve the anti-inflammatory action of corticosteroids. Nevertheless, it is still uncertain whether adding a long-acting β2-AR agonist (LABA) to an inhaled corticosteroid (ICS) results in an additive effect, or there is true synergy. Therefore, the aim of this study was to pharmacologically characterize the interaction between the ICS beclomethasone diproprionate (BDP) and the LABA formoterol fumarate (FF) in a validated human ex vivo model of bronchial asthma. Methods: Human medium and small airways were stimulated by histamine and treated with different concentrations of BDP and FF, administered alone and in combination at concentration-ratio reproducing ex vivo that of the currently available fixed-dose combination (FDC; BDP/FF 100:6 combination-ratio). Experiments were performed in non-sensitized (NS) and passively sensitized (PS) airways. The pharmacological interaction was assessed by using Bliss Independence and Unified Theory equations. Results: BDP/FF synergistically increased the overall bronchorelaxation in NS and PS airways (+15.15%±4.02%; P <0.05 vs. additive effect). At low-to-medium concentrations the synergistic interaction was greater in PS than in NS bronchioles (+16.68%±3.02% and+7.27%±3.05%, respectively). In PS small airways a very strong synergistic interaction (Combination Index: 0.08; +20.04%±2.18% vs. additive effect) was detected for the total concentrations of BDP/FF combination corresponding to 10.6 ng/ml. Conclusion: BDP/FF combination synergistically relaxed human bronchi; the extent of such an interaction was very strong at low-to-medium concentrations in PS small airways.