Both FF/VI 100/25 and FF 100 clinically and significantly suppress the EAR to an allergen challenge relative to placebo. This is supported by significant differences between active treatment and placebo being observed in (i) the wm change in FEV1 from post-saline baseline, (ii) the maximum percentage decrease in FEV1 from post-saline baseline, and (iii) the maximum absolute decrease in FEV1 from post-saline baseline. No major safety signals were observed in this crossover study, and in the one subject who discontinued due to an SAE, the event subsequently resolved.
Bronchoprotection against the early and late allergic response is a part of asthma control , and is one of the characteristics that should be expected of any asthma maintenance therapy – especially as increased levels of aeroallergens such as grasses, house dust mite or dander are associated with increased rates of asthma exacerbation and hospitalisation . When the allergic response (typically the LAR) is used as a model to test the extent of bronchoprotection provided by an intervention, the test is typically conducted shortly after dosing of the intervention . This approach is rational when seeking to establish whether a novel intervention is capable of providing bronchoprotection, given the strong negative predictive power of the allergen challenge model . However, when considering an intervention of known efficacy, the key time to test the bronchoprotective capacity of an intervention is at the trough of dosing, as this provides evidence of the sustained effect of the intervention, as has been investigated for the twice-daily dosed ICSs fluticasone propionate and budesonide [22, 23]. In the present study, the allergen challenge was initiated on Day 29, 22–23 h after the final dose of study medication, and as such total ablation of the EAR was not expected. Nevertheless, the results showed a clear and significant effect on the EAR after 28 days once-daily therapy with either FF 100 or FF/VI 100/25 yielding an approximate 150 mL reduction in the extent of the EAR over the first 2 h post-challenge relative to placebo. That this effect was also seen for maximum percentage decrease (~11%) and maximum decrease in FEV1 from post-saline baseline (~330 mL) suggests that even at the trough of once-daily dosing, FF 100 and FF/VI 100/25 continue to exhibit protection from allergen-induced EAR.
The secondary objective of this study was to assess the bronchoprotective effect of FF/VI 100/25 relative to FF 100. Previously it has been shown that a LABA/ICS combination resulted in significantly greater attenuation of the EAR compared to ICS alone , although in that study, the challenge was not conducted at the end of the dosing interval. The additional attenuation of the response provided by the LABA over the ICS response has been ascribed to ‘functional antagonism’ of the EAR/LAR by the bronchodilatory effect of the LABA . LABAs have also demonstrated protection in exercise-induced asthma models [24, 25] where the challenge was initiated at or near the end of the dosing period, suggesting that functional antagonism can persist throughout the dosing period. In the present study, no additional effect on suppression of the EAR was observed with FF/VI 100/25 relative to FF 100. There are a number of potential reasons for this observation. In the first instance, the mean pre-bronchodilator FEV1 of the subjects recruited into this study was almost 90%; therefore it is conceivable that any functional antagonism provided by VI would be obscured by the near normal baseline lung function, which was further improved after 28 days of therapy with both FF 100 and FF/VI 100/25. In the second instance, as the allergen challenge was conducted on Day 29 at trough drug levels, it is possible that any additional improvement in FEV1 provided by VI through functional antagonism had abated at that time point. It would be of interest to explore, in a further study, the EAR at 6, 12 or 18 h following dosing to investigate whether VI does provide functional antagonism and also the duration of this effect. However, studies assessing bronchodilation by VI over time have shown a 24h duration of effect of VI on lung function demonstrated by improvements relative to placebo in FEV1 measured at 24 h post-dose of 121 mL after 28 days  and 125 mL after 7 days  of dosing in subjects with persistent asthma receiving concomitant ICS.
As with all allergen challenge studies, there were strengths and limitations associated with this study. The study was limited in that only effects on the EAR were investigated, and as patients were only assessed for the presence of the EAR at screening it is not possible to know how many of those recruited were single versus dual responders. Also, while the effect of FF 100 and FF/VI 100/25 was assessed relative to placebo, the effect of VI 25mcg was not. However, a separate study (NCT01128595) investigating the effects of FF and VI alone and in combination on the EAR and LAR at 1 h post-dose in confirmed dual responders has been completed and will be reported elsewhere. A further limitation is that subjects were receiving SABA only at enrolment so the next treatment step, according to the GINA guidelines, is low-dose ICS rather than an ICS-LABA combination . However, the response to inhaled allergen can be thought of as simulating the need to increase therapy, by experimentally destabilising asthma, and, therefore, mimicking a patient in need of ICS/LABA therapy. The data from this study are strengthened by a number of factors: firstly, the challenge was conducted on Day 29 of each treatment period (i.e. at the end of the dosing interval, 22-23 h post-dose on Day 28). Despite the importance of asthma control throughout the dosing interval, testing at the time of minimal drug effect has been infrequently studied in challenge models [22, 23]; secondly, the design of the study, particularly the option to extend the washout period and the careful selection of subjects meant that the study was able to be conducted through the hay fever season (in the UK and Germany). Consequent to this, one subject reported two occurrences of seasonal allergy as an AE during the FF 100 treatment period, on days 2 and 23. One further subject reported allergic rhinitis on days 23, 21 and 4 of treatment periods 1, 2 and 3, respectively. It is possible that the AEs on days 21 and 23 may have influenced the primary endpoint; however, given the overall incidence of these events any effect would have been small.