Anti-interleukin 5 (IL-5) and anti-IL-5 receptor α monoclonal antibodies markedly decrease airway and peripheral blood eosinophil numbers and are thus highly effective in reducing asthma exacerbations. Nonetheless, these biologics do not completely resolve exacerbations. There is very little information on the cellular nature of exacerbations during treatment with biologics. Using illustrative clinical case scenarios, we highlight the importance of carefully characterizing asthmatics at the time of exacerbation and recognizing neutrophilic causes of exacerbations to ensure optimal management. While an eosinophilic exacerbation may improve with more corticosteroids or by switching to another anti-IL-5 monoclonal antibody, a noneosinophilic exacerbation will likely not. An infective exacerbation needs to be recognized, and the pathogen must be identified and treated with the appropriate antimicrobial agent.

Key words: Severe asthma, Exacerbations, Anti-IL5 biologics, Sputum cell counts, Airway infections, Eosinophils