Background Pharmaceutical counseling (PC) interventions have been shown to improve adherence to controller medication and asthma control. However, the real-life impact of these PC interventions in difficult-to-control asthma patients remains unclear. We aimed to assess the effectiveness of PC interventions in real life using nationwide claims data. Methods Demographics and drugs use of patients who received ICS in 2017 with or without pharmaceutical counseling were retrieved from a Belgian claims database. Asthma-related drug use from 1 year before first ICS dispensing in 2017 (reference period) was compared with 1 year after. Outcomes were usage of inhaled corticosteroids (ICS) in defined daily doses (DDD), proportion of users of short-acting beta-agonist (SABA), antibiotics, oral corticosteroids (OCS), asthma biologicals and controller-to-total (CTT) ratio. Results The study population consisted of difficult-to-control asthma patients aged 5–40 years with at least the first interview within 90 days after first ICS dispensing (n = 1350). ICS usage increased significantly in the year after PC intervention compared with the reference period (+ 43.3 DDD/patient, p < 0.05). A nominal decrease was observed in the proportion of SABA (48.0 to 46.2%) and antibiotics (54.5 to 52.7%) after PC intervention compared with the reference period. CTT ratio significantly increased from 0.671 to 0.749 (p < 0.05). The proportion of biological users was nominally lower in the intervention group compared with a control group (n = 50,477) in the post-intervention time period (0.22% versus 0.30%). Conclusions This first nationwide study among difficult-to-control asthma patients suggests that community pharmacist counseling is effective in real life to improve controller adherence and asthma control.

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