Sibship and dispensing patterns of asthma medication in young children—a population‐based study

PURPOSE: Our aim was to study the association between sibship and dispensing patterns of asthma medication in young children, focusing on incidence and persistence, and taking sibship status, asthma diagnoses, and siblings' medication into account. METHODS: A register-based cohort study including all children (n = 50 546) born in Stockholm, Sweden 2006 to 2007, followed up during 2006 to 2014. Exposure was sibling status; outcome was incidence of dispensed asthma medication and persistence over time. A Cox model was used to study the association between sibship and asthma medication. Persistence was defined using two different time windows (4 and 18 months) in a refill sequence model including siblings' and unrelated control children's medication. RESULTS: After 1 year of age, the adjusted hazard ratio of dispensed asthma medication was 0.85 (95% CI 0.80-0.90) among children with siblings compared with singletons. The estimated proportion of children with persistent controller medication was 7.2% (4-month model) and 64.5% (18-month model). When including the siblings' controller medication, the estimated proportion was 8.8% (4 months) and 7.8% for control children (relative risk (RR) 0.89, 95% CI 0.81-0.98). The persistence was lower for those with siblings compared with singletons (adj. RR 0.72, 95% CI 0.62-0.85 for 4 months) with similar estimates for older, younger, and full siblings and regardless of asthma diagnoses. CONCLUSIONS: Siblings have different dispensing patterns of asthma medications compared with singletons regardless of asthma diagnoses. After including the siblings' asthma medication and compared with control children, the proportion of children with persistent medication increased which may indicate that siblings share asthma medications.