Drug utilization in children with asthma : methodological approaches and practical implications

Abstract: There is limited research on drug utilization among children, despite them representing 20% of the total population in Europe. In the Priority Medicines report, the World Health Organization suggested that drug utilization in children is one of the priority areas in need of more attention, resources, and research. Asthma is the most common chronic disease in children, and asthma medications are one of the most commonly used drugs by children. Therefore, the overall aim of this thesis was to describe the drug utilization in children with asthma. In studies I and II, questionnaire data from the population-based birth cohort BAMSE were combined with dispensing data from the Swedish Prescribed Drug Register. The concordance between the two data sources was investigated as well as the association between drug usage, patient characteristics, and asthma disease control. We showed that an 18-month time window is preferable when using dispensing data to study the use of asthma medications. Most adolescents with asthma reported use of asthma medications, but a considerable proportion were neither dispensed any drugs nor reported use of someone else’s medications. Girls were less likely to achieve asthma control than boys. In study III, the association between sibship and dispensing patterns of asthma medications in young children was studied. It was a register-based cohort study including all children born in Stockholm, Sweden 2006 – 2007. Sibling status was used as exposure, and incidence of dispensed asthma medications and persistence to therapy over time were used as outcomes. We found that children with siblings had different dispensing patterns of asthma medications compared to singletons regardless of family income and asthma diagnoses. After including the siblings’ asthma medication and comparing with control children, the proportion of children with persistent medication increased which may indicate that siblings share asthma medications. In study IV, we assessed the effect of the eliminated patient fee on the dispensing patterns of asthma medication in children. We used dispensing data two years before and after the intervention (January 1st, 2016) to measure prevalence, incidence, numbers of Defined Daily Doses (DDDs)/child, and persistence to drug treatment before and after the intervention. We found that the intervention had a modest effect on the dispensing patterns of asthma medication, nevertheless the volume dispensed per child increased, particularly in children with low socioeconomic status. In conclusion, this thesis describes drug utilization in children with asthma. Four factors to consider when assessing the dispensing patterns of asthma medications were found to be important: sex, sibship, time window used in the register, and changes in the co-payment system. Different data sources of drug utilization will give different results. Dispensing data from pharmacies will underestimate drug use compared to data from self-reported (or parentalreported) use of asthma medications. Siblings share asthma medications, which may lead to an underestimation of drug use if only one of the siblings’ asthma medications is included in the measurement of drug usage when using data on dispensed drugs.