Background: Little is known about factors that determine prescribing of asthma therapy in infancy.

Objective: To describe factors related to the initiation and refill of asthma therapy in infancy.

Methods: This study included 1202 infants who participated in a prospective birth cohort study: the 'Wheezing Illnesses Study Leidsche Rijn (WHISTLER)', in the Netherlands.  Outcomes, asthma therapy initiation and refill were assessed using prescription data.  Logistic regression analysis was used to study determinants of therapy initiation in two groups: total population and infants with a respiratory system symptom diagnosis.  In addition, determinants of refilling prescriptions were studied in infants who started therapy in their first year of life.

Results: 15% of all infants started asthma therapy in their first year of life.  Respiratory symptoms were an important driver of both initiation and refill of prescriptions.  In the total population, therapy initiation was associated with male gender (odds ratio (OR): 1.6: 95% CI, 1.1-2.6), day-care attendance (OR: 1.6; 95% CI, 1.0-2.5) and breastfeeding (OR: 0.6; 95% CI, 0.3-1.0).  For infants with a respiratory system symptom diagnosis, day-care attendance was associated with an increased chance of therapy initiation (OR: 5.3; 95% CI, 1.8-16.2) and breastfeeding was associated with a lower chance of starting therapy (OR: 0.4; 95% CI, 0.1-1.1).  Dutch children had a higher chance of refilling prescriptions in infancy (OR: 5.3; 95% CI, 1.1-26.8).

Conclusions: Apart from other factors involved, the principal reason for initiation and refill of asthma therapy in infancy was the presence of respiratory symptoms.  This appeared the only reason to prescribe medication and physicians are not distracted by other factors.